JP4127897B2 - Surface light source device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an edge light type illumination device technology that illuminates a relatively wide area by converting a spot-like or linear light source into a uniform surface light source, and illuminates from the back of a liquid crystal panel, an advertising board, etc. Useful for display devices.
[0002]
[Prior art]
As shown in FIG. 2, a tubular light source lamp 22 is mounted on an end surface 26 of a transparent resin plate 21 having a high light transmittance such as an acrylic resin plate (covered with a reflecting plate 23), and screen printing is performed on one main surface 24. A fine dot-like irregular reflection layer 27 is provided by a technique such as shot blasting, and light incident and propagated from the light source lamp to the transparent resin plate is reflected by the irregular reflection layer 27 and emitted from the other main surface 25. The surface light source device 20 is frequently used for illumination of a liquid crystal display device or the like. As described above, the conventional surface light source device in which the irregular reflection layer is formed on one surface of the transparent resin plate is advantageous in that it can be easily thinned.
[0003]
Further, it is known that when a particle having a different refractive index is dispersed in a transparent resin, a scattering light guide plate is obtained. As shown in FIG. A scattering light guide type surface light source device 30 comprising a light guide plate 31 using scattering light guide portions 31a and 31b is also proposed in Japanese Patent No. 324330. In this way, in the planar light source device using a plurality of scattering light guide regions having different light scattering capabilities, the light scattering capability can be adjusted over the entire light exit surface (main surface 35) of the light guide plate, so that the light exit area is compared. If it is small, it is easy to maintain the uniformity of luminance.
[0004]
[Problems to be solved by the invention]
The conventional surface light source device as described above is suitable when the light output area is relatively small. When the light output area is increased, the conventional technique is generally difficult to apply as it is. In the conventional surface light source device system in which a halftone dot diffuse reflection layer is provided on one side of a transparent resin plate, it is difficult to keep the luminance uniform over the entire light emitting surface, and at the same time, the distance from the light source lamp increases. In order to compensate for the phenomenon of lowering the brightness, it is necessary to modulate the diffuse reflectance in conjunction with the light guide distance. A specific example is increasing the number of irregular reflection layers as the distance from the light source increases.
[0005]
On the other hand, in a method using a plurality of scattering light guide regions having different light scattering capabilities in a scattering light guide type surface light source device, in order to keep the brightness of the light exit surface uniform even when the light guide distance increases, Although it is necessary to provide a slight difference in the light scattering ability of each scattering light guiding area while reducing the light scattering ability for the light guiding area, it is not easy to industrially realize this. It is also difficult to stably produce a product having a very low scattering ability.
Further, regardless of the light guide method, there is a problem in that bright line-like luminance spots are generated in the vicinity of the light source lamp on the light exit surface of the light guide plate. Conventionally, there is no suitable method for solving this, and brightness adjustment is performed by another component.
The object of the present invention is to increase the light emission luminance and its uniformity with a relatively simple structure even when the light emission area is large, and to create a light guide plate that significantly reduces the luminance unevenness in the vicinity of the light source lamp. An object of the present invention is to provide a surface light source device capable of comprehensively solving various problems related to technology.
[0006]
[Means for solving the problems]
In the present invention, as shown in FIG. 1, at least one non-scattering light guiding region 11 a and at least one scattering light guiding region 11 b in which particles having different refractive indexes are dispersed in the same material have overlapping portions. In the light guide plate (plate-like body) 11, the light source lamp 12 is mounted on the end face 16 (the back surface of the light source lamp 12 is covered with the reflection plate 13), and the scattering light guide region is a convex light guide block. A surface light source characterized in that the non-scattering light guide region is a concave light guide block corresponding to the convex light guide block, thereby controlling the distribution of the amount of light emitted from the main surface 15. The present invention relates to the apparatus 10 and solves the above-described problems.
[0007]
[Action]
In the surface light source device 10 of the present invention, light incident from the end face 16 of the light guide plate basically has a refractive index larger than that of air, and thus proceeds while totally reflecting the light guide plate according to Snell's law. However, only the light incident on the particles is scattered there and the outgoing light spreads. This scattering phenomenon is repeated, and only light having a smaller angle than the critical angle is emitted when the guided light hits the interface between the light guide plate and the air. The intensity and distribution of the emitted light also change depending on the number and particle size of the particles. Therefore, these designs greatly affect the lighting quality. This will be described in detail in comparison with the prior art.
[0008]
Generally, a planar light source device used for illumination or the like is required to shine brightly and uniformly. In a so-called edge light type illuminating device that constitutes a planar illuminating device by making light incident on the end face of the light guiding plate and guiding it as in the illuminating device of the present invention, the volume fraction of particles included in the light guiding plate is increased. The amount of light emitted can be increased by increasing the volume fraction.However, if the volume fraction is excessively increased, light emission near the light source is promoted, and the brightness rapidly decreases as the distance from the light source increases. Spots become large.
In the prior art disclosed in Japanese Patent Laid-Open No. 6-324330, in order to give scattering power to all block regions constituting the light guide element, the area of the light guide plate increases, that is, the scattering power increases as the distance from the light source increases. The gradient cannot be increased and it becomes difficult to obtain uniform light, or uniform light is obtained, but the overall luminance value decreases. Further, if there is a small area having scattering ability in the vicinity of the light source, a linear luminance spot occurs in the vicinity of the light incident surface of the light exit surface.
[0009]
As a countermeasure, in order to increase the scattering difference in the scattering power of each block region, if at least one of the block regions is provided with a non-scattering light guiding region that does not include particles, it is bright and uniform even if the area of the light guide plate increases. A planar light source having a luminance distribution is obtained. Furthermore, since the amount of light emitted in the vicinity of the light source can be controlled by locally adjusting the particle concentration by the plate thicknesses of the non-scattering light guiding region and the scattering light guiding region, luminance unevenness in the vicinity of the light source can be eliminated. Further, by using the non-scattering light guide region, simplification in molding and cost merit can be achieved.
Further, in the conventional technology, a diffused light reflection layer such as a fine halftone dot formed by screen printing, shot blasting or the like is formed on one surface of a substrate, and light is incident from the side of the substrate to form a planar light source device. If a manufacturing error occurs with respect to the design size of the target halftone dot where light is emitted only from one side of the surface, the area ratio of the irregular reflection part to the total reflection part changes due to the square of this error, resulting in variations in luminance spots. There are disadvantages such as becoming larger.
On the other hand, in the illumination device according to the configuration of the present invention, if the volume fraction of particles in the cross section in the plate thickness direction of the light guide is the same, the state in which the portion having the scattering ability is present inside the light guide Even if the light enters, there is no change in the amount of light emitted, so that an illumination device can be obtained that emits light of uniform brightness from both sides of the light guide plate with a simple configuration.
[0010]
(Example 1)
FIG. 4 is a diagram for explaining an embodiment of the present invention. Add 0.50wt% of benzoyl peroxide (BPO) as radical polymerization initiator and 0.40wt% of n-lauryl mercaptan (n-LM) as chain transfer agent to MMA (methyl methacrylate) with no particles added, and continue at 70 ° C for 24 hours Casting polymerization was performed to obtain a concave light guide block having a length of 389 mm, a width of 286 mm, and a thickness continuously changing from 9 mm (thinnest part) to 1 mm (thickest part) toward the center. This was made into the light guide block 41a. After that, 0.20 wt% of silicone resin powder with an average particle size of 4.5 μm (Tospearl 145, manufactured by Toshiba Silicone Co., Ltd.) was added to MMA and uniformly dispersed in the sample, 0.50 wt% BPO as a radical polymerization initiator. A syrup produced by adding 0.40 wt% of n-LM as a transfer agent is poured into the concave portion of the light guide block 41a and cast polymerized at 70 ° C. for 24 hours (41b) to produce one plate-like light guide plate 41. did.
[0011]
A light source (cold-cathode fluorescent lamp) 42 having a central luminance of 28600 cd / m ² is mounted on the end face 46 of the light guide plate, and a portion not facing the incident end face of the light guide plate is covered with a light reflecting film (reflecting plate 43). In order to improve the light utilization efficiency. A diffuse reflective light reflecting layer 49 in which a pigment layer made of white fine particles is formed on a plastic film is mounted on the back surface 44 of the light guide plate via an air layer 48b, and at the same time, an air layer 48a is formed on the surface 45 of the light guide plate. The surface light source device 40 was manufactured by mounting the light deflection layer 47 through the substrate. The luminance at the light exit surface of this surface light source device was measured with a CA-1000 type luminance meter manufactured by Minolta Co., Ltd. When the luminance distribution of vertically emitted light was evaluated with an image analysis device, as shown in FIG. 7, the entire surface of the light-scattering light guide was about 7800 cd / m ² and the brightness / darkness ratio was about 85%. A surface light source device was obtained. Further, there was no sharp change in the luminance in the light guide direction, and the luminance unevenness in the vicinity of the light incident surface, which was observed when a conventionally used light guide was used, was also eliminated.
[0012]
(Example 2)
FIG. 5 is a diagram for explaining another embodiment of the present invention. Using a gravimetric feeder, 100 parts by weight of polymethyl methacrylate pellets and 0.60 part by weight of silicone resin powder with an average particle size of 4.5 μm (Toshiba Silicone Co., Ltd., Tospearl 145) were twin-screw extruder (Screw specification: L / D = 32, diameter 44mm), kneaded in a cylinder heated to 240 ° C, pelletized, then supplied to an injection molding machine, cylinder temperature 240 ° C, mold 80 ° C, Convex light guide block 51b molded under conditions of mold clamping pressure of 450t, 389mm long and 286mm wide, with thickness varying from 0.5mm (thinnest part) to 3.5mm (thickest part) toward the center. Was made. Thereafter, the convex light guide block was put into a mold having a length of 389 mm, a width of 286 mm, and a thickness of 9 mm, and a molten (51a) pellet of polymethyl methacrylate without addition of particles was poured into one flat plate. A light guide plate 51 having a shape was produced.
The luminance measurement results similar to those in Example 1 are shown in FIG. The surface light source device 50 having a very high luminance and high degree of uniformity of about 8500 cd / m ² and a light / dark ratio of about 90% over the entire surface of the light scattering light guide was obtained. Further, there was no sharp change in the luminance in the light guide direction, and the luminance unevenness in the vicinity of the light incident surface, which was observed when a conventionally used light guide was used, was also eliminated.
[0014]
【The invention's effect】
According to the surface light source device of the present invention, even when the light emission area is large, the light emission luminance and the degree of uniformity can be increased with a relatively simple configuration, and the bright line-like luminance spots near the light source lamp can be remarkably reduced. In addition, since the present invention has a wide range of selection of materials and shapes for the scattering light guide region and the non-scattering light guide region to be used and a plurality of combinations can be combined, a surface light source device excellent in mass productivity and economy is realized. Will be.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a configuration of a surface light source device as an object of the present invention.
FIG. 2 is an example of a cross-sectional view of a surface light source device that is a subject of the prior art.
FIG. 3 is an example of a cross-sectional view of a surface light source device that is a subject of the prior art.
4 is a perspective view of a surface light source device as a target of Embodiment 1. FIG.
5 is a perspective view of a surface light source device as a target of Embodiment 2. FIG.
FIG. 7 shows the relationship between the distance from the light incident surface on the light exit surface of the light guide in Example 1 and the luminance.
8 shows the relationship between the distance from the light incident surface on the light exit surface of the light guide in Example 2 and the luminance. FIG.
[Explanation of symbols]
10, 20, 30, 40, 50, 60 Surface light source device
11,21,31,41,51,61 Light guide plate
12,22,42,62 Light source
13,23,43,63 Reflector
24,44 Back side (main side)
15,25,35,45 Light exit surface (main surface)
16, 26, 46, 66 Incident surface (end face)
47,67 Light polarizing layer
27 Diffuse reflection layer in the form of fine dots
48a, 48b Air layer
49 Light reflection layer
11a, 31a, 41a, 51a, 61a Non-scattering light guiding region (transparent resin plate)
11b, 31b, 41b, 51b, 61b Scattering light guide region

Claims (3)

In a plate-like body having at least one non-scattering light-guiding region and at least one scattering light-guiding region in which particles having different refractive indexes are uniformly dispersed in the same material, a light source lamp is provided on the end surface. A surface light source device that is mounted and controls the distribution of the amount of light emitted from the main surface by locally adjusting the concentration of particles with the plate thickness of both regions , wherein the scattering light guide region Is a convex light guide block, and the non-scattering light guide region is a concave light guide block corresponding to the convex light guide block. The surface light source device according to claim 1, wherein the convex light guide block continuously changes so as to become a maximum thickness in a central direction. 3. The surface light source device according to claim 1, wherein the surface light source device is a two-lamp type or a four-lamp type.

Images