JP2013205565A - Lamination-type liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a reflection-type display panel that improves a display quality.SOLUTION: The lamination-type liquid crystal display element includes a first to third display panels 10B, 10G and 10R laminated in order from a display surface side. The first to third display panels have transparent electrodes 13B, 14B, 13G, 14G, 13R and 14R formed on a surface, have two transparent base materials 11B, 12B, 11G, 12G, 11R and 12R arranged so as to face the transparent electrode, and have liquid crystal layers 17B, 17G and 17R arranged between two transparent base materials. The transparent electrode is formed of a transparent conductive film or metal nano wire. The transparent electrode of the first display panel is formed of the transparent conductive film only. At least a part of the transparent electrodes of the second and third display panels is formed of the metal nano wire.

Description

  The disclosed embodiment relates to a multilayer liquid crystal display element.

  In the future, it is expected that electronic paper capable of holding a display even without a power source and capable of electrically rewriting display contents will be rapidly spread. Electronic paper aims to realize ultra-low power consumption that enables memory display even when the power is turned off, a reflective display that is easy on the eyes and does not get tired, and a flexible and thin display body that is flexible like paper. Research is underway. Applications of electronic paper include electronic books, electronic newspapers, electronic posters, and the like.

  Electronic paper is classified into an electrophoresis method, a twist ball method, an electrochemical method, a liquid crystal display, an organic EL display, and the like depending on the display method. The electrophoresis method is a method in which charged particles are moved in air or liquid. The twist ball method is a method of rotating charged particles that are color-coded in two colors. The electrochemical method is a display element having a structure in which a material that is colored, decolored, or discolored by an electrochemical reaction when an electric field is applied is sandwiched between electrodes. An organic EL display (organic electroluminescence display) is a self-luminous display having a structure in which a plurality of thin films made of an organic material are sandwiched between a cathode and an anode. A liquid crystal display (display element) is a non-self-luminous display having a structure in which a liquid crystal layer is sandwiched between a pixel electrode and a counter electrode.

  An advantageous method for color display of electronic paper is a liquid crystal method and an electrochemical method. Since these can be switched between a reflection mode and a transmission mode, they can be applied to a multilayer display element. For example, by stacking RGB three-color display panels, the pixel area can be utilized to the maximum, so that a bright, high-contrast, and good-color display is possible. In other methods, since light cannot be set to a transmission mode, when performing color display, it is necessary to divide each pixel by disposing color filters that are colored in three colors on the display surface. For this reason, it is inevitable that the brightness and saturation will be lower than those of the stacked type.

  In the multilayer liquid crystal display element, a cholesteric liquid crystal that selectively reflects light in a specific wavelength region is often used. However, since the reflection wavelength band of cholesteric liquid crystal is wide and includes light in an extra wavelength region, it has been proposed so far to insert a color filter for the purpose of color shift and noise reduction. For example, when the first to third liquid crystal layers are stacked in order from the display surface side, light near the reflection main wavelength of the first liquid crystal layer is absorbed between the first liquid crystal layer and the second liquid crystal layer, A first cut filter that transmits light in the vicinity of the reflection dominant wavelength of the third liquid crystal layer is disposed. As a result, light in the vicinity of the reflection main wavelength of the first liquid crystal layer that does not contribute to the display and has passed through the first liquid crystal layer is reduced. Further, a second cut filter is disposed between the second liquid crystal layer and the third liquid crystal layer, which absorbs light near the reflection main wavelength of the second liquid crystal layer and transmits light near the reflection main wavelength of the third liquid crystal layer. To do. Accordingly, light in the vicinity of the reflection main wavelength of the second liquid crystal layer that does not contribute to the display and is transmitted through the second liquid crystal layer is reduced. Since these measures are to remove noise of the reflected light of the liquid crystal layer, the color misalignment during color development can be corrected.

  However, the cause of color misregistration is not only the liquid crystal layer but also the reflection of the transparent electrode. For example, the transparent electrode is often designed to have a spectral characteristic that transmits light in the green wavelength region with high visibility to the human eye. In such a case, since the transparent electrode reflects magenta colors including blue and red, the color of the display is changed. In particular, the black display has a display color in which magenta is added. In a state where the liquid crystal layer is in a reflective state and colored, color correction can be performed by adjusting the reflectance of the liquid crystal layer. However, since the reflective color of the transparent electrode remains, when the liquid crystal layer is displayed in black in a non-reflective state (transmission state) on a panel having a black layer on the back side, the reflective color of the electrode remains, and the red color or red Colors such as bluish color are attached and the quality of black display is degraded. For this reason, it is desired to improve the contrast by making the display have a desired color and reducing the reflection during black display.

JP 2010-507199 A JP 2009-251274 A

  According to the embodiment, it is possible to realize a reflective display panel that reduces reflected light of a specific wavelength by a transparent electrode, performs high-quality display, and improves contrast.

  The multilayer liquid crystal display element of the embodiment includes first to third display panels that are sequentially stacked from the display surface side. Each of the first to third display panels has a transparent electrode formed on the surface thereof, two transparent substrates disposed so that the transparent electrodes face each other, and a liquid crystal layer disposed between the two transparent substrates. Have. The transparent electrode is formed of a transparent conductive film or metal nanowire. The transparent electrode of the first display panel is formed of only a transparent conductive film, and at least some of the transparent electrodes of the second display panel and the third display panel are formed of metal nanowires.

  According to the embodiment, it is possible to realize a reflective multilayer display panel that performs high-quality display close to an achromatic color including black display and has improved contrast.

FIG. 1 is a diagram showing a schematic structure and a display principle of a multilayer liquid crystal display element using a cholesteric liquid crystal. FIG. 2 is a diagram showing the ratio of the locations where reflected light is generated when white display and black display are performed on a general laminated electronic paper, where (A) is white display and (B) is black display. This case is shown. FIG. 3 is a schematic diagram showing the state of reflection and scattering when an opposing electrode is formed of an IZO film and a metal nanowire in a single-layer cholesteric liquid crystal panel, and interfacial spectral reflectance and scattering spectral reflection. It is a figure which shows a rate. FIG. 4 shows a schematic structure in which two transparent electrodes facing each other across the liquid crystal layers of three panels are formed of metal nanowires in a multilayer liquid crystal display element using cholesteric liquid crystal, and white display and black display It is a figure which shows the ratio of the generation | occurrence | production location of the reflected light in performing. FIG. 5 is a diagram for explaining the difference in the generation of reflected light by the electrode of the transparent conductive film and the electrode of the metal nanowire in the multilayer liquid crystal display element. FIG. 6 is a diagram illustrating a schematic structure of the multilayer liquid crystal display element using the cholesteric liquid crystal according to the first embodiment and the ratio of the locations where reflected light is generated when white display and black display are performed. FIG. 7 is a diagram illustrating a schematic structure of a multilayer liquid crystal display element using a cholesteric liquid crystal according to the second embodiment, and a ratio of locations where reflected light is generated when white display and black display are performed. FIG. 8 is a diagram illustrating a schematic structure of a multilayer liquid crystal display element using cholesteric liquid crystal according to the third embodiment, and a ratio of locations where reflected light is generated when white display and black display are performed. FIG. 9 is a diagram illustrating a schematic structure of a multilayer liquid crystal display element using cholesteric liquid crystal according to the fourth embodiment, and a ratio of locations where reflected light is generated when white display and black display are performed. FIG. 10 shows a panel of a multi-layer liquid crystal display element according to an embodiment, in which a metal nanowire electrode is formed on a substrate (lower substrate) opposite to the display surface, and a liquid crystal layer is disposed thereon. FIG. FIG. 11 is a diagram illustrating a distribution example of a plurality of metal nanowires when the belt-like electrode is viewed from the side in contact with the liquid crystal layer. FIG. 12 is a diagram for explaining a method of placing a metal nanowire on the strip electrode so that the major axis of the metal nanowire forms an angle of 45 degrees or less with the major axis of the strip electrode. FIG. 13 is a diagram showing a schematic configuration of a display device using the multilayer liquid crystal display elements of the first to fourth embodiments. FIG. 14 is a diagram showing a cross-sectional structure of the entire multilayer liquid crystal display element of the first to fourth embodiments.

FIG. 1 is a diagram showing a schematic structure and a display principle of a multilayer liquid crystal display element using a cholesteric liquid crystal.
As shown in FIG. 1, the multilayer liquid crystal display element 10 is arranged in the order of a blue panel 10B, a green panel 10G, and a red panel 10R from the display surface side. The blue (B) cut filter 21 is positioned between the blue panel 10B and the green panel 10G, and the green (G) cut filter 22 is positioned between the green panel 10G and the red panel 10R. Furthermore, the light absorption layer 15 is disposed on the back surface of the red panel 10R.

  The multilayer liquid crystal display element uses external light as a light source, and light having a specific wavelength is reflected by a panel in a planar (PL) state from light incident on the display surface from the viewer side outside the panel. This is called selective reflection. The blue, green, and red panels selectively reflect light in wavelength bands corresponding to blue (B), green (G), and red (R), respectively, in the planar state. For example, the blue panel 10B selectively reflects light near the wavelength of about 480 nm, the green panel 10G selectively reflects light near the wavelength of about 560 nm, and the red panel 10R selects light near the wavelength of about 650 nm. reflect. The center wavelength of the wavelength band that each panel selectively reflects is referred to as a reflection dominant wavelength. Various displays are realized by additive color mixing of light reflected by each panel.

  Further, the light absorption layer 15 is disposed at a position farthest from the display surface, and all light transmitted through each panel is finally absorbed by the light absorption layer 15. Therefore, the display when all of the blue, green, and red panels are in the focal conic (FC) state is black (Bk) because light is not reflected.

  Of the light transmitted through the blue panel 10 </ b> B, light in the blue wavelength band is light that is not used for display, and is finally absorbed by the light absorption layer 15. However, when the light is reflected or scattered by the green panel 10G and the red panel 10R, problems such as a reduction in display contrast and color purity occur. On the other hand, light in the wavelength bands of green and red other than blue out of the light transmitted through the blue panel 10B is controlled to be reflected or transmitted by the green panel 10G and the red panel 10R, and thus passes through the B cut filter 21. There is a need. Therefore, the B-cut filter 21 has a characteristic of absorbing only light in an unnecessary blue wavelength band that has been transmitted through the blue panel 10B and transmitting light in other wavelength bands. Similarly, the G cut filter 22 absorbs unnecessary green wavelength band light transmitted through the green panel 10G, but may absorb blue wavelength band light because it is not used. As described above, the color cut filter disposed between the panels absorbs light in a wavelength band whose reflection is controlled by the panel closer to the display surface than the color cut filter, and is disposed on the far side from the display surface. The panel has a characteristic of transmitting light in a wavelength band in which reflection is controlled.

  Note that the arrangement order of the three panels is not limited to this, and various combinations are possible according to the characteristics of the panels. For example, the green panel 10G, the blue panel 10B, and the red panel 10R may be arranged in this order from the display surface side. In that case, the G cut filter is disposed between the green panel 10G and the blue panel 10B, and the B cut filter is disposed between the blue panel 10B and the red panel 10R. Here, the arrangement order of the blue panel 10B, the green panel 10G, and the red panel 10R from the most common display surface side will be described as an example.

  The blue liquid crystal panel 10B has a structure in which a cholesteric liquid crystal layer 17B is sandwiched between two base materials 11B and 12B such as a film. Transparent electrodes 13B and 14B for applying a voltage to the liquid crystal layer 17B are formed on the opposing surfaces of the two upper and lower substrates 11B and 12B, and the threshold of pixels in the liquid crystal panel and the gap adjustment between the substrates are adjusted. Therefore, a lattice-like wall surface is arranged in the in-plane direction of the liquid crystal panel. The above-described panel configuration is the same for the green liquid crystal panel 10G and the red liquid crystal panel 10R.

  The transparent electrode of each panel is made of a material with a high refractive index, such as ITO. Therefore, reflection occurs at the interface between the substrate with a low refractive index and the liquid crystal layer, and the spectral reflectance changes depending on the material and thickness. To do. For example, the refractive index of ITO is about 2.0, the refractive index of polycarbonate used as a substrate is about 1.6, and the refractive index of cholesteric liquid crystal is also about 1.6.

  FIG. 2 is a diagram showing the ratio of the locations where reflected light is generated when white display and black display are performed on a general laminated electronic paper, where (A) is white display and (B) is black display. This case is shown.

  As shown in FIG. 2, it can be seen that the reflected light in the white display is mainly formed by the light reflected by the liquid crystal layers of the blue panel, the green panel, and the red panel. On the other hand, the reflected light in the black display is formed by the light reflected by the green panel electrode and the red panel electrode in addition to the light reflected by the blue-green-red liquid crystal layer.

  In the multilayer electronic paper, it is desired to increase the contrast ratio in order to improve display performance, and it is desirable to further darken the black display. For this purpose, the light reflected by each member must be reduced. However, since adjustment of the liquid crystal is concerned about the influence on white display, in the embodiment, the reflected light generated in the electrode layer is suppressed.

  In recent years, metal nanowires have been put into practical use and proposed to be used for transparent electrodes of liquid crystal display devices. Therefore, the use of metal nanowires for the transparent electrode of the multilayer liquid crystal display element was studied.

  FIG. 3 is a schematic diagram showing the state of reflection and scattering when an opposing electrode is formed of an IZO film and a metal nanowire in a single-layer cholesteric liquid crystal panel, and interfacial spectral reflectance and scattering spectral reflection. It is a figure which shows a rate. 3A shows the state of reflection and scattering in the case of the electrode of the IZO film, and FIG. 3B shows the state of reflection and scattering in the case of the electrode of the metal nanowire. FIG. 3C shows the interfacial spectral reflectance when IZO is an IZO film electrode and the interfacial spectral reflectance when MNW is a metal nanowire electrode. The interfacial spectral reflectance is, for example, an angle close to vertical. It is the spectral characteristic of the specular reflection component of the light which entered in. FIG. 3D shows the scattered spectral reflectance when IZO is an electrode of an IZO film and the scattered spectral reflectance when MNW is an electrode of a metal nanowire. The scattered spectral reflectance is, for example, an angle close to vertical. This is the spectral characteristic of the reflected light excluding the regular reflection component of the light incident at.

  In the transparent conductive film electrode generally used in electronic paper such as IZO film, scattering at the electrode layer does not occur. large. Therefore, the light scattered in the liquid crystal is reflected at the electrode interface. On the other hand, since the metal nanowire electrode uses a fine metal nanowire that is transparent to visible light, interface reflection does not occur at the electrode interface. However, the metal nanowire electrode scatters light because the nano-sized wires are arranged in a network. Therefore, there is a problem that the electrode layer itself is scattered.

  As described above, the metal nanowire electrode has a problem of light scattering but has an advantage of no interface reflection. Thus, it is conceivable to use metal nanowire electrodes to reduce interface reflection.

  FIG. 4 shows a schematic structure in which two transparent electrodes facing each other across the liquid crystal layers of three panels are formed of metal nanowires in a multilayer liquid crystal display element using cholesteric liquid crystal, and white display and black display It is a figure which shows the ratio of the generation | occurrence | production location of the reflected light in performing. 4A shows the schematic structure of the multilayer liquid crystal display element, FIG. 4B shows the ratio of the locations where reflected light is generated when white display is performed, and FIG. 4C shows black display. The ratio of the places where the reflected light is generated is shown. 4B and 4C, the solid line indicated by MNW indicates the ratio in the case of the stacked liquid crystal display element having the structure of FIG. 4A, and the broken line indicated by IZO indicates the three panels. The ratio in the case where two transparent electrodes facing each other with each liquid crystal layer interposed therebetween is formed of an IZO film is shown. The graphs of FIGS. 4B and 4C show the total reflected light of white display and black display as 1 when all the transparent electrodes are formed of the IZO film, and the ratio is shown as 1. Similarly, when all the transparent electrodes are formed of metal nanowires, the total reflected light when all the transparent electrodes are formed of an IZO film is set to 1, and the ratio is shown.

  As shown in FIG. 4B, in white display, the difference in the ratio of reflected light is small between the case where the transparent electrode is formed of an IZO film and the case where the transparent electrode is formed of a metal nanowire. In contrast, in black display, the light generated (reflected) from the blue and green panel electrodes is greater when the transparent electrode is formed of metal nanowires than when the transparent electrode is formed of an IZO film. . This is considered to be due to scattering of the metal nanowire itself.

  Further, in the red panel electrode, the generation of reflected light is smaller when the transparent electrode is formed of metal nanowires than when the transparent electrode is formed of an IZO film. This is because the scattered light generated by the metal nanowire has a smaller influence on the display than the light generated by the interface reflection of the transparent conductive film electrode.

  Furthermore, in the multilayer liquid crystal display element having the cross-sectional structure shown in FIG. 4A, black display is obtained when all the transparent electrodes are formed of metal nanowires than when all the transparent electrodes are formed of IZO films. It turned out that the contrast was reduced by 20%. As described above, it was found that in the multilayer liquid crystal display element, good display characteristics cannot be obtained only by replacing the transparent electrode of the IZO film with the transparent electrode of the metal nanowire.

  In the multilayer liquid crystal display element of the embodiment described below, the display characteristics are improved by balancing the interface reflection and scattering at the electrode layer by combining the electrode of the transparent conductive film and the electrode of the metal nanowire.

  FIG. 5 is a diagram for explaining the difference in the generation of reflected light by the electrode of the transparent conductive film and the electrode of the metal nanowire in the multilayer liquid crystal display element. In FIG. 5A, two transparent electrodes facing each other with the liquid crystal layer of the blue panel on the display surface side are formed of a transparent conductive film, and two transparent electrodes facing each other with the liquid crystal layer of the second green panel interposed therebetween. The case where an electrode is also formed with a transparent conductive film is shown. In FIG. 5B, two transparent electrodes facing each other with the liquid crystal layer of the blue panel on the display surface side are formed of a transparent conductive film, and two transparent electrodes facing each other with the liquid crystal layer of the second green panel interposed therebetween. The case where an electrode is formed with the electrode of metal nanowire is shown.

  As shown in FIG. 5A, part of the light incident on the multilayer liquid crystal display element is reflected by the blue panel, partly scattered by the blue panel, and partly transmitted through the blue panel. The reflection at the blue liquid crystal layer and the reflection at the interface of the transparent electrode of the blue panel are as described above. A part of the light scattered by the blue panel is reflected on the display surface, but the remaining light is incident on the second green panel and is reflected toward the display surface at the interface of the transparent electrode of the green panel. As described above, since the transparent electrode reflects magenta colors including blue and red, the color of the display is changed. This phenomenon is the same for the scattered light that is transmitted through the green panel and incident on the red panel, and the same is true for the light that is scattered on the green panel and incident on the red panel.

  As shown in FIG. 5B, the light incident on the multilayer liquid crystal display element and scattered by the blue panel is incident on the second green panel, but the transparent electrode of the green panel is formed of metal nanowires. Therefore, interface reflection by the transparent electrode does not occur.

  When the transparent electrode of the blue panel on the display surface side is an electrode of a metal nanowire, it is considered that the influence of scattering by the metal nanowire is large. When the transparent electrodes of the second and subsequent panels are formed of metal nanowires, even if light scattered by the panel on the observation surface side enters the second and subsequent panels, the interface reflection by the transparent electrode does not occur. It is thought that the taste does not change.

  Based on the above, in the multilayer liquid crystal display element of the embodiment, with respect to the arrangement of the transparent electrode, a nanowire electrode is used for the transparent electrode far from the display surface, and the transparent electrode of the conductive film is used for the transparent electrode close to the display surface side. The basic policy is to use.

  A multilayer liquid crystal display element generally has three panels, and each panel has two transparent electrodes facing each other with a liquid crystal layer interposed therebetween, and thus has a total of six transparent electrodes. There are various configurations as to which of the six is to be a nanowire electrode, and there are configurations in which display characteristics are improved and configurations that are deteriorated as compared with the case where all are made transparent electrodes of a conductive film. A configuration example with improved display characteristics will be described below.

  FIG. 6 is a diagram illustrating a schematic structure of the multilayer liquid crystal display element using the cholesteric liquid crystal according to the first embodiment, and a ratio of locations where reflected light is generated when white display and black display are performed. It is a figure to do. FIG. 6A shows a schematic structure of the multilayer liquid crystal display element of the first embodiment. FIG. 6B shows the ratio of the locations where reflected light is generated when white display is performed, and FIG. 6C shows the ratio of the locations where reflected light is generated when black display is performed. 6B and 6C, the solid line indicated by MNW indicates the ratio in the case of the multilayer liquid crystal display element of the first embodiment, and the broken line indicated by IZO indicates the liquid crystal layers of the three panels. The ratio in the case where all of the two transparent electrodes facing each other are formed of an IZO film is shown. The graphs of FIGS. 6B and 6C show the total reflected light of white display and black display when all the transparent electrodes are formed of the IZO film as 1, and the ratio is shown as 1. Similarly, when all the transparent electrodes are formed of metal nanowires, the total reflected light when all the transparent electrodes are formed of an IZO film is set to 1, and the ratio is shown. In the following description, the case where all the transparent electrodes are formed of an IZO film is referred to as a conventional example.

  As shown in FIG. 6A, in the multilayer liquid crystal display element of the first embodiment, the transparent electrodes 13B and 14B of the blue panel on the display surface side are formed of a transparent conductive film. The transparent electrodes 13G and 14G and 13R and 14R of the second and third green and red panels are formed of metal nanowires.

  As shown in FIGS. 6B and 6C, in the multilayer liquid crystal display element of the first embodiment, the reflected light generated from the electrodes of the green panel in black display is larger than in the conventional example. This is because the influence of scattering of the metal nanowire itself is larger than the reflection of the conductive film. In addition, the red panel electrode generates less reflected light than the conventional example. As a whole, the multilayer liquid crystal display element of the first embodiment has an improved contrast ratio of about 1% compared to the conventional example.

  FIG. 7 is a diagram showing a schematic structure of a multilayer liquid crystal display element using a cholesteric liquid crystal according to the second embodiment, and a ratio of locations where reflected light is generated when white display and black display are performed. 6 corresponds to FIG. FIG. 7A shows a schematic structure of the multilayer liquid crystal display element of the second embodiment. FIG. 7B shows the ratio of the places where reflected light is generated when white is displayed, and FIG. 7C shows the ratio of the places where reflected light is generated when black is displayed. The illustrated symbols and ratios are the same as those in the first embodiment.

  As shown in FIG. 7A, in the multilayer liquid crystal display element of the second embodiment, the transparent electrodes 13B and 14B of the blue panel on the display surface side and the transparent electrode 13G on the display surface side of the second green panel. Is formed of a transparent conductive film. The transparent electrode 14G opposite to the display surface of the second green panel and the transparent electrodes 13R and 14R of the third red panel are formed of metal nanowires.

  As shown in FIGS. 7B and 7C, in the multilayer liquid crystal display element according to the second embodiment, the reflected light generated from the electrode far from the display surface of the green panel in black display is larger than in the conventional example. . However, the red panel electrode generated less light than the conventional example, and the contrast ratio was finally improved by about 3% compared to the conventional example.

  FIG. 8 is a diagram showing a schematic structure of the multilayer liquid crystal display element using the cholesteric liquid crystal according to the third embodiment and the ratio of the locations where reflected light is generated when white display and black display are performed. FIG. 8 corresponds to FIG. 6 and FIG. 7. FIG. 8A shows a schematic structure of the multilayer liquid crystal display element of the third embodiment. 8B shows the ratio of the locations where the reflected light is generated when white display is performed, and FIG. 8C shows the ratio of the locations where the reflected light is generated when black is displayed. The illustrated symbols and ratios are the same as those in the first embodiment.

  As shown in FIG. 8A, in the multilayer liquid crystal display element of the third embodiment, the blue panel and the green transparent electrodes 13B and 14B and 13G and 14G on the display surface side are transparent conductive films, The transparent electrodes 13R and 14R of the red panel of the eyes are formed of metal nanowires.

  As shown in FIGS. 8B and 8C, in the multilayer liquid crystal display element of the third embodiment, the red panel electrode for black display generates less reflected light than the conventional example, and the contrast ratio. Improved by about 8%.

  FIG. 9 is a diagram showing a schematic structure of a multilayer liquid crystal display element using a cholesteric liquid crystal according to the fourth embodiment, and a ratio of locations where reflected light is generated when white display and black display are performed. FIG. 9 is a diagram corresponding to FIGS. 6 to 8. FIG. 9A shows a schematic structure of the multilayer liquid crystal display element of the fourth embodiment. FIG. 9B shows the ratio of the places where reflected light is generated when white is displayed, and FIG. 8C shows the ratio of the places where reflected light is generated when black is displayed. The illustrated symbols and ratios are the same as those in the first embodiment.

  As shown in FIG. 9A, in the multilayer liquid crystal display element of the third embodiment, the transparent electrodes 13B and 14B of the blue panel on the display surface side, and the second and third green and red panels. The transparent electrodes 13G and 14G on the display surface side are formed of a transparent conductive film. The transparent electrodes 14G and 14R opposite to the display surfaces of the second and third green and red panels are formed of metal nanowires.

  As shown in FIGS. 9B and 9C, in the multilayer liquid crystal display element of the fourth embodiment, the transparent electrode 14R on the side opposite to the display surface of the red panel in black display reflects light more than the conventional example. The occurrence of is reduced. On the other hand, the generation of reflected light is greater in the transparent electrode 14G on the side opposite to the display surface of the green panel than in the conventional example. The contrast ratio was improved by about 1%.

  From the display characteristics of the embodiment described above, by using a transparent conductive film without scattering on the transparent electrode close to the display surface, scattering at the transparent electrode can be suppressed, and metal nanowires are used for the transparent electrode far from the display surface. It was found that the effect of scattering on the display was reduced. Further, since the metal nanowire electrode does not cause interface reflection, the generation of scattered light can be suppressed, so that it can be said that the black display performance can be improved.

  Next, a method for forming a metal nanowire electrode will be described. Since the conventional manufacturing method is applied to the formation method other than the metal nanowire electrode of the multilayer liquid crystal display element, the description is omitted.

  FIG. 10 shows a single panel of the multilayer liquid crystal display element according to the embodiment, in which a metal nanowire electrode is formed on a base material (lower base material) 12 opposite to the display surface, and a liquid crystal layer 17 is formed thereon. It is a figure which shows the state arrange | positioned. 10A is a cross-sectional view, and FIG. 10B is a top view when viewed from the side in contact with the liquid crystal layer 17.

  As shown in FIG. 10A, a plurality of metal nanowires 30 having a diameter of 300 nm or less are placed on the substrate 12, and the liquid crystal layer 17 is arranged.

  The diameter of the metal nanowire 30 is 300 nm or less, and the influence of the metal nanowire 30 on the optical characteristics of the display element can be reduced by using a wire having such a diameter of a visible light wavelength or less. The metal nanowire 30 has a length of 2 μm to 10 μm. The metal nanowire 30 is realized by, for example, a silver nanowire, a gold nanowire, a platinum nanowire, or a carbon nanotube. Therefore, the metal nanowire 30 is highly conductive and has a very low line resistance.

  As shown in FIG. 10B, the metal nanowire 30 is placed on the substrate 12. The metal nanowires 30 are entangled with each other.

  As shown in FIG. 10A, the metal nanowires 30 are placed so that the height from the surface of the substrate 12 is about several μm at the maximum, for example. This is realized by mixing the metal nanowires 30 with the coating material, forming the coating material layer with a predetermined thickness, and then removing the coating material, and pressing the metal nanowires 30 against the substrate 12 as necessary. Etc. may be performed. The plurality of placed metal nanowires 30 can be regarded as forming one layer. The sheet resistance of this layer varies depending on the density of the metal nanowires 30. By applying a voltage to the ends of the entangled metal nanowires 30, it is possible to apply a voltage to the liquid crystal layer 17 in contact with the metal nanowires 30.

  In a display element that performs passive matrix display, a plurality of strip electrodes extending in a strip shape in one direction (major axis direction) are formed on a substrate.

  FIG. 11A shows an example of the distribution of the plurality of metal nanowires 30 when the strip electrode 18 is viewed from the side in contact with the liquid crystal layer 17. As shown to (A) of FIG. 11, the some metal nanowire 30 is distributed at random, and the extending | stretching direction (major axis) of each metal nanowire 30 is also random.

  Although the voltage drop in the minor axis direction does not matter for each strip electrode 18, the voltage drop in the major axis direction is a problem, and it is desirable that the sheet resistance in the major axis direction be a predetermined value or less. Therefore, it is conceivable to increase the density of the metal nanowires 30 to reduce the sheet resistance. However, if the density of the metal nanowires 30 becomes too high, the haze value increases as described above, and the brightness during black display is reduced. It gets bigger.

  FIG. 11B is a top view of one strip electrode 18 formed on the base material when the metal nanowires 30 are arranged with directionality, and is viewed from the side in contact with the liquid crystal layer 17. The example of distribution of several metal nanowire 30 of this is shown.

  In each strip electrode 18, when viewed from the side in contact with the liquid crystal layer 17, a plurality of metal nanowires 30 are distributed as shown in FIG. That is, in contrast to the distribution in which the extending direction (long axis) of each metal nanowire 30 as shown in FIG. 11A is random, the distribution in FIG. The angle formed with the long axis of the strip electrode 18 is 45 degrees or less. Thereby, the sheet resistance in the major axis direction combining the plurality of metal nanowires 30 and the transparent flat plate electrode 12 is reduced, and the voltage drop is reduced in the major axis direction of the strip electrode 18. When realizing the same area resistance in the long axis direction, the density of the metal nanowires 30 can be reduced as compared with the case where the metal nanowires 30 are oriented in a random direction.

  In addition, the shape of each metal nanowire 30 is random, and the extending direction (long axis) of each metal nanowire 30 is expressed by the direction of a straight line when approximated to a straight line extending in one direction by, for example, the least square method. Can do.

  FIG. 12 shows a method of placing the metal nanowire 30 on the strip electrode 18 so that the major axis of each metal nanowire 30 forms an angle of 45 degrees or less with the major axis of the strip electrode 18 as shown in FIG. It is a figure explaining.

  Although only one strip electrode 18 is shown in FIG. 12, a plurality of strip electrodes 18 are actually formed in parallel. A slit coater (coating apparatus) 31 is moved on the strip electrode 18 at a constant speed, and a dispersion liquid containing metal nanowires 30 such as silver nanowires is applied to form a thin film. At this time, the gap between the strip electrode 18 and the coater 31 is narrowed, and the metal nanowire 30 is applied at a moving speed and a film thickness at which an appropriate shear stress is generated. Thereby, immediately after coating, the major axis of the metal nanowire 30 is aligned so as to approach the moving direction of the coater 31, that is, the major axis direction of the strip electrode 18. When a dryer 32 that moves in the same manner as the coater 31 is provided immediately after the coater 31 and the solution is dried with warm air, the metal nanowire 30 has an angle of 45 degrees or less with the major axis of the strip electrode 18. It is fixed in an established state.

Next, a display device using the multilayer liquid crystal display element using the cholesteric liquid crystal according to the first to fourth embodiments will be described.
FIG. 13 is a diagram showing a schematic configuration of a display device using the multilayer liquid crystal display elements of the first to fourth embodiments. FIG. 14 is a diagram showing a cross-sectional structure of the entire multilayer liquid crystal display element of the first to fourth embodiments.

The display device includes a multilayer display panel 10 using cholesteric liquid crystal, a scan electrode drive circuit 41, and a data electrode drive circuit.
The multilayer liquid crystal display element 10 has a configuration in which three display panels using cholesteric liquid crystal are stacked and a light absorption layer 15 is provided on the back side. The cross-sectional structure of the multilayer liquid crystal display element 10 corresponds to the cross section of the multilayer liquid crystal display elements of the first to fourth embodiments shown in FIGS. 6A to 9A. In the following description, in order to simplify the description, description will be made with reference numerals excluding B, G, and R indicating blue, green, and red.

The display surface of the multilayer display panel 10 has a surface-side functional layer 50 bonded with a transparent adhesive layer 18. The surface-side functional layer 50 functions as an AR (Anti Reflection) layer and a protective film.
The three laminated panels have the same configuration, and are different in that the reflection dominant wavelengths are 480 nm (blue), 550 nm (green), and 650 nm (red), respectively. Three panels are laminated | stacked in order of a blue panel, a green panel, and a red panel in order from the observation side.

  The display panel 10 has an upper substrate 11 on which a plurality of parallel scanning electrodes 13 are formed and a lower substrate 12 on which a plurality of parallel data electrodes 14 are formed facing each other, and a liquid crystal is filled between the substrates. Has the structure.

  The plurality of scanning electrodes 13 and the plurality of data electrodes 14 are transparent electrodes and are arranged so as to be orthogonal when viewed from a direction perpendicular to the base material. A region where the scanning electrode 13 and the data electrode 14 intersect is a pixel region. become. Accordingly, the plurality of pixel electrodes are arranged in a matrix. A sealing material 16 is provided between the upper base material 11 and the lower base material 12 so as to surround the pixel region, and an internal space surrounded by the sealing material 16 is filled with a cholesteric liquid crystal material to form a liquid crystal layer 17. The Reference numeral 20 is an injection port for filling the internal space surrounded by the sealing material 16 with the cholesteric liquid crystal material, and is sealed after the injection of the cholesteric liquid crystal material.

  The scan electrode drive circuit 41 is mounted with a general-purpose STN driver IC having a TCP (tape carrier package) structure, for example, and drives the plurality of scan electrodes 13. The output terminal of the scan electrode drive circuit 41 is connected to the plurality of scan electrodes 13 by wiring 43 formed in the flexible circuit. The data electrode drive circuit 42 is mounted with a general-purpose STN driver IC having a TCP structure, and drives the plurality of data electrodes 14. The output terminal of the data electrode driving circuit 42 is connected to the plurality of running data electrodes 14 by wiring 44 formed in the flexible circuit. Although a circuit for supplying power and control signals to the scan electrode drive circuit 41 and the data electrode drive circuit 42 is provided, illustration is omitted. Although it is possible to provide three scan electrode drive circuits 41 according to the three panels, one scan electrode drive circuit 41 is provided and the scan electrodes 13 of the three panels are driven in common. Is also possible.

  A modification in which the data electrode 14 is formed on the upper substrate 11 and the scanning electrode 13 is formed on the lower substrate 12 is also possible.

  The liquid crystal material is a cholesteric liquid crystal obtained by adding 10 to 40% by weight of a chiral material to a nematic liquid crystal mixture. The addition ratio of the chiral material 0 is a value when the total amount of the nematic liquid crystal component and the chiral material is 100% by weight. The color of the reflected light and other various characteristics are determined by the mixing ratio of the nematic liquid crystal component and the chiral material.

  As the nematic liquid crystal component, known components can be used, but in order to relatively reduce the driving voltage of the liquid crystal layer 22, it is desirable that the dielectric anisotropy Δε is 20 ≦ Δε ≦ 50. The refractive index anisotropy Δn of the cholesteric liquid crystal is preferably 0.18 ≦ Δn ≦ 0.24. When the refractive index anisotropy Δn is smaller than this range, the reflectivity of the liquid crystal layer 17 in the planar state becomes low. On the other hand, if the refractive index anisotropy Δn is larger than this range, the scattering reflection of the liquid crystal layer 17 in the focal conic state increases, and the viscosity also increases, so the response speed decreases.

  The upper substrate 11 and the lower substrate 12 are formed of a transparent substrate. Examples of such a substrate include glass or a resin substrate. For example, a glass substrate such as quartz glass, soda glass, or borosilicate glass can be used. Furthermore, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polysulfone (PSF), ZEONOR, ZEONEX (manufactured by Nippon Zeon Co., Ltd.) can be used. Furthermore, cycloolefin resins represented by product brands such as Arton (manufactured by JSR) can be used.

  The scanning electrode 13 and the data electrode 14 formed of a transparent conductive film can be formed of a known material in addition to the above-mentioned indium zinc oxide (IZO). For example, indium tin oxide (ITO), an oxide-based transparent conductive film such as tin oxide, a metal electrode such as aluminum or silicon, or a photoconductive film such as amorphous silicon can be used. The scan electrode 13 and the data electrode 14 formed of metal nanowires are manufactured by the method described above.

  In the multilayer display element 10, the liquid crystal layer 17 is applied with a voltage between the scanning electrode 13 and the data electrode 14, so that for each pixel, the planar state reflects incident light and the focal conic state transmits incident light. Can be set.

  Therefore, as shown in FIG. 14, the blue panel has an upper substrate 11B on which a plurality of parallel scanning electrodes 13B are formed and a lower substrate 12B on which a plurality of parallel data electrodes 14B are formed facing each other. The liquid crystal layer 17B is formed by filling the liquid crystal between the substrates. A sealing material 16B is provided between the upper base material 11B and the lower base material 12B so as to surround the pixel region. The internal space surrounded by the sealing material 16B is filled with a cholesteric liquid crystal material, and the blue liquid crystal layer 17B is formed. It is formed.

  Similarly, in the green panel, an upper base material 11G in which a plurality of parallel scanning electrodes 13G are formed and a lower base material 12G in which a plurality of parallel data electrodes 14G are formed face each other, and a liquid crystal is interposed between the base materials. And a liquid crystal layer 17G is formed. A sealing material 16G is provided between the upper base material 11G and the lower base material 12G so as to surround the pixel region. The internal space surrounded by the sealing material 16G is filled with a cholesteric liquid crystal material, and the green liquid crystal layer 17G is formed. It is formed.

  Further, the red panel has an upper base material 11R on which a plurality of parallel scanning electrodes 13R are formed and a lower base material 12R on which a plurality of parallel data electrodes 14R are formed so as to face each other, and a liquid crystal is disposed between the base materials. The liquid crystal layer 17R is formed by filling. A sealing material 16R is provided between the upper base material 11R and the lower base material 12R so as to surround the pixel region. The internal space surrounded by the sealing material 16R is filled with a cholesteric liquid crystal material, and the red liquid crystal layer 17R is formed. It is formed.

  The blue panel, the green panel, and the red panel exhibit a reflection spectrum of blue, green, and red, respectively, when in a reflective state, and the respective reflection dominant wavelengths are 480 nm (blue), 550 nm (green), and 650 nm (red). It is.

  In order to keep the thickness (cell gap) of the liquid crystal layer 17 uniform, spherical spacers made of resin or inorganic oxide are dispersed over the entire display surface.

  The first blue panel and the second green panel are bonded by a blue (B) cut filter 21 having an adhesive function. The green panel of the second layer and the red panel of the third layer are bonded by a green (G) cut cut filter 22 having an adhesive function.

  The passive liquid crystal display device has been described above as an example, but the element structures of the first to fourth embodiments can be applied to an active liquid crystal display device.

  The embodiment has been described above, but all examples and conditions described herein are described for the purpose of helping understanding of the concept of the invention applied to the invention and technology. In particular, the examples and conditions described are not intended to limit the scope of the invention, and the construction of such examples in the specification does not indicate the advantages and disadvantages of the invention. Although embodiments of the invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made without departing from the spirit and scope of the invention.

10B Blue display panel 10G Green display panel 10R Red display panel 11, 12 Base material 13, 14 Transparent electrode 17 Liquid crystal layer 21 Blue (B) cut filter 22 Green (G) cut filter 30 Metal nanowire

Claims (6)

Comprising first to third display panels stacked in order from the display surface side;
Each of the first to third display panels has a transparent electrode formed on the surface thereof, and is disposed between the two transparent substrates disposed so that the transparent electrodes face each other, and the two transparent substrates. A liquid crystal layer,
The transparent electrode is formed of a transparent conductive film or metal nanowire,
The transparent electrode of the first display panel is formed only of the transparent conductive film,
At least a part of the transparent electrodes of the second display panel and the third display panel is formed of the metal nanowires.   The multilayer liquid crystal display element according to claim 1, wherein all of the transparent electrodes of the second display panel and the third display panel are formed of the metal nanowires.   2. The multilayer liquid crystal display element according to claim 1, wherein the transparent electrode on the opposite side of the display surface of the second display panel and the two transparent electrodes facing each other of the third display panel are formed of the metal nanowires. The two transparent electrodes facing each other of the second display panel are formed of the transparent conductive film,
The multilayer liquid crystal display element according to claim 1, wherein the two transparent electrodes facing each other of the third display panel are formed of the metal nanowires. The transparent electrode on the display surface side of the second and third display panels is formed of the transparent conductive film,
The multilayer liquid crystal display element according to claim 1, wherein the transparent electrode on the side opposite to the display surface of the second and third display panels is formed of the metal nanowire. The transparent flat plate electrode is a strip electrode extending in the major axis direction,
Of the plurality of wire-like electrodes placed on the transparent flat plate electrode, the proportion of the wire-like electrodes in which the angle between the wire stretching direction and the long axis of the transparent flat plate electrode is 45 degrees or less is 60% or more The display element according to any one of claims 1 to 5.

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