JPH05173125A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element which has visual angle characteristics improved more and is superior in visibility and high in contrast ratio. CONSTITUTION:A couple of substrates 4a and 4b which have electrodes 2a and 2b and orienting films 3a and 3b formed in order on the surfaces are arranged having the orienting films 3a and 3b opposite each other, a liquid crystal composition is sandwiched between them, and picture element areas and non- picture-element areas are formed of arrays of the electrodes on the couple of substrates 4a and 4b to constitute a liquid crystal cell. The liquid crystal display element consists of the cell, two polarizing plates 5a and 5b arranged with the liquid crystal cell sandwiched between them, and at least one phase difference plate 6 arranged between the polarizing plates 5a and 5b and liquid crystal cell 6; and the retardation value of the phase difference plate 6 is made different between the picture element areas and non-picture-element areas.

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 kinds of OA equipment such as liquid crystal televisions and word processors, and a liquid crystal display device which has a sufficient contrast at the time of display and is excellent in visibility is required. Is becoming.

As a liquid crystal display element for such an application, a super twist type liquid crystal display element capable of high-order division driving is mainly used.

Conventionally, this super twist type liquid crystal display element utilizes a birefringence mode for display and is colored yellow or blue. For this reason, there is a strong demand for an achromatic color from the viewpoints of easy-to-read display and compatibility with color display in combination with a 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 retardation is laminated on a liquid crystal cell as a retardation plate to compensate for the retardation caused by the liquid crystal layer.

As the retardation plate, a polymer film or the like uniformly stretched 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 in the retardation plate varies depending on the incident angle of light, which causes the apparent retardation value of the retardation plate. Therefore, there is a problem in that the visibility and the visibility are remarkably deteriorated due to a large difference in color and contrast depending on the viewing direction and angle of the screen.

In general, in a liquid crystal display element, the cell thickness (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 due to the larger cell thickness. As a result, the transmittance of the liquid crystal cell,
Differences occur in color. Therefore, 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, which causes a problem that the contrast ratio is lowered and the visibility is lowered due to coloring. there were.

The present invention has been made in order to solve such a problem, and an object thereof is to provide a liquid crystal display device having excellent visibility and a high contrast ratio.

[0010]

In a liquid crystal display device of the present invention, a liquid crystal composition is sandwiched between a pair of substrates each having an electrode and an alignment film formed on a surface thereof in this order. A liquid crystal cell in which a pixel region and a non-pixel region are constituted by an array of electrodes on a pair of substrates, two polarizing plates arranged so as to sandwich the liquid crystal cell, a polarizing plate and a liquid crystal cell In a liquid crystal display element in which at least one retardation plate is arranged between the two, the retardation value of the retardation film is different between the pixel region and the non-pixel region.

Generally, the retardation value R of the retardation plate
Is given by R = Δn · 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 retardation plate can be changed by changing the thickness d of the retardation plate or the birefringence Δn of the retardation plate.

In the present invention, one of the liquid crystal display elements in which the retardation plate has different retardation values in the pixel region and the non-pixel region is that the retardation value of the retardation plate covering the pixel region is higher than that 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 retardation plate is changed by changing the thickness d of the retardation plate, and the retardation value of the retardation plate corresponds to the central portion of the pixel region for each pixel region. From the end to the peripheral part, it is continuously changing. By appropriately adjusting the degree of this change, it is possible to reduce the deviation of the compensation degree of the phase difference based on the difference in the optical path length between the optical path of a in FIG. 1 and the optical path of b.

As a method for changing the thickness d, any method such as a cutting method or a molding method may be used. Further, as shown in FIG. 2, the retardation value of the retardation plate can be changed by changing the birefringence Δn of the retardation plate without changing the thickness d of the retardation plate. In this case, it is preferable that Δn be continuously reduced from the central portion of the pixel area to the peripheral portion of each pixel area.

As a method for 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-like polymer constituting the retardation plate, and examples thereof include a method of partially heating.

In order to improve the visual characteristics, it is sufficient to make each pixel region continuously smaller from the central portion of the pixel region to the peripheral portion thereof. As described above, it is not necessary to set the retardation value of the retardation film in the pixel region to be larger than the retardation value in the non-pixel region, and the opposite configuration can be adopted.

Further, as another example of the present invention, for example, as shown in FIG. 3, the thickness d of the retardation film is provided for each pixel region.
There is a liquid crystal display device 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 thinned structure. 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, the difference in retardation value of the liquid crystal cell in the pixel region and the non-pixel region and the phase difference plate are thus formed. The difference in the retardation values becomes close, and the color difference between the pixel region and the non-pixel region disappears.

Further, a configuration in which the shapes shown in FIGS. 1 and 3 are combined may be adopted. That is, in each pixel region, the retardation value of the retardation plate is changed so as to be continuously reduced from the central portion to the peripheral portion of the pixel region, and each non-pixel region is larger than the pixel region by the thickness of the electrode. It is also possible to use a retardation plate having a structure as shown in FIG. 4 in which the retardation value is increased.

At least one retardation plate in the present invention may be arranged 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 the case of a simple matrix type liquid crystal display element, the pixel region is a region where the electrodes on both substrates in which the electrodes are arranged to face each other in a matrix shape intersect each other. Next to
The other remaining areas are non-pixel areas.

In the active matrix type liquid crystal display device, the pixel electrode serves as the pixel region.

[0023]

When a retardation plate having a uniform retardation value is used, the visibility of the liquid crystal display device largely depends on the viewing direction and the angle. The present invention can adjust the retardation value of the liquid crystal display element by the viewing direction and the angle by using the retardation plate in which the retardation value is periodically changed over the entire display area, and the viewing angle is enlarged and the visibility is improved. Can be improved.

Further, by making the retardation value of the retardation plate covering the non-pixel region larger than the retardation value of the retardation plate covering the pixel region, the difference between the retardation values of the liquid crystal cells themselves in the pixel region and the non-pixel region can be calculated. The difference in retardation value of the phase difference plate approaches. Therefore, it is possible to reduce the deterioration of the contrast ratio due to the light leakage from the non-pixel region and the deterioration of the display color due to the color difference between the pixel region and the non-pixel region.

Further, by combining the retardation film of the present invention, it is possible to simultaneously improve the viewing angle characteristic and the color misregistration of the pixel region and the non-pixel region.

[0026]

【Example】

Example 1 A liquid crystal display element of Example 1 will be described with reference to FIGS. 1 and 5. FIG. 5 shows the main constituent elements of the liquid crystal display element and the directions of the optical axes.

In the liquid crystal display device, the transparent substrates 4a, 4
Polarizing plates 5a and 5b (LLC2-81-18, trade name of Sanritsu Electric Co., Ltd.) are provided on the outer side of b and are arranged in parallel with each other. The transparent electrodes 2a, 2b and the alignment films 3a, 3b made of polyimide are formed on the substrates 4a, 4b, and ZLI3711 (E.
A counterclockwise chiral agent S-811 (E.
The product containing Merck's product name) is enclosed.

The alignment films 3a and 3b are subjected to alignment treatment by rubbing in the directions of -30 ° for the alignment film 3a and 30 ° for 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 (distance between substrates) was 7.0 μm. Further, between the transparent substrate 4 and the polarizing plate 5, a retardation plate 6 made of a uniaxially stretched film containing polycarbonate as a component was arranged. 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 one in which projections having the same size as the pixel as shown in FIG. 1 were formed by embossing from the direction perpendicular to the surface during stretching. The surface of each protrusion is spherical, and in the cross section passing through the center, the surface has a radius of curvature of 0.3 mm and a central angle of 60 °. The retardation value of the retarder 6 is 65 at the center of the protrusion.
It was 0 nm and 600 nm in the peripheral portion. A retardation plate was placed so that the protrusions were located on the pixel region, and a liquid crystal display element was produced.

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

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

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

Comparative Example 1 A liquid crystal display element having the same constituent elements as in Example 1 was prepared except that a retardation plate having a uniform retardation value was used.

The visual angle was measured under the same conditions as in Example 1. As a result, the reference direction C and 180 ° were 40 °, the + 90 ° direction was 30 °, and the -90 ° direction was 50 °. ..

Example 2 A liquid crystal display element of Example 2 will be described with reference to FIG.

The retardation value of the organic polymer retardation plate in Example 2 is lowered by heat. Therefore, partial heating was performed to obtain a retardation plate having a retardation value distribution similar to that of the retardation plate used in Example 1. The same liquid crystal display element as in Example 1 was manufactured 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.

Example 3 The structure of the liquid crystal display element in Example 3 is shown in FIG.

The thickness of the electrodes of the liquid crystal cell used is 1000 Å, and the thicknesses of the liquid crystal layer in the pixel region and the non-pixel region are 7.0 μm and 7.1 μm, respectively. For the retardation plate, the same method as in Example 1 was used.
The retardation value of 660 nm was set in the non-pixel region, and the other conditions were the same as in Example 1.

As a result, when the display is OFF,
There was almost no difference in color between the pixel area and the non-pixel area, and a display element with good visibility was obtained. When the contrast ratio was measured at 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 Example 3, a color difference occurs between the pixel region and the non-pixel region in the non-lighted portion, the display becomes difficult to see, and the contrast ratio is 8:
It was 1.

[0042]

The liquid crystal display device of the present invention comprises two polarizing plates arranged so as to sandwich a liquid crystal cell, and at least one retardation plate arranged between the polarizing plate and the liquid crystal cell. Since the retardation value of the retardation film is made different between the pixel area and the non-pixel area, the viewing angle characteristics are improved more than the conventional liquid crystal display element, and a liquid crystal display with a high contrast ratio and good visibility can be obtained. ..

[Brief description of drawings]

FIG. 1 is a diagram showing a liquid crystal display element of Example 1.

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

FIG. 3 is a diagram showing a liquid crystal display element 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 constituent elements of a liquid crystal display element and directions of optical axes.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. A liquid crystal composition is sandwiched between a pair of substrates each having an electrode and an alignment film formed on a surface in order, and the alignment films are arranged to face each other. A liquid crystal cell including a pixel region and a non-pixel region,
A liquid crystal display element comprising two polarizing plates arranged so as to sandwich the liquid crystal cell, and at least one retardation plate arranged between the polarizing plate and the liquid crystal cell, wherein the retardation plate Retardation value of the pixel region is different from that of the non-pixel region.