Dimming sheet and screen

Abstract

To provide a dimming sheet and a screen that are capable of suppressing a whitening phenomenon and suppressing see-through of a sheet as well.SOLUTION: A dimming sheet 10 comprises: a dimming layer 20 that includes a transparent polymer layer having a plurality of voids and a liquid crystal composition filling the voids; and a pair of transparent electrode layers 31 and 32 holding the dimming layer 20 therebetween. The liquid crystal composition includes liquid crystal compounds and dichroic pigments. Orientations of the liquid crystal compounds and the dichroic pigments change in response to a variation of a potential difference between the pair of transparent electrode layers 31 and 32. Consequently, the dimming sheet 10 switches from a transparent state to a colored opaque state. The dimming sheet 10 exhibits a haze of 85% or more and less than 95% in the opaque state, and a ratio of a tolan-based compound in the liquid crystal compounds is less than 20 mass%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light control sheet and a screen having variable light transmittance. [Background technology]

[0002] The light-controlling sheet comprises a light-controlling layer containing a liquid crystal compound dispersed in a polymer material, and a pair of transparent electrode layers sandwiching the light-controlling layer, and a driving voltage is applied between the pair of transparent electrode layers. Since the orientation state of the liquid crystal compound changes depending on whether or not a driving voltage is applied, it is possible to switch between a transmission state in which light is transmitted through the light-controlling layer, and a scattering state in which light is scattered by the light-controlling layer (see, for example, Patent Document 1). A light-controlling sheet in the transmission state is transparent, and a light-controlling sheet in the scattering state appears cloudy white.

[0003] The light-controlling sheet in the scattering state is used for blocking the view for privacy protection, etc., and for projecting images. Therefore, in the scattering state, it is desired that the light-controlling sheet has low transparency, that is, a high haze, which is an index showing the degree of turbidity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-45135 A Summary of the Invention [Problem to be solved by the invention]

[0005] From the viewpoint of improving the design and contrast of the projected image, it is sometimes preferable for the light-control sheet in the scattering state to have a color other than white. For example, a light-control sheet that appears black in the scattering state has been proposed by laminating a smoke film.

[0006] However, when external light is incident on the light-controlling sheet in a scattering state, the scattered light is emitted forward or backward of the light-controlling sheet, causing a whitening phenomenon in which the light-controlling sheet appears whitish even if a smoke film is laminated thereon. When the whitening phenomenon occurs, the effects of improving the design and improving the contrast of the projected image cannot be fully obtained. In particular, when the light-controlling sheet is used outdoors or in the vicinity thereof, such as when the light-controlling sheet is attached to the windows of a vehicle, the whitening phenomenon is likely to occur when strong external light is incident on the light-controlling sheet.

[0007] Furthermore, the higher the haze, the stronger the scattering, which tends to cause whitening. Although it is possible to suppress the whitening phenomenon by lowering the haze, if the haze is low, the light-controlling film will be transparent due to the scattering, making it impossible to maintain the low transparency required for applications such as blocking visibility and projecting images. Therefore, there is a demand for a light-controlling film that can achieve low transparency while suppressing the whitening phenomenon. [Means for solving the problem]

[0008] Various aspects of a light controlling sheet and a screen for solving the above problems will be described below. [Aspect 1] A light-controlling sheet comprising a transparent polymer layer having a plurality of voids, a liquid crystal composition filling the voids, the liquid crystal composition including a liquid crystal compound and a dichroic dye, and a pair of transparent electrode layers sandwiching the light-controlling layer, the light-controlling sheet changing the orientation of the liquid crystal compound and the dichroic dye in response to a change in the potential difference between the pair of transparent electrode layers, thereby switching from a transparent state to a colored opaque state, the haze of the light-controlling sheet in the opaque state being 85% or more and less than 95%, and the proportion of a tolan-based compound in the liquid crystal compound being less than 20% by mass. A dimming sheet that is perfect.

[0009] According to the above-mentioned configuration, the low haze reduces light scattering in the light-controlling layer, thereby preventing the occurrence of the whitening phenomenon. Furthermore, the light-controlling sheet is prevented from being see-through in the opaque state even when the haze is low due to the light absorption caused by the dichroic dye.

[0010] [Aspect 2] The light-controlling sheet according to [Aspect 1], wherein the proportion of the liquid crystal compound in the light-controlling layer is less than 60 mass %. According to the above configuration, the haze of the light controlling sheet can be easily controlled within the above range.

[0011] [Aspect 3] The light-control sheet according to [Aspect 1] or [Aspect 2], wherein the thickness of the light-control layer is 10 μm or more and 22 μm or less. According to the above configuration, the haze of the light controlling sheet can be easily controlled within the above range.

[0012] [Aspect 4] The light controlling sheet according to any one of [Aspect 1] to [Aspect 3], wherein the liquid crystal composition contains the dichroic dye that exhibits black color. According to the above configuration, the light controlling sheet can be more effectively prevented from being seen through.

[0013] [Aspect 5] The light-controlling sheet according to any one of [Aspect 1] to [Aspect 4], wherein the proportion of the dichroic dye in the light-controlling layer is 2 mass % or more. According to the above configuration, the light controlling sheet can be more effectively prevented from being seen through.

[0014] [Aspect 6] A screen comprising a transparent polymer layer having a plurality of gaps, a light-adjusting layer containing a liquid crystal composition filling the gaps, the liquid crystal composition containing a liquid crystal compound and a dichroic dye, and a pair of transparent electrode layers sandwiching the light-adjusting layer, wherein the orientation of the liquid crystal compound and the dichroic dye is changed in response to a change in the potential difference between the pair of transparent electrode layers, thereby switching from a transparent state to a colored opaque state, and an image is projected in the opaque state, wherein the haze of the light-adjusting sheet in the opaque state is 85% or more and less than 95%, and the proportion of tolane-based compounds in the liquid crystal compound is less than 20% by mass.

[0015] According to the above-mentioned configuration, the low haze reduces the scattering of light in the light-adjusting layer, thereby preventing the occurrence of the whitening phenomenon. Furthermore, the dichroic dye absorbs light, so that the screen is prevented from being see-through in the opaque state even with a low haze. This allows the projection of a high-contrast image. Effect of the Invention

[0016] According to the present invention, it is possible to suppress the whitening phenomenon and to suppress the sheet from being see-through. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a diagram showing a cross-sectional structure of a normal type light controlling sheet in one embodiment. [Diagram 2] FIG. 2 is an enlarged view of a portion of a light-controlling layer according to an embodiment. [Diagram 3] FIG. 2 is a diagram showing a cross-sectional structure of a reverse-type light controlling sheet in one embodiment. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between haze in an opaque state and liquid crystal concentration in a light controlling sheet according to an embodiment. [Diagram 5] 1 is a diagram showing an example of the relationship between the haze in an opaque state and the thickness of a light-controlling layer in a light-controlling sheet according to an embodiment. [Figure 6] 1 is a diagram showing an example of the relationship between clarity in an opaque state and the thickness of a light-adjusting layer in a light-adjusting sheet according to an embodiment. [Figure 7] FIG. 4 is a graph showing an example of the relationship between contrast and dichroic dye concentration in a light adjusting sheet according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An embodiment of a light controlling sheet and screen will be described with reference to the drawings. [Composition of light control sheet] The structure of the light controlling sheet will be described with reference to Fig. 1 and Fig. 2. The light controlling sheet of the present embodiment has, for example, either a normal type or a reverse type layer structure. First, the layer structure of the normal type will be described with reference to Fig. 1.

[0019] As shown in Fig. 1, the light control sheet 10A, which is a normal type light control sheet 10, includes a light control layer 20, a first transparent electrode layer 31, a second transparent electrode layer 32, a first transparent support layer 41, and a second transparent support layer 42. The light control layer 20 is sandwiched between the first transparent electrode layer 31 and the second transparent electrode layer 32, and is in contact with these transparent electrode layers 31 and 32. The first transparent support layer 41 supports the first transparent electrode layer 31 on the side opposite the light control layer 20 with respect to the first transparent electrode layer 31, and the second transparent support layer 42 supports the second transparent electrode layer 32 on the side opposite the light control layer 20 with respect to the second transparent electrode layer 32.

[0020] Fig. 2 is an enlarged view of a region R of the light-adjusting layer 20 in Fig. 1. As shown in Fig. 2, the light-adjusting layer 20 includes a transparent polymer layer 21 and a liquid crystal composition 23. The transparent polymer layer 21 has domains 22 which are voids filled with the liquid crystal composition 23, and the liquid crystal composition 23 is held within the domains 22.

[0021] The structure of the transparent polymer layer 21 and the holding type of the liquid crystal composition 23 are either a polymer network type, a polymer dispersion type, or a capsule type. The polymer network type light control layer 20 has a polymer network having a three-dimensional mesh shape. The polymer network is an example of a transparent polymer layer, and the liquid crystal composition is held in the interconnected mesh-like voids in the polymer network. The polymer dispersion type light control layer 20 has a transparent polymer layer that partitions a large number of isolated voids, and the liquid crystal composition is held in the voids dispersed in the transparent polymer layer. The capsule type light control layer 20 holds the liquid crystal composition in the voids in capsules dispersed in the transparent polymer layer.

[0022] The transparent polymer layer 21 is a polymer of a photopolymerizable compound. The photopolymerizable compound is, for example, an ultraviolet-polymerizable compound. The ultraviolet-polymerizable compound is, for example, an acrylate compound such as butyl ethyl acrylate or cyclohexyl acrylate, a methacrylate compound such as N,N-dimethylaminoethyl methacrylate or phenoxyethyl methacrylate, a stilbene compound, a diacrylate compound, a dimethacrylate compound, a triacrylate compound, a tetraacrylate compound, a trimethacrylate compound, a tetramethacrylate compound, or an oligomer of each of these compounds. The ratio of the transparent polymer layer 21 to the total mass of the light-controlling layer 20 is preferably 20% by mass or more and 80% by mass or less.

[0023] The transparent polymer layer 21 defines a plurality of domains 22. The liquid crystal composition 23 includes a liquid crystal compound 24 and a dichroic dye 25, and is filled in the domains 22. The liquid crystal compound 24 is, for example, a liquid crystal compound having a positive dielectric anisotropy, that is, the dielectric constant of the liquid crystal compound 24 in the long axis direction is larger than the dielectric constant of the liquid crystal compound 24 in the short axis direction.

[0024] The liquid crystal compound 24 is, for example, a Schiff base type, an azo type, an azoxy type, a biphenyl type, a terphenyl type, a benzoic acid ester type, a tolan type, a pyrimidine type, a pyridazine type, a cyclohexane carboxylate type, a phenylcyclohexane type, a biphenylcyclohexane type, a dicyanobenzene type, a naphthalene type, or a dioxane type compound. The liquid crystal composition 23 may contain only a single type of liquid crystal compound 24, or may contain a plurality of types of liquid crystal compounds 24. It may include.

[0025] The dichroic dye 25 has an elongated molecular shape, and the absorbance in the visible region in the long axis direction of the molecule is greater than the absorbance in the short axis direction of the molecule. The dichroic dye 25 exhibits color when the long axis direction crosses the incident direction of light. Specifically, the dichroic dye 25 exhibits color when the long axis direction of the dichroic dye 25 crosses the normal direction of the contact surface of the light-adjusting layer 20 with the first transparent electrode layer 31 or the second transparent electrode layer 32 so as to be approximately perpendicular. The color exhibited by the dichroic dye 25 is, for example, black or a color close to black. The dichroic dye 25 exhibits color when driven by a guest-host type in which the liquid crystal compound 24 is a host.

[0026] The dichroic dye 25 is, for example, polyiodine, an azo compound, an anthraquinone compound, a naphthoquinone compound, an azomethine compound, a tetrazine compound, a quinophthalone compound, a merocyanine compound, a perylene compound, or a dioxazine compound. The liquid crystal composition 23 may contain only a single type of dichroic dye 25, or may contain multiple types of dichroic dyes 25. From the viewpoint of increasing light resistance and dichroic ratio, the dichroic dye 25 is preferably at least one of an azo compound and an anthraquinone compound, and more preferably an azo compound. The ratio of the dichroic dye 25 contained in the light-adjusting layer 20 is, for example, 2% by mass or more and 10% by mass or less with respect to the total mass of the light-adjusting layer 20.

[0027] The liquid crystal composition 23 may contain a viscosity reducing agent, an antifoaming agent, an antioxidant, a weather resistance agent, etc. in addition to the liquid crystal compound 24 and the dichroic dye 25. Examples of the weather resistance agent include an ultraviolet absorbing agent and a light stabilizer.

[0028] The photochromic layer 20 may also include spacers dispersed throughout the transparent polymer layer 21. The spacers define the thickness of the photochromic layer 20 around the spacers, thereby making the thickness of the photochromic layer 20 uniform. The spacers may be bead spacers or photospacers formed by exposing and developing a photoresist. The spacers may be colorless and transparent, or colored and transparent, so long as they are translucent. The color of the colored and transparent spacers is preferably the same color as the color of the dichroic dye 25.

[0029] Each of the first transparent electrode layer 31 and the second transparent electrode layer 32 has electrical conductivity and is transparent to light in the visible region. The material of the transparent electrode layers 31 and 32 is, for example, indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, poly(3,4-ethylenedioxythiophene), or the like.

[0030] Each of the first transparent support layer 41 and the second transparent support layer 42 is a base material that is transparent to light in the visible region. The material of the transparent support layers 41 and 42 is, for example, a synthetic resin or an inorganic compound. Examples of the synthetic resin include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polycarbonates, polyolefins, etc. Examples of the inorganic compound include silicon dioxide, silicon oxynitride, silicon nitride, etc.

[0031] A driving voltage is applied to the first transparent electrode layer 31 and the second transparent electrode layer 32, which is a voltage for changing the alignment state of the liquid crystal compound 24. The light control sheet 10 switches from one of a transparent state and an opaque state to the other based on the change in the alignment state of the liquid crystal compound 24. The transparent state is a state in which the light transmittance, i.e., the parallel line transmittance, is relatively high, and the opaque state is a state in which the light transmittance is relatively low. In addition, the transparent state is a state in which the haze is relatively low, and the opaque state is a state in which the haze is relatively high.

[0032] In the normal type light control sheet 10A, when no driving voltage is applied, the liquid crystal compound The orientation of the long axis direction of the dichroic dye 25 is irregular. Therefore, due to the birefringence of the liquid crystal compound 24 and the difference in refractive index between the liquid crystal compound 24 and the transparent polymer layer 21, the light incident on the light-adjusting sheet 10A is scattered in various directions by the light-adjusting layer 20. In addition, the orientation of the long axis direction of the dichroic dye 25 is also irregular, and at least a part of the dichroic dye 25 exhibits color. Therefore, the normal-type light-adjusting sheet 10A is in a colored, opaque state when no driving voltage is applied.

[0033] When the liquid crystal compound 24 has a positive dielectric anisotropy, the liquid crystal compound 24 is oriented so that its long axis is aligned with the electric field direction when a driving voltage is applied. That is, the orientation of the liquid crystal compound 24 changes so that its long axis is aligned with the thickness direction of the light-adjusting layer 20. At this time, the dichroic dye 25 is also oriented so that its long axis is aligned with the thickness direction of the light-adjusting layer 20. As a result, light scattering in the light-adjusting layer 20 and coloring of the dichroic dye 25 are suppressed, and light is more easily transmitted through the light-adjusting sheet 10A. Therefore, the normal type light-adjusting sheet 10A is in a colorless and transparent state when a driving voltage is applied.

[0034] Next, the layer structure of the reverse-type light controlling sheet will be described with reference to FIG. As shown in Fig. 3, the light control sheet 10B, which is a reverse-type light control sheet 10, includes a first alignment layer 51 and a second alignment layer 52 in addition to the light control layer 20, transparent electrode layers 31 and 32, and transparent support layers 41 and 42. The first alignment layer 51 is located between the light control layer 20 and the first transparent electrode layer 31, and is in contact with these layers. The second alignment layer 52 is located between the light control layer 20 and the second transparent electrode layer 32, and is in contact with these layers. The structure of region R in the light control layer 20 is the same as that of the normal type.

[0035] The first alignment layer 51 and the second alignment layer 52 regulate the alignment of the liquid crystal compound 24. The alignment layers 51 and 52 are, for example, vertical alignment films. The vertical alignment films align the liquid crystal compound 24 so that its long axis direction is along the thickness direction of the light control layer 20. When the alignment layers 51 and 52 are vertical alignment films, a liquid crystal compound having negative dielectric anisotropy, i.e., a liquid crystal compound having a smaller dielectric constant in the long axis direction than in the short axis direction, is used as the liquid crystal compound 24.

[0036] The material of the alignment layers 51 and 52 is, for example, an organic compound such as polyimide, polyamide, polyvinyl alcohol, or a cyanide compound, an inorganic compound such as silicon oxide or zirconium oxide, or silicone, etc. The alignment process for forming the alignment layers 51 and 52 is, for example, a rubbing process, a polarized light irradiation process, or a microfabrication process.

[0037] In the reverse-type light-adjusting sheet 10B, when no driving voltage is applied, the liquid crystal compound 24 receives an orientation restricting force from the orientation layers 51 and 52, and its long axis direction is oriented along the thickness direction of the light-adjusting layer 20. At this time, the dichroic dye 25 is also oriented so that its long axis direction is along the thickness direction of the light-adjusting layer 20. As a result, light scattering in the light-adjusting layer 20 and coloring of the dichroic dye 25 are suppressed, and light is more easily transmitted through the light-adjusting sheet 10B. Therefore, the reverse-type light-adjusting sheet 10B is in a colorless and transparent state when no driving voltage is applied.

[0038] When the dielectric anisotropy of the liquid crystal compound 24 is negative, the liquid crystal compound 24 is oriented so that its long axis direction is perpendicular to the electric field direction when a driving voltage is applied. That is, the orientation of the liquid crystal compound 24 changes so that its long axis direction is approximately perpendicular to the thickness direction of the light-adjusting layer 20. At this time, the dichroic dye 25 is also oriented so that its long axis direction is approximately perpendicular to the thickness direction of the light-adjusting layer 20. As a result, light scattering is easily caused in the light-adjusting layer 20, and the dichroic dye 25 is colored. Therefore, the reverse-type light-adjusting sheet 10B is in a colored, opaque state when a driving voltage is applied.

[0039] In addition, the light-controlling sheet 10 is configured to change the orientation state of the liquid crystal compound by applying a driving voltage. The layer structure of the light-adjusting sheet 10 is not limited to the above as long as the light-adjusting sheet 10 is configured to be switchable between a transparent state and an opaque state. For example, the light-adjusting sheet 10 may include a polarizing layer that controls the polarization of incident light or transmitted light to the light-adjusting layer 20, and the alignment layers 51 and 52 may be horizontal alignment films. Whether the light-adjusting sheet 10 becomes transparent or opaque when a driving voltage is applied can be changed depending on the presence or absence of the alignment layers 51 and 52, the direction in which the alignment regulating force of the alignment layers 51 and 52 acts, the positive or negative dielectric anisotropy of the liquid crystal compound, the presence or absence of a polarizing layer, and the like.

[0040] At least one of the front and back surfaces of the light controlling sheet 10 is attached to a transparent plate made of glass, resin, etc. Examples of the transparent plate include window glass in various buildings, partitions installed indoors, and window glass or windshields in moving objects such as vehicles and aircraft. The surface of the transparent plate may be flat or curved.

[0041] The light-adjusting sheet 10 may also be used as a screen onto which an image is projected. The light-adjusting sheet 10 is applicable to a screen for a transmissive projection system. That is, when projection light, which is light constituting an image, is irradiated from behind the light-adjusting sheet 10 toward the opaque light-adjusting sheet 10, scattered light based on the projection light is emitted forward of the light-adjusting sheet 10. This allows an observer positioned in front of the light-adjusting sheet 10 to view the image.

[0042] [Characteristics of light control sheet] The characteristics of the light controlling sheet 10 of this embodiment will be described. The following characteristics are common to the light controlling sheet 10 regardless of the layer structure.

[0043] The haze of the light controlling sheet 10 in the opaque state is 85% or more and less than 95%. The haze is measured in accordance with ASTM D 1003-00. Generally, conventional light-adjusting sheets that do not contain a dichroic dye and appear cloudy in an opaque state require a haze of 95% or more, preferably 97% or more, to prevent the light-adjusting sheet from being seen through in an opaque state. In other words, the light-adjusting sheet 10 of the present embodiment has a lower haze than conventional light-adjusting sheets that have sufficiently low transparency.

[0044] On the other hand, since the light-adjusting sheet 10 of the present embodiment contains the dichroic dye 25, light absorption occurs due to the dichroic dye 25, and as a result, even if the haze is low, the light-adjusting sheet 10 in an opaque state is prevented from being seen through. This makes it possible to suitably block the view with the light-adjusting sheet 10 and project an image onto the light-adjusting sheet 10. This effect is particularly pronounced when the dichroic dye 25 is black or a color close to black. In order to prevent the light-adjusting sheet 10 from being seen through, the content of the dichroic dye 25 in the light-adjusting layer 20 is preferably 2% by mass or more.

[0045] In addition, the low haze suppresses light scattering in the light-adjusting layer 20, thereby suppressing the occurrence of whitening. Thus, the light-adjusting sheet 10 of the present embodiment can obtain low transparency while suppressing the whitening phenomenon in the opaque state. This allows for improved design and projection of high-contrast images.

[0046] The characteristics of the light-adjusting sheet 10 will be further described. In the liquid crystal composition 23 contained in the light-adjusting layer 20, the ratio of the tolan-based compound to the total mass of the liquid crystal compound 24 is less than 20 mass%. Furthermore, the ratio of the tolan-based compound to the total mass of the liquid crystal compound 24 is preferably less than 15 mass%, more preferably less than 5 mass%. Furthermore, the ratio of the tolan-based compound may be 0 mass%. Liquid crystal materials that are tolan-based compounds are used for the purpose of increasing Δn, which indicates the refractive index anisotropy of the liquid crystal compound, in order to obtain high haze in the opaque state as in the conventional case. However, if the ratio of the tolan-based compound is high, the weather resistance of the light-adjusting sheet 10 decreases and the temperature range in which it can be operated is narrowed.

[0047] In this embodiment, the haze of the light controlling sheet 10 is kept low, and therefore Δn is also kept low. Specifically, in conventional light controlling sheets, Δn is 0.18 or more, and preferably 0.20 or more, whereas in the light controlling sheet 10 of this embodiment, Δn is less than 0.18. Therefore, in the light controlling sheet 10, it is possible to reduce the proportion of tolane-based compounds in the liquid crystal composition 23, which makes it possible to improve weather resistance and expand the temperature range in which the light controlling sheet can be operated. The tolan-based liquid crystal compound is a liquid crystal compound having a tolan skeleton containing an acetylene bond in the bonding group.

[0048] Next, the relationship between the haze and liquid crystal concentration of the light-adjusting sheet 10 in the opaque state will be described. Fig. 4 shows an example of the relationship between the haze and liquid crystal concentration in the opaque state when a liquid crystal compound 24 with Δn = 0.173 is used. The liquid crystal concentration is the ratio of the total mass of the liquid crystal compound 24 to the total mass of the light-adjusting layer 20.

[0049] As shown in Fig. 4, the haze tends to increase as the liquid crystal concentration increases. When Δn is less than 0.18, it can be said that the liquid crystal concentration is preferably less than 60 mass % in order to keep the haze below 95%. Note that, for optimal operation of the light controlling sheet 10, the liquid crystal concentration is preferably 20 mass % or more.

[0050] Next, the relationship between the haze of the light-adjusting sheet 10 in the opaque state and the thickness of the light-adjusting layer 20 will be described. Fig. 5 shows an example of the relationship between the haze in the opaque state and the thickness of the light-adjusting layer 20 when a liquid crystal compound 24 with Δn = 0.173 is used.

[0051] 5, the haze tends to increase as the thickness of the switchable layer 20 increases. When Δn is less than 0.18, in order to achieve a haze of 85% or more and less than 95%, it can be said that the thickness of the switchable layer 20 is preferably 10 μm or more and 22 μm or less, and more preferably 15 μm or more and 20 μm or less.

[0052] In this embodiment, the haze is suppressed to be lower than that of a conventional light-control sheet, so that the light-control layer 20 can be made thinner than before. This suppresses an increase in the driving voltage caused by a decrease in the electric field strength due to an increase in the film thickness of the light-control layer 20.

[0053] The haze can be controlled separately by the liquid crystal concentration and the thickness of the light-adjusting layer 20. As shown in Fig. 4, in order to obtain a suitable haze by having a liquid crystal concentration of less than 60 mass%, the thickness of the light-adjusting layer 20 is preferably 15 μm or more and 20 μm or less. As shown in Fig. 5, in order to obtain a suitable haze by having a thickness of the light-adjusting layer 20 of 10 μm or more and 22 μm or less, the liquid crystal concentration is preferably 40 mass% or more and less than 60 mass%.

[0054] Next, the relationship between the clarity of the light controlling sheet 10 in the opaque state and the thickness of the light controlling layer 20 will be described. Clarity is an index for evaluating the transparency of the light controlling sheet 10. Clarity is the amount of light L that travels straight along the optical axis of the parallel light that entered the light-adjusting layer 20 among the light that has passed through the light-adjusting layer 20. C The amount of narrow-angle scattered light with an angle of ±2.5° or less with respect to the optical axis of the parallel light is the light amount L R When the amount of light L is C and light intensity L R is determined by measurement in accordance with ASTM D 1003-00. 100×(L C -L R ) / (L C +L R )...(Formula 1)

[0055] The transparency of the light-controlling sheet 10 can also be evaluated by the parallel ray transmittance, but the clarity is a parameter whose evaluation results are more likely to match the human visual sense than the parallel ray transmittance. In order to prevent the view behind the light-adjusting sheet 10 from being seen through the light-adjusting sheet 10, the clarity of the light-adjusting sheet 10 in the opaque state is preferably 80% or less, and more preferably 60% or less.

[0056] Fig. 6 shows an example of the relationship between clarity in an opaque state and the thickness of the photochromic layer 20 when a liquid crystal compound 24 with Δn=0.173 is used. As shown in Fig. 6, the thicker the photochromic layer 20, the lower the clarity, that is, the smaller the sense of transparency tends to be. When Δn is less than 0.18, in order to keep the clarity below 80%, it is preferable that the thickness of the photochromic layer 20 is 15 μm or more, and in order to keep the clarity below 60%, it is preferable that the thickness of the photochromic layer 20 is 18 μm or more.

[0057] Next, the relationship between the concentration of the dichroic dye 25 and the contrast of the light-adjusting sheet 10 will be described. The concentration of the dichroic dye 25 is the ratio of the total mass of the dichroic dye 25 to the total mass of the light-adjusting layer 20. The contrast is the ratio of the total light transmittance in the transparent state to the total light transmittance in the opaque state. The total light transmittance is measured in accordance with ASTM D 1003-00.

[0058] FIG. 7 shows an example of the relationship between the concentration of the dichroic dye 25 and the contrast of the light-adjusting sheet 10 when a liquid crystal compound 24 with Δn=0.173 is used, for the cases where the thickness of the light-adjusting layer 20 is 15 μm and 18 μm. As shown in FIG. 7, the thicker the light-adjusting layer 20 is and the higher the concentration of the dichroic dye 25 is, the higher the contrast is. Therefore, depending on the application of the light-adjusting sheet 10, if high contrast is desired, it is preferable to thicken the light-adjusting layer 20 or increase the concentration of the dichroic dye 25. On the other hand, if reducing the manufacturing cost of the light-adjusting sheet 10 is a priority, the thickness of the light-adjusting layer 20 and the concentration of the dichroic dye 25 may be kept small.

[0059] [Manufacturing method of light control sheet] The manufacturing method of the light controlling sheet 10 will be described. First, a first transparent support layer 41 on which a first transparent electrode layer 31 is laminated, and a second transparent support layer 42 on which a second transparent electrode layer 32 is laminated are prepared. The transparent electrode layers 31 and 32 are formed by a known film forming method such as sputtering.

[0060] When producing a normal-type light-controlling sheet 10A, a coating film for forming the light-controlling layer 20 is formed between the first transparent electrode layer 31 and the second transparent electrode layer 32. When producing a reverse-type light-controlling sheet 10B, a first alignment layer 51 is formed on the first transparent electrode layer 31, and a second alignment layer 52 is formed on the second transparent electrode layer 32. Then, a coating film for forming the light-controlling layer 20 is formed between the first alignment layer 51 and the second alignment layer 52.

[0061] The coating film contains a photopolymerizable compound, a liquid crystal compound 24, a dichroic dye 25, and a polymerization initiator for initiating polymerization of the photopolymerizable compound. The polymerization initiator is, for example, a diketone compound, an acetophenone compound, a benzoin compound, a benzophenone compound, a thioxanthone compound, or the like. The coating film may contain only a single type of polymerization initiator, or may contain multiple types of polymerization initiators. Examples of the polymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and cyclohexyl phenyl ketone.

[0062] The laminate sandwiching the coating film is irradiated with light to polymerize the photopolymerizable compound, which causes phase separation of the liquid crystal composition 23 and forms the light control layer 20. The light that polymerizes the photopolymerizable compound is ultraviolet light or an electron beam. The light that polymerizes the photopolymerizable compound may be irradiated toward the first transparent support layer 41, may be irradiated toward the second transparent support layer 42, or may be irradiated toward both the first transparent support layer 41 and the second transparent support layer 42. As a result, The light controlling sheet 10 is formed.

[0063] [Example] The above-mentioned light controlling sheet will be described using specific examples and comparative examples. Example 1 The light-adjusting sheet of Example 1 was a normal type light-adjusting sheet having a polymer network type light-adjusting layer and containing a dichroic dye in the liquid crystal composition. The color of the dichroic dye was black. The light-adjusting sheet of Example 1 was driven by a guest-host mode in which the liquid crystal compound was the host and the dichroic dye was the guest. This caused the transparency of the light-adjusting sheet to change.

[0064] The materials used in producing the light-controlling sheet of Example 1 and the ratio of each material in the coating liquid for forming the light-controlling layer are as follows. Transparent electrode layer: Indium tin oxide Transparent support layer: Polyethylene terephthalate film Liquid crystal compound: Fluorine-based liquid crystal compound 50% by mass Dichroic dye: Azo compound mixed dye (Irgaphor Black X12 DC, manufactured by BASF) 3% by mass Photopolymerizable compound: 46% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, manufactured by BASF) 1% by mass Spacer: Spherical particles (particle size 15 μm) made of silica containing carbon black

[0065] Comparative Example 1 The light-adjusting sheet of Comparative Example 1 was provided with a light-adjusting layer made of only a liquid crystal composition without a transparent polymer layer, and contained a dichroic dye in the liquid crystal composition. The color of the dichroic dye was black. The light-adjusting sheet of Comparative Example 1 was driven by a guest-host system in which the liquid crystal compound was the host and the dichroic dye was the guest. This caused the transparency of the light-adjusting sheet to change.

[0066] Comparative Example 2 A normal type light-adjusting sheet having a polymer network type light-adjusting layer, not containing a dichroic dye in the liquid crystal composition, and laminated with a black smoke film was used as the light-adjusting sheet of Comparative Example 2. In the light-adjusting sheet of Comparative Example 2, the transparency changes according to the change in the alignment state of the liquid crystal compound due to the application of a voltage.

[0067] Comparative Example 3 A sheet using an electrochromic element was used as the light-control sheet of Comparative Example 3. In the light-control sheet of Comparative Example 3, the transparency changes due to an electrochemical oxidation-reduction reaction.

[0068] Comparative Example 4 A sheet using an SPD (Suspended Particle Device) was used as the light-adjusting sheet of Comparative Example 4. In the light-adjusting sheet of Comparative Example 4, transparency changes according to a change in the orientation state of the particles due to application of a voltage.

[0069] (evaluation) The light-adjusting sheets of Example 1 and Comparative Examples 1 to 4 were evaluated for the presence or absence of haze in the opaque state, the presence or absence of changes in black transmittance, the occurrence of whitening, and suitability for image projection. The evaluation results are shown in Table 1. The occurrence of whitening was confirmed in an environment where external light was incident on the light-adjusting sheet from behind. The suitability for image projection was confirmed by projecting an image from behind the light-adjusting sheet and checking whether the image was visible from in front of the light-adjusting sheet.

[0070] [Table 1]

[0071] As shown in Table 1, Example 1 and Comparative Example 2, which have a polymer network type light control layer, had haze in the opaque state. The haze of Example 1 was lower than that of Comparative Example 2. Comparative Examples 1, 3, and 4 did not have haze in the opaque state, i.e., in the black light-shielding state, and it was confirmed that no light scattering occurred.

[0072] In Example 1 and Comparative Examples 1, 3, and 4, a change in the transmittance of the black color was observed by applying a voltage. That is, it was possible to switch between a transparent state in which the black color was light or colorless and the sheet had high transparency, and an opaque state in which the black color was dark and the sheet had low transparency. On the other hand, in Comparative Example 2, since the concentration of the black color in the smoke film was constant, the transparency of the sheet changed due to the change in haze caused by the application of a voltage, but the transmittance of the black color did not change.

[0073] In Comparative Examples 1, 3, and 4, which were opaque and did not have haze, the whitening phenomenon was not observed because there was no emission of scattered light. On the other hand, because there was no emission of scattered light, it was difficult to project an image.

[0074] In Example 1 and Comparative Example 2, which had haze in an opaque state, it was possible to project an image. On the other hand, while the whitening phenomenon was not observed in Example 1, which had reduced haze, the whitening phenomenon was observed in Comparative Example 2, which had high haze. When an image was projected in a state in which the whitening phenomenon was occurring, the projected image looked whitish. From the above, it was confirmed that the light controlling sheet of Example 1 suppresses the occurrence of the whitening phenomenon and enables suitable image projection.

[0075] Example 2 A normal type light-control sheet having a polymer network type light-control layer and containing a dichroic dye in the liquid crystal composition was used as the light-control sheet of Example 2. The color of the dichroic dye was black.

[0076] The materials used in producing the light-controlling sheet of Example 2 and the ratio of each material in the coating liquid for forming the light-controlling layer are as follows: The haze of the light-controlling sheet of Example 2 in the opaque state was 90%. Transparent electrode layer: Indium tin oxide Transparent support layer: Polyethylene terephthalate film Liquid crystal compound: Fluorine-based liquid crystal compound 50% by mass Dichroic dye: Azo compound mixed dye (Irgaphor Black X12 DC, manufactured by BASF) 3% by mass Photopolymerizable compound: 46% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, manufactured by BASF) 1% by mass Spacer: Spherical particles (particle size 15 μm) made of silica containing carbon black

[0077] Comparative Example 5 A normal type light-control sheet having a polymer network type light-control layer, containing no dichroic dye in the liquid crystal composition, and laminated with a black smoke film was used as the light-control sheet of Comparative Example 5.

[0078] The materials used in the manufacture of the light-control sheet of Comparative Example 5 and the ratio of each material in the coating liquid for forming the light-control layer are as follows. The total light transmittance of the smoke film is 18%. The haze of the light-control sheet of Comparative Example 5 in the opaque state is 97%. Transparent electrode layer: Indium tin oxide Transparent support layer: Polyethylene terephthalate film Liquid crystal compound: Composition of cyano-based liquid crystal compound and fluorine-based liquid crystal compound 50% by mass Photopolymerizable compound: 49% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, manufactured by BASF) 1% by mass Spacer: Polymethyl methacrylate spherical particles (particle size 15 μm)

[0079] Comparative Example 6 A light-control sheet of Comparative Example 6 was obtained in the same configuration as Comparative Example 5, except that the smoke film was changed to a smoke film with a total light transmittance of 42%. The haze of the light-control sheet of Comparative Example 6 in the opaque state was 97%.

[0080] (evaluation) The opaque light-control sheets of Example 2 and Comparative Examples 5 and 6 were evaluated for the occurrence of whitening under three different conditions. The evaluation results are shown in Table 2, with "○" indicating that whitening was observed and "×" indicating that whitening was not observed.

[0081] Under observation condition 1, the presence or absence of whitening was confirmed in an environment where no external light was incident from behind the light-adjusting sheet. Under observation condition 2, the presence or absence of whitening was confirmed in an environment where external light was indirectly incident from behind the light-adjusting sheet. In other words, a light was positioned behind the light-adjusting sheet in a position that did not overlap with the sheet. Under observation condition 3, the presence or absence of whitening was confirmed in an environment where external light was directly incident from behind the light-adjusting sheet. In other words, a light was positioned behind the light-adjusting sheet in a position that overlaps with the sheet.

[0082] [Table 2]

[0083] As shown in Table 2, in Example 2, no whitening phenomenon was observed under any of the observation conditions 1 to 3. On the other hand, in Comparative Examples 5 and 6, no whitening phenomenon was observed under the observation condition 1, but whitening phenomenon was observed under the observation conditions 2 and 3. In addition, in both Comparative Examples 5 and 6, the whitening phenomenon occurred more severely under the observation condition 3 than under the observation condition 2.

[0084] From the above, the light-control sheet of Example 2, which suppresses haze while exhibiting black color by containing a dichroic dye, is superior to Comparative Examples 5 and 6, which realize a black color by laminating a smoke film with high haze. It was confirmed that the whitening phenomenon can be suppressed even in an environment with strong external light in particular in Example 2.

[0085] Example 3 A normal type light-controlling sheet having a polymer network type light-controlling layer and containing a dichroic dye in the liquid crystal composition was used as the light-controlling sheet of Example 3. The color of the dichroic dye was black.

[0086] The materials used in producing the light-controlling sheet of Example 3 and the ratio of each material in the coating liquid for forming the light-controlling layer are as follows. Transparent electrode layer: Indium tin oxide Transparent support layer: Polyethylene terephthalate film Liquid crystal compound: Fluorine-based liquid crystal compound 50% by mass Dichroic dye: Azo compound mixed dye (Irgaphor Black X12 DC, manufactured by BASF) 3.0 quality amount% Photopolymerizable compound: 46% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, manufactured by BASF) 1% by mass Spacer: Spherical particles (particle size 15 μm) made of silica containing carbon black

[0087] Example 4 A light controlling sheet of Example 4 was obtained in the same configuration as in Example 3, except that the ratio of the dichroic dye was changed to 4.0% by mass.

[0088] Example 5 A light controlling sheet of Example 5 was obtained in the same configuration as in Example 3, except that the ratio of the dichroic dye was changed to 5.0% by mass.

[0089] (evaluation) The light-controlling sheets of Examples 3 to 5 were evaluated for their operation at high and low temperatures. Evaluations were performed at high temperatures of 90°C and 80°C, and at low temperatures of -30°C, -35°C, and -40°C. In the evaluation, the case where the transparent state and the opaque state could be switched and there was no clouding in the transparent state or no see-through in the opaque state was rated as "○", the case where the transparent state and the opaque state could be switched and there was some clouding in the transparent state or some see-through in the opaque state was rated as "△", and the case where there was noticeable clouding in the transparent state or some see-through in the opaque state was rated as "×". The evaluation results are shown in Table 3.

[0090] [Table 3]

[0091] As shown in Table 3, all of Examples 3 to 5 were able to operate at all temperatures, both high and low. At high temperatures, a decrease in haze makes it easier for see-through to occur in an opaque state, but the inclusion of the dichroic dye causes light absorption, so the see-through is significantly suppressed. In particular, in Examples 4 and 5, in which the dichroic dye content is 4.0 mass % or more, see-through at high temperatures is suitably suppressed. Furthermore, no precipitation of the dichroic dye was observed even at the lowest temperature of -40°C.

[0092] As described above in the embodiments and examples, the light controlling sheet can provide the following effects. (1) The haze of the light-adjusting sheet 10 in the opaque state is 85% or more and less than 95%, and the ratio of the tolane-based compound in the liquid crystal compound 24 is less than 20 mass %. With this configuration, the low haze suppresses light scattering in the light-adjusting layer 20, thereby suppressing the occurrence of the whitening phenomenon. Furthermore, as a result of light absorption by the dichroic dye, the light-adjusting sheet 10 in the opaque state is suppressed from being see-through, even if the haze is low.

[0093] (2) By applying the light adjusting sheet 10 to the screen on which the image is projected, it is possible to project a high-contrast image. (3) By using the black dichroic dye 25, the light controlling sheet 10 can be more effectively prevented from being see-through.

[0094] (4) If the proportion of the dichroic dye 25 in the light-controlling layer 20 is 2% by mass or more, the light-controlling sheet 10 can be more effectively prevented from being seen through. (5) If the proportion of the liquid crystal compound 24 in the light-controlling layer 20 is less than 60% by mass, the haze of the light-controlling sheet 10 can be easily controlled within the above range.

[0095] (6) If the thickness of the light-controlling layer 20 is 10 μm or more and 22 μm or less, the haze of the light-controlling sheet 10 can be easily controlled within the above range. [Explanation of symbols]

[0096] 10, 10A, 10B...Light control sheet 20...Photochromic layer 21...Transparent polymer layer 22…Domain 23...Liquid crystal composition 24…Liquid crystal compound 25...Dichroic dye 31,32...Transparent electrode layer 41,42...Transparent support layer 51, 52...Alignment layer

Claims

1. a light-controlling layer including a transparent polymer layer having a plurality of voids and a liquid crystal composition filling the voids, the liquid crystal composition including a liquid crystal compound and a dichroic dye; a pair of alignment layers sandwiching the light-controlling layer; a pair of transparent electrode layers sandwiching the light control layer and the pair of alignment layers, A light-controlling sheet that changes the orientation of the liquid crystal compound and the dichroic dye in response to a change in the potential difference between the pair of transparent electrode layers, thereby switching from a transparent state to a colored opaque state, The haze of the light-controlling sheet in the opaque state is 85% or more and less than 95%, the liquid crystal compound does not contain a tolan-based compound, The refractive index anisotropy Δn of the liquid crystal compound is less than 0.18, the proportion of the liquid crystal compound in the light-controlling layer is less than 60% by mass, the proportion of the dichroic dye in the light-modulating layer is 2% by mass or more, The alignment layer is made of polyimide. Dimming sheet.

2. The thickness of the light-controlling layer is 10 μm or more and 22 μm or less. The light-controlling sheet according to claim 1 .

3. The liquid crystal composition contains the dichroic dye that exhibits black color. The light-controlling sheet according to claim 1 .

4. a light-controlling layer including a transparent polymer layer having a plurality of voids and a liquid crystal composition filling the voids, the liquid crystal composition including a liquid crystal compound and a dichroic dye; a pair of alignment layers sandwiching the light-controlling layer; a pair of transparent electrode layers sandwiching the light control layer and the pair of alignment layers, The liquid crystal compound and the dichroic dye are aligned in response to a change in the potential difference between the pair of transparent electrode layers, thereby switching the state from a transparent state to a colored opaque state, and an image is projected onto the screen in the opaque state, the haze of the screen in the opaque state is 85% or more and less than 95%; the liquid crystal compound does not contain a tolan-based compound, The refractive index anisotropy Δn of the liquid crystal compound is less than 0.18, the proportion of the liquid crystal compound in the light-controlling layer is less than 60% by mass, the proportion of the dichroic dye in the light-modulating layer is 2% by mass or more, The alignment layer is made of polyimide. screen.

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