JPH0749485A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To brighten the white display at no application of voltage, and improve illuminance and contrast by nipping a polymer dispersed liquid crystal by a transparent electrode and a black electrode absorbing light, and providing a low refraction factor layer between the polymer dispersed liquid crystal and the black electrode. CONSTITUTION:A black electrode 22 formed on a first glass base and a transparent electrode 6 formed on a second glass base 7 are constituted in such a manner as to nip a polymer dispersed liquid crystal PDLC 5, and a low refraction factor layer 3 is provided between the PDLC 5 and the black electrode 22. Since the PDLC 5 is laid in transparent state when a voltage is applied, and light straightly advances, the low refraction factor layer 3 is useless, and the light is absorbed by the black electrode 22 to provide a black display. The light scattered by the PDLC 5 when no voltage is applied is incident to the critical surface at an angle larger than an incident angle theta=sin<-1>(n/nLC), when the refraction factor of the PDLC 5 is nLC, and the refraction factor of the low refraction factor layer 3 is (n), and fully reflected and returned to the incident side, so that a bright display can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device, and more particularly to a liquid crystal display device which has no viewing angle dependency in black display, is bright in white display, and has high brightness and contrast.

[0002]

2. Description of the Related Art A liquid crystal display device using a scattering type liquid crystal such as a polymer dispersed liquid crystal (PDLC) and a polymer network liquid crystal (PNLC) is used when a voltage is not applied to a liquid crystal layer.
Liquid crystal refractive index (n _LC ) and polymer matrix refractive index (n
_{Due to} the disagreement of _P ), light scattering occurs and it becomes cloudy. In addition, when a voltage is applied, the liquid crystal is aligned in the direction of the electric field, so that the refractive index n _{LC of the} liquid crystal and the refractive index n _P of the polymer matrix are substantially the same and are in a transparent state.

As a conventional example in which these scattering type liquid crystals are used in a reflection type display, a case where PDLC is used in the scattering type liquid crystals will be specifically described. FIG. 3 is a cross-sectional explanatory view of a conventional reflective liquid crystal display device.

As shown in FIG. 3, the conventional liquid crystal display device has a structure in which a PDLC 5 is sandwiched between a reflective electrode 21 formed on a glass substrate 1 and a transparent electrode 6 formed on a glass substrate 7. There is. In the PDLC 5 in FIG. 3, the spherical one is a liquid crystal and the one filled between the liquid crystals is a polymer matrix. The operation is to control the white turbid state and the transmissive state of the PDLC 5 by the voltage applied between the reflective electrode 21 and the transparent electrode 6.

As described above, when a PDLC is used for a display, a polarizer is unnecessary, so that conventional twist nematic (TN) and super twist nematic (STN) are used.
The display can be brighter than that of the system.

However, when no voltage is applied, the PDLC
Since 5 scatters light, white display can be obtained, but when voltage is applied, the PDLC 5 becomes transparent and the reflective electrode 21 below the PDLC 5 is displayed, which makes it look like a mirror and is very difficult to see. .

In order to solve this problem, a method of blackening the reflective electrode has been studied. As this conventional technique, Japanese Patent Application Laid-Open No. 4-250425 discloses a reflective liquid crystal display device in which vacuum-deposited carbon is used as a black electrode for the reflective electrode, and Japanese Patent Application Laid-Open No. 4-248519 discloses a reflective electrode on the reflective electrode. Disclosed is a liquid crystal electro-optical element in which a dielectric multilayer film is arranged and blackened by an interference effect.

[0008]

However, in the reflection type liquid crystal display device described in Japanese Patent Laid-Open No. 4-250425, the P characteristic when no voltage is applied is due to the inherent characteristics of PLDC.
DLC does not have enough backscatter on the display surface,
Further, since the light scattered forward to the back surface of the display is absorbed by the black electrode using the vacuum-deposited carbon, there is a problem that the white display becomes dark and the brightness and the contrast decrease.

In the liquid crystal electro-optical element described in Japanese Patent Laid-Open No. 4-248519, forward scattered light is reflected by the reflective electrode and returns to the incident side, so that the brightness in white display does not decrease, but black. Since the display is performed by the interference effect, there is a problem in that black is colored purple black or green black depending on the viewing angle direction, and the contrast is lowered.

The present invention has been made in view of the above circumstances, and provides a reflective liquid crystal display device which brightens white display when no voltage is applied, has high brightness and contrast, and has no viewing angle dependency. The purpose is to

[0011]

According to a first aspect of the present invention for solving the problems of the conventional example, a liquid crystal display device has a black electrode for absorbing light on a first substrate and a low refractive index. A transparent low refractive index transparent layer are sequentially formed, a transparent electrode is formed on a second substrate, and the black electrode and the transparent electrode are opposed to each other so that the polymer dispersed liquid crystal is sandwiched therebetween.
The substrate and the second substrate are arranged.

According to a second aspect of the present invention for solving the above-mentioned problems of the conventional example, in a liquid crystal display device, a light absorbing layer for absorbing light on a first substrate, and a transparent low refractive index having a low refractive index. The transparent layer and the first transparent electrode are sequentially formed, the second transparent electrode is formed on the second substrate, and the first transparent electrode and the second transparent electrode are opposed to each other to form a high transparent layer. It is characterized in that the first substrate and the second substrate are arranged so as to sandwich the molecule-dispersed liquid crystal.

[0013]

According to the first aspect of the invention, the polymer dispersed liquid crystal is sandwiched between the transparent electrode and the light absorbing black electrode, and a low refractive index layer is provided between the polymer dispersed liquid crystal and the black electrode. Since it is a liquid crystal display device, when the light scattered by the polymer dispersed liquid crystal enters the low refractive index layer when no voltage is applied to the electrodes, the refractive index of the low refractive index layer is higher than that of the polymer dispersed liquid crystal. Is low, the angle of total reflection is small, and most of the incident light can be totally reflected, so that white display can be made bright when no voltage is applied, and black is not displayed due to the interference effect. It is possible to display the black dye directly without depending on it.

According to the second aspect of the invention, the polymer-dispersed liquid crystal is sandwiched between the first transparent electrode and the second transparent electrode, and further the first transparent electrode and the first substrate are sandwiched between the first transparent electrode and the second transparent electrode. Since the liquid crystal display device has a low refractive index layer on the transparent electrode side of No. 1 and a light absorption layer on the first substrate side, light scattered by the polymer dispersed liquid crystal when no voltage is applied to the electrode has low refraction index. When incident on the refractive index layer, since the refractive index of the low refractive index layer is lower than that of the polymer dispersed liquid crystal, the angle of total reflection is small, and most of the incident light can be totally reflected. It is possible to make the white display bright when the image is added and to display the black pigment directly without depending on the viewing angle because the black display is not performed due to the interference effect.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional explanatory view of a reflective liquid crystal display device according to an embodiment of the present invention. It should be noted that parts having the same configuration as in FIG. As shown in FIG. 1, the reflective liquid crystal display device of the present embodiment (this embodiment 1) has a first glass substrate 1, a black electrode 22 that absorbs light and is also used as an electrode, and a refractive index of It is composed of a low low refractive index transparent layer 3, a polymer dispersed liquid crystal (PDLC) 5, a transparent electrode 6, and a second glass substrate 7.

Specifically, in the reflective liquid crystal display device of the first embodiment, the black electrode 22 formed on the first glass substrate 1 is used.
And the transparent electrode 6 formed on the second glass substrate 7 sandwiches the PDLC 5, and the low refractive index transparent layer 3 is provided between the PDLC 5 and the black electrode 22. There is.

Next, a method of manufacturing the reflective liquid crystal display device of Example 1 will be described. In the method of manufacturing the reflective liquid crystal display device of Example 1 shown in FIG. 1, carbon is vacuum-deposited on the first glass substrate 1 having a thickness of 0.7 to 1.1 mm to form a black film having a thickness of about 0.5 μm. The electrode 22 is formed, and MgF ₂ (refractive index n = 1.38) is formed thereon as the low refractive index transparent layer 3 to a thickness of about 2 μm by the sputtering method. If the film thickness of the low-refractive-index transparent layer 3 is thin, coloring due to interference occurs, and if it is thick, the driving voltage becomes high, so about 1 μm to 5 μm is desirable.

Next, an Indium-Tin film is formed as a transparent electrode 6 on the second glass substrate 7 having a thickness of 0.7 to 1.1 μm.
-Oxide (ITO: indium tin oxide) is formed to a thickness of about 0.1 μm by a sputtering method.

The two substrates have a cell gap of about 1
After bonding so as to have a thickness of 0 μm, a mixture of nematic liquid crystal and acrylic ultraviolet curing resin is vacuum-injected,
After that, ultraviolet rays are irradiated to form PDLC 5.

In the reflection type liquid crystal display device of Example 1, since the PDLC 5 is in a transparent state and the light travels straight when a voltage is applied, the low refractive index layer 3 is useless and the black electrode 22 absorbs the light to display the image. It becomes black. When no voltage is applied, PD
The light scattered by the LC5 has the low refractive index layer 3 between the PDLC 5 and the black electrode 22. Therefore, when the refractive index of the PDLC 5 is n _LC and the refractive index of the low refractive index layer 3 is n, the incident angle θi = PD at a larger angle than sin ^-1 (n / n _LC ).
Light incident on the interface between the LC 5 and the low refractive index layer 3 is totally reflected,
Since it returns to the incident side, a bright white display can be obtained.

In Example 1, the refractive index of the PDLC 5 n _LC =
Since 1.5 to 1.7, for example, when n _LC = 1.5 and the refractive index n of the low refractive index layer 3 is 1.38, the incident angle θi is calculated, then θ i = 74.4 °. Therefore, light incident at an angle larger than this incident angle is totally reflected.

In the reflection type liquid crystal display device of Example 1, the brightness in white display is 3 as compared with the case where the low refractive index transparent layer 3 is not provided.
There is an effect that the white display can be made brighter by 3% and the interference effect is not utilized at the time of black display, there is no dependence on the viewing angle, coloring due to the viewing direction is not seen, and the brightness and contrast can be increased.

Next, another embodiment (second embodiment) of the present invention will be described with reference to FIG. FIG. 2 is a sectional explanatory view of a reflective liquid crystal display device according to another embodiment (Embodiment 2) of the present invention. It should be noted that portions having the same configuration as the reflection type liquid crystal display device of FIG. The reflective liquid crystal display device of Example 2 includes the first glass substrate 1
A light absorbing layer 23 for absorbing light, and a low refractive index transparent layer 3 '.
, The first transparent electrode 4, the PDLC 5, the second transparent electrode 6 ', and the second glass substrate 7.

Specifically, in the reflective liquid crystal display device of Example 2, the first transparent electrode 4 formed on the first glass substrate 1 via the light absorption layer 23 and the low refractive index layer 3 '. And the second transparent electrode 6'formed on the second glass substrate 7 is P
It is configured to sandwich the DLC 5.

Next, a method of manufacturing the reflection type liquid crystal display device of Example 2 will be described. In the method for manufacturing the reflective liquid crystal display device of Example 2, the acrylic resin containing carbon is spin-coated on the first glass substrate 1 having a thickness of 0.7 to 1.1 mm to a thickness of about 1 μm, After that, the light absorption layer 23 is formed by baking, and a fluorine-based resin having a refractive index n = 1.34 as a low-refractive-index transparent layer 3'is spin-coated to a thickness of about 2 μm, and then baked. Form and then IT
O is formed to a thickness of about 0.1 μm by a sputtering method, and the first transparent electrode 4 is patterned by photolithography etching. The formation of the other portions is the same as that of the first embodiment, and the description thereof will be omitted.

According to the reflective liquid crystal display device of Example 2,
There is an effect that the driving voltage applied to the PDLC 5 can be made constant regardless of the film thickness of the low refractive index transparent layer 3 '. Here, the refractive index n _LC of the PDLC 5 is 1.5 and the refractive index n of the low refractive index transparent layer 3 ′ is 1.34.
When i is calculated, θi = 70.3 °, and light incident at an angle larger than this incident angle is totally reflected.

In the reflective liquid crystal display device of Example 2, the brightness at the time of white display is improved by 36% and the white display can be made brighter as compared with the case without the low refractive index transparent layer 3 ', and the interference at the time of black display. Since the effect is not utilized, there is no viewing angle dependency, coloring in the viewing angle direction is not seen, and there is an effect that brightness and contrast can be increased.

Here, the case where PDLC is used as the scattering type liquid crystal has been described, but the present invention is not limited to this. PNLC, Nematic Curvilinear Aligned Phase
Similar effects can be obtained by using other scattering type liquid crystals such as (NCAP), dynamic scattering mode and nematic-cholesteric phase transition mode.

Therefore, according to the reflective liquid crystal display devices of Examples 1 and 2, since black display does not depend on the interference effect, there is no viewing angle dependency, and the low refractive index transparent layers 3, 3'when white is displayed. It is possible to increase the brightness and contrast by totally reflecting most of the light incident on the.

[0030]

According to the invention described in claim 1, the polymer dispersed liquid crystal is sandwiched between the transparent electrode and the black electrode which absorbs light,
Further, since the liquid crystal display device has a low refractive index layer provided between the polymer dispersed liquid crystal and the black electrode, the light scattered by the polymer dispersed liquid crystal enters the low refractive index layer when no voltage is applied to the electrodes. In this case, since the refractive index of the low refractive index layer is lower than that of the polymer dispersed liquid crystal, the angle of total reflection becomes small, and most of the incident light can be totally reflected, resulting in white display when no voltage is applied. In addition, since the black color is not displayed due to the interference effect, it is possible to display the black dye directly without depending on the viewing angle, and it is possible to improve the brightness and the contrast.

According to the second aspect of the present invention, the polymer-dispersed liquid crystal is sandwiched between the first transparent electrode and the second transparent electrode, and the first transparent electrode and the first substrate are provided with a first transparent electrode. Since the liquid crystal display device has a low refractive index layer on the transparent electrode side of No. 1 and a light absorption layer on the first substrate side, light scattered by the polymer dispersed liquid crystal when no voltage is applied to the electrode has low refraction index. When incident on the refractive index layer, since the refractive index of the low refractive index layer is lower than that of the polymer dispersed liquid crystal, the angle of total reflection is small, and most of the incident light can be totally reflected. Since the white display upon addition can be brightened and the black display is not performed due to the interference effect, it is possible to display the black pigment directly without depending on the viewing angle, and it is possible to improve the brightness and the contrast.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory diagram of a reflective liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional explanatory view of a reflective liquid crystal display device of another embodiment.

FIG. 3 is a cross-sectional explanatory diagram of a conventional reflective liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st glass substrate, 21 ... Reflective electrode, 22 ... Black electrode, 23 ... Light absorption layer, 3, 3 '... Low refractive index transparent layer, 4 ... 1st transparent electrode, 5 ... PDLC, 6 ... Transparent Electrode, 6 '... second transparent electrode, 7 ... second glass substrate

Claims (2)

[Claims] 1. A black electrode that absorbs light and a transparent low refractive index transparent layer having a low refractive index are sequentially formed on a first substrate, and a transparent electrode is formed on a second substrate. A liquid crystal display device, characterized in that the first substrate and the second substrate are arranged such that electrodes and the transparent electrode are opposed to each other and sandwich the polymer dispersed liquid crystal. 2. A light absorbing layer that absorbs light, a transparent low refractive index transparent layer having a low refractive index, and a first transparent electrode are sequentially formed on a first substrate, and the light absorbing layer is formed on a second substrate. A second transparent electrode is formed, and the first substrate and the second substrate are arranged so that the first transparent electrode and the second transparent electrode face each other and sandwich the polymer dispersed liquid crystal therebetween. Liquid crystal display device characterized by.