JP3306792B2 - Backlight for LCD panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a panel backlight for irradiating a transmissive or transflective panel from the back.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a thin and easy-to-see backlight mechanism has been used as a display device such as a laptop or book type word processor or computer. As such a backlight, an edge light system in which a linear light source such as a fluorescent tube is provided at one end of a light-transmitting light guide plate as shown in FIG. 1 is often used. In the case of this edge light method, as shown in FIG. 2, a light diffusing element having a function of diffusing light is formed on one wide surface of the light guide plate, for example, a light diffusion element having a refractive index larger than that of the light guide plate material. By partially covering the substance, roughening the surface of the light guide plate, or forming a dot-shaped hole in the surface, almost the entire surface is covered with a light diffusion reflector, and In many cases, a light diffusing plate is arranged on the light exit surface. The covering with the light diffusion reflection plate is for effectively utilizing the light diffusion effect of the reflection plate.

In recent years, the backlight has been driven by a battery, and it has been desired to further improve the power consumption-luminance conversion efficiency. For this purpose, a part of light incident on the light guide plate is converted into an optical fiber. In order to prevent the light from being emitted from the light source through the opposite end on the same principle, a method of covering the opposite end surface with a light reflecting plate has been proposed.

[0004] Such a method is a means for effectively utilizing light from a light source, and further effective utilization of light is desired.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to make various studies on the above-mentioned problems and to provide a backlight having good energy efficiency and a uniform luminance distribution. .

[0006]

Means for Solving the Problems The inventors of the present invention have conducted various studies on the structure of a backlight that can efficiently use light in a panel backlight using a light guide plate. It has been found that the above object can be achieved by forming an anti-reflection film on at least the surface facing the light source. Next, the present invention will be described in more detail.

FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a sectional view of the embodiment. 1 is a light guide plate in the figure,
Any substance can be used as long as the substance allows light to pass therethrough efficiently, such as quartz, glass, or a translucent natural or synthetic resin such as an acrylic resin.

Reference numeral 4 denotes a light source, usually a linear light source,
The periphery of the light guide plate is covered with a specular reflector or light diffusion reflector 5 having a gap (slit) for allowing light to enter the end surface of the light guide plate. It is installed so that it becomes almost parallel. This example is an example in which a light source is provided close to a surface facing one side end of the light guide plate, but it is also possible to provide a light source close to the opposite side end of the light guide plate, respectively. The light source may be provided opposite to one of the wide surfaces (the lower surface in FIG. 1).

When a linear light source is used as a light source, there are a fluorescent tube, a tungsten incandescent tube, an optical rod, an arrangement of LEDs, and the like, but a fluorescent tube is preferable. Light sources other than the linear light source include a flat fluorescent lamp and an incandescent lamp.

As described above, according to the present invention, when the light source is provided at least on the surface of the light guide plate facing the light source, that is, in the case where the light source is provided close to one side end of the light guide plate, FIG. In the case where the light source is provided facing one of the wide surfaces, an antireflection film is formed on the lower surface of the light guide plate in FIG.

The material of the antireflection film used in the present invention is Si
O, SiO ₂ , ZrO ₂ , TiO ₂ , MgF ₂ , Ge,
These are formed on a corresponding surface by a method such as coating (coating) or vapor deposition using CeF ₃ , CeO ₂ , ZnS, Si, or the like. The thickness of the antireflection film is within a range that does not impair the transparency of the material, and may be any range that effectively functions as an antireflection film, and is usually 0.1 to 20 μm, preferably 0.1 to 5 μm. Range. These materials are used alone or in combination as appropriate. Further, an antireflection film may be formed not only on the surface of the light guide plate facing the light source but also on the peripheral end surface of the light guide plate. Reference numeral 2 denotes a light diffusing plate that scatters light emitted from the light guide plate and allows the light to pass therethrough. In the present invention, one or a plurality of light diffusion plates are used.

In the present invention, in the case where a light source is provided close to a surface facing one side end of the light guide plate, the light guide plate has a light emitting surface in order to maintain a uniform brightness of light on a light exit surface of the light guide plate. It is preferable to form a light diffusing element having a function of diffusing light on one wide surface. In this case, the light diffusing element is formed by partially covering the light diffusing substance having a higher refractive index than the light guide plate material, as in the above-described conventional method,
The method can be performed by roughening the surface of the light guide plate or forming a dot-shaped hole in the surface. Next, a method of partially covering the light diffusion material will be described as an example.

The light scattering material 6 applied to the light guide plate is a paint, printing ink or the like containing a pigment having a higher refractive index than the material of the light guide plate and having a large diffuse reflectance. These are applied in dot form on the light guide plate surface by a method such as screen printing. The light diffusing substance applied to the light guide plate is formed in a dot shape, that is, a dot shape. However, the shape of the dot is not particularly limited, and may be any of a circle, a square, and a cross line. These are applied on intersections (grids) of orthogonal lines having a certain interval imaginary on the light guide plate, and the interval between the orthogonal lines is preferably 0.5 to 3 mm, more preferably 0.8 to 2 mm. It is appropriately selected according to the thickness of the light guide plate.

Further, the coating state of the light diffusing substance is such that the coating ratio is 1% to 50% in the vicinity of the linear light source on the light guide plate surface.
Then, the coating is performed so that the ratio of the coating gradually increases, starting from the coating point on one side end where the linear light source is brought close to the light source.
The coating ratio in the portion where the coating ratio is large is 20 to 100.
%.

A light diffusion reflector (3 in the figure) is arranged so as to cover almost the entire surface of the light guide plate on which the light diffusion element is formed. In the case where one light source is used, it is preferable to form a specular reflector on an end face of the light guide plate opposite to one side end where the linear light source is brought close to the light guide plate. Any material that reflects light almost specularly may be used, and is made of silver, aluminum, gold, copper, platinum, nickel, chromium, or the like, and is preferably silver or aluminum.

The method of forming the specular reflector is not particularly limited, and a mirror reflector or a film which is applied by a method such as hot stamping or vapor deposition or separately prepared may be used.

The main part of the present invention has such a structure and is used as a backlight of a panel, especially a liquid crystal panel.

[0018]

According to the present invention, the light from the light source can be used as efficiently as possible, the luminance distribution is uniform, sufficient luminance can be obtained, and the backlight can be used with good power consumption-luminance conversion efficiency.

[0019]

Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. A rectangular light guide plate (22) having a thickness of 2 mm as shown in FIG.
A cold cathode tube (4.8 mm diameter normal tube manufactured by Harrison Electric Co., Ltd.) having a thickness of 4.8 mm, which is 7 mm longer than the end length, is disposed at the short end of 5 mm × 127 mm).
The outer periphery of the tube was covered with a cylindrical aluminum light reflector having a slit of 2 mm, and the light emitted from the slit was arranged to enter the light guide plate from the end of the light guide plate.

On the other hand, the light diffusing substance to be coated on the light guide plate surface is a screen pattern printed with a circular dot pattern, and the screen printing plate was prepared and used by CAD under the following conditions. . Light diffusion material coverage is 6% at minimum point
The plot was used so that it increased sequentially as the distance from the light source increased and reached 80% at the maximum point.

[0021] SiO as an antireflection film on the light guide plate end face on the side to close the cold cathode tube, forming a ZrO _2, SiO ₂ in 3-coat (total thickness about 1 [mu] m), guiding the opposite side The end surface of the light plate was covered with a mirror-reflective film by a hot stamp. The light guide plate surface coated with the light diffusing material is a light diffusing reflector film (MTN-W20 manufactured by Tsujimoto Electric Co., Ltd.).
0). On the light-emitting surface side of the light guide plate, a polycarbonate film (thickness: 200 μm) having one surface embossed and roughened was arranged.

As a result of measuring the surface luminance when a 30 KHz alternating voltage was applied to the cold cathode tube from the inverter with a constant current and measured by a luminance meter (Topcon BM-8),
The average luminance was 265 cd / m ² . As a comparative example, an antireflection film was not formed on the end surface of the light guide plate, and the surface luminance was measured in the same manner as in the above example except that the average luminance was 220 cd / m ² .

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a backlight according to an embodiment of the present invention.

[Explanation of symbols]

 1: light guide plate 2: light diffusion plate 3: light diffusion reflection plate 4: linear light source 5: reflector 6: light scattering material 7: specular reflection plate 8: antireflection film

Continuation of the front page (56) References JP-A-5-297366 (JP, A) JP-A-2-160215 (JP, A) JP-A-4-62519 (JP, A) JP-A-3-9306 (JP) JP-A-1-245220 (JP, A) JP-A-57-128383 (JP, A) JP-A 62-161239 (JP, U) JP-A 62-173755 (JP, U) JP-A 62-173755 62-167243 (JP, U) Japanese Utility Model Showa 62-164336 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1335

Claims (2)

(57) [Claims] 1. A light-transmitting light guide plate made of a material and the light guide plate
In the backlight for a liquid crystal panel having a light source provided in proximity to the side, as an antireflection film on at least the light source and the opposite side surface of the light guide plate, SiO, SiO _2, Z
rO ₂ , TiO ₂ , MgF ₂ , Ge, CeF ₃ , CeO ₂ ,
Forming Then together the laminated film having a thickness of 0.1~20μm of two or more films selected from the group consisting of ZnS and Si
At the side of the light guide plate facing the side where the light source is brought close.
A backlight for a liquid crystal panel, comprising a mirror reflector . 2. A light diffusion element is provided on one wide surface of the light guide plate.
The light diffusion function increases as the distance from the light source to the light source increases
2. The backlight for a liquid crystal panel according to claim 1, wherein a light guide plate formed as described above is used .