JPH1039341A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress the luminance difference between a central part and a peripheral part to a lower level, to decrease the fluctuations in a contrast ratio by a visual field angle and to obtain high-grade display images by specifying the liquid crystal pitch length of the liquid crystal material used for a liquid crystal layer to a specific range. SOLUTION: A pair of glass substrates 2 are stuck to each other apart a prescribed spacing opened by sealants 3 and the liquid crystal layer 4 is formed between a pair of such glass substrates 2, by which the liquid crystal display device is constituted. The device is provided with transparent electrodes 5 and liquid crystal molecule oriented films 6, successively from the respective glass substrate 2 sides. The liquid crystal layer 4 is formed by using the liquid crystal material formed by adding a chiral agent which is one of optically active materials to liquid crystals. The liquid crystal material formed particularly by adjusting the amt. of the chiral agent to be added in such a manner that the liquid crystal pitch thereof is made larger than the liquid crystal pitch length (100μm) of the liquid crystal material used thus far, i.e., attains >=120μm.

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 using a liquid crystal material obtained by adding a chiral agent to liquid crystal for a liquid crystal layer of a liquid crystal panel.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device, a projection type liquid crystal display device such as a liquid crystal projector is known. In this liquid crystal display device, as shown in FIG. 12, light (hereinafter, such a light is referred to as a backlight) 13 is directed from a light source 11 toward the back side of a panel (hereinafter, referred to as a liquid crystal panel) 12 of the liquid crystal display device. Is projected on the liquid crystal panel 12
Is projected on a display screen (not shown) composed of a screen or the like disposed in front of the liquid crystal panel 12 in an enlarged manner.

[0003]

However, in the conventional liquid crystal display device, it is technically difficult to make the backlight a perfect parallel light, and as shown in FIG. The incident angle of the backlight 13 varies with the peripheral portion. For example, the incident angle of the backlight 13 to the center of the liquid crystal panel 12 is 90
When the angle is θ, the incident angle of the backlight 13 to the peripheral portion of the liquid crystal panel 12 is 90 ° −θ, and the angle difference θ between the incident angle at the central portion of the liquid crystal panel 12 and the incident angle at the peripheral portion is Occurs. As a result, a luminance difference occurs between the central part and the peripheral part of the liquid crystal panel 12. Further, if the center of the region having the highest contrast ratio (maximum contrast region) in the liquid crystal panel 12 does not coincide with the center of the viewing angle, the luminance difference 14 becomes uneven depending on the viewing angle as shown in FIG. In other words, that is, uneven brightness occurs. Such a luminance difference appears as a decrease in contrast or color unevenness on a screen or a display screen of a liquid crystal panel, and deteriorates the quality of a displayed image.

[0004]

According to the present invention, there is provided a liquid crystal display device using a liquid crystal material obtained by adding a chiral agent to liquid crystal for a liquid crystal layer of a liquid crystal panel. As the liquid crystal material, a material in which the amount of the chiral agent added is adjusted so that the liquid crystal pitch length is 120 μm or more is used.

In general, when the liquid crystal material is a nematic liquid crystal obtained by adding a chiral agent, or is a cholesteric liquid crystal, the axes of the liquid crystal molecules 41 are twisted as shown in FIG. It has been known. In this specification, the pitch P of the twist from the state where the axis of the liquid crystal molecules 41 is oriented in one direction to the original direction is referred to as a liquid crystal pitch length. In the present invention, since the addition amount of the chiral agent is adjusted so that the liquid crystal pitch length of the liquid crystal material used for the liquid crystal layer is 120 μm or more, the voltage is applied from the liquid crystal panel to the state where no voltage is applied. At this time, the liquid crystal molecules return easily. In addition, the center of the maximum contrast area substantially coincides with the center of the viewing angle.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the liquid crystal display device according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the liquid crystal display device according to the present invention,
In particular, the figure shows a liquid crystal panel having a liquid crystal layer which is a feature of the present invention. As shown in FIG.
Has a structure of a general liquid crystal panel. A pair of glass substrates 2 are bonded at a predetermined interval by a sealant 3, and a liquid crystal layer 4 is formed between the pair of glass substrates 2. It is configured. Note that a transparent electrode 5 and a liquid crystal molecule alignment film 6 are sequentially provided on the surface of each glass substrate 2 on the liquid crystal layer 4 side from the glass substrate 2 side.

The liquid crystal layer 4 is formed by using a liquid crystal material formed by adding a chiral agent, which is one of optically active substances, to liquid crystal. As the liquid crystal, for example, a fluorine-based nematic liquid crystal as shown in FIG. 2 can be used, and as the chiral agent, for example, a general chiral agent as shown in FIG. 3 can be used.

In the present invention, in particular, such a liquid crystal material is designed so that the liquid crystal pitch length (see FIG. 11) is larger than the liquid crystal pitch length (100 μm) of a conventionally used liquid crystal material, that is, 120 μm or more. The amount of the chiral agent added is adjusted so that Also,
The upper limit of the liquid crystal pitch length is determined based on the so-called contrast ratio, which is obtained by the ratio of the luminance of the display area before the voltage is applied to the liquid crystal panel 1 via the transparent electrode 5 to the luminance when the voltage is applied. It is desirable that the pitch be the liquid crystal pitch length. In this embodiment, for example, the liquid crystal pitch length is 12
The amount of the chiral agent added is adjusted so as to be a predetermined value in the range of 0 μm or more and 180 μm or less.

Here, in the present invention, the liquid crystal pitch length is set to 120 μm or more, which is longer than the conventional one, for the following reasons. That is, when the liquid crystal pitch length is made longer than the conventional one, the case where the voltage is applied to the liquid crystal panel 1 as shown in FIG. 4A and the state where no voltage is applied as shown in FIG. In addition, the liquid crystal molecules 41 lined upright by application of a voltage easily return to the original state where the axis is twisted. In other words, the state in which the light 8 is transmitted through the liquid crystal layer 4 because the liquid crystal molecules 41 are arranged vertically and the state in which the axis of the liquid crystal molecules 41 is twisted, cause the light 8 to move the liquid crystal layer 4. It is easy to shift to a state where light is not transmitted. Therefore, the present inventor has come up with the idea that the contrast ratio of the display area of the liquid crystal panel 1 can be increased as compared with the related art, when the pitch length of the liquid crystal is made longer than before.

Therefore, the pitch of the liquid crystal is made larger (for example, 120 μm) than the pitch of the conventional liquid crystal (100 μm).
An experiment for examining the relationship between the voltage and the light transmittance in the case m) was performed, and the result as shown in FIG. 5 was obtained. In FIG. 5, the horizontal axis indicates the driving voltage V of the liquid crystal panel, and the vertical axis indicates the light transmittance (%). The solid line indicates the embodiment of the present invention, and the broken line indicates the conventional example.

As is apparent from FIG. 5, when the pitch of the liquid crystal increases, the voltage-transmittance curve becomes steeper when a voltage is applied. Accordingly, when the liquid crystal panel is driven at the same driving voltage (V ₀ −V ₁ ) as the conventional _one, the difference d _{1 in} the light transmittance of the present embodiment is smaller than the difference d in the light transmittance of the conventional example. It is confirmed that the ratio increases, that is, the contrast ratio of the display area of the liquid crystal panel 1 increases.

The liquid crystal pitch length is 120 μm and 150 μm.
μm, equal contrast curves for 180 μm,
When the isocontrast curves of the conventional example in which the liquid crystal pitch length was 100 μm were examined, the results as shown in FIGS. 6 to 9 were obtained. FIG. 6 shows that the liquid crystal pitch length is 120 μm,
7 is 150 μm, FIG. 8 is 180 μm, and FIG. 9 is 100 μm.
The case of m is shown. 6 to 9, the portion where the vertical and horizontal axes intersect indicates the center of the viewing angle, and the hatched portion indicates the maximum contrast area.

From these figures, it can be seen that, when the liquid crystal pitch length is larger than that of the conventional example, the center of the maximum contrast region moves to the center of the viewing angle, and the fluctuation of the contrast ratio due to the viewing angle is smaller than that of the conventional example. It is recognized that it is low. The liquid crystal pitch length is 120 μm,
In the case of 50 μm, although the area change of the maximum contrast region is not so much recognized as in the conventional example, the maximum contrast region is widened when the liquid crystal pitch length is 180 μm, so that a higher contrast ratio can be obtained in this case. You can see that there is. From the above, in the present embodiment, the liquid crystal pitch length is longer than that of the related art, that is, 120 μm or more.

Further, it is desirable that the upper limit of the liquid crystal pitch length be a liquid crystal pitch length determined on the basis of the contrast ratio, as shown in FIG. Nation (discli
nation), which may reduce the contrast ratio of the display area of the liquid crystal panel 1.

For example, when disclination occurs at a boundary between a pixel provided substantially at the center of a liquid crystal panel and a wiring provided at the periphery thereof, a black mask is provided on the wiring side from the boundary. Also, the generated disclination protrudes from the black mask side to the pixel side. As a result, light leaks at that portion, and when there is black (darkest portion) at the boundary portion, light enters the darkest portion and changes from black to gray. Therefore, the contrast ratio decreases.

In this embodiment, the upper limit of the liquid crystal pitch is set to 180 μm as a result of setting the upper limit of the liquid crystal pitch so as to obtain a contrast ratio of, for example, 150 or more. Further, based on the finding that changing the addition amount (concentration) of the chiral agent in the liquid crystal material changes the pitch length of the liquid crystal, the present invention reduces the concentration of the chiral agent in the liquid crystal material from that of the prior art by reducing the concentration of the chiral agent. The liquid crystal pitch length is increased.

For example, when the concentration of the chiral agent required to obtain the conventional liquid crystal pitch length of 100 μm is 1.5% by weight, the concentration of the chiral agent is 1.1% by weight, 0.9% by weight,
By sequentially reducing the weight to 0.75, liquid crystal materials having liquid crystal pitch lengths of 120 μm, 150 μm, and 180 μm are obtained.

As described above, in the liquid crystal panel 1 of the present embodiment, the liquid crystal material of the liquid crystal layer has a liquid crystal pitch length of 120 μm.
Since the material in which the chiral agent is adjusted so as to have a predetermined value in the range of not less than m and not more than 180 μm is used, the contrast ratio can be increased, and the center of the maximum contrast region can be set substantially at the center of the viewing angle. Can be matched. In particular, when the liquid crystal pitch length is 180 μm, the maximum contrast region is widened, so that the contrast ratio can be further increased.

Therefore, in the liquid crystal display device provided with the liquid crystal panel 1, even if a difference occurs in the incident angle of the incident light between the central portion and the peripheral portion of the liquid crystal panel 1, the difference between the central portion and the peripheral portion. The luminance difference can be kept low. Further, it is possible to reduce a change in the contrast ratio due to the viewing angle. Accordingly, since a decrease in contrast and color unevenness on the display screen can be prevented, a liquid crystal display device capable of obtaining a high-quality display image can be realized.

[0020]

As described above, according to the liquid crystal display device of the present invention, the amount of the chiral agent added is adjusted so that the liquid crystal pitch length of the liquid crystal material used for the liquid crystal layer becomes 120 μm or more. , The contrast ratio can be increased, and the center of the maximum contrast region can be made substantially coincident with the center of the viewing angle. Therefore, even if there is a difference in the incident angle of the incident light between the central part and the peripheral part of the liquid crystal panel, the luminance difference between the central part and the peripheral part can be suppressed low, and the contrast ratio due to the viewing angle can be reduced. Can be reduced, and a high-quality display image can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a main part of an embodiment of a liquid crystal display device according to the present invention.

FIGS. 2A to 2D are diagrams showing examples of the structure of a nematic liquid crystal.

FIGS. 3A to 3D are diagrams illustrating examples of the structure of a chiral agent.

4A and 4B are diagrams illustrating states of liquid crystal molecules when a voltage is applied and when no voltage is applied, where FIG. 4A is a diagram illustrating a state when no voltage is applied, and FIG.

FIG. 5 is a diagram showing a relationship between voltage and light transmittance in a liquid crystal panel.

FIG. 6 is a diagram (part 1) showing an equal contrast curve of the embodiment, showing a case where the liquid crystal pitch length is 120 μm.

FIG. 7 is a diagram (part 2) illustrating an iso-contrast curve of the embodiment, showing a case where the liquid crystal pitch length is 150 μm.

FIG. 8 is a diagram showing an equal contrast curve of the embodiment (part 3), showing a case where the liquid crystal pitch length is 180 μm.

FIG. 9 is a diagram showing an equal contrast curve of a conventional example;
FIG. 3 is a diagram showing a case where a liquid crystal pitch length is 100 μm.

FIG. 10 is a diagram showing a relationship between a liquid crystal pitch length and disclination.

FIG. 11 is a diagram illustrating a liquid crystal pitch length.

FIGS. 12A and 12B are diagrams for explaining the problem of the present invention.

[Explanation of symbols]

 1 liquid crystal panel 4 liquid crystal layer P liquid crystal pitch length

Claims (2)

[Claims] 1. A liquid crystal display device using a liquid crystal material obtained by adding a chiral agent to liquid crystal for a liquid crystal layer of a liquid crystal panel, wherein the liquid crystal material has a liquid crystal pitch length of 120 μm or more. A liquid crystal display device characterized in that the amount of added is adjusted. 2. An upper limit value of a liquid crystal pitch length of the liquid crystal material is a liquid crystal pitch length determined based on a ratio between luminance before applying a voltage to the liquid crystal panel and luminance when a voltage is applied. The liquid crystal display device according to claim 1, wherein: