JPH05173131A - Plane light emission plate - Google Patents

Abstract

PURPOSE:To provide the plane light emission plate which has a uniform brightness distribution and high brightness by constituting a light guide plate in multi- layered structure, arranging the light guide plate so that its end part covers a fluorescent tube by polishing the end surface into a curved surface and bringing it into contact with the fluorescent tube. CONSTITUTION:The plane light emission plate 7 is equipped with the light guide plate 2 formed by laminating light guide plates 2a-2c; and the end parts of the upper light guide plate 2a and lower light guide plate 2c are cut slantingly, the cut planes are polished, and the polished surfaces cover the fluorescent tube l. One-surface sides of the light guide plates 2a-2c are coated with ink, obtained by mixing a filler which is made of glass beads, etc., and has a high refractive index with organic resin, in a circular pattern which increases in area from the side of the fluorescent tube 1 according to an exponential function to area proportional to the incidence area of the fluorescent tube 1. The light guide plates 2a 2c of the respective layers can be equalized in brightness and the overall length of the array of diffusion patterns 6 applied over the respective light guide plates 2a-2c is short, so the uniformity of light emission is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat light emitting plate used as a backlight of a liquid crystal display (hereinafter referred to as LCD).

[0002]

2. Description of the Related Art A conventional backlight system for an LCD will be described with reference to the drawings. FIG. 7 shows the basic configuration of a system to which a fluorescent tube is applied.

Since the LCD does not emit light, a backlight is indispensable. Further, in order to improve visibility, it is essential to improve the brightness of the backlight. In a conventional LCD backlight system, a flat light emitting plate 36 including a light guide plate 32, a fluorescent tube 33, a diffusing plate 34, and a reflecting plate 35 is generally used on the back surface of the LCD 31, as shown in FIG.

[0004]

However, in the conventional flat light emitting plate, a side light system in which a fluorescent tube 33 is arranged at least at one end of a light guide plate 32 as shown in FIG. Since the light guide plate 32 having a thickness equal to or smaller than the diameter of 33 is used, the amount of luminous flux entering the light guide plate 32 is small, and the conversion from the linear light source of the fluorescent tube 33 to the surface light source of the flat light emitting plate is performed. Since the efficiency, that is, the luminous flux utilization efficiency is as low as 20 to 30%, the improvement of the brightness of the flat light emitting plate has to rely on the luminous flux of the fluorescent tube.

Moreover, in order to realize uniform surface emission, it is necessary to apply a diffusion pattern composed of glass beads or the like on the light guide plate 32 in a complicated arrangement, and a great number of man-hours are required for designing the pattern. ..

[0006]

Therefore, in the present invention, the light guide plate of these flat light emitting plates has a multi-layer structure, and the light guide plate is arranged so that the end portion thereof covers the fluorescent tube, and the end surface is polished to remove the end surface. A flat light emitting plate having a uniform brightness distribution and a high brightness is formed by applying a diffusion pattern having a curved surface in close contact with a fluorescent tube and having an area corresponding to the light incident area at the end of the light guide plate. ..

[0007]

According to the present invention, the light guide plate of the flat light emitting plate has a multi-layered structure, the end portions thereof are arranged so as to cover the fluorescent tubes, and the end faces are polished, and the respective light guide plates are adjusted according to the incident area. By applying a filler having a different area, it is possible to improve the light conversion efficiency and realize a high-luminance flat light emitting plate having a good luminance distribution.

[0008]

An embodiment according to the present invention will be described with reference to the drawings. 1 is a cross-sectional view of the flat light emitting plate of the present invention, FIG. 2 is a plan view of a light guide plate having a diffusion pattern used in the flat light emitting plate of FIG. 1, and FIG. 3 is an enlarged view showing a fluorescent tube side of the light guide plate. FIG.

As shown in FIG. 1, the flat light emitting plate 7 of the present invention comprises a light guide plate 2 in which three light guide plates 2a, 2b and 2c are laminated. The upper light guide plate 2a and the lower light guide plate 2c have their ends cut obliquely and the cut surfaces are polished, and the polished surfaces are arranged so as to cover the fluorescent tube 1. Specifically, as shown in FIG. 3, at least the slope length B of the light guide plate is the fluorescent tube diameter A.
The structure satisfies the above length. With this structure, the conversion efficiency of about 20% in the past was about 30%.
Therefore, the brightness can be improved 1.5 times.

Further, as shown in FIG. 2, on one surface of each of the three light guide plates 2a, 2b, 2c, a circular pattern 6 whose area exponentially expands from the fluorescent tube 1 side, glass beads, etc. are formed. An ink obtained by mixing a filler having a high refractive index with an organic resin is applied in an area proportional to the incident area of the fluorescent tube 1. That is, if the cross-sectional areas (light incident areas) of the end portions of the light guide plates 2a, 2b, 2c are different, the light fluxes entering the light guide plate are different, so that a brightness difference occurs when a diffusion pattern having the same area is applied. .. Therefore, by applying the area of the diffusion pattern 6 that is proportional to the incident area of the light from the fluorescent tube 1, the brightness of the light guide plate of each layer can be made the same. Moreover, since the total length of the array of diffusion patterns applied to each light guide plate is short, the uniformity of light emission can be dramatically improved. The reflector 5 is made of a material having a high reflectance, such as silver, and reflects the luminous flux emitted to the opposite side of the light guide plate 2 to the light guide plate side to improve the light utilization efficiency. ..

For example, when a cold cathode tube of 54 (lm) is used as a light source and a flat light emitting plate having a light guide plate thickness of 3 (mm) and an area of 286 (square centimeter) is used, in the case of the conventional structure shown in FIG. , Average brightness is 160 (cd / square meter)
And the luminance deviation (MAX.luminance / MIN.luminance) = 1.98, the average luminance of the flat light emitting plate of the present invention is 220 (cd /
Square meter), brightness deviation (MAX. Brightness / MIN. Brightness) =
Since it becomes 1.28, both the average luminance and the luminance distribution can be greatly improved.

Next, a second embodiment according to the present invention will be described. FIG. 4 is an enlarged sectional view of a main part of a light guide plate on the fluorescent tube side showing a second embodiment of the present invention. As shown in the figure, in this embodiment, the light guide plate 11 is further multi-layered, and the diffusion pattern 13 corresponding to the incident area of the end portion is applied to each light guide plate in the same manner as described above to further increase the brightness and uniform the light. The sex can be increased. Further, it is more effective to polish the end surface of the light guide plate 11 on the fluorescent tube side.

Next, a third embodiment of the present invention will be described. FIG. 5 is an enlarged cross-sectional view of essential parts showing a third embodiment of the present invention. In the present embodiment, the brightness can be further improved by directly disposing the reflection plate 16 on the portion 15 of each light guide plate to which the filler is applied.

Further, a fourth embodiment of the present invention will be described. FIG. 6 is an enlarged cross-sectional view of the essential parts showing the fourth embodiment of the present invention. In this embodiment, the light guide plate 2 on which the light from the fluorescent tube 1 enters
The end face of No. 1 is ground to match the curved surface of the fluorescent tube. As a result, the luminous flux of the fluorescent tube 1 can be incident on the light guide plate 21 with almost no loss, and the brightness can be further improved.

[0015]

According to the present invention, in a planar light emitting plate of a light guide plate type used for a backlight of an LCD, the light guide plates are multi-layered, and each light guide plate has a light incident area at the end portion on the fluorescent tube side. By applying a diffusion pattern with an area corresponding to the above, and further cutting the end of the light guide plate on the fluorescent tube side into a predetermined shape and polishing it to cover the fluorescent tube, a high brightness and uniform high brightness distribution is obtained. Since this has been realized, if this flat light emitting plate is used for a backlight of an LCD, the visibility of the LCD can be significantly improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a flat light emitting plate showing a first embodiment of the present invention.

FIG. 2 is a plan view of a light guide plate having a diffusion pattern according to the first embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of a main part of a flat light emitting plate showing a first embodiment of the present invention.

FIG. 4 is an enlarged sectional view of an essential part of a flat light emitting plate showing a second embodiment of the present invention.

FIG. 5 is an enlarged sectional view of an essential part of a flat light emitting plate showing a third embodiment of the present invention.

FIG. 6 is an enlarged cross-sectional view of a main part of a flat light emitting plate showing a fourth embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a conventional LCD backlight system.

[Explanation of symbols]

 1,33 Fluorescent tube 2,2a, 2b, 2c, 11,14,21 Light guide plate 3 Diffusing plate 4 Reflector 5 Reflector 6 Diffusing pattern A Fluorescent tube diameter B Light guide plate slope length

Claims (7)

[Claims] 1. A flat light emitting plate having a light guide plate and a fluorescent tube, wherein the light guide plate is formed by laminating a plurality of light guide plates. 2. The flat light emitting plate according to claim 1, wherein the plurality of light guide plates are arranged so as to cover at least a part of the fluorescent tube. 3. The flat light emitting plate according to claim 1, wherein a diffusion pattern printed on the light guide plate is divided and printed for each light guide plate. 4. The flat light emitting plate according to claim 3, wherein the coating area of the diffusion pattern printed on the light guide plate and the light incident surface area of the end portion of the light guide plate are in a proportional relationship. .. 5. The flat light emitting plate according to claim 1, wherein the fluorescent tube side of the light guide plate is obliquely cut, and the cut length is equal to or larger than the diameter of the fluorescent tube. 6. The flat light emitting plate according to claim 2, wherein an end surface of the light guide plate on the fluorescent tube side is polished. 7. The flat light emitting plate according to claim 2, wherein the end surface of the light guide plate on the fluorescent tube side is a curved surface.