Display device

Abstract

This display device comprises an image display body, the optical state of which changes between a transparent state and an opaque screen state, and an image light projecting part for displaying an image by projecting visible light on the image display body in the screen state.　The image display body has: a display function layer that contains liquid crystal molecules and a light-responsive orientation change-inducing material; and a reflective layer that is laminated on the display function layer. The reflective layer has a reflection peak wavelength in a range of 10% or less of the maximum absorption peak wavelength of the light-responsive orientation change-inducing material, and the reflectivity in a wavelength range separated from the reflection peak wavelength by 100 nm or more is 10% or less. Therefore, it is possible to provide a display device wherein a reduction of the color reproducibility of an image projected on the image display body can be 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 having 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 that irradiates an image display body with ultraviolet light to increase the light scattering property of the image display body and change it to a turbid screen state, and irradiates visible light of a specific wavelength to return it to the transparent state. The display functional layer of the image display body contains liquid crystal molecules and a light-responsive alignment change-inducing material.

[0004] The light-responsive alignment change-inducing material changes from a trans form to a cis form by ultraviolet light, and the bent molecular structure of the cis form disturbs the alignment of liquid crystal molecules to increase the light scattering property of the display functional layer. It changes from the cis form to the trans form by visible light of a specific color, and the liquid crystal molecules with disordered alignment are oriented and aligned, so that the display functional layer returns to the transparent state.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the image display body described in Patent Document 1, since the light-responsive alignment change-inducing 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 projection unit onto the image display body in the screen state is absorbed.

[0007] Therefore, the intensity balance of the light scattered by the image display body changes, and the color of the image projected from the image projection unit is different from the color of the image displayed on the image display body.

[0008] The present invention has been made in view of such problems of the 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.

Means for Solving the Problems

[0009] As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by providing a reflective layer that selectively reflects light in the wavelength range absorbed by the light-responsive alignment change-inducing material, and has completed the present invention.

[0010] 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 projection unit that projects visible light onto the image display body in the screen state to display an image. The image display body has a display function layer containing liquid crystal molecules and a light-responsive alignment change-inducing material, and a reflective layer laminated on the display function layer. The reflective layer has a reflection peak wavelength in the range of ±70 nm of the maximum absorption peak wavelength of the light-responsive alignment change-inducing material, and the reflectance in a wavelength range more than 100 nm away from the reflection peak wavelength is 10% or less.

Effects of the Invention

[0011] According to the present invention, since a reflective layer that selectively reflects light in a wavelength range in which the light-responsive alignment change-inducing material in the image display body has absorption is provided, it is possible to provide a display device that suppresses a decrease in color reproducibility of an image projected onto the image display body.

Brief Description of Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] The display device of the present invention will be described in detail. The display device of the present invention includes an image display body and an image light-projecting unit, and optionally has a control light-projecting unit that controls the optical state of the image display body.

[0014] As shown in FIG. 1, the image display body is formed by sandwiching a display function layer whose optical state changes between a transparent state and a turbid screen state with two transparent substrates, and further has a reflective layer laminated on the display function layer.

[0015] The display function layer contains liquid crystal molecules and a light-responsive alignment change-inducing material between two vertical alignment films, and the alignment state of the liquid crystal molecules changes and the light scattering state changes as the molecular structure of the light-responsive alignment change-inducing material changes due to ultraviolet light or visible light.

[0016] As described above, since the light-responsive alignment change-inducing material absorbs not only ultraviolet light but also light of some wavelengths in the visible light region, among the visible light projected from the image light-projecting unit onto the image display body in the screen state, visible light of some wavelengths is absorbed.

[0017] Therefore, in the display function layer, since the reflection intensity of light of some wavelengths decreases while the reflection intensity of light of other wavelengths does not decrease, only with the display function layer, the color of the image projected from the image projection unit is different from the color of the image displayed on the image display body, and the color of the displayed image cannot be accurately reproduced on the image display body.

[0018] In the image display body of the present invention, a reflection layer that acts as a dichroic mirror reflecting light of a specific wavelength and transmitting light of other wavelengths is laminated on the display function layer.

[0019] The reflection layer has a reflection peak wavelength in the range of ±70 nm of the maximum absorption peak wavelength of the light-responsive alignment change-inducing material, and has a reflection characteristic that the reflectance in a wavelength range more than 100 nm away from the reflection peak wavelength is 10% or less.

[0020] That is, the reflection layer selectively reflects light in the wavelength range absorbed by the light-responsive alignment change-inducing material, and allows light in other wavelength ranges to pass through to the opposite side without being reflected.

[0021] Therefore, among the visible light projected from the image projection unit, the light in the wavelength range absorbed by the light-responsive alignment change-inducing material is absorbed by the display function layer and the scattering intensity becomes weak, while in the reflection layer, it is reflected to the image projection unit side and the intensity of the light traveling toward the image projection unit side becomes strong.

[0022] Also, the light outside the wavelength range absorbed by the light-responsive alignment change-inducing material is not absorbed by the display function layer, so the scattering intensity does not become weak, but since it passes through the reflection layer, the intensity of the light traveling toward the image projection unit side becomes weak.

[0023] Thus, in the image display body of the present invention, by laminating the display function layer and the reflection layer, the absorption of light by the light-responsive alignment change-inducing material in the display function layer is offset by the reflection of light in the reflection layer, and the intensity of light in the visible light region when the image display body is viewed from the image projection unit side is uniform as a whole, so that the color reproducibility can be improved.

[0024] Furthermore, since the reflectance in a wavelength range more than 100 nm away from the reflection peak wavelength is 10% or less and the reflection characteristics are sharp, the photo-responsive alignment change inducing material does not affect light outside the wavelength range it absorbs. Therefore, it can be designed without considering the reflection of light outside the above wavelength range.

[0025] In addition, the full width at half maximum of the reflection peak of the reflection spectrum of the reflection layer is narrower than the full width at half maximum of the absorption peak of the absorption spectrum of the photo-responsive alignment change inducing material, and the reflection characteristics are sharp. Thus, not all of the light in the wavelength range absorbed by the photo-responsive alignment change inducing material is reflected. Therefore, even if the reflection layer is arranged on the side of the control light projection unit rather than the display function layer, the optical state of the display function layer can be controlled, improving the degree of freedom in design.

[0026] When the image projection unit is a light source that emits monochromatic light, it is preferable that the peak wavelength of the monochromatic light is within the range of ±20 nm of the reflection peak wavelength of the reflection layer.

[0027] Generally, a visible image is displayed as a combination of three primary colors of monochromatic light: red (R), green (G), and blue (B). A decrease in color reproducibility occurs when the peak wavelength of any of the above monochromatic lights is within the wavelength range absorbed by the photo-responsive alignment change inducing material, resulting in a decrease in the light intensity of only that monochromatic light.

[0028] Therefore, the reflection layer does not need to reflect all of the light in the wavelength range absorbed by the photo-responsive alignment change inducing material, and it is sufficient to reflect the monochromatic light of the color whose light intensity decreases due to the absorption of the photo-responsive alignment change inducing material.

[0029] Since the reflection peak wavelength of the reflection layer is within the range of ±20 nm of the peak wavelength of the monochromatic light absorbed by the photo-responsive alignment change inducing 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, suppressing a decrease in color reproducibility.

[0030] As the light source of the image projection unit that emits the above-mentioned monochromatic light, there can be mentioned those that create monochromatic light of each RGB color using a color filter from a white LED, those that use LEDs or semiconductor lasers and use dedicated elements for each RGB color, those that create green light or red light by color conversion using a fluorescent material from blue light, and the like.

[0031] When the above-mentioned image display body emits a plurality of monochromatic lights with different wavelengths, it is preferable that the difference in diffuse reflectance at the peak wavelength of each monochromatic light is 10% or less.

[0032] By adjusting the reflectance of the reflective layer according to the thickness of the display functional layer and the concentration of the light-responsive alignment change-inducing material, that is, the absorption rate of the display functional layer, and making the difference in diffuse reflectance at the peak wavelength of each monochromatic light of the image display body 10% or less, the variation in the light intensity of each monochromatic light scattered toward the image projection unit side becomes smaller and the color reproducibility is improved.

[0033] Examples of the above-mentioned reflective layer include a laminated film of dielectrics with different refractive indices, a reflective diffraction grating, and a plasmon resonance reflective film.

[0034] The laminated film of dielectric thin films with different refractive indices can be manufactured by laminating dielectric thin films by sputtering or electron beam evaporation. The reflection peak wavelength can be adjusted by adjusting the film thickness according to the refractive index of the dielectric thin film, specifically, the film thickness obtained by dividing 1 / 4 of the wavelength to be reflected by the refractive index, and the reflection intensity can be adjusted by the number of those laminations.

[0035] The above-mentioned reflective diffraction grating can be manufactured by photolithography, an ion beam etching method, or the like. The reflection peak wavelength and the reflectance can be adjusted by the interval and depth of the slits.

[0036] The plasmon resonance reflective film can be formed by uniformly arranging nanoparticles on a transparent substrate, and the reflection peak wavelength can be adjusted by the particle size of the nanoparticles, and the reflectance can be adjusted by the amount of the nanoparticles.

[0037] The above reflective layer may be laminated in contact with the display functional layer, or may be laminated via a transparent substrate sandwiching the display functional layer. However, since the reflective diffraction grating has geometric irregularities, in order to avoid clouding of the display functional layer (especially the liquid crystal molecule part), it is preferable that the reflective diffraction grating and the display functional layer are laminated via a transparent substrate.

[0038] Among them, different from normal specular reflection where the reflection angle of the image light is geometrically determined based on the incident angle, the reflective diffraction grating has a function of changing the reflection angle. Therefore, the degree of freedom in the layout of the positional relationship among the projector, the image display body, and the driver is high. Furthermore, since the plasmon resonance reflection film has a diffuse reflection function, the viewing angle is wide and the visibility when viewed from various angles is improved, so it can be preferably used for an image display body installed obliquely such as the windshield of an automobile.

[0039] Also, as described above, since these reflective layers have sharp reflection characteristics, they may be laminated on the image projection part side of the display functional layer or on the side opposite to the image projection part side. However, since a wider viewing angle can be realized by the scattering effect of the display functional layer, it is desirable to be laminated on the side opposite to the image projection part side.

[0040] As the above liquid crystal molecules, 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 rod-shaped liquid crystal molecules associate with each other and are arranged with a substantially constant orientation without applying an external voltage.

[0041] Also, as the above light-responsive alignment change-inducing 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, fulgide compounds, cinnamic acid compounds, etc. can be mentioned.

[0042] The above-mentioned light-responsive alignment change-inducing material is preferably used in combination with a non-light-responsive chiral compound having optical activity different from that of the light-responsive alignment change-inducing material. By using the above-mentioned non-light-responsive chiral compound in combination, the helical twisting power (HTP) is canceled out, and the disorder of the alignment of liquid crystal molecules caused by the twisting force of the trans-form light-responsive alignment change-inducing material can be further suppressed.

[0043] 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 or the like can be used.

[0044] The image display body of the present invention can have an ultraviolet shielding layer on the side farther from the control light projection unit than the display function layer, if necessary.

[0045] The above-mentioned ultraviolet light shielding layer is a transparent film containing an ultraviolet absorber and an ultraviolet light diffusing reflector. By providing the above-mentioned ultraviolet light shielding layer, ultraviolet light incident on the display function layer from the side opposite to the control light projection unit can be shielded, and the display function layer can be prevented from becoming cloudy due to sunlight or the like.

[0046] As the above-mentioned ultraviolet absorber, a conventionally known ultraviolet absorber that absorbs ultraviolet light with a wavelength of 400 nm or less and does not absorb visible light and has little coloring property can be used. For example, benzophenone derivatives, salicylic acid ester derivatives, triazole derivatives, acrylonitrile derivatives can be mentioned. Further, as the ultraviolet light diffusing reflector, titanium oxide, zinc oxide, etc. can be mentioned.

[0047] In addition, the image display body of the present invention can have a light control layer on the side farther from the control light projection unit than the display function layer, if necessary. The light control layer is a layer whose optical state changes between a transparent state and a colored state. By setting the light control layer in the colored state, the contrast of the image displayed on the display function layer can be increased, and the visibility can be improved. Examples of the above-mentioned optical function layer include a layer containing a photochromic material.

[0048] The liquid crystal optical element of the present invention can be used, for example, for the front glass or show window of an automobile, 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 other side can be visually recognized.

Example

[0049] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0050] [Example 1] 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 alignment change-inducing 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 (IRGACURE 819, manufactured by IGM Resins B.V.) were mixed to prepare a display functional layer composition.

[0051]

Chemical formula

[0052] On one surface of a transparent glass, a reflective layer in which 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 each, resulting in 18 layers of dielectrics laminated, was formed by sputtering. Further, a vertical alignment film (polyimide) was formed over the entire surface.

[0053] The transparent glass on which this reflective film was formed and the transparent glass on which only a vertical alignment film was formed on one surface were arranged such that the vertical alignment film was on the inside, and the above display functional layer composition was injected between them to produce an image display body.

[0054] An image projection unit that emits three primary color monochromatic lights with peak wavelengths of 450 nm (B), 550 nm (G), and 630 nm (R) was arranged on one side of the above-mentioned image display body on the side where the reflective layer was not formed to fabricate a display device.

[0055] Using a spectrocolorimeter 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 combined with the display functional layer and the reflective layer was measured. The diffuse reflectances of the display functional layer, the reflective layer, and the image display body are shown in FIGS. 2 to 4, respectively.

[0056] As shown in FIG. 2, the diffuse reflectance of the display functional layer alone at 450 nm (B) was 5%, but as shown in FIG. 3, the diffuse reflectances of the entire image display body laminated with the reflective layer having a reflection peak wavelength at 450 nm (B) at 450 nm (B), 550 nm (G), and 630 nm (R) were 28%, 28%, and 30%, respectively, as shown in FIG. 4. Since the three primary color lights projected from the image projection unit were reflected almost equally, it was confirmed that the display device had high color reproducibility.

Explanation of Signs

[0057] 1 Image display body 11 Transparent substrate 12 Display functional layer 13 Reflective layer 2 Image projection unit 3 Control light projection unit

Claims

1. 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, wherein the image display body has a display functional layer containing liquid crystal molecules and a light-responsive orientation change inducing material, and a reflective layer laminated on the display functional layer, the reflective layer has a reflection peak wavelength in the range of ±70 nm of the maximum absorption peak wavelength of the light-responsive orientation change inducing material, and the reflectance in a wavelength range more than 100 nm away from the reflection peak wavelength is 10% or less. The display device is characterized by this.

2. The image light projection unit is a light source that emits monochromatic light, and the reflection peak wavelength of the reflective layer is within the range of ±20 nm of the peak wavelength of the monochromatic light within the absorption wavelength range of the light-responsive orientation change inducing material. The display device according to Claim 1 is characterized by this.

3. The light source emits a plurality of monochromatic lights with different wavelengths, and when the diffuse reflectance of the image display body is measured, the difference in the diffuse reflectance at the peak wavelength of each monochromatic light is 10% or less. The display device according to Claim 2 is characterized by this.

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

5. The image display body has a light control layer on the side farther from the control light projection unit than the display functional layer. The display device according to Claim 4 is characterized by this.

6. The reflective layer is a laminated film of dielectric thin films with different refractive indices. The display device according to any one of Claims 1 to 5 is characterized by this.

7. The reflective layer is a reflective diffraction grating. The display device according to any one of Claims 1 to 5 is characterized by this.

8. The reflective layer is a plasmon resonance reflection film. The display device according to any one of Claims 1 to 5 is characterized by this.

Images