JPS63314520A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve contrast and visibility in spite of high time-sharing driving by forming transparent electrodes and oriented films subjected to a rubbing treatment on the opposite surfaces of parallel supporting substrates of a liquid crystal display element and generating 180-260 deg. twist angle in the nematic liquid crystal sealed therebetween. CONSTITUTION:This element has the polyimide oriented films which are subjected to the rubbing treatment and are so disposed as to generate >=180 deg. twist angles in the liquid crystal molecules. Namely, the liquid crystal molecules 14a of the liquid crystal layer 14 are horizontally oriented on the oriented films 13 and the directions of the liquid crystal molecules 14a in the intermediate liquid crystal layer 14 are twisted gradually by >=180 deg.. The pitch of the twists changes and the refractive index changes when a voltage is impressed between the transparent electrodes 12. The wavelength to the passed therethrough is then changed. The light passing between polarizing plates 15 and 16 is, therefore, controlled and the display is executed. The number of scanning electrodes is thereby increased and the contrast and the visibility are improved at the high time-sharing driving of about 1/32-1/200 duty ratio.

Description

[Detailed Description of the Invention] [Summary] The present invention is a nematic liquid crystal display device in which a transparent electrode and a rubbed alignment film are formed on opposing surfaces of a parallel supporting substrate, and a chiral agent is added and sealed between the two. on 18
It is configured to produce a twisting angle of 06 to 260 degrees, and the contrast and visibility are improved even in high time division driving.

[Industrial application field]

The present invention relates to a liquid crystal display element using nematic liquid crystal, and more particularly to a liquid crystal display element suitable for high time division driving by providing a twisting angle between substrates using a polyimide alignment film.

[Conventional technology]

Conventionally, liquid crystal display has been achieved by changing the alignment state of liquid crystal molecules by changing external groups such as electric fields, and using the resulting effects such as light propagation, interference, scattering, optical rotation, and absorption. There is.

As this liquid crystal display device, twisted nematic (TN) type liquid crystal panels are widely used.

In a TN type liquid crystal panel, the liquid crystal molecules have a 90° (π/
By creating a torsion angle of 2 radians and applying a selective voltage, liquid crystal molecules are controlled and display is performed.

FIG. 5 is a diagram showing the structure of a conventional twisted nematic liquid crystal display element, and FIG. 6 is an explanatory diagram showing the twisted state of liquid crystal molecules. In these figures, a liquid crystal display element includes a parallel support substrate 1.1 made of two sheets of glass or the like, a transparent electrode 2.2 formed on the parallel support substrate 1.1, and a transparent electrode 2.2 formed on the parallel support substrate 1.1. Provided polyimide alignment film 3
．． 3, a nematic liquid crystal layer 4 sealed between the alignment films 3.3, and polarizing plates 5.5 disposed on the outside of two parallel support substrates 1.1.

The alignment film 3.3 is subjected to a rubbing treatment, and the surface of the alignment film 3.3 has an inclination angle of about 1° to 3°. The liquid crystal molecules 4a of the liquid crystal layer 4 are horizontally aligned along the tilt angle on the alignment film 3.3, and this alignment direction is
．． Between 3 and 3, the arrangement is changed by 906. Therefore, the sixth
As shown in the figure, within the intermediate liquid crystal layer 4, the orientation of the liquid crystal molecules 4a is gradually twisted over 90 degrees. In recent years, liquid crystal display elements having this structure are arranged in a matrix, and are driven by a time-division driving method in which vertical and horizontal electrodes are appropriately selected and voltages are applied time-divisionally between them.

[Problem that the invention seeks to solve]

In conventional twisted nematic liquid crystal display elements, as the number of scanning electrodes increases, the difference between the effective values of the voltages applied to the pixels to which a selection voltage is applied and the voltages applied to non-selected pixels gradually decreases, and the contrast deteriorates. There was a problem with poor visibility. Therefore, the conventional twisted nematic type liquid crystal display element cannot be subjected to high time division driving, and high display quality cannot be obtained.

The present invention was made in order to solve such problems, and its purpose is to provide a liquid crystal display element that can prevent a decrease in contrast during high time division driving and improve visibility. It is in.

[Means for solving problems]

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

In the same figure, 11.11 is a parallel support substrate, 12.12
13. 13 is a transparent electrode, 13 is a polyimide alignment film that has been subjected to a rubbing treatment and is arranged to produce a twist angle of 1000 or more in liquid crystal molecules, 14 is a layer of nematic liquid crystal added with a chiral agent, 15 is a purple polarizing plate, 16 is a neutral gray polarizing plate.

[For production]

The liquid crystal molecules 14a of the liquid crystal Ji14 are horizontally aligned on the alignment film 13.13, and the orientation of the liquid crystal molecules 14a is gradually twisted over 1000 degrees within the intermediate liquid crystal Jfflld. By applying a voltage between the transparent electrodes 1, 2, and 12, the twist pitch changes, the refractive index changes, and the wavelength that passes through changes. This controls the light passing between the polarizing plates 15 and 16 to perform display. In this liquid crystal display, the number of scanning electrodes increases and the duty ratio is 1/32 to 1.
Contrast and visibility are improved in high time division driving of about /200.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a liquid crystal display element for high time division driving according to an embodiment of the present invention.

In the same figure, the liquid crystal display element consists of two parallel supporting substrates 11.
Transparent electrodes 12.12 and alignment films 13.13 are formed on opposite surfaces of the liquid crystal display device 1, respectively, and a liquid crystal layer 14 is sealed between them. The transparent electrodes 12.12 are formed, for example, in a matrix shape vertically and horizontally. The liquid crystal layer 14 is formed by adding 1 to 2% chiral nematic (cholesteryl nonanoate) to a nematic liquid crystal having positive dielectric constant anisotropy, so that the liquid crystal molecules 14a have a natural pitch P (length when twisted by 360"). and d/p is set to a value between 0.40 and 0.48.Also, the alignment film 13.13 is made of a polyimide material, and the film thickness is set to 700 to 1500 by printing or spin coding. The surface of the alignment film 13.13 has an inclination angle of about 1° to 3° by rubbing with a cloth or the like.Also, the alignment film 13.13 covers the thickness d of the liquid crystal N14, with the liquid crystal molecules 14a having an angle of about 180°. ” (π radians). In addition, the thickness d of the liquid crystal N14 and the refractive index anisotropy Δn of the liquid crystal
Product Δn- of (difference n, -n0 in refractive index between extraordinary light and normal light)
The value of d is between 0.8 and 1.2, and the isotropic transition temperature of the liquid crystal itself (the temperature at which the liquid crystal liquefies when the temperature rises) is 90° C. or higher.

Further, a purple polarizing plate 15 is placed on the front side (top side) of one parallel support substrate 11, and a neutral gray polarizing plate 15 is placed on the back side (bottom side) of the other parallel support substrate 11. 16 are arranged.

In the liquid crystal display element having the above configuration, the liquid crystal I
The liquid crystal molecules 14a of J14 are horizontally aligned along the inclination angle on the alignment film 13.13, and within the intermediate liquid crystal layer 14, the direction of the liquid crystal molecules 14a is gradually twisted over 180e. By applying a voltage between the transparent electrodes 12 and 12, the twist pitch P changes, the refractive index changes, and the transmitted wavelength changes. As a result, the polarizing plate 15
・The light passing through the 16 spaces is controlled and the display is performed.

In this liquid crystal display, the number of scanning electrodes increases especially in high time division driving, and the contrast improves when the duty ratio is about 1/32 to 1/200, and the visibility is also about twice that of the conventional display. Has a visual angle. The best results in terms of color appearance, contrast, and brightness are obtained when the product Δn-d of the thickness d of the liquid crystal layer 14 and the refractive index anisotropy Δn is from 0.8 to 1.2. It will be done. Furthermore, in the liquid crystal display element of this example, if both polarizing plates are neutral gray, the color will be green, but since one uses the purple polarizing plate 15, the background color is white and the text color is white due to the three primary colors of light. becomes dark blue and becomes easier to see.

FIG. 3 is a diagram showing the structure of a liquid crystal display element for high time division driving according to another embodiment of the present invention.

In the same figure, the liquid crystal display element is similar to the above embodiment.
Transparent electrodes 22.22 and alignment films 23.23 are formed on the opposing surfaces of parallel support substrates 21.21 made of two sheets of glass, etc. and arranged at an interval of d" (μm), and a liquid crystal is placed between them. The liquid crystal layer 24 is made by adding 1 to 2% chiral nematic to a nematic liquid crystal having positive dielectric constant anisotropy, as in the previous embodiment, to give a natural pinch P', and d'/ p' from 0.60 to 0.
The value is between 69 and 69. The alignment film 23.23 is made of a polyimide material, and the film thickness is 700 to 1500, and the surface is coated with 5e by rubbing with a cloth or the like.
It has an inclination angle of about ~76. And alignment film 2
3.23 is arranged in proportion to the thickness d' of the liquid crystal layer 24, so that the liquid crystal molecules 24a thereof produce a molecular torsion angle of approximately 240° to 260°. Further, as in the above embodiment, the value of the product Δn'·d' of the thickness d' of the liquid crystal layer 24 and the refractive index anisotropy Δn' of the liquid crystal is between 0.8 and 1.2, and the value of the liquid crystal itself is between 0.8 and 1.2. The isotropic transition temperature is set to 90'' or higher.Furthermore, as in the previous embodiment, parallel supporting substrates 21 and 21 are provided.
A purple polarizing plate 25 and a neutral gray polarizing plate 26 are arranged on both sides.

In the liquid crystal display element having the above structure, as shown in FIG.
The liquid crystal molecules 24a of No. 4 are horizontally aligned along the inclination angle on the alignment film 23.23, and within the intermediate liquid crystal layer 24, the orientation of the liquid crystal molecules 24a is gradually twisted over a range of 240° to 260°. As in the above embodiment, by applying a voltage between the transparent electrodes 23 and 23, the twist pitch P'
changes, the light passing between the polarizing plates 25 and 26 is controlled, and a display is performed. This liquid crystal display also functions in the same manner as the embodiment described above, and improves contrast and visibility.

In the above embodiment, the liquid crystal layer 14, 24 may contain a small amount of chiral substance added to the nematic liquid crystal so as to provide a natural pitch. In addition, the alignment film 13.23 has an inclination angle of 1° to 3° or 5″ to 7″ by rubbing treatment corresponding to a twist angle of 180° or 240° to 260″.
'' is selected. It has been confirmed that this inclination angle is required to be approximately 5° to 7° in order to produce a torsional angle of 240° to 2600°.Furthermore, In the embodiment, a purple polarizing plate 15.25 is arranged on one side of the parallel support substrate 11.21, but it is used when the background color is white and the text color is dark blue, and it can also be used when displaying in green etc. If appropriate, neutral gray may be used.Furthermore, in this embodiment, a transmissive structure is used, but a reflective structure may be used.

〔Effect of the invention〕

As explained in detail above, according to the present invention, a transparent electrode and a polyimide alignment film are formed on opposing surfaces of a parallel support substrate, and a liquid crystal layer added with a chiral substance that provides a natural pitch is sealed between them. The alignment film is arranged so that the liquid crystal molecules in the liquid crystal layer produce a twisting angle of 180° to 260″, and by applying a voltage between the transparent electrodes, the twisting pinch changes and the light passing through is controlled. This improves contrast and visibility even in high time division driving.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a liquid crystal display element for high time division driving according to an embodiment of the present invention, FIG. 2 is a diagram explaining the twisted state of the liquid crystal molecules in FIG. 1, and FIG. A diagram showing the configuration of a liquid crystal display element for high time division driving according to another embodiment of the invention, FIG. 4 is a diagram explaining the twisted state of the liquid crystal molecules in FIG. 3, and FIG. A diagram showing the structure of a nematic liquid crystal display element. FIG. 6 is a diagram illustrating the twisted state of the liquid crystal molecules in FIG. 5. 11.21... Parallel support substrate, 12.22... Transparent electrode, 13.23... Alignment film, 14.24... Liquid crystal layer, 14a, 24a... Liquid crystal molecule, 15.25. ...Purple polarizing plate, 16.26...Neutral gray polarizing plate. Along with the large w1 of the Kineseki, the crystal nose of the child is 91. Figure 1. Figure 41. The broken state of the liquid crystal molecules in figure 2. Figure 3. 's grandson lmu 1 dog! ＆lt hard eyes) Whistle 5
Figure 5: Night-cutting resistant 9-metal J-hat l and trap ■chi illustration 6 M

Claims (1)

[Claims] 1) Transparent electrodes (12, 12, 22, 22) and polyimide alignment films (13, 13, 23, 23) on opposing surfaces of parallel support substrates (11, 11, 21, 21). In a liquid crystal display element in which a nematic liquid crystal to which a chiral substance is added is sealed between the alignment films (13, 13, 23).
, 23) is subjected to rubbing treatment to give liquid crystal molecules 180° to 2
A liquid crystal display element characterized in that it is arranged to produce a twisting angle of 60°. 2) The alignment film (13, 13) is characterized in that an inclination angle of 1° to 3° is formed by rubbing when the twist angle is 180°. liquid crystal display element. 3) The alignment film (23, 23) has a twist angle of 240° to
2. The liquid crystal display element according to claim 1, wherein an inclination angle of 5° to 7° is formed by rubbing when the angle is 260°. 4) The product Δn·d of the layer thickness d (μm) of the liquid crystal and the refractive index anisotropy Δn of the liquid crystal is 0.8 to 1.2. The liquid crystal display element according to any one of Item 2 and Item 3. 5) The parallel support substrate (11, 11, 21, 21) is
Any one of claims 1 to 4, characterized in that a purple polarizing plate (15, 25) is disposed on one side and a neutral gray polarizing plate (16, 26) is disposed on the other side. The liquid crystal display element described in . 6) The liquid crystal display element according to claim 1, wherein the liquid crystal has an isotropic transition temperature of 90° or higher.