JPH09281489A - Reflection display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection liquid crystal display device capable of a bright, clear color display by making a light reflection layer reflecting external light made incident on the device a mirror surface reflection plate. SOLUTION: AN electrooptical material layer 11 is provided between upper/ lower two pieces of a display side transparent substrate 13 and a rear side transparent substrate 14, a mirror surface reflecting plate 12 is provided below the substrate 14. The light passing through the electrooptical material layer 11 is reflected by the mirror surface reflection plate 12 to be emitted from the front of a panel again. Thus, the bright display is obtained. Further, when the electrooptical material layer 11 is in a light transmission state, through an observer views directly the mirror surface reflection plate 12, the luminance of the mirror surface reflection plate 12 isn't so large unless strong direct reflection light from a certain specified direction exists, and a display state darker than peripheral pixels is recognized as black. As the mirror surface reflection plate 12, the plate having reflection light including n-o diffused reflection component or hardly containing it is used, and metallic material such as aluminum, silver, platinum, nickel, chromium, and the material coated with these materials are used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reflective display device that does not require an illumination device such as a backlight, and more particularly to a color liquid crystal display device using polymer dispersed liquid crystal in a liquid crystal layer.

[0002]

2. Description of the Related Art Liquid crystal display devices have come to be used in various fields, and CRTs have a strong momentum as information display devices. In particular, in devices requiring portability, they are used in many devices because of their small size, light weight, and low power consumption. Among them, the reflection type liquid crystal display device which does not require a lighting device such as a backlight is used for portable equipment such as an electronic notebook because of its low power consumption, but most of them are monochrome display. Has been used from the past,
Since a polarizing plate is used in the TN and STN display systems,
Light utilization efficiency is low. Therefore, it is difficult to produce a bright reflective display device, particularly a reflective liquid crystal display device capable of color display, by these methods. A display device using polymer dispersed liquid crystal has been proposed as a bright display method that does not use a polarizing plate. JP-A-6-186544
A reflective color liquid crystal display device using polymer-dispersed liquid crystal has been proposed in JP-A-6-01.
8874 proposes a reflective color liquid crystal display device using polymer-dispersed liquid crystal.

[0003]

In a direct-viewing type liquid crystal display device using a conventional polymer dispersion type liquid crystal, a light absorbing layer or a color reflecting layer is provided on the back side of the liquid crystal layer (the side opposite to the display surface),
Many have been proposed that exhibit a background color when the liquid crystal layer is in a light transmitting state. In the STN and TN modes, the liquid crystal layer plays a role of an optical shutter, and black can be displayed without transmitting light. However, since the polymer-dispersed liquid crystal exhibits a light transmitting state and a light scattering state, it shows white in the light scattering state and a background color in the light transmitting state. For this reason,
White display is possible, but black cannot be displayed unless black is used as the background color. Therefore, JP-A-6-186
In 544, the reflection pixel is divided into four, red, green, blue,
A black color reflection layer is provided to enable black display. However, in this method, the area of the color reflection layer other than black is small, which causes a problem that the brightness at the time of color display is reduced. In addition, since all the pixels in the scattering state display white, the color at the time of color display is entirely white, and vivid color display cannot be performed. An object of the present invention is to provide a reflective liquid crystal display device which is capable of bright and vivid color display.

[0004]

It is difficult for the human eye to distinguish the color of an object under very bright or very dark illumination. In particular, when distinguishing between white and black, it is judged that the brighter one is white and the darker one is black. The reflective display device of the present invention solves the above-described problem by not performing black display, but expressing a darker display state as black display by realizing a brighter reflective display state. An explanatory view of the reflective display device of the present invention is shown in FIG.
FIG. 2 shows an explanatory view of a conventional reflective display device. In FIG. 2, when the electro-optical material layer 11 is in the light-scattering state, part of the light incident from the front surface of the display panel is scattered by the electro-optical material layer and is emitted again from the front surface of the panel. However, the light passing through the electro-optical material layer is absorbed by the light absorption layer 22 on the back surface of the electro-optical material layer and does not return to the observer side. On the other hand, in the reflection type display device of FIG. 1, the light passing through the electro-optical material layer is reflected by the specular reflection plate 12 and emitted again from the front surface of the panel. As a result, the display device having the configuration shown in FIG. 1 can perform brighter display than the display device having the configuration shown in FIG. Further, in the display device of FIG. 1, when the electro-optical material layer is in the light transmitting state, the observer directly looks at the specular reflection plate, but unless there is strong direct reflection light from a certain specific direction, The brightness of the reflector is not high, and if the display is darker than the surrounding pixels, it is recognized as black.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the electro-optical material layer 11 is provided between the upper and lower two display-side transparent substrates 13 and the back-side transparent substrate 14, and the specular reflector 1 is provided under the back-side transparent substrate 14.
I put two. In the configuration of FIG. 1, in order to minimize the distance between the electro-optic material layer 11 and the specular reflection plate 12, the rear transparent substrate 14 and the specular reflection plate 12 are arranged in contact with each other. In addition, the specular reflector 12 is used in Example 3 (FIG. 6) below.
It may be provided inside the rear transparent substrate 14 as shown in FIG. Examples of the electro-optical material layer 11 include polymer dispersion type liquid crystal (PDLC), dynamic scattering type liquid crystal, transient scattering type liquid crystal,
A phase transition type liquid crystal or the like can be used. The specular reflection plate 12 refers to one that has little or no diffuse reflection component in the reflected light, and includes metal materials such as aluminum, silver, platinum, nickel, and chrome, and those coated with these materials. Display-side transparent substrate 13 and back-side transparent substrate 14
As the glass substrate, a glass substrate or a plastic substrate such as polyethylene terephthalate, polyethylene naphthalate, or polyether sulfone that is commonly used for liquid crystal display devices is used. In the liquid crystal display device of the present invention, as shown in FIGS. 5 to 8, a color filter layer may be provided for each display pixel patterned in a matrix. As the color filter layer, as shown in FIGS.
Micro color filter consisting of micro color filters consisting of primary colors red, green and blue, or yellow, magenta which are the three primary colors of the subtractive color mixture method,
A micro color filter made of cyan can be used, but as shown in Example 4 below, it is brighter to use a micro color filter based on the subtractive color mixing method 3 primary colors because the amount of light passing through the filter layer is larger. Reflective display is possible. As a driving method of the reflection type display device of the present invention, both passive and active are effective, but depending on the material, only active driving is possible,
In that case, an MIM element having a high aperture ratio is preferable.

[0006]

【Example】

Example 1 In the display device shown in FIG. 1, two glass substrates having transparent electrode patterns are used as the display-side transparent substrate 13 and the back-side transparent substrate 14, and the distance between the substrates is 8 μm. The substrates were laminated and sealed around the substrate, leaving the liquid crystal injection port. Nematic liquid crystal 30w in this cell
A polymer-dispersed liquid crystal cell was prepared by injecting a mixed material consisting of t%, 70% by weight of a prepolymer and a small amount of a photopolymerization initiator by a vacuum injection method, and then irradiating with ultraviolet rays while heating in an isotropic phase. . 2 on black paper and glass plate by vacuum evaporation method
A 0 nm aluminum film was prepared and placed on the back surface of the back transparent substrate 14 of the liquid crystal cell prepared above, and comparison was performed under diffuse illumination. The measuring system is shown in FIG. The measurement system irradiated the illumination light from the light 32 above the diffusing sphere 31, arranged the measurement cell 33 in the direction perpendicular to the illumination direction, and measured the reflection brightness of the cell from the measurement window installed in the front direction of the measurement cell. A color luminance meter (BM-5 manufactured by Topcon) was used for the measurement. As a result of the measurement, the surface brightness at the time of light scattering of the cell provided with the aluminum reflection plate was about 2.5 times as large as that of the black paper. 500 (lx)
As a result of a visual evaluation in a room with the above brightness, it was confirmed that the one using the aluminum reflector was easier to see.

Example 2 FIG. 4 shows a conventional example of a reflective color display device using a polymer dispersed liquid crystal. In the conventional method, a color filter 41 composed of R (red), G (green) and B (blue) and a diffuse reflection plate 42 are provided on the back surface of the polymer dispersed liquid crystal layer 44 and when the liquid crystal layer is in a light transmitting state. It takes on the color of a color reflector. Therefore, a diffuse reflection surface is used as the light reflection surface. In this example, unlike the one shown in FIG. 4, the micro color filter layer was provided on the display surface side of the liquid crystal layer. That is, in the display device of the present embodiment, as shown in FIG. 5, the color filter 41 is arranged outside the upper transparent electrode layer 43. In the conventional method, since the light reflected by the color reflector and the scattered light from the liquid crystal layer were added, it was not possible to display with high color purity, but in the display device of the present embodiment, the color filter layer is provided on the display surface side. As a result, color display is performed when the liquid crystal layer is in the light scattering state,
Display with high color purity is possible.

Embodiment 3 FIG. 6 shows a structural example of a display device in which a reflective plate / electrode 62 is provided inside the rear transparent substrate 14 in the reflective color display device of Embodiment 2. By thus providing the electrode 62 also serving as the reflector inside the liquid crystal cell, it is possible to prevent not only the deterioration of the brightness due to the light absorption of the rear substrate 14 but also the deterioration of the display quality due to the stray light. Further, by using a conductive material as the material of the reflective layer, it is possible to serve as both the reflective layer and the voltage applying electrode. In particular, when the reflective layer is also used as the pixel electrode of an active element such as TFT or MIM, matrix driving becomes possible and the display capacity can be increased. FIG. 7 shows a configuration example in which an MIM element is used as a switching element, and the specular reflection layer is also used as a voltage application electrode. In this embodiment, the electrodes of the MIM element 71 and the display pixel electrodes 72 are made of aluminum. In this way, when the pixel electrode is also used as a specular reflection plate, the surface of the reflection plate is exposed to liquid crystal and the like, so that the surface of the reflection layer is made of an inorganic material such as SiO ₂ or alumina, an acrylic resin, or a polyimide resin. It is desirable to provide a protective film made of an organic material such as.

Example 4 FIG. 8 shows an example in which a micro color filter composed of three primary colors of the subtractive color mixture method, cyan, magenta and yellow, is used for the color filter layer 81. A conventional transmissive liquid crystal display device uses a micro color filter composed of red, green and blue which are the three primary colors of the additive color mixing method. FIG. 9 shows the transmittance characteristics of the conventional color filter and the color filter of the present invention. 9A, 9B, and 9C show examples of the light transmittances of the red, green, and blue filters, respectively, and FIGS. 9D, 9E, and 9F are shown. ) Is an example of yellow, magenta, and cyan. As can be seen from these figures, the amount of light transmitted through the filter layer in the micro color filter using the three primary colors of the subtractive color mixture method is about twice as large as that in the additive color mixture method. Therefore, by using the three primary colors of the subtractive color mixture method for the color filter layer, brighter reflective display is possible.

Example 5 In the present invention, since the specular reflection layer is used as the reflection plate, the surrounding background may be visible on the reflection plate depending on the viewing angle of the observer. To avoid this, the liquid crystal display device is provided with a light shield. An example is shown in FIG.
(A) is seen from the front of the display panel 101,
(B) is a side view of the panel when the light shade 102 is actually used. The observer can prevent the background from being reflected on the reflector by adjusting the angle of the light shade. In this embodiment, the cover is used as the light shield, but other types of light shield include a folding type and a bellows type. When the liquid crystal layer is in the light transmitting state, the observer sees the reflection image of the light shield, and therefore the panel surface side of the light shield is preferably dark color such as black or gray. Although the light shield is provided on the other side of the display panel in this embodiment, it may be provided on the left and right sides or both sides of the display panel. Further, the light shield can be used as a lid for protecting the display surface when the device is not used.

The embodiments of the present invention will be described below. 1. A reflective display in which information is displayed by sandwiching an electro-optical material layer that can be electrically controlled into a light transmitting state and a scattering state between two opposing transparent substrates and applying an electric field to the electro-optical material layer. In the device, the light reflection layer that reflects the external light incident on the device is a specular reflection plate, and the display device. 2. The display device according to 1 above, wherein the electro-optical material is a polymer-dispersed liquid crystal layer. 3. The display device according to 1 or 2 above, wherein the color filter layer is provided on the display surface side of the electro-optical material layer. 4. 3. The display device according to 3 above, wherein the color filter layer is composed of red, green and blue which are the three primary colors of the additive color mixture method. 5. The color filter layer is composed of three primary colors of the subtractive color mixture method, that is, cyan, magenta, and yellow.
Display device. 6. The display device according to any one of 1 to 5 above, wherein the light reflection layer is provided inside the substrate opposite to the display surface sandwiching the electro-optical material layer.

7. The display device according to any one of 1 to 6 above, wherein the electrode liquid crystal display device for applying a voltage to the electro-optical material layer has a function of a specular reflector. 8. 7. The display device according to 7, wherein the electrode is a pixel electrode of an active element. 9. 7. The display device according to 7 to 8 above, wherein the active element is a TFT or MIM. Ten. 10. The display device according to 1 to 9 above, which has a protective layer on the surface of the light reflecting layer. 11. The display device according to any one of 1 to 10 above, which has a light shield capable of preventing the surrounding background from being reflected in the light reflecting layer.

[0013]

【effect】

1. A bright reflection type liquid crystal display device can be provided by using a specular reflection plate as the light reflection layer for reflecting the external light incident on the device. 2. According to claim 3, color display with high color purity is possible. 3. According to claim 4, brighter reflective color display is possible. 4. Claim 5 It is possible to achieve a bright display and prevent deterioration of display quality due to stray light. 5. Claim 6 The structure of the liquid crystal cell is simplified and the manufacturing cost can be reduced. 6. Claim 7 It was possible to prevent the background around the device from being reflected on the specular reflection plate, and to obtain a good display.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a reflective display device of the present invention.

FIG. 2 is a schematic explanatory diagram of a conventional reflective display device.

FIG. 3 is a diagram showing a system for measuring the reflection luminance of the liquid crystal display device used in Example 1.

FIG. 4 is a diagram showing a conventional example of a reflective color liquid crystal display device using polymer dispersed liquid crystal.

5 is a schematic cross-sectional view of a reflective liquid crystal display device of Example 2. FIG.

FIG. 6 is a schematic cross-sectional view of a reflective liquid crystal display device of Example 3 in which a specular reflector is provided inside a back side substrate.

FIG. 7 is a schematic cross-sectional view of a reflective liquid crystal display device of Example 3 in which a pixel electrode of an active element also serves as a specular reflector.

FIG. 8 is a schematic cross-sectional view of a reflective liquid crystal display device of Example 4 in which a micro color filter made of three primary colors of a subtractive color mixture method is used for a color filter layer.

FIG. 9 is a diagram showing the light transmittance of each color filter. (A) Light transmittance of red filter (b) Light transmittance of green filter (c) Light transmittance of blue filter (d) Light transmittance of yellow filter (e) Light transmittance of magenta filter (F) Light transmittance of cyan filter

FIG. 10 (a) is a front view showing a usage state of the liquid crystal display panel provided with a light shield. (B) It is a side view of the (a).

[Explanation of symbols]

 11 Electro-Optical Material Layer 12 Mirror Reflector 13 Display Side Transparent Substrate 14 Back Side Substrate 22 Light Absorbing Layer 31 Diffusing Sphere 32 Light 33 Measuring Cell 34 Luminometer 41 Color Filter 42 Diffuse Reflecting Plate 43 Transparent Electrode 44 Polymer Dispersion Liquid Crystal Layer 62 Electrode also serving as a reflector 71 MIM element 72 Display pixel electrode 81 Color filter layer 101 Display panel 102 Light shield

Claims (7)

[Claims] 1. Information is provided by sandwiching an electro-optical material layer capable of electrically controlling a light transmission state and a scattering state between two opposing transparent substrates and applying an electric field to the electro-optical material layer. In a reflective display device for displaying, a light reflection layer for reflecting external light incident on the device is a specular reflection plate. 2. The display device according to claim 1, wherein the electro-optical material layer is a polymer-dispersed liquid crystal layer. 3. The display device according to claim 1, wherein the color filter layer is provided on the display surface side of the electro-optical material layer. 4. The display device according to claim 3, wherein the color filter layer is composed of cyan, magenta and yellow which are the three primary colors of the subtractive color mixture method. 5. The light reflection layer is provided inside the substrate opposite to the display surface sandwiching the electro-optical material layer.
The display device according to 2, 3, or 4. 6. The electrode for applying a voltage to the electro-optical material layer has a function of a specular reflector.
The display device according to 3, 4, or 5. 7. The light shield for preventing the surrounding background from being reflected on the specular reflector.
The display device according to 4, 5, or 6.