Liquid crystal light control element, and display device and light shielding device using same

Abstract

The present invention provides a means which is capable of suppressing a decrease in transparency in a transparent state under high temperature conditions in a liquid crystal light control element in which light scattering properties are increased by receiving ultraviolet light and the light scattering properties are decreased by receiving visible light. The present disclosure relates to a liquid crystal light control element that comprises: a pair of transparent substrates which each have a transparent electrode and an alignment function layer that is disposed on one surface of the transparent electrode, and which are arranged so that the alignment function layers face each other; and a liquid crystal layer which contains liquid crystal molecules, a photoisomerization material, a non-photoresponsive chiral compound, and a polymer of a photopolymerizable monomer, and which is interposed between the pair of transparent substrates. The light scattering properties of the liquid crystal light control element are increased by receiving ultraviolet light, and the light scattering properties are decreased by receiving visible light. The liquid crystal light control element is characterized in that the average diameter of voids contained in the polymer of the photopolymerizable monomer in a cross section in the plane direction of the liquid crystal layer is smaller than the theoretical value of the helical pitch of the liquid crystal molecules caused by a temperature change from 27°C to 70°C of the helical twisting power (HTP) of the non-photoresponsive chiral compound.

Description

Liquid crystal light control element, display device, and light shielding device using the same

[0001] The present invention relates to a liquid crystal light control element, a display device using the same, and a light shielding device.

[0002] In recent years, technologies for displaying images on transparent glasses such as the windshield of automobiles and the window glass of buildings have been developed. For example, a display device is known that includes an image display body whose optical state changes between a state of transmitting light and a state of scattering light, and a projector that projects visible light onto the image display body to display an image.

[0003] Specifically, Japanese Patent Application Laid-Open No. 2011-154388 discloses a liquid crystal optical element (liquid crystal light control element) in which an electro-optical functional layer containing liquid crystal and a polymer is sandwiched between a pair of electrode-attached substrates at least one of which is transparent, and the alignment state of the liquid crystal is changed in response to the application of a voltage so as to exhibit a light transmission state (transparent state) and a light scattering state (screen state).

[0004] The inventors of the present invention attempted to produce a liquid crystal light control element having a function of increasing light scattering properties and exhibiting a screen state by receiving ultraviolet light and decreasing light scattering properties and exhibiting a transparent state by receiving visible light by adding a light-responsive material such as a photo-isomerization material to the liquid crystal layer of the liquid crystal light control element disclosed in the above publication together with a non-light-responsive chiral compound. As a result, it was found that in some cases, there is a problem that the transparency in the transparent state of the liquid crystal light control element decreases under high temperature conditions of about 70 to 80°C. A liquid crystal light control element with reduced transparency under high temperature conditions is limited in use in areas where the environmental temperature (air temperature) is very high or in environments that temporarily become high temperature.

[0005] Therefore, an object of the present invention is to provide a means capable of suppressing a decrease in transparency in a transparent state under high temperature conditions in a liquid crystal light control element in which light scattering properties increase by receiving ultraviolet light and light scattering properties decrease by receiving visible light.

[0006] The inventors of this invention conducted intensive studies in view of the above problems. As a result, they found that the above problems can be solved by including a polymer of liquid crystal molecules, a photoisomerizing material, a non-photoresponsive chiral compound, and a photopolymerizable monomer in a liquid crystal layer interposed between a pair of transparent substrates having an orientation functional layer, and by making the average diameter of the voids contained in the photopolymerizable monomer polymer in the cross-section in the plane direction of the liquid crystal layer smaller than the theoretical value of the helical pitch of liquid crystal molecules caused by the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C.

[0007] In other words, one embodiment of the present invention relates to a liquid crystal dimming element comprising a pair of transparent substrates having a transparent electrode and an orientation functional layer disposed on one surface of the transparent electrode, wherein the orientation functional layers are arranged facing each other, and a liquid crystal layer interposed between the pair of transparent substrates, wherein the light scattering increases upon reception of ultraviolet light and decreases upon reception of visible light. The liquid crystal dimming element is characterized in that the average diameter of the voids contained in the polymer of the photopolymerizable monomer in the cross-section in the planar direction of the liquid crystal layer is smaller than the theoretical value of the helical pitch of the liquid crystal molecules due to the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C.

[0008] Figure 1 is a perspective view showing a schematic configuration of a display device according to one embodiment of the liquid crystal dimming element according to the present invention. Figure 2A is a cross-sectional view showing a schematic configuration of an image display body. Figure 2B is a modified example of the image display body shown in Figure 2A. Figure 3 is an explanatory diagram for explaining the change in helical induced force of a non-photoresponsive chiral compound and the helical pitch of liquid crystal molecules due to a temperature change from room temperature (27°C; Figure 3(a)) to high temperature (70°C; Figure 3(b)). Figure 4 is a diagram for explaining the operation of the display device 10 when an image is displayed. Figure 5 is a diagram for explaining the operation of the display device 10 when an image is not displayed. Figure 6 is a photograph showing scanning electron microscope (SEM) images of the cross-section when the average diameter of voids contained in the polymer of photopolymerizable monomers was calculated in the planar cross-section of the liquid crystal layer of the liquid crystal dimming element made in Comparative Example 1(a) and Example 1(b), respectively. Figure 7 is a layout diagram of a measuring device for measuring the visible light transmittance of the liquid crystal dimming element.

[0009] One embodiment of the present invention is a liquid crystal dimming element comprising a pair of transparent substrates having a transparent electrode and an orientation functional layer disposed on one surface of the transparent electrode, the orientation functional layers being disposed facing each other, and a liquid crystal layer interposed between the pair of transparent substrates, the liquid crystal layer containing a polymer of liquid crystal molecules, a photoisomerization material, a non-photoresponsive chiral compound, and a photopolymerizable monomer, wherein the light scattering increases upon reception of ultraviolet light and decreases upon reception of visible light, and the average diameter of the voids contained in the polymer of the photopolymerizable monomer in the cross-section in the plane direction of the liquid crystal layer is smaller than the theoretical value of the helical pitch of the liquid crystal molecules due to the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C. According to the liquid crystal dimming element of the present invention, the decrease in transparency in the transparent state under high temperature conditions is suppressed.

[0010] The embodiments of the liquid crystal dimming element according to the above-described embodiment will be explained below with reference to the drawings, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] 《Display Device》 Figure 1 is a perspective view showing a schematic configuration of a display device 10 according to one embodiment of the liquid crystal dimming element according to the present invention. The display device 10 of this embodiment includes an image display unit 100, a first projector 200, a second projector 300, a third projector 400, and a control unit 500.

[0012] The image display unit 100 is a thin plate-shaped member whose optical state changes between a transparent state and an opaque state, and has a front surface 100a facing the first to third projectors 200 to 400, and a back surface 100b opposite to the front surface 100a. The image display unit 100 changes from a transparent state to an opaque state when it receives ultraviolet light, and changes from an opaque state to a transparent state when it receives first visible light. The image display unit 100 can be attached, for example, to the front windshield, side windows, roof glass, rear window, etc. of an automobile. Furthermore, the image display unit 100 can be mounted not only on automotive glass, but also on building material glass such as glass in houses and shops. A detailed explanation of the image display unit 100 will be given later.

[0013] The first projector 200 is a projector that emits ultraviolet light and is positioned opposite the front surface 100a of the image display unit 100. The first projector 200, as an ultraviolet light emitting unit, emits ultraviolet light with a wavelength of, for example, 365 nm. The first projector 200 projects ultraviolet light onto the front surface 100a of the image display unit 100, changing the ultraviolet light emitting area 100c on the image display unit 100 from a transparent state to an opaque state.

[0014] The second projector 300 is a projector that emits visible light of a specific wavelength and is positioned opposite the front surface 100a of the image display unit 100. The second projector 300, as a first visible light emitting unit, emits, for example, first visible light with a wavelength of around 450 nm. The second projector 300 projects the first visible light onto the image display unit 100, which is in an opaque state, to change the ultraviolet light emitting area 100c on the image display unit 100 from an opaque state to a transparent state.

[0015] The third projector 400 is a color projector and is positioned opposite the front surface 100a of the image display unit 100. The third projector 400, as a second visible light emitter, emits second visible light which is light of one of three colors: blue (wavelength 450 nm), green (wavelength 532 nm), and red (wavelength 640 nm), or light which is a combination of two or more colors. The third projector 400 projects second visible light onto the non-transparent image display unit 100 to display the image 600 on the image display unit 100.

[0016] The control unit 500 controls the operation of the first to third projectors 200 to 400. The control unit 500 communicates with a higher-level control device (not shown) and switches the first and second projectors 200 and 300 between projection and non-projection. The control unit 500 also communicates with the higher-level control device and sends image information to the third projector 400.

[0017] Furthermore, the first and third projectors 200 and 400 project ultraviolet light and second visible light, respectively, so that the image 600 displayed on the image display unit 100 by the second visible light is contained within the ultraviolet light projection area 100c on the image display unit 100. In addition, the second projector 300 projects first visible light so that the ultraviolet light projection area 100c is contained within the first visible light projection area on the image display unit 100.

[0018] Next, with reference to Figure 2A, the image display body 100 of the display device 10 will be described in detail. Figure 2A is a cross-sectional view showing the schematic configuration of the image display body 100. The image display body 100 of this embodiment includes a liquid crystal dimming element 110, a dimming layer 120, and an ultraviolet light shielding layer 130. The liquid crystal dimming element 110 is located on the front 100a side of the image display body 100, and the ultraviolet light shielding layer 130 is located on the back 100b side of the image display body 100. The dimming layer 120 is located between the liquid crystal dimming element 110 and the ultraviolet light shielding layer 130.

[0019] The liquid crystal dimming element 110 is a film material whose optical state changes between a transparent state and an opaque state. The liquid crystal dimming element 110 has optical properties in which its light scattering increases and it becomes opaque when it receives ultraviolet light, and decreases and returns to a transparent state when it receives first visible light. The liquid crystal dimming element 110 also plays a role in displaying images in the image display unit 100.

[0020] The ultraviolet light shielding layer 130 is a transparent film member that shields ultraviolet light. The ultraviolet light shielding layer 130 is made of a transparent resin containing an ultraviolet light reflector or an ultraviolet light absorber, and shields light in the wavelength region near ultraviolet light by reflecting or absorbing it. The ultraviolet light shielding layer 130 is positioned on the back surface 100b of the image display unit 100 to prevent ultraviolet light from entering the liquid crystal dimming element 110 from the back surface 100b of the image display unit 100.

[0021] The image display body 100 of the display device 10 may include a liquid crystal dimming element 110 and an ultraviolet light shielding layer 130, as shown in Figure 2B. In this case, the liquid crystal dimming element 110 also serves as the dimming layer.

[0022] 《Liquid Crystal Dimming Element》The following describes the components of a liquid crystal dimming element according to one embodiment of the present invention.

[0023] [Transparent Substrate] The liquid crystal dimming element comprises a pair of transparent substrates. Each transparent substrate has a transparent electrode and an alignment functional layer disposed on one side of the transparent electrode. The pair of transparent substrates are arranged so that their alignment functional layers face each other, and a liquid crystal layer, described later, is disposed in the gap between the transparent substrates. Here, a transparent substrate such as a glass substrate or a resin substrate may be used as the transparent substrate. Furthermore, an ITO film may be used as the transparent electrode.

[0024] As the alignment functional layer, conventionally known materials such as a film made of polyimide that has been subjected to an alignment film treatment can be used. Examples of alignment film treatments include physical treatments such as rubbing and mechanical surface treatments. Of course, an alignment functional layer that has been given orientation by means other than these may also be used. The alignment functional layer may cause the liquid crystal molecules to undergo homogeneous orientation (horizontal orientation) or homeotropic orientation (vertical orientation).

[0025] There are no particular restrictions on the thickness of the gap between the pair of transparent substrates (cell gap; equal to the thickness of the liquid crystal layer), but from the viewpoint of sufficiently reducing the transmittance in the screen state after ultraviolet light irradiation, it is preferably greater than 2 μm, more preferably 3 μm or more, even more preferably 4 μm or more, even more preferably 5 μm or more, particularly preferably 8 μm or more, and most preferably 10 μm or more.

[0026] [Liquid Crystal Layer] The liquid crystal layer is a layer containing polymers of liquid crystal molecules, photoisomerized materials, non-photoresponsive chiral compounds, and photopolymerizable monomers.

[0027] (Liquid Crystal Molecules) There are no particular restrictions on the liquid crystal molecules, and known nematic liquid crystal molecules can be used. Liquid crystal molecules are compounds in which two to four cyclic compounds such as benzene rings, cyclohexane rings, cyclohexene rings, pyrimidine rings, dioxane rings, and pyridine rings are linked by single bonds, ester bonds, acetylene bonds, ethane bonds, ethylene bonds, azo bonds, etc., and have cyano groups, fluoro groups, alkyl groups, alkenyl groups, or alkoxy groups at their ends. These compounds may be substituted with cyano groups, fluoro groups, alkyl groups, alkenyl groups, or alkoxy groups. In other words, as liquid crystal molecules, biphenyl-based, biphenylcyclohexane-based, terphenyl-based, phenylcyclohexane-based, Schiff base-based, azo-based, azoxy-based, benzoic acid ester-based, cyclohexanecarboxylic acid ester-based, pyrimidine-based, dioxane-based, cyclohexylcyclohexane ester-based, cyclohexylethane-based, cyclohexene-based, fluorine-based, and tran-based liquid crystal molecules can be used. Examples of liquid crystal molecules include 4-cyano-4'-ethylbiphenyl, 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-propylbiphenyl, 4-cyano-4''-p-terphenyl, 4-cyano-4'-propoxy-1,1'-biphenyl, 4-cyano-4'-(4-pentylcyclohexyl)biphenyl, 4-hexyl-4'-cyanophenylpyridine, 4-hexyl-4'-propylphenylcyclohexane, 4-methyl-4'-propyldicyclohexane, and 4-hexyl-4'-methoxydicyclohexane. Liquid crystal molecules can be used individually or as a mixture of two or more. Liquid crystal molecules can be used as synthetic or commercially available products.

[0028] The liquid crystal molecule content in the liquid crystal layer is, for example, 60 to 95% by mass, preferably 65 to 90% by mass, more preferably 70 to 85% by mass, and particularly preferably 75 to 80% by mass, based on the total mass of the liquid crystal molecules, the photoresponsive material including the photoisomerized material, and the polymer of the photopolymerizable monomer.

[0029] (Photoisomerized materials) Photoisomerized materials are compounds that undergo structural changes such as rearrangement of bonds upon absorption of light, for example, compounds that undergo cis-trans isomerization upon absorption of light. In the photoisomerized materials according to this embodiment, the structure changes from the trans isomer to the cis isomer upon exposure to ultraviolet light, and the liquid crystal helix induced force changes reversibly along with the structural change.

[0030] Examples of photoisomerized materials include azobenzene compounds, chalcone derivatives, sulfoxide compounds, fulgide compounds, and cinnamic acid compounds.

[0031] Examples of azobenzene compounds include those represented by the following chemical formula (1).

[0032]

[0033] In the above chemical formula (1), R １ ~R １０ Each of the following groups is independently selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a halogen group, a hydroxyl group, a carboxyl group, an ester group (-COOR'), and combinations thereof, and R' is a group selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted alkoxy group.

[0034] Examples of alkyl groups include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, and n-hexadecyl; and isopropyl, isobutyl, sec-butyl, tert-butyl, isoamyl, and tert-pentyl groups. Examples include branched alkyl groups such as neopentyl group, 1-methylpentyl group, 4-methyl-2-pentyl group, 3,3-dimethylbutyl group, 2-ethylbutyl group, 1-methylhexyl group, tert-octyl group, 1-methylheptyl group, 2-ethylhexyl group, 2-propylpentyl group, 2,2-dimethylheptyl group, 2,6-dimethyl-4-heptyl group, 3,5,5-trimethylhexyl group, 1-methyldecyl group, and 1-hexylheptyl group.

[0035] Examples of alkoxy groups include linear alkoxy groups such as methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy, n-dodecyloxy, n-tridecyloxy, n-tetradecyloxy, n-pentadecyloxy, and n-hexadecyloxy; isopropoxy, tert-butoxy, and 1-methylpentyloxy. Examples include branched alkoxy groups such as 1-I group, 4-methyl-2-pentyloxy group, 3,3-dimethylbutyloxy group, 2-ethylbutyloxy group, 1-methylhexyloxy group, tert-octyloxy group, 1-methylheptyloxy group, 2-ethylhexyloxy group, 2-propylpentyloxy group, 2,2-dimethylheptyloxy group, 2,6-dimethyl-4-heptyloxy group, 3,5,5-trimethylhexyloxy group, 1-methyldecyloxy group, and 1-hexylheptyloxy group.

[0036] When the alkyl group and the alkoxy group have substituents, the introduced substituents are not particularly limited. Specifically, examples include a halogen group, an unsubstituted alkyl group, an unsubstituted alkoxy group, and combinations thereof. The halogen group refers to a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or an iodo group (-I).

[0037] The azobenzene compound may be one obtained by esterifying isosorbide or isomannide with the compound represented by the above chemical formula (1).

[0038] In a preferred embodiment, the azobenzene compound is selected from the compounds represented by the following chemical formulas (2) to (6).

[0039]

[0040] Examples of the chalcone derivative include the compound represented by the following chemical formula (7).

[0041]

[0042] Examples of the sulfoxide compound include the compound represented by the following chemical formula (8).

[0043]

[0044] Examples of the fulgide compound include the compound represented by the following chemical formula (9).

[0045]

[0046] Examples of the cinnamic acid compound include the compounds represented by the following chemical formulas (10) to (11).

[0047]

[0048] From the viewpoint of a high reaction rate of photoisomerization, the photoisomerization material preferably contains an azobenzene compound, more preferably contains the compounds represented by the chemical formulas (2) to (6), and still more preferably contains the compound represented by the chemical formula (5) or (6). The photoisomerization material can be used alone or as a mixture of two or more. The synthesis method of the photoisomerization material is not particularly limited, and a conventionally known synthesis method can be applied.

[0049] The amount of photoisomerizing material in the liquid crystal layer is, for example, 3 to 10 parts by mass per 100 parts by mass of liquid crystal molecules, and is preferably 4 to 8 parts by mass from the viewpoint of being able to better exhibit the effects of the present invention.

[0050] (Non-photoresponsive chiral compounds) Non-photoresponsive chiral compounds are compounds that have different optical activity than the photoisomerized materials described above. By using a photoisomerized material and a non-photoresponsive chiral compound in combination, a compensatory state is reached where the helical twisting power (HTP) between the photoisomerized material and the non-photoresponsive chiral compound cancels each other out. In other words, the disorder of the arrangement of liquid crystal molecules and the phase change caused by the helical twisting power of the trans-isomerized photoisomerized material can be further suppressed. As a result, the transparency of the liquid crystal dimming element, which is in a transparent state, can be increased. The helical twisting power can be determined by the Cano wedge method.

[0051] Examples of non-photoresponsive chiral compounds include 4-[4-(hexyloxy)benzoyloxy]benzoic acid (R)-2-octyl, 4-[4-(hexyloxy)benzoyloxy]benzoic acid (S)-2-octyl, 4'-[(S)-2-methylbutyl]-1,1'-biphenyl-4-carbonitrile, bis[4-(trans-4-pentylcyclohexyl)benzoic acid] (R)-1-phenyl-1,2-ethanediyl, bis[4-(trans-4-pentylcyclohexyl)benzoic acid] (S)-1-phenyl-1,2-ethanediyl, and bis[4-(4-pentyloxyphenyl)benzoic acid] (aS)-1,1'-binaphthalene-2,2'-diyl ((S)-BN-OCO). Non-photoresponsive chiral compounds may be commercially available or synthesized. The synthesis method for non-photoresponsive chiral compounds is not particularly limited, and conventionally known synthesis methods can be applied.

[0052] When using azobenzene compounds as photoisomerized materials, non-photoresponsive chiral compounds include 4-[4-(hexyloxy)benzoyloxy]benzoic acid (R)-2-octyl, 4'-[(S)-2-methylbutyl]-1,1'-biphenyl-4-carbonitrile, bis[4-(trans-4-pentylcyclohexyl)benzoic acid] (R)-1-phenyl-1,2-ethanediyl, and bis[4-(4-pentyloxy It is preferable to include a compound selected from [(aS)-1,1'-binaphthalene-2,2'-diyl((S)-BN-OCO)], and more preferably to include 4-[4-(hexyloxy)benzoyloxy]benzoic acid (R)-2-octyl or bis[4-(4-pentyloxyphenyl)benzoic acid](aS)-1,1'-binaphthalene-2,2'-diyl((S)-BN-OCO).

[0053] The content of the non-photoresponsive chiral compound in the liquid crystal layer is, for example, 2 to 10 parts by mass per 100 parts by mass of liquid crystal molecules, and is preferably 3 to 8 parts by mass from the viewpoint of being able to better exhibit the effects of the present invention.

[0054] (Polymers of Photopolymerizable Monomers) Polymers of photopolymerizable monomers are polymers obtained by polymerizing photopolymerizable monomers by light irradiation in the presence of a photopolymerization initiator. Details of the polymerization method will be described later, but here we will explain the photopolymerizable monomers and photopolymerization initiators that are the raw materials for polymers of photopolymerizable monomers.

[0055] Examples of photopolymerizable monomers include monomers that have one or more common photopolymerizable groups in their molecule, such as acryloyl groups, methacryloyl groups, and vinyl groups.

[0056] Examples of photopolymerizable monomers include monofunctional acrylate compounds such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, butyl ethyl acrylate, butoxyethyl acrylate, 2-cyanoethyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-hydroxypropyl acrylate, 2-ethoxyethyl acrylate, N,N-diethylaminoethyl acrylate, N,N-dimethylaminoethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate, isovonyl acrylate, isodecyl acrylate, lauryl acrylate, morpholine acrylate, phenoxyethyl acrylate, and phenoxydiethylene glycol acrylate; methyl acrylate Monofunctional methacrylate compounds such as methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, butyl ethyl methacrylate, butoxyethyl methacrylate, 2-cyanoethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, 2-hydroxypropyl methacrylate, 2-ethoxyethyl acrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, isovonyl methacrylate, isodecyl methacrylate, lauryl methacrylate, morpholine methacrylate, phenoxyethyl methacrylate, and phenoxydiethylene glycol methacrylate;Polyfunctional acrylate compounds such as 4,4'-bis[6-(acryloyloxy)hexyloxy]biphenyl, 2-methyl-1,4-phenylenebis(4-3-(acryloyloxy)propoxy)benzoate, diethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,3-butylene glycol diacrylate, dicyclopentanyl diacrylate, glycerol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, and dipentaerythritol monohydroxypentaacrylate; 4,4'-bis[6- Examples of polyfunctional methacrylate compounds include (methacryloyloxy)hexyloxy]biphenyl, 2-methyl-1,4-phenylenebis(4-3-(methacryloyloxy)propoxy)benzoate, diethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,3-butylene glycol dimethacrylate, dicyclopentyl dimethacrylate glycerol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, ditrimethylolpropane tetramethacrylate, dipentaerythritol hexamethacrylate, and dipentaerythritol monohydroxypentamethacrylate.

[0057] The photopolymerizable monomer preferably comprises at least one selected from polyfunctional acrylate compounds and polyfunctional methacrylate compounds, more preferably at least one selected from liquid crystalline polyfunctional acrylate compounds and polyfunctional methacrylate compounds, and even more preferably 4,4'-bis[6-(acryloyloxy)hexyloxy]biphenyl (BAB6), 4,4'-bis[6-(methacryloyloxy)hexyloxy] It contains at least one selected from the group consisting of xy]biphenyl, 4,4'-bis{4-[6-(acryloyloxy)hexyloxy]benzoate}biphenylene (BABB6), bis[4-[3-(acryloyloxy)propoxy]benzoic acid]2-methyl-1,4-phenylene, 2-methyl-1,4-phenylenebis(4-3-(methacryloyloxy)propoxy)benzoate), and 6-(4'-cyano-1,1'-biphenyl-4-yloxy)hexyl acrylic acid. The photopolymerizable monomer may be used alone or in combination of two or more.

[0058] The photopolymerization initiator is not particularly limited, and conventionally known photopolymerization initiators can be used. The photopolymerization initiator can be appropriately selected depending on the photoisomerized material used. However, from the viewpoint of transparency in the transparent state, it is preferable that the photopolymerization initiator can generate radicals that can initiate polymerization of the photopolymerizable monomer by exposure to light of a wavelength different from the wavelength that promotes isomerization of the photoisomerized material. In this specification, "light of a wavelength different from the wavelength that promotes isomerization of the photoisomerized material" means "light of a wavelength different from the wavelength that promotes isomerization from the trans isomer to the cis isomer of the photoisomerized material," or "light of a wavelength different from the wavelength that promotes isomerization from the cis isomer to the trans isomer of the photoisomerized material."

[0059] From the viewpoint of curability, the photopolymerization initiator preferably has absorbance at visible light wavelengths, and more preferably at wavelengths included in the range of 400 to 500 nm. Furthermore, from the viewpoint of curability, the photopolymerization initiator preferably has an absorbance of 0.5 or higher, and more preferably 1.0 or higher, at a concentration of 0.1% by mass, a path length of 1 cm, and a wavelength of 400 nm. The upper limit of the absorbance is not particularly limited, for example, 3.0 or less.

[0060] The absorbance of the photopolymerization initiator can be measured using a spectrophotometer (Shimadzu Corporation, UV-2550) in accordance with JIS K0115:2004. The sample used for measurement is a solution of the photopolymerization initiator dissolved at a concentration of 0.1% by mass in a solvent that does not absorb wavelengths of 400-500 nm (e.g., acetonitrile, 1-methyl-2-pyrrolidone).

[0061] Examples of photopolymerization initiators include phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, bis(2,4-cyclopentadienyl)bis[2,6-difluoro-3-(1-pyryl)phenyl]titanium(IV), (benzene)tricarbonylchromium, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(dimethylamino)benzophenone, 2-chlorothioxanthene-9-one, 4-(dimethylamino)benzophenone, phenanthrenequinone, and thioxanthene-9-one. Photopolymerization initiators may be commercially available or synthetically produced. Examples of commercially available products include IRGACURE 819, 784 (manufactured by IGM Resins B.V.), and DAROCUR® TPO (manufactured by BASF). The photopolymerization initiator may be used alone or in combination of two or more types.

[0062] The content of photopolymerizable monomer polymers (resin amount) in the liquid crystal layer is preferably 1 to 40 parts by mass, more preferably 3 to 38 parts by mass, and even more preferably 5 to 36 parts by mass, per 100 parts by mass of liquid crystal molecules.

[0063] (Other components) The liquid crystal layer may contain other components as long as they do not impair the effects of the present invention. Examples of other components include nanoparticles, dichroic dyes, photopolymerization initiators, and dye sensitizers.

[0064] Examples of nanoparticles include nanoparticles made from metal oxides such as silicon, titanium, zirconium, and barium.

[0065] Examples of dichroic pigments include acridine pigments, oxazine pigments, cyanine pigments, naphthalene pigments, and anthraquinone pigments.

[0066] Examples of photopolymerization initiators include methyldiethanolamine and 4-dimethylaminobenzoic acid.

[0067] The dye sensitizer is not particularly limited as long as it is a dye that can be excited by light irradiation and transfer energy to a photopolymerization initiator. Examples of dye sensitizers include coumarin dyes, rhodamine dyes, oxazine dyes, carbocyanine dyes, styryl dyes, xanthene dyes, merocyanine dyes, rhodacyanine dyes, porphyrin dyes, and acridine dyes.

[0068] [Characteristics of the Liquid Crystal Dimming Element] As described above, the liquid crystal dimming element according to this embodiment has the property that its light scattering increases when it receives ultraviolet light and decreases when it receives visible light. Here, in the transparent state (state in which light scattering is reduced), it is preferable that the visible light transmittance of the liquid crystal dimming element according to this embodiment is high. Specifically, the visible light transmittance (transmittance for light with a wavelength of 650 nm) of the liquid crystal dimming element in the state in which light scattering is reduced (transparent state) is preferably 70% or more, more preferably 80% or more, even more preferably 84% or more, and particularly preferably 87% or more at 30°C. On the other hand, in the screen state (state in which light scattering is increased), it is preferable that the visible light transmittance of the liquid crystal dimming element according to this embodiment is low. Specifically, the visible light transmittance (transmittance for light with a wavelength of 650 nm) of the liquid crystal dimming element in the screen state is preferably 30% or less, more preferably 20% or less, even more preferably 10% or less, and particularly preferably 5% or less at 30°C.

[0069] Furthermore, the liquid crystal dimming element according to this embodiment also has the characteristic that the average diameter of the voids contained in the polymer of the photopolymerizable monomer in the cross-section in the planar direction of the liquid crystal layer is smaller than the theoretical value of the helical pitch of the liquid crystal molecules caused by the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C. This characteristic will be explained below with reference to Figure 3.

[0070] As described above, the liquid crystal layer of the liquid crystal dimming element according to this embodiment contains a photoisomerized material and a non-photoresponsive chiral compound having optical activity different from that of the photoisomerized material. Therefore, at room temperature (for example, 27°C), the helical twisting power (HTP) between the photoisomerized material and the non-photoresponsive chiral compound cancels each other out, resulting in a compensation state (Figure 3(a)). As a result, no helical twisting force acts on the liquid crystal molecules at room temperature, and no twisting occurs in the liquid crystal molecules. Thus, the transparency of the liquid crystal dimming element in its transparent state is maintained at a high level.

[0071] On the other hand, the helical induced force of non-photoresponsive chiral compounds is temperature-dependent, and under high temperature conditions (e.g., 70°C), the helical induced force of non-photoresponsive chiral compounds decreases by ΔHTP as shown in Figure 3(b). Consequently, under high temperature conditions, the helical induced force of the photoisomerized material is not sufficiently canceled, and the helical induced force acts on the liquid crystal molecules, creating room for twisting of the liquid crystal molecules. Here, the length of the liquid crystal molecules corresponding to one turn of the helix when the liquid crystal molecules twist due to the temperature change from 27°C to 70°C (helical pitch) depends on the temperature change (decrease amount; ΔHTP) of the helical induced force of the non-photoresponsive chiral compound and the mass ratio of the non-photoresponsive chiral compound to the liquid crystal molecules (c), and its theoretical value is calculated according to Equation 1 below.

[0072]

[0073] In the formula, P is the helical pitch of the liquid crystal molecule [μm], ΔHTP is the temperature change (decrease) of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C, and c is the mass ratio of the non-photoresponsive chiral compound to the liquid crystal molecule (mass of the non-photoresponsive chiral compound / mass of the liquid crystal molecule). The value of ΔHTP can be calculated by adding 1% by mass of the non-photoresponsive chiral compound to 100% by mass of the liquid crystal molecule, measuring the HTP values ​​at 27°C and 70°C, and taking the difference between them.

[0074] As described above, in the liquid crystal layer, liquid crystal molecules exist within voids contained in the polymer of photopolymerizable monomers. In this case, if the size of the voids is greater than or equal to the theoretical value of the helical pitch calculated according to the above formula 1, the liquid crystal molecules contained within the voids can twist. When liquid crystal molecules twist within the voids contained in the polymer of photopolymerizable monomers, the transparency of the liquid crystal dimming element in its transparent state decreases. In contrast, in the liquid crystal dimming element according to this embodiment, by making the average diameter of the voids contained in the polymer of photopolymerizable monomers smaller than the theoretical value of the helical pitch of liquid crystal molecules caused by the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C, the liquid crystal molecules do not twist even under high-temperature conditions, maintaining their aligned orientation and solving the problem of decreased transparency. For this reason, the liquid crystal dimming element according to one embodiment of the present invention can be suitably used in areas with very high ambient temperatures (air temperature) or in environments where high temperatures occur temporarily. The average diameter of the voids contained in the photopolymerizable monomer polymer in the cross-section of the liquid crystal layer in the planar direction shall be calculated using the method described in the Examples section below. Furthermore, from the viewpoint of more significantly exhibiting the effects of the present invention, the average diameter value is preferably 0.4 to 0.7 times the theoretical value, and more preferably 0.45 to 0.65 times. Furthermore, there are no particular restrictions on the absolute value of the average diameter, but from the viewpoint of more significantly exhibiting the effects of the present invention, it is preferably 2.0 μm or less.

[0075] The visible light transmittance (transmittance for light with a wavelength of 650 nm) at 70°C in a state where the light scattering properties of the liquid crystal dimming element are reduced (transparent state) is not particularly limited, but is preferably 70% or more, more preferably 73% or more, even more preferably 74% or more, particularly preferably 90% or more, and most preferably 92% or more.

[0076] Furthermore, in other preferred embodiments, the average diameter value is preferably 0.5 times or more the theoretical value, more preferably 0.55 to 0.75 times, and even more preferably 0.6 to 0.7 times. With such a configuration, the diffuse reflectance value when the liquid crystal dimming element is in a screen state is increased, and the visibility of the image displayed on the liquid crystal dimming element in a state where the light scattering properties of the liquid crystal dimming element are reduced (screen state) can be improved. The diffuse reflectance value for light with a wavelength of 550 nm at 25°C in the screen state is not particularly limited, but is preferably 10% or more, more preferably 11% or more, and even more preferably 12% or more.

[0077] 《Method for Manufacturing a Liquid Crystal Light-Damping Element》 The method for manufacturing a liquid crystal light-dampening element according to the above-described embodiment of the present invention is not particularly limited, and conventionally known knowledge can be referenced as appropriate.

[0078] As an example, a liquid crystal dimming element according to one embodiment of the present invention may be manufactured by a manufacturing method that includes applying an electric field to a liquid crystal composition, which is filled between a pair of transparent substrates arranged so that the orientation functional layers face each other, and polymerizing the photopolymerizable monomer while filling the composition with the liquid crystal molecules, a photoisomerization material, a non-photoresponsive chiral compound, a photopolymerizable monomer, and a photopolymerization initiator (hereinafter also referred to as the "polymerization step").

[0079] The liquid crystal composition is the composition of the liquid crystal layer before curing by photopolymerization described above, and contains the components of the liquid crystal layer described above, and optionally further contains a solvent. The solvent is not particularly limited as long as it is compatible with liquid crystal molecules, photoisomerization materials, non-photoresponsive chiral compounds, photopolymerizable monomers, and photopolymerization initiators. Examples of solvents include toluene, acetone, ethyl acetate, methyl ethyl ketone, and hexanediol diacrylate.

[0080] In the polymerization process, the liquid crystal composition described above is first filled between a pair of transparent substrates, each having a transparent electrode and an alignment functional layer disposed on one side of the transparent electrode, with the alignment functional layers facing each other. There are no particular restrictions on the method of filling the liquid crystal composition.

[0081] Next, the photopolymerizable monomer is polymerized while an electric field is applied to the liquid crystal composition. To polymerize the photopolymerizable monomer, light with a wavelength absorbed by the photopolymerization initiator used can be irradiated. Here, from the viewpoint of further improving the transparency of the liquid crystal dimming element in its transparent state, it is preferable to carry out the process in an environment that blocks ultraviolet light and the wavelength absorbed by the polymerization initiator used. For example, this process can be carried out under orange light (wavelength 595 to 610 nm). Furthermore, it is preferable that the wavelength of the light irradiated at this time is different from the wavelength that promotes the isomerization of the photoisomerization material. This suppresses the isomerization of the trans or cis photoisomerization material to the cis or trans isomerization during polymerization, and also suppresses the disorder of the orientation of liquid crystal molecules associated with the isomerization of the photoisomerization material. Therefore, a liquid crystal layer with higher transparency can be obtained in the transparent state. The wavelength of the light irradiated can be appropriately selected depending on the photoisomerization material and photopolymerization initiator used.

[0082] In one embodiment, from the viewpoint of further suppressing disorder in the orientation of liquid crystal molecules, it is preferable to irradiate with visible light, and more preferably to irradiate with light having a wavelength in the range of 400 to 500 nm, and / or light having an emission peak wavelength in the range of 420 to 460 nm. In particular, when the above-mentioned azobenzene compound is used as the photoisomerized material, the transparency of the liquid crystal layer in the transparent state can be improved by irradiating with light having a wavelength in this range. When irradiating with light, a filter that allows only a specific wavelength range to pass through may be used as needed. The amount of light to be irradiated is, for example, 1,000 to 50,000 mJ / cm². ２ Furthermore, the temperature conditions during light irradiation are, for example, 10 to 40°C.

[0083] In the polymerization process, an electric field is applied to the filled liquid crystal composition simultaneously with the polymerization of the photopolymerizable monomer by light irradiation as described above. This electric field should be applied along the lamination direction between the transparent substrate and the liquid crystal layer. Furthermore, the period of light irradiation for polymerization of the photopolymerizable monomer and the period of application of the electric field do not need to coincide perfectly; it is sufficient that there is at least a period during which light irradiation and electric field application are performed simultaneously. However, it is preferable that an electric field is applied to the liquid crystal composition throughout the entire period of light irradiation. The electric field applied to the liquid crystal composition may be a DC electric field or an AC electric field. The frequency of the AC electric field is usually around 40 to 80 Hz.

[0084] Furthermore, when manufacturing a liquid crystal dimming element using the above-described manufacturing method, the average diameter of the voids contained in the polymer of the photopolymerizable monomer can be controlled by, for example, changing the type of photopolymerizable monomer, adjusting the polymerization rate (slowering it reduces the voids), adjusting the viscosity of the liquid crystal molecules (lower viscosity reduces the voids), or adjusting the intensity of the light irradiated during polymerization (lowering the intensity reduces the voids).

[0085] <Operation of the Display Device> Next, the operation of the display device 10, which displays an image on the image display unit 100, will be explained with reference to Figures 4 and 5. Figure 4 is a diagram illustrating the operation of the display device 10 when an image is displayed, and Figure 5 is a diagram illustrating the operation of the display device 10 when the image is not displayed.

[0086] As shown in Figure 4, when displaying an image on the image display unit 100, first, the first projector 200 projects ultraviolet light onto the front surface 100a of the image display unit 100. The ultraviolet light projection area 100c on the image display unit 100 changes from transparent to opaque. Then, the third projector 400 projects second visible light onto the projection area 100c on the opaque image display unit 100 to display the image 600 on the image display unit 100. While the image 600 is displayed on the image display unit 100, the first projector 200 continues to project ultraviolet light onto the image display unit 100 to prevent the image display unit 100 from returning from opaque to transparent due to the reception of second visible light. Specifically, the first projector 200 continuously projects ultraviolet light at an output such that, for example, the rate at which the photoisomerized material isomerizes due to ultraviolet light (for example, the rate at which it isomerizes from the trans isomer to the cis isomer) is greater than the rate at which it isomerizes due to the second visible light (for example, the rate at which it isomerizes from the cis isomer to the trans isomer).

[0087] On the other hand, as shown in Figure 5, when no image is displayed on the image display unit 100 (when the image is erased), first, the first and third projectors 200 and 400 stop emitting ultraviolet light and second visible light, respectively. Then, the second projector 300 emits first visible light onto the front surface 100a of the image display unit 100, returning the ultraviolet light emission area 100c on the image display unit 100 from an opaque state to a transparent state. At this time, it is also possible to return to a transparent state (erase the image) in a short time by applying a voltage between the transparent electrodes of the liquid crystal dimming element provided in the display device 10.

[0088] As described above, the display device 10 of this embodiment switches between a transparent state and an opaque state of the image display body 100 by switching between emitting ultraviolet light and first visible light. Then, second visible light is emitted onto the opaque image display body 100 to display the image 600 on the opaque image display body 100. With this configuration, the image display body 100, which is normally transparent, can be temporarily made opaque to display the image 600 on the image display body 100.

[0089] The embodiments described above have used the application of liquid crystal dimming elements to display devices as an example, but the applications of liquid crystal dimming elements are not limited to this. Liquid crystal dimming elements can also be applied to, for example, light-shielding devices for suppressing temperature rise in greenhouses or indoor living spaces caused by sunlight. In any of these applications, improved transparency in the transparent state under high-temperature conditions is extremely advantageous.

[0090] The following embodiments are also included in the scope of the present invention: a liquid crystal dimming element according to claim 1 having the features of claim 2; a liquid crystal dimming element according to claim 1 having the features of claim 3; a liquid crystal dimming element according to claim 1 having the features of claim 4; a liquid crystal dimming element according to claim 1 having the features of claim 5; a display device using a liquid crystal dimming element according to any one of claims 1 to 5; a light-shielding device using a liquid crystal dimming element according to any one of claims 1 to 5.

[0091] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, the following operations were carried out under conditions of 25°C and 50% RH.

[0092] 《Fabrication of Liquid Crystal Dimming Elements》 Liquid crystal dimming elements for the examples and comparative examples were fabricated using the following method. The specifications of the liquid crystal dimming elements fabricated in this way are shown in Table 1 below.

[0093] [Comparative Example 1] The liquid crystal molecule is Sb-826010 (manufactured by Shanben), a p-type liquid crystal; the photoisomer material is BN-OCO-Ph-8, an azobenzene compound; the non-photoresponsive chiral compound is (S)-BN-OCO(bis[4-(4-pentyloxyphenyl)benzoic acid](aS)-1,1'-binaphthalene-2,2'-diyl); the photopolymerizable monofunctional monomer is 4-[(6-acryloyloxy)hexyloxy]-4'-cyanobiphenyl (CB6); the photopolymerizable polyfunctional monomer is 4,4'-bis[6-(acryloyloxy)-hexyloxy]biphenyl (BAB6) and polyethylene glycol diacrylate (number of repeating oxyethylene groups n=9) (PEGDA); and the photopolymerization initiator is IRGACURE 819 (IGM Resins A liquid crystal composition was prepared by mixing (manufactured by B.V. Co.) in a mass ratio of 76.85:4.65:3.35:14.2:0.72:0.08:0.15.

[0094] The liquid crystal composition prepared above was heated to 100°C on a hot plate and injected into a liquid crystal evaluation glass cell placed on the same hot plate. Here, a vertically aligned liquid crystal evaluation glass cell (cell gap 10 μm, manufactured by EHC Corporation; comprising a pair of transparent substrates with a vertical alignment film arranged as an alignment functional layer on the surface of a transparent electrode) using a polyimide film (AL63201, manufactured by JSR Corporation) was used as the liquid crystal evaluation glass cell. After injecting the liquid crystal composition, the evaluation glass cell was allowed to cool under room temperature conditions. The above process was carried out in an environment where light with a wavelength of 500 nm or less was blocked.

[0095] Subsequently, while applying an AC electric field of 30V, 50Hz to the evaluation glass cell, light with a wavelength of 420nm was emitted at 30mW / cm². ２ The liquid crystal composition was cured by irradiating it with light intensity for 20 minutes to form a liquid crystal layer, and the liquid crystal dimming element of this comparative example was fabricated.

[0096] [Example 1] The liquid crystal dimming element of this example was fabricated using the same method as in Comparative Example 1 described above, except that the mixing ratio of the components of the liquid crystal composition was changed to 63.72:4.65:3.35:26.36:0.29:1.35:0.28 by mass ratio.

[0097] [Example 2] A liquid crystal composition was prepared by mixing Sb-826010 (manufactured by Shanben), a p-type liquid crystal molecule, BN-OCO-Ph-8, an azobenzene compound, as a photoisomerizing material, (S)-BN-OCO (bis[4-(4-pentyloxyphenyl)benzoic acid](aS)-1,1'-binaphthalene-2,2'-diyl), a non-photoresponsive chiral compound, 4,4'-bis{4-[6-(acryloyloxy)hexyloxy]benzoate}biphenylene (BABB6), a photopolymerizable polyfunctional monomer, and IRGACURE 819 (manufactured by IGM Resins B.V.), in a mass ratio of 86.95:4.65:3.35:5.0:0.05. Then, the liquid crystal dimming element of this embodiment was fabricated using the same method as in Comparative Example 1 described above, except that this liquid crystal composition was used.

[0098] [Example 3] The liquid crystal dimming element of this example was fabricated using the same method as in Example 2 described above, except that the mixing ratio of the components of the liquid crystal composition was changed to 84.42:4.65:3.35:7.5:0.08 by mass ratio.

[0099] [Example 4] The liquid crystal dimming element of this example was fabricated using the same method as in Example 2 described above, except that the mixing ratio of the components of the liquid crystal composition was changed to 81.90:4.65:3.35:10.0:0.10 by mass ratio.

[0100]

[0101] 《Measurement of the average diameter of voids contained in the photopolymerizable monomer polymer in the liquid crystal layer of a liquid crystal dimming element》 For the liquid crystal dimming elements prepared in Comparative Example 1 and Examples 1 to 4 described above, the average diameter of voids contained in the photopolymerizable monomer polymer in the liquid crystal layer was measured using the following method.

[0102] First, the liquid crystal dimming element was immersed in hexane for more than three days to remove components other than the resin. Next, one side of the transparent substrate of the evaluation glass cell was peeled off to expose the liquid crystal layer. After depositing platinum onto this exposed surface of the liquid crystal layer, the platinum deposition surface was observed using a scanning electron microscope (SEM). The observation magnification was set to 2000x, and the image was 2.6 × 10⁻⁶.－９ I understand ２ The major axis of all voids observed in an observation area of ​​(40 μm vertical × 65 μm horizontal) was measured, and the average of these measurements was calculated as the average diameter. Image processing software ImageJ was used for the measurements. The results are shown in Table 2 below. Table 2 also shows the theoretical value of the helical pitch of the liquid crystal molecule (Sb-826010) due to the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound ((S)-BN-OCO), calculated according to Equation 1 below. Furthermore, cross-sectional SEM images of the average diameters of Comparative Example 1 and Example 1 are shown in Figures 6(a) and (b), respectively.

[0103]

[0104] In the formula, P is the helical pitch of the liquid crystal molecule [μm], ΔHTP is the temperature change (decrease) of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C, and c is the mass ratio of the non-photoresponsive chiral compound to the liquid crystal molecule (mass of the non-photoresponsive chiral compound / mass of the liquid crystal molecule). The value of ΔHTP was calculated to be 8.15 [μm] in a preliminary experiment in which the HTP values ​​at 27°C and 70°C were measured by adding 1% by mass of the non-photoresponsive chiral compound to 100% by mass of liquid crystal molecules, and this value was used.

[0105] 《Measurement of Visible Light Transmittance of Liquid Crystal Dimmer Elements》 The visible light transmittance of the liquid crystal dimmer elements fabricated in Comparative Example 1 and Examples 1 to 4 above was measured using the measuring apparatus shown in Figure 7. Figure 7 is a layout diagram of the measuring apparatus for measuring the transmittance of liquid crystal dimmer elements. In the measuring apparatus shown in Figure 7, the liquid crystal dimmer element 110 is placed between a laser diode that emits laser light with a wavelength λ of 650 [nm] and a photodiode that receives the laser light. The distance between the liquid crystal dimmer element and the photodiode was set to approximately 8 cm. The distance between the liquid crystal dimmer element and the laser diode was set to approximately 20 cm. Here, the photodiode receives the laser light that has passed through the liquid crystal dimmer element 110, converts the intensity of the received laser light into the intensity of a current, and outputs it to an oscilloscope.

[0106] The following are the model names of the equipment used to measure the transmittance of the liquid crystal dimming element 110: Laser diode: THORLAB HANDHELD LASER SOURCE Photodiode: HAMAMATSU Photodiode module C10439 Oscilloscope: Tektronix TBS 1052B Digital Oscilloscope.

[0107] The visible light transmittance of the liquid crystal dimming element 110 was measured using the apparatus described above (Figure 7). This measurement of visible light transmittance was performed under temperature conditions of 30°C and 70°C, respectively. The results of the visible light transmittance measurements are shown in Table 2 below. A higher visible light transmittance value indicates higher transparency of the liquid crystal dimming element in its transparent state.

[0108] Measurement of Diffuse Reflectance of Liquid Crystal Dimmers The diffuse reflectance of the liquid crystal dimmers fabricated in Comparative Example 1 and Examples 1 to 4 above was measured at 25°C in a screen state. In order to create a screen state, ultraviolet light was projected using an ultraviolet light source (THORLAB M365LP1-C1). In all experimental examples, the visible light transmittance of the liquid crystal dimmers decreased upon irradiation with ultraviolet light.

[0109] White light was shone onto the liquid crystal dimming element, which was set to the screen state as described above, and the diffuse reflectance was measured using a colorimeter (CM3600, manufactured by Konica Minolta, Inc.) based on the light intensity of the diffuse reflectance component. The evaluation wavelength used was 550 nm, which is the wavelength for which human visual sensitivity is highest. The results of the diffuse reflectance measured in this way are shown in Table 2 below. Note that a higher diffuse reflectance value indicates higher visibility of the image displayed on the liquid crystal dimming element in the screen state.

[0110]

[0111] As shown in Table 2, the liquid crystal dimming elements of Examples 1 to 4 maintained a high visible light transmittance even under high temperature conditions (70°C). This is thought to be because the average diameter of the voids in the polymer of the photopolymerizable monomer constituting the liquid crystal layer was smaller than the theoretical value of the helical pitch of the pre-liquid crystal molecules due to the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C in each example, thereby suppressing the twisting of the liquid crystal molecules under high temperature conditions. In contrast, the liquid crystal dimming element of Comparative Example 1 showed a significant decrease in visible light transmittance under high temperature conditions (70°C). This is thought to be because the average diameter of the voids was greater than the theoretical value mentioned above, and therefore the twisting of the liquid crystal molecules was not suppressed under high temperature conditions.

[0112] Furthermore, in Examples 1 and 2, where the average diameter of the voids was 0.5 times or more than the theoretical value, the diffuse reflectance values ​​were particularly high. This is thought to be because the large voids provide space for the liquid crystal molecules to move, making it easier for the liquid crystal molecules to move. In addition, in Examples 2 and 3, the visible light transmittance under high-temperature conditions was higher than at room temperature. At room temperature, the refractive index of liquid crystal molecules differs depending on the orientation of the molecules. Even if the material appears transparent to the naked eye, a slight difference in the orientation of the molecules will cause a difference in refractive index, scattering light and reducing transmittance. In contrast, under high-temperature conditions, the liquid crystal undergoes a phase change, and the refractive index becomes equal regardless of the orientation of the liquid crystal molecules. As a result, light does not refract or scatter as it passes through the liquid crystal layer, resulting in high transmittance.

[0113] 10 Display device, 100 Image display unit, 100a Front, 100b Back, 100c Light projection area, 110 Liquid crystal dimming element, 120 Dimming layer, 130 Ultraviolet light shielding layer, 200 First projector, 300 Second projector, 400 Third projector, 500 Control unit, 600 Image.

Claims

1. A liquid crystal dimming element comprising: a pair of transparent substrates having a transparent electrode and an orientation functional layer disposed on one surface of the transparent electrode, wherein the orientation functional layers are arranged facing each other; and a liquid crystal layer interposed between the pair of transparent substrates, comprising a polymer of liquid crystal molecules, a photoisomerization material, a non-photoresponsive chiral compound, and a photopolymerizable monomer, wherein the light scattering increases upon reception of ultraviolet light and decreases upon reception of visible light, and the average diameter of the voids contained in the photopolymerizable monomer polymer in the cross-section in the planar direction of the liquid crystal layer is smaller than the theoretical value of the helical pitch of the liquid crystal molecules due to the temperature change of the helical induced force (HTP) of the non-photoresponsive chiral compound from 27°C to 70°C.

2. The liquid crystal dimming element according to claim 1, wherein the average diameter is 2.0 μm or less.

3. The liquid crystal dimming element according to claim 1, wherein the average diameter is 0.5 times or more the theoretical value.

4. The liquid crystal dimming element according to claim 1, wherein the transmittance to light with a wavelength of 650 nm at 70°C in a state of increased light scattering is 70% or more.

5. The liquid crystal dimming element according to claim 1, wherein the diffuse reflectance for light with a wavelength of 550 nm at 25°C in a state where light scattering is reduced is 10% or more.

6. A display device using a liquid crystal dimming element according to any one of claims 1 to 5.

7. A light-shielding device using a liquid crystal dimming element according to any one of claims 1 to 5.

Images