JPH03137618A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the irregularity of an illuminance distribution greatly by providing light-reflective light scattering dots on the surface of the back light side of a light diffusing plate roughly and closely in matching the illuminance distribution of the back light. CONSTITUTION:A back light unit consisting of the back light 13 and a reflecting plate 14 is provided beneath a liquid crystal panel 12 and the light diffusing plate 15 where the reflecting dots 10 are formed is interposed between the liquid crystal panel 12 and back light 13. The reflecting dots 10 are arranged closely right below the light source and roughly with the distance from it so as to match a back light position 17; and light is reflected by reflecting dots 10 and reflected by the reflecting plate 14 again to the panel side to obtain multiple reflection. Consequently, the irregularity of the illuminance distribution can be improved from + or -20% to + or -8% and mean illuminance can be improved by 30%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device, and particularly to a light diffusing plate for a transmissive liquid crystal display device.

[Conventional technology]

Liquid crystal display devices are broadly classified into reflective type and transmissive type. In recent years, with the spread of color liquid crystal display devices, large-sized transmissive display devices have come into widespread use. A backlight 33 is provided at the bottom of the liquid crystal panel 32, which has polarizing plates 31 on both sides.
A backlight unit is provided with a reflecting plate 34 on its back surface, and a light diffusing plate 35 is provided to make the illuminance of the backlight 33 uniform.

In a large display device, it is difficult to obtain uniform illuminance only by designing the curvature of the reflecting plate 34. Therefore, a light diffusing plate as described above is usually used. Also, since fluorescent tubes are used as the backlight light source, the illuminance directly above the light source is inevitably high.As a solution to this problem, a milky white translucent plate is used as the light diffusion plate so that the tube shape of the fluorescent tube is not visible. This prevents the illuminance distribution from becoming uneven due to the position of the backlight. On the other hand, there is also a method of correcting the non-uniformity of the illuminance distribution by blocking the light in a dot-like manner by adjusting the intensity of the illuminance, an example of which is shown in FIG.

As shown in FIG. 3(a), black resin light-shielding dots 36 are provided on the lower surface of the light diffusion plate 35 on the backlight 33 side, and the dense portions of the light-shielding dots 36 are arranged to match the position of the backlight 33. are doing. If you look at the relationship in a plan view, it is as shown in Figure 3 (b), and the backlight position 3 of the fluorescent tube
7, the light shielding dots 36 are arranged sparsely and densely to correct non-uniform illuminance of the backlight unit.

[Problem to be solved by the invention]

The conventional light diffusion plates mentioned above were milky-white and translucent, and the light-shielding dots were patterned with black resin such as emulsion, so although it was possible to correct the unevenness of the light source, it was difficult to reduce the brightness of areas with high illuminance. Due to its basic characteristic of correction, it had the disadvantage that it was unable to increase the average illuminance.

[Means to solve the problem]

The present invention provides a transmissive liquid crystal display device having a liquid crystal display panel having polarizing plates on both sides, a backlight unit having a reflecting plate, and a light diffusing plate inserted between these, in which a backlight source of the light diffusing plate is provided. It is characterized by having light reflective light scattering dots provided on the side surface in a sparse and dense manner in accordance with the illuminance distribution of the backlight unit. The light scattering dots provided on the side surface of the backlight source may be conical. Alternatively, the surface on the backlight source side may be made into a rough surface, and light scattering dots may be provided on this rough surface.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1(a) is a sectional view of an embodiment of the present invention. Polarizing plate 11
A backlight unit consisting of a backlight 13 and a reflection plate 14 is provided at the bottom of the liquid crystal panel 12 which is provided on both sides, and a light diffusion plate is provided with reflection dots 10 between the liquid crystal panel 12 and the backlight unit. 15 has been inserted. The reflective dots 10 of the light diffusing plate 15 are shown in FIG.
As shown in b), in accordance with the backlight position 17, the areas directly above the light sources are provided in a dense manner, with the areas directly above the light sources becoming denser and coarser as they are further away.

FIG. 2(a) is an enlarged sectional view of the light diffusing plate 15. The conical reflective dots 10 are provided on one side of the transparent substrate 20. The conical reflective dots 10 do not need to have an exact conical shape, but only have an inclined surface. This is because multiple reflections can be tolerated when the light from the dot hits the reflective dot 10 in a state where it is blocked, is reflected by the slope, and then reflected again to the liquid crystal panel 12 side by the reflective plate 14. The density distribution of the reflective dots 10 may be determined by including the design value of the curvature and the three-dimensional positional relationship of the backlight 13.

When the light diffusing plate of this example was used, the uniformity of the illuminance distribution was improved from ±20% to ±8%, and the average illuminance was improved by 30% compared to the conventional one.

FIG. 2(b) is a sectional view showing another example of the light diffusing plate used in the present invention. As shown in FIG. 2(b), as a substrate, a transparent scattering surface substrate 2 with at least one side having a rough surface.
1 was used. If the degree of roughness of the surface is 10 times or more the film thickness of the reflective dots 22 provided, then the reflective dots 22 can be formed without damaging the roughness of the substrate 21.The reflective dots 22 have wavelengths in the visible light range. Any material may be used as long as it has a reflectance of 80% or more in the area, but since glass was used as the substrate 21 here, 2000 chromium layers were provided. When a resin substrate is used instead of glass, the film is formed at a low temperature, but the reflectance deteriorates by only about 3%, making it practical to pattern the 0-reflection dot 22 as shown in Figure 2(a). Similarly, they are arranged sparsely and densely so as to correct the non-uniformity of the illuminance distribution of the backlight unit, which is determined by the backlight position 17 and the relationship with the reflection plate 14. Further, since the rough surface of the substrate is utilized, the reflective dots 22 are naturally provided with slopes simply by patterning after M is formed by a normal film forming method such as sputtering.

In this case as well, the illuminance distribution was improved from ±20% to ±3%, and the average illuminance was improved by 33% compared to the conventional method.

FIG. 2(c) is a sectional view showing still another example of the light diffusing plate used in the present invention. The substrate 23 is a transparent resin film, and one surface thereof is provided with titanium planar reflective dots 24 formed by an ion plating method. The planar reflective dots 24 are provided by conventional etching patterning. In this example, the reflective dot is a flat reflective dot 24.
However, the light from the backlight that is shielded and reflected by the dots is reflected by the curved surface of the reflecting plate 14 as shown in FIG. 1(a), so it is reused as dispersed light when illuminating the liquid crystal panel 12. can. The patterning of the planar reflective dots 24 is also arranged sparsely and densely so as to correct the non-uniformity of illuminance. In this case as well, the illuminance distribution was improved from ±20% to ±10%, and the average illuminance was improved by 15% compared to the conventional method.

〔Effect of the invention〕

As explained above, the present invention has the following advantages: by providing reflective dots sparsely and densely on a light diffusing plate, by providing slopes on reflective dots, and by providing reflective dots on a rough surface of a substrate,
The non-uniformity of the illuminance distribution of the backlight unit can be significantly improved, and the average illuminance can also be improved.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view of a transmission type liquid crystal display device according to an embodiment of the present invention, FIG. 1(b) is an enlarged plan view of a part of a light diffusing plate used in the present invention, and FIG. ) to (c) are cross-sectional views showing examples of light diffusion plates used in the present invention, FIG. 3(a) is a cross-sectional view of a transmission type liquid crystal display device using a conventional light diffusion plate, and FIG.
b) is a plan view of a conventional light diffusing plate. 10... Conical reflective dot, 11.31... Polarizing plate, 12.32... Liquid crystal panel, 13.33... Backlight, 14.34... Reflecting plate, 15.35...・
Light diffusion plate, 17. 37... Backlight position, 20° 23... Transparent substrate, 21... Substrate with scattering surface, 22
...Reflection dot, 24...Flat reflection dot, 36.
...shading dot. Figure 1

Claims (1)

[Scope of Claims] 1. A transmissive liquid crystal display device comprising a liquid crystal display panel having polarizing plates on both sides, a backlight unit having a reflecting plate, and a light diffusing plate inserted between these, wherein the light A liquid crystal display device characterized in that light-reflective light-scattering dots are provided on a backlight source side surface of a diffusion plate in a sparse and dense manner in accordance with the illuminance distribution of a backlight unit. 2. The liquid crystal display device according to claim 1, wherein the light scattering dots provided on the backlight source side surface of the light diffusing plate have a conical shape. 3. The liquid crystal display device according to claim 1, wherein the surface of the light diffusing plate on the backlight source side is a rough surface, and light-reflective light scattering dots are provided on the rough surface.