JP2767158B2 - Liquid crystal element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device configuration for stably obtaining an optical contrast against a temperature change.

[Prior Art] Conventionally, liquid crystal display devices have been widely used for personal computer displays, TV displays, and the like. TN (twisted nematic) conventionally used for such liquid crystal display devices
In recent years, ferroelectric liquid crystal (FLC), whose development is remarkable, has been regarded as very promising for wider application of liquid crystal display devices due to its high-speed response and memory properties.

[Problems to be Solved by the Invention] However, one of the drawbacks of the liquid crystal element is the temperature dependency of the material. The temperature dependency of the TN liquid crystal has been considerably improved by many years of efforts, but the FLC is still a major problem.

One of the temperature characteristics of the FLC is that the electric field threshold varies depending on the temperature. This problem can be dealt with by taking a drive margin in anticipation of the temperature characteristic, or by detecting the temperature and thereby changing the drive voltage.

Another temperature characteristic that is difficult to deal with in the conventional FLC is that the orientation direction with respect to the polarizer shifts with temperature. The adverse effect of this is that it leads to a reduction in contrast (for example, black is no longer black).

An object of the present invention is to solve the problems in the above conventional example,
An object of the present invention is to provide a liquid crystal display element capable of performing stable display by eliminating inconveniences such as a decrease in contrast due to a temperature change.

[Means and Actions for Solving the Problems] A liquid crystal display device according to the present invention includes a first liquid crystal panel that selectively drives a ferroelectric liquid crystal with an electric field and a second liquid crystal panel with hybrid alignment. Are laminated. Further, the second liquid crystal panel may be provided with a transparent conductive film on the upper and lower substrates.

The second liquid crystal panel is in a hybrid alignment state and has an action of rotating linearly polarized light. Therefore, the temperature dependence of the display characteristics such as contrast is improved by making the temperature characteristic of the twist angle of the second liquid crystal panel close to or substantially equal to the temperature characteristic of the tilt angle of the first liquid crystal panel in the operating temperature range. Is done.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 shows a matrix drive cell 1 for selectively driving an FLC in a pixel and a temperature compensation cell 3 for stacking on the matrix drive cell 1 to compensate for a tilt angle dependency due to temperature. An example of the model correlation of the liquid crystal alignment angle is shown. However, in the example of FIG. 1, both the matrix driving cell 1 and the temperature compensation cell 3 have the liquid crystal molecules 10A to 11B and 12a to 1A.
As the arrangement state of 3d, a typical arrangement state of the liquid crystal layer bulk near the cell inner wall or in the cell is schematically shown.

FIGS. 3 and 4 show examples of tilt angle temperature characteristics of the matrix driving cell (FIG. 3) and the temperature compensation cell (FIG. 4).

The features of the temperature compensation cell according to the present invention will be described with reference to FIG. That is, as an alignment film to be used, for example, a rubbing film of polyvinyl alcohol PVA on one side and a rubbing film of a selected polyimide (PI) such as LQ1802 can be used to obtain a hybrid alignment state. In this example, on the PVA side, the molecules receive a strong alignment regulating force, and the molecules are oriented at a relatively low pretilt angle so that the molecules are difficult to move. In addition, the PI side can have a higher pretilt angle than the PVA side, and the molecule exhibits a property of easily moving with respect to a temperature change and an electric field. As a result, the temperature characteristic of the tilt angle becomes as shown in FIG. 4, in for example a temperature T _B may be an angle of twist structure (θ _b -θ _a). As a result, it has the function of rotating the linearly polarized light. In the present invention, the temperature change of the twist angle in the temperature compensation cell is selected to be close to or substantially equal to the change in the tilt angle temperature of the matrix drive cell shown in FIG. 3 in the operating temperature range (T _{B to} T _A ). Doing so has an effective effect.

Next, the working principle of the present invention will be further described with reference to FIGS.

FIG. 5 shows an example in which the arrangement of the display element and the polarizing plate 11 according to the present invention is shown as a reflection configuration using the reflection plate 5.
The arrangement relationship between the matrix cell 7 and the temperature compensation cell 9 is based on the initial molecular arrangement direction of the matrix cell in FIG.
The 10A and 10B and the PI side of the temperature compensation cell 9 are arranged adjacent to each other. That is, in the case of driving in the normally white mode in the example of FIG. 5, the molecular arrangement directions 12d and 13d in FIG. 1 are arranged so as to substantially coincide with the above 10A and 10B, respectively. In this way, in each temperature characteristic shown in FIG. 4, for example, 12d and 10A, 13d and 10B
And the transmission axis direction of the polarizing plate 11 in FIG. 5 may be positioned parallel to the molecular arrangement on the PVA side of the compensation cell as an example.

At this time, an electric field is applied to the matrix driving cell,
In the figure, when the molecular arrangement is changed at each temperature T _A , T _{B as} in 11 A, 11 B, this portion becomes relatively black.

Here, the thickness of the liquid crystal layer in the matrix drive cell is set so that the retardation is 1/4 wavelength with respect to the incident light (1/2 wavelength for reciprocation), and the molecular arrangement direction is changed by electric field driving. The best contrast is obtained when the angle changes by 45 °. In order to adjust the contrast, the transmission axis direction of the polarizing plate may be adjusted and arranged in a direction other than the direction parallel to the molecular arrangement direction on the PVA side.

When FIG. 5 is driven in the normally black mode, the initial molecular arrangement direction of the matrix cell and the direction rotated by 45 ° with respect to the normal white mode arrangement direction of the temperature compensation cell molecular arrangement direction. do it.

In the above description, a uniform electric field may be applied to the entire surface of each cell as needed in order to obtain the initial orientation direction of FIG. 1 uniformly over the entire surface of the matrix drive cell 7 and the temperature compensation cell 9. For example, for the matrix driving cell 7, an initial orientation direction of 10A or 10B is obtained by a substantially positive electric field, and selective driving is performed in the 11A and 11B directions by a substantially negative electric field. In addition, the temperature compensation cell can obtain a desired twist alignment with a positive electric field, for example.

6A and 6B show a configuration example of a transmission type display element.

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

In this case, the molecular initial orientation direction on the PI side of each temperature compensation cell is set symmetrically with respect to the PVA side molecular orientation direction in the temperature compensation cells 1 (13) and 2 (15).

In order to obtain such an initial alignment direction of the temperature compensation cell, for example, a positive electric field is applied to the temperature compensation cell 1 (13),
In (15), a negative electric field may be applied first.

If the orientation direction on the PI side of the cells on both sides of the matrix drive cell 17 is arranged so that the temperature characteristics match the initial molecular orientation direction of the matrix drive cell 17,
A normally black mode can be stably achieved by cross Nicol. At this time, the thickness of the retardation of the liquid crystal layer of the matrix drive cell 17 is optimally set to be 1/2 wavelength with respect to the incident light.

The temperature compensation cell is sufficiently smaller than the liquid crystal tilt angle in a matrix driving cell to be used (for example, a driving cell in which a PI matrix is used on both sides using CS1014 manufactured by Chisso and a simple matrix or active matrix electrode configuration is used). It is desirable to use a liquid crystal having a tilt angle. Such a liquid crystal will show SmA at room temperature,
It is obtained by blending a small amount of chiral smectic liquid crystal, and its tilt angle temperature dependence can be adjusted.
For such a liquid crystal, a film treatment (an alignment film obtained by a PVA film or a strong rubbing treatment) having an alignment ability with a large alignment regulating force is used on one side as in the above-described example, and the other alignment film is the polyimide PI. it is convenient to configure the cell by a process and align the liquid crystal in high pretilt angle as obtained by oblique evaporation of SiO _2.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a liquid crystal display element capable of performing stable display in a wide range of uses such as a flat television, a projection television, and an OA panel without a decrease in contrast due to temperature characteristics. .

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the principle of the liquid crystal display device according to the present invention. FIG. 2 is a partial cross-sectional view showing the principle of a temperature compensation cell used in the liquid crystal display device according to the present invention. Is a graph showing a tilt angle temperature characteristic of a matrix driving cell, FIG. 4 is a graph showing a tilt angle temperature characteristic of a temperature compensating cell, and FIG. 5 is a graph showing a reflection type display element according to an embodiment of the present invention. FIG. 6A and FIG. 6B are cross-sectional views showing the configuration of a transmission type 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, 10B, 11A, 11B: liquid crystal molecules in matrix drive cell, 12a, 12b, 12c, 12d, 13
a, 13b, 13c, 13d: liquid crystal molecules in the temperature compensation cell.

Continuation of front page (56) References JP-A-56-94331 (JP, A) JP-A-2-113220 (JP, A) JP-A-61-179418 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) G02F 1/1347 G02F 1/135 G02F 1/137 510

Claims (8)

(57) [Claims] 1. A liquid crystal device comprising: a first liquid crystal panel for selectively driving a ferroelectric liquid crystal by an electric field on a pixel basis; and a second liquid crystal panel having a hybrid orientation. 2. The liquid crystal device according to claim 1, wherein transparent conductive films are provided on upper and lower substrates of said second liquid crystal panel. 3. A temperature characteristic of a twist angle of the second liquid crystal panel is close to or substantially equal to a temperature characteristic of a tilt angle of the first liquid crystal panel in an operating temperature range. Or the liquid crystal element of 2. 4. The liquid crystal device according to claim 1, wherein the first liquid crystal panel is disposed on a side of the second liquid crystal panel where liquid crystal molecules have a high pretilt angle. 5. The liquid crystal device according to claim 1, wherein a polarizing plate is provided on a side of said second liquid crystal panel opposite to said first liquid crystal panel. 6. The liquid crystal device according to claim 5, wherein a reflection plate is provided on a side of said first liquid crystal panel opposite to said second liquid crystal panel. 7. The liquid crystal device according to claim 6, wherein an orientation direction of liquid crystal molecules adjacent to the substrate on the polarizing plate side of the second liquid crystal panel is parallel to a transmission axis of the polarizing plate. 8. The liquid crystal device according to claim 1, wherein a polarizing plate, a second liquid crystal panel, a first liquid crystal panel, a second liquid crystal panel, and a polarizing plate are arranged in this order.