JP3363640B2 - Liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display having low viewing angle dependence. 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. In other words, even if the display is viewed from the front, the display tends to be dark, and a large screen has a disadvantage that the contrast is reduced or the contrast is inverted because the image is viewed obliquely with respect to the peripheral portion of the display. Such a large restriction on the viewing angle is referred to as having a high viewing angle dependency. [0003] The viewing angle dependence is caused by the twist of liquid crystal molecules (such as the helix direction and the helical start position of the liquid crystal molecules determined by the rubbing direction), and the birefringence anisotropy of the liquid crystal (the light Due to the difference in retardation depending on the passing direction), due to the characteristics of the polarizing plate (such as the selectivity of the light vibration direction), or due to the directivity of the light source that irradiates the liquid crystal with light. And the like. In general, in the liquid crystal display device, in consideration of the above-described viewing angle dependency, a design in which a position where the display is most easily viewed falls within a normal visual field range of an observer, for example, a contrast near a normal direction in the center of the screen is adjusted. It is designed to be higher than the surroundings. The applicant of the present invention has applied a special film to the surface of a liquid crystal cell to deal with the viewing angle dependency that occurs in a liquid crystal display device due to the above various reasons. Made a proposal (Japanese Patent Application No. 6-25)
No. 6877). However, the above-mentioned special film is made of a polymer thin film having a special structure set so as to scatter incident light within a range of about 30 ° in a predetermined direction from a normal line (φ = 0 °). As shown in FIG. 2, when observing the target object through it, for example, the incident light is opaque in a range of 0 to 30 degrees in one direction from the viewpoint to the front in one direction, and the other range is transparent so as to be transparent. It has a function of selectively diffusing, and in particular, the haze ratio (the ratio of the scattered light transmittance to the total light transmittance) changes steeply inside and outside the above-mentioned angle range (from an opaque state to a transparent state or vice versa) From the opaque state to the transparent state, or vice versa, the boundary part from the transparent state to the opaque state becomes clear, and the display continues at the boundary part. A new problem occurs that is display quality is lowered impaired. Therefore, it is a main object of the present invention to solve this. SUMMARY OF THE INVENTION The present invention provides a liquid crystal cell having a predetermined liquid crystal layer, light introducing means for guiding light to the liquid crystal layer of the liquid crystal cell, and light A light diffusing means for selectively diffusing light incident within a predetermined angle range, wherein the light diffusing means has a haze ratio (a ratio of a scattered light transmittance to a total light transmittance) according to an incident angle. Between the minimum angle area and the maximum angle area, an angle area where the haze ratio gradually changes according to the incident angle is formed, and the viewpoint of viewing the fixed position of the liquid crystal cell through the light diffusing means is viewed from the liquid crystal cell. When the angle between the line of sight and the normal line is in the range of about 20 degrees to about 10 degrees when moved from the upper side to the lower side, the light coming out of the liquid crystal cell is incident upon the haze ratio of the light diffusing means, which gradually increases. Enter the angle range and range from upper 10 degrees to lower 30 degrees In the above, light coming out of the liquid crystal cell enters the incident angle region where the haze ratio of the light diffusing means is maximum, and light coming out of the liquid crystal cell falls within the range of about 30 degrees to about 50 degrees below. It is characterized in that the rate falls in an incident angle region where the rate gradually decreases. According to the present invention, there is provided a light diffusing means for selectively diffusing light incident from a liquid crystal cell within a predetermined angle range, thereby torsion of liquid crystal molecules. The light diffusing means can select and diffuse light in the desired direction from the light coming out of the liquid crystal under the influence of the birefringence anisotropy of the liquid crystal, the characteristics of the polarizing plate, the directivity of the light source, etc. It is possible to reduce the viewing angle dependency. Further, the light diffusing means forms an angle region where the haze ratio gradually changes according to the incident angle between the angle region where the haze ratio according to the incident angle is minimum and the angle region where the haze ratio is maximum according to the incident angle. There is no sharp change in the haze ratio, and it is possible to gradually change from an opaque state to a transparent state, or vice versa, from a transparent state to an opaque state, thereby maintaining the display continuity of the liquid crystal cell and preventing the display quality from deteriorating. Can be. FIG. 1 is a sectional view of a main part of a liquid crystal display device according to an embodiment of the present invention, wherein 1 is a liquid crystal cell having a liquid crystal layer 10 having a predetermined thickness, and 2 is a liquid crystal cell 1 thereof. The light introducing means 3 for guiding light in a direction substantially perpendicular to the liquid crystal layer 10 is a light diffusing means for diffusing light coming out of 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 spirally aligned at 70 degrees is supported by a substrate 11 on which an electrode 12 for applying an electric field for each pixel is provided so as to be orthogonal to the inner surface. When the polarizing plate 13 is necessary for the liquid crystal cell 1, the substrate 1
It is simple and preferable to be attached to the front and back of the outside of 1. Also,
On the substrate 11, an alignment film 14 for forming a predetermined alignment on the liquid crystal molecules is formed so as to sandwich the liquid crystal layer 10. However, when the alignment is performed by directly rubbing the substrate 11, the alignment film 14 is omitted. Can also. Here, an alignment process is performed such that a region where a 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 includes, for example, a fine prism having an apex angle of about 90 to 100 degrees on the entire upper surface.
It is composed of a lens sheet made of plastic such as polycarbonate formed at a pitch of 0 μm, and has a function of condensing light incident from the flat back surface and converting the light into light with improved directivity. Further, the light introducing means 2 may be formed 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 composed of a flat convex lens array, 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. On the back side of the light introducing means 2, a surface illumination means 4 can be provided as required. This surface illumination means 4
Are a light guide plate 41 such as an acrylic resin flat plate, a linear light source 42 such as a cold cathode tube provided on a side surface of the light guide plate 41, and a surface light diffusion sheet 43 provided on the light guide plate 41 as necessary. Or a back reflection sheet 44 or a cylindrical reflection sheet (not shown) covering the linear light source. 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 that is set so as to diffuse incident light in an angle range from about 50 degrees above to about 20 degrees below the normal (φ = 0 degree) with a diffusion degree corresponding to the incident angle. Consists of a thin film. And this light diffusion means 3
As shown in FIG. 4, the haze ratio (the larger the numerical value, the higher the degree of light diffusion) indicating the ratio of the scattered light transmittance to the total light transmittance when the light incident angle is changed is set as shown in FIG. That is, the haze ratio in the angle range where the incident angle (the angle between the normal and the incident light) is from lower 90 degrees to lower 20 degrees is set to a minimum of almost 0%, and the incident light is transmitted without being diffused and is transparent. The haze ratio is set to approximately 80% of the maximum in an angle range where the incident angle is from about 10 degrees to about 30 degrees, and most of the incident light is diffused to exhibit an opaque state. The light diffusion means 3
In the opaque state, it has the same degree of light transmittance as the transparent state and diffuses most of the transmitted light to give a bright ground glass appearance. Further, the angle of incidence between the angle region where the haze ratio is the smallest and the angle region where the haze ratio is the largest is about 20 degrees below and about 10 degrees above (at least 20 degrees).
The haze ratio is set so as to gradually increase monotonically from the minimum value to the maximum value while changing monotonically, and the haze ratio in the angle region where the incident angle is from about 30 degrees to about 50 degrees. The rate is set so as to gradually decrease monotonically from the maximum value to the minimum value. The polymer thin film constituting the light diffusing means 3 can be an acrylic resin molded product having, for example, a blind phase structure inside. When the internal structure of this molded article is observed with an optical microscope, a phase of a certain length is formed although it is cut in a folded shape in the surface observation, and about 50 μm from the film surface in the longitudinal section.
A phase structure having shades of light and shade is formed from a depth of m. The interval 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 in accordance with the desired light diffusion direction and light diffusion degree. Also, by changing the direction of the phase structure to change the inclination of the phase structure with respect to the light irradiation surface, it is possible to freely set the appearance angle of the opaque state, and to pass the ultraviolet light intensity during resin molding or under ultraviolet light. By controlling the speed at which the light is diffused, the haze ratio according to the incident angle can be set freely, so that the haze ratio according to the incident angle range and the incident angle of the light to be diffused can be set as necessary. it can. Furthermore, there is a large difference in the composition distribution between the phase structures. For example, the refractive index is as large as 1.55 in one phase, 1.51 in the other phase, and 0.4 as the refractive index difference between the phases. Could be set to. 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 3 is to be obtained as a commercial product, an optical control film (product name "Lumisty") manufactured by Sumitomo Chemical Co., Ltd. It is preferable to specify the characteristics and use them. The light diffusing means 3 is attached to the surface of the liquid crystal cell 1 using an adhesive. At this time, the light diffusing means 3 is positioned so as to correspond to a predetermined viewing angle dependent direction of the liquid crystal cell 1. Is performed. Causes of the viewing angle dependence include, for example, those caused by twisting of liquid crystal molecules (helix direction and helix start position of liquid crystal molecules determined by rubbing direction) and birefringence anisotropy of liquid crystal (light passing direction). Due to the difference in retardation of the polarizing plate), the characteristics due to the characteristics of the polarizing plate (such as the selectivity of the light vibration direction),
It is caused by the directivity of the light source that irradiates the liquid crystal with light.
One or a combination thereof is conceivable, and the positioning corresponding to the viewing angle dependent direction is performed in consideration of these. In the present embodiment, for example, a case where the viewing angle is improved so that the observer looks from the lower side to the upper side of the liquid crystal cell 1 is illustrated, and as shown in FIG. 3, the range of the line of sight (shown by oblique lines) in which the object looks opaque due to the presence of the light diffusing means 3 is about 50 degrees from the upper 50 degrees to the lower 20 degrees with respect to the normal passing through the viewpoint. The light diffusing means 3 is positioned and adhered to the liquid crystal cell 1 so as to fall within the range. In particular, the light diffusing means 3 is positioned such that light traveling from the liquid crystal cell 1 in the viewing angle direction (observer side direction) to be improved is diffused by the light diffusing means 3 (mainly the haze ratio maximum angle area). Then, it is attached to the liquid crystal cell 1. Here, since the light diffusing means 3 is formed of a thin film, the thickness of the display device can be reduced, and the light diffusing means 3 can be easily attached to the liquid crystal cell 1 using an adhesive or the like. Simplification can be achieved. Thus, the light diffusing means 3 is connected to the liquid crystal cell 1
As a result, as shown in FIG. 3, when the viewpoint of viewing the fixed position of the liquid crystal cell 1 via the light diffusing means 3 was moved from the upper side to the lower side of the liquid crystal cell 1 and the liquid crystal cell 1 was observed, When the angle between the normal and the normal line is in the range of about 90 degrees to 20 degrees, the light coming out of the liquid crystal cell 1
When the haze ratio of the liquid crystal cell 1 falls within the minimum incident angle region, and the angle between the line of sight and the normal line is in the range of about 20 degrees to about 10 degrees, the haze rate of the light diffusing unit 3 is reduced. When the light enters the gradually increasing incident angle region and the angle between the line of sight and the normal line is in the range of about 10 degrees to about 30 degrees, the light coming out of the liquid crystal cell 1 has the maximum haze ratio of the light diffusing means 3. When the angle between the line of sight and the normal line is in the range of about 30 degrees to about 50 degrees below the incident angle range, the light coming out of the liquid crystal cell 1 is incident angle at which the haze ratio of the light diffusing unit 3 is gradually reduced. 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 unit 3 is the largest, and the region has at least two regions.
Since the haze ratio extends to an angle region of 0 degrees, the haze ratio can be prevented from sharply changing between a maximum (opaque state) angle region and a minimum (transparent state) angle region, thereby maintaining image continuity. Good display quality can be maintained. still,
As a result of attaching the light diffusing means 3, the incident angle of the light incident on the light diffusing means 3 from the liquid crystal cell 1 is from upper 10 to upper 30
Most of the light in the order of degrees and a part of the light in the angle region in the vicinity thereof are selectively diffused, so that the light coming out of the liquid crystal cell 1 can be averaged and output, and the brightness and contrast can be reduced as a whole. It is possible to increase the brightness and contrast of the peripheral portion by flattening. Here, since the haze ratio is the maximum or the maximum angle region deviates from the normal direction (generally, the brightness and contrast are the highest), it is possible to prevent the brightness and contrast from decreasing in the normal direction. In the above-described embodiment, the case of improving the viewing angle in the downward direction (when the display surface is viewed from the lower side of the normal line with the line of sight disposed above) is described as an example. In order to improve the viewing angle in the case where the line of sight is arranged from the upper side to the lower side of the normal line), the light diffusing unit 3 may be attached upside down to the liquid crystal cell 1. However, in order to improve the viewing angle in the right or 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 embodiment, 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 type, but may be a TFT type or MIM type. According to the present invention, since light diffusing means for selectively diffusing light incident within a predetermined angle range from light emitted from a liquid crystal cell is provided, twisting of liquid crystal molecules, The light in the desired direction can be selected and diffused by the light diffusion means, out of the light coming out of the liquid crystal under the influence of the birefringence anisotropy of the liquid crystal, the characteristics of the polarizing plate, the directivity of the light source, etc. , The viewing angle dependency can be reduced. Further, the light diffusing means forms an angle region in which the haze ratio gradually changes according to the incident angle between the angle region where the haze ratio according to the incident angle is the minimum and the maximum angle region. There is no sharp change in the haze ratio, and it is possible to gradually change from an opaque state to a transparent state, or vice versa, from a transparent state to an opaque state, thereby maintaining the display continuity of the liquid crystal cell and preventing the display quality from deteriorating. Can be. Further, the light diffusing means arranges the angle region where the scattered light transmittance is maximum on the viewer side of the liquid crystal cell in correspondence with 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 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 showing an arrangement of a liquid crystal cell and light diffusing means according to an embodiment of the present invention. FIG. 3 is an explanatory diagram for explaining a function of a light diffusing unit according to the embodiment of the present invention. FIG. 4 is an optical characteristic diagram of the light diffusing means according to the example of the present invention. [Description of Signs] 1 Liquid crystal cell 2 Light introducing means 3 Light diffusing means 4 Surface lighting means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-234017 (JP, A) JP-A-60-202464 (JP, A) JP-A-64-40905 (JP, A) JP-A-60-204 140322 (JP, A) JP-A-7-64069 (JP, A) JP-A-7-209637 (JP, A) JP-A-8-171087 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1335 G02F 1/13357

Claims (1)

(57) Claims 1. A liquid crystal cell having a predetermined liquid crystal layer, light introducing means for guiding light to the liquid crystal layer of the liquid crystal cell, and light out of the liquid crystal cell, Light diffusing means for selectively diffusing light incident in a predetermined angle range, wherein the light diffusing means has a minimum haze ratio (ratio of scattered light transmittance to total light transmittance) according to the incident angle. An angle region where the haze ratio gradually changes according to the incident angle is formed between the angle region and the maximum angle region of the liquid crystal.
View the fixed position of the cell from the top to the bottom of the liquid crystal cell
When moving, the angle between the line of sight and the normal is 20 degrees
Exits the liquid crystal cell within a range of about 10 degrees below
Light that the haze ratio of the light diffusing means gradually increases
Enter the angle range, and from the upper 10 degrees to the lower 30 degrees
Light coming out of the liquid crystal cell
The noise rate falls within the maximum incident angle range, from lower 30 degrees to lower 5 degrees.
The light coming out of the liquid crystal cell in a range of about 0 degrees
Incident angle region where the haze ratio of the light diffusing means gradually decreases
A liquid crystal display device characterized by entering a region .