Transmission type projection screen

Abstract

A transmissive projection screen is provided with: a dimming sheet provided with two transparent electrode layers and a polymer dispersed liquid crystal positioned between the transparent electrode layers; the polymer dispersed liquid crystal contains at least one type of dichroic dye, the light control sheet reversibly changes from a transparent state to a scattering state by changing a voltage applied between the transparent electrode layers, the polymer dispersed liquid crystal has a film thickness D, and the thickness D of the film thickness D is greater than the thickness D of the light control sheet. The ratio of the mass of the dichroic dye to the mass of the polymer dispersed liquid crystal is dye concentration C, and C * D > = 48 is satisfied.

Description

Technical Field

[0001] The present disclosure relates to a transmissive 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 switching is made between a transparent state in which light passes through the light control layer and a scattering state in which the light control layer scatters light. The light control film in the scattering state is used for an image screen for projecting an image (see, for example, Patent Documents 1 and 2).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-76802

[0006] Patent Document 2: International Publication No. 2016 / 035227 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] The back surface of the light control film included in the transmissive projection screen is adhered to the surface of a transparent substrate such as glass or resin. In this case, the front surface of the light control film functions as an image incident surface that receives light from a projection device in the transmissive projection screen. The back surface of the transparent substrate functions as an image exit surface that exits the image to an observer. In such a transmissive projection screen, an image can be seen with the light control film in the scattering state, but the light scattered between the image incident surface and the image exit surface reduces the clarity of the image at the image exit surface.

[0009] Means for Solving the Problems

[0010] One aspect of the transmissive projection screen is a transmissive 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 polymer-dispersed liquid crystal including at least one dichroic pigment, and the light control film reversibly changing from a transparent state to a scattering state by a change in the voltage applied between the transparent electrode layers. The thickness of the polymer-dispersed liquid crystal is a film thickness D, and the ratio of the mass of the dichroic pigment to the mass of the polymer-dispersed liquid crystal is a pigment concentration C, and C×D≥48 is satisfied.

[0011] One type of transmissive projection screen is a transmissive projection screen that includes: a light control film having two transparent electrode layers and a polymer-dispersed liquid crystal disposed between the transparent electrode layers; and a transparent substrate having a surface that adheres to the back surface of the light control film. The polymer-dispersed liquid crystal contains at least one dichroic dye, and the light control film reversibly changes from a transparent state to a scattering state by changing the voltage applied between the transparent electrode layers. When an image having a white region formed of linear light and a black region surrounded by the white region is projected onto the surface of the light control film in the scattering state, the ratio of the transmittance of the black region to the transmittance of the white region in the back surface of the transparent substrate is 3% or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 FIG. is a configuration diagram showing a transmissive projection screen together with a projection device.

[0013] Figure 2 FIG. is a cross-sectional view showing the cross-sectional configuration of the transmissive projection screen.

[0014] Figure 3 FIG. is a partial cross-section showing the cross-sectional configuration of the light control film.

[0015] Figure 4 FIG. is a top view showing an evaluation image of the transmissive projection screen.

[0016] Figure 5 FIG. is a device configuration diagram showing an evaluation method of the transmissive projection screen.

[0017] Figure 6 FIG. is a table showing the evaluation results of the test examples.

[0018] Figure 7 FIG. is a diagram showing the optical action of the transmissive projection screen.

[0019] Figure 8 FIG. is a graph showing the relationship between absorbance and film thickness.

[0020] Figure 9 FIG. is a graph showing the relationship between the effective film thickness increase rate and haze.

[0021] Figure 10 FIG. is a graph showing the relationship between transmittance and film thickness. DETAILED DESCRIPTION

[0022] [Transmissive Projection Screen 10]

[0023] As Figure 1As shown, the transmissive projection screen 10 is connected to the driving device 51. The driving device 51 inputs a voltage signal for making the transmissive projection screen 10 in a transparent state to the transmissive projection screen 10. The driving device 51 inputs a voltage signal for making the transmissive projection screen 10 in a scattering state to the transmissive projection screen 10. The transmissive projection screen 10 reversibly changes from the transparent state to the scattering state according to the change of the voltage signal output by the driving device 51.

[0024] The surface 10F of the transmissive projection screen 10 faces the projection device 101. The surface 10F of the transmissive projection screen 10 is the image incident surface. The back surface 10R of the transmissive projection screen 10 faces the observer 102. The back surface 10R of the transmissive projection screen 10 is the image exit surface. The projection device 101 projects the image 10P onto the back surface 10R of the transmissive projection screen 10 in the scattering state. The observer 102 observes the image 10P from the side opposite to the projection device 101 with respect to the transmissive projection screen 10.

[0025] As Figure 2 As shown, the transmissive 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 transmissive projection screen 10. The back surface of the transparent substrate 11 is the back surface 10R of the transmissive projection screen 10.

[0026] 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 aircraft, or a window glass provided in a building, or a partition arranged inside a vehicle or a room. The surface of the transparent substrate 11 can be planar or curved.

[0027] The thickness of the transparent substrate 11 is sufficiently thicker than the thickness 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 can be 1.4 or more and 1.6 or less.

[0028] The dimming sheet 20A includes a dimming 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 dimming layer 20 is clamped by 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 a side opposite to the dimming 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 a side opposite to the dimming 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.

[0029] 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, or conductive resins such as poly(3,4-ethylenedioxythiophene), or metals such as silver or silver alloys, or composite materials of metals and resins.

[0030] The first transparent support layer 13F and the second transparent support layer 13R are respectively 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 a polyester such as polyethylene terephthalate or polyethylene naphthalate, or a polyacrylate such as polymethyl methacrylate, or a polycarbonate or a polyolefin. The inorganic compound can be a silicon compound such as silicon dioxide, silicon oxynitride, and silicon nitride.

[0031] [Dimming layer 20]

[0032] As Figure 3 shown, the dimming layer 20 includes a transparent polymer layer 21, a liquid crystal composition 22, and spacers 23. The dimming layer 20 is a polymer-dispersed liquid crystal.

[0033] 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 having 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.

[0034] 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 controllability of the size of the voids 21D is improved. The photopolymerizable compound can be one polymerizable compound or a combination of two or more polymerizable compounds.

[0035] An example of the ultraviolet curable compound is an acrylate compound, a methacrylate compound, a thiol compound, a styrene compound, and oligomers of these respective compounds. The acrylate compound includes a diacrylate compound, a triacrylate compound, and a tetraacrylate compound. An example of the acrylate compound is butyl ethyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. The methacrylate compound includes a dimethacrylate compound, a trimethacrylate compound, and a tetramethacrylate compound. 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.

[0036] 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 weathering agent, etc. An example of the weathering agent is an ultraviolet absorber or a light stabilizer. The proportion of the liquid crystal composition 22 relative to the light control layer 20 can be 40% by mass or more and 70% by mass or less. When it is required to increase the transmittance of the light control sheet 20A in the transparent state and increase 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.

[0037] The liquid crystal compound 22L is a non-polymeric 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.

[0038] 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 by a guest-host mode with the liquid crystal compound 22L as the host.

[0039] The dichroic dye 22P may be at least one selected from polyiodine, azo compounds, anthraquinone compounds, naphthoquinone compounds, methyleneimine 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.

[0040] The ratio of the dichroic pigment 22P to the light control layer 20, i.e., the pigment concentration C, can be 0.5% by mass or more and 10% by mass or less. The ratio of the dichroic pigment 22P to the light control layer 20 can also be 1% by mass or more and 5% by mass or less, or can be 1.6% by mass or more and 4.0% by mass or less. When the ratio of the dichroic pigment 22P is 0.5% by mass or more, in the opaque state, the color development is easily and clearly recognizable, and the light transmittance can be sufficiently reduced. When color development clarification is required, the ratio of the dichroic pigment 22P is preferably 1% by mass or more. When further clarification of the image 10P is required, the ratio of the dichroic pigment 22P is more preferably 1.6% by mass or more. When the ratio of the dichroic pigment 22P is 10% by 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% by mass or less, and more preferably 4.0% by mass or less.

[0041] The spacers 23 are dispersed throughout the entire transparent polymer layer 21. The spacers 23 define the thickness of the light control layer 20 around the periphery of 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 transparent or colored transparent. The color exhibited by the colored transparent spacers 23 is preferably the same color as the color exhibited by the dichroic pigment 22P.

[0042] The film thickness D as the thickness of the light control layer 20 can be 10 μm or more and less than 50 μm. The thickness of the light control layer 20 is substantially the same as the size of the spacers 23. The thickness of the light control layer 20 is adjusted by changing the average particle diameter of the spacers 23. The average particle diameter of the spacers 23 can be 10 μm or more and less than 50 μm in terms of the median particle diameter D50. When further clarification of the image 10P is required and a reduction in the driving voltage is required, the thickness of the light control layer 20 is preferably 32 μm or less. When further clarification of the image 10P is required and uniformization of the dichroic pigment 22P is required, the thickness of the light control layer 20 is preferably 15 μm or less.

[0043] The light control sheet 20A can also have an alignment layer between the first transparent electrode layer 12F and the light control layer 20. The light control sheet 20A can 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.

[0044] The reverse-type light-dimming sheet 20A changes from a transparent state to a scattering state by applying a voltage between the first transparent electrode layer 12F and the second transparent electrode layer 12R. The reverse-type light-dimming sheet 20A returns from the scattering state to the transparent state by the alignment restraining force of the alignment layer as the application of the voltage stops. The forward-type light-dimming sheet 20A changes from a scattering state to a transparent state by applying a voltage between the first transparent electrode layer 12F and the second transparent electrode layer 12R. The forward-type light-dimming sheet 20A returns from the transparent state to the scattering state as the application of the voltage stops.

[0045] [Optical properties]

[0046] As Figure 4 shown, the image 10P for determining the optical properties of the transmissive projection screen 10 includes a black area 10B and a white area 10W. The white area 10W is a rectangular frame image that surrounds the entire black area 10B. The black area 10B is a rectangular image with black set throughout the area. 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 transmissive projection screen 10. The periphery of the black area 10B is filled with the white area 10W. The white area 10W is irradiated with collimated light from the projection device 101 on the surface 10F of the transmissive projection screen 10. The black area 10B is not irradiated with collimated light from the projection device 101 on the surface 10F of the transmissive projection screen 10. The collimated 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.

[0047] As Figure 5As shown, the brightness for determining the optical characteristics of the transmissive projection screen 10 is obtained using the projection device 101 and the luminance meter 103. The projection device 101 is arranged on the side opposite to the luminance meter 103 with respect to the transmissive projection screen 10. The height H1 of the projection device 101 is 780 mm, and the distance L1 between the projection device 101 and the surface 10F of the transmissive projection screen 10 is 565 mm. The height H3 of the luminance meter 103 is 1180 mm, and the distance L3 between the luminance meter 103 and the back surface 10R of the transmissive projection screen 10 is 1140 mm. The luminance meter 103 uses a circle with a diameter of 3 cm as the measurement range, and calculates the average value of the brightness of each measurement point included in the circle as the measurement value. For the brightness of the black area 10B, the geometric center in the black area 10B is made to coincide with the center of the circle of the measurement range, and the average value of the measurement range in the central part of the black area 10B is calculated as the measurement value of the brightness. It should be noted that the luminance meter can use CS-1000 (manufactured by Konica Minolta). Here, the illuminance of the space where the projection device 101 is provided is 6 lx. The illuminance of the space where the transmissive projection screen 10 is provided becomes 23 lx by the projection of the image 10P. That is, the transmissive projection screen 10 is provided in a space that is hardly affected by ambient light. The illuminance meter can use LX-204 (manufactured by CUSTOM).

[0048] The brightness of the area on the back surface 10R of the transmissive projection screen 10 that faces the white area 10W depends on the transmittance of the linear light that irradiates the white area 10W. The brightness of the area on the back surface 10R of the transmissive projection screen 10 that faces the black area 10B depends on the leakage of the linear light that irradiates the white area 10W. The ratio of the transmittance of the black area 10B in the back surface 10R to the transmittance of the white area 10W is the ratio of scattering to parallel light transmission in the transmissive projection screen 10. In the back surface 10R, the ratio of the transmittance of the area that faces the black area 10B to the transmittance of the area that faces the white area 10W is the transmittance area ratio. The transmittance area ratio is obtained as the ratio of the brightness of the area on the back surface 10R that faces the black area 10B to the brightness of the area that faces the white area 10W. The transmittance area ratio of the transmissive projection screen 10 is 3% or less.

[0049] [Test Example]

[0050] Figure 6 The pigment concentration C and the film thickness D in the dimming film 20A of Test Examples 1 to 10 are shown respectively. The dimming films 20A of Test Examples 1 to 10 and the transmissive projection screen 10 are obtained by the materials, formulations, and methods shown below.

[0051] 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 fluorine-based liquid crystal compound with a positive dielectric anisotropy is used. For the photopolymerizable compound used to form the transparent polymer layer 21, a mixture of polyfunctional acrylate, polyfunctional methacrylate, monofunctional acrylate, and urethane acrylate is used. Then, by mixing the liquid crystal composition 22, the photopolymerizable compound, the polymerization initiator, and the spacer 23, a coating liquid for forming the light control layer 20 of Test Example 1 is obtained. At this time, the photopolymerizable compound is incorporated into the coating liquid such that the ratio of the photopolymerizable compound to the coating liquid is 52% by mass. In addition, a spacer 23 with a median particle size D50 of 20 μm is incorporated.

[0052] Next, for the dichroic pigment 22P, a black mixed pigment composed of an azo-based compound and an anthraquinone-based compound is used. Then, by mixing the liquid crystal composition 22, the photopolymerizable compound, the polymerization initiator, the spacer 23, and the dichroic pigment 22P of Test Example 1, a coating liquid for forming the light control layer 20 of Test Example 2 is obtained. At this time, the photopolymerizable compound is incorporated into the coating liquid such that the ratio of the photopolymerizable compound to the coating liquid is 52% by mass. In addition, the dichroic pigment 22P is incorporated into the coating liquid such that the ratio of the dichroic pigment 22P to the coating liquid, i.e., the pigment concentration C, is 2.5% by mass.

[0053] Next, the pigment concentration C in the coating liquid of Test Example 2 is changed within the range of 1.6% by mass or more and 4.5% by mass or less, and the average particle size is changed within the range of 11.1 μm or more and 35.7 μm or less in terms of the median particle size D50, and the same operations as in Test Example 2 are performed except for this, whereby coating liquids of Test Examples 3 to 10 are obtained respectively.

[0054] Next, the above coating liquid is applied to the following method to obtain the light control films 20A of Test Examples 1 to 10.

[0055] First, for the first transparent electrode layer 12F and the second transparent electrode layer 12R, indium tin oxide films with a thickness of 100 nm are 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 are used respectively.

[0056] Next, the 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 by 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 with 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.

[0057] Thus, the dimming sheets 20A of Test Examples 1 to 10 having a dimming layer 20 with a thickness equivalent to the average particle diameter of the spacers 23 were obtained. Then, using float plate glass with a thickness of 3 mm as the transparent substrate 11, the dimming sheet 20A was adhered to the transparent substrate 11 using the transparent adhesive layer 14, thereby obtaining the transmissive projection screens 10 of Test Examples 1 to 10.

[0058] [Evaluation: Transmittance Region Ratio]

[0059] Using the transmissive projection screens 10 of Test Examples 1 to 10, the transmittance region ratio described in the reference Figure 4 and Figure 5 was measured.

[0060] The luminance in the white region 10W of Test Example 1 was 1000 cd / m 2 . The luminance in the black region 10B of Test Example 1 was 100 cd / m 2 . The transmittance region ratio of Test Example 1 was 10%. In the image 10P obtained in Test Example 1, a white tone was confirmed at the edge of the black region 10B in contact with the white region 10W. Moreover, the boundary between the white region 10W and the black region  10B in the image 10P obtained in Test Example 1 was not clear.

[0061] The luminance in the white region 10W of Test Example 2 was 100 cd / m 2 . The luminance in the black region 10B of Test Example 2 was 2.8 cd / m 2 . The transmittance region ratio of Test Example 2 was 2.8%. In the image 10P obtained in Test Example 2, no white tone was confirmed at the edge of the black region 10B in contact with the white region 10W. Moreover, compared with the image 10P obtained in Test Example 1, the boundary between the white region 10W and the black region 10B was clearly seen in the image 10P obtained in Test Example 2. In addition, the transmittance region ratios of Test Examples 3 to 8 were all 3% or less, and like Test Example 2, the boundary between the white region 10W and the black region 10B was clearly seen.

[0062] The transmittance region ratios of Test Examples 9 and 10 were values lower than that of Test Example 1, but were 4.2% and 6.0% exceeding 3%. In the images 10P obtained in Test Examples 9 and 10, a black region 10B with suppressed white tone compared to Test Example 1 was confirmed, but some white tone was confirmed at the edge of the black region 10B in contact with the white region 10W. Moreover, the images 10P obtained in Test Examples 9 and 10 did not reach the level where the boundary between the white region 10W and the black region 10B was clearly seen.

[0063] As confirmed above, if the transmittance area ratio is 3% or less, the clarification of Image 10P can be achieved.

[0064] It should be noted that the transmissive projection screen 10 of Test Example 6 has a transmittance area ratio of 3% or less. Although no white tone level was confirmed in the black area 10B, aggregation occurred in a part of the dichroic pigment 22P. Therefore, when beauty in a transparent state is required for the transmissive projection screen 10, it was also confirmed that the pigment concentration C is preferably 4.0 mass% or less.

[0065] In addition, the transmissive projection screen 10 of Test Example 4 also has a transmittance area ratio of 3% or less. Although no white tone level was confirmed in the black area 10B, a voltage of 50V or more is required to switch from the scattering state to the transparent state. Therefore, when low power consumption is required for the transmissive projection screen 10, it was also confirmed that the film thickness D is preferably 32μm or less.

[0066] [Evaluation: Absorbance A]

[0067] As Figure 7 shown, a part of the linear light LF for forming the white area 10W passes through the light control layer 20 and the transparent substrate 11. The transmitted light LC passing through the light control layer 20 and the transparent substrate 11 is seen as the white area 10W. On the other hand, a part of the linear light LF for forming the white area 10W is scattered by the light control layer 20 and leaks into the black area 10B. The leaked light LR leaking from the white area 10W to the black area 10B gives the black area 10B a white tone.

[0068] In Test Examples 1, 9, and 10 where the transmittance area ratio is higher than 3%, the leaked light LR passes through the black area 10B, giving the black area 10B a white tone. In contrast, in Test Examples 2 to 8 where the transmittance area ratio is 3% or less, while the leaked light LR is scattered into the black area 10B, the dichroic pigment 22P in the black area 10B absorbs the leaked light LR, thus suppressing the leaked light LR from being seen. In this way, since the transmittance in the black area 10B is large in Test Examples 1, 9, and 10 where the transmittance area ratio is higher than 3%, the black area 10B has a white tone. In contrast, in Test Examples 2 to 8 where the transmittance area ratio is 3% or less, the transmittance in the black area 10B is suppressed, thereby clarifying the black area 10B.

[0069] Increasing the probability of the presence of the dichroic pigment 22P in the optical path through which the leaked light LR passes is effective for suppressing the transmittance in the black area 10B.

[0070] Figure 8It shows the relationship between the film thickness D of the light-dimming layer 20 and the absorbance A of the light-dimming sheet 20A. It should be noted that the absorbance A is obtained by logarithmizing the reciprocal of the total light transmittance in the visible region of the light-dimming sheet 20A. Additionally, Figure 8 The light-dimming sheet 20A in Test Example 12 in Figure 8 was obtained by omitting the photopolymerizable compound and the polymerization initiator in the coating liquid of Test Example 2, changing the average particle diameter of the spacer 23 to 6 μm and 25 μm, and further changing the coating amount corresponding to the film thickness D of 6 μm and 25 μm. That is, the light-dimming sheet 20A in Test Example 12 does not have the voids 21D partitioned by the transparent polymer layer 21, and the absorbance A of Test Example 12 can be regarded as the absorbance A of only the liquid crystal composition 22 in an orientation state approximately equal to the random orientation state in Test Example 2. It should be noted that

[0071] As Figure 8 shown, the absorbance A of the light-dimming sheet 20A in Test Example 12 increases linearly with the increase in the film thickness D. The absorbance A of the light-dimming sheet 20A in Test Example 11 increases non-linearly with the increase in the film thickness D. The film thickness dependence of the absorbance A in the light-dimming sheet 20A of Test Example 11 has a sharply increasing part compared with that of the light-dimming sheet 20A in Test Example 12. Additionally, as the film thickness D is higher than 20 μm, the increase amount of the absorbance A per unit increase in the film thickness D is approximately equal between Test Example 11 and Test Example 12.

[0072] In this way, the light transmission suppression effect of the light-dimming sheet 20A is non-linearly improved by enhancing scattering in the presence of the transparent polymer layer 21, that is, in the presence of the dichroic pigment 22P. In other words, on the basis of having the transparent polymer layer 21, (i) the higher the pigment concentration C, or (ii) the larger the film thickness D, the higher the light transmission suppression effect of the light-dimming sheet 20A. Moreover, as shown by the tendency of the increase amount of the absorbance A per unit increase in the film thickness D, the light transmission suppression effect in the light-dimming sheet 20A is particularly significant at a film thickness D of 20 μm or less. It should be noted that the tendency of the significant light transmission suppression effect at a film thickness D of 20 μm or less is confirmed in the range of 2.0 mass% or more and 3.0 mass% or less.

[0073] Return Figure 6 , the product of (i) the pigment concentration C and (ii) the film thickness D, that is, the effective pigment amount, in Test Examples 1, 9, and 10 is 45 or less. In contrast, the product of the pigment concentration C and the film thickness D in Test Examples 2 to 8 is 48 or more.

[0074] As confirmed above, when the product of the pigment concentration C and the film thickness D, i.e., the effective pigment amount, is 48 or more, the clarification of the image 10P can be achieved.

[0075] In addition, the transmissive projection screen 10 of Test Example 6 has a product of the pigment concentration C and the film thickness D of 48 or more, and no white tone is confirmed in the black region 10B. However, as described above, agglomeration occurs in a part of the dichroic pigment 22P in Test Example 6. Therefore, when the aesthetics in the transparent state is required for the transmissive projection screen 10, it is preferable that the pigment concentration C is 4.0 mass% or less.

[0076] In addition, the transmissive projection screen 10 of Test Example 4 also has a product of the pigment concentration C and the film thickness D of 48 or more, and no white tone is confirmed in the black region 10B. However, as described above, a voltage of 50 V or more is required to switch between the transparent state and the scattering state. Therefore, when low power consumption is required for the transmissive projection screen 10, it is preferable that the film thickness D is 32 μm or less.

[0077] [Evaluation: Haze]

[0078] The effective film thickness increase rate is the ratio of the absorbance A in the scattering state in each test example based on the absorbance A of the liquid crystal composition 22. For example, in Figure 8 , when the film thickness D is 25 μm, the absorbance A of the liquid crystal composition 22 is 0.65, the absorbance A of Test Example 12 is 2.5, and the effective film thickness increase rate is 385%. For example, in Figure 8 , when the film thickness D is 15 μm, the absorbance A of the liquid crystal composition 22 is 0.45, the absorbance A of Test Example 12 is 1.6, and the effective film thickness increase rate is 355%.

[0079] The effective film thickness increase rate is based on the level without the transparent polymer layer 21 as in Test Example 12. The effective film thickness increase rate is determined between two levels where the presence or absence of the transparent polymer layer 21 is different and other points are regarded as equal. Thus, the effective film thickness increase rate makes the contribution of the scattering structure of the transparent polymer layer 21 stand out from various factors such as the pigment concentration C and the film thickness D that contribute to the absorption of the leakage light LR.

[0080] Figure 9 The relationship between the haze of the dimming sheet 20A in the scattering state and the effective film thickness increase rate of the dimming sheet 20A is shown. Figure 9The haze in [the relevant context] was obtained for each level of Test Example 11 using the method based on JIS K 7136:2000. The haze of the light control film 20A depends on the scattering structure of the transparent polymer layer 21. For example, when the number of voids 21D per unit area of the light control film 20A is relatively large, the haze of the light control film 20A is more likely to be higher than the level with a smaller number of voids 21D. For example, when the surface area of the voids 21D per unit volume of the light control film 20A is relatively large, the haze of the light control film 20A is more likely to be higher than the level with a smaller surface area of the voids 21D.

[0081] As Figure 9 shown, when the haze of the light control film 20A is less than 90%, the higher the haze of the light control film 20A, the higher the effective film thickness increase rate of the light control film 20A. That is, the contribution of the scattering structure to the absorption of the leakage light LR is greater when the scattering caused by the scattering structure is higher. On the other hand, when the haze of the light control film 20A is 90% or more, regardless of the haze of the light control film 20A, the effective film thickness increase rate of the light control film 20A reaches saturation in a high range of 350% or more. That is, even when the scattering caused by the scattering structure increases, the absorption of the dichroic pigment 22P and the like reaches the rate-limiting stage, and the contribution of the scattering structure to the absorption of the leakage light LR also basically reaches saturation.

[0082] Thus, if (iii) the haze of the light control film 20A is 90% or more, the contribution of the scattering structure itself saturates, and thus the light transmission suppression effect of the light control film 20A can be stabilized.

[0083] Based on the above confirmation, if the haze of the light control film 20A is 90% or more, even if there are deviations in the size, number, etc. of the voids 21D, the clarification of the image 10P can be stably achieved.

[0084] [Evaluation: Liquid crystal ratio]

[0085] Figure 10 It shows the relationship between the film thickness D of the light control layer 20 and the total light transmittance in the light control film 20A. It should be noted that Figure 10 the light control film 20A in Test Example 13 in [the relevant context] was obtained by changing the liquid crystal ratio in the coating liquid of Test Example 2 to 55% by mass, changing the average particle diameter of the spacer 23 in the range of 7.5 μm or more and 25 μm or less, and then changing the coating amount corresponding to the film thickness D in the range of 7.5 μm or more and 25 μm or less. In addition, Figure 10 the light control film 20A in Test Example 14 in [the relevant context] was obtained by changing the liquid crystal ratio in the coating liquid of Test Example 2 to 45% by mass, changing the average particle diameter of the spacer 23 in the range of 7.5 μm or more and 25 μm or less, and then changing the coating amount corresponding to the film thickness D in the range of 7.5 μm or more and 25 μm or less.

[0086] As Figure 10 shown, when the film thickness D is less than 15 μm, the higher the liquid crystal ratio, the greater the transmittance difference of the light control film 20A. For example, when the film thickness D is 7.5 μm, the transmittance at a liquid crystal ratio of 55% by mass is 65%, and the transmittance at a liquid crystal ratio of 45% by mass is 40%. For example, when the film thickness D is 10 μm, the transmittance at a liquid crystal ratio of 55% by mass is 40%, and the transmittance at a liquid crystal ratio of 45% by mass is 30%. On the other hand, when the film thickness D is 15 μm or more, regardless of the liquid crystal ratio, the transmittance difference of the light control film 20A is substantially equal. That is, even if the liquid crystal ratio changes, the contribution of the film thickness D itself becomes the rate-limiting factor, and the contribution of the liquid crystal ratio to the transmittance of the light control film 20A is basically stable.

[0087] Thus, if (iv) the film thickness D of the light control film 20A is 15 μm or more, the transmission variation caused by the liquid crystal ratio can be suppressed, and thus the transmission suppression effect of the light control film 20A can be stabilized.

[0088] [Effect]

[0089] As described above, according to the above-described embodiment, the following effects can be obtained.

[0090] (1) Since the effective pigment amount, which is the product of the pigment concentration C and the film thickness D in the transmissive projection screen 10, is 48 or more, the image 10P can be sharpened.

[0091] (2) Since the transmittance region ratio in the transmissive projection screen 10 is 3% or less, the image 10P can be sharpened.

[0092] (3) When the film thickness D of the light control layer 20 is 15 μm or more, the deviation of sharpness caused by the liquid crystal ratio is suppressed.

[0093] (4) When the film thickness D of the light control layer 20 is 32 μm or less, power consumption reduction in the transmissive projection screen 10 can also be achieved.

[0094] (5) When the haze of the light control film 20A is 90% or more, the deviation of sharpness caused by the deviation of the scattering structure in the transparent polymer layer 21 can be suppressed.

[0095] In addition, the above-described embodiment can be implemented with the following changes.

[0096] · The dichroic pigment 22P is not limited to a black mixed pigment, and may be a single black pigment, may be a blue mixed pigment, or may be 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.

[0097] · Within the range where the effective pigment amount is 48 or more, or the transmittance region ratio is 3% or less, the driving pattern of the dimming sheet 20A can be reverse type or forward type.

Claims

1. A transmissive projection screen, characterized in that, It includes: a light control film having two transparent electrode layers and a polymer-dispersed liquid crystal located between the transparent electrode layers; and a transparent substrate having a surface adhered to the back surface of the light control film, the polymer-dispersed liquid crystal contains at least one dichroic pigment, and by changing the voltage applied between the transparent electrode layers, the light control film reversibly changes from a transparent state to a scattering state, wherein the thickness of the polymer-dispersed liquid crystal is a film thickness D, and the ratio of the mass of the dichroic pigment to the mass of the polymer-dispersed liquid crystal is a pigment concentration C, satisfying C×D≥48.

2. The transmissive projection screen according to claim 1, wherein, The film thickness D is 15 μm or more and 32 μm or less.

3. The transmissive projection screen according to claim 2, wherein, The film thickness D is 20 μm or less.

4. The transmissive projection screen according to claim 2, wherein, The pigment concentration C is 1.6% by mass or more and 4.0% by mass or less.

5. A transmissive projection screen, characterized in that, It includes: a light control film having two transparent electrode layers and a polymer-dispersed liquid crystal located between the transparent electrode layers; and a transparent substrate having a surface adhered to the back surface of the light control film, the polymer-dispersed liquid crystal contains at least one dichroic pigment, and by changing the voltage applied between the transparent electrode layers, the light control film reversibly changes from a transparent state to a scattering state, wherein when an image having a white area formed by linear light and a black area surrounded by the white area is projected onto the surface of the light control film in the scattering state, the ratio of the transmittance of the black area to the transmittance of the white area on the back surface of the transparent substrate is 3% or less.

6. The transmissive projection screen according to claim 5, wherein, The haze of the light control film in the scattering state is 90% or more.

7. The transmissive projection screen according to any one of claims 1 to 6, wherein, The ratio of the mass of the liquid crystal composition to the mass of the polymer-dispersed liquid crystal is 45% by mass or more and 55% by mass or less.

8. The transmissive projection screen according to any one of claims 1 to 6, wherein, The dichroic pigment is a black mixed pigment.

Images