Reflection type liquid crystal display device

Abstract

To provide a reflection type liquid crystal display device that makes it possible to increase the efficiency of light utilization.SOLUTION: There is provided a reflection type liquid crystal display device comprising a reflection type liquid crystal panel, and an optical element located on the observer side of the reflection type liquid crystal panel and including a polarizing plate and a Pancharatnam-Berry phase diffraction grating. The optical element may include, for example, the polarizing plate, a λ / 4 plate, and the Pancharatnam-Berry phase diffraction grating, in order from the reflection type liquid crystal panel side toward the observer side. The Pancharatnam-Berry phase diffraction grating may include a phase difference layer having a phase difference Δnd that satisfies following formulae (1) and (2) below with respect to wavelengths λ of 450 nm, 550 nm, and 650 nm.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] The following disclosure relates to a reflective liquid crystal display device.

Background Art

[0002] As a technology related to a reflective liquid crystal display device, Patent Document 1 discloses a reflector including a substrate, a relief layer formed with repeated undulations disposed thereon, and a light reflecting layer covering the relief layer, wherein the relief layer forms the undulations by arranging convex portions or concave portions in a predetermined direction, each convex portion or concave portion has an arcuate pattern of an arc shape or an elliptical arc shape, and a center line bisecting the opening angle of each arcuate pattern is set to face the predetermined direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a reflective liquid crystal display device capable of enhancing light utilization efficiency.

Means for Solving the Problems

[0005] (1) One embodiment of the present invention is a reflective liquid crystal display device including a reflective liquid crystal panel, and an optical element disposed on the observer side of the reflective liquid crystal panel and including a polarizing plate and a puncharatnam berry phase diffraction grating.

[0006] (2) Further, in an embodiment of the present invention, in addition to the configuration of (1) above, the optical element includes, in order from the reflective liquid crystal panel side toward the observer side, the polarizing plate, a λ / 4 plate, and the puncharatnam berry phase diffraction grating.

[0007] (3) Further, in a certain embodiment of the present invention, in addition to the configuration of (2) above, the polarizing plate is a linear polarizing plate or a circular polarizing plate, and the reflective liquid crystal display device.

[0008] (4) Further, in a certain embodiment of the present invention, in addition to the configuration of (1) above, the optical element includes a λ / 4 plate, the puncharatnam berry phase diffraction grating, and a circular polarizing plate as the polarizing plate in order from the reflective liquid crystal panel side toward the observer side, and the reflective liquid crystal display device.

[0009] (5) Further, in a certain embodiment of the present invention, in addition to the configuration of (1) above, the optical element includes the puncharatnam berry phase diffraction grating and a circular polarizing plate as the polarizing plate in order from the reflective liquid crystal panel side toward the observer side, and does not include a λ / 4 plate between the reflective liquid crystal panel and the puncharatnam berry phase diffraction grating, and the reflective liquid crystal display device.

[0010] (6) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), or (5) above, the puncharatnam berry phase diffraction grating includes a retardation layer containing a cured product of a polymerizable liquid crystal, and the slow axis of the polymerizable liquid crystal rotates periodically in the x-axis direction from one end to the other end of the retardation layer within the plane of the retardation layer and does not rotate periodically in the y-axis direction orthogonal to the x-axis direction, and the x-axis direction corresponds to the left-right direction of the reflective liquid crystal panel, and the reflective liquid crystal display device.

[0011] (7) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), or (6) above, the puncharatnam berry phase diffraction grating includes a retardation layer having a retardation Δnd that satisfies the following (Formula 1) or (Formula 2) for wavelengths λ of 450 nm, 550 nm, and 650 nm, and the reflective liquid crystal display device.

[0012]

Equation

[0013]

Number

[0014] (8) Further, in a certain embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), or (7) above, the puncharatnam berry phase diffraction grating includes a retardation layer containing a cured product of a polymerizable liquid crystal, and the slow axis of the polymerizable liquid crystal rotates periodically in the in-plane direction of the retardation layer in the x-axis direction from one end to the other end of the retardation layer. The molecular alignment pattern Φ(x) [°] of the alignment direction of the polymerizable liquid crystal arranged at a position separated by a distance x [μm] from the position where the slow axis of the polymerizable liquid crystal is parallel to the x-axis direction in the x-axis direction satisfies the following (Equation 3): a reflective liquid crystal display device.

[0015]

Number

[0016] (9) Further, in a certain embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), (7), or (8) above, a reflective liquid crystal display device further includes a diffusion layer on the observer side of the optical element or between the members constituting the optical element.

[0017] (10) Further, in a certain embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), (7), (8), or (9) above, a reflective liquid crystal display device further includes a refractive element on the observer side of the optical element.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a reflective liquid crystal display device capable of enhancing light utilization efficiency.

Brief Description of the Drawings

[0019]

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Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the content described in the following embodiments, and design changes can be appropriately made within the scope that satisfies the configuration of the present invention. In the following description, the same reference numerals are commonly used for the same parts or parts having the same functions among different drawings as appropriate, and the repeated description thereof will be omitted as appropriate. Each aspect of the present invention may be appropriately combined within the scope not departing from the gist of the present invention.

[0021] (Definition of Terms) Refractive Index (nx, ny, nz) "nx" is the refractive index in the direction where the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane, and "nz" is the refractive index in the thickness direction. Unless otherwise specified, the refractive index refers to the value for light at 23°C and a wavelength of 550 nm.

[0022] In-Plane Phase Difference (Re) The in-plane phase difference (Re) refers to the in-plane phase difference of the layer (film) at 23°C and a wavelength of 550 nm unless otherwise specified. Re is obtained by Re = (nx - ny) × d, where d (nm) is the thickness of the layer (film). In this specification, unless otherwise specified, "phase difference" refers to the in-plane phase difference.

[0023] Note that the measurement wavelength of optical parameters such as the principal refractive index and phase difference in this specification is 550 nm unless otherwise specified.

[0024] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the content described in the following embodiments, and design changes can be appropriately made within the scope that satisfies the configuration of the present invention.

[0025] (Embodiment 1) FIG. 1A is a schematic cross-sectional view of a reflective liquid crystal display device according to Embodiment 1. FIGS. 1B and 1C are schematic cross-sectional views showing an example of a polarizing plate included in the reflective liquid crystal display device according to Embodiment 1. As shown in FIG. 1A, the reflective liquid crystal display device 1 of the present embodiment includes a reflective liquid crystal panel 10 and an optical element 20 disposed on the observer 1U side of the reflective liquid crystal panel 10 and including a polarizing plate 21P and a Pancharatnam-Berry Phase (PBP) diffraction grating 23.

[0026] A reflective liquid crystal display (RLCD) is a display that uses external light as a light source. In a general reflective liquid crystal display device, for example, the directivity of light can be controlled in the visual direction while suppressing the occurrence of rainbow due to interference by using an electrode having a micro reflective structure (MRS) (hereinafter also referred to as an MRS electrode).

[0027] FIG. 2 is a schematic diagram for explaining the case where a general reflective liquid crystal display device is used for mobile applications. FIG. 3 is a schematic diagram for explaining the case where a general reflective liquid crystal display device is used as a wall-mounted display or the like. FIG. 4 is a schematic cross-sectional view for explaining the case where a general reflective liquid crystal display device including a diffusion layer is used as a wall-mounted display or the like.

[0028] As shown in FIG. 2, for mobile applications, since the reflective liquid crystal display device 1R including the reflective liquid crystal panel 10R and the circular polarizing plate 21R is held by hand and used in a state where the reflective liquid crystal display device 1R is tilted obliquely, it is easy to control the direction of the emitted light also in the direction of the eyes.

[0029] However, when the reflective liquid crystal display device is used as a wall-mounted unit, or when the panel is facing the driver or passengers in a vehicle, as shown in FIG. 3, with respect to the normal direction of the display surface of the reflective liquid crystal display device 1R (i.e., the front direction of the reflective liquid crystal display device 1R), incident light enters the reflective liquid crystal display device 1R from the upper oblique 45° direction, and the emitted light exits in the vicinity of the lower oblique 45° direction of the reflective liquid crystal display device. Therefore, in the front direction of the reflective liquid crystal display device 1R, which is the position direction (visual recognition direction) of the viewer's (observer 1U) eyes, the light from the reflective liquid crystal display device 1R becomes weak.

[0030] This is due to the fact that when the holding method of the reflective liquid crystal display device is different under the same external light conditions, a difference occurs in the angle (incident angle) of the incident light with respect to the display surface of the reflective liquid crystal display device, and the direction of the emitted light changes significantly. Since there are limitations on the direction of the emitted light that can be controlled using the MRS electrodes, there may be cases where the emitted light cannot be controlled in the position direction of the viewer's eyes.

[0031] For this reason, usually, as shown in FIG. 4, a diffusion layer 30R is used to enable the observer 1U to visually recognize the emitted light from the reflective liquid crystal display device 1R. However, there are limitations to the light scattering by the diffusion layer 30R, and there are problems with light utilization efficiency.

[0032] To solve this problem, in this embodiment, a PBP diffraction grating 23 is used. As shown in FIG. 1A, the reflective liquid crystal display device 1 of this embodiment has a PBP diffraction grating 23 on the observer 1U side of the reflective liquid crystal panel 10, and includes an optical element 20 for controlling the directivity of light. Thus, even for incident light having an incident angle such that the direction of the emitted light does not face the front direction when the optical element 20 is not provided, the direction of the emitted light can be controlled to face the front direction. Thereby, the utilization efficiency of external light can be increased.

[0033] The reflective liquid crystal display device of Patent Document 1 has a reflector with a rugged structure and can specularly reflect light incident obliquely to the front. However, there is still room for improvement in enhancing the light utilization efficiency. Further, in the reflective liquid crystal display device of Patent Document 1, since the liquid crystal is aligned on the rugged structure, there is a possibility that the liquid crystal alignment may be disturbed. Therefore, there are limitations to the rugged structure in order to maintain the liquid crystal alignment.

[0034] On the other hand, as described above, the reflective liquid crystal display device 1 of the present embodiment can diffract light with the PBP diffraction grating 23 and bend obliquely incident light to the front. Thus, in the reflective liquid crystal display device 1 of the present embodiment, a rugged structure is not essential, and the problem of liquid crystal alignment disturbance as in Patent Document 1 does not occur. Hereinafter, the reflective liquid crystal display device 1 of the present embodiment will be described in detail.

[0035] As shown in FIG. 1A, the optical element 20 of the present embodiment includes a polarizing plate 21P and a PBP diffraction grating 23. The optical element 20 may include a polarizing plate 21P, a λ / 4 plate 22, and a PBP diffraction grating 23 in this order from the side of the reflective liquid crystal panel 10 toward the observer 1U side. It may include a λ / 4 plate 22, a PBP diffraction grating 23, and a circular polarizing plate 21 as the polarizing plate 21P. It may include a PBP diffraction grating 23 and a circular polarizing plate 21 as the polarizing plate 21P, and may not include the λ / 4 plate 22 between the reflective liquid crystal panel 10 and the PBP diffraction grating 23. By providing such an optical element 20, the specular reflection component of obliquely incident light is observed by the observer 1U standing in front of the reflective liquid crystal display device 1, so that the light utilization efficiency can be increased compared to the case of using a diffusive structure (MRS electrode). Further, the disturbance of the liquid crystal alignment can be suppressed.

[0036] In the present embodiment, a mode in which the optical element 20 includes a polarizing plate 21P, a λ / 4 plate 22, and a PBP diffraction grating 23 in this order from the side of the reflective liquid crystal panel 10 toward the observer 1U side will be described as an example.

[0037] When the optical element 20 includes a polarizing plate 21P, a λ / 4 plate 22, and a PBP diffraction grating 23 in order from the side of the reflective liquid crystal panel 10 toward the observer 1U side, the polarizing plate 21P is the circular polarizing plate 21 shown in FIG. 1B or the linear polarizing plate 21A shown in FIG. 1C. The circular polarizing plate 21 is composed of a linear polarizing plate 21A and a λ / 4 plate 21B as shown in FIG. 1B. In the present embodiment, the case where the polarizing plate 21P is the circular polarizing plate 21 shown in FIG. 1B will be described as an example, but when the polarizing plate 21P is the linear polarizing plate 21A, the same effect as when the polarizing plate 21P is the circular polarizing plate 21 can be obtained.

[0038] FIG. 5 is a schematic cross-sectional view of the reflective liquid crystal panel included in the reflective liquid crystal display device of Embodiment 1. As shown in FIG. 5, the reflective liquid crystal panel 10 includes a first substrate 100, a liquid crystal layer 300, and a second substrate 200 in order from the back side toward the observer 1U side. The first substrate 100 is a TFT substrate including thin film transistors (TFTs). The second substrate 200 is a color filter substrate including a color filter layer 220.

[0039] The first substrate 100 includes a support substrate 110, a reflective layer 120, an insulating film 130, and a pixel electrode 140 in order from the back side toward the observer 1U side. The second substrate 200 includes a support substrate 210, a color filter layer 220, and a common electrode 230 in order from the observer 1U side toward the back side. The liquid crystal layer 300 includes liquid crystal molecules 310. In the reflective liquid crystal display device 1, incident light from the observer 1U side is reflected by the reflective layer 120, and the reflected light passes through the liquid crystal layer 300 to perform display.

[0040] Between the first substrate 100 and the liquid crystal layer 300, and between the second substrate 200 and the liquid crystal layer 300, a first alignment film 100A and a second alignment film 200A having a function of controlling the alignment of the liquid crystal molecules 310 contained in the liquid crystal layer 300 may be disposed, respectively. The first alignment film 100A and the second alignment film 200A each have a function of aligning the liquid crystal molecules 310 in the liquid crystal layer 300 substantially perpendicular to the main surfaces of the first substrate 100 and the second substrate 200 when no voltage is applied to the liquid crystal layer 300 (when the applied voltage to the liquid crystal layer 300 is less than the threshold voltage).

[0041] Here, when the liquid crystal molecules are aligned substantially perpendicular to the main surface of the substrate, it means that the pretilt angle of the liquid crystal molecules is 85° or more and 90° or less with respect to the main surface of the substrate, preferably 88° or more and 90° or less, more preferably 89° or more and 90° or less. The pretilt angle of the liquid crystal molecules means the angle at which the long axis of the liquid crystal molecules is inclined with respect to the main surface of each substrate when no voltage is applied to the liquid crystal layer.

[0042] The reflective liquid crystal display device 1 has a circular polarizing plate 21. By adopting such an aspect, the following effects can be realized. The external light incident on the reflective liquid crystal panel 10 after passing through the circular polarizing plate 21 has a phase shift of 1 / 4 wavelength in the linearly polarized light and becomes, for example, right-handed polarized light. Since the initial alignment of the liquid crystal molecules 310 (the alignment direction of the liquid crystal molecules 310 in a state where no voltage is applied between the pixel electrode 140 and the common electrode 230) is vertical alignment, the external light passes through the liquid crystal layer 300 as it is and is reflected by the reflective layer 120, so that the polarization is reversed from right-handed circular polarization to left-handed circular polarization. Therefore, the external light that has traveled in the reverse direction of the incident direction and returned to the circular polarizing plate 21 becomes linearly polarized light at an angle perpendicular to the transmission axis of the linear polarizing plate and cannot pass through the circular polarizing plate 21, and black display can be realized.

[0043] When a voltage is applied between the pixel electrode 140 and the common electrode 230 and the liquid crystal molecules 310 rotate, the situation is as follows. That is, the external light that passes through the circular polarizing plate 21 and enters the reflective liquid crystal panel 10 has a phase shift of 1 / 4 wavelength in the linear polarization, for example, right-handed polarization. Since the external light further has a phase shift of 1 / 4 wavelength in the liquid crystal layer 300, when it reaches the reflective layer 120, it has a phase difference of 1 / 2 wavelength and is reflected as linear polarization. After reflection, since the external light travels the reverse path as when it enters, it can pass through the circular polarizing plate 21 to achieve white display.

[0044] The λ / 4 plate 22 is a retardation layer that imparts an in-plane retardation of 107.5 nm to 167.5 nm with respect to light having a wavelength of 550 nm. Here, the retardation layer is a layer that has a function of changing the state of incident polarization by imparting a phase difference to two orthogonal polarization components using a birefringent material or the like.

[0045] Examples of the material of the λ / 4 plate 22 include a photopolymerizable liquid crystal material. Examples of the structure of the photopolymerizable liquid crystal material include a structure having a photopolymerizable group such as an acrylate group or a methacrylate group at the end of the skeleton of the liquid crystal molecule.

[0046] The λ / 4 plate 22 can be formed, for example, by the following method. First, a photopolymerizable liquid crystal material is dissolved in an organic solvent such as propylene glycol monomethyl ether acetate (PGMEA). Next, the obtained solution is applied onto the surface of a substrate (for example, a polyethylene terephthalate (PET) film) to form a coating film of the solution. Then, the coating film of this solution is subjected to pre-baking, light irradiation (for example, ultraviolet irradiation), and final baking in this order, whereby the λ / 4 plate 22 is formed.

[0047] As the λ / 4 plate 22, for example, a stretched polymer film can also be used. Examples of the material of the polymer film include cycloolefin polymer, polycarbonate, polysulfone, polyethersulfone, polyethylene terephthalate, polyethylene, polyvinyl alcohol, norbornene, triacetyl cellulose, diacetyl cellulose, etc.

[0048] FIG. 6 is a diagram showing the molecular orientation of the polymerizable liquid crystal on a polarized light microscopic observation photograph of the PBP diffraction grating included in the reflective liquid crystal display device of Embodiment 1. FIG. 7 is a schematic cross-sectional view of the PBP diffraction grating included in the reflective liquid crystal display device of Embodiment 1. FIG. 8 is a schematic diagram for explaining the polarization dependence of the PBP diffraction grating included in the reflective liquid crystal display device of Embodiment 1.

[0049] As shown in FIGS. 6 and 7, the PBP diffraction grating 23 of the present embodiment sequentially includes a support substrate 23A, an alignment film 23B (for example, an optical alignment film), and a retardation layer 23C containing a cured polymerizable liquid crystal (RM: Reactive methogen) 23LC.

[0050] The PBP diffraction grating 23 has a structure in which the slow axes of the cured polymerizable liquid crystal 23LC rotate periodically in the plane. As shown in FIG. 8, the PBP diffraction grating 23 having a diffraction angle θ [°] diffracts the right circularly polarized light RCP incident from the normal direction of the main plane of the PBP diffraction grating 23 in the direction of +θ [°] with respect to the normal direction, and diffracts the left circularly polarized light LCP in the -θ direction. That is, it is a polarization-dependent diffraction element in which the diffraction direction is reversed according to the polarization. The PBP diffraction grating 23 is also referred to as a PBP diffraction element or a PB diffraction grating.

[0051] In this specification, when the reflective liquid crystal display device is viewed from the normal direction of the display surface of the reflective liquid crystal display device, the normal direction is set to 0°, the upper side with respect to the normal direction is a positive angle, and the lower side is a negative angle.

[0052] The diffraction efficiency η of the PBP diffraction grating 23 is expressed as η = sin 2 (Δndπ / λ), and the efficiency becomes 100% when the retardation Δnd = λ / 2. Therefore, usually, the retardation layer 23C is designed so that Δnd = λ / 2. Since the PBP diffraction grating 23 functions as a λ / 2 plate, the incident circularly polarized light is converted into reverse circularly polarized light and emitted.

[0053] The principle of improving the light utilization efficiency by the reflective liquid crystal display device 1 of the present embodiment will be described. As shown in Fig. 1A, when the incident angle θin [°] of the incident light on the PBP diffraction grating 23 is twice the diffraction angle θ [°] of the PBP diffraction grating 23, among the left circularly polarized light LCP and the right circularly polarized light RCP contained in the incident light, the left circularly polarized light LCP is diffracted by the PBP diffraction grating 23 by -θin / 2 [°] (that is, -θ [°]) and becomes the right circularly polarized light RCP. The light converted into linearly polarized light LP by the λ / 4 plate 22 passes through the circular polarizing plate 21. When a voltage is applied between the pixel electrode 140 and the common electrode 230, the light specularly reflected by the reflective liquid crystal panel 10 passes through the circular polarizing plate 21 as linearly polarized light LP and is converted into right circularly polarized light RCP by the λ / 4 plate 22. The right circularly polarized light RCP is diffracted by the PBP diffraction grating 23 by θin / 2 (that is, θ [°]), and the light emitted in the front direction of the reflective liquid crystal display device 1 is visually recognized by the observer 1U. Thus, in the reflective liquid crystal display device 1 of the present embodiment, since the specular reflection component of light is used, the light utilization efficiency can be improved as compared with the case of using a diffusion structure as in the above Patent Document 1.

[0054] In this way, the PBP diffraction grating 23 has the characteristic that when circularly polarized light is incident, circularly polarized light of opposite phase is emitted. In a display device using polarization such as a liquid crystal display device, by using the PBP diffraction grating 23, light can be diffracted without reducing the light utilization efficiency.

[0055] The incident angle of the incident light on the reflective liquid crystal display device 1 is preferably 1.5 times or more and 2.5 times or less the diffraction angle θ of the PBP diffraction grating 23. By adopting such a mode, the light utilization efficiency can be further improved. The incident angle of the incident light on the reflective liquid crystal display device 1 is more preferably 1.8 times or more and 2.2 times or less the diffraction angle θ of the PBP diffraction grating 23, and even more preferably 2 times. In this specification, the incident angle is the angle of the incident light with respect to the normal direction (front direction) of the display surface of the reflective liquid crystal display device, and the exit angle is the angle of the emitted light with respect to the normal direction of the display surface of the reflective liquid crystal display device.

[0056] Also, it is preferable that the incident angle of the incident light to the reflective liquid crystal display device 1 is 0.5 times or more and 1.5 times or less of the diffraction angle θ of the PBP diffraction grating 23. By adopting such an embodiment, the light utilization efficiency can be further improved. It is more preferable that the incident angle of the incident light to the reflective liquid crystal display device 1 is 0.8 times or more and 1.2 times or less of the diffraction angle θ of the PBP diffraction grating 23, and it is even more preferable that it is 1 time.

[0057] FIG. 9 is a schematic plan view of the PBP diffraction grating included in the reflective liquid crystal display device of Embodiment 1. As shown in FIG. 9, the PBP diffraction grating 23 is an optical film having a retardation layer 23C obtained by ultraviolet-curing a polymerizable liquid crystal called polymerizable liquid crystal 23LC.

[0058] The PBP diffraction grating 23 has a support substrate 23A and a retardation layer 23C provided on the support substrate 23A and containing the cured polymerizable liquid crystal 23LC. An alignment film 23B may be disposed between the support substrate 23A and the retardation layer 23C. In the PBP diffraction grating 23, diffraction occurs when the cured polymerizable liquid crystal 23LC is periodically aligned in the plane of the retardation layer 23C, and the PBP diffraction grating 23 can exhibit a lens function. The PBP diffraction grating 23 can control the diffraction angle by changing the pitch of the polymerizable liquid crystal 23LC.

[0059] As shown in FIG. 9, the slow axis (optical axis) of the polymerizable liquid crystal 23LC rotates periodically in the x-axis direction from one end to the other end of the retardation layer 23C within the plane of the retardation layer 23C, and does not rotate periodically in the y-axis direction orthogonal to the x-axis direction. The x-axis direction corresponds to the left-right direction (horizontal direction) of the reflective liquid crystal panel 10.

[0060] As shown in FIG. 9, in plan view, the slow axis of the cured polymeric liquid crystal 23LC rotates periodically within the plane of the retardation layer 23C. More specifically, in plan view, the direction of the slow axis of the cured polymeric liquid crystal 23LC changes while rotating in the x-axis direction from one end to the other end of the retardation layer 23C. That is, the retardation layer 23C provided in the PBP diffraction grating 23 has a liquid crystal alignment pattern in which the direction of the optical axis derived from the cured polymeric liquid crystal 23LC changes while continuously rotating along the x-axis direction in the plane. In plan view, the slow axis of the polymeric liquid crystal 23LC of the present embodiment rotates periodically in the x-axis direction, but does not rotate periodically in the y-axis direction orthogonal to the x-axis. Here, the major axis of the cured polymeric liquid crystal 23LC is the slow axis. The direction of the slow axis can be confirmed using a polarized light microscope or Axoscan (Axo Metrics).

[0061] The PBP diffraction grating 23 can be manufactured, for example, by the methods described in International Publication No. 2019 / 189818, Japanese Patent Application Laid-Open No. 2008-532085, and the like.

[0062] The PBP diffraction grating 23 preferably includes a retardation layer 23C having a retardation Δnd that satisfies the following formula (1) or (2) for wavelengths λ of 450 nm, 550 nm, and 650 nm. By adopting such an aspect, the light utilization efficiency can be further improved.

[0063]

Equation

[0064]

Equation

[0065] The retardation Δnd can be measured using "Axo Scan FAA-3series" manufactured by Axo Metrics.

[0066] (Embodiment 2) In this embodiment, the features specific to this embodiment will be mainly described, and the description of the content overlapping with the above Embodiment 1 will be omitted. This embodiment is substantially the same as Embodiment 1 except that the arrangement of the members included in the optical element 20 is different.

[0067] FIG. 10 is a schematic cross-sectional view showing a white display state of the reflective liquid crystal display device according to Embodiment 2. FIG. 11 is a schematic cross-sectional view showing a black display state of the reflective liquid crystal display device according to Embodiment 2. As shown in FIGS. 10 and 11, the optical element 20 of this embodiment includes a quarter-wave plate 22, a PBP diffraction grating 23, and a circular polarizing plate 21 as the polarizing plate 21P in order from the side of the reflective liquid crystal panel 10 toward the observer 1U side. By adopting such an aspect, the light utilization efficiency can be increased in the same manner as in Embodiment 1.

[0068] FIG. 10 assumes a white display, and the reflective liquid crystal panel 10 has the same function as a mirror. In the white display shown in FIG. 10, the specular reflection component enters the human eye in the same manner as in Embodiment 1. In the black display shown in FIG. 11, the reflective liquid crystal panel 10 has the function of a "quarter-wave plate + mirror". Therefore, the light incident on the reflective liquid crystal panel 10 is reflected by the reflective liquid crystal panel 10, passes through the quarter-wave plate 22, and becomes right-circularly polarized light RCP, resulting in a polarization state different from that in the case of white display. Therefore, the diffraction direction at the PBP diffraction grating 23 is opposite to that in the case of white display, and the emitted light does not enter the eyes of the observer 1U. This means that it becomes bright in white display and dark in black display, improving the contrast.

[0069] (Embodiment 3) In this embodiment, the features specific to this embodiment will be mainly described, and the description of the content overlapping with the above Embodiment 1 will be omitted. This embodiment is substantially the same as Embodiments 1 and 2 except that the arrangement of the members included in the optical element 20 is different.

[0070] FIG. 12 is a schematic cross-sectional view of a reflective liquid crystal display device according to Embodiment 3. As shown in FIG. 12, the optical element 20 of the present embodiment includes a PBP diffraction grating 23 and a circular polarizing plate 21 as a polarizing plate 21P in order from the side of the reflective liquid crystal panel 10 toward the observer 1U side, and does not include a λ / 4 plate between the reflective liquid crystal panel 10 and the PBP diffraction grating 23. By adopting such a mode, the light utilization efficiency can be increased as in Embodiment 1.

[0071] In the reflective liquid crystal display device 1 of the present embodiment, the λ / 4 plate 22 disposed between the PBP diffraction grating 23 and the reflective liquid crystal panel 10 in Embodiments 1 and 2 is unnecessary. The reflective liquid crystal panel 10 of the present embodiment functions as a "λ / 4 plate + mirror" during white display and as a mirror during black display.

[0072] In the following Modification Examples 1 to 3, three modes for suppressing color breakup of the reflective liquid crystal display device 1 of Embodiments 1 to 3 will be described.

[0073] (Modification Example 1 of Embodiments 1 to 3) As the first mode for suppressing color breakup, the PBP diffraction grating 23 included in the reflective liquid crystal display device 1 of this modification example includes a retardation layer 23C containing a cured product of a polymerizable liquid crystal 23LC. The slow axis of the polymerizable liquid crystal 23LC rotates periodically in the x-axis direction from one end to the other end of the retardation layer 23C within the plane of the retardation layer 23C. The molecular alignment pattern Φ(x) [°], which is the alignment direction of the polymerizable liquid crystal 23LC disposed at a position x [μm] away from the position where the slow axis of the polymerizable liquid crystal 23LC is parallel to the x-axis direction, preferably satisfies the following (Equation 3). By adopting such a mode, color breakup of the reflective liquid crystal display device 1 can be suppressed.

[0074] [Equation] (In the above (Equation 3), Λ represents the pitch [μm] at which the slow axis of the polymerizable liquid crystal rotates 180° within the plane of the retardation layer, and m, n, and A are arbitrary constants.)

[0075] In the above (Formula 3), the closer m and n are to 0, the greater the luminance improvement effect, but the higher the possibility of color breakage. The greater the absolute values of m and n, the smaller the luminance improvement effect, but color breakage can be improved.

[0076] In the above (Formula 3), A is, for example, 0.

[0077] Note that any position in the x-axis direction of the PBP diffraction grating 23 may be set as the position of x = 0 (the position where the molecular orientation is 0°).

[0078] The PBP diffraction grating 23 of this modification example can be manufactured, for example, as follows.

[0079] FIG. 13 is a schematic diagram showing a coating film forming process for an alignment film, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIG. 14 is a schematic diagram showing a first light irradiation process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIG. 15 is a schematic diagram showing a second light irradiation process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIG. 16 is a schematic diagram showing a third light irradiation process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIG. 17 is a schematic diagram showing a fourth light irradiation process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIG. 18 is a schematic diagram showing a firing process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIGS. 19 and 20 are schematic diagrams showing a polymerizable liquid crystal film forming process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. FIG. 21 is a schematic diagram showing a polymerizable liquid crystal curing process, which is included in a manufacturing method of a PBP diffraction grating provided in a reflective liquid crystal display device according to Modification Example 1 of Embodiments 1 to 3. The double-headed arrows shown in FIGS. 14 to 19 and FIG. 21 indicate the alignment regulating force direction.

[0080] The manufacturing method of the PBP diffraction grating 23 of this modification example includes an alignment film coating film forming process shown in FIG. 13, a first light irradiation process shown in FIG. 14, a second light irradiation process shown in FIG. 15, a third light irradiation process shown in FIG. 16, a fourth light irradiation process shown in FIG. 17, a firing process shown in FIG. 18, a polymerizable liquid crystal film forming process shown in FIGS. 19 and 20, and a polymerizable liquid crystal curing process shown in FIG. 21. Specific explanations are given below.

[0081] First, in the alignment film coating film forming process shown in FIG. 13, an alignment film material containing a photo-isomerizable polymer is coated on a support substrate 23A (for example, a glass substrate) to form an alignment film coating film 23B1. For example, the spin coating method can be used for coating the alignment film material, and the rotation speed can be set to, for example, 1000 rpm. The photo-isomerizable polymer is a polymer having a photo-isomerizable functional group. Examples of the photo-isomerizable functional group include an azobenzene group and the like.

[0082] Next, in the first light irradiation process shown in FIG. 14, a linearly polarized light (for example, ultraviolet light with a wavelength of 365 nm) having a polarization direction in the first direction (for example, the 0° direction) is irradiated through a binary mask 23D in which openings 23D1 (for example, width 2 μm) and closed portions 23D2 (for example, width 6 μm) are periodically arranged in the x-axis direction, for example, at 100 mJ / cm 2 by irradiation.

[0083] Next, in the second light irradiation process shown in FIG. 15, the binary mask 23D is shifted by 2 μm in the periodic direction (x-axis direction), and a linearly polarized light (for example, ultraviolet light with a wavelength of 365 nm) having a polarization direction in a second direction different from the first direction (for example, the 45° direction) is irradiated with the same energy as in the first light irradiation process.

[0084] Next, in the third light irradiation process shown in FIG. 16, the binary mask 23D is shifted by 2 μm in the periodic direction (x-axis direction), and a linearly polarized light (for example, ultraviolet light with a wavelength of 365 nm) having a polarization direction in a third direction different from the first and second directions (for example, the 90° direction) is irradiated with the same energy as in the first and second light irradiation processes.

[0085] Next, in the fourth light irradiation step shown in FIG. 17, the binary mask 23D is shifted by 2 μm in the periodic direction (x-axis direction), and linearly polarized light (for example, ultraviolet light with a wavelength of 365 nm) having a polarization direction in a fourth direction (for example, 135° direction) different from the first, second, and third directions is irradiated with the same energy as in the first, second, and third light irradiation steps.

[0086] Next, in the firing step shown in FIG. 18, for example, firing is performed at 160° C. for 20 minutes to form an alignment film 23B on the support substrate 23A.

[0087] Next, in the polymerizable liquid crystal film forming step shown in FIGS. 19 and 20, the polymerizable liquid crystal 23LC is applied onto the alignment film 23B. The polymerizable liquid crystal 23LC can be applied, for example, at a spin speed of 1000 rpm using a spin coating method so that the retardation Δnd of the retardation layer 23C becomes λ / 2.

[0088] Next, in the polymerizable liquid crystal curing step shown in FIG. 21, the polymerizable liquid crystal 23LC is irradiated with light to cure the polymerizable liquid crystal 23LC, and the retardation layer 23C is formed. The polymerizable liquid crystal 23LC can be cured, for example, by irradiation with ultraviolet light (wavelength 365 nm) of 200 mJ / cm 2 . In this way, the PBP diffraction grating 23 including the support substrate 23A, the alignment film 23B, and the retardation layer 23C in this order is obtained.

[0089] (Modification Example 2 of Embodiments 1 to 3) FIG. 22 is a schematic cross-sectional view of a reflective liquid crystal display device according to Modification 2 of Embodiments 1 to 3. As a second aspect of suppressing color breakup, the reflective liquid crystal display device 1 of this modification preferably further includes a diffusion layer 30 on the observer 1U side of the optical element 20 or between the members constituting the optical element 20, as shown in FIG. 22. By adopting such an aspect, the specular reflection component of the emitted light will have a certain spread, and by the overlapping of the red light R, green light G, and blue light B, it is possible to suppress color breakup due to the wavelength dependence of the diffraction angle. For example, the red light R is light with a wavelength of 650 nm, the green light G is light with a wavelength of 550 nm, and the blue light B is light with a wavelength of 450 nm.

[0090] The diffusion layer 30 has light-scattering properties. Examples of the diffusion layer 30 include an adhesive layer containing particles of several μm. For example, in FIG. 1A, when the reflective liquid crystal panel 10 and the circular polarizing plate 21 are bonded together using an adhesive layer containing particles of several μm, the adhesive layer can be used as the diffusion layer 30 disposed between the reflective liquid crystal panel 10 and the circular polarizing plate 21. Also, as shown in FIG. 22, when the λ / 4 plate 22 and the PBP diffraction grating 23 are bonded together using an adhesive layer containing particles of several μm, the adhesive layer can be used as the diffusion layer 30 disposed between the λ / 4 plate 22 and the PBP diffraction grating 23.

[0091] (Modification 3 of Embodiments 1 to 3) FIG. 23 is a schematic cross-sectional view for explaining the state of light in a reflective liquid crystal display device according to Modification 3 of Embodiments 1 to 3. FIG. 24 is a schematic diagram for explaining the difference between a diffractive element and a refractive element. FIG. 25 is a schematic cross-sectional view for explaining the state of light in the reflective liquid crystal display device of Embodiment 1. FIGS. 23 to 25 show the state of light when white light W is incident.

[0092] As a third aspect for suppressing color breakup, the reflective liquid crystal display device 1 of this modification preferably further includes a refractive element 40 on the observer 1U side of the optical element 20, as shown in FIG. 23. As shown in FIG. 24, the PBP diffraction grating 23, which is a diffraction type diffraction element (diffraction type element), bends longer wavelength light more, while the refractive element 40 has the characteristic of bending shorter wavelength light more. Therefore, as shown in FIG. 25, color breakup may occur in the reflective liquid crystal display device 1 of the first embodiment having the PBP diffraction grating 23 and not having the refractive element 40. However, as shown in FIG. 23, in the reflective liquid crystal display device 1 of this modification having both the PBP diffraction grating 23 and the refractive element 40, the light color-separated by the refractive element 40 overlaps again at the PBP diffraction grating 23, so that color breakup can be suppressed.

[0093] FIG. 26 is a perspective schematic view of a lenticular lens. The refractive element 40 is, for example, a lenticular lens. As shown in FIG. 26, the lenticular lens 41 includes a plurality of convex cylindrical lenses protruding toward the observer 1U on the surface on the observer 1U side. The refractive element 40 is, for example, arranged on the side closest to the observer 1U of the reflective liquid crystal display device 1.

[0094] Hereinafter, the effects of the present invention will be described by giving examples, comparative examples, and reference examples, but the present invention is not limited by these examples.

[0095] (Example 1) FIG. 27A is a cross-sectional schematic view of a demonstration device according to Example 1. In order to demonstrate the principle of the reflective liquid crystal display device 1 of the first embodiment, a demonstration device 1A of Example 1 shown in FIG. 27A was fabricated. The demonstration device 1A of Example 1 had the same configuration as the reflective liquid crystal display device 1 of the first embodiment, except that it included a mirror 10A instead of the reflective liquid crystal panel 10 and the circular polarizing plate 21. The mirror 10A has the same function as the optical member composed of the reflective liquid crystal panel 10 and the circular polarizing plate 21. Therefore, the principle of the reflective liquid crystal display device 1 of the first embodiment can be demonstrated using the demonstration device 1A.

[0096] In the proof-of-concept experiment of Example 1, a laser beam with a wavelength of 532 nm was used as the incident light, and it was measured whether diffraction as expected could be obtained when the reflective liquid crystal panel 10 and the circular polarizing plate 21 were replaced with the mirror 10A.

[0097] In the demonstration apparatus 1A of Example 1, as shown in FIG. 6, a PBP diffraction grating 23 with a distance (pitch Λ [μm]) of 4 μm in which the slow axis of the polymerizable liquid crystal 23LC rotates 180° in the plane was used. The diffraction angle θ by the PBP diffraction grating 23 is represented by θ = arcsin(λ / Λ). In this example, θ = 7.6°. As the λ / 4 plate 22, a retardation film containing a cycloolefin polymer (COP: Cyclo-olefin Polymer) was used.

[0098] The emission angle of the emitted light when the incident angle of the incident light was 15.2° was measured. Although it should have been emitted at 0° according to the theory, the experimental result was 0°. Thus, it was confirmed that the principle of the above Embodiment 1 was correct. The incident angle and the emission angle were measured as follows. As shown in FIG. 27B, the mirror 10A was arranged at the center of the board on a large-area rotating breadboard (Solarboard) such that the straight line connecting 0° and 180° of the memory of the board became the normal. The incident angle was determined by making the laser beam emitted from the light source 11 enter from the 15.2° direction so that the laser beam passed through 15.2° and 195.2° of the memory of the board. The emission angle was measured by reading the memory of the board at the position through which the reflected light passed. FIG. 27B is a schematic diagram showing a method of measuring the incident angle and the emission angle using a large-area rotating breadboard.

[0099] (Example 2 and Comparative Example) In this example and the comparative example, in the reflective liquid crystal display device 1 of the above Embodiment 1, regarding the retardation (that is, the retardation of the PBP diffraction grating 23) of the retardation layer 23C included in the PBP diffraction grating 23, the range in which the effect of improving the light utilization efficiency can be obtained was examined. As Example 2, the reflective liquid crystal display device 1 of the above Embodiment 1 was used. As the comparative example, a general reflective liquid crystal display device 1R provided with a diffusion layer 30R shown in FIG. 4 was used.

[0100] When using the reflective liquid crystal display device 1R of the comparative example, if the light reflected by the reflective liquid crystal panel 10R is scattered equally in all azimuthal angles, the light intensity per unit solid angle is, as shown in the following (Equation A), (incident light intensity) × (1 / 4π). If a light intensity stronger than this value can be realized, it is considered that there is an effect of improving the light utilization efficiency.

[0101]

Number

[0102] FIG. 28 is a diagram for explaining the generation of the zero-order light. FIG. 29 is a cross-sectional schematic diagram for explaining the state of light in the reflective liquid crystal display device according to Example 2. When the phase difference Δnd of the PBP diffraction grating 23 is not λ / 2, as shown in FIG. 28, in addition to the diffracted first-order light, non-diffracted zero-order light is generated. The ratio of this light intensity, that is, (first-order light intensity):(zero-order light intensity) = sin 2 (Δndπ / λ) : cos 2 (Δndπ / λ). Also, the directions of circular polarization of the first-order light and the zero-order light are opposite. For example, when the incident light is left circular polarization LCP, the first-order light is right circular polarization RCP and the zero-order light is left circular polarization LCP.

[0103] In the reflective liquid crystal display device 1 of this example, when zero-order light is generated, the light intensity of the emitted light is as shown in FIG. 29. Here, the incident light is left circular polarization LCP and the light intensity is 1. When the incident light passes through the PBP diffraction grating 23, it splits into zero-order light (left circular polarization LCP) and first-order light (right circular polarization RCP). At this time, the first-order light intensity is sin 2 (Δndπ / λ). When passing through the λ / 4 plate 22, both the zero-order light and the first-order light become linearly polarized light LP, but the vibration planes are orthogonal. Therefore, if the circular polarizer 21 is designed so that the first-order light (right circular polarization RCP) passes through, the zero-order light is absorbed. Thus, only the first-order light is reflected by the reflective liquid crystal panel 10, exits from the circular polarizer 21, and returns to circular polarization by the λ / 4 plate 22. At this time, the polarization state is right circular polarization RCP. When this light passes through the PBP diffraction grating 23 again, it splits into zero-order light (right circular polarization RCP) and first-order light (left circular polarization LCP).

[0104] In FIG. 29, it was described that the first-order light (left circularly polarized light LCP) enters the eye, but the zero-order light may also enter the eye. For example, a case where it is set such that "(diffraction angle of PBP diffraction grating) = (incident angle of incident light)" can be considered. Therefore, either the zero-order light intensity or the first-order light intensity may exceed 1 / 4π of the light intensity per unit solid angle of the reflective liquid crystal display device 1R of the comparative example. That is, it can be understood that the phase difference Δnd of the phase difference layer 23C of the PBP diffraction grating 23 only needs to satisfy the above (Equation 1) or (Equation 2) for wavelengths of 450 nm, 550 nm, and 650 nm.

[0105] (Example 3 and Reference Example) In Example 3 and the reference example, a configuration for further improving the light utilization efficiency was examined. FIG. 30 is a schematic diagram for explaining the diffraction angle θ of the PBP diffraction grating and the light intensity distribution U(θ) on the screen. FIG. 31 is a graph showing the molecular orientation pattern Φ(x) of the PBP diffraction grating of the reference example. FIG. 32 is a graph showing the light intensity distribution U(θ) of the PBP diffraction grating of the reference example. The molecular orientation pattern Φ(x) is also referred to as the molecular orientation Φ(x). FIG. 33 is a graph showing the molecular orientation pattern Φ(x) of the PBP diffraction grating of Example 3. FIG. 34 is a graph showing the light intensity distribution U(θ) of the PBP diffraction grating of Example 3. The molecular orientation pattern Φ(x) is also referred to as the molecular orientation Φ(x). FIG. 35 is a schematic diagram for explaining the state of light in the PBP diffraction gratings of Example 3 and the reference example.

[0106] The diffraction angle of the PBP diffraction grating depends on the wavelength. For example, Fraunhofer diffraction can be used for the calculation of the diffraction angle. In plan view, assuming that the molecular orientation of the polymerizable liquid crystal arranged at a position x [μm] away from the position where the slow axis of the polymerizable liquid crystal 23LC is parallel to the x-axis direction is Φ(x) [°], as shown in FIG. 30, when light is incident from the PBP diffraction grating 23 with a diffraction angle of θ [°] onto the screen 50, the light intensity distribution U(θ) on the screen 50 is given by the following (Equation 4).

[0107] [Number]

[0108] θ represents the diffraction angle of the PBP diffraction grating, λ represents the wavelength of light, and k represents a proportionality constant. In this embodiment and the reference example, the value of k is determined such that the integral of U(θ) in the range of θ = -π to π is 100%. U(θ) at this time is also called the diffraction efficiency.

[0109] As shown in FIG. 31, for the PBP diffraction grating of the reference example having a molecular orientation pattern of "Φ(x) = x × 180° / 4 μm", the light intensity distribution U(θ) when the wavelength of the incident light is 450 nm, 550 nm, and 650 nm was calculated. This means that the case where the pitch is 4 μm is being calculated.

[0110] The results are shown in FIG. 32. For example, when the wavelength of the incident light is 550 nm, U(θ) was 100% at θ = 8°. This indicates that all the incident light bends in the direction of θ = 8°, which can be easily confirmed by experiments. The problem of the reference example was that the diffraction angles of red light R, green light G, and blue light B were different from each other. This causes problems such as color breakup and degrades the display quality.

[0111] Therefore, in this embodiment, U(θ) was calculated with the molecular orientation as "Φ(x) = kx + m × sin(nx + A)". Specifically, the above (Equation 3) where k = 180° / Λ in "Φ(x) = kx + m × sin(nx + A)" was used. More specifically, as shown in FIG. 33, U(θ) was calculated with Λ = 4 μm (i.e., k = 180° / 4 μm), n = 2π / 800 μm, and A = 0. This is a calculation used in the concept of FM modulation, and it is known that multiple peaks appear. Actually, looking at the calculation results in FIG. 34, the peaks of each wavelength are split and overlapping. As a result, as shown in FIG. 35, it was found that the PBP diffraction grating of Example 3 that satisfies the above (Equation 3) can solve the problem of color breakup better than the PBP diffraction grating 23 of the reference example. Note that since the second term on the right side of the above (Equation 3) is very small, FIGS. 31 and 33 appear similar, but they are different graphs.

[0112] (Example 4) The reflective liquid crystal display device 1 of this embodiment corresponds to the reflective liquid crystal display device 1 of Modification 2 of Embodiments 1 to 3 and has the configuration shown in FIG. 22. The reflective liquid crystal display device 1 of this embodiment can suppress color breakup in the same manner as in the above-described Embodiment 3. In the reflective liquid crystal display device 1 of Embodiment 3, color breakup due to the wavelength dependence of the diffraction angle is suppressed by the PBP diffraction grating 23 having the molecular alignment pattern Φ(x) that satisfies the above (Equation 3). However, in the reflective liquid crystal display device 1 of this embodiment, color breakup due to the wavelength dependence of the diffraction angle can be suppressed by using the diffusion layer 30.

[0113] As shown in FIG. 22, the reflective liquid crystal display device 1 of this embodiment includes a diffusion layer 30 between the PBP diffraction grating 23 and the λ / 4 plate 22. By adopting such an aspect, the specular reflection component of the emitted light has a certain spread, and color breakup can be suppressed by the overlapping of RGB lights.

[0114] (Embodiment 5) The reflective liquid crystal display device 1 of this embodiment corresponds to the reflective liquid crystal display device 1 of Modification 3 of Embodiments 1 to 3 and has the configuration shown in FIG. 23. The reflective liquid crystal display device 1 of this embodiment can suppress color breakup in the same manner as in the above-described Embodiments 3 and 4. In this embodiment, instead of adjusting the molecular alignment pattern of the PBP diffraction grating 23 as in Embodiment 3 or providing the diffusion layer 30 as in Embodiment 4, a refractive element 40 (for example, a lenticular lens) is used. As shown in FIG. 25, color breakup may occur in the reflective liquid crystal display device 1 including only the PBP diffraction grating 23 without the refractive element 40. However, in the reflective liquid crystal display device 1 of this embodiment, as shown in FIG. 23, by combining the refractive element 40 and the PBP diffraction grating 23, the light separated by color by the refractive element 40 overlaps again at the PBP diffraction grating 23, and color breakup can be suppressed.

[0115] (Embodiment 6) The reflective liquid crystal display device 1 of this embodiment corresponds to the reflective liquid crystal display device 1 of the above-described Embodiment 2. Also in the reflective liquid crystal display device 1 of this embodiment, the light utilization efficiency can be improved. Further, the contrast can be enhanced.

[0116] (Example 7) The reflective liquid crystal display device 1 of this example corresponds to the reflective liquid crystal display device 1 of the above-described Embodiment 3. Also in the reflective liquid crystal display device 1 of this example, the light utilization efficiency can be improved.

[0117] As described above, the embodiments of the present disclosure and their modifications have been described. However, the present disclosure is not limited to the above-described embodiments and their modifications, and can be implemented in various aspects and their modifications without departing from the gist thereof. Further, the plurality of components disclosed in the above-described embodiments and their modifications can be appropriately modified. For example, a certain component among all the components shown in a certain embodiment or modification may be added to the components of another embodiment or modification, or some of the components among all the components shown in a certain embodiment or modification may be deleted from the embodiment or modification.

[0118] Also, for the purpose of facilitating understanding of the invention, the drawings schematically show each component mainly. The thickness, length, number, interval, etc. of each component shown in the drawings may be different from the actual ones for convenience in drawing preparation. Also, the configuration of each component shown in the above-described embodiment is an example and is not particularly limited. Needless to say, various changes can be made without substantially departing from the effects of the present disclosure.

Explanation of Reference Numerals

[0119] 1, 1R: Reflective liquid crystal display device 1A: Demonstration device 1U: Observer 10, 10R: Reflective liquid crystal panel 10A: Mirror 11: Light source 20: Optical element 21, 21R: Circular polarizing plate 21A: Linear polarizing plate 21B, 22: λ / 4 plate 21P: Polarizing plate 23: Pancharatnam Berry phase (PBP) diffraction grating 23A: Support substrate 23B: Alignment film 23B1: Coating film for alignment film 23C: Retardation layer 23D: Binary mask 23D1: Opening 23D2: Closed portion 23LC: Polymerizable liquid crystal 30, 30R: Diffusion layer 40: Refractive element 41: Lenticular lens 50: Screen 100: First substrate 110, 210: Support substrate 120: Reflective layer 130: Insulating film 140: Pixel electrode 100A: First alignment film 200: Second substrate 200A: Second alignment film 220: Color filter layer 230: Common electrode 300: Liquid crystal layer 310: Liquid crystal molecules B: Blue light G: Green light LCP: Left circular polarization LP: Linear polarization R: Red light RCP: Right circular polarization W: White light

Claims

1. A reflective liquid crystal panel, and an optical element disposed on the observer side of the reflective liquid crystal panel and including a polarizing plate and a Pancharatnam-Berry phase diffraction grating.

2. The optical element includes, in order from the reflective liquid crystal panel side toward the observer side, the polarizing plate, a λ / 4 plate, and the Pancharatnam-Berry phase diffraction grating. The reflective liquid crystal display device according to claim 1.

3. The polarizing plate is a linear polarizing plate or a circular polarizing plate. The reflective liquid crystal display device according to claim 2.

4. The optical element includes, in order from the reflective liquid crystal panel side toward the observer side, a λ / 4 plate, the Pancharatnam-Berry phase diffraction grating, and a circular polarizing plate as the polarizing plate. The reflective liquid crystal display device according to claim 1.

5. The optical element includes, in order from the reflective liquid crystal panel side toward the observer side, the Pancharatnam-Berry phase diffraction grating and a circular polarizing plate as the polarizing plate, and does not include a λ / 4 plate between the reflective liquid crystal panel and the Pancharatnam-Berry phase diffraction grating. The reflective liquid crystal display device according to claim 1.

6. The Pancharatnam-Berry phase diffraction grating includes a retardation layer containing a cured product of a polymerizable liquid crystal, the slow axis of the polymerizable liquid crystal rotates periodically in the x-axis direction from one end to the other end of the retardation layer within the plane of the retardation layer, and does not rotate periodically in the y-axis direction perpendicular to the x-axis direction, wherein the x-axis direction corresponds to the left-right direction of the reflective liquid crystal panel. The reflective liquid crystal display device according to any one of claims 1 to 5.

7. The Pancharatnam-Berry phase diffraction grating includes a retardation layer having a retardation Δnd satisfying the following (Equation 1) or (Equation 2) for wavelengths λ of 450 nm, 550 nm, and 650 nm. The reflective liquid crystal display device according to any one of claims 1 to 5. 【Number 1】 【Number 2】

8. The Pancharatnam-Berry phase diffraction grating includes a retardation layer containing a cured product of a polymerizable liquid crystal, the slow axis of the polymerizable liquid crystal rotates periodically in the x-axis direction from one end to the other end of the retardation layer within the plane of the retardation layer, The molecular alignment pattern Φ(x) [°], which is the alignment direction of the polymerizable liquid crystal disposed at a position separated by a distance x [μm] in the x-axis direction from the position where the slow axis of the polymerizable liquid crystal is parallel to the x-axis direction, satisfies the following (Equation 3). The reflective liquid crystal display device according to any one of claims 1 to 5. 【Number 3】 (In the above (Equation 3), Λ represents the pitch [μm] at which the slow axis of the polymerizable liquid crystal rotates 180° in the plane of the retardation layer, and m, n, and A are arbitrary constants.)

9. Furthermore, the reflective liquid crystal display device according to any one of claims 1 to 5, further comprising a diffusion layer on the observer side of the optical element or between members constituting the optical element.

10. Furthermore, the reflective liquid crystal display device according to any one of claims 1 to 5, further comprising a refractive element on the observer side of the optical element.

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