JPH04121711A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To improve the display characteristics of a ferroelectric liquid crystal panel by laminating a 2nd liquid crystal panel subjected to a hybrid orientation to a 1st liquid crystal panel which drives the ferroelectric liquid crystal by an electric field. CONSTITUTION:The hybrid orientation state is obtd. with a temp. compensation cell 9 by forming one side of polyvinyl alcohol (PVA) and the other of a rubbing film of polyimide (PI) and, therefore, the cell with which the temp. change of the twist angle is approximate to the temp. change of the tilt angle of the matrix driving cell is selected. The disposition relation of a matrix driving cell 7 and a temp. compensation cell 9 is set to attain the disposition that the initial molecular arranging directions 10A, 10B of the matrix driving cell and the PI side of the temp. compensation cell 9 are adjacent to each other. Namely, the temp. characteristics of both are always matched if these cells are are so disposed that the molecular arranging directions 12d, 13d coincide respectively with 10A, 10b in the case of driving in a white mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element configuration for stably obtaining optical contrast against temperature changes.

[Prior Art] Liquid crystal display elements have been widely used in personal computer displays, TV displays, and the like. In contrast to TN (twisted nematic) liquid crystals, which have traditionally been used in such liquid crystal display elements, strong electrostatic liquid crystals (FLCs), which have been rapidly developed in recent years, are being used in a wider range of liquid crystal display elements due to their high-speed response and memory properties. It shows great promise for applications.

[Problems to be Solved by the Invention] However, one of the drawbacks of liquid crystal elements is the temperature dependence of the material. The temperature dependence of the above-mentioned TN liquid crystal has been considerably improved through many years of efforts, but the above-mentioned FLC
This is still a big issue.

One of the temperature characteristics of FLC is that the electric field threshold varies depending on temperature. The second problem, i[, can be dealt with by providing a drive margin that takes into account the temperature characteristics, or by detecting the temperature and changing the drive voltage accordingly.

Another temperature characteristic that is difficult to deal with in conventional FLCs is that the orientation direction of the polarizer shifts depending on the temperature. The negative effect of this is that it greatly leads to a decrease in contrast (for example, black is no longer black).

SUMMARY OF THE INVENTION In view of the problems in the conventional example described above, an object of the present invention is to eliminate inconveniences such as a decrease in contrast due to temperature changes,
An object of the present invention is to provide a liquid crystal display element capable of stable display.

[Means and Effects for Solving the Problems] The liquid crystal display element according to the present invention includes a first liquid crystal panel in which strongly electrostatic liquid crystals are driven pixel-selectively by an electric field, and a second liquid crystal panel in which hybrid alignment is applied. It is characterized in that it is made by laminating. Furthermore, transparent conductive films can be provided on the upper and lower substrates of the second liquid crystal panel.

The second liquid crystal panel is in a hybrid alignment state and has the effect of optically rotating linearly polarized light. Therefore, by making the temperature characteristics of the twist angle of the second liquid crystal panel close to or almost the same as the temperature characteristics of the tilt angle of the first liquid crystal panel in the operating temperature range, the temperature dependence of display characteristics such as contrast can be improved. be done.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a matrix drive cell 1 for pixel-selectively driving an FLC, and a temperature compensation cell 3 for compensating the dependence of the tilt angle on temperature by laminating the matrix drive cell 1. An example of model correlation of liquid crystal alignment angles is shown. However, in the example of FIG. 1, both the matrix drive cell 1 and the temperature compensation cell 3 have liquid crystal molecules 10A to
The arrangement state of IIB, 12a to 13d is near the inner wall of the cell,
Alternatively, a typical arrangement state of the bulk liquid crystal layer within the cell is schematically shown.

Note that FIGS. 3 and 4 show examples of tilt angle temperature characteristics of the matrix drive cell (FIG. 3) and the temperature compensation cell (FIG. 4), respectively.

The features of the temperature compensation cell in the present invention will be explained with reference to FIG. That is, as an alignment film to be used, for example, one side is a rubbed film of polyvinyl alcohol PvA, and the other side is a selected polyimide (pH
A hybrid alignment state can be obtained by using the rubbing film.

In this example, on the PVA side, the molecules are subjected to a strong alignment regulating force, and the molecules are oriented with a relatively low pretilt angle so that they are difficult to move. Furthermore, the PI side can have a higher pretilt angle than the PVA side, and molecules exhibit a property of being more mobile in response to temperature changes and electric fields. As a result, the temperature characteristic of the tilt angle becomes as shown in FIG. 4, and for example, at a temperature T, a twisted structure with an angle of (θb-θ,) can be obtained. As a result, it has the effect of optically rotating linearly polarized light. In the present invention, a temperature compensation cell is selected in which the temperature change in the twist angle is close to or approximately the same as the change in tilt angle temperature of the matrix drive cell shown in FIG. 3 in the operating temperature range (ra to TA). This has an effective effect.

Next, the principle of operation of the present invention will be further explained using FIG. 5 and FIG.

FIG. 5 is an example showing the arrangement of the display element and polarizing plate 11 according to the present invention as a reflection configuration using a reflection plate 5. In FIG.

The arrangement relationship between the matrix self and the temperature compensation cell 9 is based on the initial molecular arrangement direction 1 of the matrix cell in FIG.
0A, IOB and the PI side of the temperature compensation cell 9 are arranged adjacent to each other. That is, in the example of FIG. 5, when driving in the normally white mode, the molecular arrangement directions 12d and 13d in FIG.
Arrange it so that it almost coincides with 0A and IOB. In this way, in each temperature characteristic shown in FIG. 4, for example, 12d and IOA, and 13d and 10B can always match, and the direction of the transmission axis of the polarizing plate 11 in FIG. For example, it is sufficient to position it in a parallel direction.

At this time, an electric field is applied to the matrix drive cell, and in FIG. 1, the molecular arrangement is IIA and II at each temperature TA and TB.
If you change the arrangement like in B, this part will become relatively black.

Here, the thickness of the liquid crystal layer in the matrix drive cell is set so that its retardation is 1/4 wavelength with respect to the incident light (1/2 wavelength in round trip), and the cell is driven by an electric field.
The best contrast can be obtained when the molecular arrangement direction changes by 45 degrees.

Incidentally, in order to adjust the contrast, the transmission axis direction of the polarizing plate may be adjusted in a direction other than parallel to the molecular arrangement direction on the PVA side.

In addition, when driving in the normally black mode in FIG. do it.

In the above explanation, in order to obtain the initial alignment direction shown in FIG. 1 in a --like manner over the entire surface of the matrix-driven self-temperature compensation cell 9, it is sufficient to apply a --like electric field over the entire surface of each cell as necessary. For example, for a matrix drive self, the initial orientation direction of IOA or IOB is obtained by a substantially positive electric field, and selectively driven in the 11A111B direction by a substantially negative electric field. Furthermore, the temperature-compensated cell can be modified by, for example, obtaining a desired twist orientation using a positive electric field.

FIG. 6A and FIG. 6B show a configuration example of a transmissive display element.

In this example, two layers (13, 15) of temperature compensation cells are used.

In this case, the initial molecular orientation directions on the PI side of each temperature compensation cell are mutually P in temperature compensation cells 1 (13) and 2 (15).
The position should be symmetrical with respect to the VA side molecular orientation direction.

To obtain such an initial orientation direction of the temperature-compensated cell, for example, a positive electric field is applied to the temperature-compensated cell 1 (13), and a positive electric field is applied to the temperature-compensated cell 1 (13).
15) It is recommended to first apply a negative electric field.

If the cells on both sides of the matrix drive cell 17 are arranged so that the orientation direction on the PI side matches the initial molecular orientation direction of the matrix drive cell 17 in terms of temperature characteristics, normally black mode can be achieved due to crossed Nicols. It can be achieved stably. At this time, the thickness of the liquid crystal layer of the matrix drive cell 17 is 1/2 of the thickness of the incident light.
It is optimal to make it equal to the wavelength.

The above temperature compensation cell is sufficiently smaller than the liquid crystal tilt angle of the matrix drive cell used (for example, a drive cell using Chisso C51014, provided with PI alignment films on both sides, and having a simple matrix or active matrix electrode configuration). It is desirable to use a liquid crystal that forms a tilt angle. Such a liquid crystal can be obtained by blending a small amount of chiral smectic liquid crystal with a liquid crystal that exhibits SmA at room temperature, and its tilt angle temperature dependence can be adjusted. For such a liquid crystal, as in the above example, one side is treated with a film having a large alignment ability (PVA film or an alignment film obtained by strong rubbing treatment) with a large alignment control force, and the other alignment film is made of the polyimide PI. It is advantageous to construct the cell by a process that orients the liquid crystal at a high pretilt angle, such as that obtained by oblique evaporation of Si or Sin.

[Effects of the Invention] As explained above, according to the present invention, it is possible to provide a liquid crystal display element that does not suffer from contrast deterioration due to temperature characteristics and can provide stable display in a wide range of applications such as flat televisions, projection televisions, and OA panels. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the principle of a liquid crystal display element according to the present invention, FIG. 2 is a partial sectional view showing the principle of a temperature compensation cell used in the liquid crystal display element according to the present invention, and FIG. 4 is a graph showing the tilt angle temperature characteristics of the matrix drive cell. FIG. 4 is a graph showing the tilt angle temperature characteristics of the temperature compensation cell. FIG. 5 is a graph showing the tilt angle temperature characteristics of the temperature compensation cell. FIG. FIGS. 6A and 6B are cross-sectional views showing the structure of a transmissive display element according to another embodiment of the present invention. 1.7.17: Matrix drive cell, 3.9.13.15: Temperature compensation cell, 5: Reflector, 10A, IOB, IIA, 11B: Liquid crystal molecules in matrix drive cell, 12a, 12b, 12c, 12d, 13a. 13b, 13c, 13d: liquid crystal molecules in temperature compensated cells. Patent applicant Canon Co., Ltd.

Claims (2)

[Claims] (1) A liquid crystal element characterized by laminating a first liquid crystal panel in which ferroelectric liquid crystal is driven pixel-selectively by an electric field and a second liquid crystal panel in which hybrid alignment is applied. (2) The liquid crystal element according to claim 1, wherein the second liquid crystal panel has transparent conductive films applied to the upper and lower substrates.