JPH06202068A - Liquid crystal display element - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a high-quality liquid crystal display device capable of ensuring high-speed response, easy to manufacture. A lower substrate 4 on which one electrode 2 and an alignment film 3 covering the electrode 2 are formed, another electrode 5 facing the one electrode 2 at right angles, and an alignment film covering the other electrode 5. The upper substrate 7 on which the liquid crystal material 6 is formed and the liquid crystal material 9 enclosed between the upper and lower substrates 4 and 7 are provided.
The ratio (K33 / K11) / (Δε / ε⊥) of the elastic constant ratio K33 / K11 and the dielectric constant ratio Δε / ε⊥ of 0.8 is set to 0.8 or more, and the liquid crystal molecules are set between the alignment films 3 and 6 to 190. ~ 210 °
Twist alignment at an angle of about
The pretilt angle of the liquid crystal molecules of the liquid crystal material 9 near 6 was set to about 2 to 4 °, and the gap d between the alignment films 3 and 6 was set to about 5.5 to 6.5 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast response type liquid crystal display device.

[0002]

Liquid crystal display devices are widely used as display devices for office automation equipment. This display device is required to have high-definition display, has a large number of pixels, requires high time-division driving, and is required to have high contrast as display characteristics. In order to meet such a demand, as a display device such as a personal computer, a super twisted nematic type (hereinafter referred to as STN type) simple matrix that can be driven in a high time division manner among liquid crystal display devices and has a relatively high contrast. A liquid crystal display device having a structure is widely used. This STN-type liquid crystal display device having a simple matrix structure includes a pair of substrates which are arranged to face each other with a predetermined space therebetween, electrodes which are arranged so as to be orthogonal to each other on inner surfaces of the pair of substrates which face each other, and the electrodes are formed. A structure in which a liquid crystal cell is formed by an alignment film formed to cover the electrodes on the surface and a liquid crystal material enclosed between the alignment films, and a pair of polarizing plates is arranged outside the liquid crystal cell so as to sandwich the liquid crystal cell. Has become. Then, liquid crystal molecules in the vicinity of the alignment film of the liquid crystal material enclosed between the alignment films are arranged in a predetermined alignment treatment direction by the alignment regulating force of the alignment film, and the liquid crystal molecules are unidirectionally aligned in accordance with a predetermined alignment treatment. Is twist-oriented at an angle of about 240 ° from one substrate to the other substrate. In this liquid crystal display device, an alignment of liquid crystal molecules is changed by applying an electric field by time-division driving between opposed electrodes, and an optical change associated with this alignment change is visualized by a pair of polarizing plates. Displays the desired display.

[0003]

By the way, in such a liquid crystal display device, the gap d between the alignment films of the liquid crystal cell is formed as narrow as about 4 to 5 .mu.m in order to obtain a high time division property and a high speed response. And, the twist angle of the liquid crystal material is 230 to 2
The steepness of the brightness change is improved by increasing it to about 50 °. The pretilt angle is increased to 6 ° or more in order to stably obtain the twisted orientation with a large angle. However, in the liquid crystal display device, the narrower the gap d between the alignment films, the more difficult it is to control the gap d, and the poorer the alignment properties of the liquid crystal molecules. The larger the pretilt angle, the worse the alignment stability becomes. Therefore, when manufacturing a STN type liquid crystal display device having a high-speed response, it is difficult to secure the above-mentioned narrow gap (liquid crystal layer thickness) d between the alignment films and a large pretilt angle with high accuracy, and the quality and the manufacturing yield are improved. There is a problem of causing a decrease. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display element that can secure a high-speed response, is easy to manufacture, has an improved yield, and has good quality. .

[0004]

In order to achieve the above object, the present invention provides a pair of substrates which are arranged to face each other, and electrodes which are formed on the inner surfaces of the pair of substrates which face each other and which face each other by intersecting each other. 4. A pair of substrates are provided with an alignment film formed to cover the electrodes on the inner surfaces facing each other, and a twist-aligned liquid crystal material interposed between the alignment films of the pair of substrates. The pretilt angle of the liquid crystal molecules of the liquid crystal material in the vicinity of the alignment film is set to 5 to 6.5 μm by 2 to 4 °.
Liquid crystal molecules are twist-aligned between the alignment films at an angle of 190 to 210 °, and the bent elastic constant K3 of the liquid crystal material is
Elastic constant ratio K, which is the ratio of 3 to the spray elastic constant K11
33 / K11 and the dielectric constant ratio Δ, which is the ratio of the dielectric anisotropy Δε of the liquid crystal material and the dielectric constant ε⊥ in the direction orthogonal to the liquid crystal molecular axis.
The ratio of ε / ε⊥ (K33 / K11) / (Δε / ε⊥) is set to 0.8 or more.

[0005]

According to the present invention, the elastic constant ratio K3 of the liquid crystal material is
Ratio of 3 / K11 and dielectric constant ratio Δε / ε⊥ (K33 / K1
By setting 1) / (Δε / ε⊥) to 0.8 or more, the steepness of the luminance change with respect to the applied voltage is improved, so that the twist angle of the liquid crystal molecules can be reduced to about 190 to 210 °. Since the twist angle is small, stable orientation can be obtained in the range where the pretilt angle is as small as 2 to 4 °. Further, since the steepness is good, the gap d between the alignment films is set to 5.5.
Even if it is increased to ~ 6.5 μm, high-speed response can be secured,
As a result, it is possible to obtain a high-speed, fast-response STN type liquid crystal display device which is easy to manufacture and has a high yield.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. FIG. 1 shows a sectional view of the liquid crystal display device. In this figure, a liquid crystal cell 1 includes a substrate 4 on which one electrode 2 and an alignment film 3 covering the electrode 2 are formed, an electrode 5 on the other side which is orthogonal to the electrode 2 on the one side, and the other electrode 5 on the other side. The other substrate 7 on which the alignment film 6 covering the electrode 5 is formed, the sealing material 8 that joins the pair of substrates 4 and 7 at a predetermined interval, and the pair of substrates 4 and 7 and the sealing material 8. Liquid crystal material 9 enclosed in enclosed area
It consists of A polarizing plate 10 is provided on each side of the liquid crystal cell 1 across the liquid crystal cell 1.

In this liquid crystal cell 1, the alignment film 3 on the lower substrate 4 is formed.
And the alignment film 6 on the upper substrate 7 has a gap d of 5.5 to
The thickness is about 6.5 μm. And the liquid crystal cell 1
In the liquid crystal material 9, the pretilt angle of the liquid crystal molecules adjacent to the alignment films 3 and 6 is about 2 to 4 °, and the liquid crystal molecules are twist-aligned between the alignment films 3 and 6 at an angle of about 190 to 210 °. It has been enclosed. The liquid crystal material 9 has an elastic constant ratio K33 / K11 represented by a ratio of the vent elastic constant K33 and the splay elastic constant K11, a dielectric anisotropy Δε, and a dielectric constant (dielectric constant) in a direction orthogonal to the liquid crystal molecular axis. Vertical component) ε⊥ and the ratio (K33 / K11) / (Δε / ε⊥) with the dielectric constant ratio Δε / ε⊥ are set to 0.8 or more.

In such a liquid crystal display device, the ratio (K33 / K11) / (Δε / ε⊥) of the elastic constant ratio K33 / K11 of the liquid crystal material and the dielectric constant ratio Δε / ε⊥ is set to 0.8 or more. By doing so, the steepness of the luminance change becomes extremely good. That is, as shown in FIG. 2 showing the relationship between the reciprocal of (K33 / K11) / (Δε / ε⊥) and the steepness γ of the luminance change, the steepness γ of the liquid crystal display device has a value of The value of the elastic constant ratio (K33 / K11) is larger than the value of (Δε / ε⊥), and the smaller the value of the dielectric constant ratio Δε / ε⊥ is, the closer to 1.0 the steepness is improved. . In particular, when the ratio (K33 / K11) / (Δε / ε⊥) of the elastic constant ratio K33 / K11 to the dielectric constant ratio Δε / ε⊥ is 0.8 or more, that is, in FIG. 2, (Δε / ε⊥) / (K
When 33 / K11) is 1.25 or less, the steepness becomes extremely good.

Thus, the liquid crystal material (K33 / K11)
When / (Δε / ε⊥) is set to 0.8 or more, when the liquid crystal of d / p margin (natural pitch p is enclosed between the upper and lower substrates of the gap d, the liquid crystal molecules are twist-aligned at a predetermined twist angle. And a gap d for obtaining uniform twist orientation without unevenness even when a voltage is applied.
3), the upper limit of the d / p margin becomes
However, in the liquid crystal display element of the present invention, the twist angle of the liquid crystal molecules is small in the range of 190 to 210 °, and the d / p margin and the twist are small. As is clear from FIG. 4 showing the relationship of the angles for each pretilt angle, a smaller pretilt angle is sufficient for decreasing the twist angle.
Since a margin can be obtained, a stable alignment state can be obtained. In this case, even if the twist angle of the liquid crystal molecule is reduced,
Elastic constant ratio K33 / K11 of liquid crystal material and dielectric constant ratio Δε /
Since the ratio to ε⊥ is 0.8 or more, it is possible to prevent the steepness of the luminance change from decreasing and to secure a high contrast.

As a result, even if the twist angle of the liquid crystal molecules is small and the gap d between the alignment films 3 and 6 is widened to about 5.5 to 6.5 μm, the pretilt angle is small, so these values should be controlled. Therefore, it is possible to obtain a high-speed response liquid crystal display device with improved yield and improved yield.

Next, a specific example of the liquid crystal display device of the present invention and a conventional liquid crystal display device will be described in comparison. Gap d
Is 5.8 μm, the twist angle is 200 °, and the pretilt angle is 4 °, the steepness is 1.059.
The response speed is 230 msec. On the other hand, in the conventional liquid crystal display device, the gap d is set to 5.0 μm, the twist angle is set to 230 °, and the pretilt angle is set to 7 °. The steepness is 1.059 and the response speed is 220 ms.
ec. Therefore, in the embodiment of the present invention, the steepness is the same and the high-speed response is ensured, although the gap d is larger and the twist angle is smaller than the conventional one. Moreover, in this specific example,
Since the gap d is larger and the pretilt angle is smaller than the conventional one, it is possible to obtain a high-speed liquid crystal display device which is easy to manufacture and has good quality.

[0012]

As described above, according to the present invention, the elastic constant ratio K33 / K11 and the dielectric constant ratio Δ of the liquid crystal material are
Since the ratio of ε / ε⊥ (K33 / K11) / (Δε / ε⊥) is set to 0.8 or more, the twist angle of liquid crystal molecules can be reduced to about 190 to 210 ° without lowering the steepness. , The twist angle has been reduced, so the pretilt angle is
Since it can be reduced to about 4 ° and the steepness is good, the liquid crystal molecules can be stably aligned, and high-speed response can be secured even if the gap d between the alignment films is widened to about 5.5 to 6.5 μm. As a result, it is possible to obtain a high-speed response liquid crystal display element which is easy to manufacture and has good quality.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display device as an embodiment of the present invention.

[FIG. 2] Elastic constant ratio K33 / K11 and dielectric constant ratio Δε / ε
The figure which shows the characteristic of steepness with respect to the ratio with ⊥.

[FIG. 3] Elastic constant ratio K33 / K11 and dielectric constant ratio Δε / ε
The figure which shows the characteristic of the upper limit of d / p margin with respect to the ratio with ⊥.

FIG. 4 is a diagram showing a relationship between a twist angle and a d / p margin for each pretilt angle.

[Explanation of symbols]

 1 Liquid crystal cell 2, 5 Electrode 3, 6 Alignment film 4, 7 Substrate 9 Liquid crystal material

Claims (1)

[Claims] 1. A pair of substrates that are arranged to face each other, electrodes that are formed on the inner surfaces of the pair of substrates that face each other and that face each other by intersecting each other, and a pair of substrates that are formed to cover the electrodes on the inner surfaces that face each other. Aligned alignment film and a twisted alignment liquid crystal material interposed between the alignment films, the gap d between the alignment films is set to 5.5 to 6.5 μm, and the liquid crystal material is aligned to the alignment film. The liquid crystal molecules near the film have a pretilt angle of 2 to 4 °, the liquid crystal molecules are twist-aligned between the alignment films at an angle of 190 to 210 °, and the vent elastic constant K33 and the splay elastic constant K11 of the liquid crystal material are The ratio of the elastic constant ratio K33 / K11, which is the ratio of the above, and the dielectric constant ratio Δε / ε⊥, which is the ratio of the dielectric anisotropy Δε of the liquid crystal material and the dielectric constant ε⊥ in the direction orthogonal to the liquid crystal molecular axis ( K33 / K11) / (Δε / ε⊥) is 0 The liquid crystal display element characterized by 8 or more.