JPH07294934A - Liquid crystal device - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal device having a small viewing angle dependence of display. In a TFT or MIM type liquid crystal device, each pixel is divided into two regions having different liquid crystal orientations.
Each liquid crystal alignment is a homogeneous twist-free alignment having a small pretilt angle, and the alignment directions in the two regions are different by 180 degrees. As the liquid crystal, a nematic liquid crystal containing no chiral material is used by adding a dichroic dye prepared in black. Only one polarizing plate is arranged so that its absorption axis is orthogonal to the liquid crystal alignment direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device, and more particularly to an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art An active matrix type liquid crystal device in which a TN liquid crystal is combined with an active element such as a TFT or an MIM diode is now flat because of its features such as high contrast, high speed response, large capacity display, full color display and low power consumption. Became the mainstream type display.

A conventional liquid crystal device in which a TN liquid crystal and a TFT are combined is shown in FIG.
The liquid crystal cell includes an upper substrate 2, a lower substrate 3, and a lower polarizing plate 4. Between the upper and lower substrates of the liquid crystal cell, a color filter 5, a common electrode 6, a pixel electrode 7, a liquid crystal 8, a TFT 9,
The scanning line 10 and the signal line 11 are provided. In FIG. 6, only 9 pixels are shown for the sake of simplicity.
× 480 × 3 pixels are provided. Further, in order to avoid making the drawing complicated, the orientation film, the insulating film, the storage capacitor and the like are omitted.

FIG. 7 shows a typical viewing angle characteristic of such a conventional liquid crystal device. Here, the center of the drawing is the substrate normal direction, and the six concentric circles surrounding it are in order from the inside, the inclination angles from the substrate normal are 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, and 60 degrees.
Shows the direction of degrees. Also 31, 32, 33, 34,
35 are contrast ratios of 1: 1, 1: 3, and 1: 1, respectively.
It is an isocontrast curve of 0, 1:30, and 1: 100. A high contrast exceeding 1: 100 is obtained in the substrate normal direction.

[0005]

However, the viewing angle dependence as shown in FIG.
It is extremely large as compared with a light emitting display such as L, and its solution has been an important issue in the conventional liquid crystal device.

As a means for alleviating the viewing angle dependence of such display, a means has been proposed in which a pixel is divided into two and the orientations of the pixels are made different, which has been effective. Regarding such means, JP-A-54-5754 and JP-A-59-21
1019, JP-A-60-212421, and JP-A-62.
-67517, JP-A-63-106624, JP-A-64-88520, JP-A-1-182829, JP-A-1-245223, JP-A-5-107544, JP-A-5-173135, and JP-A-5-173135. 5-17317, JP-A-5-188374, JP-A-5-196942, JP-A-5-203951, and JP-A-5-210099.
JP-A-5-224207, JP-A-5-224210,
JP-A-5-257147 and JP-A-5-281545
And JP-A-5-289082.

However, all of these conventionally proposed means are obtained by dividing the pixel of the TN liquid crystal. T
The viewing angle characteristics of the N liquid crystal are wide in the left-right direction but narrow in the vertical direction as shown in FIG. Therefore, JP-A 64-88520
Even if the pixels of the TN liquid crystal are divided into two so that the clear viewing directions are reversed as in the embodiment of the publication, only the viewing angles in the upper and lower directions are averaged, and the viewing angles in the up and down direction are still the same. Narrows. An example thereof is shown in FIG. In addition, Japanese Patent Laid-Open No. 5-1
If the pixel is divided into four as disclosed in Japanese Patent No. 73135, the difference between the upper, lower, left and right sides can be eliminated, but a decrease in contrast and an increase in coloring due to the viewing angle are unavoidable. These originate from the narrow viewing angle of the original TN liquid crystal. Furthermore, in a commonly-used normally-mode TN liquid crystal, when the pixels are divided, the boundary part of the TN liquid crystal becomes white, which is a problem, and a black mask is essential.

Therefore, in the present invention, it has been decided to use a GH liquid crystal having a wide viewing angle. A general Heilmeier type GH liquid crystal has a structure as shown on page 317 of "Liquid Crystal Device Handbook" (published by Nikkan Kogyo Shimbun, first edition in 1989), and its viewing angle characteristics are shown in FIG. . Unlike the TN liquid crystal, the GH liquid crystal originally has less contrast deterioration and coloring change depending on the viewing angle. Inversion tends to occur in the upward direction, but the downward and leftward and rightward directions have wide viewing angle characteristics. Therefore, the viewing angle can be effectively expanded by dividing the pixel into two and averaging the viewing angles in the upper and lower directions. Further, since a general GH liquid crystal is normally black, even if the pixels are divided, no white spots occur at the boundary, and a black mask is unnecessary.

It is an object of the present invention to provide a liquid crystal device which has less viewing angle dependence of display by dividing a pixel using a GH liquid crystal.

[0010]

A liquid crystal device according to the present invention comprises a pair of substrates having electrodes on opposite inner surfaces thereof, a liquid crystal sandwiched between the substrates, and at least one polarizing plate. In above, the liquid crystal is divided into a plurality of regions having different alignment directions, and the liquid crystal contains a dichroic dye.

The liquid crystal is divided into two regions which are oriented in a homogeneous state without twist and are antiparallel to each other,
Further, it is characterized in that only one of the polarizing plates is used and the absorption axis thereof is arranged to be orthogonal to the long axis direction of the liquid crystal molecules.

Further, the liquid crystal is orientated in a state of being twisted by 90 degrees, and two polarizing plates are used and are arranged in parallel with each other with the substrate interposed therebetween.

[0013]

【Example】

(Example 1) A liquid crystal device in Example 1 of the present invention is composed of an upper substrate 2, a lower substrate 3 and a lower polarizing plate 4 of a liquid crystal cell, as shown in FIG. A backlight or a reflector is arranged under the plate as needed. A color filter 5, a common electrode 6, a pixel electrode 7, a liquid crystal 8, a TFT 9, a scanning line 10 and a signal line 11 were provided between the upper and lower substrates of the liquid crystal cell. The liquid crystal in the pixel electrode portion is divided into two regions 12 and 13, respectively, and hereinafter, 12 is referred to as A region and 13 is referred to as B region. The applied voltage is the same in both regions AB, only the orientation of the liquid crystal is different. As the liquid crystal, ZLI-4756 / 1 (manufactured by Merck Ltd.) containing 3.76% of an azo-based dichroic dye prepared in black was used. The cell thickness is 7.4 μm. Figure 1
For simplicity, only 9 pixels are shown in the figure, but it is actually 64 pixels.
0x480x3 pixels were provided. Further, in order to avoid making the drawing complicated, the orientation film, the insulating film, the storage capacitor and the like are omitted.

FIG. 2A shows the liquid crystal alignment directions in the A region and the B region and the axial relationship with the polarizing plate, respectively.
Is shown in FIG. 22 is the rubbing direction of the upper substrate, 23 is the rubbing direction of the lower substrate, and 24 is the absorption axis direction of the lower polarizing plate. The twist angle of the liquid crystal determined by 22 and 23 is 0 degree, and 24 and 23 are orthogonal to each other. The polarizing plate may be placed on the upper side or both sides of the liquid crystal cell, and in that case, the axial direction may be 24 directions. However, since it is easier to provide the antireflection coating layer, the antiglare layer, and the hard coating layer on the glass surface than on the polarizing plate surface,
The polarizing plate is preferably on the lower side. When placed on both sides,
Although the display is slightly darkened, the reliability of the dichroic dye against light is improved.

The liquid crystal alignment in the A region and the B region was controlled by the following method. First, an alignment film was applied to the entire surface and baked, and then the entire surface was rubbed in the liquid crystal alignment direction in the A region. Next, a resist was applied, only the region B was exposed and removed, and the region B was rubbed in the liquid crystal alignment direction. Finally, all the resist was removed and the alignment treatment was completed. This alignment treatment was performed on both the upper substrate and the lower substrate.

FIG. 3 shows the viewing angle characteristics of the liquid crystal device according to the first embodiment of the present invention. Here, the center of the figure is the substrate normal direction,
The six concentric circles surrounding it are, in order from the inside, tilt angles from the substrate normal of 10 °, 20 °, 30 °, 40 °, 50 °,
The direction of 60 degrees is shown. Further, 33 and 34 are isocontrast curves with contrast ratios of 1:10 and 1:30, respectively. As compared with FIG. 9, which is the viewing angle characteristic of the undivided GH liquid crystal, the viewing angle in the upward direction, which was conventionally narrow, widened, and the contrast ratio did not fall below 1: 3 within the range of the tilt angle of 60 degrees. Further, compared with FIG. 7, which is the viewing angle characteristic of the conventional TN liquid crystal, the abrupt change of the contrast ratio depending on the viewing angle is eliminated. Further, in Example 1, since only one polarizing plate was used, there was no change in coloring due to birefringence interference that occurred in the TN liquid crystal.

(Embodiment 2) A liquid crystal device according to Embodiment 2 of the present invention has an upper polarizing plate 1 as shown in FIG.
The liquid crystal cell is composed of an upper substrate 2, a lower substrate 3, and a lower polarizing plate 4, and a backlight or a reflecting plate is arranged under the lower polarizing plate as required. Between the upper and lower substrates of the liquid crystal cell, a color filter 5, a common electrode 6, a pixel electrode 7,
A liquid crystal 8, a TFT 9, a scanning line 10 and a signal line 11 are provided. Further, the liquid crystal in the pixel electrode portion has 12 A regions and 1 liquid crystal, respectively.
It is divided into two B areas. ZLI-5080 (manufactured by Merck) containing 3.22% of an azo dichroic dye compounded in black and 0.10% of chiral material S-811 in the liquid crystal.
Was used. The cell thickness is 5.3 μm.

FIG. 5 (a) shows the liquid crystal alignment directions in the regions A and B and the axial relationship with the polarizing plate, respectively.
And shown in FIG. 21 is the absorption axis direction of the upper polarizing plate, 22 is the rubbing direction of the upper substrate, 23 is the rubbing direction of the lower substrate, and 24 is the absorption axis direction of the lower polarizing plate.
21 and 22 are parallel, the twist angle of the liquid crystal determined by 22 and 23 is 90 degrees to the left, and 24 and 23 are orthogonal.

Example 2 is a normally black mode T
The dichroic dye is added to the N liquid crystal to divide the pixels, but the contrast ratio has been improved to about twice as much as the conventional normally black mode TN liquid crystal, and the contrast change due to the viewing angle is suppressed. This has the effect of eliminating the inversion of the display.

In the above embodiment, a method of rubbing the upper and lower substrates twice each in order to divide the pixel into two is adopted. However, as disclosed in JP-A-5-173137, only the upper substrate is used. As a method of rubbing twice and lower rubbing the lower substrate once, or as disclosed in Japanese Laid-Open Patent Publication No. 5-210099, a high pretilt area and a low pretilt area are formed in advance. The same effect can be obtained by adopting the method of rubbing once for both substrates. In addition, JP-A-4-149
As disclosed in Japanese Patent No. 410, the same effect can be obtained even if the electrode shape is devised so that the electrodes rise from different directions when a voltage is applied.

Further, in the above embodiment, the pixel is divided into two, but as the number of divisions increases such as division into three and four, the viewing angle dependence of the display becomes smaller. Also, the liquid crystal orientation was a homogeneous orientation with a small pretilt angle, but if the pretilt angle is increased or a so-called hybrid orientation in which one side of the substrate is vertically oriented, the threshold voltage and the saturation voltage decrease, and It becomes easy to drive. Of course, there is the same effect of expanding the viewing angle as when the pretilt angle is small. Further, although the TFT has been taken as an example of the active element, the same effect can be obtained even if this is an MIM diode.

[0022]

As described above, according to the present invention, the GH
By dividing a pixel using liquid crystal, a liquid crystal device with less viewing angle dependence of display can be provided.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating a structure of a liquid crystal device according to a first embodiment of the invention.

FIG. 2 (a) of the liquid crystal device in Embodiment 1 of the present invention.
It is a figure which shows the axial relationship of the liquid crystal aligning direction of A area | region and (b) area | region, and a polarization axis.

FIG. 3 is a diagram showing viewing angle characteristics of the liquid crystal device according to the first embodiment of the present invention.

FIG. 4 is a diagram schematically showing a structure of a liquid crystal device according to a second embodiment of the invention.

FIG. 5 (a) of a liquid crystal device according to a second embodiment of the invention.
It is a figure which shows the axial relationship of the liquid crystal aligning direction of A area | region and (b) area | region, and a polarization axis.

FIG. 6 is a diagram schematically showing the structure of a conventional liquid crystal device in which a TN liquid crystal and a TFT are combined.

FIG. 7 is a diagram showing viewing angle characteristics of a conventional liquid crystal device in which a TN liquid crystal and a TFT are combined.

FIG. 8 is a diagram showing viewing angle characteristics of a conventional liquid crystal device in which a TN liquid crystal and a TFT are combined and divided into two regions.

FIG. 9 is a diagram showing viewing angle characteristics of a conventional liquid crystal device in which a GH liquid crystal and a TFT are combined.

[Explanation of symbols]

 1 Upper Polarizing Plate 2 Upper Substrate of Liquid Crystal Cell 3 Lower Substrate of Liquid Crystal Cell 4 Lower Polarizing Plate 5 Color Filter 6 Common Electrode 7 Pixel Electrode 8 Liquid Crystal 9 TFT 10 Scan Line 11 Signal Line 12 A Region of Liquid Crystal of Pixel Electrode 13 B Region of Liquid Crystal in Pixel Electrode Part 21 Absorption Axis Direction of Upper Polarizer 1 22 Rubbing Direction of Upper Substrate 2 of Liquid Crystal Cell 23 Rubbing Direction of Lower Substrate 3 of Liquid Crystal Cell 24 Absorption Axis Direction of Lower Polarizer 4 31 Isocontrast curve with a contrast ratio of 1: 1 32 Isocontrast curve with a contrast ratio of 1: 3 33 Isocontrast curve with a contrast ratio of 1:10 34 Isocontrast curve with a contrast ratio of 1:30 35 Isocontrast curve with a contrast ratio of 1: 100

Claims (3)

[Claims] 1. A liquid crystal device comprising a pair of substrates provided with electrodes on opposing inner surfaces, a liquid crystal sandwiched between the substrates, and at least one polarizing plate, wherein the liquid crystals have a plurality of different alignment directions. A liquid crystal device characterized by being divided into regions and containing a dichroic dye in the liquid crystal. 2. The liquid crystal is divided into two regions that are oriented in a homogeneous state without twist and are antiparallel to each other, and only one polarizing plate is used, and its absorption axis is orthogonal to the major axis direction of liquid crystal molecules. The liquid crystal device according to claim 1, wherein the liquid crystal device is arranged so that 3. The liquid crystal device according to claim 1, wherein the liquid crystal is oriented in a twisted state of 90 degrees, and two polarizing plates are used and are arranged in parallel with each other with the substrate interposed therebetween.