JPH04115224A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make a black display and to obtain improved visual dependency by laminating a optically positive liquid crystal layer which is oriented in parallel and an optical negative optical compensating layer which has an optical axis in an in-surface direction parallel to the parallel orientation direction on a substrate. CONSTITUTION:The optical axes of a homogeneous cell 101 wherein optically positive liquid crystal molecules are oriented in parallel and the optically negative optical compensating layer 102 are set parallel. When incident linear polarized light 103 which is polarized at 45 deg. to the optical axis is made incident, (x)-axial linear polarized light 104 (shown in figure) is delayed behind (y)-axial linear polarized light 105 in the homogeneous cell 101. The optical compensating layer 102, however, is optically negative, so the (x)-axial linear polarized light leads the (y)-axial linear polarized light. The phase speed in the optical axis direction is faster than the phase speed in a direction crossing it at right angles in an optically negative medium, so birefringence quantities of the both become zero and light wavelength dispersion is eliminated, so that the black display can be made.

Description

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

[Conventional technology]

Development of liquid crystal display devices is being carried out in various places. Among these, several modes called electric field-controlled birefringence modes have been proposed. In this method, a liquid crystal cell is inserted between orthogonal polarizing plates, and the birefringence of the liquid crystal cell is changed by an applied voltage to obtain a display by changing the amount of transmitted light. However, in this electric field controlled birefringence mode, since the amount of transmitted light has wavelength dispersion in cells other than vertically aligned cells, the cells are colored and a black display cannot be obtained. Further, although a vertically aligned cell is one in which liquid crystal molecules are arranged perpendicularly to a substrate, it has been known that the direction of alignment is difficult.

In order to cancel the coloring of the electric field controlled birefringence mode and obtain a black display, a liquid crystal cell having the same structure was formed into two layers.

Among these, a liquid crystal display device in which two layers of homogeneous cells in which liquid crystal molecules are aligned parallel to the substrate has been announced (Proceedings of the 37th Japan Society of Applied Physics Association Conference, p. 808).

Saito, Takahashi “Compensated homogeneously oriented nematic (CH
ON) Uncolored display by LCD"), this is shown in Figure 2 (
As shown in a), it has a structure in which the parallel orientation directions of two layers of homogeneous cells are orthogonal to each other. In this way, by using a compensated homogeneous cell, coloring can be compensated and a black display can be obtained.

[Problem to be solved by the invention]

However, the compensated homogeneous cell described above has a problem in that it is dependent on viewing angle, and it is difficult to recognize the display when viewed from an angle.

[Means to solve the problem]

The liquid crystal display device of the present invention has an optically positive liquid crystal layer aligned parallel to the substrate, and an optically negative optical compensation layer having an optical axis in the in-surface direction parallel to the parallel alignment direction. It consists of things.

[Effect]

First, a conventional compensated homogeneous cell will be explained using FIG.

As shown in FIG. 2(a), a homogeneous cell 201.
202 are arranged so that their parallel orientation directions are orthogonal. Now, consider the case where the direct *@ light 203 shown in FIG. 2(b) is perpendicularly incident on the first homogeneous cell. When the direction of the incident linearly polarized light 203 is tilted by 45 degrees to the parallel alignment direction, the incident linearly polarized light 203 becomes the linearly polarized light 20 with the same phase in the X-axis direction and the y@left direction, as shown in FIG. 2(c). 4
It can be considered as 205 combinations. When these two linearly polarized lights enter the first homogeneous cell 201,
The phase velocities in the axial direction and the y-axis direction are different. For this reason, the first
When the light is not emitted from the homogeneous cell, the two linearly polarized lights 206 and 207 already have a phase difference, not the same phase, as shown in FIG. It is determined by the characteristics of the homogeneous cell. Therefore, in a single layer of a homogeneous cell, coloration occurs due to the wavelength dependence of the retardation.

Nematic liquid crystals or smectic liquid crystals that can be homogeneously aligned are optically positive. This optically positive means that the phase velocity in the long axis direction of the liquid crystal is slower than the phase velocity in the vertical direction. Therefore, when emitted from the first homogeneous cell 207 in FIG. 2(a), the phase of the linearly polarized light 206 in the X-axis direction is delayed compared to the phase in the y-axis direction 207.

Furthermore, in FIG. 2, it can be seen that when light enters the second homogeneous cell 202, the direction of the slow phase velocity is swapped with that of the first homogeneous cell because the long axis direction of the liquid crystal is rotated by 90''. , the linearly polarized light in the y-axis direction that advances in the first homogeneous cell is delayed in the second homogeneous cell, and the linearly polarized light in the X-axis direction that is delayed in the first homogeneous cell advances in the second homogeneous cell. If the homogeneous cell and the second homogeneous cell are exactly the same, the light emitted from the second homogeneous cell will be the linearly polarized light 208 and 209 before entering the first homogeneous cell, as shown in FIG. 2(e). Therefore, the total amount of birefringence of the two layers is zero and has no wavelength dependence.Therefore, no coloring occurs and a black display is obtained.

Next, the viewing angle dependence of the homogeneous cell 301 will be explained using FIG. The amount of birefringence of the liquid crystal layer is determined by the angle between the direction of the light beam and the long axis direction of the liquid crystal molecules. If the direction of the light beam and the long axis direction of the liquid crystal molecules are parallel, the amount of birefringence is zero. Also, when the light beam direction and the long axis direction of liquid crystal molecules are perpendicular to each other,
The amount of birefringence becomes maximum. Therefore, as the light ray 302 is inclined from the normal direction 303 of the substrate of the homogeneous cell 301 as shown in FIG. 3(a), the amount of birefringence decreases as shown in FIG. 3(b).

Next, the viewing angle dependence of the compensated two-layer homogeneous cell will be explained using FIG. 4. As shown in FIG. 4(a), the light ray 404 is directed in the normal direction 4
03, the amount of birefringence 4i0 from the first homogeneous cell 401 changes as shown in FIG. 3, as shown in FIG. 4(b). On the other hand, in the second homogeneous cell 402, since the angle between the long axis of the liquid crystal molecules and the light beam does not change, the amount of birefringence 411 hardly changes even if the light beam is tilted. Therefore, as shown in FIG. 4(b), The total birefringence amount 412 of the two layers shows viewing angle dependence.

Next, the liquid crystal display device of the present invention will be explained with reference to FIG. 102. However, both optical axes must be parallel. In the present invention, the incident linearly polarized light 103 is polarized in a direction tilted by 45 degrees from the optical axis.
(Fig. 1(b)), homogeneous cell 1
01, linearly polarized light 10 in the X-axis direction shown in FIG. 1(c)
4 lags behind the direct M polarized light 105 in the y-axis direction, as shown in FIG. 1(d). However, optical compensation layer 1
02, since it is optically negative, the linearly polarized light in the X-axis direction travels relative to the linearly polarized light in the y-axis direction, as shown in FIG. 1(e). This is because in an optically negative medium, the phase velocity in the direction of the optical axis is faster than the phase velocity in the direction orthogonal thereto. Therefore, the amount of birefringence of both becomes zero, optical wavelength dispersion disappears, and black display is possible.

Furthermore, the viewing angle dependence of the present invention will be explained using FIG. As shown in FIG. 5(a), when the light ray 504 is tilted from the substrate normal 503 of the homogeneous cell, the amount of birefringence 510 from the homogeneous cell 501 is as shown in FIG. 3 as shown in FIG. 5(b). decrease as well. On the other hand, the amount of birefringence 511 from the optical compensation layer 502 is negative when the light is incident perpendicularly to the substrate, and approaches zero as the light ray becomes more inclined. Therefore, the total amount of birefringence 512 of the two layers does not show a large change with respect to the inclination from the light beam direction.

Examples of the above-mentioned optically negative optical compensation layer include a polymer film having a basic skeleton of calcite or polystyrene.

As described above, the liquid crystal display device of the present invention is capable of displaying black and has improved viewing angle dependence.

〔Example〕

First, the manufacturing process of the liquid crystal cell used in the examples of the present invention will be described below. The glass substrate was cleaned with a surfactant. Further, the parallel alignment treatment was performed by spin-coating a polyimide layer on a glass substrate, baking it at 200° C., and performing a rubbing treatment. The two parallel-aligned substrates that have gone through the above steps have a thickness of 5 μm.
They were bonded together using a thermosetting adhesive as a sealing agent via a glass bulb spacer of the same diameter. However, an opening was prepared in a part of the sealant pattern to serve as a liquid crystal injection hole.

After the above step, the bonded substrates were carried into a vacuum chamber. After evacuation, liquid crystal was injected between the substrates through the liquid crystal injection hole. After the above step, the liquid crystal cell is carried out to the atmosphere and the liquid crystal injection hole is sealed with a thermosetting adhesive to complete a liquid crystal cell (bomogeneous cell).The liquid crystal injected here was a Henn-01 nematic liquid crystal.

The viewing angle dependence of the liquid crystal cell (homogeneous cell) produced through the above steps was measured using the measurement system shown in FIG. The light from the He-Ne laser 601 as a light source passes through the polarizing plate 60.
2, the light enters a sample 604 on a rotation stage 603. After passing through the sample, the light passes through an analyzer 605 and is detected by a silicon photodetector 606. Here, the polarizer 602 and the analyzer 605 are orthogonal to each other. After the above settings, the angle of incidence of light on the sample 604 was changed by rotating the rotation stage 603, and the signal from the silicon photodetector 606 was recorded.

Examples of the present invention will be described below. The homogeneous cell produced by the above steps was arranged as shown in FIG. 7(a) to form a liquid crystal display device. In FIG. Here, the polystyrene film 70 used as the optical compensation layer is
No. 2 was uniaxially stretched using a roller. Here, the amount of birefringence Δnd of the polystyrene film is adjusted to be 0.1, which is the same as that of the homogeneous cell.

The liquid crystal display device shown in FIG. 7(a) was installed in the measurement system shown in FIG. 6, and changes in the amount of transmitted light with respect to changes in the incident angle of light were measured. The results are shown in FIG. 7(b).

For comparison, the measurement results for the conventional compensated homogeneous cell shown in FIG. 2 also show that the viewing angle dependence is improved in the embodiment of the present invention shown in FIG. 7(b). I understand.

〔Effect of the invention〕

As shown above, by using the liquid crystal display device of the present invention, it is possible to obtain a liquid crystal display device that can display black and has less viewing angle dependence.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the present invention, FIG. 2, FIG. 3, and FIG. 4 are diagrams for explaining a conventional example. FIG. 5 is a diagram for explaining the present invention. FIG. 7 is a diagram for explaining the present invention in detail. 101... Homogeneous cell, 102... Optical compensation layer, 103... Incident linearly polarized light, 104... Linearly polarized light in the X-axis direction, 105... Linearly polarized light in the y-axis direction, 201...
...First homogeneous cell, 202...Second homogeneous cell, 203...Incoming linearly polarized light, 204...X
Linearly polarized light in the axial direction, 205... linearly polarized light in the y-axis direction,
206...Linearly polarized light in the X-axis direction, 207...Linearly polarized light in the y-axis direction, 208...Linearly polarized light in the X-axis direction, 20
9... Linearly polarized light in the Y-axis direction, 301... Homogeneous cell, 401... First homogeneous cell, 402...
- Second homogeneous cell, 501 - Homogeneous cell, 502 - Optical compensation layer, 601 - HeNe laser, 602 - Polarizing plate, 603 - Rotation stage, 60
4...Sample, 605.Analyzer, 606., Silicon photodetector 701..Homogeneous cell, 70
2...Polystyrene film.

Claims (1)

[Claims] An optically positive liquid crystal layer aligned parallel to the substrate and an optically negative optical compensation layer having an optical axis in an in-plane direction parallel to the parallel alignment direction are laminated with their optical axes parallel to each other. A liquid crystal display device characterized by: