JP3218750B2 - Backlight for 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 type, as shown in FIG. 2, one surface of the light guide plate is partially covered with a light diffusing substance, and almost the entire surface is arranged to be covered with a specular reflection plate or a light diffusion reflection plate. Many have been done.

In recent years, in particular, in order to improve the performance of these word processors and personal computers, it has been desired to further reduce the size, improve the visibility, and improve the power consumption-luminance conversion efficiency. In addition, it has been proposed to arrange a light diffusion reflection sheet having a high light diffusion reflectance or a mirror reflection sheet having a high mirror reflection rate, and fix the light diffusion plate to the end of the light guide plate with glue or the like.

However, in the vicinity of the linear light source of the light guide plate, if the specular reflection plate and the surface of the light guide plate are completely in contact with each other or are fixed with an adhesive or the like, the light guide plate surface Because the air existing in the light guide plate is eliminated, the critical angle of the light beam in the light guide plate becomes large, and the resulting light scattering increases the brightness as compared with other parts, and the brightness distribution on the light guide plate surface Therefore, the so-called effective display area (VA), which is uniform, is reduced by that amount, so that there is a problem that the above-described outer shape and power-luminance conversion efficiency are deteriorated.

[0005]

Recently, as devices using a backlight have been miniaturized, a backlight having an efficient display area and a flat luminance distribution characteristic has been required. An object of the present invention is to provide a backlight having a VA as large as possible with respect to the outer shape.

[0006]

The present inventors have conducted various studies on the brightness distribution on the light guide plate surface near the linear light source of the backlight. As a result, the edge light type backlight has a linear light source. At the point of contact between the covered reflector and the light guide plate, the mirror surface of the reflector is on the light guide plate side, and these are arranged via an air layer, so that the light guide in the vicinity of the linear light source is obtained. It has been found that the luminance distribution on the light plate surface becomes uniform.

That is, according to the present invention, a light guide plate made of a light-transmitting material has a linear light source at least at one side end thereof, and a refractive index of the light guide plate material is provided on one surface of the light guide plate. Partially coated with a light diffusing substance having a refractive index equal to or less than
Alternatively, the same surface is provided with a light diffusing function, the surface is covered with a light diffusing reflector or sheet, and in a panel backlight in which a light diffusing plate or sheet is disposed on a light exit surface of a light guide plate, a linear light source is a specular reflector or The end of the specular reflector covering the linear light source is covered by a specular reflection film (hereinafter abbreviated as a specular reflector), and the light exit surface of the light guide plate end and the surface of the back surface thereof and the air layer are interposed therebetween. The present invention relates to a panel backlight arranged in a stacked manner. Next, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a sectional view of the embodiment. In the figure, reference numeral (1) denotes a light guide plate, which may be any substance that allows light to pass therethrough efficiently, such as a translucent natural or synthetic resin such as an acrylic resin.
(2) is a light diffusion plate which scatters the light emitted from the light guide plate surface and passes it. In the present invention, one or more light diffusion plates are used.

The light scattering substance (6) applied to the light guide plate (1) is
Paints, printing inks and the like having a refractive index equal to or smaller than the refractive index of the light guide plate material and containing a pigment for diffusing light. These are printed in dot form on the light guide plate surface by a method such as screen printing. Alternatively, it is possible to use one having a light diffusion function on the same surface, for example, one having perforations formed on the light guide plate surface.

The light diffusion reflector (3) is arranged so as to cover almost the entire surface of the light guide plate coated with a light scattering substance or having a light diffusion function. (4) is a linear light source. In a preferred embodiment, a reflector (lamp case) (5) having a gap (slit) for allowing light to enter the end of the light guide plate. The specular reflection plate or the specular reflection film (8) is covered. The light source is installed close to at least one end surface of the light guide plate so that its central axis is substantially parallel to the end surface of the light guide plate.

In the present invention, the specular reflector covering the linear light source is:
Any material can be used as long as it can reflect light specularly, and is made of a material made of silver, aluminum, platinum, nickel, chromium, or the like, preferably silver on a plastic film substrate such as polyester.
The surface of aluminum or the like is coated by vapor deposition or sputtering.

Both ends of the specular reflector covering the linear light source are shown in FIG.
As shown in (1), the light guide plate is laminated and arranged on the light exit surface at the end of the light guide plate and the front surface of the back surface via the air layer (7). The thickness of the air layer referred to here is not particularly limited, but the minimum thickness may be at least as long as the monolayer air exists.

In another preferred embodiment of the present invention, as shown in FIG. 4, a specular reflector covering the linear light source is provided with a light exit surface at the end of the light guide plate and its rear surface and an air layer (7). It is the same as that described above, but the light diffusing plate or sheet on the light emitting surface side of the light guide plate is bonded between the lamp case and its ends by a normal adhesive such as a double-sided tape. (9) Further, the light diffusion reflector or sheet on the side of the light guide plate partially covered with the light diffusion material is a mirror reflection plate or a mirror reflection film, and the mirror reflection plate or the mirror reflection film is on the light guide plate side. In this state, the ends are bonded together (10). With such a configuration, workability such as assembly is improved.

The linear light source 4 includes a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, and the like, but a fluorescent tube is preferable. It is preferable that the length of the portion is equal to the length of the end portion of the adjacent light guide plate.

In the present invention, the width of the portion to be laminated via the air layer is such that the mechanical strength when assembled as a backlight can be sufficiently maintained, and the width is preferably as small as possible.

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. In the present invention, it is preferable to adopt the following configuration.

That is, the light diffusing substance applied to the light guide plate of the present invention is, for example, formed in a dot shape, that is, a dot shape. However, the shape of the dot is not particularly limited, and may be a circle, a square, or an intersection. Any line may be formed. 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 0.5
To 3 mm, more preferably 0.8 to 2 mm, depending on the thickness of the light guide plate. Further, the coating state of the light diffusing substance is preferably 1% to 50% in the vicinity of the linear light source on the light guide plate surface, and 20% to 100% in the farthest part from the light source. It is preferable to cover the linear light source from the light source in such a manner that as the distance becomes larger, the coating rate gradually increases starting from the coating point on one side end where the linear light source is brought closer to the light source. Here, the covering ratio means the ratio of the covering area of the light scattering substance applied per unit area of the light guide plate surface.

[0018]

As described above, the present invention can be used as a backlight having a small size, a sufficient VA, a good luminance distribution, and a large power consumption-luminance conversion efficiency.

[0019]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. First, a comparative example was tested by the following method. As shown in FIG. 1, a rectangular light guide plate having a thickness of 2 mm (225 mm × 127
mm), a cold cathode fluorescent tube (4.1 mm diameter normal tube manufactured by Harrison Electric Co., Ltd.) having a diameter of 4.1 mm, which is 7 mm longer than the length of the end, is disposed at the short end of the tube. With a gap of 2 mm on the outer circumference, 2 mm
, And a silver-evaporated polyester sheet (thickness: 75 μm) was wrapped around the inner surface of the case and fixed to the end of the light guide plate with double-sided tape. The light emitted from the slit was arranged so as to enter the light guide plate from the end of the light guide plate.

On the other hand, the light-diffusing substance containing silica coated on the surface of the light guide plate is obtained by screen-printing a circular dot pattern, and the screen plate is prepared by CAD under the following conditions. Used. The plot was made so that the coverage of the light-diffusing material was 7% at the minimum point, 80% at the maximum point, and increased exponentially in the middle.

FIG. 5 shows the result of measurement of the surface luminance when the cold cathode tube was driven at a constant current by applying an alternating voltage of 30 KHz from the inverter with a luminance meter (Topcon BM-8). The vertical axis indicates the luminance (%), and the horizontal axis indicates the scanning distance of the device under test.

Next, FIG. 6 shows the result of similarly measuring the surface luminance of a backlight in which the silver-evaporated polyester sheet was fixed to the end of the light guide plate without using a double-sided tape as the structure shown in FIG.

As can be seen from both figures, the one in which the silver-evaporated polyester sheet and the end of the light guide plate are fixed via an air layer,
Even near the light source, the luminance distribution becomes uniform. As a result, the average luminance was 5% in the luminance measurement of 15 points in VA.
It turned out that it improved to the extent.

[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.

FIG. 3 is a diagram showing an arrangement of a mirror reflector covering a linear light source and an end of a light guide plate;

FIG. 4 is a diagram showing an arrangement of a mirror reflector covering a linear light source and an end of a light guide plate;

FIG. 5 is a diagram showing a luminance distribution in a comparative example.

FIG. 6 is a diagram showing a luminance distribution in the embodiment.

[Explanation of symbols]

 1: Light guide plate 2: Light diffusion plate 3: Specular reflection plate or light diffusion reflection plate 4: Linear light source 5: Reflector (lamp case) 6: Light scattering material 7: Air layer 8: Specular reflection covering linear light source Plate 9: Contact point between light diffuser and reflector 10: Contact point between specular reflection film and light diffuser

Claims (1)

(57) [Claims] At least one side end of a light guide plate made of a translucent material has a linear light source close to the light guide plate, and one surface of the light guide plate has a refractive index equal to that of the light guide plate material. Partially coated with a light-diffusing substance having a small refractive index, or provided a light-diffusing function on the same surface, covered the surface with a light-diffusing reflector or sheet, and arranged a light-diffusing plate or sheet on the light-emitting surface of the light guide plate. in panel backlight, a linear light source is covered with specular reflector or specularly reflective film, further, specular reflector also
Is a specular reflection film covered with a lamp case, and the end of the specular reflection plate or the end of the specular reflection film that covers the linear light source is laminated to the light exit surface of the light guide plate end and the surface of the back surface via an air layer. Light on the light exit surface side of the light guide plate
The diffuser or sheet is glued to the lamp case and its end
Surface of the light guide plate partially covered with the light diffusing material
The light diffusion reflector or sheet on the side is a specular reflector or specular reflector
Film and specular reflection plate or specular reflection film are light guide plate
A panel backlight that is glued and fixed at its end in the side position .