JPH0990335A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display element which makes display with excellent visibility and high grade by providing this element with color filters provided with means for making parallel light incident on the inside of liquid crystal cells and diffusing the light emitted through the liquid crystal cells at every pixel, thereby improving the visual angle characteristics. SOLUTION: A liquid crystal panel 1 has a large change in luminance according to angles. Then, the incident light rays 2, 1 on the liquid crystal panel 1 are controlled by such a paralleling element 4 as to parallel these light rays to the parallel light rays having the certain specific angle thereof and the light rays 2, 2 transmitted through the liquid crystal panel 1 are widened by a diffusing element 3, by which the dependency of the liquid crystal display element on the visual angles is eliminate. The liquid crystal panel is applicable not only to an LCD of an active matrix type, such as TFT-LCD but also to the LCDs of all display modes, such as ST type LCDs. The places where the color filters are arranged may be any places, insofar as such places are on the optical path where the light passes as the directions of the light rays are controlled. The color filters may be arranged on one or both sides of the diffusing element 3 or the paralleling element 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive liquid crystal display element, and more particularly to a liquid crystal display element having improved viewing angle dependence of brightness and color during gradation display.

[0002]

2. Description of the Related Art Liquid crystal display elements are widely used in a wide variety of products such as wrist watches, calculators, Japanese word processors, personal computers, etc., because they have the great advantages of being thin and lightweight and of low power consumption. Most of these liquid crystal display elements use twisted nematic liquid crystals.

Such liquid crystal display elements, particularly those used in personal computers and the like, generally have a large area and large capacity display, and the size of the display surface is about 10 inches diagonal. , 640 x 480 display pixels have become mainstream. At present, the mainstream liquid crystal display elements for large-area, large-capacity display are the simple matrix method and the active matrix method.

A simple matrix type liquid crystal display device is
It has a simple structure in which liquid crystals twisted and aligned more than 80 ° are sandwiched between glass substrates with comb-shaped transparent electrodes (SΤ method). In order to display multiple digits with this structure, a high steepness is required in the applied voltage-transmittance characteristic of the liquid crystal cell. The higher the steepness, the larger the difference in transmittance can be obtained with a smaller voltage difference. The applied voltage-transmittance characteristic of the liquid crystal cell becomes steeper as the twist angle of the alignment of the liquid crystal layer (hereinafter referred to as the twist angle) increases. -Generally, a twist angle of 180 ° or more is required to obtain a contrast satisfying practical use with a simple matrix structure having about 400 scanning lines. When the twist angle becomes large like this, the display color is colored due to the optical rotation dispersion. This display is colored by disposing a second liquid crystal cell in which the liquid crystal layer is twisted in the opposite direction between the polarizing plate and the liquid crystal cell, or by using a plurality of retardation plates instead of the second liquid crystal cell. It can be erased by doing.

In the active matrix system, since each display pixel is equipped with a switching element composed of a thin film transistor, a diode or the like, a voltage can be supplied to the liquid crystal layer of each pixel regardless of the number of scanning lines. Therefore, since the steepness of the electro-optical characteristics of the liquid crystal cell does not need to be so high as in the ST method, generally, in the active matrix method, the twist angle is 90 ° (ΤN method) with small optical rotation dispersion and high contrast. ing. Therefore, in the ΤN method, there is almost no coloring, so color compensation is not required, and since the voltage difference can be made large by the active element, the response speed is faster than the simple matrix method.

In both the simple matrix system and the active matrix system described above, color display is realized by providing a color filter for each pixel under the transparent electrode of one substrate. However, in such a conventional technique, since the liquid crystal cell itself has an angle dependency, a display image is inverted depending on a viewing angle, an extreme decrease in luminance, coloring, etc. are observed, which is a serious problem. In particular, such a display abnormality is remarkable when gradation display is performed.

As a technique for reducing the viewing angle dependence of such a display, a liquid crystal cell and a polymer film having a negative optical anisotropy in the thickness direction between two polarizing plates are disclosed in JP-A-62-21423. Disposing a birefringent layer that is Further, it has been announced that a liquid crystal cell made of cholesteric liquid crystal called UST is arranged between polarizing plates. (Hato et al., Journal of the SID, 1/3, 1993, p.
319)

[0008]

The display principle of the conventional liquid crystal display element is to change the state of light transmitted through the liquid crystal cell by inclining the direction of liquid crystal molecules by a voltage. When the liquid crystal molecules in the liquid crystal cell are arranged parallel to the upper and lower substrate surfaces, the change due to the direction of the transmitted light is small,
When the liquid crystal molecules are arranged with a slight inclination (corresponding to the case where halftone is displayed), the change due to the direction of the transmitted light is large. Therefore, the optical compensation by the birefringent layer shown in the prior art is effective only when the liquid crystal molecules of the liquid crystal cell have a certain inclination, and the liquid crystal display element of binary display has the effect of improving the viewing angle. In the case of a liquid crystal display element that performs gradation display, the effect of enlarging the viewing angle cannot be obtained in all directions. Particularly, when performing full-color display in combination with a color filter, the reproducibility of the display image is significantly reduced, which is a serious problem.

The present invention has been made in consideration of such a conventional situation, and can improve the viewing angle dependence of brightness and display color at the time of gradation display, and can provide a high-quality display excellent in visibility. The present invention aims to provide a liquid crystal display device that can be used.

[0010]

According to a first aspect of the present invention, a liquid crystal cell having a plurality of pixels, collimating means for allowing parallel light to enter the liquid crystal cell, and light emitted through the liquid crystal cell. It is characterized by comprising a diffusing means for diffusing light and a color filter provided for each pixel.

According to a second aspect of the present invention, in the liquid crystal display element according to the first aspect, the liquid crystal cell includes a substrate on which active elements such as thin film transistors and thin film diodes are formed for each pixel, and the color filter comprises It is characterized in that it is arranged on this substrate.

According to a third aspect of the present invention, in the liquid crystal display element according to the first aspect, the color filter is arranged in the parallelizing means.

According to a fourth aspect of the present invention, in the liquid crystal display element according to the first aspect, the color filter is provided in the diffusing means.

According to a fifth aspect of the present invention, in the liquid crystal display element according to the first aspect, the color filter is provided in both the parallelizing means and the diffusing means. According to a sixth aspect of the present invention, in the liquid crystal display element according to the first to fifth aspects, the color filter is an interference filter.

According to a seventh aspect of the present invention, in the liquid crystal display device according to the first to fifth aspects, the color filter is made of cholesteric liquid crystal or polymer liquid crystal exhibiting selective reflection.

The invention of claim 8 is the liquid crystal display element according to any one of claims 1 to 7, characterized in that a polymer layer in which a liquid crystal is dispersed in a polymer is used as the diffusing means.

The invention of claim 9 is characterized in that, in the liquid crystal display element of claim 8, means for applying a voltage to the polymer layer is provided.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the liquid crystal display element of the present invention will be described below with reference to the accompanying drawings.

According to the present invention, the viewing angle dependence of the contrast ratio and the display color of the liquid crystal display device is simultaneously reduced, or the region of the liquid crystal display device where a certain contrast ratio is obtained is controlled to a certain azimuth and viewing angle. It is what

In FIG. 6, in a conventional TN liquid crystal display device, when tilted from 0 ° to 60 ° in the vertical direction from the display surface normal (the tilt angle from the display surface normal is hereinafter referred to as the viewing angle). 8) shows the luminance vs. viewing angle characteristics when displaying 8 gradations.
As shown in the figure, in the conventional liquid crystal display element, the brightness of the intermediate gradation is largely changed depending on the viewing angle. As described above, the polarization state of the light propagating in the liquid crystal display element is different between the case where the light is vertically incident on the display surface of the liquid crystal display element and the case where the light is obliquely incident on the display surface. Cause a change.

Therefore, the present invention solves the above problem by adopting a configuration as shown in FIG. That is, FIG.
Shows a cross-sectional structure of a liquid crystal display element in the present invention, 1 is a liquid crystal panel, 2 is an incident light flux, 3 is a diffusion element, and 4 is a collimating element. As shown in the view angle characteristic diagram of FIG. 6, the liquid crystal panel 1 has a large luminance change depending on the angle. Therefore, the angle of the light 2.1 incident on the liquid crystal panel 1 is controlled by the collimating element 4 so as to be parallel light of a certain angle, and the light 2.2 transmitted through the liquid crystal panel 1 is spread by the diffusing element 3. As a result, the viewing angle dependence of the liquid crystal display element is eliminated.

As mentioned above, the basic principle of the invention is shown in FIG.
As shown in FIG. 3, since it is basically based on making the parallel light incident on the liquid crystal cell 1 and diffusing the light emitted from the liquid crystal cell 1, the liquid crystal panel is not limited to the active matrix type LCD such as the ΤFΤ-LCD and the SΤ. It can be applied to LCDs of all display modes such as a shape LCD.

In the case of color display by controlling the transmission brightness by the liquid crystal layer, it is common to use color filters of three primary colors of red, blue and green. In the present invention, since the direction of the light incident on the liquid crystal cell is controlled, an interference filter or polysiloxane having a main chain, which cannot be applied to a direct-viewing type liquid crystal display element in view point characteristics, has been used. Further, it is possible to use a polymer liquid crystal having selective reflection which can be prepared from a polymer copolymer having a biphenylbenzoate and a cholesteryl group in an appropriate ratio.

The color filter is arranged at the conventional ΤF.
In the case of the Τ-LCD, it is on the side of the substrate that faces the substrate provided with the ΤFΤ element, but in the present invention, the direction of light is controlled, so it may be anywhere on the optical path through which the light is diffused. The same display performance can be obtained by arranging the same in the parallelizing element or in the diffusing element and the paralleling element. It is needless to say that the same effect can be obtained by providing it on the side of the substrate provided with the TFT element, and in this case, alignment becomes unnecessary when the two substrates are bonded together, and a more desirable liquid crystal display element can be obtained.

As the diffusing element, desired characteristics can be obtained even if a liquid crystal is dispersed in a polymer, and in particular, by providing a means for applying a voltage to the liquid crystal, the diffusing state is changed by the voltage. It is possible to control the viewing angle of the liquid crystal display element. It goes without saying that the display mode of the liquid crystal used in the present invention can be applied to TN having a twist angle of 70 ° to 120 ° and STN having a twist angle of 180 ° or more.

[0026]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 2 shows a sectional structure of a liquid crystal display element in this embodiment. As shown in the figure, the liquid crystal display device has a structure in which a liquid crystal cell 10 for compensating a viewing angle is sandwiched between two polarizing plates 11 and 12 (SH-1832AW; manufactured by Sumitomo Chemical Co., Ltd.).

A diffusion film 1 is formed on the polarizing plate 11.
3 are arranged adjacent to each other. This diffusion film 13
Is formed by laminating five layers having different refractive indexes to prevent reflection. Further, below the polarizing plate 11, a film substrate 16 having a transparent electrode (common electrode) 14 and an alignment film 15 is arranged. In this way, the film substrate 1
By using 6, the effect of reducing the weight and reducing the blurring of the image can be obtained.

The liquid crystal layer 17 is a liquid crystal (twisted nematic liquid crystal (ZLI-4287 (E. Merck Co., ltd
(Manufactured by E. Merck Co., Ltd.)) is used). This liquid crystal layer 1
7 retardation is 550 nm (light source wavelength: 550 nm)
Therefore, the conditions were set so that the highest transmittance was obtained with respect to the substrate normal.

On the glass substrate 18 arranged so as to face the film substrate 16 with the liquid crystal layer 17 interposed therebetween,
A ΤFΤ element 19 and a pixel electrode 20 are formed, and a color filter (interference filter) 2 for each of R, G and B colors formed of a multilayer film of SiO 2 and TiO 2 is formed under the pixel electrode 20.
1 is provided. These color filters 21 also have a function as an insulating layer of the gate electrode 22. An alignment film 23 is provided so as to cover the surface of the pixel electrode 20 and the like.

The above-mentioned polarizing plate 12 is adhered to the lower surface of the glass substrate 18 of the TFF substrate having the above structure, and the collimating element 24 is arranged below the polarizing plate 12. This parallelizing element 2
4 is disposed adjacent to the light guide plate 26 that guides the light from the cold cathode tubes 25.

When the ΤFΤ-LCD constructed as described above was produced, the gradation display contents could be identified even when the azimuth and the viewing angle were changed, and bright and good full-color display with high transmittance could be performed.

(Embodiment 2) With the same construction as in Embodiment 1 described above, a color filter 21 is twisted and oriented with a polymer copolymer having a main chain of polysiloxane and a side chain of biphenylbenzoate and a cholesteryl group. I used the one. When the twist pitch was changed for each pixel of red, blue and green and the product of the refractive index and the pitch length was set to around 450 nm, 550 nm and 650 nm, a color filter showing selective reflection of red, green and blue was obtained.

When a ΤF-Τ-LCD was produced with this structure, a wide viewing angle in which the display image did not change even if the azimuth or viewing angle was changed, and good full-color display could be performed.

(Embodiment 3) With the same construction as in Embodiment 1 described above, instead of the diffusion film 13, a liquid substance in which 4% by weight of liquid crystal is mixed in a UV-curable polymer is sandwiched between the substrates, and then UV light is emitted. A scattering element constituted by irradiating with and curing was used.

When a liquid crystal display element similar to that of Example 1 was produced using such a scattering element, good diffusion characteristics could be obtained.

Example 4 The same scattering element as in Example 3 was prepared by using two substrates with transparent electrodes.
The transparent electrode was electrically connected so that a voltage could be applied to the liquid crystal.

When a liquid crystal display element similar to that of Example 1 was manufactured using such a diffusing element, the viewing angle was changed by changing the magnitude of the voltage applied to the diffusing element, and when the voltage was 0, it was slanted. Although the display does not change even in the direction, when the voltage is increased, the display becomes invisible from the diagonal direction, and it is possible to realize a display that can be used when the display content is not desired to be shown to others.

Example 5 As the liquid crystal cell used in Example 1, a S-LCD having a twist angle of 240 degrees was used. SΤ
-For the LCD, two retardation plates obtained by stretching polycarbonate are used for color compensation. When I observed only this liquid crystal panel by changing the angle, the color changed greatly,
With the structure shown in FIG. 2, a good display was obtained even in an oblique direction (Example 6). FIG. 3 shows a sectional structure of a liquid crystal display element in this example. It should be noted that the collimating element and the light source are the same as those shown in FIG.

In this embodiment, a color filter 61 is provided at a portion corresponding to each pixel of the liquid crystal cell (TFT cell) 60.
The diffusing element 62 provided with is a polarizing plate 63 of the liquid crystal cell 60.
Is located on the upper surface of. In the figure, reference numeral 64 is a polarizing plate on the lower surface side. Further, unlike Example 1, the liquid crystal cell 60 is not provided with a color filter.

In such a configuration, the diffusion element 62
Since the color filter 61 of 1. does not require the high flatness accuracy required for the conventional color filter, it can be manufactured at low cost.

With this configuration, a TFF-L consisting of a diagonal of 10 inches
When a CD was created, it was possible to perform good full-color display in which the gradation display content could be identified even when the azimuth and viewing angle were changed.

(Embodiment 7) FIG. 4 shows a sectional structure of a liquid crystal display element in the present embodiment. In the figure, the collimating element and the light source are the same as those in FIG.

In this embodiment, no color filter is arranged in the liquid crystal cell (TFT cell) 70, and the diffusion element 71 is provided with a red color so as to correspond to each pixel position of the liquid crystal cell (TFT cell) 70. The color filters 72 of (R) and green (G) are arranged, and the color filter 74 of blue (B) is arranged at the position in the parallelizing element 73. In the figure, reference numerals 75 and 76 denote polarizing plates.

With this configuration, the TFF-L consisting of 10 inches diagonal
When a CD was created, it was possible to perform good full-color display in which the gradation display content could be identified even when the azimuth and viewing angle were changed.

(Embodiment 8) FIG. 5 shows a cross-sectional structure of a liquid crystal display element in this embodiment. In the figure, the collimating element and the light source are the same as those in FIG.

In this embodiment, no color filter is arranged in the liquid crystal cell (TFT cell) 80, and the parallelizing element 81 is provided so as to correspond to each pixel position of the liquid crystal cell (TFT cell) 80. Red, blue and green color filters 82
Are placed in position. In the figure, 83, 8
4 is a polarizing plate, and 85 is a diffusion element.

With this configuration, the TFF-L consisting of a diagonal of 10 inches
When a CD was created, it was possible to perform good full-color display in which the gradation display content could be identified even when the azimuth and viewing angle were changed.

(Comparative Example) In Example 1, a liquid crystal display element having no diffusing element and no collimating element was produced, and when the display screen was observed by changing the angle, inversion of display or blackout occurred depending on the angle. , There is a direction where the visibility is extremely bad,
It became a big problem in practical use. In particular, when the diagonal size was increased to 13 inches or more, the display colors were observed differently on the upper and lower screens, the brightness was drastically reduced, and fatigue was severe during long-term use.

[0050]

As described above, according to the present invention,
It is possible to provide a high-quality display liquid crystal display device having an improved viewing angle characteristic of the liquid crystal display device and excellent visibility. Needless to say, the present invention can be applied to an active matrix liquid crystal display element using a three-terminal or two-terminal element such as ΤFΤ or MIM or a simple matrix liquid crystal display element to obtain excellent effects.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a liquid crystal display element of the present invention.

FIG. 2 is a diagram showing a configuration of a liquid crystal display element of Example 1 of the present invention.

FIG. 3 is a diagram showing a configuration of a liquid crystal display element of Example 6 of the present invention.

FIG. 4 is a diagram showing a configuration of a liquid crystal display element of Example 7 of the present invention.

FIG. 5 is a diagram showing a configuration of a liquid crystal display element of Example 8 of the present invention.

FIG. 6 is a diagram showing the viewing angle dependence of luminance at the time of each gradation display in the conventional example.

[Explanation of symbols]

 1 ... Liquid crystal panel 2 ... Incident light 3 ... Diffusing element 4 ... Parallelizing element

Claims (9)

[Claims] 1. A liquid crystal cell having a plurality of pixels, a collimating means for allowing parallel light to enter the liquid crystal cell, a diffusing means for diffusing light emitted through the liquid crystal cell, and each of the pixels. And a color filter provided on the liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal cell includes a substrate on which active elements such as thin film transistors and thin film diodes are formed for each pixel, and the color filter is disposed on the substrate. A liquid crystal display element characterized by being provided. 3. The liquid crystal display element according to claim 1,
A liquid crystal display device, wherein the color filter is provided in the parallelizing means. 4. The liquid crystal display element according to claim 1,
A liquid crystal display device, wherein the color filter is provided in the diffusion means. 5. The liquid crystal display device according to claim 1, wherein
A liquid crystal display device, wherein the color filter is provided in both the parallelizing means and the diffusing means. 6. The liquid crystal display element according to claim 1, wherein the color filter is an interference filter. 7. The liquid crystal display element according to claim 1, wherein the color filter is made of cholesteric liquid crystal or polymer liquid crystal exhibiting selective reflection. 8. The liquid crystal display element according to claim 1, wherein a polymer layer in which a liquid crystal is dispersed in a polymer is used as the diffusing means. 9. The liquid crystal display element according to claim 8,
A liquid crystal display device comprising means for applying a voltage to the polymer layer.