Display device

Abstract

This display device is provided with: an image display body, the optical state of which changes between a transparent state and a cloudy screen state; and an image projection unit that projects visible light onto the image display body in the screen state and displays an image. Furthermore, the image display body has a display function layer containing liquid crystal molecules and a photoresponsive change-of-orientation sensing material, and a reflective layer laminated on the display function layer, and the reflective layer has a reflection peak wavelength within a range of 10% or less of the maximum absorption peak wavelength of the photoresponsive change-of-orientation sensing material. The reflectance in a wavelength region away from the reflection peak wavelength by 100 nm or more is 10% or less, so that it is possible to provide a display device in which a reduction in color reproducibility of an image projected on an image display body is suppressed.

Description

Technical Field

[0001] The present invention relates to a display device, and more particularly to a display device having an image display body whose optical state changes between a transparent state and a turbid screen state. Background Art

[0002] There is known a display device comprising: an image display body whose optical state changes between a transparent state and a turbid screen state; and an image projection unit (projector) that projects visible light onto the image display body in the screen state to display an image.

[0003] Patent document 1 discloses a display device, which irradiates an image display body with ultraviolet light to increase the light scattering property of the image display body and turn the screen into a turbid state, and then irradiates visible light of a specific wavelength to return to a transparent state. The display function layer of the above-mentioned image display body has liquid crystal molecules and light-responsive orientation change sensing materials.

[0004] As for the above-mentioned light-responsive orientation change sensing material, it changes from the trans isomer to the cis isomer by ultraviolet light, and the curved molecular structure of the cis isomer disrupts the arrangement of the liquid crystal molecules, thereby increasing the light scattering of the display functional layer. It changes from the cis isomer to the trans isomer by visible light of a specific color, and the disordered liquid crystal molecules are oriented and arranged neatly, so that the display functional layer returns to a transparent state.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-185511

[0008] Problems to be solved by the invention

[0009] However, in the image display described in Patent Document 1, since the photoresponsive orientation change sensing material that changes its optical state absorbs light of a specific wavelength in the visible light region, part of the light projected from the image projection unit to the image display in a screen state is absorbed.

[0010] Therefore, the intensity balance of light scattered by the image display changes, and the color of the image projected from the image projection unit and the color of the image displayed on the image display differ. Summary of the invention

[0011] The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a display device having an image display capable of suppressing a decrease in the color reproducibility of an image displayed on the image display.

[0012] Technical solutions to solve problems

[0013] The present inventors have conducted intensive studies to achieve the above object and have found that the above object can be achieved by providing a reflective layer that selectively reflects light in the wavelength region absorbed by the photoresponsive orientation change sensing material, thereby completing the present invention.

[0014] That is, the display device of the present invention comprises: an image display body whose optical state changes between a transparent state and a turbid screen state; and an image projection unit that projects visible light onto the image display body in the screen state to display an image.

[0015] Furthermore, the display device is characterized in that the image display body comprises: a display function layer containing liquid crystal molecules and a light-responsive orientation change sensing material, and a reflective layer stacked on the display function layer.

[0016] The reflective layer has a reflection peak wavelength within the range of ±70 nm of the maximum absorption peak wavelength of the photoresponsive orientation change sensing material, and a reflectivity in a wavelength region 100 nm or more away from the reflection peak wavelength is 10% or less.

[0017] Effects of the Invention

[0018] According to the present invention, a display device can be provided in which a reflection layer that selectively reflects light in a wavelength region absorbed by a light-responsive orientation change sensing material is provided on an image display, thereby suppressing a decrease in color reproducibility of an image projected on the image display. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram showing an example of a display device according to the present invention.

[0020] Figure 2 It is a graph showing the reflection spectrum of the display functional layer of the example.

[0021] Figure 3 It is a graph showing the reflection spectrum of the reflection layer of the Example.

[0022] Figure 4 It is a graph showing the reflection spectrum of the image display of the Example. DETAILED DESCRIPTION

[0023] The display device of the present invention will be described in detail.

[0024] The display device of the present invention includes an image display and an image projection unit, and, if necessary, includes a control light projection unit that controls the optical state of the image display.

[0025] like Figure 1As shown, the image display is formed by sandwiching a display function layer whose optical state changes between a transparent state and a turbid screen state between two transparent substrates, and further includes a reflective layer stacked on the display function layer.

[0026] The display function layer contains liquid crystal molecules and light-responsive orientation change sensing materials between two vertical orientation films. As the molecular structure of the light-responsive orientation change sensing materials changes due to ultraviolet light or visible light, the orientation state of the liquid crystal molecules changes, and the scattering state of light changes.

[0027] As described above, the photoresponsive orientation change sensing material absorbs light of a part of wavelengths in the visible light region in addition to ultraviolet light. Therefore, visible light of a part of wavelengths projected from the image projecting unit to the image display body in the screen state is absorbed.

[0028] Therefore, in the display function layer, since the reflection intensity of light of some wavelengths is reduced, while the reflection intensity of light of other wavelengths is not reduced, only in the display function layer, the color of the image projected from the image projection part is different from the color of the image displayed on the image display body, and the color of the displayed image cannot be correctly reproduced on the image display body.

[0029] The image display of the present invention includes a reflective layer that reflects light of a specific wavelength and transmits light of other wavelengths and functions as a dichroic mirror, which is stacked on the display function layer.

[0030] The reflective layer has the following reflective characteristics: it has a reflection peak wavelength within the range of ±70nm of the maximum absorption peak wavelength of the photoresponsive orientation change sensing material, and the reflectivity in the wavelength region 100nm or more away from the reflection peak wavelength is 10% or less.

[0031] That is, the reflective layer selectively reflects light in the wavelength region absorbed by the photo-responsive orientation change sensing material, and does not reflect light in other wavelength regions but transmits them to the opposite side.

[0032] Therefore, among the visible light projected from the image projection unit, light in the wavelength region absorbed by the photoresponsive orientation change sensing material is absorbed by the display functional layer, and the scattering intensity becomes weaker. On the other hand, the intensity of light reflected toward the image projection unit side in the reflective layer and toward the image projection unit side becomes stronger.

[0033] In addition, since light outside the wavelength region absorbed by the photoresponsive orientation change sensing material is not absorbed by the display function layer, the scattering intensity does not decrease, but since it passes through the reflection layer, the intensity of light toward the image projection unit side decreases.

[0034] In this way, the image display of the present invention is formed by stacking a display functional layer and a reflective layer. The absorption of light caused by the light-responsive orientation change sensing material in the display functional layer is offset by the reflection of light in the reflective layer. The intensity of light in the visible light region when the image display is observed from the image projection side is uniformed as a whole, thereby improving color reproducibility.

[0035] Furthermore, since the reflectivity in the wavelength region 100 nm or more away from the reflection peak wavelength is less than 10%, the reflection characteristics are sensitive and will not affect the light outside the wavelength region absorbed by the photoresponsive orientation change sensing material. Therefore, the design can be performed without considering the reflection of light outside the above-mentioned wavelength region.

[0036] In addition, since the half-value width of the reflection peak of the reflection spectrum of the reflective layer is narrower than the half-value width of the absorption peak of the absorption spectrum of the light-responsive orientation change sensing material, the reflective property is sensitive, and thus the light in the wavelength region absorbed by the light-responsive orientation change sensing material cannot be fully reflected. Therefore, even if the reflective layer is arranged on the control light projection side of the display function layer, the optical state of the display function layer can be controlled, and the degree of freedom in design is improved.

[0037] When the image projection unit is a light source that emits monochromatic light, it is preferable that a peak wavelength of the monochromatic light be within a range of ±20 nm of a reflection peak wavelength of the reflective layer.

[0038] Typically, visible images are displayed by a combination of monochromatic lights of red (R), green (G), and blue (B). The reduction in color reproducibility occurs because the peak wavelength of any of the above monochromatic lights is within the wavelength region absorbed by the photoresponsive orientation change sensing material, and only the light intensity of this monochromatic light is reduced.

[0039] Therefore, the reflective layer does not need to reflect all the light in the wavelength region absorbed by the photoresponsive orientation change sensing material, and only needs to reflect monochromatic light of a color whose light intensity is reduced by absorption by the photoresponsive orientation change sensing material.

[0040] By ensuring that the reflection peak wavelength of the above-mentioned reflective layer is within the range of ±20nm of the peak wavelength of the monochromatic light absorbed by the photoresponsive orientation change sensing material, even if the peak wavelength of the monochromatic light emitted by the light source is shifted due to heat, etc., the monochromatic light of the color with reduced light intensity can be reliably reflected, thereby suppressing the reduction in color reproducibility.

[0041] As the light source of the image projection unit that emits the above-mentioned monochromatic light, there can be cited a light source that uses a filter to generate monochromatic light of RGB colors from a white LED, a light source that uses elements dedicated to each RGB color in a light source using an LED or a semiconductor laser, a light source that generates green light or red light from blue light by color conversion using a fluorescent material, and the like.

[0042] In the image display, when the light source is a light source that emits a plurality of monochromatic lights having different wavelengths, the difference in diffuse reflectance at the peak wavelength of each monochromatic light is preferably 10% or less.

[0043] The reflectivity of the reflective layer is adjusted according to the thickness of the display functional layer and the concentration of the light-responsive orientation change sensing material, that is, the absorbance of the display functional layer. By making the difference in diffuse reflectivity of each monochromatic light of the image display body at the peak wavelength less than 10%, the deviation in the light intensity of each monochromatic light scattered to the image projection side is reduced, thereby improving color reproducibility.

[0044] Examples of the reflective layer include a laminated film of dielectrics having different refractive indices, a reflection type diffraction grating, and a plasmon resonance reflection film.

[0045] The laminated film of dielectric thin films with different refractive indices can be produced by laminating dielectric thin films by sputtering or electron beam evaporation. The reflection peak wavelength can be adjusted by adjusting the film thickness corresponding to the refractive index of the dielectric thin film, specifically, by adjusting the film thickness obtained by dividing 1 / 4 of the reflected wavelength by the refractive index. In addition, the reflection intensity can be adjusted by the number of laminations.

[0046] The above-mentioned reflective diffraction grating can be produced by photolithography, ion beam etching, etc. The reflection peak wavelength and reflectivity can be adjusted by the interval and depth of the slits.

[0047] The plasmon resonance reflection film can be formed by uniformly disposing nanoparticles on a transparent substrate. The reflection peak wavelength can be adjusted by the particle diameter of the nanoparticles, and the reflectivity can be adjusted by the amount of the nanoparticles.

[0048] The reflective layer may be laminated in contact with the display function layer, or may be laminated via a transparent substrate sandwiching the display function layer. However, since the reflective diffraction grating has geometrical concavities and convexities, it is preferred to laminate the reflective diffraction grating and the display function layer via a transparent substrate in order to avoid turbidity of the display function layer (particularly the liquid crystal molecule portion).

[0049] Among them, the reflective diffraction grating is different from the usual regular reflection in which the reflection angle of the image light is geometrically determined based on the incident angle. Since it has the function of changing the reflection angle, the degree of freedom in designing the positional relationship between the projector, the image display, and the driver is high. In addition, since the plasma resonance reflection film has the diffuse reflection function, the viewing angle is wide, and the visibility when observed from various angles is improved. Therefore, it can be preferably used for an image display installed at an angle, such as a car windshield.

[0050] In addition, since these reflective layers have sharp reflective characteristics as described above, they can be stacked on the image projection side of the display functional layer or on the side opposite to the image projection side. However, since a wider viewing angle can be achieved through the scattering effect of the display functional layer, it is desirable to stack them on the side opposite to the image projection side.

[0051] As the liquid crystal molecules, nematic liquid crystals having a rigid mesogenic skeleton and a soft long-chain alkyl group and having optical anisotropy and dielectric anisotropy can be used. The nematic liquid crystals have the property that rod-shaped liquid crystal molecules converge and are arranged in a substantially constant direction when no external voltage is applied.

[0052] In addition, as the above-mentioned light-responsive orientation change sensing material, a compound that absorbs ultraviolet light or visible light to cause cis-trans isomerization can be used, for example, a compound having an azobenzene structure in which two benzene rings are connected by an azo group, a chalcone derivative, a sulfoxide compound, a cinnamic acid compound, a cinnamic acid compound, etc.

[0053] The above-mentioned photoresponsive orientation change sensing material is preferably used together with a non-photoresponsive chiral compound having an optical rotation different from that of the photoresponsive orientation change sensing material. By using the above-mentioned non-photoresponsive chiral compound together, the helical twisting forces (Helical Twisting Power: HTP) cancel each other out, and the disorder of the arrangement of liquid crystal molecules caused by the torsion of the trans-isomer photoresponsive orientation change sensing material can be further suppressed.

[0054] As the transparent substrate, glass, resin, or the like can be used, and as a transparent electrode when an electric field is applied to the display function layer, an ITO film or the like can be used.

[0055] The image display of the present invention may include an ultraviolet shielding layer on the side farther from the control light projecting portion than the display function layer, as necessary.

[0056] The above-mentioned ultraviolet light shielding layer is a transparent film containing an ultraviolet light absorber and an ultraviolet light diffuse reflector. By setting the above-mentioned ultraviolet light shielding layer, it is possible to shield the ultraviolet light incident on the display function layer from the side opposite to the control light projection part, thereby preventing the display function layer from becoming turbid due to sunlight, etc.

[0057] As the above-mentioned ultraviolet light absorber, it is possible to use a known ultraviolet light absorber that absorbs light outside the ultraviolet region with a wavelength of less than 400 nm, cannot absorb light in the visible region and has little coloration, for example, benzophenone derivatives, salicylate derivatives, triazole derivatives, acrylonitrile derivatives. In addition, as the ultraviolet light diffuse reflector, titanium dioxide or zinc oxide etc. can be mentioned.

[0058] In addition, the image display of the present invention may have a dimming layer on the side farther from the control light projection unit than the display function layer as required. The dimming layer is a layer whose optical state changes between a transparent state and a colored state. By making the dimming layer a colored state, the contrast of the image displayed on the display function layer becomes higher, which can improve the visibility.

[0059] Examples of the optical functional layer include a layer containing a photochromic material.

[0060] The liquid crystal optical element of the present invention can be used, for example, for a windshield or display window of a car, and can switch between a screen state in which a visible light image can be projected and displayed and a transparent state in which the opposite side can be recognized.

[0061] Example

[0062] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited to the following examples.

[0063] [Example 1]

[0064] A display function layer composition is prepared by mixing 83.75 mass% of liquid crystal molecules (nematic liquid crystal: E44, manufactured by Merck), 5.1 mass% of photoresponsive chirality represented by the following structural formula (1) (photoresponsive orientation change sensing material, absorption peak wavelength: 440 nm), 2.9 mass% of photonon-responsive chirality represented by the following structural formula (2), 7.5 mass% of polymerizable monomer represented by the following structural formula (3), and 0.75 mass% of a photopolymerization initiator (IRGACURE819, manufactured by IGM Resins BV).

[0065] [Chemical formula 1]

[0066]

[0067] On one side of the transparent glass, CaF 2 film (refractive index 1.42), and MgF 2 Nine layers of dielectric films (refractive index 1.387) were alternately stacked to form a reflective layer having 18 layers of dielectric layers, and a vertical alignment film (polyimide) was further formed on the entire surface.

[0068] The transparent glass having the reflective film formed thereon and the transparent glass having only the vertical alignment film formed thereon on one surface were arranged so that the vertical alignment film was on the inner side, and the display function layer composition was injected therebetween to produce an image display.

[0069] On one side of the image display body, on the side where the reflective layer is not formed, an image projection unit emitting three colors of monochromatic light with peak wavelengths of 450nm (B), 550nm (G), and 630nm (R) is arranged to produce a display device.

[0070] The diffuse reflectance in the visible light region of the display function layer, the reflective layer, and the image display body including the display function layer and the reflective layer was measured using a spectrocolorimeter CM3600A (manufactured by Konica Minolta).

[0071] The diffuse reflectances of the display function layer, the reflective layer, and the image display body are shown in Figure 2 to Figure 4 .

[0072] like Figure 2 As shown, the diffuse reflectance of the functional layer monomer at 450nm (B) is 5%, but Figure 3 The diffuse reflectances at 450nm (B), 550nm (G), and 630nm (R) of the entire image display formed by stacking reflective layers having a reflection peak wavelength at 450nm (B) are as shown in FIG. Figure 4 The values ​​shown are 28%, 28%, and 30%, respectively, and the three colors of light projected from the image projection unit are reflected approximately equally, so it is confirmed that the color reproducibility is high.

[0073] Explanation of symbols

[0074] 1: Image display body

[0075] 11: Transparent substrate

[0076] 12: Display function layer

[0077] 13: Reflection layer

[0078] 2: Image projection unit

[0079] 3: Control light projection part

Claims

1. A display device comprising: An image display body whose optical state changes between a transparent state and a cloudy screen state; an image projection unit for projecting visible light onto the image display body in the screen state to display an image, It is characterized in that The image display body comprises: a display function layer containing liquid crystal molecules and a light-responsive orientation change sensing material, and a reflective layer stacked on the display function layer. The reflective layer has a reflection peak wavelength within a range of ±70 nm from the maximum absorption peak wavelength of the photoresponsive orientation change sensing material, and a reflectivity in a wavelength region 100 nm or more away from the reflection peak wavelength is 10% or less.

2. The display device according to claim 1, wherein: The image projection unit is a light source that emits monochromatic light. The reflection peak wavelength of the reflection layer is within the range of ±20 nm of the peak wavelength of monochromatic light in the absorption wavelength region of the photoresponsive orientation change sensing material.

3. The display device according to claim 2, wherein: The light source emits a plurality of monochromatic lights with different wavelengths. When the diffuse reflectance of the image display is measured, the difference in diffuse reflectance at the peak wavelength of each monochromatic light is 10% or less.

4. The display device according to claim 1, wherein: A control light projection unit is provided for projecting ultraviolet light for making the image display body into a screen state, The image display has an ultraviolet shielding layer on a side farther from the control light projecting portion than the display function layer.

5. The display device according to claim 4, characterized in that The image display has a light-adjusting layer on a side farther from the control light projecting section than the display function layer.

6. The display device according to any one of claims 1 to 5, characterized in that The reflective layer is a laminated film of dielectric thin films having different refractive indices.

7. The display device according to any one of claims 1 to 5, characterized in that The reflective layer is a reflective diffraction grating.

8. The display device according to any one of claims 1 to 5, characterized in that The reflective layer is a plasmon resonance reflective film.

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