JPH0961636A - Surface type light source device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high luminance and decrease the number of components as to the surface type light source device which is constituted by making a linear fluorescent lamp abut against an end surface of a transparent resin plate body and providing a reflecting layer containing a light diffusing and reflecting material partially on the reverse surface of the transparent resin plate body. SOLUTION: When a scatter pattern 3 is formed by covering the reverse surface 2 of a light guide plate 1 made of a light-transmissive material with a light diffusive material 17, the film thickness of the coating is increased in proportion to the distance from the fluorescent lamp 8 as a light source. Consequently, high luminance can be obtained without lowering the transmissivity of the diffusion plate 6 since no light beam is projecting from the light guide plate 1 because of diffuse reflection or without lowering the transmissivity by increasing the number of elements of the diffusion plates 6, so that the surface type light source device which has high efficiency, low cost, and handling improved can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin planar light source device used for back lighting of signboards and various lighting devices, and is particularly preferably used as a back lighting means of a liquid crystal display device. .

[0002]

2. Description of the Related Art A sidelight type (light guide plate type) planar light source has been conventionally known as a means for realizing a thin planar light source of this type. FIG. 6 shows an example thereof. In this figure, reference numeral 1 denotes a light guide plate, which has a substantially short shape made of a highly transparent material such as acrylic. On the back surface 2 of this light guide plate 1, white or milky white ink is provided, for example, as shown in JP-A-63-62105, so that the density thereof changes from one end side to the other end side. The scattering pattern 3 is printed by being divided into.

Further, a light reflecting plate 4 is arranged behind it. Further, a diffusion plate 6 is placed above the surface 5 (observation side) of the light guide plate 1. On the other hand, at least one or more end portions 7 of the light guide plate 1 are provided with one or more linear (straight tubular) light sources such as cold cathode tubes or hot cathode fluorescent tubes 8 in close proximity. The outer circumference thereof is covered with a reflective film 9 which is vapor-deposited with silver or the like. A reflective material 10 such as a reflective tape is added to the end portion of at least one or more transparent resin substrates 1 except where the fluorescent tubes 8 are placed.

FIG. 7 is a schematic cross-sectional view for explaining the behavior of light rays in the sidelight type thin planar light source configured as described above. Explaining this, the fluorescent tube 8
The emitted light from is confined by the reflection film 9, and most of it reaches the end portion 7 of the light guide plate 1 and enters the inside of the light guide plate 1. Of these light rays, only the light ray 11 that hits the scattering pattern 3 printed on the back surface of the light guide plate 1 is scattered and reflected as it is to reach the front surface 5 of the light guide plate 1, and the light ray 12 that escapes to the back surface 2 Two of the light rays 13 which are reflected by the reflection plate 4 and are directed to the surface 5 of the light guide plate 1 pass through the diffusion plate 6 and are emitted to the surface 5 of the light guide plate 1 as indicated by reference numeral 14.

A light ray 15 that does not hit the scattering pattern 3 on the back surface 2 of the light guide plate 1 and a light ray 16 that hits the front surface 5 side proceed by repeating total reflection inside the light guide plate 1 until they reach the scattering pattern 3. . By giving a density distribution to the scattering pattern so that the emitted light has a uniform emission intensity on the entire screen, it is possible to realize a planar light source having a relatively high brightness and being uniform.

[0006]

When the planar light source device using the scattering pattern as described above is used, the visibility of the pattern becomes a problem. In order to solve this, it is necessary to diffuse the pattern appearing by the pattern by using a member such as a diffuser plate having a large diffusivity and a low transmissivity, which hinders high brightness. This is not desirable for a planar light source device that aims to achieve high brightness with low power consumption, and the use of such a member leads to an increase in the number of parts and an increase in the unit price of the planar light source device itself. Connect

The present invention has been made in view of the above points, and realizes high brightness without using a member such as a diffuser plate that hinders high brightness, and the number of parts by omitting the diffuser plate It is an object of the present invention to provide a surface light source device and a manufacturing method thereof that can reduce the number of manufacturing processes, simplify the manufacturing process, and reduce the cost.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. The invention described in claim 1 has a linear light source adjacent to at least one side surface of a light guide plate made of a translucent material, and at least one of the front and back surfaces of the light guide plate diffuses light. In a planar light source device in which a light-scattering material is coated to form a scattering pattern and the surface is covered with a light-reflecting plate, the thickness of the light-diffusing material increases in proportion to the distance from the linear light source. It is characterized by using a light guide plate coated so that it becomes larger as the distance increases.

According to a second aspect of the present invention, as a method of manufacturing a planar light source device, when a light diffusing substance is applied to a light guide plate, the printing area of the light diffusing substance is reduced stepwise, and a linear light source is provided. It is characterized in that a distribution in which the film thickness increases in proportion to the distance from the linear light source is realized by performing printing a plurality of times by advancing to the side away from.

According to a third aspect of the present invention, as another method of manufacturing a planar light source device, a recess is provided in the light guide plate so that the depth increases as the distance from the planar light source increases. It is characterized in that a liquid light diffusing substance is poured therein and cured to realize a distribution in which the film thickness of the light diffusing substance increases in proportion to the distance from the linear light source.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a light guide plate, which is similar to that shown in FIG. 6, and has a substantially short shape made of a highly translucent material such as acrylic. Back surface 2 of this light guide plate 1
Is coated with a white or milky white ink so that the film thickness continuously increases from one end side to the other end side as the distance from the linear light source increases.
Are formed. The other parts are the same as those in FIG. 6, and therefore the same reference numerals are given and the description thereof is omitted.

FIG. 2 is a diagram for explaining a method of manufacturing the one shown in FIG. When the light diffusing substance is uniformly applied to the light guide plate 1, the screen printing method is effective. In this example, this technique was used to realize printing with a change in film thickness. First, the light diffusion material 17 is uniformly applied to the entire light emitting surface of the light guide plate 1. In this example, an acrylic transparent resin substrate was used as the light guide plate 1, and white ink (Seiko Advance 2500 ultra slow drying 120) was used as the light diffusing substance. The ink viscosity is 5000 cp, and the screen used for the plate is Tetron 305 mesh S standard. Printing was performed using the above, and a film thickness of 10 and several microns was obtained by the first printing. This finally becomes a film thickness of several microns due to the scattering of the solvent, and the following work will be carried out using this film thickness as a reference d of the film thickness obtained by one coating.

Next, the printing area is reduced only in a direction perpendicular to the fluorescent tube 8 which is the light source, and the printed area is brought close to the end 18 where the fluorescent tube 8 is not located and overlapped on the previous printing and printing is performed again. went. The ink used here will dry if left unattended for about 5 minutes (when the temperature is around 25 ° C and the humidity is around 60%), so if you print multiple times over the previous print, the drying time will be that much. Good. Further, by repeating this procedure a plurality of times while gradually decreasing the printing area, a distribution is realized in which the film thickness increases as the distance from the linear light source 8 increases. Finally, the film thickness D was several tens of microns at the farthest point from the linear light source.

FIG. 3 is a diagram for explaining the manufacturing method described in claim 3. As mentioned above, the white ink used this time is Seiko Advance 2500 ultra slow drying 120,
When applied at 10's of microns, it becomes a few microns by drying (in the case of a single application by screen printing). In consideration of this, the depression 19 is formed on the printed surface of the light guide plate 1 in advance.
Is provided, and the light-diffusing substance 17 (white ink described above) in a liquid state is poured therein and cured. As a result, the light diffusing substance 17 can be applied with a film thickness corresponding to the depression 19 provided in advance.

In this embodiment, considering the above matters,
The recess 19 is provided such that its depth increases as the distance from the linear light source 8 increases. As a result, it was possible to realize a distribution in which the film thickness increases as the distance from the fluorescent tube 8 increases. That is, by forming a recess 19 so that the side closer to the fluorescent tube 8 is a few microns and the far side is a little less than 100 microns, the target film thickness D '(several microns on the side closer to the fluorescent tube 8 It has been confirmed that the above can obtain several tens of microns). Further, in this embodiment, the recesses 19 formed in the light guide plate 1 were created by cutting, but the processing method for the present invention is not limited to this, and injection molding, extrusion molding, compression molding, and other processing methods. Can also be manufactured by

Finally, a planar light source device having the structure shown in FIG. 1 was manufactured by using two kinds of light guide plates 1 according to the manufacturing method of the present invention. As a result, a highly bright planar light source device having no dot image was obtained. It was realized. In implementing the present invention, the transparent resin substrate used as the light guide plate 1 is most preferably acrylic resin because of its transparency and workability. However, the embodiment of the present invention is not particularly limited to this, and instead of this, various thermoplastic transparent resins such as vinyl chloride resin, polycarbonate resin, olefin resin, and styrene resin can be used. . Further, a thermosetting transparent resin such as allyl diglycol carbonate resin and an inorganic transparent material such as various glass materials can be used depending on the case.

Further, in the present embodiment, a general white ink for screen printing is used, but the light diffusing substance 1 according to the present invention is not particularly limited as long as it exhibits a light scattering property. For example, TiO ₂ , SiO ₂ , CaCO ₃ ,
Inorganic light-scattering agent such as Al ₂ O ₃ , BaSO ₄ , ZnO, fine glass powder, or organic light-scattering agent such as acryl or polystyrene is dispersed in a transparent resin vehicle to form an ink. Etc. can be used. Further, it is possible to use two or more of these in admixture.

Next, the light reflection characteristics of the planar light source device according to the present invention shown in FIG. 4 and the conventional planar light source device shown in FIG.
In the case of FIG. 4, since the light diffusion material 17 is applied thinly in the vicinity of the fluorescent tube 8 and becomes thicker as the distance increases, all the light is diffusely reflected in the vicinity of the fluorescent tube 8. Instead, the thing that propagates by total reflection appears. In the figure, the light hitting points b and d corresponds to this. In FIG. 5, which will be described later, diffuse reflection is performed, but in FIG. 4, since this corresponds to a place where the film thickness of the light diffusion material 17 is thin, total reflection is performed, and the light is separated from the fluorescent tube 8. The light propagates to the position, is diffusely reflected at the points b ′ and d ′ where the film pressure is increased, and is emitted from the light guide plate 1. According to the present invention having the above-described mechanism, it is possible to obtain a uniform luminance distribution even though the light diffusing substance 17 is applied to the entire surface.

On the other hand, as shown in FIG. 5, in the case where the light diffusing substance 17 is uniformly applied, the light incident on the inside of the light guide plate 1 passes through the respective optical paths shown in the figure, and the lower surface of the light guide plate 1 is shown. When the light diffusing substance is first contacted with the light, such as points a to f in FIG. Therefore, one of the major functions of the light guide plate is a state in which light is not sufficiently propagated. Therefore, the distribution is such that the brightness decreases as the distance from the linear light source increases.

[0020]

As described above, according to the present invention, a surface using a light guide plate coated with a light diffusing substance so that the film thickness increases as the distance from the linear light source increases. Since it is a planar light source device, it is possible to solve the problem of pattern recognition, which is a drawback of the planar light source device that has been made uniform by using a conventional dot pattern or the like. As a result, a member for erasing the pattern image, such as a diffusion plate, which has been used in the past, becomes unnecessary. Therefore, it is possible to increase the brightness and reduce the number of parts and the number of work steps.

Further, in each of the manufacturing methods, since mass production is possible, the individual accuracy can be improved and a good yield can be obtained.

From the above, the present invention enables the stable production of a planar light source device which is cheaper and has high brightness.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a side light type planar light source device of the present invention.

FIG. 2 is an explanatory view illustrating an example of a method for manufacturing the planar light source device of the present invention.

FIG. 3 is an explanatory diagram illustrating another example of the method for manufacturing the planar light source device of the present invention.

FIG. 4 is an explanatory diagram illustrating a function of that of FIG. 1;

FIG. 5 is an explanatory diagram illustrating a function of a conventional planar light source device.

FIG. 6 is a cross-sectional view of a conventional side light type planar light source device.

FIG. 7 is an enlarged cross-sectional view illustrating the trajectory of a light beam in a conventional side light type planar light source device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Back surface 3 Scattering pattern 4 Light reflecting plate 6 Diffusing plate 7 Edge part 8 Fluorescent tube 9 Reflecting film 10 Reflecting material 17 Light diffusing substance 19 Dimple

Claims (3)

[Claims] 1. A light guide plate made of a translucent material, having a linear light source adjacent to the light guide plate on at least one side surface, and at least one of the front and back surfaces of the light guide plate being covered with a light diffusing substance. In a planar light source device in which a scattering pattern is formed and the surface of which is covered with a light reflecting plate, the coating of the light diffusing material is such that the film thickness thereof becomes large in proportion to the distance from the linear light source. A planar light source device using a light guide plate. 2. When the light diffusing substance is applied to the light guide plate according to claim 1, the printing area of the light diffusing substance is reduced stepwise, and the light diffusing substance is applied to the side away from the linear light source and overlapped a plurality of times. A method for manufacturing a planar light source device, which realizes a distribution in which the film thickness increases in proportion to the distance from the linear light source by performing printing. 3. The light guide plate according to claim 1, wherein a recess is formed so that the depth increases as the distance from the planar light source increases, and a liquid light diffusing substance is poured into the recess to be cured. As a result, a method for manufacturing a planar light source device that realizes a distribution in which the film thickness of the light diffusing substance increases in proportion to the distance from the linear light source.