JPH087614A - Surface light source - Google Patents

Abstract

(57) [Summary] [Object] To provide a planar light source capable of whitening using a blue light emitting diode, and to provide a planar light source capable of observing uniform white light emission. A light emitting diode 1 is optically connected to an end surface of a transparent light guide plate 2, and a scattering layer 3 coated with a white powder that scatters fluorescence on one of the main surfaces of the light guide plate 2. A transparent film 6 is provided on the main surface side of the light guide plate 2 opposite to the scattering layer 3, and the film 6 emits fluorescence when excited by the light emission of the light emitting diode 1. Material is equipped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar light source used for display backlights, illuminated operation switches and the like, and more particularly to a planar light source that can be suitably used as a liquid crystal display backlight.

[0002]

2. Description of the Related Art Generally, for example, an EL or a cold cathode tube is used as a surface light source for a backlight of a liquid crystal display used in a notebook type personal computer, a word processor or the like. EL
Is a surface light source itself, and the cold cathode tube is a surface light source using a diffusion plate, and most of the emission colors of their backlights are currently white.

On the other hand, a light emitting diode (hereinafter referred to as an LED) is also partially used as a light source for a backlight. However, in the case of obtaining white light emission using an LED, the emission output of the blue LED is only about several tens of μW in the related art,
In order to realize white light emission by using other red LEDs and green LEDs, there is a drawback that it is difficult to match the characteristics of the respective color light emitting LEDs and the color change is large. Also, the three primary colors L
Even if EDs are aggregated and arranged geometrically at the same position on the same plane, it is impossible to make a uniform white light source because the LEDs visually recognize the LEDs at close positions as a backlight. It was Therefore, for a white light source of a liquid crystal backlight, a large-sized cold cathode fluorescent lamp is used, and small to medium-sized fluorescent lamps are E-shaped.
At present, it is properly used as L, and white light emitting backlights using LEDs are hardly known.

As a white light emitting or monochrome light source, there has been an attempt to partially surround a blue LED chip with a resin containing a fluorescent material for color conversion, but the periphery of the chip has a radiation intensity higher than that of sunlight. Because it is exposed to the rays,
Deterioration of the fluorescent substance poses a problem, especially in organic fluorescent pigments. Further, the ionic organic dye may cause electrophoresis due to a DC electric field in the vicinity of the chip to change the color tone. Further, the conventional blue LED does not have a sufficient output for color conversion with a fluorescent substance, and even if color conversion is performed, it is not practical.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve such a drawback, and an object of the present invention is to use an LED and obtain a white light-emitting surface shape that can be mainly used as a backlight. The aim is to provide a surface light source that can realize a uniform white light emission while realizing a light source. Furthermore, it provides a surface light source that can emit light of any color other than white, and has excellent LED characteristics. Is used for various operation switches and the like.

[0006]

In the surface light source of the present invention, a blue light emitting diode 1 is optically connected to at least one position of an end surface of a transparent light guide plate 2, and the main surface of the light guide plate 2 is further provided. Has a scattering layer 3 coated with white powder (hereinafter, the main surface on the scattering layer side is referred to as a second main surface), and the main surface of the light guide plate 2 opposite to the scattering layer 3 A transparent film 6 is provided on the (hereinafter, referred to as the first main surface) side, and a fluorescent substance that emits fluorescence when excited by the light emission of the blue light emitting diode 1 is provided on the surface or inside of the film 6. Is provided.

FIG. 1 is a plan view of the light guide plate 2 of the planar light source of the present invention as viewed from the second main surface side. The light guide plate 2 is made of a transparent material such as acrylic or glass, and the blue LED 1 is embedded in the end surface of the light guide plate 2, so that the light guide plate 2 and the blue LED 1 are optically connected. In the present invention, the fact that the blue LED 1 and the end face of the light guide plate 2 are optically connected means simply introducing the light of the blue LED from the end face of the light guide plate 2. It is possible to embed the blue LED 1 as shown in (1), or to bond the blue LED, or to guide the light emission of the blue LED to the end face of the light guide plate 2 by using an optical fiber or the like.

Next, the scattering layer 3 scatters light in the light guide plate 2 with a white pigment. In particular, in FIG. 1, the scattering layer 3 is formed into a stripe shape, and as the LED 1 is approached, the scattering layer 3 per unit area on the second main surface side has a stripe shape so that the surface luminance on the first main surface side is constant. The pattern is such that the area is reduced, and the area of the end of the second main surface farthest from the LED 1 is slightly smaller than the maximum area.
Here, ▪ in FIG. 1 represents the pattern of the scattering layer 3. In FIG. 1, six blue LEDs are arranged on one end face, but it goes without saying that if the light guide plate is a quadrangle, the LEDs may be connected to all four end faces.
The number of D is also not limited. Furthermore, the coating shape and coating state of the scattering layer 3 can be appropriately changed so that the light emission observed from the first main surface side becomes uniform in a planar manner depending on the arrangement of the LEDs.

[0009]

FIG. 2 is a schematic sectional view when the planar light source of the present invention is mounted as a backlight of a liquid crystal panel, for example.
This is a reflection plate in which a scattering reflection layer 7 made of, for example, barium titanate, titanium oxide, aluminum oxide, etc. and a base 8 made of, for example, Al are laminated on the second main surface side of the planar light source shown in FIG. And a transparent film 6 having fine irregularities on the surface is installed on the first main surface side, and the surface of the film 6 having irregularities is excited by the light emission of the blue LED 1. A fluorescent substance that emits fluorescence is applied.

First, as shown by the arrow in FIG. 2, a blue LED
The light emitted from 1 is radiated to the outside of the light guide plate 2 in the vicinity of the chip, but most of the light reaches the end surface of the light guide plate 2 while repeating total reflection inside the light guide plate 2. The light reaching the end face is reflected by the reflection film 4 formed on all the end faces, and the total reflection is repeated. At this time, the light is scattered by the scattering layer 3 provided on the second main surface side of the light guide plate 2, and a part of the scattered light is absorbed by the fluorescent layer 5 and is simultaneously wavelength-converted and radiated. The light emission color observed from the first main surface side of 2 can be observed by combining these lights. For example, in the planar light source provided with the fluorescent layer 5 made of an orange fluorescent pigment, the emission color from the blue LED 1 can be observed as white due to the above-described action.

Particularly in the present invention, the emission wavelength of one blue LED is such that its main emission peak is shorter than 500 nm and its emission output is required to be 200 μW or more, more preferably 300 μW or more. Because the emission wavelength is 500 nm
If it is above, it is difficult to realize all colors, and if the emission output is less than 200 μW, even if the number of blue LEDs optically connected to the end surface of the light guide plate is increased, sufficient brightness is obtained. This is because it tends to be difficult to obtain a light source of planar light emission.

The present inventor has disclosed in Japanese Patent Application No. 5-318267 a surface light source capable of uniform white light emission by forming a fluorescence scattering layer on the main surface side of the light guide plate opposite to the light emission observation surface. Proposed. However, in this method, in the obtained planar light source, in order to change the color tone, the fluorescent light scattering layer formed on the light guide plate had to be peeled off and the fluorescent light scattering layer with the desired color tone had to be printed again. . However, in the present invention,
The fluorescent layer 5 and the scattering layer 3 are independent of each other, and in particular, the fluorescent layer 5 that determines the color tone is formed on the removable film, so that the color tone can be easily changed only by changing the film on which the fluorescent layer 5 is formed. be able to. Also, it is possible to simultaneously emit light of a plurality of colors separately.

Moreover, since the surface of the film 6 in contact with the first main surface side is uneven, it is very useful for scattering the emitted light, and the film 6 is used as the light guide plate 2.
It is possible to prevent interference fringes from sticking to the.

[0014]

【Example】

[Example 1] One side of an acrylic plate having a thickness of about 2 mm was
The scattering layer 3 was formed by screen printing in the stripe pattern shown in FIG. The scattering layer 3 was formed by printing a white substance made of barium titanate dispersed in an acrylic binder.

The acrylic plate on which the scattering layer 3 has been formed as described above is cut according to a desired pattern, and after polishing all the end faces (cut faces) of the acrylic plate, the reflective layer 4 made of Al is formed on the polished face. By forming, the light guide plate 2 having the scattering layer 3 formed thereon was obtained.

Next, the fluorescent layer 5 was formed on the film 6 having fine irregularities on the surface. The fluorescent layer 5 is formed by applying a dispersion of an acrylic binder in which a fluorescent pigment, which is a red fluorescent pigment FA-001 manufactured by Shin Loihi Chemical Co., and a green fluorescent pigment FA-005 manufactured by the same company, are mixed in an equal amount. did.

Six holes are provided on the end surface of the light guide plate 2,
Blue LED made of gallium nitride-based compound semiconductor having emission wavelength of 480 nm and emission output of 1200 μW in the hole
I embedded one each. Then, the film 6 having the fluorescent layer 5 formed on the emission observation surface side as described above
On the scattering layer 3 side, a reflection plate in which the barium titanate layer 7 was applied on the Al base 8 was installed to provide a light source for a backlight, and the surface was completely uniform from the first main surface side. White light emission was obtained. The brightness was 55 cd / m ² .

[Example 2] BASF as a yellow fluorescent dye
Lumogen F Yellow-083 of the same company and Orenge-240 manufactured by the same company as orange fluorescent dye are mixed in substantially equal amounts, and a fluorescent dye obtained by dissolving them and acrylic resin in butyl carbitol acetate is formed on the film 6 having fine irregularities. Applied. When a planar light source of the present invention was obtained in the same manner as in Example 1 except for the above, substantially uniform planar light emission was observed. Further, when a light source for a backlight was similarly prepared, completely uniform planar light emission was observed.

[0019]

As described above, the planar light source of the present invention uses the blue LED, and has the scattering layer 3 coated with the white powder on one main surface side of the light guide plate. By disposing the transparent film 6 coated with a fluorescent substance capable of wavelength conversion with a blue LED on one main surface side, it becomes possible to realize a highly reliable LED surface light source. Moreover, the white powder of the scattering layer 3 is blue L
Since it has a function of reflecting and diffusing the light emitted from the ED, the amount of the fluorescent substance used can be small. Further film 6
By forming fine irregularities on the surface, it is possible to enhance the action of scattering light and prevent the film from sticking to the light guide plate 2 to form interference fringes. More conveniently, L
Since there is no direct contact between the ED chip and the fluorescent substance,
There is little deterioration of the fluorescent substance, and the color tone of the planar light source does not change over a long period of time. Regarding the color tone, it is possible to provide any color tone including white depending on the type of the fluorescent substance of the fluorescent layer 5, and since the fluorescent substance is included in the film, it is possible to easily change the film to easily obtain the planar light source. The color tone of can be changed.

On the other hand, as the side that excites the fluorescent layer 5, most preferably the blue LED used has a light emission output of 200 μW or more, whereby a bright planar light source having a large area which is efficiently wavelength-converted by the fluorescent substance. Can be realized. As described above, the planar light source of the present invention can be used not only as a light source for a backlight but also as an illuminated operation switch using a fluorescent substance.

[Brief description of drawings]

FIG. 1 is a plan view of a light guide plate 2 of a planar light source according to an embodiment of the present invention viewed from a scattering layer 3 side.

FIG. 2 is a schematic cross-sectional view when the planar light source according to the embodiment of the present invention is mounted as a backlight.

[Explanation of symbols]

 1 ... Blue LED 2 ... Light guide plate 3 ... Scattering layer 4 ... Reflecting layer 5 ... Fluorescent layer 6 ... Film 7 ... ... Scattering reflection layer 8 ... Al base

Claims (2)

[Claims] 1. A blue light emitting diode 1 is optically connected to at least one location on an end face of a transparent light guide plate 2,
Further, a scattering layer 3 coated with white powder is provided on one of the main surfaces of the light guide plate 2, and a transparent film 6 is provided on the main surface side of the light guide plate 2 opposite to the scattering layer 3. The surface light source is characterized in that the surface or inside of the film 6 is provided with a fluorescent substance that is excited by the light emission of the blue light emitting diode 1 to emit fluorescence. 2. The planar light source according to claim 1, wherein the surface of the film in contact with the light guide plate is provided with fine irregularities.