JPH1062777A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the dependence of visual angles which occurs in a liquid crystal display device by various reasons by including light diffusion means for selectively diffusing the light in the direction deviated approximately to the light and left with respect to the prescribed direction where the light is emitted from a liquid crystal cell. SOLUTION: This liquid crystal display device is provided with the liquid crystal cell 1 set with the central visual field in a prescribed direction and the light diffusing means 2 for selectively diffusing the light in the direction deviated to approximately the right and left with respect to the direction where the light 1 is emitted from the liquid crystal cell 1. The light diffusing means 2 preferably consists of a visual field control film which selectively diffuses the light in the direction deviated to approximately the right and left with respect to the prescribed direction set as the central visual field. In such a case, for example, the direction deviating to the right and left signifies ±θ=±90 deg. when the prescribed direction of the central visual field is (ϕ>0, θ=0). The light diffusing means 2 has a square flat shape which is approximately the same as the shape of the liquid crystal cell 1 and, in such a case, the means consists of high-polymer films which are used by superposing two sheets and have the special structure so set as to selectively diffuse the incident light in the prescribed range out of the incident light.

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 wide viewing angle for setting a central visual field.

[0002]

2. Description of the Related Art Conventionally, in a display device using a liquid crystal cell (Japanese Patent Application Laid-Open No. 60-107020), a viewing angle (observation direction) at which a certain level of contrast and brightness can be obtained.
Is limited. That is, even if the display can be clearly read by observing the display from the front side, when viewed from the oblique side or the back side, there is a disadvantage that the contrast is reduced or the contrast is inverted (negative / positive inversion).

[0003] Such viewing angle dependence is caused by twisting of liquid crystal molecules (helix start position of liquid crystal molecules determined by rubbing direction, helix direction, etc.), birefringence anisotropy of liquid crystal. (Such as differences in retardation depending on the light passing direction), characteristics due to the characteristics of the polarizing plate (such as the selectivity of the light vibration direction), and
The light source that irradiates the liquid crystal with light may be caused by directivity.

In general, in a liquid crystal display device,
In consideration of the above viewing angle dependency, a design in which the most visible position is within the normal viewing range of the user, for example, so that the contrast in the vertical direction at the center of the screen or a slightly downward direction is enhanced as compared with the surroundings. Design is done.

[0005]

However, unlike a palmtop computer or a clock, a laptop computer or the like is not limited to a viewer who always looks at the display surface from the front. When the screen is large, for example, if the display is viewed from the front and the center part can be clearly read, it means that the display is viewed from an oblique direction with respect to the periphery of the display. There are drawbacks in that the contrast at the corners of the display surface is reduced and that the contrast is inverted.

It is a main object of the present invention to improve the viewing angle dependency which occurs in a liquid crystal display device for the above various reasons, and to realize the improvement of the viewing angle dependency by a simple configuration. .

[0007]

According to the present invention, there is provided a liquid crystal cell 1 having a central field of view set in a predetermined direction, and a direction substantially shifted left and right with respect to a predetermined direction emitted from the liquid crystal cell. Light diffusing means 2 for selectively diffusing the light.

In the present invention, more preferably, the liquid crystal cell is constituted by a display mode utilizing birefringence, and the light diffusing means is constituted by a visibility control film. Liquid crystal molecules are 180 degrees or more 3
It has a helical structure of 60 degrees or less, and the predetermined direction of the central visual field is an angle (φ し た 0) inclined from the perpendicular B of the surface A of the liquid crystal cell 1 in a certain direction. The target diffusion direction (direction in which α is directed) is a direction (± θ = ± 30 to 100 degrees) rotated left and right by 30 to 100 degrees with respect to the direction of projection onto the surface of the liquid crystal cell in a predetermined direction. More preferably, the selected diffusion angle is 20 degrees or more and 90 degrees or more.
Degrees or less (20 <= α <= 90).

[0009]

FIG. 1 is a sectional view of a main part of a liquid crystal display device according to an embodiment of the present invention. Reference numeral 1 denotes a liquid crystal layer 11 having a central field of view set in a predetermined direction and a polarizing plate 12. It is a liquid crystal cell. The liquid crystal layer 11 is a so-called super-twisted nematic liquid crystal layer having, for example, a helical structure in which the liquid crystal molecules are 180 degrees or more and 360 degrees or less when no electric field is applied.
An electrode 13 for applying an electric field to each pixel is supported by a substrate 14 provided on the inner surface so as to be orthogonal to each other. An alignment film 15 for forming a predetermined alignment on liquid crystal molecules is formed on the substrate 14 so as to sandwich the liquid crystal layer 11.
In the case where the alignment is performed by directly rubbing the substrate 14, the alignment film 15 is used.
Can also be omitted. The polarizing plate 12 laminated on the liquid crystal layer 11 is attached to the front and back of the outside of the substrate 14, and the relationship between the alignment direction and the polarization axis or the absorption axis at this time is such that the liquid crystal cell 1 is configured in a display mode utilizing birefringence. Thus, they are provided to intersect as appropriate. If necessary, a phase plate 16 for eliminating coloring due to birefringence interference may be inserted between the liquid crystal layer 11 and the polarizing plate 12, or a color filter layer (not shown) for color display. May be provided on the inner surface of the substrate 14 or the like.

Here, the viewing direction will be described.
As shown in FIG. 2, it is assumed that the line of sight C is at an angle inclined in a certain direction from a perpendicular line B of the surface A of the liquid crystal cell 1. As a method of expressing the line of sight C, an angle (reference) inclined from a perpendicular line B of the surface A of the liquid crystal cell is indicated, and is represented by φ. How much the direction of projection of the line of sight C onto the surface A of the liquid crystal cell 1 rotates from the front of the liquid crystal cell 1 is referred to clockwise as θ (or ± θ). Therefore, the line of sight C is represented by the angle φ inclined from the perpendicular B and the rotation angle θ of the projection direction. For convenience, 270 ° <= θ <= 90 ° and φ> = 0, 9
0 degree <θ <270 degree and φ <0 may be indicated.

In the liquid crystal display device shown in FIG.
In the case of a 0-degree helix, the orientation direction is crossed in an X-shape (± θ = ± 45 degrees) toward the display surface, and the helix direction is located on the back side (the front side is the rotationally open portion of the liquid crystal molecule helix). If you choose the polarization axis for optimal contrast,
The angle φ at which the central visual field is inclined from the perpendicular B is 0
The selected angle of 30 degrees, the rotation angle θ in the projection direction is 35
The selected predetermined direction may be 0 to 10 degrees. By setting the central visual field in a predetermined direction in this manner, the characteristic of the dependence of the visual field angle is determined, and a range with a high contrast is specified.

The liquid crystal cell 1 preferably has illumination means 3 on the back. It comprises, for example, a light source, light guiding means and diffusing means. More specifically, a light guide plate 31 such as an acrylic resin flat plate, a linear light source 32 such as a cold cathode tube provided on a side surface of the light guide plate 31, and a surface light provided on the light guide plate 31 as necessary. It can be configured by a diffusion sheet 33, a back reflection sheet 34, a tubular reflection sheet that covers a linear light source (can also be used as the back reflection sheet 34), or the like. The surface light diffusion sheet 33 is, for example,
It is composed of a plastic lens sheet such as a polycarbonate in which minute prisms having an apex angle of about 90 to 100 degrees are formed at a pitch of 10 to several 100 μm, and collects and directs light incident from a substantially flat back surface. It has the function of producing light with enhanced properties. In addition, this may be formed by forming a microlens in a transparent flat plate such as acrylic resin or optical glass with a transparent material having a different refractive index such as silicon, epoxy resin, silver chloride, or the like, a flat convex lens array, Alternatively, it may be constituted by a laminate of a convex lens array and a concave lens array, or a laminate of a plurality of convex lens arrays and concave lens arrays.
It is more preferable to have directivity of light as a whole.

Reference numeral 2 denotes a light diffusing means for selectively diffusing light emitted from the liquid crystal cell 1, and selectively diffusing light in a direction substantially shifted left and right with respect to a predetermined direction set as a central visual field. And preferably comprises a visibility control film.
Here, for example, the predetermined direction of the central visual field is (φ> 0, θ =
In the case of 0), the direction shifted left and right means ± θ = ± 90 degrees. As shown in FIG. 3, the light diffusing means 2 has a substantially quadrangular planar shape similar to that of the liquid crystal cell 1. Here, two light diffusing means 2 are used to overlap each other, and select a predetermined range of incident light from incident light. It is composed of a polymer thin film having a special structure that is set so as to diffuse diffusely. In FIG. 1, the light diffusing means 2 is arranged outside the polarizing plate 12, but the substrate 14 and the polarizing plate 1
2 may be inserted.

Here, the central viewing direction when the liquid crystal cell 1 is observed is such that the line of sight is located on the near side (φ> 0) with respect to the perpendicular (φ = 0 degree) of the display surface (φ> 0). ) Is set. The first light diffusing means 2A disposed above the liquid crystal cell 1 is provided with a perpendicular (φ =
0 degree), light incident in a predetermined angle range in the left (right) direction (for example, a range from a perpendicular (φ = 0 degree) to approximately left to α1 = about 30 degrees) is selectively diffused. The second light diffusing unit 2B disposed on the upper surface of the first light diffusing unit 3A includes:
Light incident in a right angle (left direction) direction with respect to a perpendicular line (preferably in a range from a perpendicular line (φ = 0 degree) to approximately rightward α2 = about 30 degrees) is selectively diffused. ing. That is, the incident direction θ1 of the light diffused by the first light diffusing means 2A and the incident direction θ2 of the light diffused by the second light diffusing means 2B are different from each other, and are preferably perpendicular to the display surface as described above. As shown in the left-right relationship to B,
Direction rotated by more than 180 degrees (direction of central visual field φ> 0 and θ
(1> θ2, θ1−θ2> = 180 degrees).

As the liquid crystal display device, when the liquid crystal layer 11 uses a liquid crystal molecule having a helical structure of 180 degrees or more and 360 degrees or less when no electric field is applied, the predetermined direction of the central visual field is constant from a perpendicular to the surface of the liquid crystal cell. Angle (φ>
0), and in such a case, the selective diffusion direction of the light diffusion means 2 is preferably a direction rotated 30 degrees to 100 degrees left and right with respect to the direction of projection on the surface of the liquid crystal cell in a predetermined direction, For example, when the projection direction of the predetermined direction on the surface of the liquid crystal cell is θ = 0, preferably θ1 = 35 to 50 degrees, θ2
= 310-325 degrees is the most suitable.

As shown in FIG. 3, when each of the light diffusing means 2 observes an object through one of the light diffusing means 2A and 2B, for example, the light diffusing means 2 extends from 0 ° to 30 ° in one direction from the viewpoint. The range has an opaque state, and the other ranges have a function of selectively diffusing incident light so as to appear transparent. In the transparent state, each of the light diffusing means 2 has little reflection and absorption (for example, a total transmittance of 88%, of which a linear transmittance is 85%), and in the opaque state, the same light transmission as the transparent state. (E.g., 88% overall, of which 22% is a linear transmittance) and diffuses most of the transmitted light (e.g., 74% of incident light by combining transmitted and reflected scattering).
Is scattered) to form a ground glass-like appearance.

The polymer thin film constituting the light diffusing means 2 can be an acrylic resin molded product having a thickness of 75 to 500 μm and having, for example, a blind phase structure inside. When the internal structure of this molded product is observed by an optical microscope, a phase having a certain length is formed although it is cut in a folded shape in surface observation. Also,
In the longitudinal section observation, a phase structure having shades of light and shade is formed from a depth of about 50 μm from the film surface. The interval of such a phase structure is about 2μ at the top of the film.
m, it is 3 to 4 μm at a depth of about 300 μm from the irradiation surface, and the distance gradually increases along the depth direction. Thus, a desired light diffusion direction and light diffusion degree can be set. In addition, by changing the direction of the phase structure to change the inclination of the phase structure with respect to the light irradiation surface, the angle of appearance of the opaque state can be freely set, and the incident angle range of the light to be diffused can be set as required. Can be set. Since the present invention diffuses a light beam in a specific direction according to the path of light, the selective diffusion direction (direction in which α is directed) is determined with respect to the projection direction on the surface of the liquid crystal cell in a predetermined direction. 30 ° to 100 ° rotated left and right (± θ = ± 30 to 100
Degrees) is preferable, and the selective diffusion angle is preferably 20 degrees or more and 90 degrees or less (20 <= α <= 90).

Further, there is a large difference in composition distribution between the phase structures. For example, the refractive index is 1.55 in one phase, 1.51 in the other phase, and the refractive index difference between the phases is about 0.04. Could be set to a large value. These values can be formed so as to show the same value at any position in the depth direction of the film. The above-mentioned light scattering having a viewing angle dependence generated in the polymer thin film can be controlled largely due to the refractive index difference between the phase structures.
If a polymer thin film constituting the light diffusing means 2 is to be obtained as a commercial product, an optical control film (product name "Lumisti") manufactured by Sumitomo Chemical Co., Ltd. It can be used by specifying its characteristics.

Each of the light diffusing means 2 is adhered to the surface of the liquid crystal cell 1 using an adhesive as necessary. At this time, the light diffusing means 2 is moved in the direction in which the viewing angle of the liquid crystal cell 1 is to be improved. Are positioned so as to match Here, since the first and second light diffusing means 2A and 2B are both formed of a thin film, it is possible to reduce the thickness of the display device, and to simplify the liquid crystal cell 1 using an adhesive or the like. Can be affixed to the device, so that the structure can be simplified.

FIG. 4 is an isocontrast characteristic diagram showing such a viewing angle dependency, and shows an angle φ at which the contrast is inverted (negative / positive inversion) depending on the viewing direction. Four straight lines and three concentric circles intersecting at the center are coordinate axes and scales. Accordingly, the characteristic curve in the figure is used as an association, and the blue mode (negative) is displayed inside the characteristic curve (center of the circle), and the color outside the characteristic curve is inverted to a positive color and cannot be read. A portion where the characteristic curve is interrupted and is not a closed curve (for example, the axial direction at θ = 90 degrees of the characteristics b and c) has φ = 70 at the angle θ.
This means that the contrast is not inverted at all.

In this figure, a shows the case where the light diffusion means is not provided, b shows the light diffusion area according to the present invention where α = φ = 20 degrees or more and 70 degrees or less, and the direction is θ = 90 degrees and θ = 270 degrees.
In the case where the light diffusion regions are set and arranged at degrees, c is a characteristic when the light diffusion region is set to α = φ = 20 degrees or more and 70 degrees or less according to the present invention, and the directions are set to θ = 45 degrees and θ = 315 degrees, respectively. Yes, the area is larger than the internal area of a, that is, the normal observation area (viewing angle) is larger.

As described above, the liquid crystal molecules emerge from the liquid crystal cell 1 under the influence of one of the twist of the liquid crystal molecules, the birefringence anisotropy of the liquid crystal, the characteristics of the polarizing plate, and the directivity of the light source, or a combination thereof. First light diffusing means 2A for selectively diffusing light in a predetermined direction with respect to light; and first light diffusing means 2A
Display device having a second light diffusing means 2B for selectively diffusing light in a predetermined direction from the light diffused by the light source, and setting a central visual field in a predetermined direction, for example, setting a good visual field direction in a vertical direction. In the above, when the selective diffusion direction of the first light diffusing unit and the second light diffusing unit is set to the opposite side or swung left and right with respect to the central viewing direction, a good viewing direction (viewing angle improving direction)
Brightness and contrast at
Since the contrast was flattened and the maximum value range could be expanded, a stable display in which the luminance and the contrast did not change even when the line of sight was changed could be performed with a simple configuration. In addition, the range in which the contrast in the lower front direction is inverted has a much wider viewing angle than in the case where the light diffusion means 3 is not provided, and φ has expanded to 40 degrees or more and around 70 degrees. Was able to do.

[0023]

According to the present invention, one of the following effects is obtained: twist of liquid crystal molecules, birefringence anisotropy of liquid crystal, characteristics of a polarizing plate, and directivity of a light source.
Of the light coming out of the liquid crystal cell under the influence of one or a combination of them, the light in the desired direction is selectively and uniformly diffused to the left and right by the light diffusion means, and the brightness and contrast are made uniform to achieve a viewing angle. Dependencies can be reduced. Further, the light diffusing means can reduce the viewing angle dependency with a simple configuration.

[Brief description of the drawings]

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

FIG. 2 is a perspective view illustrating the orientation of a liquid crystal cell.

FIG. 3 is a perspective view showing an arrangement of a liquid crystal cell and light diffusing means according to an embodiment of the present invention.

FIG. 4 is an isocontrast characteristic diagram showing viewing angle dependency according to the example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal cell 2 light diffusing means 2A first light diffusing means 2B second light diffusing means 3 lighting means 11 liquid crystal layer 12 polarizing plate

Claims (3)

[Claims] 1. A liquid crystal cell having a liquid crystal layer having a central field of view set in a predetermined direction and a polarizing plate, and selecting light emitted from the liquid crystal cell in a direction substantially shifted left and right with respect to the predetermined direction. A liquid crystal display device comprising a light diffusing means for diffusing light. 2. The liquid crystal display device according to claim 1, wherein said liquid crystal cell is configured in a display mode utilizing birefringence, and said light diffusing means is a visibility control film. 3. The liquid crystal layer has 18 liquid crystal molecules when no electric field is applied.
It has a helical structure of 0 degrees or more and 360 degrees or less,
The predetermined direction is an angle inclined in a certain direction from a perpendicular to the surface of the liquid crystal cell, and the selective diffusion direction of the light diffusion means is 30 degrees with respect to the projection direction of the predetermined direction onto the surface of the liquid crystal cell. 2. The liquid crystal display device according to claim 1, wherein the rotation direction is from right to left by 100 degrees.