Reflection type projection screen

Abstract

A reflective projection screen provided with a transparent substrate having a front surface on which a light control sheet is attached, the transparent substrate being thicker than the light control sheet, and a polymer dispersed liquid crystal containing at least one dichroic dye and reversibly changing from a transparent state to a scattering state by a change in voltage applied between transparent electrode layers, the reflectivity of a first image reflecting surface, which is the surface of the light control sheet in a scattering state, is Rs, the reflectivity of a second image reflecting surface, which is the back surface of the transparent substrate, is Rn, and the transmittance of the light control sheet in the scattering state is T, and Rd = T2 * Rn and (Rs + Rd) / Rs < = 1.3 are satisfied.

Description

Technical Field

[0001] The present disclosure relates to a reflective projection screen whose light transmittance is changed. Background Art

[0002] A light control film includes a light control layer containing a liquid crystal composition dispersed in a transparent resin and a pair of transparent electrode layers sandwiching the light control layer. The alignment state of the liquid crystal compound changes according to a change in the driving voltage between the pair of transparent electrode layers. By changing the alignment state of the liquid crystal compound, a transparent state in which light passes through the light control layer and a scattering state in which the light control layer scatters light are switched. The light control film in the scattering state is used for a projection screen for projecting an image (see, for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-184693 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] The back surface of the light control film included in the reflective projection screen is adhered to the surface of a transparent substrate such as glass or resin. In this case, the surface of the light control film functions as a first image reflection surface that reflects an image toward an observer in the reflective projection screen. On the other hand, the back surface of the transparent substrate also functions as a second image reflection surface based on the refractive index difference between the transparent substrate and the air layer. As a result, the above-described reflective projection screen causes the observer to see a double image in which the image obtained on the first image reflection surface overlaps the image obtained on the second image reflection surface.

[0008] Means for Solving the Problems

[0009] One aspect of the reflective projection screen is a reflective projection screen including: a light control film including two transparent electrode layers and a polymer-dispersed liquid crystal located between the transparent electrode layers; and a transparent substrate having a surface to which the back surface of the light control film is adhered, the thickness of the transparent substrate being thicker than that of the light control film, the polymer-dispersed liquid crystal including at least one dichroic pigment, and reversibly changing from a transparent state to a scattering state by changing the voltage applied between the transparent electrode layers. Moreover, the reflectance of the surface of the light control film, i.e., the first image reflection surface, is Rs, the reflectance of the back surface of the transparent substrate, i.e., the second image reflection surface, is Rn, and the transmittance of the light control film is T, satisfying Rd = T 2 ×Rn, (Rs + Rd) / Rs ≤ 1.3. Brief Description of the Drawings

[0010] Figure 1It is a configuration diagram showing a reflective projection screen together with a projection device.

[0011] Figure 2 It is a cross-sectional view showing the cross-sectional configuration of the reflective projection screen.

[0012] Figure 3 It is a partial cross-section showing the cross-sectional configuration of the light control film.

[0013] Figure 4 It is a device layout diagram showing the evaluation form of the reflective projection screen.

[0014] Figure 5 It is a top view showing the evaluation image of the reflective projection screen.

[0015] Figure 6 It is a functional diagram showing the optical function of the reflective projection screen. Detailed implementation

[0016] [Reflective projection screen 10]

[0017] As Figure 1 shown, the reflective projection screen 10 is connected to the driving device 51. The driving device 51 inputs a voltage signal for making the reflective projection screen 10 in a transparent state to the reflective projection screen 10. The driving device 51 inputs a voltage signal for making the reflective projection screen 10 in a scattering state to the reflective projection screen 10. The reflective projection screen 10 reversibly changes from a transparent state to a scattering state according to the change of the voltage signal output by the driving device 51.

[0018] The surface 10F of the reflective projection screen 10 faces the projection device 101. The surface 10F of the reflective projection screen 10 is the first image reflection surface. The back surface 10R of the reflective projection screen 10 faces the air layer such as the indoor environment and the outdoor environment. The back surface 10R of the reflective projection screen 10 is the second image reflection surface. The projection device 101 projects the image 10P onto the surface 10F of the scattering reflective projection screen 10. The observer 102 observes the image 10P from the side of the projection device 101 relative to the reflective projection screen 10.

[0019] As Figure 2 shown, the reflective projection screen 10 includes a transparent substrate 11 and a light control film 20A. The surface of the light control film 20A is the surface 10F of the reflective projection screen 10. The back surface of the transparent substrate 11 is the back surface 10R of the reflective projection screen 10.

[0020] The transparent substrate 11 can be a transparent glass substrate or a transparent resin substrate. The transparent substrate 11 can be a window glass mounted on a moving body such as a vehicle or an airplane, can also be a window glass installed in a building, and can also be a partition arranged inside a vehicle or a room. The surface of the transparent substrate 11 can be planar or curved.

[0021] The thickness of the transparent substrate 11 is sufficiently thicker than that of the light control film 20A. The thickness of the transparent substrate 11 can be 1 mm or more and 20 mm or less. The thickness of the light control film 20A can be 200 μm or more and 500 μm or less. The transparent substrate 11 can be a single-layer structure or a laminated structure. The transparent substrate 11 can be float plate glass, laminated glass, multi-layer glass, or tempered glass. When the transparent substrate 11 is a laminated structure, in order to regard the transparent substrate 11 as one transparent structure, the refractive index of the structure constituting the transparent substrate 11 is 1.4 or more and 1.6 or less.

[0022] The light control film 20A includes a light control layer 20, a first transparent electrode layer 12F, a second transparent electrode layer 12R, a first transparent support layer 13F, and a second transparent support layer 13R. The light control layer 20 is sandwiched between the first transparent electrode layer 12F and the second transparent electrode layer 12R and is in contact with the first transparent electrode layer 12F and the second transparent electrode layer 12R. The first transparent support layer 13F supports the first transparent electrode layer 12F on the side opposite to the light control layer 20 with respect to the first transparent electrode layer 12F. The second transparent support layer 13R supports the second transparent electrode layer 12R on the side opposite to the light control layer 20 with respect to the second transparent electrode layer 12R. The second transparent support layer 13R is bonded to the transparent substrate 11 via a transparent adhesive layer 14.

[0023] The first transparent electrode layer 12F and the second transparent electrode layer 12R are respectively conductive and transparent to visible light. The materials constituting the first transparent electrode layer 12F and the second transparent electrode layer 12R can be transparent inorganic oxides such as indium tin oxide, fluorine-doped tin oxide, tin oxide, and zinc oxide. The materials constituting the first transparent electrode layer 12F and the second transparent electrode layer 12R can also be carbon nanotubes, conductive resins such as poly(3,4-ethylenedioxythiophene), metals such as silver or silver alloys, or composite materials of metals and resins.

[0024] The first transparent support layer 13F and the second transparent support layer 13R are respectively substrates that are transparent to visible light. The first transparent support layer 13F and the second transparent support layer 13R can be single-layer structures or multi-layer structures. The materials constituting the first transparent support layer 13F and the second transparent support layer 13R are synthetic resins or inorganic compounds. The synthetic resin can be polyester such as polyethylene terephthalate and polyethylene naphthalate, polyacrylate such as polymethyl methacrylate, polycarbonate, or polyolefin. The inorganic compound can be silicon compounds such as silicon dioxide, silicon oxynitride, and silicon nitride.

[0025] [Light control layer 20]

[0026] AsFigure 3 As shown, the light control layer 20 includes a transparent polymer layer 21, a liquid crystal composition 22, and spacers 23. The light control layer 20 is a polymer dispersed liquid crystal.

[0027] The transparent polymer layer 21 is a cured product of a photopolymerizable compound. The transparent polymer layer 21 defines a plurality of voids 21D dispersed in the light control layer 20. The shape of the voids 21D can be spherical, ellipsoidal, or irregular. The liquid crystal composition 22 is filled in the voids 21D. The proportion of the transparent polymer layer 21 relative to the light control layer 20 can be 30% by mass or more and 60% by mass or less. When the proportion of the transparent polymer layer 21 is within the above range, voids 21D with an appropriate density required for image observation can be obtained. In addition, the greater the proportion of the transparent polymer layer 21, the higher the mechanical strength of the light control layer 20. The smaller the proportion of the transparent polymer layer 21, the lower the voltage required for driving the light control sheet 20A.

[0028] The photopolymerizable compound used to form the transparent polymer layer 21 can be an ultraviolet curable compound or an electron beam curable compound. The photopolymerizable compound is compatible with the liquid crystal composition 22. When the photopolymerizable compound is an ultraviolet curable compound, the dimensional controllability of the voids 21D is improved. The photopolymerizable compound can be one polymerizable compound or a combination of two or more polymerizable compounds.

[0029] Examples of the ultraviolet curable compound include acrylate compounds, methacrylate compounds, thiol compounds, styrene compounds, and oligomers of these compounds. The acrylate compounds include diacrylate compounds, triacrylate compounds, and tetraacrylate compounds. An example of the acrylate compound is butyl ethyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. The methacrylate compounds include dimethacrylate compounds, trimethacrylate compounds, and tetramethacrylate compounds. An example of the methacrylate compound is N,N-dimethylaminoethyl methacrylate, phenoxyethyl methacrylate, methoxyethyl methacrylate, and tetrahydrofurfuryl methacrylate. An example of the thiol compound is 1,3-propanedithiol and 1,6-hexanedithiol. An example of the styrene compound is styrene and methylstyrene.

[0030] The liquid crystal composition 22 contains a liquid crystal compound 22L and a dichroic dye 22P. It should be noted that the liquid crystal composition 22 may further contain a viscosity reducing agent, an antifoaming agent, an antioxidant, a weather resistance agent, etc. An example of the weather resistance agent is an ultraviolet absorber or a light stabilizer. The proportion of the liquid crystal composition 22 relative to the light control layer 20 may be 40% by mass or more and 70% by mass or less. When it is required to improve the transmittance of the light control sheet 20A in the transparent state and the haze of the light control sheet 20A in the scattering state, the proportion of the liquid crystal composition 22 is preferably 45% by mass or more and 55% by mass or less.

[0031] The liquid crystal compound 22L is a non-polymerizable compound. The dielectric constant in the long axis direction of the liquid crystal compound 22L is higher than the dielectric constant in the short axis direction of the liquid crystal compound 22L. That is, the liquid crystal compound 22L has a positive dielectric anisotropy. The liquid crystal compound 22L may be at least one selected from Schiff base liquid crystal compounds, azo liquid crystal compounds, azoxy liquid crystal compounds, biphenyl liquid crystal compounds, terphenyl liquid crystal compounds, benzoate liquid crystal compounds, diphenylacetylene liquid crystal compounds, pyrimidine liquid crystal compounds, pyridazine liquid crystal compounds, cyclohexanecarboxylate liquid crystal compounds, phenylcyclohexane liquid crystal compounds, biphenylcyclohexane liquid crystal compounds, cyano liquid crystal compounds, dicyanobenzene liquid crystal compounds, naphthalene liquid crystal compounds, dioxane liquid crystal compounds, and fluorine liquid crystal compounds. The liquid crystal compound 22L may be one liquid crystal compound or a combination of two or more liquid crystal compounds.

[0032] The dichroic dye 22P has an elongated molecular shape, and the absorbance in the visible region in the long axis direction of the molecule is larger than the absorbance in the short axis direction. The dichroic dye 22P exhibits a specified color in a state where the long axis direction is substantially orthogonal to the light incident direction. The color exhibited by the dichroic dye 22P is, for example, black or a color close to black. The dichroic dye 22P is driven to develop color in a guest-host mode with the liquid crystal compound 22L as the main body.

[0033] The dichroic dye 22P may be at least one selected from polyiodine, azo compounds, anthraquinone compounds, naphthoquinone compounds, azomethine compounds, tetrazine compounds, quinophthalone compounds, phthalocyanine compounds, perylene compounds, and dioxazine compounds. The dichroic dye 22P may be one dye or a combination of two or more dyes. From the viewpoints of improving light resistance and dichroic ratio, the dichroic dye 22P is preferably at least one selected from azo compounds and anthraquinone compounds, and more preferably an azo compound.

[0034] The ratio of the dichroic pigment 22P to the light control layer 20 can be 0.5 mass% or more and 10 mass% or less. The ratio of the dichroic pigment 22P to the light control layer 20 can also be 1 mass% or more and 5 mass%. When the ratio of the dichroic pigment 22P is 0.5 mass% or more, in the opaque state, it is easy to clearly identify the color development, and the light transmittance can be sufficiently reduced. When further suppressing the blurring caused by the ghost of the image 10P is required, it is further preferred that the ratio of the dichroic pigment 22P is 2.0 mass% or more. When the ratio of the dichroic pigment 22P is 10 mass% or less, precipitation of particles formed by aggregation of the dichroic pigment 22P can be suppressed. When suppression of aggregation of the dichroic pigment 22P is required, the ratio of the dichroic pigment 22P is preferably 5 mass% or less, and more preferably 4.0 mass% or less.

[0035] The spacers 23 are dispersed throughout the entire transparent polymer layer 21. The spacers 23 determine the thickness of the light control layer 20 around the spacers 23, thereby making the thickness of the light control layer 20 uniform. The spacers 23 can be bead spacers or photo spacers formed by exposure and development of a photoresist. As long as the spacers 23 have light transmittance, they can be colorless and transparent or colored and transparent. The color presented by the colored and transparent spacers 23 is preferably the same color as the color presented by the dichroic pigment 22P.

[0036] The thickness of the light control layer 20 can be 15 μm or more and less than 30 μm. The thickness of the light control layer 20 is substantially the same as the size of the spacers 23. By changing the average particle diameter of the spacers 23, the thickness of the light control layer 20 can be controlled. The average particle diameter of the spacers 23 can be 15 μm or more and less than 30 μm in terms of the median particle diameter D50.

[0037] The light control sheet 20A may also have an alignment layer between the first transparent electrode layer 12F and the light control layer 20. The light control sheet 20A may also have an alignment layer between the second transparent electrode layer 12R and the light control layer 20. The driving mode of the light control sheet 20A can be a reverse type. The driving mode of the light control sheet 20A can also be a forward type.

[0038] The reverse-type light control sheet 20A changes from the transparent state to the scattering state by applying a voltage between the first transparent electrode layer 12F and the second transparent electrode layer 12R. The reverse-type light control sheet 20A returns from the scattering state to the transparent state by the alignment restraining force of the alignment layer as the voltage application stops. The forward-type light control sheet 20A changes from the scattering state to the transparent state by applying a voltage between the first transparent electrode layer 12F and the second transparent electrode layer 12R. The forward-type light control sheet 20A returns from the transparent state to the scattering state as the voltage application stops.

[0039] [Optical properties]

[0040] The reflectance Rs of the first image reflection surface in the reflective projection screen 10, the reflectance Rn of the second image reflection surface in the reflective projection screen 10, the transmittance T of the light-dimming sheet 20A, and the screen back reflectance Rd satisfy the following optical conditions.

[0041] Using the reflectance Rs of the first image reflection surface, the transmittance T of the light-dimming sheet 20A, and the screen back reflectance Rd, the double-image evaluation value is expressed as (Rs + Rd) / Rs.

[0042] (Optical condition) Rd = T 2 ×Rn, (Rs + Rd) / Rs ≤ 1.3

[0043] The first image reflection surface is the surface 10F of the reflective projection screen 10 and is also the surface of the light-dimming sheet 20A. The first image reflection surface reflects the image toward the observer 102 in the reflective projection screen 10. The second image reflection surface is the back surface 10R of the reflective projection screen 10 and is also the back surface of the transparent substrate 11. The second image reflection surface reflects the image toward the observer 102 based on the refractive index difference between the transparent substrate 11 and the air layer.

[0044] The reflectance Rs of the first image reflection surface is the total light reflectance in the visible region of the surface 10F, and is obtained from the reflective projection screen 10 provided with the light-dimming sheet 20A having a scattering state with a hue brought by the dichroic pigment. The reflectance Rs of the first image reflection surface is measured as the total light reflectance of the first image reflection surface of the reflective projection screen 10 in a state where a light-shielding sheet is pasted on the back surface 10R so as to prevent the reflection of the back surface 10R.

[0045] The reflectance Rn of the second image reflection surface is the reflectance generated on the back surface of the transparent substrate 11 by the light incident from the surface of the transparent substrate 11. The reflectance Rn of the second image reflection surface is obtained from the reflective projection screen 10 provided with the light-dimming sheet 20A having a scattering state with a hue brought by the dichroic pigment. The reflectance Rn of the second image reflection surface is calculated from the reflectance of the surface 10F of the reflective projection screen 10 provided with the light-dimming sheet 20A in a scattering state, i.e., the screen surface reflectance R (= Rs + Rd), the reflectance Rs of the first image reflection surface, and the transmittance T of the light-dimming sheet 20A.

[0046] The transmittance T of the light-dimming sheet 20A is the total light transmittance in the visible region of the light-dimming sheet 20A itself, and is obtained from the light-dimming sheet 20A itself having a scattering state with a hue brought by the dichroic pigment.

[0047] White regions 10W (see Figure 5 ) and black regions 10B (see Figure 5) When (i) the reflectance of the portion of the white area 10W far from the black area 10B is the screen surface reflectance R. (ii) the reflectance of the portion of the black area 10B close to the white area 10W is the screen back surface reflectance Rd. (iii) the reflectance of the portion of the white area 10W close to the black area 10B is the reflectance Rs of the first image reflecting surface.

[0048] The screen surface reflectance R is the reflectance of the reflection type projection screen 10 itself, and is represented by the sum of the reflectance Rs of the first image reflecting surface and the screen back surface reflectance Rd (R = Rs + Rd). The screen surface reflectance R collectively represents the degree (Rs) of light incident on the surface 10F being reflected on the surface 10F, and the degree (Rd) of light incident on the surface 10F passing through the light control film 20A and the transparent substrate 11, being reflected on the back surface 10R, and then passing through the transparent substrate 11 and the light control film 20A again.

[0049] The screen back surface reflectance Rd represents the degree of light incident on the white area 10W passing through the light control film 20A and the transparent substrate 11, being reflected on the back surface 10R, and then passing through the transparent substrate 11 and the light control film 20A toward the black area 10B.

[0050] [Example]

[0051] The light control film 20A of Example 1 was obtained using the materials, formulations, and methods shown below.

[0052] First, for the liquid crystal compound 22L, a mixture of a nematic liquid crystal compound mainly composed of a cyano-based liquid crystal compound and a fluoro-based liquid crystal compound with positive dielectric anisotropy was used. For the photopolymerizable compound used to form the transparent polymer layer 21, a mixture of a polyfunctional acrylate, a polyfunctional methacrylate, a monofunctional acrylate, and a urethane acrylate was used. For the dichroic pigment 22P, a black mixed pigment composed of an azo-based compound and an anthraquinone-based compound was used. Then, by mixing the liquid crystal composition 22, the photopolymerizable compound, the polymerization initiator, the spacer 23, and the dichroic pigment 22P, a coating liquid for forming the light control layer 20 was obtained.

[0053] At this time, the photopolymerizable compound was incorporated into the coating liquid such that the proportion of the photopolymerizable compound relative to the coating liquid was 52% by mass. And the dichroic pigment 22P was incorporated into the coating liquid such that the proportion of the dichroic pigment 22P relative to the coating liquid was 2.5% by mass.

[0054] Next, for the first transparent electrode layer 12F and the second transparent electrode layer 12R, indium tin oxide films with a thickness of 100 nm were used respectively. For the first transparent support layer 13F and the second transparent support layer 13R, polyethylene terephthalate films with a thickness of 125 μm were used respectively.

[0055] Next, a coating liquid is applied onto the first transparent electrode layer 12F laminated on the first transparent support layer 13F, and the coating film formed from the coating liquid is sandwiched between the second transparent electrode layer 12R laminated on the second transparent support layer 13R and the first transparent electrode layer 12F, thereby forming a laminate. Next, the entire laminate is exposed to ultraviolet light having a center wavelength of 360 nm, causing phase separation between the transparent polymer layer 21 formed from the photopolymerizable compound and the liquid crystal composition 22. Thus, a dimming sheet 20A having a dimming layer 20 with a thickness of 20 μm is obtained. Then, a float plate glass with a thickness of 3 mm is used as the transparent substrate 11, and the dimming sheet 20A is adhered to the transparent substrate 11 using the transparent adhesive layer 14, thereby obtaining a reflective projection screen 10.

[0056] It should be noted that for the first transparent electrode layer 12F and the second transparent electrode layer 12R, silver ink layers with a thickness of 50 nm are respectively used, and except for this, the dimming sheet 20A and the reflective projection screen 10 of Example 2 are obtained in the same manner as in Example 1. The silver ink layer is formed by coating an ink in which silver wires are dispersed.

[0057] In addition, except for omitting the dichroic pigment 22P from the coating liquid, the dimming sheet 20A and the reflective projection screen 10 of the comparative example are obtained in the same manner as in Example 1.

[0058] [Evaluation]

[0059] Using the dimming sheets 20A and the transparent substrates 11 of Example 1, Example 2, and the comparative example, the total light reflectance and total light transmittance of the dimming sheet 20A in the scattering state and the back reflectance of the transparent substrate 11 are measured. In addition, the contrast and ghost visibility are evaluated using the reflective projection screens 10 of Example 1, Example 2, and the comparative example.

[0060] The reflectance Rs of the first image reflection surface as the total light reflectance of the dimming sheet 20A, the reflectance Rn of the second image reflection surface as the back reflectance of the transparent substrate 11, the transmittance T as the total light transmittance of the dimming sheet 20A, and the screen back reflectance Rd are shown in Table 1. For the surface 10F of the specimen with a light-shielding sheet adhered to the back surface 10R of the reflective projection screen 10, the reflectance Rs of the first image reflection surface is measured using the method according to JIS K 7361-1. The transmittance T and the screen surface reflectance R of the dimming sheet 20A are measured using the method according to JIS K 7361-1. The reflectance Rn of the second image reflection surface is calculated using the screen surface reflectance R, the reflectance Rs of the first image reflection surface, and the transmittance T of the dimming sheet 20A.

[0061] As Figure 4As shown, the evaluation of contrast and ghost visibility is measured using the projection device 101 and the luminance meter 103. The height H1 of the projection device 101 is set to 780 mm, and the distance L1 between the projection device 101 and the surface 10F of the reflective projection screen 10 is set to 565 mm. The height H3 of the luminance meter 103 is set to 1180 mm, and the distance L3 between the luminance meter 103 and the surface 10F of the reflective projection screen 10 is set to 1140 mm. Here, for the illuminance of the space where the reflective projection screen 10 is set, a dark condition of 6 lx to 30 lx and a bright condition of 250 lx to 350 lx are respectively set.

[0062] As Figure 5 shown, for the evaluation of contrast and ghost visibility, an image 10P showing a white area 10W and a black area 10B is used. The black area 10B is a rectangular image with black set in the entire area. The white area 10W is a rectangular frame image surrounding the entire black area 10B. The periphery of the black area 10B is filled with the white area 10W. The black area 10B is projected as a rectangular frame image with a size of 5 cm × 5 cm on the surface 10F of the reflective projection screen 10. The white area 10W is irradiated with direct light from the projection device 101 on the surface 10F of the reflective projection screen 10. The black area 10B is not irradiated with direct light from the projection device 101 on the surface 10F of the reflective projection screen 10. The direct light travels along the normal direction of the surface 10F at an angle within ±2.5° with respect to the optical axis of the parallel light emitted from the projection device 101.

[0063] The contrast is obtained as the ratio of the luminance of the white area 10W to the luminance of the black area 10B using the respective luminances of the white area 10W and the black area 10B measured by the luminance meter 103. The luminance meter 103 uses a circle with a diameter of 3 cm as the measurement range and calculates the average value of the luminances of the respective measurement points included in the circle as the measurement value. The luminance of the black area 10B is obtained by making the geometric center in the black area 10B coincide with the center of the circle of the measurement range and calculating the average value of the measurement range in the central part of the black area 10B as the measurement value of the luminance. It should be noted that the luminance meter used is CS-1000 (manufactured by Konica Minolta).

[0064] Here, the illuminance of the space where the projection device 101 is provided is 6 lx under dark conditions. The illuminance of the space where the reflective projection screen 10 is provided becomes 23 lx under dark conditions by the projection of the image 10P. The reflective projection screen 10 is provided in a space that is hardly affected by ambient light. The illuminance meter used is LX-204 (manufactured by CUSTOM Corporation). The double-image visibility is obtained by visually observing the image 10P displayed on the surface 10F of the reflective projection screen 10. In Table 1, an "〇" mark is shown for the level where the image 10P is not observed doubly, and an "×" mark is shown for the level where the image 10P is observed doubly.

[0065] Table 1

[0066] Example 1 Example 2 Comparative Example Reflectance Rs (%) 0.041 0.057 0.063 Reflectance Rn (%) 0.074 0.074 0.074 Transmittance T (%) 0.062 0.034 0.708 <![CDATA[Reflectance Rd(T 2 *Rn)]]> 0.0003 0.0001 0.0373 (Rs + Rd) / Rs 1.007 1.002 1.719 Ghosting evaluation 〇 〇 ×

[0067] As shown in Table 1, the reflectance Rs of the comparative example is a high value of 0.06 or more. On the other hand, the reflectance Rs of Example 1 and Example 2 is less than 0.06 due to the absorption of the dichroic pigment 22P and the like. In addition, the transmittance T of the comparative example is a high value of 0.7 or more. On the other hand, the transmittance T of Example 1 is a low value of 0.1 or less, and further less than 0.05 in Example 2.

[0068] The double-image evaluation values of Example 1 and Example 2 are both 1.3 or less. On the other hand, the double-image evaluation value of the comparative example is 1.7 which exceeds 1.3. In the evaluation of the double-image visibility of Example 1 and Example 2, no double image was seen, and a double image was seen in the comparative example. 1.3 as the double-image evaluation value is the intermediate value between Example 1 and the comparative example. In addition, 1.3 as the double-image evaluation value is the boundary value equivalent to the luminance ratio of the visible limit capable of obtaining the double-image suppression effect.

[0069] The contrast of Example 1 under dark conditions is 1.6 or more and 3.5 or less, and it is confirmed that the contrast increases as the illuminance of the space decreases. The contrast of Example 1 under bright conditions is 1.6 or more and 3.0 or less, and here too, it is confirmed that the contrast increases as the illuminance of the space decreases. It should be noted that the contrast of Example 2 shows a higher value than that of Example 1 under both dark and bright conditions. On the other hand, the contrast of the comparative example under dark conditions is 1.5 or more and 2.0 or less, and it is confirmed to be lower than that of Example 1 if the illuminance of the space is the same. In addition, the contrast of the comparative example under bright conditions is 1.5 or more and 1.8 or less, and here too, it is confirmed that it is lower than that of Example 1 if the illuminance of the space is the same.

[0070] [Function]

[0071] As Figure 6As shown, the surface 10F of the reflective projection screen 10 is the surface of the light control sheet 20A. The surface of the light control sheet 20A functions as a first image reflection surface that reflects an image toward the observer 102 in the reflective projection screen 10. On the other hand, the back surface 10R of the reflective projection screen 10 is the back surface of the transparent substrate 11. The back surface of the transparent substrate 11 functions as a second image reflection surface based on the refractive index difference between the transparent substrate 11 and the air layer.

[0072] As Figure 6 As shown in the upper part, visible light LF is incident from the projection device 101 onto the portion of the surface 10F of the reflective projection screen 10 that forms the white area 10W. The light reflected by the light control sheet 20A in the visible light LF is seen as the white area 10W by the observer 102. On the other hand, the transmitted light LC that passes through the light control sheet 20A and the transparent substrate 11 in the visible light LF is reflected by the back surface 10R of the reflective projection screen 10 and enters the light control sheet 20A from the back surface of the light control sheet 20A. And, the transmitted light LR that has passed through the light control sheet 20A is seen in the upper part of the white area 10W that is located Figure 6 in the upper part. Thus, (i) in the portion of the white area 10W that is far from the black area 10B, strong light equivalent to the sum of the reflectance Rs of the first image reflection surface and the reflectance Rd of the screen back surface (Rs + Rd = R) is seen.

[0073] On the other hand, the portion 10B1 of the black area 10B that is close to the white area 10W also sees the transmitted light LR that has passed through the light control sheet 20A. That is, (ii) in the portion of the black area 10B that is close to the white area 10W, the light used to form the black area 10B and the light equivalent to the reflectance Rd of the screen back surface are seen. And, when a part of the visible light LF used to form the white area 10W is strongly seen as the transmitted light LR, the boundary between the white area 10W and the black area 10B becomes blurred, and the image 10P is seen as a double image.

[0074] Regarding this point, when the reflective projection screen 10 satisfies the above optical conditions, the reflectance Rd of the screen back surface with respect to the reflectance Rs of the first image reflection surface is sufficiently suppressed. Therefore, (ii) in the portion 10B1 of the black area 10B that is close to the white area 10W, it is difficult to see the transmitted light LR compared to the strong light equivalent to the sum of the reflectance Rs of the first image reflection surface and the reflectance Rd of the screen back surface. As a result, double imaging due to the transmitted light LR can be suppressed.

[0075] As Figure 6As shown on the lower side of (iii), part 10W2 of the white area 10W close to the black area 10B does not receive the transmitted light LR from the black area 10B and is seen darker in terms of the amount of transmitted light LR compared to part of the white area 10W far from the black area 10B in (i). That is, in part 10W2 of the white area 10W close to the black area 10B in (iii), only the light equivalent to the reflectance Rs of the first image reflecting surface is seen. Moreover, since part 10W2 of the white area 10W close to the black area 10B in (iii) is different from part of the white area 10W far from the black area 10B where the transmitted light LR is seen on the lower side than this part 10W2, the image 10P is seen as a double image.

[0076] Also in this regard, when the reflective projection screen 10 satisfies the above optical conditions, since the screen back reflectance Rd with respect to the reflectance Rs of the first image reflecting surface is sufficiently suppressed, double imaging due to the transmitted light LR can be suppressed.

[0077] [Effect]

[0078] As described above, according to the above embodiment, the following effects can be obtained.

[0079] (1) Since the reflective projection screen 10 satisfies the above optical conditions, double imaging of the image 10P can be suppressed.

[0080] (2) When the transmittance T of the light control film 20A is 0.1 or less as in Example 1, the effectiveness of obtaining the effect based on (1) is improved.

[0081] (3) When the reflectance Rs of the surface of the light control film 20A is 0.05 or more and the transmittance T of the light control film 20A is 0.05 or less as in Example 2, the effect based on (1) can be obtained, and the contrast can be further improved.

[0082] (4) When the first transparent electrode layer 12F and the second transparent electrode layer 12R are silver ink layers as in Example 2, compared with the transparent inorganic oxide layer, it is easier to increase the reflectance Rs and also easier to decrease the transmittance T. Thus, the effectiveness of obtaining the effect based on (3) is also improved.

[0083] In addition, the above embodiment can be implemented with the following changes.

[0084] · The silver ink layer can be changed to a silver vapor deposition layer formed by sputtering or vacuum evaporation. If it is a silver electrode layer such as a silver ink layer or a silver vapor deposition layer, it is easy to obtain the effect based on the above (3).

[0085] · The dichroic pigment 22P is not limited to a black mixed pigment, and may also be a single black pigment, a blue mixed pigment, or a single blue pigment. The type and mixing ratio of the dichroic pigment 22P can be appropriately changed within the range that satisfies the above optical conditions.

[0086] · Within the range that satisfies (Rs + Rd) / Rs ≤ 1.3, the driving pattern of the dimming sheet 20A can be a reverse type or a forward type.

Claims

1. A reflective projection screen, characterized in that, It includes: a light control sheet having two transparent electrode layers and a polymer-dispersed liquid crystal located between the transparent electrode layers; and a transparent substrate having a surface on the back side to which the light control sheet is adhered, wherein the thickness of the transparent substrate is thicker than that of the light control sheet, the polymer-dispersed liquid crystal contains at least one dichroic pigment, and reversibly changes from a transparent state to a scattering state by changing the voltage applied between the transparent electrode layers, Wherein, the reflectivity of the surface of the light-dimming film in the scattering state, i.e., the first image reflection surface, is Rs, the reflectivity of the back surface of the transparent substrate, i.e., the second image reflection surface, is Rn, and the transmittance of the light-dimming film in the scattering state is T, satisfying Rd = T 2 ×Rn, (Rs + Rd) / Rs ≤ 1.

3.

2. The reflective projection screen according to claim 1, wherein, wherein the transmittance of the light control sheet in the scattering state is 0.1 or less.

3. The reflective projection screen according to claim 2, wherein, The transmittance of the light control sheet in the scattering state is 0.05 or less.

4. The reflective projection screen according to claim 3, wherein, The reflectance of the first image reflection surface in the scattering state is 0.05 or more.

5. The reflective projection screen according to claim 3 or 4, wherein, The dichroic pigment is a black mixed pigment, and the transparent electrode layer is a silver electrode layer.

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