JPH02264920A - liquid crystal electro-optical element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal electrooptical element which is less colored in display by specifying the wavelength dispersion value nuRF of the double refractive index DELTAn of an optically anisotropic body to the value larger than the wavelength dispersion value nuLC of DELTAn of a liquid crystal cell. CONSTITUTION:The wavelength dispersion value nuRF of the double refractive index DELTAn of a uniaxially stretched film 3 of the liquid crystal electrooptical element using the FTN mode of the constitution consisting in inserting the liquid crystal cell 2 which crimps a twist-oriented liquid crystal 8 between two sheets of electrode substrates facing each other and the uniaxially stretched film 3 of a high polymer as the optically anisotropic body in a pair of polarizing plates 1, 4 is specified to the value larger than the wavelength dispersion value nuLC of DELTAn of the liquid crystal cell 2 and to the value preferably larger than 1.3. Certain one refractive index N3e among the three main refractive indices N10, N20, N3e possessed by the optically anisotropic body is so determined that the value thereof is smaller than the other two refractive indices N10, N20 and the axis corresponding to the refractive index N3e exists in the direction approximately horizontal with the substrate surface of the liquid crystal cell 2. The coloration is decreased down to about the level at which the coloration of the display is negligible.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid crystal electro-optical device.

[Prior Art] In the conventional super twisted nematic mode, there was a unique coloration in the display. In order to reduce this,
A liquid crystal display mode that includes an optically anisotropic body separate from the liquid crystal cell that performs display has been proposed in Japanese Patent Application No. 121701/1982. The mode in which a uniaxially stretched polymer film is used as the optically anisotropic body is hereinafter referred to as the FTN mode.

Figure 1 shows a cross-sectional view of a conventional liquid crystal electro-optical element using FTN mode, in which 1 is an upper polarizing plate, 2 is a liquid crystal cell, 3 is a uniaxially stretched film, and 4 is a lower polarizing plate. .

The liquid crystal 8 of the liquid crystal cell is a nematic liquid crystal 3 manufactured by Chisso.
8-4008 was used. The birefringence Δn of this liquid crystal for light with a wavelength of 590 nm is 0.15. Since the cell gap d was set to 6°0 μm, the retardation Δnd was 0°90 μm. On the other hand, a polycarbonate-based polymer film was used as the -axis stretched film.

Its Δn (590nm) is 0.005, and d is 115μ
m and Δnd are 0.575 μm.

Here, the wavelength dispersion value V of Δn is defined by Δn for light with a wavelength of 450 nm and Δn for light with a wavelength of 650 nm as shown in the following equation.

y=Δn (450 nm)/Δn (650 nm) The y values of the above-mentioned liquid crystal (LC) and -axis stretched film (RF) are as follows.

VLC=1. 17 y*F=1.12 Conventionally, the y value of a uniaxially stretched film was smaller than that of a liquid crystal. This is mainly because films with smaller y values are easier to manufacture.

FIG. 2 shows a relationship diagram of each axis of a conventional liquid crystal electro-optical element. The angle 20 that the polarization @ (absorption axis) direction 10 of the upper polarizing plate makes with the rubbing direction 11 of the upper substrate of the liquid crystal cell is 4 to the left.
5°, the twist angle 21 of the liquid crystal of the liquid crystal cell is 230° to the left -
The angle 22 that the stretching direction 13 of the axially stretched film makes with the rubbing direction 12 of the lower substrate of the liquid crystal cell is 90 @, and the angle 23 that the polarization axis (absorption axis) direction 14 of the lower polarizing plate makes with 13 is 4 on the left.
5'.

Figure 5 shows the spectral characteristics of the conventional liquid crystal electro-optical device manufactured under the above conditions when it is on and off.The display contrast is about 1:25, which is sufficient for practical use. .

[Problems to be Solved by the Invention] However, the conventional liquid crystal electro-optical device using the FTN mode has a problem in that coloring remains when the device is off due to insufficient optical compensation.

The present invention has been made to solve these problems, and aims to provide a liquid crystal electro-optical element with less coloring in display by making the VRF value larger than the YTC value.

[Means for Solving the Problems] The liquid crystal electro-optical device of the present invention includes a liquid crystal cell comprising a twistedly oriented liquid crystal sandwiched between two opposing electrode substrates, and at least one optically different layer in addition to the liquid crystal. In a liquid crystal electro-optical element comprising a parallelepiped and a pair of polarizing plates disposed on both sides of the parallelepiped, the birefringence Δ of the optically anisotropic body is
A wavelength dispersion value VRF of n is larger than a wavelength dispersion value VLC of Δn of the liquid crystal cell, and more preferably a value larger than 1.3.

In addition, the three main refractive indices N that the optically anisotropic body has
One refractive index N3 among 1o, N2o, and N3e
e is smaller than the other two refractive indices N1o and N2o,
Further, the axis corresponding to the refractive index N3e is located in a direction substantially horizontal to the substrate surface of the liquid crystal cell.

[Operation] The coloring of the FTN mode depends on the wavelength dispersion value VRF of Δn of the optically anisotropic body.

Under the conditions of the prior art described above, only the VRF value is set to 1.
0 to 1. Figure 3 shows the change in color when off when changed to 7. The * mark in the center of Figure 6 is the white point.
The closer you are to this point, the less colored it is. The 1'RF value of normal polymers is approximately 1.0 degrees,
If you make this value larger than VLC (1.17 in this case), the coloring will become smaller. The optimal value of al'RF, at which coloring is minimal at 5, is slightly affected by the tarpaulsion value of the uniaxially stretched film, but if vRF > 1.3, coloring will be reduced to an unnoticeable level. You can say that.

Hereinafter, the details of the present invention will be shown by examples.

[Implementation g4] In order to make the VRF value larger than the VLC value, the VRF
A method using a polymer material with a large value, and V3. There is a method using a liquid crystal material with a small value. These two methods will be introduced in turn below.

(Example 1) FIG. 1 shows a cross-sectional view of a liquid crystal electro-optical element in Example 1 of the present invention. In the six figures, 1 is an upper polarizing plate, 2 is a liquid crystal cell, 3 is a uniaxially stretched film, and 4 is a lower part. It is a side polarizing plate.

The liquid crystal 8 of the liquid crystal cell is a nematic liquid crystal 3 manufactured by Chisso.
8-4008 was used, and the cells with a cell gap d of 6.0 μm were twisted and oriented. One of the optically anisotropic bodies used was a film obtained by blending polyvinyl chloride with a polymeric liquid crystal compound and then stretching the mixture in the -axial direction. Film thickness is 50μ
m, retardation is 0.57 μm.

The V values of the liquid crystal and the uniaxially stretched film in this example are as follows.

yL0=1. 17 vR, = 1.30 Figure 2 shows a diagram of the relationship between each axis. The angle 20 between the polarization axis (absorption axis) direction 10 of the upper polarizing plate and the rubbing direction 11 of the upper substrate of the liquid crystal cell is 45 degrees to the left; the twist angle 21 of the liquid crystal of the liquid crystal cell is 230" to the left - the stretching direction 13 of the axially stretched film The angle 22 formed by the rubbing direction 12 of the lower substrate of the liquid crystal cell was 90°, and the angle 23 formed by the polarization axis (absorption axis) direction 14 of the lower polarizing plate 13 was 45° to the left.

FIG. 4 shows the spectral characteristics when on and off. A comparison with the spectral characteristics of the conventional liquid crystal electro-optical element shown in FIG. 5 shows that coloration during off-time is reduced without impairing high display contrast.

(Example 2) In Example 2, a liquid crystal material with a small VLC value is used to create a VR
F>VLC. Cyclohexylcyclohexane (C
Since CH)-based liquid crystal materials generally have a small wavelength dispersion of Δn, a liquid crystal mixture with a small ytc was prepared using this as a main component. On the other hand, optically anisotropic materials include polystyrene (
A film obtained by stretching PS) in the -axial direction was used. In addition,
The device configuration, cell conditions, axial relationships, etc. are the same as in Example 1.

The V values of the liquid crystal and the uniaxially stretched film in this example are as follows.

S/Lc=1. 09)'1lF=1.11 Here again, since the VRF value exceeds the VLC value, the coloring of the display is less than before.

Note that PS is a substance that exhibits negative uniaxiality, and its refractive index is N1o = 1.516, N2o = 1.518, N5
e=1.509 (N3e is the refractive index in the stretching direction of the film, that is, in the optical axis direction).Therefore, the liquid crystal electro-optical element of this example is shown in Japanese Patent Application No. 1-10405. Due to this effect, it exhibits wider viewing angle characteristics than before.

[Effects of the Invention] As described above, according to the present invention, the VRF value is
By making the value larger than the above value, it has the effect of reducing the coloring of the display.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal electro-optical element according to the present invention and a conventional liquid crystal electro-optical element. FIG. 2 is a diagram showing the relationship between the axes of the present invention and a conventional liquid crystal electro-optical element. FIG. 3 is a diagram showing the influence of the wavelength dispersion value yRF of Δn of an optically anisotropic body on coloring in the off state. FIG. 4 is a diagram showing the spectral characteristics of the liquid crystal electro-optic cable according to Example 1 of the present invention when it is on and when it is off. FIG. 5 is a diagram showing the spectral characteristics of a conventional liquid crystal electro-optical element when it is on and when it is off. 1. Upper polarizing plate 2, liquid crystal cell 3, -axis stretched film 4, lower polarizing plate 5, upper substrate 6 of liquid crystal cell, lower substrate 7 of liquid crystal cell, transparent electrode 8, twisted oriented nematic liquid crystal 10, upper side The direction 11 of the polarization axis (absorption axis) of the polarizing plate 1, the rubbing direction 12 of the upper substrate 5 of the liquid crystal cell, the rubbing direction 13 of the lower substrate 6 of the liquid crystal cell, the stretching direction 14 of the -axis stretched film 3, the lower polarizing plate The direction 20 of the polarization axis (absorption axis) of 4, the angle 21 that the direction 10 of the polarization axis of the upper polarizing plate makes with the rubbing direction 11 of the upper substrate of the liquid crystal cell, the twist angle 22 of the liquid crystal of the liquid crystal cell, the -axis stretched film The stretching direction 13 of the liquid crystal cell forms an angle 23. with the rubbing direction 12 of the lower substrate of the liquid crystal cell. The direction 14 of the polarization axis of the lower polarizing plate is the stretching direction 1 of the -axis stretched film.
3 and the angle 30, spectral characteristics when on is 31, and spectral characteristics when off ) Figure 4 Figure 5

Claims (2)

[Claims] (1) A liquid crystal cell consisting of a twistedly oriented liquid crystal sandwiched between two opposing electrode substrates, at least one layer of optically anisotropic material other than the liquid crystal, and a pair of liquid crystal cells disposed on both sides with the liquid crystal interposed therebetween. In a liquid crystal electro-optical element equipped with a polarizing plate,
Chromatic dispersion value ν_R_ of the birefringence Δn of the optically anisotropic body
F(≡Δn(450nm)/Δn(650nm)) is
A liquid crystal electro-optical element characterized in that the wavelength dispersion value ν_L_C of Δn is larger than the wavelength dispersion value ν_L_C of the liquid crystal cell. (2) Three main refractive indices N that the optically anisotropic body has
1o, N2o, and N3e, one refractive index N3e is smaller than the other two refractive indexes N1o and N2o, and the axis corresponding to the refractive index N3e is substantially parallel to the substrate surface of the liquid crystal cell. 2. The liquid crystal electro-optical element according to claim 1, wherein the liquid crystal electro-optical element is oriented in the same direction.