JPH03264920A - Time-division driving liquid crystal display element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a time-division drive liquid crystal display element, and particularly a twisted nematic (TN) device having excellent time-division drive characteristics.
The present invention relates to a type time-division drive liquid crystal display element.

[Conventional technology]

In a liquid crystal display element, in order to align the liquid crystal molecules between two electrode substrates so that they form a spiral structure, for example, a method of rubbing the surface of the electrode substrate in contact with the liquid crystal in one direction with a cloth or the like, the so-called rubbing method, is used. It will be done. The two electrode substrates that have been oriented in this way are placed opposite each other so that their respective rubbing directions, that is, the alignment directions intersect with each other at approximately 90 degrees, and the two electrode substrates are bonded together with a sealing material. When a nematic liquid crystal with positive dielectric anisotropy is filled in the gap, the liquid crystal molecules are approximately 90%
Arrange molecules in a helical structure rotated by degrees.

Polarizing plates are provided above and below the liquid crystal cell configured in this manner. This polarizing plate is arranged so that its absorption axis or polarization axis substantially coincides with the rubbing direction of the two upper and lower electrode substrates (Japanese Patent Publication No. 13666/1982).

FIG. 3 is a model showing the relationship between the rubbing direction 1.2 and the polarizing plate axis 3.4 of such a conventional TN type liquid crystal display element. In the figure, 1 is the rubbing direction of the upper electrode substrate, 2 is the rubbing direction of the lower electrode substrate, 3 is the absorption axis or polarization axis of the upper polarizing plate, 4 is the absorption axis or polarization axis of the lower polarizing plate, and 5 is the rubbing direction of the lower electrode substrate. The twist direction and angle of liquid crystal molecules are shown respectively.

[Problem to be solved by the invention]

The relationship between the rubbing direction and the axis of the polarizing plate in a conventional TN type liquid crystal display element is as shown in Figure 3, but in recent years, the electro-optical characteristics of liquid crystal display elements, especially the display area of liquid crystal display elements, have been improved. With the increase in the number of scanning lines (therefore, the number of scanning lines), the requirements for time-division drive characteristics have become stricter, and the configuration shown in FIG. 3 is no longer able to satisfy the required specifications.

An object of the present invention is to provide a time-division drive liquid crystal display element having excellent time-division drive characteristics by improving the twist angle of liquid crystal molecules and the arrangement of the axes of polarizing plates.

[Means to solve the problem]

In order to achieve this objective, the present invention aims to achieve two opposing objectives.
In a time-division drive liquid crystal display element in which a twisted oriented nematic liquid crystal is sandwiched between two electrode substrates, and a polarizing plate is arranged on the outside of both electrode substrates, by adding an optically active substance to the nematic liquid crystal, The twist angle is approximately 270 degrees, the angle between the normal to the surface of the liquid crystal display element and the observation direction is φ, and the voltage applied to the nematic liquid crystal layer is set to Vsat so that the brightness at the angle φ = 10° is 50%. The voltage applied to the nematic liquid crystal layer is Vtha, m = Vt so that the brightness at the angle φ = 40° is 90%.
hx/Vsat, the angle α formed by the absorption axes or polarization axes of the pair of polarizing plates is within the range of 90±20 degrees, and the absorption axes or polarization axes of these polarizing plates are within the range of the upper and lower two plates. 2 of the angle formed by the liquid crystal alignment directions of the electrode substrate
If the angle β formed with the equal dividing direction is within the range of ±20 degrees, the m is 0.
This is characterized in that α and β are set so as to satisfy 81<m≦1.0.

[Effect]

FIG. 2 shows typical voltage-luminance characteristics of a liquid crystal display element having a helical structure of twisted liquid crystal molecules. This is the relative value of the reflected brightness with respect to the applied voltage,
The initial value of brightness is 100%.

The final value (value when the applied voltage is sufficiently large) is set to 0%. Generally, the voltage at which the relative brightness becomes 90% is the threshold value Vth, and the voltage at which the relative brightness is 10% is the saturation value Vsat, which is used as a guideline for the characteristics of the liquid crystal. However, in practice, if it is 90% or more, the pixel is sufficiently bright and the liquid crystal is not lit, and if it is 50% or less, the pixel is sufficiently dark and the liquid crystal is lit.Hereinafter, in this specification, the relative brightness is 90%. ,50%
The voltages at which the voltage becomes the threshold voltage vth and the saturation voltage Vsat, respectively, are assumed to be the threshold voltage vth and the saturation voltage Vsat.

Further, the electro-optical characteristics of the liquid crystal display element vary depending on the viewing direction, which limits the field of view in which good display image quality can be obtained. Here, the viewing angle φ is the angle between the normal to the surface of the liquid crystal display element and the observation direction.

In Fig. 2, the voltage at which the brightness at angle φ = 10 degrees becomes 90% is vth, and the voltage at which the brightness becomes 50% is Vsa1.
When the voltage at which the brightness at angle φ = 40 degrees becomes 90% is Vthl, γ = V, which indicates the steepness of the brightness-applied voltage characteristic.
satt/Vth has a value of 1 or more, and the closer it gets to 1, the better the time-division drive characteristics are. Δφ = Vth, which indicates the observation direction angle dependent characteristic. Satt/Vth has a value of 1 or less, and The closer it gets, the wider the viewing angle range is.

Therefore, in order to simultaneously ensure good time-division drive characteristics (equivalent to characteristics that can increase the number of scanning lines) and a wide viewing angle range, m = Δφ/γ = (vthz/V thl)/
(V 5atl / vth,): Vth! /V
5att, and set the twist angle of the liquid crystal molecules and the angle formed by the absorption axis or polarization axis of the polarizing plate with respect to the liquid crystal alignment direction of the electrode substrate so that the value of m is less than 1 and closer to 1. By doing so, good time-division drive characteristics can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The liquid crystal molecule orientation at the upper electrode substrate interface substantially matches the rubbing direction 11 of the upper electrode substrate, and the liquid crystal molecule orientation at the lower electrode substrate interface substantially matches the rubbing direction 12 of the lower electrode substrate. however.

The rubbing directions 1 and 12 are substantially perpendicular to each other.

Here, an optically active substance is added to the nematic liquid crystal, and the helical pitch P of the mixed liquid crystal is larger than the liquid crystal layer thickness d, and 2
By making it smaller than d, the liquid crystal molecules take on a structure twisted by approximately 270 degrees as shown by arrow 15.

The absorption axis 13 of the upper polarizing plate and the absorption axis 14 of the lower polarizing plate are substantially perpendicular to each other. Moreover, the absorption axes 13 and 14 of these polarizing plates are in the rubbing direction 11 of the two upper and lower electrode substrates.
12 into two equal parts as shown in the figure. In addition.

As the axis of the polarizing plate, the polarizing axis may be used instead of the absorption axis.

Next, in order to explain the effects of the time-division drive liquid crystal display element having such a configuration, a quantity representing one time-division drive characteristic will be defined.

FIG. 2 shows typical voltage-luminance characteristics of a TN type liquid crystal display element. In the figure, the angle φ is the angle between the normal to the surface of the liquid crystal display element and the fRWs direction, and is defined as the direction in which the contrast increases. Then, when the voltage at which the brightness at angle φ = 10° is 50% is Vsatl, and the voltage at which the brightness at angle φ = 40° is 90% is vthx, the quantity m representing the time-division drive characteristic is m = V th z/V
Define as sat t t. m has a value of 1 or less, and the closer it is to 1, the better the time-division drive characteristics are.

Therefore, by using the same mixed liquid crystal mainly composed of ester cyclohexane (ECH) and biphenyl liquid crystals, we used
When m was measured under the condition that d is 0.6 μ■, the value of m in the conventional 1゛N type liquid crystal display element was 0.81, and in the time-division drive liquid crystal display element according to the present invention, it was significantly improved from the above value. It was 0.92. As described above, the time-division driving liquid crystal display element according to the present invention has significantly improved time-division driving characteristics. Furthermore, it was confirmed that the time-divisionally driven liquid crystal display element of the present invention exhibits higher contrast over a wider viewing angle range than the conventional time-divisionally driven liquid crystal display element.

Note that the angle α formed by the axes 13 and 14 of the upper and lower polarizing plates is preferably within the range of 90±20 degrees from the viewpoint of coloring and contrast. Further, for the same reason, it is desirable that the deviation angle β from the direction of bisection is also within ±20 degrees.

If the angles α and β are set so that the quantity m representing the time-division drive characteristic satisfies 0°81 x m≦1.0 as described above, a wide viewing angle range and excellent time-division drive characteristics (large A liquid crystal display element having the following characteristics (characteristics capable of area display) is obtained. Further, from the viewpoint of coloring, it is desirable that the Δn-d be within a range of 0.5 to 0.9 μm.

〔Effect of the invention〕

According to the present invention, the time-sharing drive characteristics such as the steepness of the change in the transmittance of the liquid crystal display element versus the voltage applied to the liquid crystal layer and the expansion of the viewing angle range are excellent, and the viewing angle is wide and the area can be increased. A time-divisionally driven liquid crystal display element can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the relationship between the rubbing direction and the polarizing plate of the time-division driving liquid crystal display element according to the present invention, and FIG.
FIG. 3 is an explanatory diagram showing the brightness characteristics. FIG. 3 is an explanatory diagram showing the relationship between the rubbing direction and the axis of the polarizing plate of a conventional T-type and N-type liquid crystal display element. 1.11...Rubbing direction of upper electrode substrate, 2.12
...Rubbing direction of the lower electrode substrate, 3.13...Absorption axis or polarization axis of the upper polarizing plate, 4.14...Absorption axis or polarization axis of the lower polarizing plate, 5.15... Twisting direction and angle of liquid crystal molecules.

Claims (1)

[Claims] 1. In a time-division drive liquid crystal display element in which a twisted oriented nematic liquid crystal is sandwiched between two opposing electrode substrates, and polarizing plates are respectively arranged on the outside of both electrode substrates,
By adding an optically active substance to the nematic liquid crystal, the twist angle is approximately 270 degrees, the angle between the normal to the surface of the liquid crystal display element and the observation direction is φ, and the brightness at angle φ = 10 degrees is 50%. The voltage applied to the nematic liquid crystal layer is Vsat_1, and the voltage applied to the nematic liquid crystal layer is Vth so that the brightness at angle φ=40° is 90%.
When defining _2, m=Vth_2/Vsat_1,
Angle α between the absorption axes or polarization axes of the pair of polarizing plates
is within the range of 90 ± 20 degrees, and the angle β between the absorption axis or polarization axis of these polarizing plates and the bisecting direction of the angle formed by the liquid crystal alignment directions of the upper and lower two electrode substrates is ± 20 degrees. α, β so that the above m satisfies 0.81<m≦1.0 within the range
What is claimed is: 1. A time-division drive liquid crystal display element characterized in that: