JPH04329521A - Lighting device for liquid crystal - Google Patents

Abstract

PURPOSE:To increase the brightness of the lighting device for liquid crystal. CONSTITUTION:Many small recessed parts 18 are formed in the light projection surface 16 and light reflection surface 17 of a light guide plate 11 and the light in the light guide plate 11 is projected perpendicularly to a liquid crystal display plate to increase the brightness on a lighted surface. A light diffusion layer 19 which has a higher refractive index than the light guide body 11 is formed on the surface of the light guide body 11 which is made large in area by the small recessed parts 18 and the formation area of the light diffusion layer 19 is made large to increase the light scattering performance. The formation density of the light scattering layer 19 is gradually increased with the distance from a light source 12 to increase the scattering performance of the center part of the light guide plate 11 where the brightness is easy to decrease.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge-light illumination device used as a backlight for a light-receiving liquid crystal display device.

0002

2. Description of the Related Art Conventionally, as shown in FIG. 3, an edge-light type illumination device used as a liquid crystal display device uses a lamp such as a cold cathode tube or a hot cathode tube as a light source 1, which is made of a transparent material. A diffusion sheet 3 made of a milky-white synthetic resin plate having a light scattering effect is provided on the top surface of the light guide 2 to make the brightness of the illumination surface uniform over the entire surface. Further, as the reflective sheet 4, a specular reflective plate, a light scattering acrylic plate, or the like is used. This reflective sheet 4 is provided to improve the efficiency of light utilization by reflecting the light emitted from the light source and directed toward the back surface and guiding it toward the front surface.

[0003] Particularly in the field of color LCD unit panels, it is essential to use the optical isomerism of liquid crystals to overlap polarizing plates.
% was cut off, which caused a decrease in brightness. For this reason, there is a strong demand for high-brightness backlight systems in the market.

In the figure, 7 is a light source reflector that reflects outward light from the light source toward the light guide 2, and X is a liquid crystal display plate.

[0005]

[Problems to be Solved by the Invention] In the conventional edge-light LCD lighting device in which light enters from the light incident end surfaces 5 at both left and right ends of the light guide 2, the light rays are repeatedly totally reflected in the light guide 2. Although it is possible to achieve a very uniform brightness distribution due to the propagation, it has been pointed out that the brightness decreases. Therefore, in order to realize a thin edge-light type backlight system with high brightness and low power consumption, a reflective sheet 4 is attached to the lower surface of the light guide 2, and in order to scatter the light reflected by the reflective sheet 4, the light guide A white ink 8 (light scattering layer) having a higher refractive index than the light guide such as TiO2 or BaSO4 was patterned by printing between the lower surface of the body 2 and the reflective sheet 4.

By the way, in order to meet the recent demand for realizing thin color LCD units, the thickness of the light guide has been reduced to 5 to 6 mm.
It may be as thin as below. However, in this case, the light incident end surfaces 5 at both left and right ends of the light guide 2 must also be formed thin, and the light incident area must be reduced. In this case, the above configuration has insufficient brightness, and there remains a problem in realizing a high-brightness lighting device for liquid crystal.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a lighting device for a liquid crystal display that has high brightness and can be made thinner.

[0008]

[Means for Solving the Problem] The problem solving means according to claim 1 of the present invention is to illuminate the liquid crystal display board X from the rear, as shown in FIGS. It is equipped with a light guide 11 arranged parallel to the plate Light incidence end face 15
and a light emitting surface 16 facing the liquid crystal display board X and from which light is emitted.
and a light reflecting surface 17 that reflects the light that enters from the light incident end surface 15 and travels backward to the light emitting surface 16. Among the light emitting surface 16 and the light reflecting surface 17, A large number of concave portions 18 or convex portions are formed on at least one of the two to scatter light and make the brightness uniform.

The means for solving the problem according to claim 2 is as follows:
A light scattering layer 19 that scatters and reflects light is formed in the recessed portions 18 or convex portions described.

The means for solving the problem according to claim 3 is as follows:
The described light scattering layer 19 is formed in the form of scattered dots, and the formation density thereof is set to gradually become denser as the distance from the light source 12 increases.

[0011]

[Operation] In the problem solving means according to claim 1, the light from the light source 12 enters the inside of the light guide 11 from the light incident end face 15, and then forwards at the light reflection surface 17 of the light guide 11. The light is reflected from the light exit surface 16 and irradiated onto the back surface of the liquid crystal display panel X.

At this time, the light emitting surface 16 and the light reflecting surface 1
Since a large number of concave portions 18 or convex portions are formed on at least one of the light guide members 7, the concave portions 18 or convex portions cause the light guide 11 to be The light inside can be adjusted to be emitted at an angle close to perpendicular to the liquid crystal display panel X.

[0013] In the problem solving means according to claim 2, the light guide 11 has a large area due to the concave portions 18 or the convex portions.
Since the light scattering layer 19 is formed on the surface of the light guide 11, the formation area can be increased compared to forming the light scattering layer 19 on the surface of the flat light guide 11, and the light scattering layer 19 can be made larger. can increase the scattering properties of

According to claim 3 of the present invention, the formation density of the light scattering layer 19 is set to gradually become denser as the distance from the light source 12 increases.
The portions spaced apart from 2 can be adjusted to particularly increase the scattering of light, and the brightness of the illumination surface can be made uniform.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal lighting device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a liquid crystal illumination device according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part showing the optical path thereof.

As shown in the figure, the liquid crystal lighting device of this embodiment illuminates the liquid crystal display board X from behind using an edge light method, and includes a light guide 11 arranged parallel to the liquid crystal display board , a light source 12 arranged at both ends of the light guide 11;
It is provided with a reflection sheet 13 that reflects the backward light from the light guide 11 toward the liquid crystal display panel X side, and a diffusion sheet 14 that makes the brightness of the illumination surface uniform over the entire surface.

The light guide 11 is made of acrylic resin with a total light transmittance of 93% and a refractive index n=1.49, as shown in FIGS. It has an end surface 15, a light exit surface 16 that faces the liquid crystal display board do,
It is formed into a flat plate shape with a length of 20.5 cm, a width of 15.5 cm, and a thickness of 5 to 6 mm.

The light reflecting surface 17 of the light guide 11 is shown in FIGS.
As shown in FIG. 2, a large number of small recesses 18 are formed over the entire surface to scatter the reflected light onto the light exit surface 16 and make the brightness uniform. As shown in FIG. 2, the small recess 18 is formed to have an arcuate cross section with a diameter of 4.0 mm so as to reflect light in all directions.

By forming the small recess 18, the total surface area of the lower surface of the light reflecting surface 17 is increased. By forming the light scattering layer 19 on the lower surface of the large-area light reflecting surface 17, the flat light guide 11 is
It is structured to increase the scattering of light compared to forming it on the surface of. The light scattering layer 19 is formed with a white paint such as TiO2 or BaSO4 having a higher refractive index than the light guide 11 in a scattered pattern (white dot pattern) using a general curved surface printing method, and the film thickness is 6. ~15 μm. Here, the reason why the light scattering layer 19 is made to have a higher refractive index than the light guide 11 is to refract light at the interface between the light guide 11 and the light scattering layer 19 to increase its scattering property. be.

As shown in FIG. 2, the printing density of the dot pattern on the light scattering layer 19 varies from the vicinity of each light source 12 arranged at both ends of the light guide 11 to the center of the light guide 11, that is, The illumination surface is set to gradually become denser toward the farthest point from the light source 12 so that the illumination surface becomes uniform. This density adjustment is calculated using a higher-order function, an exponential function, or the like with respect to the distance from the light source 12.

As the light source 12, a straight hot cathode tube or the like is used, which is made up of a light emitting body such as a filament and an exterior tube that covers it. , the lamp effective length is set to 230 mm, and the lamp current is set to 6 mA.

The reflective sheet 13 is for reflecting forward the light leaking backward from between the light scattering layers 19 on the light reflecting surface 17 of the light guide 11, and has a thickness of 0.18 m.
Existing materials such as mirror reflectors and light-scattering acrylic are used.

The diffusion sheet 14 is a milky white synthetic resin plate and has a thickness of 0.25 mm.

In FIG. 1, reference numeral 22 denotes a light source reflector that reflects light from the light source 12 toward the side opposite to the light guide 11 toward the light guide 11 side.

In the above configuration, the inward light from the light source 12 directly enters the inside of the light guide 11 from the light incident end surface 13 thereof.

On the other hand, the outward light from the light source 12 is reflected by the light source reflector 22 and then enters the inside of the light guide 11 from the light incident end surface 13 thereof.

Thereafter, the incident light is reflected forward by the light reflecting surface 17 and distributed from the light emitting surface 14 to the diffusion sheet 14. Then, the back surface of the liquid crystal display board X is irradiated with substantially uniformly distributed light through the diffusion sheet 14.

At this time, since a large number of small recesses 18 having an arcuate cross section are formed in the light reflecting surface 17 of the light guide 11, when the light is reflected on the light reflecting surface 17, the light is emitted as shown in FIG. The light can be reflected at an angle close to the angle perpendicular to the surface 16, and the transmittance at the light emitting surface 16 can be increased compared to the conventional case, thereby increasing the amount of emitted light.

Furthermore, when the light scattering layer 19 is applied to the light reflecting surface 17 as in the conventional case, the amount of light scattering layer 19 is reduced by the amount of the small recess 18 formed.
The area of the light reflecting surface 17 will increase. By doing so, the surface area of the light scattering portion on the light reflecting surface 17 can be increased compared to the conventional case, and the scattering effect of the light scattering layer 19 can be significantly improved.

Furthermore, the formation density of the light scattering layer 19 is adjusted to the light source 1.
Since the density is set to gradually increase as the distance from the light source 12 increases, the scattering properties can be increased and the brightness can be improved in the part away from the light source 12 where the brightness tends to decrease, and the brightness of the illuminated surface can be made uniform. obtain.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, in the above embodiment, a large number of small recesses 18 were provided in the light reflecting surface 17 on the rear side of the light guide 11, and a light scattering layer 19 was formed therein. If so, it may be provided on the light exit surface 16 on the front side of the light guide 11.

Further, in the above embodiment, small hemispherical recesses are formed, but the present invention is not limited to this, and any structure may be used as long as it increases the surface area of the scattering portion. For example, a large number of recesses may be formed. You may.

Furthermore, in the above embodiment, a white paint was used as the material for the light scattering layer, but it may be blue, orange, or other colors, and is limited to this as long as it scatters and reflects light. It's not a thing.

[0036]

As is clear from the above description, according to claim 1 of the present invention, a large number of concave portions or convex portions are formed on at least one of the light emitting surface and the light reflecting surface. The convex portion allows the light inside the light guide to be adjusted to be emitted perpendicularly to the liquid crystal display panel. Therefore, the brightness on the illumination surface can be improved.

According to claim 2 of the present invention, since the light scattering layer is formed on the surface of the light guide which has a large area due to the concave portions or convex portions, the area where the light scattering layer is formed is larger than that of the conventional method. Therefore, the light scattering property can be increased accordingly.

According to claim 3 of the present invention, the formation density of the light scattering layer is set so that it gradually becomes denser as the distance from the light source increases, so that the light scattering layer is formed in a manner that the light scattering layer is formed at a density that becomes gradually denser as the distance from the light source increases. It has excellent effects such as increasing the brightness and uniformizing the brightness of the illumination surface.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a liquid crystal lighting device according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a main part showing the optical path.

FIG. 3 is a cross-sectional view of a conventional LCD lighting device.

[Explanation of symbols]

11 Light guide 12 Light source 15 Light incidence end face 16 Light exit surface 17 Light reflecting surface 18 Recessed part 19 Light scattering layer X Liquid crystal display board

Claims (3)

[Claims] Claim 1: A device for illuminating a liquid crystal display board from behind, comprising: a light guide arranged parallel to the liquid crystal display board behind the liquid crystal display board; and a light source arranged at both ends of the light guide. The light guide includes a light input end surface facing the light source and into which light is incident, a light exit surface facing the liquid crystal display panel and through which light is emitted, and a light input end surface that enters from the light input end surface and goes backward. In a liquid crystal lighting device including a light reflecting surface that reflects advancing light to a light emitting surface, at least one of the light emitting surface and the light reflecting surface scatters light to make brightness uniform. 1. A lighting device for a liquid crystal display, characterized in that a large number of concave portions or convex portions are formed. 2. An illumination device for a liquid crystal, characterized in that a light scattering layer is formed in the concave portion or convex portion according to claim 1, which scatters and reflects light. 3. A lighting device for a liquid crystal display according to claim 2, wherein the light scattering layer is formed in the form of scattered dots, and the formation density thereof is set to gradually become denser as the distance from the light source increases. .