Dimming sheets and screens

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 dimming sheet with variable light transmittance and a screen.

Background Art

[0002] The dimming sheet includes a dimming layer containing a liquid crystal compound dispersed in a polymer material, and a pair of transparent electrode layers sandwiching the dimming layer, and a driving voltage is applied between the pair of transparent electrode layers. Since the alignment state of the liquid crystal compound changes according to the presence or absence of the applied driving voltage, it is possible to switch between a transmission state in which light passes through the dimming layer and a scattering state in which light is scattered by the dimming layer (see, for example, Patent Document 1). The dimming sheet in the transmission state is transparent, and the dimming sheet in the scattering state appears white and turbid.

[0003] The dimming sheet in the scattering state is used for blocking the view for protecting privacy and for projecting images. Therefore, in the scattering state, it is desirable that the transparency of the dimming sheet is low, that is, the haze, which is an index indicating the degree of turbidity, is high.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] From the viewpoints of improving the design property and the contrast of the projected image, the dimming sheet in the scattering state may preferably be colored differently from white. For example, a dimming sheet that appears black when in the scattering state has been proposed by laminating a smoke film.

[0006] However, when ambient light strikes a light-filtering sheet in a scattered state, scattered light is emitted in front of or behind the sheet. This can cause a whitening phenomenon, where the sheet appears whitish, even if a smoked film is laminated over it. When whitening occurs, the desired effects, such as improved aesthetics and enhanced contrast of projected images, cannot be fully achieved. Whitening is particularly likely to occur when the light-filtering sheet is used outdoors or in the vicinity of such environments, such as when it is installed on vehicle windows, and is exposed to strong ambient light.

[0007] Furthermore, the higher the haze, the stronger the scattering, which tends to exacerbate the whitening phenomenon. While lowering the haze can suppress the whitening phenomenon, if the haze is too low, the light-adjusting sheet becomes transparent in the scattered state, making it impossible to maintain the low transparency required for applications such as blocking visibility or projecting images. Therefore, there is a need for a light-adjusting sheet that can achieve low transparency while suppressing the whitening phenomenon. [Means for solving the problem]

[0008] This document describes various forms of dimming sheets and screens designed to solve the above problems. [Aspect 1] A light-adjusting sheet comprising a transparent polymer layer having a plurality of voids, a liquid crystal composition filling the voids, the liquid crystal composition comprising a liquid crystal compound and a dichroic dye, and a pair of transparent electrode layers sandwiching the light-adjusting sheet, 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, wherein the haze of the light-adjusting sheet in the opaque state is 85% or more and less than 95%, and the proportion of trans-based compounds in the liquid crystal compound is 20% by mass or less A fully dimmable light-adjusting sheet.

[0009] With the above configuration, the low haze suppresses light scattering in the photochromic layer, thus preventing the occurrence of whitening. Furthermore, due to light absorption by the dichroic dye, the photochromic sheet does not become transparent in the opaque state, even with low haze.

[0010] [Aspect 2] The dimming sheet according to [Aspect 1], wherein the proportion of the liquid crystal compound in the dimming layer is less than 60% by mass. The above configuration makes it easier to control the haze of the dimming sheet within the above range.

[0011] [Aspect 3] The dimming sheet according to [Aspect 1] or [Aspect 2], wherein the thickness of the dimming layer is 10 μm or more and 22 μm or less. The above configuration makes it easier to control the haze of the dimming sheet within the above range.

[0012] [Aspect 4] The dimming sheet according to any one of [Aspect 1] to [Aspect 3], wherein the liquid crystal composition comprises the dichroic dye that exhibits black color. According to the above configuration, the transparency of the light-adjusting sheet can be more effectively suppressed.

[0013] [Aspect 5] The light-adjusting sheet according to any one of [Aspect 1] to [Aspect 4], wherein the proportion of the dichroic dye in the light-adjusting layer is 2% by mass or more. According to the above configuration, the transparency of the light-adjusting sheet can be more effectively suppressed.

[0014] [Aspect 6] A screen comprising a transparent polymer layer having a plurality of voids, a light-adjusting layer comprising a liquid crystal composition for filling the voids, the liquid crystal composition comprising 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 trans-based compounds in the liquid crystal compound is less than 20% by mass.

[0015] According to the above configuration, since light scattering in the dimming layer is suppressed due to low haze, the occurrence of whitening phenomenon can be suppressed. And as a result of light absorption by the dichroic dye, even when the haze is low, the screen can be prevented from being seen through in the opaque state. Thereby, projection of an image with high contrast is possible.

Effects of the Invention

[0016] According to the present invention, it is possible to suppress the whitening phenomenon and suppress the sheet from being seen through.

Brief Description of the Drawings

[0017] [Figure 1] A diagram showing a cross-sectional structure of a normal type dimming sheet in one embodiment. [Figure 2] A diagram showing an enlarged view of a part of the dimming layer in one embodiment. [Figure 3] A diagram showing a cross-sectional structure of a reverse type dimming sheet in one embodiment. [Figure 4] A diagram showing an example of the relationship between the haze in the opaque state and the liquid crystal concentration in the dimming sheet of one embodiment. [Figure 5] A diagram showing an example of the relationship between the haze in the opaque state and the thickness of the dimming layer in the dimming sheet of one embodiment. [Figure 6] A diagram showing an example of the relationship between the clarity in the opaque state and the thickness of the dimming layer in the dimming sheet of one embodiment. [Figure 7] A diagram showing an example of the relationship between the contrast and the dichroic dye concentration in the dimming sheet of one embodiment.

Modes for Carrying Out the Invention

[0018] Referring to the drawings, one embodiment of the dimming sheet and the screen will be described. [Configuration of Dimming Sheet] The configuration of the dimming sheet will be described with reference to Figures 1 and 2. The dimming sheet of this embodiment has, for example, a layer configuration of either a normal type or a reverse type. First, the layer configuration of the normal type will be described with reference to Figure 1.

[0019] As shown in Figure 1, the dimming sheet 10A, which is a normal type dimming sheet 10, comprises a dimming 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 dimming 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 to the dimming layer 20, and the second transparent support layer 42 supports the second transparent electrode layer 32 on the side opposite to the dimming layer 20.

[0020] Figure 2 is an enlarged view of region R of the light-adjusting layer 20 in Figure 1. As shown in Figure 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 into which the liquid crystal composition 23 is filled, and the liquid crystal composition 23 is held within the domains 22.

[0021] The structure of the transparent polymer layer 21 and the type of holding the liquid crystal composition 23 are one of the following: polymer network type, polymer dispersion type, or capsule type. The polymer network type light-adjusting layer 20 comprises a polymer network having a three-dimensional mesh structure. The polymer network is an example of a transparent polymer layer, and the liquid crystal composition is held in the interconnected mesh-like voids within the polymer network. The polymer dispersion type light-adjusting layer 20 comprises a transparent polymer layer that partitions a number of isolated voids, and the liquid crystal composition is held in the voids dispersed in the transparent polymer layer. The capsule type light-adjusting layer 20 holds the liquid crystal composition in the voids within 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. Examples of ultraviolet polymerizable compounds include acrylate compounds such as butyl ethyl acrylate and cyclohexyl acrylate, methacrylate compounds such as N,N-dimethylaminoethyl methacrylate and phenoxyethyl methacrylate, stilbene compounds, diacrylate compounds, dimethacrylate compounds, triacrylate compounds, tetraacrylate compounds, trimethacrylate compounds, tetramethacrylate compounds, and oligomers of these compounds. The ratio of the transparent polymer layer 21 to the total mass of the light-adjusting layer 20 is preferably 20% by mass or more and 80% by mass or less.

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

[0024] The liquid crystal compound 24 is, for example, a Schiff base, azo, azoxy, biphenyl, terphenyl, benzoic acid ester, tran, pyrimidine, pyridazine, cyclohexanecarboxylic acid ester, phenylcyclohexane, biphenylcyclohexane, dicyanobenzene, naphthalene, or dioxane compounds. The liquid crystal composition 23 may contain only one type of liquid crystal compound 24, or it may contain multiple types of liquid crystal compounds 24. It may be included.

[0025] The dichroic dye 25 has an elongated molecular shape, and its absorbance in the visible region along the long axis of the molecule is greater than its absorbance along the short axis of the molecule. The dichroic dye 25 exhibits color when its long axis intersects the direction of incident light. Specifically, the dichroic dye 25 exhibits color when its long axis intersects approximately perpendicular to the normal direction of the contact surface with the first transparent electrode layer 31 or the second transparent electrode layer 32 in the light-adjusting layer 20. 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 with the liquid crystal compound 24 as the host.

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

[0027] Furthermore, the liquid crystal composition 23 may contain, in addition to the liquid crystal compound 24 and the dichroic dye 25, viscosity reducers, defoamers, antioxidants, weather stabilizers, etc. Examples of weather stabilizers include ultraviolet absorbers and light stabilizers.

[0028] Furthermore, the light-adjusting layer 20 may include spacers dispersed throughout the transparent polymer layer 21. The spacers uniformize the thickness of the light-adjusting layer 20 by defining its thickness around the spacers. The spacers may be bead spacers or photospacers formed by exposure and development of the photoresist. The spacers may be colorless and transparent or colored and transparent, as long as they are translucent. Preferably, the color exhibited by a colored and transparent spacer is the same as the color exhibited by the dichroic dye 25.

[0029] Each of the first transparent electrode layer 31 and the second transparent electrode layer 32 is conductive and transparent to visible light. The materials for the transparent electrode layers 31 and 32 are, for example, indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, poly(3,4-ethylenedioxythiophene), etc.

[0030] Each of the first transparent support layer 41 and the second transparent support layer 42 is a substrate that is transparent to light in the visible region. The materials of the transparent support layers 41 and 42 are, for example, synthetic resins and inorganic compounds. Synthetic resins include, for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polycarbonates, and polyolefins. Inorganic compounds include, for example, silicon dioxide, silicon oxynitride, and silicon nitride.

[0031] A driving voltage, which is a voltage for changing the orientation state of the liquid crystal compound 24, is applied to the first transparent electrode layer 31 and the second transparent electrode layer 32. The dimming sheet 10 switches from one transparent state to one opaque state based on the change in the orientation 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. Also, 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 dimmable sheet 10A, when no driving voltage is applied, the liquid crystal compound The orientation of the material 24 along its long axis 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 dimming sheet 10A is scattered in various directions by the dimming layer 20. In addition, the orientation of the dichroic dye 25 along its long axis is also irregular, and at least a portion of the dichroic dye 25 exhibits color. Consequently, the normal type dimming sheet 10A becomes a colored opaque state when no driving voltage is applied.

[0033] When the dielectric anisotropy of the liquid crystal compound 24 is positive, when a driving voltage is applied, the liquid crystal compound 24 is oriented so that its long axis is aligned with the direction of the electric field. 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 the 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 becomes colorless and transparent when a driving voltage is applied.

[0034] Next, with reference to Figure 3, the layer structure of the reverse-type dimming sheet will be described. As shown in Figure 3, the reverse-type dimming sheet 10B includes a dimming layer 20, transparent electrode layers 31 and 32, transparent support layers 41 and 42, as well as a first orientation layer 51 and a second orientation layer 52. The first orientation layer 51 is located between the dimming layer 20 and the first transparent electrode layer 31 and is in contact with these layers. The second orientation layer 52 is located between the dimming layer 20 and the second transparent electrode layer 32 and is in contact with these layers. The structure of region R in the dimming 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 orientation of the liquid crystal compound 24. The alignment layers 51 and 52 are, for example, vertical alignment films. The vertical alignment films orient the liquid crystal compound 24 so that its long axis is aligned with the thickness direction of the light-adjusting layer 20. When the alignment layers 51 and 52 are vertical alignment films, the liquid crystal compound 24 used is a liquid crystal compound with negative dielectric anisotropy, that is, a liquid crystal compound in which the dielectric constant in the long axis direction is smaller than the dielectric constant in the short axis direction.

[0036] The materials for the orientation layers 51 and 52 include, for example, organic compounds such as polyimide, polyamide, polyvinyl alcohol, and cyanide compounds, inorganic compounds such as silicon oxide and zirconium oxide, and silicone. Orientation treatments for forming the orientation layers 51 and 52 include, for example, rubbing treatment, polarized irradiation treatment, and microfabrication treatment.

[0037] In the reverse-type dimming sheet 10B, when no driving voltage is applied, the liquid crystal compound 24 is oriented so that its long axis is aligned with the thickness direction of the dimming layer 20, due to the orientation restricting force from the alignment layers 51 and 52. At this time, the dichroic dye 25 is also oriented so that its long axis is aligned with the thickness direction of the dichroic layer 20. As a result, light scattering in the dimming layer 20 and the coloring of the dichroic dye 25 are suppressed, making it easier for light to pass through the dimming sheet 10B. Therefore, the reverse-type dimming sheet 10B becomes colorless and transparent when no driving voltage is applied.

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

[0039] Furthermore, based on the change in the orientation state of the liquid crystal compound due to the application of the driving voltage, the dimming sheet 10 The layer configuration of the dimming sheet 10 is not limited to the above, as long as it is configured to switch between a transparent state and an opaque state. For example, the dimming sheet 10 may include a polarizing layer that controls the polarization of incident or transmitted light to the dimming layer 20, and the alignment layers 51 and 52 may be horizontal alignment films. Whether the dimming sheet 10 becomes transparent or opaque when a driving voltage is applied can be changed by the presence or absence of the alignment layers 51 and 52, the direction in which the alignment restricting force by 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, etc.

[0040] At least one of the front and back surfaces of the dimming sheet 10 is attached to a transparent plate made of glass, resin, or the like. The transparent plate is, for example, a windowpane in various buildings, a partition installed indoors, or a windowpane or windshield in a moving object such as a vehicle or aircraft. The surface of the transparent plate may be flat or curved.

[0041] Furthermore, the dimmable sheet 10 may be used as a screen onto which an image is projected. The dimmable sheet 10 is applicable to the screen of a transmissive projection system. That is, when projection light, which constitutes an image, is shone from behind the dimmable sheet 10 toward the opaque dimmable sheet 10, scattered light based on the projection light is emitted in front of the dimmable sheet 10. As a result, an observer positioned in front of the dimmable sheet 10 can view the image.

[0042] [Characteristics of dimmable sheets] The characteristics of the dimming sheet 10 of this embodiment will now be described. The following characteristics are common regardless of the layer configuration of the dimming sheet 10.

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

[0044] On the other hand, since the light-adjusting sheet 10 of this embodiment contains a dichroic dye 25, light absorption occurs due to the dichroic dye 25, and as a result, even with low haze, the light-adjusting sheet 10 does not appear transparent in an opaque state. Therefore, blocking the view with the light-adjusting sheet 10 and projecting images onto the light-adjusting sheet 10 are suitably possible. These effects are particularly high when the dichroic dye 25 is black or close to black. In order to suppress the transparency of the light-adjusting sheet 10, it is preferable that the content ratio of the dichroic dye 25 in the light-adjusting layer 20 be 2% by mass or more.

[0045] Furthermore, because the haze is low, light scattering in the dimming layer 20 is suppressed, thus preventing the occurrence of whitening. In this way, the dimming sheet 10 of this embodiment can achieve low transparency while suppressing the whitening phenomenon in the opaque state. Therefore, it is possible to improve the design and project high-contrast images.

[0046] The characteristics of the dimming sheet 10 will be further explained. In the liquid crystal composition 23 contained in the dimming layer 20, the proportion of the trans-based compound to the total mass of the liquid crystal compound 24 is less than 20% by mass. Furthermore, the proportion of the trans-based compound to the total mass of the liquid crystal compound 24 is preferably less than 15% by mass, and more preferably less than 5% by mass. Furthermore, the proportion of the trans-based compound may be 0% by mass. Liquid crystal materials that are trans-based compounds are used to increase Δn, which is the refractive index anisotropy of the liquid crystal compound, in order to obtain high haze in the opaque state as in the conventional method. However, if the proportion of trans-based compounds is high, the weather resistance of the dimming sheet 10 will decrease and the operating temperature range will be reduced.

[0047] In this embodiment, since the haze of the dimming sheet 10 is kept low, Δn is also kept low. Specifically, in conventional dimming sheets, Δn is 0.18 or more, preferably 0.20 or more, whereas in the dimming sheet 10 of this embodiment, Δn is less than 0.18. Therefore, in the dimming sheet 10, it is possible to reduce the proportion of trans-based compounds in the liquid crystal composition 23, thereby improving weather resistance and expanding the drivable temperature range. Furthermore, trans-based liquid crystal compounds are liquid crystal compounds that have a trans skeleton containing an acetylene bond as a bonding group.

[0048] Next, we will explain the relationship between the haze and liquid crystal density of the dimming sheet 10 in the opaque state. Figure 4 shows an example of the relationship between the haze and liquid crystal density in the opaque state when using a liquid crystal compound 24 with Δn = 0.173. The liquid crystal density is the ratio of the total mass of the liquid crystal compound 24 to the total mass of the dimming layer 20.

[0049] As shown in Figure 4, the haze tends to increase as the liquid crystal density increases. When Δn is less than 0.18, it is preferable that the liquid crystal density is less than 60% by mass in order to keep the haze below 95%. Furthermore, for proper driving of the dimming sheet 10, it is preferable that the liquid crystal density is 20% by mass or more.

[0050] Next, we will explain the relationship between the haze of the dimming sheet 10 in the opaque state and the thickness of the dimming layer 20. Figure 5 shows an example of the relationship between the haze in the opaque state and the thickness of the dimming layer 20 when using a liquid crystal compound 24 with Δn = 0.173.

[0051] As shown in Figure 5, the haze tends to increase as the thickness of the dimming layer 20 increases. When Δn is less than 0.18, in order to keep the haze between 85% and 95%, the thickness of the dimming layer 20 is preferably between 10 μm and 22 μm, and preferably between 15 μm and 20 μm.

[0052] In this embodiment, since the haze is kept lower than that of conventional dimming sheets, it is possible to make the dimming layer 20 thinner than in conventional designs. This suppresses the increase in driving voltage caused by the decrease in electric field strength due to the increase in the thickness of the dimming layer 20.

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

[0054] Next, we will explain the relationship between the clarity of the light-adjusting sheet 10 in its opaque state and the thickness of the light-adjusting layer 20. Clarity is an index used to evaluate the transparency of the light-adjusting sheet 10. Clarity is the amount of light L of the straight-traveling light that travels in a straight line along the optical axis of the parallel light incident on the photochromic layer 20, among the light that has passed through the photochromic layer 20. C The amount of light from narrow-angle scattered light, where the angle with respect to the optical axis of parallel light is within ±2.5°, is defined as the amount of light L. R In this case, it is calculated by the following (Equation 1). Note that the light intensity L C and light intensity L R This is determined by measurements in accordance with ASTM D 1003-00. 100×(L C -L R ) / (L C +L R )...(Formula 1)

[0055] The transparency of the photochromic sheet 10 can also be evaluated by parallel line transmittance, but clarity is a parameter whose evaluation results are more likely to match human perception than parallel line transmittance. In order to prevent the scenery behind the toe 10 from being visible through the dimming sheet 10, the clarity of the dimming sheet 10 in the opaque state is preferably 80% or less, and more preferably 60% or less.

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

[0057] Next, the relationship between the concentration of the dichroic dye 25 and the contrast of the photochromic sheet 10 will be explained. 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 photochromic 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] Figure 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 using a liquid crystal compound 24 with Δn = 0.173, for cases where the thickness of the light-adjusting layer 20 is 15 μm and 18 μm. As shown in Figure 7, the thicker the light-adjusting layer 20 and the higher the concentration of the dichroic dye 25, the greater the contrast. Therefore, depending on the application of the light-adjusting sheet 10, if high contrast is desired, it is preferable to make the light-adjusting layer 20 thicker and 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 low.

[0059] [Manufacturing method for dimmable sheets] A method for manufacturing the dimming sheet 10 will now 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 known film deposition methods such as sputtering.

[0060] When manufacturing a normal type dimming sheet 10A, a coating film for forming the dimming layer 20 is formed between the first transparent electrode layer 31 and the second transparent electrode layer 32. When manufacturing a reverse type dimming sheet 10B, a first orientation layer 51 is formed on the first transparent electrode layer 31, and a second orientation layer 52 is formed on the second transparent electrode layer 32. Then, a coating film for forming the dimming layer 20 is formed between the first orientation layer 51 and the second orientation 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 the polymerization of the photopolymerizable compound. Examples of polymerization initiators include diketone compounds, acetophenone compounds, benzoin compounds, thioxanthone compounds, etc. The coating film may contain only one type of polymerization initiator or may contain multiple types of polymerization initiators. Examples of polymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, cyclohexylphenyl ketone, etc.

[0062] By irradiating the laminate with the coating film in between with light, the photopolymerizable compound is polymerized, causing phase separation of the liquid crystal composition 23 and forming the light-adjusting layer 20. The light used to polymerize the photopolymerizable compound is ultraviolet light or an electron beam. The light used to polymerize the photopolymerizable compound may be directed towards the first transparent support layer 41, or towards the second transparent support layer 42, or towards both the first transparent support layer 41 and the second transparent support layer 42. As a result, A dimming sheet 10 is formed.

[0063] [Examples] The dimming sheets described above will be explained using specific examples and comparative examples. (Example 1) The light-adjustable sheet of Example 1 was a normal type light-adjustable sheet equipped with a polymer network-type light-adjustable layer and containing a dichroic dye in the liquid crystal composition. The color of the dichroic dye is black. The light-adjustable sheet of Example 1 is driven by a guest-host type, with the liquid crystal compound as the host and the dichroic dye as the guest. This changes the transparency of the light-adjustable sheet.

[0064] The materials used in the production of the dimming sheet in Example 1, and the ratio of each material in the coating solution for forming the dimming 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: A mixture of isobonyl acrylate, pentaerythritol triacrylate, and urethane acrylate (46% by mass) Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, BASF) 1% by mass Spacer: Spherical silica particles containing carbon black (particle size 15 μm)

[0065] (Comparative Example 1) Comparative Example 1's light-adjusting sheet was a light-adjusting sheet comprising a light-adjusting layer consisting solely of a liquid crystal composition without a transparent polymer layer, and containing a dichroic dye in the liquid crystal composition. The color of the dichroic dye was black. The light-adjusting sheet of Comparative Example 1 is driven by a guest-host type, with the liquid crystal compound as the host and the dichroic dye as the guest. This changes the transparency of the light-adjusting sheet.

[0066] (Comparative Example 2) Comparative Example 2 was a normal type of dimmable sheet equipped with a polymer network-type dimmable layer, without dichroic dyes in the liquid crystal composition, and laminated with a black smoke film. In the dimmable sheet of Comparative Example 2, the transparency changes in accordance with the change in the orientation state of the liquid crystal compound due to the application of voltage.

[0067] (Comparative Example 3) A sheet using an electrochromic element was used as the dimmable sheet in Comparative Example 3. In the dimmable 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 dimmable sheet in Comparative Example 4. In the dimmable sheet of Comparative Example 4, the transparency changes in accordance with the change in the orientation state of the fine particles due to the application of voltage.

[0069] (evaluation) For the dimmable sheets of Example 1 and Comparative Examples 1-4, we evaluated the presence or absence of haze in the opaque state, the presence or absence of changes in black transmittance, the presence or absence of whitening, and the suitability for image projection. The evaluation results are shown in Table 1. The occurrence of whitening was confirmed in an environment where ambient light was incident on the dimmable sheet from behind. To check the suitability for image projection, we projected an image from behind the dimmable sheet and confirmed whether the image was visible from the front of the dimmable sheet.

[0070] [Table 1]

[0071] As shown in Table 1, Example 1 and Comparative Example 2, which have a polymer network-type light-adjusting layer, exhibited 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 exhibit haze in the opaque state, i.e., the black light-shielding state, confirming that no light scattering occurred.

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

[0073] In comparative examples 1, 3, and 4, where no haze occurred in the opaque state, no whitening phenomenon was observed because there was no emission of scattered light. On the other hand, projection of images was difficult due to the absence of scattered light emission.

[0074] In Example 1 and Comparative Example 2, where haze was present in an opaque state, image projection was possible. On the other hand, while no whitening phenomenon was observed in Example 1, where haze was suppressed, whitening was observed in Comparative Example 2, where haze was high. When an image was projected in a state where whitening was present, the projected image appeared whitish. Based on the above, it was confirmed that the dimming sheet of Example 1 suppresses the occurrence of whitening and allows for suitable image projection.

[0075] (Example 2) The light-adjustable sheet of Example 2 was a normal type light-adjustable sheet equipped with a polymer network-type light-adjustable layer and containing a dichroic dye in the liquid crystal composition. The color of the dichroic dye was black.

[0076] The materials used in the production of the dimming sheet in Example 2, and the ratio of each material in the coating solution for forming the dimming layer, are as follows. The haze of the dimming sheet in Example 2 in its 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: A mixture of isobonyl acrylate, pentaerythritol triacrylate, and urethane acrylate (46% by mass) Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, BASF) 1% by mass Spacer: Spherical silica particles containing carbon black (particle size 15 μm)

[0077] (Comparative Example 5) Comparative Example 5 was a normal type of dimming sheet equipped with a polymer network-type dimming layer, without dichroic dyes in the liquid crystal composition, and laminated with a black smoke film.

[0078] The materials used in the manufacture of the light-adjusting sheet in Comparative Example 5, and the ratio of each material in the coating solution for forming the light-adjusting layer, are as follows. The total light transmittance of the smoke film is 18%. The haze of the light-adjusting sheet in Comparative Example 5 in its opaque state was 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: A mixture of isovonyl acrylate, pentaerythritol triacrylate, and urethane acrylate (49% by mass) Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, BASF) 1% by mass Spacer: Spherical particles made of polymethyl methacrylate (particle size 15 μm)

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

[0080] (evaluation) The opaque dimming 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 the presence of whitening and "×" indicating the absence of whitening.

[0081] Under observation condition 1, the presence or absence of whitening was checked in an environment where there was no ambient light incident from behind the dimming sheet. Under observation condition 2, the presence or absence of whitening was checked in an environment where ambient light was indirectly incident from behind the dimming sheet. That is, the lighting was positioned behind the dimming sheet but not overlapping with it. Under observation condition 3, the presence or absence of whitening was checked in an environment where ambient light was directly incident from behind the dimming sheet. That is, the lighting was positioned behind the dimming sheet but overlapping with it.

[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 observation condition 1, but whitening was observed under observation conditions 2 and 3. Furthermore, in both Comparative Examples 5 and 6, the whitening phenomenon was more pronounced under observation condition 3 than under observation condition 2.

[0084] Based on the above, the dichroic sheet of Example 2, which exhibits black color due to the inclusion of a dichroic dye while suppressing haze, is superior to Comparative Examples 5 and 6, which achieved black color by laminating a smoke film with high haze. It was also confirmed that the whitening phenomenon can be suppressed. In particular, in Example 2, the whitening phenomenon can be effectively suppressed even in environments with strong ambient light.

[0085] (Example 3) The light-adjusting sheet of Example 3 was a normal type light-adjusting sheet equipped with 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.

[0086] The materials used in the production of the dimming sheet in Example 3, and the ratio of each material in the coating solution for forming the dimming 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: A mixture of isobonyl acrylate, pentaerythritol triacrylate, and urethane acrylate (46% by mass) Polymerization initiator: Photopolymerization initiator (Irgacure Oxe04, BASF) 1% by mass Spacer: Spherical silica particles containing carbon black (particle size 15 μm)

[0087] (Example 4) The light-adjusting sheet of Example 4 was obtained using 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) The light-adjusting sheet of Example 5 was obtained using 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 dimming sheets of Examples 3-5 were evaluated for their operation at high and low temperatures. High temperatures were evaluated at 90°C and 80°C, and low temperatures at -30°C, -35°C, and -40°C. In the evaluation, "○" was used if switching between transparent and opaque states was possible without clouding in the transparent state or transparency in the opaque state; "△" was used if switching between transparent and opaque states was possible but slight clouding in the transparent state or transparency in the opaque state was observed; and "×" was used if significant clouding in the transparent state or transparency in the opaque state was observed. 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, transparency in the opaque state tends to occur due to a decrease in haze, but significant transparency is suppressed because light absorption occurs due to the presence of dichroic dyes. In particular, in Examples 4 and 5, where the dichroic dye content is 4.0% by mass or more, transparency 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 dimming sheet can provide the following effects. (1) The haze of the dimming sheet 10 in the opaque state is 85% or more and less than 95%, and the proportion of trans-type compounds in the liquid crystal compound 24 is less than 20% by mass. With this configuration, the low haze suppresses light scattering in the dimming layer 20, thus suppressing the occurrence of whitening. Furthermore, as a result of light absorption by the dichroic dye, the transparency of the dimming sheet 10 in the opaque state is suppressed even with low haze.

[0093] (2) By applying the dimming sheet 10 to the screen on which the image is projected, it is possible to project an image with high contrast. (3) By using a dichroic dye 25 that exhibits black color, the transparency of the light-adjusting sheet 10 can be more effectively suppressed.

[0094] (4) If the proportion of dichroic dye 25 in the light-adjusting layer 20 is 2% by mass or more, the transparency of the light-adjusting sheet 10 can be more effectively suppressed. (5) If the proportion of liquid crystal compound 24 in the dimming layer 20 is less than 60% by mass, it becomes easier to control the haze of the dimming sheet 10 within the above range.

[0095] (6) If the thickness of the dimming layer 20 is 10 μm or more and 22 μm or less, it becomes easier to control the haze of the dimming sheet 10 within the above range. [Explanation of symbols]

[0096] 10, 10A, 10B… Dimmable sheets 20…Dimming layer 21...Transparent polymer layer 22…domain 23…Liquid crystal composition 24…Liquid crystal compound 25… Dichroic pigments 31,32...Transparent electrode layer 41,42...Transparent support layer 51, 52… Orientation layers

Claims

1. A light-adjusting layer comprising a transparent polymer layer having multiple voids, and a liquid crystal composition filling the voids, the liquid crystal composition comprising a liquid crystal compound and a dichroic dye, A pair of orientation layers sandwiching the aforementioned dimming layer, The device comprises the light-adjusting layer and a pair of transparent electrode layers sandwiching the pair of orientation layers, A light-adjusting 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 dimming sheet in the opaque state is 85% or more and less than 95%. The aforementioned liquid crystal compound does not contain a trans-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-adjusting layer is less than 60% by mass. The proportion of the dichroic dye in the light-adjusting layer is 2% by mass or more. The orientation layer is made of polyimide. Dimming sheet.

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

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

4. A light-adjusting layer comprising a transparent polymer layer having multiple voids, and a liquid crystal composition filling the voids, the liquid crystal composition comprising a liquid crystal compound and a dichroic dye, A pair of orientation layers sandwiching the aforementioned dimming layer, The device comprises the light-adjusting layer and a pair of transparent electrode layers sandwiching the pair of orientation layers, A screen on which an image is projected in the opaque state, 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, The haze of the screen in the opaque state is 85% or more and less than 95%. The aforementioned liquid crystal compound does not contain a trans-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-adjusting layer is less than 60% by mass. The proportion of the dichroic dye in the light-adjusting layer is 2% by mass or more. The orientation layer is made of polyimide. screen.

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