JP2000171783A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the coloration of scattered images by the presence of dichromatic dyestuffs of a liquid crystal display panel using high polymer dispersion type liquid crystals and to obviate the generation of haze to illumination light of a diagonal direction. SOLUTION: A liquid crystal phase 101 is composed of liquid crystal molecules 102 and dichromatic dyestuffs 103b. A polymer phase 113 is subjected to homeotropic alignment by using a liquid crystal polymer. At this time, the double refractive characteristic of the polymer phase 113 is made the same as that of the liquid crystal phase 101. When drive voltage is impressed to transparent electrodes 107 patterned on one glass substrate 105 and transparent electrodes 109 of another glass substrate 106, a PDLC layer 100 turns to a transparent state and the haze is no more generated in these portions. When the drive voltage is not impressed to another transparent electrodes 108 and transparent electrodes 109, these portion turn turbid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device which realizes see-through characteristics using a polymer dispersed liquid crystal.

[0002]

2. Description of the Related Art As a liquid crystal display device using a polymer dispersed liquid crystal (hereinafter referred to as PDLC), a projection display device,
There is a paper-like monochrome reflective display device. In the principle view of the liquid crystal display panel shown in FIGS. 3A and 3B, the PDLC layer 3 sandwiched between two transparent substrates is shown.
01 is a transparent polymer phase 30 which is a polymer matrix.
2 is obtained by dispersing a liquid crystal phase 303 in the form of particles. P
The thickness of the DLC layer 301 is about 10 μm. In the state where no voltage is applied to the transparent electrodes 305 and 306 formed on the upper and lower transparent substrates, as shown in FIG.
The liquid crystal molecules in 03 are oriented in random directions, and the parallel light incident from the upper transparent substrate is scattered by the liquid crystal phase 303. When a voltage is applied to the transparent electrodes 305 and 306, the liquid crystal molecules are oriented in the direction of the electric field as shown in FIG. 3B, and the PDLC layer 301 looks transparent when viewed from a direction substantially perpendicular to the surface of the liquid crystal display panel. . In the state shown in FIG. 3A in which the liquid crystal molecules are not oriented in a specific direction, the light incident toward the liquid crystal phase 303 is scattered, so that the liquid crystal phase looks opaque. By using the clouded state and the transparent state as a shutter, a projection display device can be configured. Also, make the background of the transparent part black,
By forming a display image with cloudy and transparent parts,
A monochrome type reflective display device can be configured.

As a further application of the PDLC, a see-through type display device has been developed as a device utilizing the fact that the PDLC layer becomes transparent when a voltage is applied. When sufficient external light is obtained, such as during the daytime, the amount of reflected light increases in the cloudy portion of the PDLC layer due to the scattered light of the external light, and the transparent portion has no reflected light, so that sufficient display contrast can be obtained. However, when sufficient external light cannot be obtained, such as at night, it is necessary to illuminate the liquid crystal display panel using a light source. In this case, the transparent substrate on one side of the PDLC layer is thickened and used as a light guide plate, and a light source such as a cold cathode tube is arranged at the lower end of the light guide plate. Light from the light source is guided while repeating total reflection at the interface between the light guide plate and air and the interface between the liquid crystal display panel and air. PDL
Light that reaches the cloudy portion of the C layer is scattered there, and when the cloudy portion constitutes a pixel or a segment of an image,
A white display image is observed by the observer. In the light guide type illuminator, since the light source is completely invisible to the observer from the front of the liquid crystal display panel, a complete see-through type display device can be realized.

[0004]

In order to make the light source invisible to the observer, the light source is placed at a position far away from the line of sight of the observer looking at the liquid crystal display panel, and from there the illuminating light is applied to the PDLC layer. Must be irradiated.
Therefore, as shown in FIG. 4, the illumination light L is incident on the liquid crystal display panel at a shallow angle, that is, an angle θ between the surface of the PDLC layer and the illumination light is reduced. Considering the transparent portion of the PDLC layer, the liquid crystal molecules are aligned in a direction perpendicular to the display panel surface (y direction) by an electric field applied to the transparent electrode. Considering PDLC layer 301, in the case where the voltage is applied, the refractive indices n _x of the major axis perpendicular to the direction of the liquid crystal molecules 307 (x-direction), the polymer phase 302
Is matched with the refractive index m. Therefore, the PDLC layer 301 is transparent to the illumination light Ly having a vibration plane parallel to the long axis of the liquid crystal molecules. Conversely, liquid crystal molecules 307
In the major axis direction (the refractive index n _{y in the} y direction and the polymer phase 302
Does not match the refractive index m of the liquid crystal molecule 3
07 illumination light Lx on the vibration plane perpendicular to the long axis
01 scattered.

As a result, a thin cloudiness called haze appears in the transparent portion of the PDLC layer 301. For the above-mentioned reasons, in the see-through type liquid crystal display device with the illuminator using the conventional PDLC, the haze generated in the transparent portion at the time of night illumination impairs the sense of clearness,
There is a disadvantage that the contrast is reduced.

Further, since the external light that enters the PDLC layer 301 in the daytime is direct sunlight or scattered sunlight, the color component can be said to be white. Therefore, the scattered light from the PDLC layer 301 also becomes white inevitably. At this time, if the background is light-colored, the contrast is weak, and there is a disadvantage that the displayed image is very difficult to identify. Therefore, as a means for compensating for these disadvantages, a method of adding a dichroic dye to the PDLC layer 301 can be considered. In this case, since the cloudy portion is colored in a predetermined color, the image portion becomes dark, and the discriminability is improved with respect to the light color of the background. However, in this method, when a voltage is applied to the transparent electrode, the orientation direction of the dye molecules in the polymer layer does not change. For this reason, the entire color including the background is colored, and the visibility of the liquid crystal display panel is rather deteriorated.

The present invention has been made in view of such conventional problems, and is a see-through type liquid crystal display capable of displaying an image having a high contrast without being influenced by external light or a color component of a light source. It is intended to realize the device.

[0008]

In order to solve such a problem, an invention according to claim 1 of the present application is provided on a gazing side of a display image, and a first transparent electrode having a transparent electrode patterned on one surface. A second substrate having a transparent electrode patterned on one side thereof so as to face the transparent electrode of the first transparent substrate;
, And the dichroic dye is dispersed in a liquid crystal polymer, and the dichroic dye is homeotropically formed by a crosslinking reaction of the liquid crystal polymer. And a liquid crystal phase in which liquid crystal molecules and a dichroic dye are mixed before the polymer layer is crosslinked, and the first and second liquid crystal phases are mixed. When a voltage is applied between the transparent electrodes of the transparent substrate, the liquid crystal molecules of the liquid crystal phase are homeotropically aligned.

According to a second aspect of the present invention, there is provided a first transparent substrate provided on a gazing side of a display image and having a transparent electrode patterned on one side, and facing a transparent electrode of the first transparent substrate. A second transparent substrate having a transparent electrode formed entirely on one side thereof, sandwiched between the first transparent substrate and the second transparent substrate, a dichroic dye is dispersed in a liquid crystal polymer,
The dichroic dye was homeotropically oriented by the crosslinking reaction of the liquid crystal polymer, and the polymer layer was filled into the liquid crystal polymer before crosslinking of the polymer layer, and the liquid crystal molecules and the dichroic dye were mixed. And a liquid crystal phase, wherein when a voltage is applied between the transparent electrodes of the first and second transparent substrates, the liquid crystal molecules of the liquid crystal phase are homeotropically aligned. .

According to a third aspect of the present invention, there is provided a first transparent substrate provided on a gazing side of a display image and having a transparent electrode formed entirely on one surface, and facing a transparent electrode of the first transparent substrate. , A transparent electrode is patterned on one side,
A second transparent substrate having a thickness greater than that of the transparent substrate, and a dichroic dye dispersed in the liquid crystal polymer, sandwiched between the first transparent substrate and the second transparent substrate; The polymer layer in which the dichroic dye is homeotropically aligned by the reaction, the liquid crystal polymer is filled in the liquid crystal polymer before crosslinking of the polymer layer, and a liquid crystal phase in which liquid crystal molecules and a dichroic dye are mixed, A light source for providing illumination light from one end surface of the second transparent substrate;
The liquid crystal molecules of the liquid crystal phase are homeotropically aligned when a voltage is applied between the transparent electrodes of the transparent substrate.

According to a fourth aspect of the present invention, there is provided a first transparent substrate provided on a gazing side of a display image and having a transparent electrode patterned on one side, and facing a transparent electrode of the first transparent substrate. A second transparent substrate having a transparent electrode patterned on one side thereof and having a thickness greater than that of the first transparent substrate;
A polymer sandwiched between the first transparent substrate and the second transparent substrate, a dichroic dye is dispersed in a liquid crystal polymer, and the dichroic dye is homeotropically aligned by a crosslinking reaction of the liquid crystal polymer. A liquid crystal phase filled with the liquid crystal polymer before the polymer layer is crosslinked, and a liquid crystal phase in which liquid crystal molecules and a dichroic dye are mixed, and a light source that provides illumination light from one end surface of the second transparent substrate. And the first
And when a voltage is applied between the transparent electrodes of the second transparent substrate, the liquid crystal molecules of the liquid crystal phase are homeotropically aligned.

The invention of claim 5 of the present application is directed to claim 3 or 4
In the liquid crystal display device of the above, the second transparent substrate is attached to the back surface of the transparent substrate having a transparent electrode formed on one surface and the rear surface of the transparent substrate, and has a thickness greater than the thickness of the transparent substrate. And a light guide plate for guiding the illumination light along the plate surface.

[0013]

(Embodiment 1) A liquid crystal display device according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing a configuration of the liquid crystal display device according to the first embodiment. This liquid crystal display device has a polymer dispersed liquid crystal layer (hereinafter, referred to as P) as a liquid crystal display panel.
100 (referred to as a DLC layer).
06. Assuming that the glass substrate 105 located on the observer side is the first transparent substrate, patterned transparent electrodes 107 and 108 are formed at a plurality of locations on the PDLC layer 100 side of the glass substrate 105. A glass substrate 1 which is a second transparent substrate facing the glass substrate 1
06 on the side of the PDLC layer 100, the solid transparent electrode 109
Are provided on the entire surface.

The PDLC layer 100 includes a polymer phase 113 and a liquid crystal phase 101. A polymerizable liquid crystal polymer is used for the polymer phase 113, and the dichroic dye 103a is dispersed and mixed in the liquid crystal polymer. Then, alignment control is performed by a crosslinking reaction of the liquid crystal polymer, and the dichroic dye 103a is homeotropically aligned. On the other hand, the liquid crystal phase 101 contains liquid crystal molecules 102 and a dichroic dye 103b. The refractive index n of the liquid crystal phase 101 used here is a refractive index n ₁ ≒ 1.5 in a molecular axis direction and a refractive index n ₂ ≒ 1.7 in a direction perpendicular to the molecular axis. It is necessary to select the refractive index m of the polymer phase 113 close to the refractive index n of the liquid crystal phase 101. Transparent electrodes 107 and 108 of the liquid crystal display panel
Is connected to one end of a drive voltage source 110 via respective switches 112 and 111, and the common transparent electrode 109 is connected to the other end of the drive voltage source 110. The image of this liquid crystal display device is an observer 1 located in front of the glass substrate 105.
14.

The operation of the liquid crystal display device having such a configuration will be described. When the liquid crystal panel is viewed from an observer 114 in the upper part of the figure, the refractive index m ≒ 1.5 because the polymer phase 113 is homeotropically oriented, and the dichroic dye 103a contained therein is included. Are also homeotropically oriented according to the polymer, so that they are colorless and transparent. If one switch 111 is closed, the transparent electrode 10
A driving voltage is applied to the liquid crystal layers 7 and 109 by the driving power supply 110, and the liquid crystal molecules 102 in the liquid crystal phase 101a are aligned in the voltage direction. In this case, since the refractive index of the surrounding polymer phase 113 and the liquid crystal phase 101a can be matched in all directions, this portion becomes transparent in any direction. Also, the dichroic dye 10 contained in the liquid crystal phase 101a
3b is also oriented according to the liquid crystal molecules 102, so that the PDLC sandwiched by the transparent electrode 107 is viewed from the observer 114.
The layer 100 becomes colorless and transparent.

Assuming that the other switch 112 is open, no drive voltage is applied between the transparent electrodes 108 and 109. Therefore, the liquid crystal molecules of the liquid crystal phase 101b in this portion remain oriented in a random direction, the refractive index cannot be matched with the surrounding polymer phase 113, and the PDCL layer 100 in this portion is in a scattering state. Furthermore, the liquid crystal phase 10
Since the dichroic dye 103b included in 1b is also oriented in a random direction, it does not become transparent, and the PDLC layer 100 sandwiched between the transparent electrodes 108 becomes a colored scatterer.
As described above, the homeotropic liquid crystal polymer is used for the polymer phase 113, and the dichroic dye is also homeotropically aligned, so that the observer 114 can obtain a scattering image colored in a completely colorless and transparent back. I make it visible. In particular, the dichroic dye 103a in the polymer phase 113
Since is oriented perpendicular to the glass substrate, haze does not occur in the transparent portion of the liquid crystal panel. Therefore, the visibility of the image on the liquid crystal panel can be greatly improved.

It is assumed that a solid transparent electrode is formed on the second transparent substrate constituting the above liquid crystal display panel, but the transparent electrode of the second transparent substrate is the transparent electrode of the first transparent substrate. A transparent electrode patterned on one surface of the second transparent substrate so as to face the transparent electrode may be used.

Embodiment 2 Next, a liquid crystal display device according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a sectional view showing a configuration of the liquid crystal display device according to the second embodiment. This liquid crystal display device has a structure in which a PDLC layer 100 is sandwiched between two glass substrates 105 and 201 as a liquid crystal display panel.
The configuration of 00 is the same as that of the first embodiment. A transparent electrode 109 is formed on the entire surface (on the side of the PDLC layer) of the glass substrate 105 as the first transparent substrate, and a patterned transparent electrode 107 and a transparent electrode 107 are formed inside the glass substrate 201 as the second transparent substrate. 108 are configured. FIG.
In the example shown in FIG. 6, the thickness of the glass substrate 201 is larger than the thickness of the glass substrate 105 for introducing illumination light from the side. The reason for increasing the thickness of the glass substrate 201 is that
This is because a light guide for introducing illumination light is used. Second
The PDLC layer 100 is sandwiched on one surface of the glass substrate 106 of FIG.
6 may be configured by attaching a thick glass substrate as a light guide plate to the other surface of the light guide plate 6.

The transparent electrode 109 and the upper and lower transparent electrodes 10 in FIG.
7, a drive voltage source and a switch (not shown) are provided between the central portion and the transparent electrode 108 in FIG. By opening and closing the switch, application or non-application of a driving voltage to the transparent electrodes 107 and 109 and the transparent electrodes 108 and 109 is selected. A cold cathode tube 202 serving as an illumination light source is attached to an end surface of the glass substrate 201, and a reflection plate 209 is provided outside the cold cathode tube 202. The image on the liquid crystal display device is viewed by an observer 210 located in front of the glass substrate 105.

The operation of the liquid crystal display device having such a configuration will be described. When a driving voltage is applied between the transparent electrodes 107 and 109, the region 204 becomes transparent. on the other hand,
If no driving voltage is applied between the transparent electrodes 108 and 109, the region 203 is in a scattering state. The illumination light from the cold cathode tube 202 is directly incident on the end face of the glass substrate 201 together with the reflected light from the reflection plate 209. The glass substrate 201 guides the illumination light throughout the substrate. At this time, the illumination light incident on the glass substrate 201 repeats total reflection in the substrate, and a part of the illumination light is incident on the transparent region 204 of the PDLC layer 100. Some other illumination light is P
The light enters the scattered region 203 of the DLC layer 100.

In the transparent region 204, liquid crystal molecules and dichroic dyes in the liquid crystal phase 101 are oriented in the direction of the electric field.
The refractive indexes of the liquid crystal phase 101a and the surrounding polymer phase 113 are matched. In particular, since the refractive index of the liquid crystal polymer of the polymer phase 113 is matched with that of the liquid crystal molecules in the liquid crystal phase 101a including its birefringence characteristics, the liquid crystal polymer is not scattered at all into the obliquely incident light 206, and Also does not occur. Therefore, most of this incident light 206 is P
A part penetrates through the DLC layer 100 and a part is reflected again on the surface of the glass substrate 105 and returns to the glass substrate 201 side. At this time, since no haze occurs, there is no leakage light, and a completely transparent state can be realized.

On the other hand, in the scattered area 203, the liquid crystal phase 1
Since the liquid crystal molecules and the dichroic dye in 01b are oriented in random directions, the refractive indices of the liquid crystal molecules and the surrounding polymer phase cannot be matched. Therefore, the incident light 207 in the oblique direction is scattered at the interface between the liquid crystal phase 101b and the polymer phase 113 to generate scattered light 208. At this time, the liquid crystal phase 1
The scattered light 208 is colored by the dichroic dye in 01b. The colored scattered light 208 reaches the observer 210, and the observer 210 sees a colored scattered image, that is, a colored character or image, in a completely transparent background without haze. Therefore, by selecting an appropriate dichroic dye, it is possible to realize a see-through type liquid crystal display device which is easy to identify even when the background is pale and has excellent visibility without haze.

In the prior art and embodiments of the present application,
Although the present invention has been described using PDLC, the effects of the present invention can be applied to other polymer-dispersed liquid crystal structures such as polymer networks and PSCT and SPAN.

[0024]

As described above, according to the first and second aspects of the present invention, when a voltage is applied to the PDLC layer composed of a polymer phase and a liquid crystal phase, the voltage application portion is transparent when viewed from all directions. And haze does not occur. Moreover,
Only a portion to which no voltage is applied is colored, so that a see-through type liquid crystal display device with high contrast can be realized.

According to the third to fifth aspects of the invention, in addition to the effects of the first and second aspects of the invention, a see-through type excellent in visibility without haze without being affected by the illuminance of external light. A liquid crystal display device can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a liquid crystal display device according to Embodiment 2 of the present invention.

FIG. 3 is an operation principle diagram of a liquid crystal display device using a polymer dispersed liquid crystal.

FIG. 4 is an explanatory diagram showing the principle of haze generation in a liquid crystal display device using a polymer dispersed liquid crystal.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 PDLC layer 101 Liquid crystal phase 101 a Liquid crystal phase (when aligned) 101 b Liquid crystal phase (when not aligned) 102 Liquid crystal molecule 103 a, 103 b Dichroic dye 105, 106, 201 Glass substrate 107, 108 Transparent electrode (patterning) 109 Transparent electrode (Solid) 110 Drive voltage source 111, 112 Switch 113 Polymer phase 114, 210 Observer 202 Cold cathode tube 203 Scattered area 204 Transparent area 206, 207 Incident light 208 Scattered light 209 Reflector

Claims (5)

[Claims] 1. A first transparent substrate provided on a gazing side of a display image and having a transparent electrode patterned on one side, and a transparent electrode formed on one side by a pattern so as to face the transparent electrode of the first transparent substrate. A second transparent substrate, which is sandwiched between the first transparent substrate and the second transparent substrate, a dichroic dye is dispersed in a liquid crystal polymer, and the dichroic dye is cross-linked by the liquid crystal polymer. A polymer layer in which a hydrophilic dye is homeotropically aligned, and a liquid crystal phase in which the liquid crystal polymer is filled before the polymer layer is crosslinked and a liquid crystal molecule and a dichroic dye are mixed. A liquid crystal display device characterized in that, when a voltage is applied between the transparent electrodes of the first and second transparent substrates, the liquid crystal molecules of the liquid crystal phase are homeotropically aligned. 2. A first transparent substrate provided on a gazing side of a display image and having a transparent electrode patterned on one surface, and a transparent electrode on one surface entirely facing the transparent electrode of the first transparent substrate. A second transparent substrate formed, sandwiched between the first transparent substrate and the second transparent substrate, a dichroic dye is dispersed in a liquid crystal polymer, and the dichroic dye is crosslinked by the liquid crystal polymer. A polymer layer in which a hydrophilic dye is homeotropically aligned, and a liquid crystal phase in which the liquid crystal polymer is filled before the polymer layer is crosslinked and a liquid crystal molecule and a dichroic dye are mixed. A liquid crystal display device characterized in that, when a voltage is applied between the transparent electrodes of the first and second transparent substrates, the liquid crystal molecules of the liquid crystal phase are homeotropically aligned. 3. A first transparent substrate provided on a gazing side of a display image and having a transparent electrode formed entirely on one surface, and a transparent electrode formed on one surface by a pattern so as to face the transparent electrode of the first transparent substrate. A second transparent substrate having a thickness greater than that of the first transparent substrate, sandwiched between the first transparent substrate and the second transparent substrate, and a dichroic dye dispersed in a liquid crystal polymer. A polymer layer in which the dichroic dye is homeotropically aligned by a cross-linking reaction of the liquid crystal polymer, and the liquid crystal polymer is filled into the liquid crystal polymer before cross-linking of the polymer layer, and the liquid crystal molecules and the dichroic dye are mixed. And a light source for providing illumination light from one end surface of the second transparent substrate. When a voltage is applied between transparent electrodes of the first and second transparent substrates, the liquid crystal phase Liquid crystal molecules become homeotropic The liquid crystal display device characterized in that it is directed. 4. A first transparent substrate provided on a gazing side of a display image and having a transparent electrode patterned on one surface, and a transparent electrode formed on one surface by a pattern so as to face the transparent electrode of the first transparent substrate. A second transparent substrate having a thickness greater than that of the first transparent substrate, sandwiched between the first transparent substrate and the second transparent substrate, and a dichroic dye dispersed in a liquid crystal polymer. A polymer layer in which the dichroic dye is homeotropically aligned by a cross-linking reaction of the liquid crystal polymer, and the liquid crystal polymer is filled into the liquid crystal polymer before cross-linking of the polymer layer, and the liquid crystal molecules and the dichroic dye are mixed. And a light source for providing illumination light from one end surface of the second transparent substrate. When a voltage is applied between transparent electrodes of the first and second transparent substrates, the liquid crystal phase Liquid crystal molecules are homeotropic The liquid crystal display device characterized in that it is oriented to the click. 5. The second transparent substrate includes: a transparent substrate having a transparent electrode formed on one side; a rear surface of the transparent substrate; a plate having a thickness greater than the thickness of the transparent substrate; The liquid crystal display device according to claim 3, further comprising: a light guide plate for guiding the illumination light along the plate surface.