Display device

Abstract

The display device of the present invention includes: an image display body whose optical state changes between a transparent state and a turbid screen state; and an image light projection unit that projects visible light onto the image display body in the screen state to display an image. Further, the image display body has a display functional layer containing liquid crystal molecules and a light-responsive orientation change sensing material, and a reflective layer laminated on the display functional layer. The reflective layer has a reflection peak wavelength within a range of 10% or less of the maximum absorption peak wavelength of the light-responsive orientation change sensing material, and a reflectance in a wavelength region more than 100 nm away from the reflection peak wavelength is 10% or less. Therefore, a display device can be provided that suppresses a reduction in color reproducibility of an image projected onto the image display body.

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 having: an image display body whose optical state changes between a transparent state and a turbid screen state; and an image light 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 that irradiates an image display body with ultraviolet light to increase the light scattering property of the image display body and make it into a turbid screen state, and irradiates visible light of a specific wavelength to return to the transparent state. The display function layer of the image display body has liquid crystal molecules and a light-responsive orientation change sensing material.

[0004] Regarding the above light-responsive orientation change sensing material, it changes from a trans form to a cis form by ultraviolet light, and the bent molecular structure of the cis form disrupts the arrangement of liquid crystal molecules to increase the light scattering property of the display function layer. It changes from the cis form to the trans form by visible light of a specific color, and the display function layer returns to the transparent state by the orientation and orderly arrangement of the disordered liquid crystal molecules.

[0005] Prior Art Documents

[0006] Patent Documents

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

[0008] Problems to be Solved by the Invention

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

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

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

[0012] Technical Means for Solving the Problems

[0013] The inventors of the present invention have conducted intensive research repeatedly to achieve the above object, and as a result, it has been found that the above object can be achieved by providing a reflective layer that selectively reflects light in the wavelength region absorbed by the light-responsive alignment change sensing material, and thus the present invention has been completed.

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

[0015] Moreover, the display device is characterized in that the image display body has: a display functional layer containing liquid crystal molecules and a light-responsive alignment change sensing material, and a reflective layer laminated on the display functional layer.

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

[0017] Advantages of the Invention

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

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

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

[0021] Figure 3 is a graph showing the reflection spectrum of the reflective layer of the example.

[0022] Figure 4 is a graph showing the reflection spectrum of the image display body of the example. DETAILED DESCRIPTION OF THE INVENTION

[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 body and an image light projection unit, and may have a control light projection unit for controlling the optical state of the image display body as needed.

[0025] As Figure 1As shown, the above-described image display body 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 laminated on the display function layer.

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

[0027] As described above, the light-responsive orientation change induction material absorbs not only ultraviolet light but also light of a part of wavelengths in the visible light region. Therefore, a part of the visible light with wavelengths in the visible light projected from the image light projection unit onto the image display body in the screen state is absorbed.

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

[0029] The image display body of the present invention has a reflective layer laminated on the above-described display function layer, which functions as a dichroic mirror that reflects light of a specific wavelength and transmits light of other wavelengths.

[0030] The above-described reflective layer has the following reflection characteristics: it has a reflection peak wavelength within the range of ±70 nm of the maximum absorption peak wavelength of the above-described light-responsive orientation change induction material, and the reflectance in the wavelength region more than 100 nm away from the above-described reflection peak wavelength is 10% or less.

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

[0032] Therefore, among the visible light projected from the image light projection unit, the light in the wavelength region absorbed by the light-responsive orientation change induction material is absorbed by the display function layer, and the scattering intensity becomes weak. On the other hand, the intensity of the light reflected by the reflective layer toward the image light projection unit side and directed toward the image light projection unit side becomes strong.

[0033] In addition, the light outside the wavelength region absorbed by the light-responsive orientation change induction material is not absorbed by the display function layer, so the scattering intensity does not become weak, but since it transmits through the reflective layer, the intensity of the light directed toward the image light projection unit side becomes weak.

[0034] Thus, the image display body of the present invention stacks a display functional layer and a reflective layer, and the absorption of light caused by the light-responsive orientation change sensing material in the display functional layer is canceled out by the reflection of light in the reflective layer. The intensity of light in the visible light region when observing the image display body from the side of the image light projection unit is homogenized as a whole. Therefore, color reproducibility can be improved.

[0035] Furthermore, since the reflectance in the wavelength region more than 100 nm away from the reflection peak wavelength is 10% or less, the reflection characteristics are sharp, so that light outside the wavelength region absorbed by the light-responsive orientation change sensing material is not affected. Therefore, design can be carried out without considering the reflection of light outside the above 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 reflection characteristics are sharp, and thus not all the light in the wavelength region absorbed by the light-responsive orientation change sensing material can be reflected. Therefore, even if the reflective layer is disposed closer to the control light projection unit side than the display functional layer, the optical state of the display functional layer can be controlled, and the degree of freedom in design is improved.

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

[0038] Generally, a visible image is displayed by a combination of three primary colors of monochromatic light: red (R), green (G), and blue (B). The reduction in color reproducibility occurs because the peak wavelength of any one of the above monochromatic lights is within the wavelength region absorbed by the light-responsive orientation change sensing material, and only the light intensity of that monochromatic light decreases.

[0039] Therefore, the above reflective layer does not need to reflect all the light in the wavelength region absorbed by the light-responsive orientation change sensing material, and only needs to reflect the monochromatic light of the color whose light intensity decreases due to the absorption of the light-responsive orientation change sensing material.

[0040] By having the reflection peak wavelength of the above reflective layer within the range of ±20 nm of the peak wavelength of the monochromatic light absorbed by the light-responsive orientation change sensing material, even if the peak wavelength of the monochromatic light emitted by the light source shifts due to heat or the like, the monochromatic light of the color whose light intensity decreases can be reliably reflected, and a reduction in color reproducibility can be suppressed.

[0041] Examples of the light source of the image light projection unit that emits the above monochromatic light include a light source that generates monochromatic light of each of RGB from white LED using a filter, a light source that uses dedicated components of each of RGB in a light source using an LED or a semiconductor laser, and a light source that generates green light or red light from blue light through color conversion using a fluorescent material.

[0042] When the above-described image display body preferably uses a light source that emits a plurality of monochromatic lights with different wavelengths, the difference in diffuse reflectance at the peak wavelength of each monochromatic light is 10% or less.

[0043] The reflectance of the reflective layer is adjusted according to the thickness of the display functional layer and the concentration of the light-responsive orientation-changing sensing material, that is, the absorptance of the display functional layer. By making the difference in diffuse reflectance at the peak wavelength of each monochromatic light of the image display body 10% or less, the deviation of the light intensity of each monochromatic light scattered toward the image light projection part becomes smaller, and the color reproducibility is improved.

[0044] Examples of the above-described reflective layer include a laminated film of dielectrics with different refractive indices, a reflective diffraction grating, and a plasmon resonance reflective film.

[0045] The laminated film of the above-described dielectric thin films with different refractive indices can be produced by laminating dielectric thin films using sputtering or electron beam evaporation. The peak reflection 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 their laminations.

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

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

[0048] The above-described reflective layer can be laminated in contact with the display functional layer, or can be laminated via a transparent substrate sandwiching the display functional layer. However, since the reflective diffraction grating has geometric irregularities, in the sense of avoiding clouding of the display functional layer (especially the part of liquid crystal molecules), it is preferable to laminate the reflective diffraction grating and the display functional layer via a transparent substrate.

[0049] Among them, the reflective diffraction grating is different from the normal specular 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 of the light projector, the image display body, and the driver is high. Moreover, since the plasmon resonance reflective film has a diffuse reflection function, the viewing angle is wide, and the recognizability when viewed from various angles is improved. Therefore, it can be preferably used for an image display body such as a windshield of an automobile that is inclined.

[0050] In addition, since these reflective layers have sharp reflection characteristics as described above, they can be stacked on the image projection side of the display function 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 function layer, it is desirable to stack them on the side opposite to the image projection side.

[0051] As the liquid crystal molecules described above, nematic liquid crystals having a rigid mesogenic skeleton and a flexible long-chain alkyl group, and having optical anisotropy and dielectric anisotropy can be used. This nematic liquid crystal has the property that, in a state where no external voltage is applied, rod-shaped liquid crystal molecules converge with each other and are arranged with substantially constant directionality.

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

[0053] The above-mentioned light-responsive orientation change sensing material is preferably used in combination with a non-light-responsive chiral compound having a different optical rotation from the light-responsive orientation change sensing material. By using the above-mentioned non-light-responsive chiral compound in combination, the helical twisting power (HTP) cancels each other out, and it is possible to further suppress the disorder of the arrangement of liquid crystal molecules caused by the torsional force of the trans-form light-responsive orientation change sensing material.

[0054] As the above-mentioned transparent substrate, glass, resin, etc. can be used, and as the transparent electrode when applying an electric field to the display function layer, an ITO film, etc. can be used.

[0055] The image display body of the present invention may have an ultraviolet shielding layer on the side farther from the control light projection unit than the display function layer as needed.

[0056] The above-mentioned ultraviolet light shielding layer is a transparent film containing an ultraviolet absorber and an ultraviolet light diffusing agent. By providing the above-mentioned ultraviolet light shielding layer, it is possible to shield ultraviolet light incident on the display function layer from the side opposite to the control light projection unit, and prevent the display function layer from becoming cloudy due to sunlight or the like.

[0057] As the above-mentioned ultraviolet absorber, known ultraviolet absorbers that absorb light in the ultraviolet region with a wavelength of 400 nm or less, do not absorb light in the visible region, and have little coloring property can be used. For example, benzophenone derivatives, salicylate derivatives, triazole derivatives, acrylonitrile derivatives can be cited. In addition, as the ultraviolet light diffusing agent, titanium dioxide, zinc oxide, etc. can be cited.

[0058] In addition, according to requirements, the image display body of the present invention may have a dimming layer on a side farther from the above-mentioned control light projection part than the display function layer. The dimming layer is a layer whose optical state changes between a transparent state and a colored state. By making the dimming layer in the colored state, the contrast of the image displayed on the display function layer becomes higher, and the recognizability can be improved.

[0059] As the above-mentioned optical function layer, a layer containing a photochromic material can be cited.

[0060] The liquid crystal optical element of the present invention can be used, for example, for the windshield or display window of an automobile, and can switch between a screen state capable of projecting and displaying a visible light image and a transparent state capable of recognizing the opposite side.

[0061] Examples

[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] 83.75% by mass of liquid crystal molecules (nematic liquid crystal: E44, manufactured by Merck & Co., Inc.), 5.1% by mass of a photo-responsive chiral (photo-responsive orientation change induction material, absorption peak wavelength: 440 nm) represented by the following structural formula (1), 2.9% by mass of a photo-non-responsive chiral represented by the following structural formula (2), 7.5% by mass of a polymerizable monomer represented by the following structural formula (3), and 0.75% by mass of a photoinitiator (IRGACURE819, manufactured by IGM Resins B.V.) were mixed to prepare a display function layer composition.

[0065] [Chemical formula 1]

[0066]

[0067] On one side of a transparent glass, a CaF2 film (refractive index 1.42) with a thickness of 79 nm and a MgF2 film (refractive index 1.387) with a thickness of 81 nm were alternately laminated 9 layers by sputtering to form a reflective layer with 18 dielectric layers laminated, and then an alignment film (polyimide) was formed on the entire surface.

[0068] The transparent glass on which the reflective film was formed and the transparent glass on which only an alignment film was formed on one side were arranged such that the alignment film was on the inner side, and the above-mentioned display function layer composition was injected between them to fabricate an image display body.

[0069] On one side of the above-mentioned image display body, an image projection part that emits monochromatic light of three colors with peak wavelengths of 450 nm (B), 550 nm (G), and 630 nm (R) was arranged on the side where the reflective layer was not formed to fabricate a display device.

[0070] Using a spectrophotometer CM3600A (manufactured by Konica Minolta), the diffuse reflectance in the visible light region of the display functional layer, the reflective layer, and the image display body formed by combining the display functional layer and the reflective layer was measured.

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

[0072] As Figure 2 shown, the diffuse reflectance of the display functional layer monomer at 450 nm (B) is 5%, but Figure 3 as shown in Figure 4 the diffuse reflectances of the entire image display body formed by laminating the reflective layer having a reflection peak wavelength at 450 nm (B) at 450 nm (B), 550 nm (G), and 630 nm (R) are 28%, 28%, and 30% respectively, and it reflects the three-color light projected from the image light projection unit substantially equally. Therefore, it is confirmed to have high color reproducibility.

[0073] Symbol Explanation

[0074] 1: Image display body

[0075] 11: Transparent substrate

[0076] 12: Display functional layer

[0077] 13: Reflective layer

[0078] 2: Image light projection unit

[0079] 3: Control light projection unit

Claims

1. A display device comprising: An image display body whose optical state changes between a transparent state and a turbid screen state; An image light projecting unit that projects visible light onto the image display body in the screen state to display an image, Characterized in that, The image display body has: a display functional layer containing liquid crystal molecules and a light-responsive orientation change sensing material, and a reflective layer laminated on the display functional layer, The reflective layer has a reflection peak wavelength within the range of ±70 nm of the maximum absorption peak wavelength of the light-responsive orientation change sensing material, and the reflectance in the wavelength region more than 100 nm away from the reflection peak wavelength is 10% or less.

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

3. The display device according to claim 2, characterized in that, The light source emits a plurality of monochromatic lights with different wavelengths, When measuring the diffuse reflectance of the image display body, the difference in the diffuse reflectance of the peak wavelengths of each monochromatic light is 10% or less.

4. The display device according to claim 1, characterized in that, It has a control light projecting unit that projects ultraviolet light to make the image display body in the screen state, The image display body has an ultraviolet shielding layer on the side farther from the control light projecting unit than the display functional layer.

5. The display device according to claim 4, characterized in that, The image display body has a light control layer on the side farther from the control light projecting unit than the display functional 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 with different refractive indexes.

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 surface plasmon resonance reflection film.

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