Display device

Abstract

A see-through display is provided that is thin and can achieve high contrast and brightness even when the display area is increased. The display device comprises: a liquid crystal panel having a polymer-dispersed liquid crystal layer; and a light source disposed on the back side of the liquid crystal panel. The polymer-dispersed liquid crystal layer comprises a polymer network and liquid crystal components dispersed in the polymer network. The light source is spaced apart from the liquid crystal panel via an air layer and disposed along at least one outer edge of the liquid crystal panel, irradiating light toward the liquid crystal panel from an oblique direction. The end portions and the central portion of the polymer-dispersed liquid crystal layer each have an angular dependency in which the transmittance of light emitted from the front surface side in a scattered state varies depending on the angle of light incident from the back side. The angular dependency of the end portions is different from the angular dependency of the central portion, and the light source irradiates the end portions and the central portion with light at different angles.

Description

Technical Field

[0001] The following disclosure relates to a display device, and more specifically, to a see-through display including a polymer-dispersed liquid crystal panel and a light source. Background Art

[0002] Liquid crystal displays (LCDs) utilize liquid crystal compositions for display. A typical display method involves applying a voltage to a liquid crystal composition sealed between a pair of substrates. This voltage changes the alignment of the liquid crystal components within the composition, thereby controlling the amount of light transmitted. These LCDs utilize their advantages of being thin, lightweight, and having low power consumption, and are therefore used in a wide range of fields.

[0003] In recent years, see-through displays, which enable a see-through display through the back of a liquid crystal display (LCD), have attracted significant attention. Liquid crystal displays using polymer-dispersed liquid crystals (PDLCs) have been developed. PDLCs have liquid crystal components dispersed within a polymer network. The application of a voltage changes the orientation of the liquid crystal components, switching between a transparent state and a scattering state by utilizing the refractive index difference between the liquid crystal components and the polymer network.

[0004] For example, Patent Document 1 discloses a display device comprising: a pair of transparent substrates that are separated and arranged relative to each other; a light modulation layer having a plurality of light modulation elements, the plurality of light modulation elements being arranged between the pair of transparent substrates, having a predetermined refractive index anisotropy, and having different responsiveness to an electric field generated by electrodes provided on the transparent substrates; and a light source that irradiates the light modulation layer with light of a predetermined color from the side of the light modulation layer, wherein the light modulation layer transmits the incident light from the light source when the electric field is not generated, and scatters the incident light and emits it to the transparent substrate when the electric field is generated.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-85452 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] An example of a light source for a see-through display is an edge-lit backlight. Using an edge-lit backlight allows for thinner liquid crystal display devices. For example, an edge-lit backlight utilizes a light guide plate. These light guide plates have a light source positioned on the side of the light guide plate. Light incident on the side of the light guide plate from these light sources is repeatedly reflected within the light guide plate before being emitted to the front surface.

[0010] On the other hand, part of the light reflected by the light guide plate is diffracted by components such as thin film transistors (TFTs) in the liquid crystal panel, resulting in loss. Therefore, the farther away from the light source, the greater the light loss, and the front characteristics such as contrast and brightness in the center of the display screen may sometimes decrease. According to the research of the inventors of the present invention, when a liquid crystal panel with PDLC is displayed using a light guide backlight, in a 19-inch large display device, the contrast of the center of the display screen in the scattered state is less than 2, and the brightness is 60cd / m 2 Furthermore, the brightness of the center portion of the display screen is approximately 1 / 4 of the brightness of the end portions of the display screen. There is a large brightness gradient between the end portions and the center portion of the display screen, making it difficult to display uniform brightness.

[0011] The larger the display area, the more pronounced the degradation of frontal characteristics in the center of the display. Furthermore, when light passes through the PDLC, some of the transmitted light is lost due to scattering. Therefore, achieving both large display areas and good frontal characteristics (high contrast and high brightness) is difficult in thin see-through displays.

[0012] Since light enters the display device described in Patent Document 1 from the side of the light modulation layer, as in the case of a backlight source using a light-guiding method, the light loss increases toward the center of the display screen. Therefore, when a large screen is used, sufficient front characteristics cannot be obtained.

[0013] An object of the present invention is to provide a thin see-through display that can achieve high contrast and brightness even when the display screen area is increased.

[0014] Solutions for solving problems

[0015] (1) One embodiment of the present invention is a display device comprising: a liquid crystal panel having a pair of substrates and a polymer dispersed liquid crystal layer sandwiched by the pair of substrates; and a light source disposed on the back side of the liquid crystal panel, the pair of substrates having electrodes for applying a voltage to the polymer dispersed liquid crystal layer, the polymer dispersed liquid crystal layer comprising a polymer network and liquid crystal components dispersed in the polymer network, the light source being spaced apart from the liquid crystal panel via an air layer and being disposed along at least one outer edge of the liquid crystal panel to irradiate light toward the liquid crystal panel from an oblique direction, the polymer dispersed liquid crystal layer being controlled to be in a state where no voltage is applied. When voltage is applied, it becomes a transparent state through which the background can be seen, and when voltage is applied, it becomes a scattering state in which the light incident from the above-mentioned light source is scattered. When viewed from above, when the area of the above-mentioned polymer dispersed liquid crystal layer close to the above-mentioned light source is set as the end, and the area farther from the above-mentioned light source than the above-mentioned end is set as the central part, the above-mentioned end and the above-mentioned central part respectively have an angle dependence in which the transmittance of the light emitted from the front side of the front surface in the above-mentioned scattering state changes according to the angle of the light incident from the back side, and the above-mentioned angle dependence of the above-mentioned end is different from the above-mentioned angle dependence of the above-mentioned central part, and the above-mentioned light source irradiates light to the above-mentioned end and the above-mentioned central part from different angles.

[0016] (2) In addition, a certain embodiment of the present invention is a display device, based on the structure of the above-mentioned (1), wherein the refractive index anisotropy of the above-mentioned liquid crystal component contained in the above-mentioned central portion is higher than the refractive index anisotropy of the above-mentioned liquid crystal component contained in the above-mentioned end portion.

[0017] (3) In addition, a certain embodiment of the present invention is a display device, based on the structure of (1) or (2) above, wherein the polymer-dispersed liquid crystal layer contains a chiral agent at the above-mentioned end portion, and does not contain a chiral agent at the above-mentioned central portion.

[0018] (4) In addition, a certain embodiment of the present invention is a display device, based on the structure of the above-mentioned (1) or (2), when the above-mentioned voltage is not applied, the twist angle of the above-mentioned liquid crystal component contained in the above-mentioned end part is larger than the twist angle of the liquid crystal component contained in the above-mentioned central part.

[0019] (5) In addition, a certain embodiment of the present invention is a display device, based on the structure of the above-mentioned (1), the above-mentioned polymer dispersed liquid crystal layer in the above-mentioned central portion and the above-mentioned polymer dispersed liquid crystal layer at the above-mentioned end portion both contain a chiral agent, and the thickness of the above-mentioned polymer dispersed liquid crystal layer in the above-mentioned end portion is thicker than the thickness of the above-mentioned polymer dispersed liquid crystal layer in the above-mentioned central portion.

[0020] (6) In addition, a certain embodiment of the present invention is a display device, based on any one of the above-mentioned structures (1) to (5), wherein the density of the polymer network in the above-mentioned polymer-dispersed liquid crystal layer in the above-mentioned central portion is higher than that in the above-mentioned polymer-dispersed liquid crystal layer in the above-mentioned end portion.

[0021] (7) In addition, a certain embodiment of the present invention is a display device, based on any one of the above-mentioned structures (1) to (6), wherein the above-mentioned electrodes are a pair of electrodes respectively arranged on the side of the above-mentioned pair of substrates opposite to the above-mentioned polymer-dispersed liquid crystal layer.

[0022] (8) In addition, a certain embodiment of the present invention is a display device, based on any one of the above-mentioned structures (1) to (7), wherein the above-mentioned light source includes light-emitting elements of multiple colors, and the above-mentioned light-emitting elements of multiple colors are driven in a field sequential manner with time-sharing lighting.

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide a thin see-through display that can achieve high contrast and brightness even when the display screen area is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a schematic cross-sectional view illustrating an example of a display device according to an embodiment.

[0026] Figure 2A It explains Figure 1 Schematic cross-sectional view of the transparent state of the liquid crystal panel shown.

[0027] Figure 2B It explains Figure 1 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0028] Figure 3 yes Figure 1 A schematic top view of the display device is shown.

[0029] Figure 4 It is a perspective view explaining a method for measuring the front transmittance of a polymer-dispersed liquid crystal layer.

[0030] Figure 5 is a graph showing the angle dependence of the polymer dispersed liquid crystal layer.

[0031] Figure 6 1 is a schematic cross-sectional view showing a transparent state of the display device of Example 1.

[0032] Figure 7 It shows Figure 6 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0033] Figure 8 3 is a schematic cross-sectional view showing a transparent state of the display device of Example 2.

[0034] Figure 9 It shows Figure 8 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0035] Figure 10 3 is a schematic cross-sectional view showing a transparent state of the display device of Example 3.

[0036] Figure 11 It shows Figure 10 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0037] Figure 12A It is a schematic top view illustrating the alignment treatment method for a substrate used in Example 3.

[0038] Figure 12B It is a schematic top view illustrating the alignment treatment method for another substrate used in Example 3.

[0039] Description of Reference Numerals

[0040] 1, 101, 201, 301: LCD panel

[0041] 2A, 102A: First light source

[0042] 2B, 102B: Second light source

[0043] 4: Air layer

[0044] 5A, 105A, 205A, 305A: First end

[0045] 5B, 105B, 205B, 305B: Second end

[0046] 6, 106, 206, 306: Central

[0047] 8.108: Sealing materials

[0048] 10, 20, 110, 120, 310, 320: transparent substrate

[0049] 11, 21, 111, 121: transparent substrate

[0050] 12, 22, 112, 122: electrodes

[0051] 13, 23, 113, 123, 313, 323: oriented films

[0052] 30, 130: Polymer dispersed liquid crystal layer

[0053] 31, 131: Polymer Network

[0054] 32, 132A, 132B, 232A, 232B, 332A, 332B: Liquid crystal molecules

[0055] 100: Display device

[0056] 107: Partition wall. DETAILED DESCRIPTION

[0057] The present invention will be described in further detail below with reference to the accompanying drawings and by way of examples, but the present invention is not limited to these examples.

[0058] Figure 1 : is a schematic cross-sectional view showing an example of a display device according to an embodiment. Figure 1 As shown, the display device 100 includes a liquid crystal panel 1 and a light source 2 arranged on the back side of the liquid crystal panel 1. The light source 2 can be fixed to a housing (not shown), for example. In this specification, the "front surface side" refers to the side closer to the observer, meaning the side closer to the display screen of the display device. The "back side" refers to the side farther from the display screen of the display device, meaning the side opposite to the front surface side.

[0059] The liquid crystal panel 1 includes a pair of substrates 10 and 20, and a polymer-dispersed liquid crystal layer 30. The pair of substrates 10 and 20 sandwich the polymer-dispersed liquid crystal layer 30. The substrate 10 may include a transparent base material 11, an electrode 12, and an alignment film 13. The substrate 20 may include a transparent base material 21, an electrode 22, and an alignment film 23.

[0060] Examples of transparent substrates 11 and 21 include glass substrates and plastic substrates. Transparent substrates 11 and 21 are, for example, substrates having a total light transmittance of 90% or greater. The total light transmittance is measured using a method in accordance with JIS K7361-1. The total light transmittance can be measured using, for example, a turbidimeter such as the "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries.

[0061] The substrates 10 and 20 have electrodes for applying voltage to the polymer dispersed liquid crystal layer 30. Figure 1 In the example, the electrodes are a pair of electrodes 12 and 22 respectively arranged on the sides of the substrates 10 and 20 facing the polymer dispersed liquid crystal layer 30. The electrodes 12 and 22 are preferably connected to different power supplies and supplied with different potentials. Figure 1In this case, when a voltage is applied to the polymer-dispersed liquid crystal layer 30, a longitudinal electric field is generated between the electrodes 12 and 22 along the thickness direction of the polymer-dispersed liquid crystal layer 30. Examples of materials for the electrodes 12 and 22 include transparent conductive materials such as indium tin oxide (ITO) and indium zinc oxide (IZO).

[0062] The display device 100 may have a plurality of pixels arranged in a matrix when viewed from above. In this case, the display device 100 can be set as an active matrix driven display device. It may be that any one of the electrodes 12 and 22 includes a plurality of pixel electrodes arranged for each pixel, and the on / off control is performed for each pixel electrode by a switching element such as a TFT arranged for each pixel. The other electrode is, for example, a whole-surface electrode formed in a planar shape, and may be a common electrode supplied with a common potential. On the other hand, it may be that both the electrodes 12 and 22 are whole-surface electrodes formed in a planar shape, and the transmittance of the entire surface of the display device 100 is uniformly controlled without being divided into pixels. In this case, the display device 100 can be used as a dimming panel, a lighting fixture, etc.

[0063] The alignment film 13 is preferably arranged on the side of the substrate 10 opposite to the polymer-dispersed liquid crystal layer 30 and in contact with the polymer-dispersed liquid crystal layer 30. The alignment film 23 is preferably arranged on the side of the substrate 20 opposite to the polymer-dispersed liquid crystal layer 30 and in contact with the polymer-dispersed liquid crystal layer 30. The alignment films 13 and 23 control the orientation of the liquid crystal components dispersed in the polymer network when no voltage is applied to the polymer-dispersed liquid crystal layer 30. The alignment films 13 and 23 are preferably aligned in parallel when no voltage is applied, so that the long axis direction of the liquid crystal components becomes a uniform orientation parallel to the surface of the substrate 10 and the surface of the substrate 20. The material of the alignment films 13 and 23 is not particularly limited, and materials commonly used in the field of liquid crystal display devices, such as rubbing alignment film materials and photo-alignment film materials, can be used. The alignment films 13 and 23 are preferably aligned by rubbing or light irradiation.

[0064] The polymer dispersed liquid crystal (PDLC) layer 30 includes a polymer network and a liquid crystal component dispersed in the polymer network. The polymer dispersed liquid crystal layer 30 is controlled to be in a transparent state where the background is visible when no voltage is applied, and to be in a scattering state where the light incident from the above-mentioned light source is scattered when a voltage is applied. The above-mentioned display method in which the display is in a transparent state when no voltage is applied and in a scattering state when a voltage is applied is also referred to as a reverse mode. In addition, the display method in which the display is in a scattering state when no voltage is applied and in a transparent state when a voltage is applied is also referred to as a normal mode. The above-mentioned no voltage applied means that the voltage applied to the polymer dispersed liquid crystal layer 30 is less than the threshold voltage of the liquid crystal component (including no voltage applied), and the voltage applied means that the voltage applied to the polymer dispersed liquid crystal layer 30 is greater than the threshold voltage of the liquid crystal component.

[0065] Below, use Figure 2A and Figure 2B To illustrate the alignment states of liquid crystal molecules in the transparent state and the scattering state. Figure 2A It explains Figure 1 Schematic cross-sectional view of the transparent state of the liquid crystal panel shown. Figure 2B It explains Figure 1 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown. Figure 2A and Figure 2B The center portion of the liquid crystal panel is shown.

[0066] like Figure 2A As shown, it is preferred that when no voltage is applied, the orientation directions of the polymer network 31 and the liquid crystal component 32 are substantially equal. Figure 2A In the figure, the polymer network 31 and the liquid crystal component 32 are oriented uniformly relative to the surfaces of the substrates 10 and 20. When no voltage is applied, there is virtually no difference in refractive index between the liquid crystal component 32 and the polymer network 31 (the extraordinary refractive index ne), or between the liquid crystal component 32 and the polymer network 31 (the ordinary refractive index no) in all directions, including the thickness direction of the polymer-dispersed liquid crystal layer 30. Therefore, light irradiated from a light source passes through the polymer-dispersed liquid crystal layer 30, resulting in a transparent state.

[0067] The transparent state refers to a state of transparency with respect to light. The transmittance of the polymer-dispersed liquid crystal layer 30 in the transparent state can be 80% or greater, or 90% or greater. The upper limit of the transmittance of the polymer-dispersed liquid crystal layer 30 in the transparent state is, for example, 100%. In this specification, the transmittance of the polymer-dispersed liquid crystal layer in the transparent and scattering states refers to the parallel light transmittance. This parallel light transmittance can be measured using the "LCD5200 (photol)" manufactured by Otsuka Electronics.

[0068] like Figure 2B As shown, when a voltage is applied, the polymer network 31 remains horizontally aligned relative to the surfaces of substrates 10 and 20, while the liquid crystal components 32 are vertically aligned. When a voltage is applied, the electric field formed in the polymer-dispersed liquid crystal layer 30 changes the orientation of the liquid crystal components 32. Meanwhile, the polymer network 31 is unaffected by the electric field. Consequently, the refractive index difference between the extraordinary refractive index ne of the liquid crystal components 32 and the polymer network 31, as well as the refractive index difference between the ordinary refractive index no of the liquid crystal components 32 and the polymer network 31, increases in all directions, including the thickness direction of the polymer-dispersed liquid crystal layer 30. When unpolarized light enters the polymer-dispersed liquid crystal layer 30, it is scattered regardless of polarization, resulting in the polymer-dispersed liquid crystal layer 30 being in a scattering state.

[0069] The above-mentioned scattering state refers to a state in which light is scattered, and has a frosted glass-like appearance. The transmittance of the polymer dispersed liquid crystal layer 30 in the scattering state can be less than 10%, or less than 8%. The lower limit of the transmittance of the polymer dispersed liquid crystal layer 30 in the scattering state is, for example, 0%. The haze representing the light scattering rate of the polymer dispersed liquid crystal layer 30 in the scattering state varies depending on the applied voltage, and can be, for example, more than 80%, or more than 90%. The upper limit of the haze representing the light scattering rate of the polymer dispersed liquid crystal layer 30 in the scattering state is, for example, 100%. In this specification, the haze is measured by a method in accordance with JIS K7136. The above-mentioned haze is measured, for example, using a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries. The above-mentioned light can be visible light.

[0070] The display device 100 adjusts the amount of light transmitted through the liquid crystal panel 1 by changing the refractive index difference between the liquid crystal component 32 in the polymer dispersed liquid crystal layer 30 and the ne of the polymer network 31, as well as the refractive index difference between the liquid crystal component 32 in the polymer dispersed liquid crystal layer 30 and the no of the polymer network 31. Therefore, the polarizing plate required in a general liquid crystal panel is not required.

[0071] The thickness of the polymer-dispersed liquid crystal layer 30 is preferably 3 μm or more and 10 μm or less.

[0072] The liquid crystal component 32 may have a positive or negative dielectric anisotropy (Δε) as defined by the following formula, but preferably has a positive dielectric anisotropy. The dielectric anisotropy of the liquid crystal component 32 is more preferably greater than 0 and less than 20. Furthermore, the long axis of the liquid crystal component is in the direction of the slow axis.

[0073] Δε=(dielectric constant in the long axis direction)-(dielectric constant in the short axis direction)

[0074] The refractive index anisotropy Δn of the liquid crystal component 32 is preferably 0.14 or greater. The upper limit of Δn is, for example, 0.28. A larger Δn is preferred, as it increases the refractive index difference between the extraordinary refractive index ne of the liquid crystal component 32 and the polymer network 31, as well as the refractive index difference between the ordinary refractive index no of the liquid crystal component 32 and the polymer network 31.

[0075] The rotational viscosity γ of the liquid crystal component 32 is preferably not less than 100 mPa·s and not more than 400 mPa·s. By setting γ within this range, the response speed of the liquid crystal component 32 can be increased, and color mixing can be suppressed when the light source 2 is driven using the field sequential method described later. More preferably, γ is not more than 200 mPa·s.

[0076] As the liquid crystal component 32, for example, a tolan-based liquid crystal material (a liquid crystal material having -C≡C- (carbon-carbon triple bond) as a connecting group) can be used. Specific examples of tolan-based liquid crystal materials include liquid crystal materials having a structure represented by the following general formula (L1).

[0077] [Chemical Formula 1]

[0078]

[0079] (In the above formula, Q1 and Q2 each independently represent an aromatic ring group, X represents a fluoro group or a cyano group, and n1 and n2 each independently represent 0 or 1.)

[0080] In the general formula (L1), n1 and n2 are not simultaneously 0. That is, the sum of n1 and n2 is 1 or 2.

[0081] The aromatic ring group in the above-mentioned general formula (L1) may have a substituent.

[0082] In the above general formula (L1), Q1 and Q2 are preferably each independently any one of the structures of the following general formulae (L2-1) to (L2-7).

[0083] [Chemical Formula 2]

[0084]

[0085] Specific examples of the liquid crystal material having the structure represented by the general formula (L1) include the following structures.

[0086] [Chemical Formula 3]

[0087]

[0088] The polymer network 31 is preferably a cured product of a polymerizable liquid crystal compound. For example, the polymer network 31 may be a fibrous solid formed in a three-dimensional matrix. The liquid crystal component 32 is dispersed in the polymer network 31 in a phase-separated manner.

[0089] To enhance the transparency of the polymer-dispersed liquid crystal layer 30 in a transparent state, the polymerizable liquid crystal compound constituting the polymer network preferably has an extraordinary refractive index ne and a normal refractive index no comparable to those of the liquid crystal component when no voltage is applied. For example, the difference between the extraordinary refractive index ne and the normal refractive index no of the polymerizable liquid crystal compound and the liquid crystal component is preferably Δno, Δne ≤ 0.02. More preferably, Δno, Δne ≤ 0.01 or less.

[0090] The polymerizable liquid crystal compound preferably exhibits a liquid crystal phase at room temperature and is compatible with the liquid crystal component, and phase-separates from the liquid crystal component after solidification and formation of a polymer network. The polymerizable liquid crystal compound may be a photopolymerizable liquid crystal compound that solidifies by ultraviolet irradiation.

[0091] As the above-mentioned photopolymerizable liquid crystal compound, for example, monomers having the following groups can be cited: substituents such as biphenyl, terphenyl, naphthyl, phenylbenzoate, azophenyl, and their derivatives (hereinafter also referred to as mesogenic groups); photoreactive groups such as cinnamoyl, chalcone, cinnamylene, β-(2-phenyl)acryloyl, and their derivatives; and polymerizable groups such as acrylate, methacrylate, maleimide, N-phenylmaleimide, and siloxane. The above-mentioned polymerizable group is preferably acrylate. In addition, although the number of polymerizable groups per molecule of the above-mentioned photopolymerizable liquid crystal compound is not particularly limited, it is preferably 1 or 2. In addition, the above-mentioned liquid crystal component may not have polymerizable groups such as acrylate, methacrylate, maleimide, N-phenylmaleimide, and siloxane.

[0092] The content of the polymerizable liquid crystal compound in the polymer-dispersed liquid crystal layer 30 is preferably 5% by weight or more and 10% by weight or less relative to the weight of the liquid crystal component.

[0093] The polymer dispersed liquid crystal layer 30 may contain a polymerization initiator. The content of the polymerization initiator in the polymer dispersed liquid crystal layer 30 is preferably 5% by weight or more and 10% by weight or less based on the weight of the polymerizable liquid crystal compound.

[0094] The polymerization initiator is not particularly limited, and conventionally known polymerization initiators can be used. For example, Omnirad 184 (registered trademark) (manufactured by IGM Resins BV) represented by the following chemical formula (IN1) and OXE03 (manufactured by BASF) represented by the following chemical formula (IN2) can be used.

[0095] [Chemical Formula 4]

[0096]

[0097] [Chemical Formula 5]

[0098]

[0099] The polymer-dispersed liquid crystal layer 30 may contain a chiral agent. When the polymer-dispersed liquid crystal layer 30 contains a chiral agent, it is preferably contained in a partial region of the liquid crystal panel 1 rather than the entire surface of the liquid crystal panel 1 .

[0100] The content of the chiral agent in the polymer-dispersed liquid crystal layer 30 is preferably 0.5 wt % or more and 4 wt % or less based on the total weight of the liquid crystal component, the polymerizable liquid crystal compound, and the polymerization initiator.

[0101] The chiral agent is not particularly limited, and conventionally known chiral agents can be used. Examples of chiral agents that can be used include CM-51L (manufactured by JNC Corporation) and S-811 (manufactured by Merck & Co., Ltd.) represented by the following chemical formula (C1).

[0102] [Chemical Formula 6]

[0103]

[0104] Figure 3 yes Figure 1 Schematic diagram of a top view of the display device shown in FIG. When viewed from above, the area of the polymer dispersed liquid crystal layer close to the light source is defined as the end portion 5, and the area farther from the light source than the end portion is defined as the center portion 6. Figure 3 In the example, the area close to the first light source 2A is defined as the first end 5A, and the area close to the second light source 2B is defined as the second end 5B. Figure 3 In the embodiment, a center portion 6 is disposed between the two end portions (the first end portion 5A and the second end portion 5B). In the description of this specification, when the first end portion 5A and the second end portion 5B are not particularly distinguished, they are simply referred to as the end portion 5.

[0105] The end portion 5 and the central portion 6 each have an angular dependence in which the transmittance of light emitted from the front side of the front surface in the above-mentioned scattering state varies according to the angle of light incident from the back side, and the above-mentioned angular dependence of the end portion 5 is different from the above-mentioned angular dependence of the central portion 6. The above-mentioned "transmittance of light emitted from the front side of the front surface" refers to the parallel light transmittance measured for the liquid crystal panel at an acceptance angle of approximately 3°, hereinafter also referred to as "front transmittance". The higher the front transmittance, the stronger the scattering when the liquid crystal panel 1 is viewed from the front surface side (observer side), indicating that the brightness of the liquid crystal panel 1 in the scattering state is higher.

[0106] The above-mentioned angular dependence refers to the following property: in the above-mentioned scattering state, the transmittance of light emitted from the front surface side of the polymer-dispersed liquid crystal layer changes depending on the angle of light incident from the back side of the polymer-dispersed liquid crystal layer. Because the angular dependence of the end portion 5 is different from the angular dependence of the central portion 6, more uniform front characteristics (high contrast and high brightness) can be obtained within the plane of the liquid crystal panel 1. In addition, since the front scattering characteristics in the transparent state are independent of the type of polymer-dispersed liquid crystal layer and are almost unchanged regardless of the angle of incident light, by making the polymer-dispersed liquid crystal layer include multiple types of structures, it is possible to improve both brightness and contrast.

[0107] (Study on the Angle Dependence of Polymer Dispersed Liquid Crystal Layers)

[0108] The following uses Figure 4 and Figure 5 The angle dependence of the polymer-dispersed liquid crystal layer will be described. Figure 4 It is a perspective view explaining a method for measuring the front transmittance of a polymer-dispersed liquid crystal layer.

[0109] Figure 5 is a graph showing the angle dependence of the polymer dispersed liquid crystal layer. Figure 5 In FIG, the horizontal axis is set as the projection angle (°) and the vertical axis is set as the front transmittance.

[0110] The inventors of the present invention prepared a liquid crystal cell consisting of only one polymer-dispersed liquid crystal layer having a specific angle dependency, and studied the angle dependency of the polymer-dispersed liquid crystal layer. Figure 4 As shown, the liquid crystal unit used for the study is a liquid crystal unit having a polymer dispersed liquid crystal layer 30 including a polymer network 31 and a liquid crystal component 32, and a pair of substrates 10 and 20 clamping the polymer dispersed liquid crystal layer 30. Although omitted from the figure, the pair of substrates 10 and 20 are respectively configured to have a planar electrode and an orientation film on the side of the polymer dispersed liquid crystal layer 30.

[0111] like Figure 4As shown, in this study, light L1 was irradiated from the back of the liquid crystal cell at a specific angle θx, 180° from the normal to the liquid crystal cell. Light L2 emitted from the entire surface of the liquid crystal cell was measured to obtain the front transmittance. This θx is also called the projection angle. When the liquid crystal component 32 is aligned perpendicularly to the thickness direction of the polymer-dispersed liquid crystal layer 30, i.e., the surfaces of the substrates 10 and 20, in a scattered state, the projection angle θx is the angle between the alignment direction of the liquid crystal component and the irradiation direction.

[0112] The following liquid crystal units of Reference Examples 1 to 3 were prepared, and the relationship between the projection angle and the front transmittance was studied using the above-mentioned method. The polymer-dispersed liquid crystal layer of Reference Example 1 includes a polymer network, a liquid crystal component with a refractive index anisotropy Δn of 0.14, and a chiral agent. The polymer-dispersed liquid crystal layer of Reference Example 2 includes a polymer network and a liquid crystal component with a refractive index anisotropy Δn of 0.14, but does not include a chiral agent. The polymer-dispersed liquid crystal layer of Reference Example 3 includes a polymer network and a liquid crystal component with a refractive index anisotropy Δn of 0.18, but does not include a chiral agent.

[0113] like Figure 5 As shown, in Reference Example 1, the scattering toward the front becomes strongest within the range of a projection angle of approximately 4° to 12°. In Reference Example 2, the scattering toward the front becomes strongest within the range of a projection angle of approximately 12° to 40°. In Reference Example 3, the scattering toward the front becomes strongest within the range of a projection angle of approximately 40° or more. Based on these results, it can be seen that when the polymer dispersed liquid crystal layer is not made of one structure but includes multiple structures, in the scattering state, the brightness (brightness) of the entire surface of the liquid crystal panel can be increased, and the scattering characteristics when observed from the front (front scattering characteristics) can be improved.

[0114] Since the end portion 5 is close to the light source, the brightness is high, and the projection angle of the light incident on the end portion 5 is small. On the other hand, since the central portion 6 is far from the light source, the brightness is lower than that of the end portion. In addition, the projection angle of the light incident on the central portion 6 is larger than that of the end portion 5. Therefore, it is preferable to use a PDLC material that can obtain a high front transmittance at a small projection angle at the end portion 5, and to use a PDLC material that can obtain a high front transmittance at a large projection angle at the central portion 6. In addition, as Figure 5 As shown, materials with different angular dependencies can also be said to have an angle at which the front transmittance is reversed when the projection angle is increased.

[0115] As a method for making the angular dependence of the end portion 5 and the central portion 6 different, based on the above research, the following method (i) or (ii) can be cited. As a method other than the above research, the following methods (iii) to (v) can be cited. In addition, the following method (ii) can be combined with the following method (i) or (iii), and the following method (v) can be combined with any of the following methods (i) to (iv).

[0116] (i) Preferably, the polymer-dispersed liquid crystal layer 30 contains a chiral agent at the end portions 5, and preferably does not contain a chiral agent at the center portion 6. For example, the structure of Reference Example 1 used in the above-mentioned study can be arranged at the end portions 5, and the structure of Reference Example 2 can be arranged at the center portion 6.

[0117] (ii) The refractive index anisotropy of the liquid crystal component contained in the central portion 6 is preferably higher than that of the liquid crystal component contained in the end portions 5. For example, the structure of Reference Example 2 used in the above-mentioned study can be arranged in the end portions 5, and the structure of Reference Example 3 can be arranged in the central portion 6.

[0118] (iii) When no voltage is applied, the twist angle of the liquid crystal component contained in the end portion 5 is preferably greater than the twist angle of the liquid crystal component contained in the central portion 6. The twist angle refers to the angle formed between the orientation of the liquid crystal component located near one substrate and the orientation of the liquid crystal component located near the other substrate when the liquid crystal panel 1 is viewed from the normal direction. The orientation of the liquid crystal component can be varied by changing the orientation treatment direction of the alignment films 13 and 23.

[0119] The twist angle is preferably not less than 70° and not more than 90°, and the more preferred lower limit is 80°.

[0120] (iv) Preferably, both the polymer-dispersed liquid crystal layer in the central portion 6 and the polymer-dispersed liquid crystal layer 30 in the end portion 5 contain a chiral agent, and the polymer-dispersed liquid crystal layer 30 in the end portion 5 is thicker than the polymer-dispersed liquid crystal layer 30 in the central portion 6 .

[0121] Because both the end portions 5 and the central portion 6 contain a chiral agent, the polymer network and liquid crystal components are twisted at a specific pitch in each of the end portions 5 and the central portion 6. However, the twisting of the polymer network and liquid crystal components is greater in the thicker end portions 5 than in the thinner central portion 6. Therefore, when in a scattering state, light in the central portion 6 is emitted toward the front side due to diffused scattered light. However, light in the end portions 5 is more strongly scattered and diffused away from the front side than in the central portion, resulting in less light appearing toward the front side. Consequently, scattering is stronger in the central portion 6 than in the end portions 5.

[0122] The thickness of the polymer-dispersed liquid crystal layer 30 in the end portions 5 can be made thicker than the thickness of the polymer-dispersed liquid crystal layer 30 in the central portion 6 by forming an overcoat layer with a resin or the like on the portion corresponding to the central portion 6 on the electrode 12 of the substrate 10 and / or the electrode 22 of the substrate 20. Furthermore, regarding the spacers supporting the polymer-dispersed liquid crystal layer 30, it is preferable that the spacers arranged at the end portions 5 are taller than the spacers arranged in the central portion 6. Alternatively, two spacers of different heights may be used in the two regions of the central portion 6 and the end portions 5, but it is more preferable to use three or more spacers of different heights to form three or more regions, thereby gradually increasing the thickness of the polymer-dispersed liquid crystal layer 30 from the central portion toward the end portions.

[0123] The difference between the thickness of the polymer-dispersed liquid crystal layer 30 in the end portion 5 and the thickness of the polymer-dispersed liquid crystal layer 30 in the central portion 6 is preferably 2 μm or greater. The upper limit of this difference is not particularly limited, but is, for example, 8 μm. Specifically, the thickness of the polymer-dispersed liquid crystal layer 30 in the central portion 6 can be set to 3 μm, and the thickness of the polymer-dispersed liquid crystal layer 30 in the end portion 5 can be set to 10 μm.

[0124] (v) The polymer-dispersed liquid crystal layer 30 in the central portion 6 preferably has a higher density of the polymer network than the polymer-dispersed liquid crystal layer in the end portion 5. The density of the network can be adjusted by adjusting the concentration of the polymerizable compound relative to the weight of the liquid crystal component. Assuming that the polymerizable compound is completely reacted by ultraviolet irradiation, the density of the network is approximated by the concentration of the polymerizable compound.

[0125] As a method for increasing the density of the polymer network in the polymer-dispersed liquid crystal layer 30 in the central portion 6, for example, there is a method of increasing the content of the polymerizable compound and / or polymerization initiator in the polymer-dispersed liquid crystal layer 30 in the central portion 6 compared to the end portions 5. For example, the content of the polymerization initiator in the central portion 6 is preferably: the content of the polymerization initiator in the end portions 5 = 2 to 5 wt% relative to the polymerizable compound: 5 to 10 wt% relative to the polymerizable compound.

[0126] As another method, for example, when forming the polymer network, the amount of ultraviolet light or the illuminance applied to the central portion 6 may be higher than the amount of ultraviolet light or the illuminance applied to the end portions 5. As an example of such an ultraviolet light irradiation method, after a first ultraviolet light irradiation is performed on the end portions 5 and the central portion 6, the end portions 5 may be masked and only the central portion 6 may be irradiated with ultraviolet light a second time. Furthermore, by placing a halftone mask on the end portions 5, the amount of ultraviolet light or the illuminance applied to the central portion 6 may be higher than that applied to the end portions 5 with only a single ultraviolet light irradiation.

[0127] The above-mentioned methods (i), (ii) and (v) of changing the content of polymerizable compounds and / or polymerization initiators at the end portion 5 and the central portion 6 include a method of setting a partition wall between the end portion 5 and the central portion 6 for demarcation. The above-mentioned partition wall can be formed, for example, by setting linear rib protrusions, or by arranging spacers in a high-density row in place of the above-mentioned rib protrusions. In addition, the above-mentioned rib protrusions can be formed using organic resins such as acrylic acid, polyimide, polyimide amide, epoxy resin, or inorganic insulating materials such as silicon oxide, silicon nitride, and silicon oxynitride. As other methods, for example, a method of bonding one substrate to another substrate after dripping liquid crystals with different materials at the end portion 5 and the central portion 6 on one substrate (hereinafter also referred to as ODF method) can be cited.

[0128] If the width of the end portion 5 perpendicular to the side where the light source 2 is arranged is W1 and the width of the center portion 6 is W2, the ratio of W1 to W2 is preferably 1:3 to 1:10. W1 can be, for example, 3 cm to 10 cm. W2 can be, for example, 20 cm to 30 cm.

[0129] Furthermore, when the above-mentioned partition walls are provided, the end portions 5 and the central portion 6 are defined by a sealing material or a partition wall, respectively. The width W1 of the end portions 5 is the distance from the side where the light source 2 is provided to the partition wall, and the width W2 of the central portion 6 is the distance between the partition walls defining the central portion 6. In the above-mentioned case (iii), the end portions 5 and the central portion 6 can be defined by making the orientation treatment directions relative to the orientation film different. The width W1 of the end portions 5 and the width W2 of the central portion 6 can be set by confirming the orientation direction of the liquid crystal molecules in a state where no voltage is applied. In the above-mentioned case (iv), the width W1 of the end portions 5 and the width W2 of the central portion 6 can be confirmed by measuring the thickness of the polymer-dispersed liquid crystal layer 30.

[0130] Although the example shows a case where the structure is divided into two regions, the central portion and the end portion, it may further include other regions. For example, it may be configured as an end portion, a middle region, a central portion, a middle region, and an end portion.

[0131] The light source is spaced apart from the liquid crystal panel via an air layer 4. In previous display devices, an edge-type backlight having a light guide plate is sometimes used, or a transparent optical sheet (OCA) is used to bond the liquid crystal panel to the light guide plate. Light irradiated from the side of the light guide plate in a horizontal direction is reflected inside the light guide plate and emitted toward the liquid crystal panel, but light is lost during internal reflection of the light guide plate or when passing through the OCA, and the brightness of the display device sometimes becomes low. In the display device of this embodiment, since the light source is spaced apart from the liquid crystal panel via an air layer 4, there is no internal reflection of the light guide plate or light loss when passing through the OCA as in the past, and the brightness can be improved. Therefore, even if the area of the display screen is increased, high contrast and brightness can be obtained.

[0132] The distance H from the light source to the rear surface of the liquid crystal panel (thickness of the air layer) is appropriately selected depending on the size of the display device, and is, for example, not less than 1 cm and not more than 15 cm.

[0133] The light source irradiates light toward the liquid crystal panel from an oblique direction. This configuration reduces light attenuation compared to conventional methods in which the light source irradiates light from the side of a light guide plate or from the side of a light modulation layer as in Patent Document 1. This improves the brightness near the center of the liquid crystal panel (more specifically, the front brightness). Consequently, even when the display screen of the display device is large, high contrast and brightness can be achieved.

[0134] Irradiating light toward the liquid crystal panel from an oblique direction means that the light irradiated from the light source is not parallel to the panel surface of the liquid crystal panel. Although the angle is appropriately selected based on the size of the display panel and the type of liquid crystal material used, when the normal direction of the liquid crystal panel is set to 0°, the main surface of the light source is greater than 30° and less than 80°.

[0135] The light source 2 is arranged along at least one outer edge of the liquid crystal panel. Figure 3 As shown, the first light source 2A and the second light source 2B can be arranged along the two opposite short sides of the liquid crystal panel. In this specification, when the first light source 2A and the second light source 2B are not specifically distinguished, they are simply represented as light source 2. The light source 2 preferably irradiates light toward the bisector of the outer edge different from the outer edge where the light source 2 is arranged when viewed from above. When the first light source 2A and the second light source 2B are arranged along the two opposite short sides of the liquid crystal panel, it is preferred that the first light source 2A and the second light source 2B are respectively directed toward the bisector of the outer edge when viewed from above. Figures 1 to 3 Light is irradiated along a line bisecting the long side of the liquid crystal panel indicated by a dashed line.

[0136] The light source irradiates light to the end portion and the center portion from different angles. Figure 1As shown, when the normal direction of the liquid crystal panel 1 is set to 0° and the outer edge where the light source 2 is arranged is the short side of the liquid crystal panel, the angle of the light incident on the central part (hereinafter also referred to as the projection angle to the central part) θ1 is the angle between the light irradiated toward the second line of the long side of the liquid crystal panel and the above-mentioned 0°. In addition, the angle of the light incident on the end part (hereinafter also referred to as the projection angle to the end part) θ2 is the angle between the light irradiated toward the end edge of the end part 5 farthest from the light source and the above-mentioned 0°. When the end part is adjacent to the central part, the angle between the light irradiated toward the boundary between the end part and the central part and the above-mentioned 0° becomes the projection angle θ2 to the end part.

[0137] The projection angle θ1 toward the center is preferably larger than the projection angle θ2 toward the end. The projection angle θ1 toward the center can be, for example, 5° to 20°. The projection angle θ2 toward the end can be, for example, 30° to 80°.

[0138] The light source may be monochromatic or may include a plurality of color light emitting elements. Examples of the light emitting elements include light emitting diodes (LEDs). The light emitting elements preferably emit light in an equidirectional manner. The plurality of color light emitting elements may include, for example, red, green, and blue light emitting elements.

[0139] Alternatively, the light source may include a plurality of light-emitting elements of different colors, and the light-emitting elements of the plurality of colors are driven in a field sequential manner of time-sharing lighting (hereinafter also referred to as FSC driving). FSC driving can perform color display by sequentially lighting the light-emitting elements of the plurality of colors at staggered times for each color. Color display is performed by FSC driving, and since no color filter is required, the display device can be thinned. In addition, since not only a polarizing plate but also a color filter and a black matrix for dividing the color filter are not required, the brightness of the display device can be increased compared to a general liquid crystal display device with a planar backlight.

[0140] The display device 100 can be used as, for example, a television, an electronic advertisement, a shop window, a lighting fixture, a dimming panel, an entertainment device, a guide board, a mobile terminal, or the like.

[0141] The following embodiments are disclosed to further illustrate the present invention, but the present invention is not limited to these embodiments. The display devices of the following embodiments 1 to 4 are all reverse mode display devices driven in a field sequential manner.

[0142] <Example 1>

[0143] Example 1 is a specific example of a display device fabricated by combining (i) and (v) above. Specifically, the display device of Example 1 is a display device in which the polymer-dispersed liquid crystal layer at the end portions contains a chiral agent, while the polymer-dispersed liquid crystal layer at the center portion does not contain a chiral agent, and the polymer-dispersed liquid crystal layer at the center portion has a higher density of the polymer network than the polymer-dispersed liquid crystal layer at the end portions. Figure 6 1 is a schematic cross-sectional view showing a transparent state of the display device of Example 1. Figure 7 It shows Figure 6 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0144] In Example 1, a PDLC material containing a chiral agent is used at the ends (first end 105A and second end 105B) of the polymer dispersed liquid crystal layer 130 having a small projection angle, in which the scattering toward the front becomes strongest within a projection angle range of approximately 4° to 12°, and a PDLC material not containing a chiral agent is used at the central portion 106 of the polymer dispersed liquid crystal layer 130 having a large projection angle, in which the scattering toward the front becomes strongest within a projection angle range of approximately 12° to 40°.

[0145] The polymer dispersed liquid crystal (PDLC) material used in the first end portion 105A and the second end portion 105B includes a liquid crystal component, a polymerizable compound, a polymerization initiator, and a chiral agent. The liquid crystal component uses a liquid crystal component having a refractive index anisotropy Δn of 0.14, a dielectric constant anisotropy Δε that is positive and less than 20, and a rotational viscosity γ of 120 mPa·s. As the polymerizable compound, a photopolymerizable compound that is cured by ultraviolet irradiation is used, and is added in an amount of 5% by weight relative to the weight of the liquid crystal component. The polymerization initiator is added in an amount of 5% by weight relative to the weight of the polymerizable compound. The chiral agent is added in an amount of 4% by weight relative to the weight of the liquid crystal component, the polymerizable liquid crystal compound, and the polymerization initiator added together.

[0146] The PDLC material used in the central portion 106 does not contain a chiral agent and instead consists of a liquid crystal component, a polymerizable compound, and a polymerization initiator. The liquid crystal component used has a refractive index anisotropy Δn of 0.14, a positive dielectric constant anisotropy Δε of 20 or less, and a rotational viscosity γ of 170 mPa·s. The polymerizable compound used in the end portions was the same as that used in the end portions and was added to a concentration of 9% by weight relative to the weight of the liquid crystal component. The polymerization initiator was added to a concentration of 10% by weight relative to the weight of the polymerizable compound.

[0147] Reference Figure 6As transparent substrates 111 and 121, a pair of glass substrates with a length of about 30 cm and a width of about 40 cm were prepared, and transparent planar electrodes (whole-surface electrodes) were formed on the surfaces of the two glass substrates using ITO as electrodes 112 and 122. Orientation films 113 and 123 were formed on the surfaces of the electrodes 112 and 122 to produce a pair of substrates 110 and 120. The orientation films 113 and 123 used photo-orientation films and were photo-oriented in a manner that uniformly oriented the liquid crystal components. Subsequently, partition walls 107 were made on the orientation film 113 of the substrate 110 using the above-mentioned organic resin or inorganic insulating material at the boundary between the first end portion 105A and the central portion 106 and at the boundary between the second end portion 105B and the central portion 106. By the ODF method, after the above-mentioned PDLC material was dripped onto the first end portion 105A, the second end portion 105B, and the central portion 106, the substrates 110 and 120 were bonded together using the sealing material 108, thereby producing a liquid crystal unit.

[0148] The central portion 106 of the obtained liquid crystal cell was irradiated with 50 mW / cm 2 , 2J / cm 2 The first end portion 105A and the second end portion 105B are irradiated with ultraviolet light (wavelength: 365 nm) at 5.5 mW / cm 2 , 2J / cm 2 Ultraviolet rays (wavelength: 365 nm) are then applied. This ultraviolet irradiation cures the photopolymerizable compound, forming a polymer-dispersed liquid crystal layer 130 in which liquid crystal components 132A and 132B are dispersed within a polymer network 131. The thickness of polymer-dispersed liquid crystal layer 130 is set to 3 μm. In this manner, a 19-inch liquid crystal panel 101 is formed. Figure 6 As shown, the width W1 of the first and second end portions 105A, 105B is approximately 2 cm, and the width of the central portion 206 is approximately 36 cm.

[0149] Light sources were arranged at intervals on the back of the resulting liquid crystal panel 101, completing the display device of Example 1. As shown in FIG2 , a first light source 102A and a second light source 102B were arranged along two opposing short sides of the liquid crystal panel. Each of the first light source 102A and the second light source 102B included LEDs for red (R), green (G), and blue (B). The distance H (thickness of the air layer) between the first light source 102A and the second light source 102B and the liquid crystal panel was set to approximately 5 cm. Figure 6 In the example shown, θ1 is set to approximately 12°, and θ2 is set to approximately 63°. That is, the angles of light emitted from the first light source 102A and the second light source 102B toward the first end portion 105A and the second end portion 105B are respectively greater than 0° and less than 12°, and the angles of light emitted from the first light source 102A and the second light source 102B toward the center portion 106 are respectively greater than 12° and less than 63°.

[0150] like Figure 6 As shown, in the transparent state (when no voltage is applied), the liquid crystal component 132B and polymer network 131 contained in the first and second end portions 105A, 105B are aligned horizontally relative to the surfaces of the pair of substrates 110, 120 and twisted at the same pitch. The liquid crystal component 132A and polymer network 131 contained in the central portion 106 are aligned horizontally relative to the surfaces of the pair of substrates 110, 120 and along the longitudinal direction of the pair of substrates 110, 120. In the transparent state, there is almost no refractive index difference between the extraordinary refractive index ne of the liquid crystal component 132B and the polymer network 131, and the ordinary refractive index no of the liquid crystal component 132B and the polymer network 131. Therefore, light irradiated from the light source transmits through the polymer-dispersed liquid crystal layer 130, resulting in a transparent state.

[0151] like Figure 7 As shown, when a voltage is applied between electrodes 112 and 122, a longitudinal electric field is generated along the thickness direction of polymer-dispersed liquid crystal layer 130, causing liquid crystal components 132A and 132B to stand upright. Meanwhile, the orientation of polymer network 131 remains unchanged. Consequently, the refractive index difference between liquid crystal components 132A and 132B and the extraordinary refractive index ne of polymer network 131, as well as the refractive index difference between liquid crystal components 132A and 132B and the ordinary refractive index no of polymer network 131, increases, causing light irradiated from a light source to be scattered by polymer-dispersed liquid crystal layer 130.

[0152] The display device of Example 1 achieves a front contrast ratio of 5 or more and a luminance ratio of 100 cd / m² in the central portion 106 of the liquid crystal panel 101 in the scattering state. 2 The brightness of the liquid crystal panel 101 is more than 5, and the front contrast ratio of 200 cd / m 2 Brightness above.

[0153] <Example 2>

[0154] Example 2 is a specific example of a display device fabricated according to (ii) above. That is, the display device of Example 2 is a display device in which the refractive index anisotropy of the liquid crystal component contained in the central portion is higher than that of the liquid crystal component contained in the end portions. Figure 8 3 is a schematic cross-sectional view showing a transparent state of the display device of Example 2. Figure 9 It shows Figure 8 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0155] In Example 2, a PDLC material containing a liquid crystal component with a low refractive index anisotropy Δn and whose scattering toward the front becomes strongest within a range of about 12° to 40° is used at the ends (the first end 205A and the second end 205B) of the polymer-dispersed liquid crystal layer 130 having a small projection angle, and whose scattering toward the front becomes strongest within a range of about 40° or more is used at the central portion 206 of the polymer-dispersed liquid crystal layer 130 having a large projection angle.

[0156] The polymer-dispersed liquid crystal (PDLC) material used in the first end portion 205A and the second end portion 205B does not contain a chiral agent, but instead comprises a liquid crystal component, a polymerizable compound, and a polymerization initiator. The liquid crystal component, the polymerizable compound, and the polymerization initiator are the same as those used in the end portion of Example 1. The polymerizable compound was added to provide 9% by weight relative to the weight of the liquid crystal component. The polymerization initiator was added to provide 5% by weight relative to the weight of the polymerizable compound.

[0157] The polymer dispersed liquid crystal (PDLC) material used in the central portion 206 does not contain a chiral agent and comprises a liquid crystal component, a polymerizable compound, and a polymerization initiator. The liquid crystal component used has a refractive index anisotropy Δn of 0.18, a dielectric constant anisotropy Δε that is positive and less than 20, and a rotational viscosity γ of 170 mPa·s. The polymerizable compound and the polymerization initiator used are the same as those used in the end portions of Example 1. The polymerizable compound was added to a concentration of 9% by weight relative to the weight of the liquid crystal component. The polymerization initiator was added to a concentration of 10% by weight relative to the weight of the polymerizable compound.

[0158] A pair of substrates 110 and 120 were fabricated in the same manner as in Example 1, and alignment films 113 and 123 were subjected to an alignment treatment. Separator walls 107 were then formed at the boundaries between the first end portion 205A and the center portion 206, and at the boundaries between the second end portion 205B and the center portion 206, respectively, on the alignment film 113, in the same manner as in Example 1. The PDLC material was dripped onto the first end portion 205A, the second end portion 205B, and the center portion 206 using the ODF method. The substrates 110 and 120 were then bonded together using a sealant 108, thereby fabricating a liquid crystal cell.

[0159] The central portion 206, the first end portion 205A, and the second end portion 205B of the obtained liquid crystal cell were irradiated with 50 mW / cm 2 , 2J / cm 2Ultraviolet rays (wavelength: 365 nm) are then applied. This ultraviolet irradiation cures the photopolymerizable compound, forming a polymer-dispersed liquid crystal layer 130 in which liquid crystal components 232A and 232B are dispersed within a polymer network 131. The thickness of polymer-dispersed liquid crystal layer 130 is set to 3 μm. Thus, a 19-inch liquid crystal panel 201 is completed. Figure 8 As shown, the width W1 of the first end portion 205A and the second end portion 205B is approximately 2 cm, and the width of the central portion 206 is approximately 36 cm.

[0160] The same light sources as those in Example 1 were spaced apart on the back of the obtained liquid crystal panel 201 to complete the display device of Example 2. The distance H (thickness of the air layer) between the first light source 102A and the second light source 102B and the liquid crystal panel 201 was set to about 5 cm. Figure 8 In the illustration, θ1 is set to approximately 40°, and θ2 is set to approximately 63°. That is, the angle of light emitted from first light source 102A and second light source 102B toward first end portion 205A and second end portion 205B is greater than 0° and less than 40°, and the angle of light emitted from first light source 102A and second light source 102B toward center portion 206 is greater than 40° and less than 63°.

[0161] like Figure 8 As shown, in the transparent state, which is when no voltage is applied, the liquid crystal components 232A and 232B and the polymer network 131 contained in the first end portion 205A, the second end portion 205B, and the central portion 206 are aligned horizontally with respect to the surfaces of the pair of substrates 110 and 120 and along the longitudinal direction of the pair of substrates 110 and 120. In the transparent state, there is almost no refractive index difference between the extraordinary refractive index ne of the liquid crystal components 232A and 232B and the polymer network 131, and there is almost no refractive index difference between the ordinary refractive index no of the liquid crystal components 232A and 232B and the polymer network 131. Therefore, light irradiated from the light source transmits through the polymer-dispersed liquid crystal layer 130, resulting in a transparent state.

[0162] like Figure 9 As shown, when a voltage is applied between electrodes 112 and 122, a longitudinal electric field is generated along the thickness direction of polymer-dispersed liquid crystal layer 130, causing liquid crystal components 232A and 232B to stand upright. Meanwhile, the orientation of polymer network 131 remains unchanged. Therefore, the refractive index difference between the extraordinary refractive index ne of liquid crystal components 232A and 232B and the polymer network 131, as well as the refractive index difference between the ordinary refractive index no of liquid crystal components 232A and 232B and the polymer network 131, increases, causing light irradiated from the light source to be scattered by polymer-dispersed liquid crystal layer 130.

[0163] The display device of Example 2 achieved a front contrast ratio of 7 or more and a brightness of 150 cd / m² in the central portion 206 of the liquid crystal panel 201 in the scattering state. 2 The brightness of the LCD panel 201 is more than 7, and the front contrast ratio of 300 cd / m 2 Compared with Example 1, Example 2 achieved high front contrast and brightness, especially at the end.

[0164] In addition, embodiments 1 and 2 may be combined, and a PDLC material that does not contain a chiral agent but contains a liquid crystal component having a higher refractive index anisotropy than the liquid crystal component contained in the end portion may be used in the central portion of the polymer dispersed liquid crystal layer, and a PDLC material that contains a chiral agent and contains a liquid crystal component having a lower refractive index anisotropy than the liquid crystal component contained in the central portion may be used in the end portion of the polymer dispersed liquid crystal layer.

[0165] <Example 3>

[0166] Example 3 is a specific example of a display device fabricated according to (iii) above. Specifically, the display device of Example 3 is a display device in which the twist angle of the liquid crystal component contained in the end portion is larger than the twist angle of the liquid crystal component contained in the central portion when no voltage is applied. Figure 10 3 is a schematic cross-sectional view showing a transparent state of the display device of Example 3. Figure 11 It shows Figure 10 Schematic cross-sectional view of the scattering state of the liquid crystal panel shown.

[0167] In Example 3, a PDLC material containing a liquid crystal component with a low refractive index anisotropy Δn and whose scattering toward the front becomes strongest within a range of about 12° to 40° is used at the ends (the first end 305A and the second end 305B) of the polymer-dispersed liquid crystal layer 130 having a small projection angle, and whose scattering toward the front becomes strongest within a range of about 40° or more is used in the central portion 306 of the polymer-dispersed liquid crystal layer 130 having a large projection angle.

[0168] The polymer-dispersed liquid crystal (PDLC) material used in the first end portion 305A, the second end portion 305B, and the central portion 306 does not contain a chiral agent, but instead comprises a liquid crystal component, a polymerizable compound, and a polymerization initiator. Specifically, the liquid crystal material 323A contained in the central portion 206 and the liquid crystal material 323B contained in the first end portion 305A and the second end portion 305B are the same. The liquid crystal component, polymerizable compound, and polymerization initiator are the same as those used in the end portions of Example 1. Furthermore, the amounts of the polymerizable compound and polymerization initiator are equal to those used in the end portions of Example 1.

[0169] As in Example 1, electrodes 112 and 122 were formed on the surfaces of a pair of glass substrates, and alignment films 313 and 323 were formed on the surfaces of the electrodes 112 and 122 to produce a pair of substrates 310 and 320. The alignment films 313 and 323 were photo-alignment films.

[0170] The following uses Figure 12A and 12B The orientation treatment direction of the orientation film in Example 3 will be described. Figure 12A It is a schematic top view illustrating the alignment treatment method for a substrate used in Example 3. Figure 12B It is a schematic top view illustrating the alignment treatment method for another substrate used in Example 3. Figure 12A 31 is a schematic plan view of the substrate 310 when the substrate 310 is viewed from the alignment film 313 side. Figure 12B This is a schematic top view of the substrate 320 when the substrate 320 is viewed from the orientation film 323 side. Figure 12A and Figure 12B In the figure, the arrows indicate the direction of the alignment treatment.

[0171] like Figure 12A As shown, the alignment film 313 formed on the substrate 310 is subjected to photo-alignment treatment (ultraviolet irradiation) in the same direction in the regions corresponding to the first end 305A, the second end 305B, and the center 306. Specifically, the photo-alignment treatment is performed parallel to the longitudinal direction of the substrate 310.

[0172] like Figure 12B As shown, the alignment film 323 formed on the substrate 320 was photo-aligned in a direction parallel to and opposite to the direction of the alignment treatment performed on the region corresponding to the central portion 306 by the alignment film 313. The regions corresponding to the first end portion 305A and the second end portion 305B of the alignment film 323 were photo-aligned in an orientation 89° to the direction of the alignment treatment performed on the regions corresponding to the first end portion 305A and the second end portion 305B by the alignment film 313.

[0173] After dropping the above-mentioned PDLC material onto the alignment film 313 of the substrate 310, the substrates 310 and 320 were bonded together using the sealant 108 so that the alignment films 313 and 323 faced each other, thereby producing a liquid crystal cell. The central portion 306, the first end portion 305A, and the second end portion 305B of the obtained liquid crystal cell were irradiated with 50 mW / cm 2 , 2J / cm 2Ultraviolet rays (wavelength: 365 nm) are then applied. This ultraviolet irradiation cures the photopolymerizable compound, forming a polymer-dispersed liquid crystal layer 130 in which liquid crystal components 332A and 332B are dispersed within a polymer network 131. The thickness of polymer-dispersed liquid crystal layer 130 is set to 3 μm. Thus, a 19-inch liquid crystal panel 301 is completed. Figure 10 As shown, the width W1 of the first end portion 305A and the second end portion 305B is approximately 2 cm, and the width of the central portion 306 is approximately 36 cm.

[0174] The same light sources as those in Example 1 were spaced apart on the back of the obtained liquid crystal panel 301 to complete the display device of Example 3. The distance H between the first light source 102A and the second light source 102B and the liquid crystal panel 301 (thickness of the air layer) was set to about 5 cm. Figure 10 In the example shown, θ1 is set to approximately 12°, and θ2 is set to approximately 63°. That is, the angles of light emitted from the first light source 102A and the second light source 102B toward the first end portion 305A and the second end portion 305B are respectively greater than 0° and less than 12°, and the angles of light emitted from the first light source 102A and the second light source 102B toward the center portion 306 are respectively greater than 12° and less than 63°.

[0175] like Figure 10 As shown, in the transparent state when no voltage is applied, the liquid crystal component 332A contained in the central portion 306 and the polymer network 131 are aligned horizontally with respect to the surfaces of the pair of substrates 310 and 320 and along the longitudinal direction of the pair of substrates 310 and 330. In other words, the twist angle of the liquid crystal component in the central portion 306 is 0°.

[0176] On the other hand, the liquid crystal components 332A and polymer network 131 contained in the first end portion 305A and the second end portion 305B are twisted from the substrate 310 side toward the substrate 320. When the liquid crystal panel 301 is viewed from the normal direction, the orientation of the liquid crystal components 332B located near one substrate 310 forms an angle of 89° with the orientation of the liquid crystal components 332B located near the other substrate 320. In other words, the twist angle of the liquid crystal components 332B in the first end portion 305A and the second end portion 305B is 89°.

[0177] In the transparent state, there is almost no refractive index difference between the liquid crystal components 332A and 332B and the extraordinary light refractive index ne of the polymer network 131, and there is almost no refractive index difference between the liquid crystal components 332A and 332B and the normal light refractive index no of the polymer network 131, so the light irradiated from the light source passes through the polymer dispersed liquid crystal layer 130 and becomes a transparent state.

[0178] like Figure 11As shown, when a voltage is applied between electrodes 112 and 122, a longitudinal electric field is generated along the thickness direction of polymer-dispersed liquid crystal layer 130, causing liquid crystal components 332A and 332B to stand upright. Meanwhile, the orientation of polymer network 131 remains unchanged. Consequently, the refractive index difference between the liquid crystal components 332A and 332B and the extraordinary refractive index ne of polymer network 131, as well as the refractive index difference between the liquid crystal components 332A and 332B and the ordinary refractive index no of polymer network 131, increases, causing light irradiated from a light source to be scattered by polymer-dispersed liquid crystal layer 130.

[0179] The display device of Example 3 achieved a front contrast ratio of 5 or more and a luminance of 100 cd / m² in the central portion 306 of the liquid crystal panel 301 in the scattering state. 2 The brightness of the liquid crystal panel 301 is more than 5, and the front contrast ratio of 150cd / m 2 In Example 3, although the scattering at the edge is weaker than in Example 1, strong scattering can be obtained within the plane.

Claims

1. A display device, characterized in that: The invention comprises: a liquid crystal panel having a pair of substrates and a polymer dispersed liquid crystal layer sandwiched by the pair of substrates; and a light source arranged on the back side of the liquid crystal panel. The pair of substrates have electrodes for applying voltage to the polymer dispersed liquid crystal layer. The polymer dispersed liquid crystal layer comprises a polymer network and liquid crystal components dispersed in the polymer network. The light source is spaced apart from the liquid crystal panel via an air layer and is disposed along at least one outer edge of the liquid crystal panel to irradiate light toward the liquid crystal panel from an oblique direction. The polymer dispersed liquid crystal layer is controlled to be in a transparent state where the background is visible when no voltage is applied, and to be in a scattering state where the light incident from the light source is scattered when a voltage is applied. In a plan view, when a region of the polymer-dispersed liquid crystal layer closer to the light source is defined as an end portion and a region farther from the light source than the end portion is defined as a central portion, the end portion and the central portion each have an angular dependency in which the transmittance of light emitted from the front surface side in the scattering state varies depending on the angle of light incident from the rear surface side, and the angular dependency of the end portion is different from the angular dependency of the central portion. The refractive index anisotropy of the liquid crystal component contained in the central portion is higher than the refractive index anisotropy of the liquid crystal component contained in the end portions. The light source irradiates light to the end portion and the center portion from different angles.

2. The display device according to claim 1, wherein When no voltage is applied, the twist angle of the liquid crystal component included in the end portion is larger than the twist angle of the liquid crystal component included in the central portion.

3. The display device according to claim 1 or 2, characterized in that The polymer-dispersed liquid crystal layer in the central portion has a higher density of the polymer network than that in the polymer-dispersed liquid crystal layer in the end portions.

4. The display device according to claim 3, wherein: The polymer-dispersed liquid crystal layer in the central portion and the polymer-dispersed liquid crystal layer in the end portions both contain a chiral agent, and the polymer-dispersed liquid crystal layer in the end portions is thicker than the polymer-dispersed liquid crystal layer in the central portion.

5. The display device according to claim 1 or 2, characterized in that The electrodes are a pair of electrodes disposed on the sides of the pair of substrates facing the polymer-dispersed liquid crystal layer.

6. The display device according to claim 1 or 2, characterized in that: The light source includes light-emitting elements of multiple colors, and the light-emitting elements of multiple colors are driven in a field sequential manner of time-sharing lighting.

7. A display device, characterized in that: The invention comprises: a liquid crystal panel having a pair of substrates and a polymer dispersed liquid crystal layer sandwiched by the pair of substrates; and a light source arranged on the back side of the liquid crystal panel. The pair of substrates have electrodes for applying voltage to the polymer dispersed liquid crystal layer. The polymer dispersed liquid crystal layer comprises a polymer network and liquid crystal components dispersed in the polymer network. The light source is spaced apart from the liquid crystal panel via an air layer and is disposed along at least one outer edge of the liquid crystal panel to irradiate light toward the liquid crystal panel from an oblique direction. The polymer dispersed liquid crystal layer is controlled to be in a transparent state where the background is visible when no voltage is applied, and to be in a scattering state where the light incident from the light source is scattered when a voltage is applied. In a plan view, when a region of the polymer-dispersed liquid crystal layer closer to the light source is defined as an end portion and a region farther from the light source than the end portion is defined as a central portion, the end portion and the central portion each have an angular dependency in which the transmittance of light emitted from the front surface side in the scattering state varies depending on the angle of light incident from the rear surface side, and the angular dependency of the end portion is different from the angular dependency of the central portion. The polymer-dispersed liquid crystal layer contains a chiral agent at the end portions, and does not contain a chiral agent at the center portion. The light source irradiates light to the end portion and the center portion from different angles.

8. The display device according to claim 7, wherein: The polymer-dispersed liquid crystal layer in the central portion has a higher density of the polymer network than that in the polymer-dispersed liquid crystal layer in the end portions.

9. The display device according to claim 7 or 8, characterized in that The electrodes are a pair of electrodes disposed on the sides of the pair of substrates facing the polymer-dispersed liquid crystal layer.

10. The display device according to claim 7 or 8, characterized in that The light source includes light-emitting elements of multiple colors, and the light-emitting elements of multiple colors are driven in a field sequential manner of time-sharing lighting.

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