JP3058971B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a high contrast ratio and excellent visibility.

[0002]

2. Description of the Related Art A liquid crystal display device is widely used as a display device for various OA devices such as a liquid crystal television and a word processor, and a liquid crystal display device having a sufficient contrast at the time of display and excellent in visibility is required. It is becoming.

[0003] As a liquid crystal display element for such a purpose, a super twist type liquid crystal display element which can be driven in a higher order is mainly used.

Conventionally, this super twist type liquid crystal display device utilizes a birefringent mode for display and is colored yellow or blue. For this reason, there is a strong demand for achromatic color in view of the visibility of the display and the color display in combination with the color filter. Various methods for performing achromatic coloring have been developed, and one of them is a method using a retardation plate. In this method, a polymer film or the like that causes an optical phase difference is laminated on a liquid crystal cell as a phase difference plate to compensate for the phase difference caused by the liquid crystal layer.

As the retardation plate, one obtained by uniformly stretching a polymer film or the like is used, and its optical properties are uniform over the entire surface.

[0006]

However, even in a liquid crystal display device using a retardation plate, the distance traveled through the retardation plate varies depending on the incident angle of light, whereby the apparent retardation value of the retardation plate is apparent. Therefore, there is a problem that the color and the contrast greatly differ depending on the viewing direction and the angle of the screen, and the visibility is remarkably reduced.

In general, in a liquid crystal display device, the cell thickness (the thickness of the liquid crystal layer) in the non-pixel region is larger than that in the pixel region by the thickness of the electrode.

Therefore, the retardation value of the liquid crystal cell itself is larger in the non-pixel region than in the pixel region by the larger cell thickness. As a result, the transmittance of the liquid crystal cell,
Differences occur in color. For this reason, even if a retardation plate having a uniform retardation value is used, the pixel portion and the non-pixel portion cannot be compensated at the same time, resulting in a problem that the contrast ratio is reduced and the visibility is reduced due to coloring. there were.

The present invention has been made to solve such a problem, and has as its object to provide a liquid crystal display device having excellent visibility and a high contrast ratio.

[0010]

Means for Solving the Problems In a liquid crystal display device of the present invention, a liquid crystal composition is sandwiched between a pair of substrates, each having a surface on which an electrode and an alignment film are sequentially formed, with the alignment films facing each other. A liquid crystal cell in which a pixel region and a non-pixel region are formed by an arrangement of electrodes on the pair of substrates; two polarizing plates disposed so as to sandwich the liquid crystal cell; and the polarizing plate. In a liquid crystal display element having at least one retardation plate disposed between the liquid crystal cell and the liquid crystal cell, a retardation value of the retardation plate is set such that a retardation value of each pixel region is
It should be continuously smaller from the center to the periphery
And features.

Generally, a retardation value R of a retardation plate
Is given by R = △ n · d. Here, Δn represents the birefringence of the retardation plate, and d represents the thickness of the retardation plate. Therefore,
The retardation value of the phase difference plate can be changed by changing the thickness d of the phase difference plate or the birefringence Δn of the phase difference plate.

In the present invention, one of the liquid crystal display elements having different retardation values in the phase difference plate between the pixel region and the non-pixel region is such that the retardation value of the phase difference plate covering the pixel region is larger than the retardation value of the non-pixel region. Is large and changes periodically over the entire display area.

FIG. 1 shows, as an example, the structure of a liquid crystal display device showing such a retardation plate and its arrangement in the present invention.

In this case, the retardation value of the phase difference plate is changed by changing the thickness d of the phase difference plate, and the retardation value of the phase difference plate corresponds to the central portion of the pixel region for each pixel region. From the point to the peripheral portion. By appropriately adjusting the degree of this change, it is possible to reduce the deviation of the degree of compensation for the phase difference based on the difference in the optical path length between the optical path in FIG.

As a method of changing the thickness d, any method such as a cutting method and a molding method may be used. Also, as shown in FIG. 2, the retardation value of the phase difference plate can be changed by changing the birefringence Δn of the phase difference plate without changing the thickness d of the phase difference plate. In this case, it is preferable to reduce Δn continuously from the portion corresponding to the center of the pixel region to the portion corresponding to the peripheral portion of each pixel region.

As a method of changing the birefringence Δn,
There is no particular limitation as long as it is a method capable of changing the molecular state of the film polymer constituting the retardation plate, and for example, there is a method of partially heating.

In order to improve the visual characteristics, it is only necessary to change each pixel region so as to continuously decrease from a portion corresponding to the center of the pixel region to a portion corresponding to the peripheral portion thereof. As described above, it is not necessary to make the retardation value of the phase difference plate in the pixel region larger than the retardation value in the non-pixel region, and the configuration may be reversed.

Further, as another example of the present invention, for example, as shown in FIG.
There is a liquid crystal display element in which the retardation value of the retardation plate covering the non-pixel region is made larger than the retardation value of the retardation plate covering the pixel region by using a retardation plate having a structure in which the thickness is reduced. In this case, since the non-pixel region has a larger retardation value of the liquid crystal cell itself than the pixel region by the thickness of the electrode, such a configuration makes the difference between the retardation value of the liquid crystal cell itself in the pixel region and the non-pixel region equal to the phase difference plate. Are closer to each other, and there is no color difference between the pixel region and the non-pixel region.

Further, a configuration in which the shapes shown in FIGS. 1 and 3 are combined may be employed. That is, each pixel region is changed in retardation value of the phase difference plate so as to continuously decrease from a portion corresponding to the central portion of the pixel region to a portion corresponding to the peripheral portion, and each non-pixel region is shifted from the pixel region by the thickness of the electrode. A retardation plate having a structure as shown in FIG. 4 in which the retardation value is increased can also be used.

In the present invention, at least one retardation plate may be disposed between the polarizing plate and the liquid crystal cell, and a plurality of retardation plates may be superposed.

In the present invention, the pixel region and the non-pixel region are, for example, in a simple matrix type liquid crystal display element, a region where electrodes on both substrates in which electrodes are opposed to each other in a matrix form intersects a pixel region. Becomes
Other remaining areas are non-pixel areas.

In an active matrix type liquid crystal display device, a pixel electrode is a pixel region.

[0023]

When a retardation plate having a uniform retardation value is used, the visibility of the liquid crystal display element greatly depends on the viewing direction and angle. According to the present invention, the retardation value of the liquid crystal display element can be adjusted according to the viewing direction and angle by using a retardation plate in which the retardation value is periodically changed over the entire display area, and the viewing angle can be increased and the visibility can be improved. Can be improved.

Further, by making the retardation value of the phase difference plate covering the non-pixel region larger than the retardation value of the phase difference plate covering the pixel region, the difference between the retardation value of the liquid crystal cell itself in the pixel region and that of the non-pixel region is reduced. The difference between the retardation values of the retardation plates approaches. For this reason, it is possible to reduce a decrease in the contrast ratio due to light leakage from the non-pixel region and a deterioration in display color due to a difference in color between the pixel region and the non-pixel region.

Further, by combining the retardation plate of the present invention, the viewing angle characteristic and the color shift in the pixel region and the non-pixel region can be simultaneously improved.

[0026]

【Example】

Example 1 A liquid crystal display device of Example 1 will be described with reference to FIGS. FIG. 5 shows the main components of the liquid crystal display element and the direction of the optical axis.

In the liquid crystal display device, the transparent substrates 4a, 4a
Polarizing plates 5a and 5b (LLC2-81-18, trade name, manufactured by Sanritsu Electric Co., Ltd.) are provided outside b and are arranged in parallel with each other. Transparent electrodes 2a, 2b and alignment films 3a, 3b made of polyimide are formed on the substrates 4a, 4b, and a liquid crystal composition 1 is formed between the substrates 4a, 4b as ZLI3711 (E.
Counterclockwise chiral agent S-811 (E.C. product name)
It contains a product to which Merck's trade name is added.

The alignment films 3a and 3b are rubbed in the direction of -30.degree. In the alignment film 3a and 30.degree. In the alignment film 3b with respect to the reference direction C shown in FIG. Is oriented counterclockwise with a twist angle of 240 °. Here, the cell thickness (substrate spacing) was 7.0 μm. Further, between the transparent substrate 4 and the polarizing plate 5, a retardation plate 6 composed of a uniaxially stretched film containing polycarbonate as a component was disposed. The directions of the optical axes of the retardation plate 6 and the polarizing plates 5a and 5b were set to 40 °, 20 ° and 30 ° with respect to the reference direction C, respectively.

The retardation plate 6 used was formed by forming a projection approximately the same size as a pixel as shown in FIG. 1 by embossing in a direction perpendicular to the plane during stretching. The surface of each projection is spherical, and in the cross section passing through the center, the surface has an arc with a radius of curvature of 0.3 mm and a central angle of 60 °. The retardation value of the phase difference plate 6 is 65 at the center of the protrusion.
It was 0 nm and 600 nm at the periphery. A liquid crystal display element was manufactured by installing a retardation plate such that the projections were located on the pixel region.

The viewing angle was measured using the obtained liquid crystal display device.

The measurement was performed in the reference direction C and in directions of ± 90 ° and 180 ° from the reference direction C. The contrast ratio of the display surface was 10: 1 when measured in the normal direction, whereas 5: The angle of the point below 1 from the normal direction was examined.

As a result, in Example 1, it was 50 ° in the direction of C and 180 °, 40 ° in the + 90 ° direction, and 60 ° in the −90 ° direction.

Comparative Example 1 A liquid crystal display device having the same components as in Example 1 except that a retardation plate having a uniform retardation value was used was produced.

As a result of measuring the visual angle under the same conditions as in Example 1, it was 40 ° in the reference direction C and 180 °, 30 ° in the + 90 ° direction, and 50 ° in the −90 ° direction. .

Embodiment 2 A liquid crystal display device of Embodiment 2 will be described with reference to FIG.

The retardation value of the retardation film made of an organic polymer in Example 2 is reduced by heat. Then, heating was partially performed to obtain a retardation plate having the same distribution of retardation values as the retardation plate used in Example 1. A liquid crystal display device was produced in the same manner as in Example 1 except that this retardation plate was used.

As a result of measuring the viewing angle under the same conditions as in Example 1, almost the same results as in Example 1 were obtained.

Embodiment 3 FIG. 3 shows the structure of a liquid crystal display element in Embodiment 3.

The thickness of the electrodes of the used liquid crystal cell is 1000 angstroms, and the thicknesses of the liquid crystal layers in the pixel region and the non-pixel region are 7.0 μm and 7.1 μm, respectively. A retardation plate is used in the same manner as in the first embodiment.
The non-pixel region was set to have a retardation value of 660 nm, and the other conditions were the same as those in Example 1.

As a result, in the display OFF state,
There was almost no difference in color between the pixel region and the non-pixel region, and a display element with good visibility was obtained. Also, when the contrast ratio was measured at the time of 1/200 duty driving, it was 10: 1.

On the other hand, using the liquid crystal display device of Comparative Example 1,
As a result of performing the pattern display under the same conditions as in the third embodiment, a color difference occurs between the pixel region and the non-pixel region in the non-lighted portion, making the display difficult to see, and the contrast ratio is 8:
Was one.

[0042]

According to the liquid crystal display device of the present invention, two polarizing plates are arranged so as to sandwich a liquid crystal cell, and at least one retardation plate is arranged between the polarizing plate and the liquid crystal cell. Since the retardation value of the phase difference plate is different between the pixel region and the non-pixel region, the viewing angle characteristics are further improved, and a liquid crystal display with a high contrast ratio and high visibility is obtained as compared with the conventional liquid crystal display device. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a liquid crystal display device according to a first embodiment.

FIG. 2 is a diagram illustrating changes in retardation values of a liquid crystal display element and a phase difference plate of Example 2.

FIG. 3 is a diagram illustrating a liquid crystal display device of Example 3 in which a polarizing plate is omitted.

FIG. 4 illustrates one embodiment of the present invention.

FIG. 5 is a diagram showing main components of the liquid crystal display element and directions of optical axes.

[Explanation of symbols]

1 ... Liquid crystal layer, 2a, 2b ... Transparent electrodes, 3a, 3
b ... Alignment film, 4a, 4b ... Substrate, 5a, 5b ...
...... Polarizing plate, 6 ... Phase plate, 7 ... Liquid crystal cell.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/13363 G02F 1/1335

Claims (4)

(57) [Claims] 1. A liquid crystal composition is sandwiched between a pair of substrates on each of which a surface and an alignment film are sequentially formed, and a liquid crystal composition is sandwiched between the alignment films. A liquid crystal cell comprising a pixel region and a non-pixel region;
A liquid crystal display device comprising: two polarizing plates disposed to sandwich the liquid crystal cell; and at least one retardation plate disposed between the polarizing plate and the liquid crystal cell. The retardation value of each pixel area
Continuously smaller from the center to the periphery of the pixel area
The liquid crystal display element characterized in that it it. 2. The method according to claim 1 , wherein the thickness of the phase difference plate is different for each of the pixel regions.
Continuously small from the center to the periphery of the pixel area
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is formed in a thin film . 3. The method according to claim 1, wherein the retardation plate has a birefringence Δn.
Continuous from the center to the periphery of the pixel area for each elementary area
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is reduced in size . 4. The liquid crystal display device according to claim 1 , wherein a retardation value of said retardation plate in said pixel region is larger than a retardation value of said non-pixel region.