JPS62247329A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve time division driving characteristic by specifying angle of torsion, angle formed by light absorption axes or polarization axes of a pair of polarizing plates, and product of refractive index anisotropy and thickness of a liquid crystal layer. CONSTITUTION:An upper electrode substrate and a lower electrode substrate are arranged opposite to each other to make the direction 6 of rubbing of the upper electrode substrate nearly conform to liquid crystal molecule orientation and the direction 7 of rubbing of the lower electrode substrate nearly conform to liquid crystal molecule orientation and to make the direction and angle 10 of liquid crystal molecule in the range of above 200 deg.. On the other hand, the upper polarizing plates is placed on the outer face of the upper electrode substrate and the lower polarizing plate is placed on the outer face of the lower electrode substrate to make the angle 11 formed by the absorption axis 8 of the upper polarizing plate and absorption axis 9 of the lower polarizing plate within the range from 60 deg. to 120 deg.. It is desirable to make the product of refractive index anisotropy DELTAn of the liquid crystal and thickness (d) of the liquid crystal layer within the range from 0.2mum to 0.7mum. Thereby, sufficient contrast can be obtained in time division driving when duty ratio is less than 1/100.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element, and more particularly to a t-twist chit nematic (TN) type liquid crystal display element with improved time division characteristics.

[Conventional technology]

In general, in a liquid crystal display device, in order to align the liquid crystal molecules between two electrode substrates so that they form a spiral structure, for example, there is a method called ``rubbing the surface of the electrode substrate that contacts the liquid crystal in one direction with a cloth, etc.'' It is done by rubbing method. The two electrode substrates that have been oriented in this way are placed facing each other in the rubbing direction, that is, the orientation direction, for example, in a manner that intersects each other at approximately 90 degrees, and the two electrode substrates are then exposed to a sealant. When a t-nematic liquid crystal having a positive dielectric anisotropy t is filled in the gap, the liquid crystal molecules rotate about 90° at the electrodes and form a nine-helical molecular arrangement.

Polarizing plates are provided above and below this L-shaped T liquid crystal cell, and the light absorption axis or polarization axis of the polarizing plates substantially coincides with the rubbing direction of the two upper and lower T-pole substrates, respectively.

FIG. 2 is a model showing the relationship between the rubbing direction of the conventional TN type liquid crystal display element and the axis of the polarizing plate as described above. In the figure, 1tl'i is the rubbing direction of the upper electrode substrate, 2 is the rubbing direction of the lower electrode substrate, 5 is the light absorption axis of the upper polarizing plate, or A: 4 optical axis, 4 is the lower @ light absorption of the polarizing plate. 41 or the polarization axis, 5ri is the twist direction of the liquid crystal molecules and the angle change.

In recent years, electro-optical characteristics of liquid crystal display devices, especially in the time division section, have been developed.
Requirements for iJ characteristics are becoming stricter, and we have reached a situation where it is not possible to meet these required specifications.

[Problems that the invention attempts to solve]

In a liquid crystal display device, when the duty ratio is low (ms), such as a duty ratio of 1/10 G or less, sufficient contrast cannot be obtained, which poses a problem.

[The child actor who solves the intervening vertices]

In order to solve this problem, in the display device of the present invention, the internal twist of the liquid crystal molecules is in the range of 200 degrees or more, and the angle between the light absorption axes or polarization axes of the pair of polarizing plates is from 60 degrees to 120 degrees. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the thickness d (μm) of the liquid crystal layer is from 12 μm to 17
All characteristics are that it is within the μm range.

[Effect]

With the present invention, sufficient contrast can be obtained in time-division driving with a duty ratio of 1/100 or less.

[Implementation row]

FIGS. 1(a), (b), and (C) are model diagrams showing the relationship between the rubbing direction of the ninth liquid crystal display element and the axis of the polarizing plate, illustrating an example of the liquid crystal display element according to the present invention. . In the figure, 61j is the rubbing direction of the upper electrode substrate, 7 is the rubbing direction of the lower electrode substrate, 8 is the absorption axis or polarization axis of the upper polarizing plate, 9 is the absorption axis or polarization axis of the lower polarizing plate, and 10 is the liquid crystal Molecular twist direction and angle, 1
1ri indicates the angle formed by the absorption axis or polarization axis of the upper and lower polarizing plates.

That is, the 2-pin direction 6 of the upper electrode substrate almost matches the liquid crystal molecule orientation, the rubbing direction 7 of the lower f11 electrode board almost matches the liquid crystal molecule orientation, and the twist direction and angle 10 of the liquid crystal molecules are 200 degrees. In order to achieve the above range, the upper electrode substrate and the lower electrode substrate are arranged facing each other. In this case, the twist direction L and angle 10 of this liquid crystal molecule are above,
A photochromic substance that induces a twisting angle of 10 in the twist direction of liquid crystal molecules is added to the nematic liquid crystal sandwiched between the lower electrode substrates, and the helical pitch P of the mixed liquid crystal is at least equal to the thickness d of the liquid crystal layer. ? <3 (In order to have the relationship of
The angle 11 formed between this and the absorption axis 9 of the lower light plate is 60 degrees to 1
The upper a polarizing plate is electrically distributed to the outer surface of the upper electrode substrate, and the lower polarizing plate is electrically distributed to the outer surface of the lower electrode substrate so that the range is up to 20 degrees. Note that the polarizing plate can also be used with the polarizing axis instead of the absorption axis.

FIG. 3 shows the voltage-luminance characteristics in the vertical direction of a 'rN type liquid crystal display element in which the angle between the absorption axes of a pair of polarizing plates is 90e. In the same figure, the voltage t”Vto s at which i4I& becomes 10% and the voltage t”Ve at which 909k
・When , the quantity β representing the time division drive characteristic is β” Vto/Ve.

It is defined as In this case, β shows a value of 1 or more, and the closer it gets to 1, the better the time-division drive characteristics are.

Using a nine-mixed liquid crystal mainly composed of lf, ester microhexane (KCH) liquid crystal, we measured the change in tC in the cell capacity with respect to voltage under conditions of twist angles of 90 degrees and 240 degrees for the △ndΣα5μ beak liquid crystal molecules. However, results as shown in FIG. 4 were obtained, in which the t0 curve has a twist of 90 degrees and the curve has a twist angle of 240 degrees.

As is clear from FIG. 4, the capacitance C becomes more abrupt when the twist angle of the liquid crystal molecules is 240 degrees than when it is 90 degrees, indicating bistability. This suddenness becomes noticeable at temperatures above 200 degrees.

Furthermore, the twist angle of the liquid crystal molecules and the time-division characteristic value β were measured under the conditions that Δnd: 15 μm and the angle between the absorption axes of the pair of polarizing plates was 90 degrees, and the results were as shown in Figure 5. Obtained.

As is clear from Figure 5, the twist angle of the liquid crystal molecules is 200
The torsion angle of 90 degrees or more shows a good value. Both values are effective power ratio 1.10 with duty ratio 17100.
5 and a duty ratio of 1/100 driving provides contrast in static driving amount.

Furthermore, △ndχ15μm, the twist angle of liquid crystal molecules is 24
When the absorption axis of the upper polarizing plate and the rubbing direction of the upper substrate were made to match under the 0 degree condition, the transmittance of the selected part with respect to the angle formed by the absorption axes of the pair of polarizing plates was measured, as shown in Figure 6. I got the results.

As is clear from FIG. 6, when the angle formed by the absorption axes of the pair of polarizing plates is around 90 degrees, the transmittance of the selective portion is the smallest, and the contrast ratio is improved. However, if the angle formed by the absorption axes of a pair of polarizing plates is less than 60 degrees or more than 120 degrees, the transmittance will be 3.
The contrast ratio becomes more than 0 and a sufficient contrast ratio cannot be obtained. Therefore, the angle formed by the absorption axes of a pair of polarizing plates is 60 degrees to 1
A range of up to 20 degrees is preferred. The best contrast is obtained when the angle between the absorption axis of the upper polarizing plate and the rubbing direction of the upper substrate ranges from 0 degrees to 50 degrees.

FIG. 7 shows an example of the structure of the present invention. The upper and lower north electrode substrates 100° 101 are aligned by rubbing, and the upper and lower 'Ii electrode substrates 100, 101 are used as a sealant. J[L, 7j E with positive ru'1 anisotropy in the gap
Filled with CH-based nematic liquid crystal 102, upper and lower polarizing plates 1
05 and 104 are arranged on the outer surfaces of the upper and lower electrode substrates 100 and 101, respectively.
is made to coincide with the rubbing direction 106 of the upper electrode substrate 10G.

The absorption axis 107 of the lower polarizing plate 104 is at 90 degrees with the absorption axis 105 of the upper polarizing plate 105. The twist angle of liquid crystal molecules is 240 degrees.

g7 In Figures (a), (b), and (c), the upper polarizing plate 10
When the light enters vertically into the upper polarizing plate 105, it becomes linearly polarized light, and when it passes through the TN liquid crystal layer, it becomes elliptically polarized light. (a) is an explanatory diagram of the principle, (b) is an explanatory diagram of the OFF state, and (C) is an explanatory diagram of the ON state. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer is [lL
If it is less than 7 μm, the date wheel becomes a little larger and cannot follow the twisting of the liquid crystal, so the long sleeve direction of the oval is approximately 90 degrees from the second pin direction 106 of the upper electrode substrate 100, and the lower This almost coincides with the direction of the absorption axis 107 of the polarizing plate 104. In other words, it becomes brighter when no voltage is applied. However, when voltage is applied, the liquid crystal molecules stand up and the upper polarizing plate 1
05, the nine straight-polarized light is absorbed as it is by the absorption axis 107 of the lower polarizing plate 104. That is, it becomes dark when voltage is applied. Refractive index anisotropy △n of liquid crystal and thickness d' of liquid crystal layer
7) When the product Δnd becomes 12 μm or less, the angle that the long sleeve direction of the ellipse makes with the rubbing direction 106 of the upper electrode substrate 100 becomes smaller and becomes darker. However, the refractive index anisotropy of liquid crystal △
The product of n and the thickness d of the liquid crystal 1 △n (l is from 12 μm to (1
A range of up to 7 μm is preferred.

〔Effect of the invention〕

According to the present invention as described above, a liquid crystal display device with excellent oscillation characteristics can be realized.

[Brief explanation of drawings]

11th drawing←+〒← is an explanatory diagram showing the relationship between the rubbing direction of a liquid crystal display element and the axis of a light plate by Akira Honkaku,
The figure is an explanatory diagram showing the relationship between the rubbing direction and the polarization axis of a conventional TNM liquid crystal display element, and Fig. 5 is a voltage-luminance! Figure 4C is an explanatory diagram showing the relationship between capacitance IC and applied voltage in the embodiment of the present invention, and Figure M5 is an explanatory diagram showing the relationship between the twist angle of liquid crystal molecules and the time-division drive characteristic in the embodiment of the present invention. The sixth factor is an explanatory diagram showing the relationship between the twist angle of the liquid crystal molecules and the transmittance of the selective part in the embodiment of the present invention. Figure 7 is the diagram showing the structure of the liquid crystal display element in the embodiment of the present invention. FIG. The above person is the representative of Seiko Nibunon Co., Ltd., a patent attorney. fj4 (skin) Fig. 5 411 circleffl/'1jLQK axis tr'jJ angle 1 degree]
Figure 6 4-1-1 Figure 7

Claims (2)

[Claims] (1) A liquid crystal cell comprising a twisted oriented nematic liquid crystal sandwiched between two electrode substrates disposed facing each other, and a pair of polarizing plates disposed on both sides sandwiching the liquid crystal cell,
The nematic liquid crystal has a twist angle of 200 degrees or more, the angle formed by the absorption axis or polarization axis of the pair of polarizing plates is in the range of 60 degrees to 120 degrees, and the refractive index of the nematic liquid crystal is A liquid crystal display element characterized in that the product Δn·d of the anisotropy Δn and the thickness d of the liquid crystal is set within a range of 0.2 μm to 0.7 μm. (2) The twist angle of the nematic liquid crystal is from 220 degrees to 2
A liquid crystal display element according to claim 1, characterized in that it has a range of up to 60 degrees.