JPH08201794A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display device whose dependency of a visual angle is low and whose display quality is excellent. CONSTITUTION: This device is equipped with a liquid crystal cell 1 having a specified liquid crystal layer, a light introducing means 2 introducing light into the liquid crystal layer 10 of a liquid crystal cell 1, and a light diffusion means 3 selectively diffusing light made incident within a specified angle range out of the light exiting from the liquid crystal cell 1; and the light diffusion means 3 forms an angle area where a haze rate (the rate of the transmissivity of a scattered light beam to the transmissivity of all the light beams) is gradually changed in accordance with an incident angle between the angle area where the haze rate in accordance with the incident angle is minimum and the angle area where it is maximum. Thus, the steep change of the haze rate is eliminated and the continuity of display is enhanced.

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 low viewing angle dependency.

[0002]

2. Description of the Related Art Conventionally, in a display device using a liquid crystal cell (Japanese Unexamined Patent Publication No. 60-107020), a viewing angle (observation direction) at which a certain degree of contrast and brightness can be obtained.
Is limited. That is, even if the display is observed from the front, the display tends to be dark, and in a large screen, it is observed from an oblique direction with respect to the display peripheral portion, so that there is a drawback that the contrast is lowered or the contrast is inverted. Such a large viewing angle limitation is said to have a high viewing angle dependency.

The viewing angle dependence is caused by the twist of the liquid crystal molecules (the direction of the helix, the helix start position of the liquid crystal molecules determined by the rubbing direction, etc.) and the birefringence anisotropy of the liquid crystal (light Due to the difference in retardation depending on the passage direction, due to the characteristics of the polarizing plate (whether the selectivity of the optical vibration direction is good or bad), and due to the directivity of the light source that irradiates the liquid crystal with light. Things are included.

In general, in a liquid crystal display device, in consideration of the above viewing angle dependence, the design is such that the position where the display is most easily seen is within the normal visual field range of the observer, for example, the contrast in the vicinity of the normal line direction at the center of the screen. It is designed to be higher than the surroundings.

[0005]

The applicant of the present application improves the viewing angle dependency by attaching a special film to the surface of the liquid crystal cell in order to deal with the viewing angle dependency occurring in the liquid crystal display device for the above various reasons. Proposed (Japanese Patent Application No. 6-25
No. 6877).

However, the special film is made of, for example, a polymer thin film having a special structure set so as to scatter incident light within a range of about 30 degrees in a predetermined direction from a normal line (φ = 0 degree). As shown in FIG. 2, when observing an object through it, for example, the incident light is made so that the range of 0 ° to 30 ° from the viewpoint to the front direction is opaque, and the other range is transparent. It has the function of selectively diffusing, and in particular, the haze ratio (ratio of the scattered light transmittance to the total light transmittance) changes sharply inside and outside the above-mentioned angle range (transparent state from opaque state or vice versa). The change from opaque state to transparent state, or vice versa, the boundary line from transparent state to opaque state becomes clear, and the continuous display of the boundary line A new problem occurs that is display quality is lowered impaired. Then, this invention makes it a main subject to eliminate this.

[0007]

According to the present invention, a liquid crystal cell having a predetermined liquid crystal layer, a light introducing means for guiding light to the liquid crystal layer of the liquid crystal cell, and a predetermined light out of the light emitted from the liquid crystal cell are provided. And a light diffusing means for selectively diffusing incident light in the angle range of the light diffusing means, wherein the light diffusing means has an angle of incidence between a minimum angle region and a maximum angle region in which the haze ratio according to the incident angle is large. It is characterized in that an angle region in which the haze ratio gradually changes according to the above is formed.

Further, the light diffusing means is characterized in that the angle region where the scattered light transmittance is maximum is arranged on the observer side of the liquid crystal cell so as to correspond to a predetermined viewing angle dependent direction of the liquid crystal cell.

[0009]

According to the present invention, since the light diffusing means for selectively diffusing the light coming out of the liquid crystal cell and entering within a predetermined angle range is provided, the twist of the liquid crystal molecule and the birefringence difference of the liquid crystal. Of the light emitted from the liquid crystal that is affected by the orientation, the characteristics of the polarizing plate, the directivity of the light source, etc., the light in the desired direction can be selected and diffused by the light diffusing means, and the viewing angle dependency can be improved. Can be lowered.

Further, since the light diffusing means forms an angular region in which the haze ratio gradually changes according to the incident angle, between the angular region in which the haze ratio depends on the incident angle and the maximum angle region. There is no sharp change in the haze ratio, and it is possible to gradually change from the opaque state to the transparent state, or vice versa, to maintain the display continuity of the liquid crystal cell and prevent the deterioration of the display quality. You can

Further, since the light diffusing means is arranged on the observer side of the liquid crystal cell so that the angular region where the scattered light transmittance is maximum corresponds to the predetermined viewing angle dependence direction of the liquid crystal cell, The good visual field range can be expanded by the light diffusing means.

[0012]

1 is a cross-sectional view of a main part of a liquid crystal display device according to an embodiment of the present invention, in which 1 is a liquid crystal cell having a liquid crystal layer 10 having a predetermined thickness, and 2 is a liquid crystal layer 10 of the liquid crystal cell 1. Light introducing means 3 for guiding light in a vertical direction is a light diffusing means for diffusing the light emitted from the liquid crystal cell 1.

The liquid crystal cell 1 has, for example, 90 to 2 liquid crystal molecules.
A so-called twisted nematic liquid crystal layer 10 arranged in a spiral form of 70 degrees is supported by a substrate 11 provided with electrodes 12 for applying an electric field for each pixel so as to be orthogonal to the inner surface. When the liquid crystal cell 1 requires the polarizing plate 13, the substrate 1
It is easy and preferable to be attached to the front and rear of the outer side of 1. Also,
An alignment film 14 for forming a predetermined alignment on liquid crystal molecules is formed on the substrate 11 so as to sandwich the liquid crystal layer 10. However, when the alignment film 14 is directly rubbed on the substrate 11 for alignment, the alignment film 14 is omitted. You can also Here, orientation processing is performed such that a region where high contrast is obtained is a predetermined region of the liquid crystal cell 1, for example, a normal direction or a downward direction (see the observation direction in FIG. 2).

The light-introducing means 2 has, for example, a small prism having an apex angle of about 90 to 100 degrees on the entire upper surface thereof for 10 to several tens.
It is composed of a plastic lens sheet such as polycarbonate formed at a pitch of 0 μm, and has a function of condensing the light incident from the flat back surface and converting it into light having enhanced directivity. Further, the light introducing means 2 may be configured by forming a microlens with a transparent material having a different refractive index such as silicon, epoxy resin, or silver chloride in a transparent flat plate such as acrylic resin or optical glass. It may be configured by a flat convex lens array, a laminated body of a convex lens array and a concave lens array, or a laminated body of a plurality of convex lens arrays or concave lens arrays.

If necessary, surface illumination means 4 can be provided on the back side of the light introducing means 2. This surface illumination means 4
Is a light guide plate 41 such as an acrylic resin flat plate, a linear light source 42 formed of a cold cathode tube or the like provided on the side surface of the light guide plate 41, and a surface light diffusion sheet 43 provided on the light guide plate 41 as necessary. Alternatively, the back reflection sheet 44 or a cylindrical reflection sheet (not shown) that covers the linear light source may be used. Here, the surface light diffusion sheet 43
Can also be used as the light introducing means 2.

As shown in FIG. 2, the light diffusing means 3 has the same rectangular plane shape as the liquid crystal cell 1, and has a predetermined range,
For example, a polymer having a special structure set to diffuse incident light in an angle range of about 50 degrees above to about 20 degrees below the normal (φ = 0 degree) at a diffusion degree according to the incident angle. It consists of a thin film. And this light diffusing means 3
4, the haze ratio (the higher the numerical value, the higher the degree of light diffusion), which is the ratio of the scattered light transmittance to the total light transmittance when the incident angle of light is changed, is set as shown in FIG. That is, the haze ratio in the angle region where the incident angle (the angle formed by the normal and the incident light) is below 90 degrees to below 20 degrees is set to a minimum value of almost 0%, and the incident light is transmitted without diffusion and is transparent. In this state, the haze ratio is set to about 80%, which is the maximum, in the angle region in which the incident angle is from upper 10 degrees to upper 30 degrees, and most of the incident light is diffused so that an opaque state is exhibited. The light diffusing means 3
In the opaque state, has a light transmittance similar to that in the transparent state, and diffuses most of the transmitted light to have a bright frosted glass appearance. Further, the incident angle between the angle region having the minimum haze rate and the angle region having the maximum haze rate is about 20 degrees below and about 10 degrees above (at least 20 degrees).
The haze ratio in the angle range of 30 degrees or more) is set so as to gradually increase from the minimum value to the maximum value while monotonically increasing. The rate is set so that it gradually decreases monotonically from the maximum value to the minimum value.

The polymer thin film forming the light diffusing means 3 can be an acrylic resin molded product having a blind phase structure inside, for example. The internal structure of this molded product, when observed by an optical microscope, formed a phase having a certain length, although it was cut in a contiguous shape in the surface observation, and about 50 μm from the film surface in the longitudinal section observation.
A blind phase-like phase structure is formed from a depth of m. The spacing of such a phase structure is about 2 μm at the upper part of the film and 3 to 4 μm at a depth of about 300 μm from the irradiation surface.
The distance gradually increases along the depth direction, but these may be set according to the desired light diffusion direction and light diffusion degree. Further, by changing the direction of the phase structure to change the inclination of the phase structure with respect to the light irradiation surface, the expression angle of the opaque state can be freely set, and the ultraviolet intensity at the time of resin molding or passing under ultraviolet rays can be set. It is possible to freely set the haze ratio according to the incident angle by controlling the speed to be performed, and thus it is possible to set the haze ratio according to the incident angle range and the incident angle of the light to be diffused. it can. Furthermore, there is a large difference in composition distribution between phase structures, and the refractive index is, for example, 1.55 in one phase, 1.51 in the other phase, and the refractive index difference between phases is as large as 0.4. Could be set to. These values can be molded so as to show the same value at any position in the depth direction of the film. The above-mentioned light scattering with a viewing angle dependency that occurs in the polymer thin film can be controlled largely due to the phase structure and the difference in refractive index between the phase structures. If a polymer thin film that constitutes such a light diffusing means 3 is to be obtained as a commercial product, it is optically compatible with the series of visibility control films (product name "Lumisty") manufactured by Sumitomo Chemical Co., Ltd. It is preferable to specify and use a characteristic.

The light diffusing means 3 is attached to the surface of the liquid crystal cell 1 by using an adhesive. At this time, the light diffusing means 3 is positioned so that the light diffusing means 3 corresponds to a predetermined viewing angle dependent direction of the liquid crystal cell 1. Is done. The causes of the viewing angle dependence are, for example, those caused by the twist of the liquid crystal molecules (the direction of the helix, the spiral start position of the liquid crystal molecules determined by the rubbing direction, etc.), and the birefringence anisotropy of the liquid crystal (the light passage direction). Caused by the difference in the retardation due to the above), the characteristics of the polarizing plate (whether or not the selectivity of the optical vibration direction is good or bad),
1 due to the directivity of the light source that illuminates the liquid crystal
Since one or a combination thereof can be considered, the positioning corresponding to the viewing angle dependent direction is performed in consideration of them. In the present embodiment, for example, the case where the viewer is improved so as to widen the viewing angle when viewing the liquid crystal cell 1 from the lower side to the upper side, and as shown in FIG. When viewed through 3, due to the presence of the light diffusing means 3, the range of the line of sight (indicated by diagonal lines) in which the object appears to be opaque is about 50 degrees up to 20 degrees below the normal line passing through the viewpoint. The light diffusing means 3 is positioned and attached to the liquid crystal cell 1 so as to be within the range. In particular, the light diffusing means 3 is positioned so that the light traveling from the liquid crystal cell 1 in the viewing angle direction (viewer side direction) to be improved is diffused by the light diffusing means 3 (mainly the maximum haze rate angular region). Then, it is attached to the liquid crystal cell 1. Here, since the light diffusing means 3 is composed of a thin film, the display device can be thinned and can be easily attached to the liquid crystal cell 1 by using an adhesive or the like. It can be simplified.

In this way, the light diffusing means 3 is connected to the liquid crystal cell 1.
As shown in FIG. 3, when the liquid crystal cell 1 is observed by moving the viewpoint for viewing the fixed position of the liquid crystal cell 1 from the upper side to the lower side of the liquid crystal cell 1 as shown in FIG. When the angle formed by the normal line and the normal is in the range of about 90 degrees to about 20 degrees, the light emitted from the liquid crystal cell 1 is diffused by the light diffusing means 3.
In the incident angle region in which the haze ratio is the minimum, and the angle formed by the line of sight and the normal is in the range of about 20 degrees to about 10 degrees below, the light emitted from the liquid crystal cell 1 has The light emitted from the liquid crystal cell 1 has the maximum haze ratio of the light diffusing means 3 when the angle of incidence and the normal line is in the range of about 10 degrees to about 30 degrees below the gradually increasing incident angle region. The incident angle at which the light emitted from the liquid crystal cell 1 gradually decreases the haze ratio of the light diffusing means 3 in the range where the angle formed by the line of sight and the normal is in the range of about 30 degrees to about 50 degrees below. Enter the area. Therefore, there is a region where the haze ratio gradually changes before and after the incident angle region where the haze ratio of the light diffusing means 3 is maximum, and the region is at least 2
Since it extends to the 0 degree angle region, it is possible to prevent a sharp change in the haze ratio between the maximum (opaque state) angle region and the minimum (transparent state) angle region, and to maintain the continuity of the image. The display quality can be kept good. still,
As a result of attaching the light diffusing means 3, the incident angles of the light entering the light diffusing means 3 from the liquid crystal cell 1 are from top 10 to top 30.
Most of the light of a degree and a part of the light in the angular region in the vicinity thereof are selectively diffused, so that the light emitted from the liquid crystal cell 1 can be averaged and output, and the brightness and the contrast can be improved as a whole. It is possible to increase the brightness and contrast of the peripheral portion by flattening. Here, since the haze ratio maximum or maximum angle region is out of the normal direction (generally, the highest brightness and contrast are high), it is possible to prevent the decrease in brightness and contrast in the normal direction.

In the above embodiment, the case of improving the viewing angle in the downward direction (when observing the display surface from the lower side to the upper side of the normal line) is taken as an example. In order to improve the viewing angle in the case of observing by arranging the line of sight from the upper side to the lower side of the normal line, the light diffusing means 3 may be inverted and attached to the liquid crystal cell 1. However, in order to improve the viewing angle in the right direction or the left direction, the light diffusing means 3 may be rotated 90 degrees left and right and attached to the liquid crystal cell 1, but the good viewing direction is set to the lower side. In this example, the viewing angle could not be improved as much as in the vertical direction.

The liquid crystal cell to which the light diffusing means is attached is not limited to the STN system, but may be a TFT system or a MIM system.

[0022]

According to the present invention, a light diffusing means for selectively diffusing light coming out of a liquid crystal cell, which is incident in a predetermined angle range, is provided. Of the light emitted from the liquid crystal that is affected by the refractive anisotropy, the characteristics of the polarizing plate, the directivity of the light source, etc., the light in the desired direction can be selected and diffused by the light diffusing means. Sex can be lowered.

Further, since the light diffusing means forms an angle region in which the haze ratio gradually changes according to the incident angle, between the angle region in which the haze ratio depends on the incident angle and the maximum angle region. There is no sharp change in the haze ratio, and it is possible to gradually change from the opaque state to the transparent state, or vice versa, to maintain the display continuity of the liquid crystal cell and prevent the deterioration of the display quality. You can

Further, the light diffusing means is arranged on the observer side of the liquid crystal cell in such a manner that the angular region where the scattered light transmittance is maximized is arranged on the observer side of the liquid crystal cell so as to correspond to the predetermined viewing angle dependent direction of the liquid crystal cell. The good visual field range can be expanded by the light diffusing means.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing an arrangement of a liquid crystal cell and a light diffusing means of an embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining the function of the light diffusing unit of the embodiment of the present invention.

FIG. 4 is an optical characteristic diagram of a light diffusing unit according to an example of the present invention.

[Explanation of symbols]

 1 liquid crystal cell 2 light introducing means 3 light diffusing means 4 surface illuminating means

Claims (2)

[Claims] 1. A liquid crystal cell having a predetermined liquid crystal layer, a light introducing unit for guiding light to the liquid crystal layer of the liquid crystal cell, and a light incident on the liquid crystal cell in a predetermined angle range among light emitted from the liquid crystal cell. And a light diffusing means for selectively diffusing, wherein the light diffusing means has a haze ratio (ratio of scattered light transmittance to total light transmittance) according to an incident angle of a minimum angle region and a maximum angle region. A liquid crystal display device, wherein an angle region in which a haze ratio gradually changes according to an incident angle is formed therebetween. 2. A liquid crystal cell having a viewing angle dependency, and a light diffusing means whose scattered light transmittance gradually changes depending on an incident angle with respect to light passing through the liquid crystal cell, the light diffusing means comprising: A liquid crystal display device, characterized in that an angular region where the transmittance of scattered light is maximum is arranged on the viewer side of the liquid crystal cell so as to correspond to a predetermined viewing angle dependent direction of the liquid crystal cell.