JP2768082B2 - 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 system, as shown in FIG. 2, a light diffusing element (a light scattering substance applied to the light guide plate surface) is formed on one wide surface of the light guide plate, and the light guide surface is other than the light entrance surface and the light exit surface. Are often arranged to cover the surface with a reflector.

In recent years, it has been desired to further improve the uniformity of the luminance of the light emitting surface. As a means for achieving this, the light diffusing ability of the light diffusing element formed on the light guide plate is reduced by one side end on the side of the linear light source. A method has been proposed in which the distance is changed so as to increase as the distance from the portion increases.

However, although this method is excellent in maintaining the uniformity of the brightness of the light emitting surface, the rate of change of the light diffusing ability on the light guide plate surface is determined by the size of the light emitting surface of the light guide plate. Each time the (length and / or width) and / or the thickness of the light guide plate is different, specific conditions need to be set, which requires a great deal of labor, cost, and time. Increases the light diffusing ability of the light diffusing element on the light guide plate (for example, in a variation range of 1% to 60% in haze value).
There is a problem that the yield must be changed in the manufacturing process when such a light diffusing element is formed on the light guide plate.

[0005]

As a result of various studies on the above-mentioned problems, the inventors of the present invention have found that, in an edge-light type backlight, a light diffusion plate is formed on a light guide plate made of a transparent material. When forming the element, the specific condition is satisfied by forming the light diffusing element uniformly at a substantially constant ratio regardless of the distance from the side end of the light guide plate on the side of the linear light source. It has been found that it is possible to provide a panel backlight having a uniform luminance distribution over the entire light emitting surface without the necessity of such formation.

[0006] Specifically, the present invention can be present in one or both side ends of the light guide plate made of a translucent material, a backlight of the edge light type to have a linear light source in proximity thereto, before
On one wide surface of the light guide plate, compared to the material of the light guide plate
A light-diffusing substance with a high refractive index and a large diffuse reflectance
By coating in the form of dots, the light guide plate having a light diffusing function such that the haze value of the wide surface of the light guide plate is substantially constant, and also to the linear light source unit at the side edge described above. The present invention relates to a panel backlight comprising a light guide plate in which a side end other than an adjacent side is covered with a light reflection plate or a light reflection film.

Next, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a perspective view of one embodiment of the present invention, and FIG.
Is a sectional view of the same. In the figure, reference numeral 1 denotes a light guide plate, which may be any substance that can efficiently transmit light, such as quartz, glass, or a translucent natural or synthetic resin such as an acrylic resin. 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, having the light diffusion function is described in FIG.
As shown in 6 of the above, whether the light diffusing substance is printed in the form of dots directly on the light guide plate surface, or the light guide plate surface is roughened,
Moreover, refers to the formation of the light diffusing function in Runado provided a large number of small holes in the light guide plate surface.

When the light guide plate is provided with a light diffusing function by using a light scattering substance, a paint, a printing ink or the like containing a pigment (for example, titania) having a large diffuse reflectance is used. These are printed in a dot shape or the like on the light guide plate surface by a method such as screen printing.

The method for forming the light diffusing substance is not limited to a dot shape. For example, a light guide plate having a low light diffusing ability (for example, a material obtained by diluting titania with a considerable amount of translucent resin) is used. The light-diffusing substance may be formed on the entire light-emitting surface. However, in the present invention, no matter which method is used to provide the light diffusing function, the head on the surface of the light guide is not affected.
It is essential that the size value be substantially constant.

In the present invention, the fact that the haze value is substantially constant means that the haze value is substantially constant over substantially the entire surface of the light guide, as in a conventional backlight. In addition, this is not an aspect in which the light diffusion function is consciously changed, for example, the light diffusion function is changed as the distance from the light source on the light guide surface increases. Therefore, the unconscious variation in the light diffusion function (haze value) that occurs when the light diffusion function is provided is:
In the present invention, it is included in the category of being substantially constant.

In the present invention, the haze value is determined by the size of the light guide plate.
0.5% -50 depending on thickness and number of light sources
% Is substantially constant at any value in the range of %. If the haze value is out of this range, the effect of the present invention is reduced. The haze value referred to here is JIS-K7105.
Means the value when measured according to

A feature of the present invention resides in that the light diffusing element having the light diffusing ability is uniformly formed on the light guide plate at a constant rate as described above. In this state, light that has entered from the end of the light guide plate is not immediately emitted from the light exit surface, but is repeatedly reflected internally within the light guide plate .
Further, the light emitted from the surface of the light guide plate other than the light exit surface is returned to the inside of the light guide plate again by the light reflecting plate covering the surface other than the light exit surface of the light guide plate, so that the light incident from the end of the light guide plate. Light is confined inside the light guide plate for a certain period of time, so that the light is made uniform, so that a backlight having a uniform luminance distribution can be obtained.

The light diffusion reflection plate 3 is disposed so as to cover substantially the entire surface of the light guide plate provided with the light diffusion element. Reference numeral 4 denotes a linear (bar-shaped) light source. In a preferred embodiment, the periphery of the light guide plate is covered with a specular reflector or light diffuse reflector 5 having a gap (slit) for allowing light to enter the end face of the light guide plate. The light guide plate is installed near the one end surface so that the central axis thereof is substantially parallel to the end surface of the light guide plate. The linear light source 4 includes a fluorescent tube,
There are a tungsten incandescent tube, an optical rod, an arrangement of LEDs, and the like, but a fluorescent tube is preferable.

Further, in order to increase the utilization efficiency of the light incident on the light guide plate and to provide a high-brightness backlight, at least the light-entering surface and the light-exiting surface of the light guide plate must be provided at least on the end of the light guide plate opposite to the light source. Needless to say, it is more preferable to cover the surface with a light reflecting plate or a light reflecting film.

In the present invention, a transmissive or transflective display panel such as a liquid crystal panel is installed on the upper surface of a light diffusing plate.

According to the present invention, the light diffusing ability of the light diffusing element formed on the light guide plate is formed such that its ratio becomes constant irrespective of the distance from the side end on the side of the linear light source, and the luminance distribution is uniform. since the backlight is obtained, relatively easy to design the light diffusion ability of the light diffusing element, and yield in the manufacturing process for forming a light diffusing element on the light guide plate is good.

[0018]

Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. First, as an example, a test was performed 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 tube (4.8 mmφ normal tube manufactured by Harrison Electric Co., Ltd.) having a diameter of 4.8 mm, which is 7 mm longer than the end of the tube, is disposed at the short end of the tube. Was covered with a cylindrical light reflector having a silver-evaporated film disposed on the inner surface 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 is formed by screen-printing a circular dot pattern at a pitch of 1.2 mm. The plot was used so that the coverage was constant at 6%. Here, the ratio of the coating (covering ratio) means the ratio of the light diffusing element formed per unit area of the light guide plate. The haze value of the light diffusing ability of the light diffusing element of the light guide was 1.4% when measured according to JIS-K7105. Furthermore, on the light emitting surface side of the light guide plate,
One light diffusion film (Tsujimoto D-204) was arranged. Then, the surface other than the light entrance surface and the light exit surface of the light guide plate is covered with a light diffusion reflector film (MT manufactured by Tsujimoto Electric Co., Ltd.).
N-W200).

FIG. 5A shows 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). 1). FIG. 5A shows that the luminance distribution is uniform.

The measurement was carried out in the same manner as in the above example, except that the coating rate of the light diffusing substance was kept constant at 7%, and the results are shown in FIG. 5B (Example 2). The haze value of the light diffusing ability of the light diffusing element of the light guide was 1.5% when measured according to JIS-K7105. FIG. 5b shows that the luminance distribution is uniform.

FIG. 5C shows the measurement results in the same manner as in the above example, except that the coating ratio of the light diffusing substance was kept constant at 9%. The haze value of the light diffusing ability of the light diffusing element of the light guide was 1.9% when measured according to JIS-K7105. FIG. 5c shows that the luminance distribution is uniform.

[0023]

Further, the coating of the light diffusing material, is shown in the measured view 5 d in the same manner as in the above example except coated so as to be constant at 100% (Comparative Example 1). The haze value of the light diffusing ability of the light diffusing element of the light guide was 91% when measured according to JIS-K7105. Figure 5 luminance distribution from d is can be seen quite heterogeneous.

Further, without coating the light diffusing substance (coverage 0
%), And the results are shown in FIG. 5e (Comparative Example 2 ). When the light diffusing ability of the light diffusing element of the light guide was measured in accordance with JIS-K7105, the haze value was 0.3%. FIG. 5e shows that the luminance is extremely low.

The following example was tested in the following manner. As shown in FIG. 3, a rectangular light guide plate having a thickness of 3 mm (235 mm
× 160mm) at both ends of the short side, 7m from the end length
A cold cathode tube (4.8 mm diameter normal tube manufactured by Harrison Electric Co., Ltd.) with a diameter of 4.8 mm long is arranged, and a light diffusion sheet is provided on the inner surface of the tube with a 3 mm slit on the outer periphery. It was covered with a laminated cylindrical light reflector, and 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 coated on the surface of the light guide plate is obtained by screen-printing a circular dot pattern at a pitch of 1.2 mm. The plot was used so that the coverage was constant at 16%. When the light diffusing ability of the light diffusing element of the light guide was measured according to JIS-K7105, the haze value was 3.4%.

Further, one light diffusion film (D-204, Tsujimoto Electric Co., Ltd.) was arranged on the light exit surface side of the light guide plate. Then, a surface other than the light entrance surface and the light exit surface of the light guide plate is covered with a light diffusion reflector film (MTN-W20 manufactured by Tsujimoto Electric Co., Ltd.).
0).

FIG. 6A shows the surface luminance measured by a luminance meter (Topcon BM-8) when the cold cathode tube was driven at a constant current by applying an alternating voltage of 30 KHz from the inverter. 4). FIG. 6A shows that the luminance distribution is uniform.

[0030]

The following example was tested in the following manner. As shown in FIG. 4, a rectangular light guide plate (86 mm ×
65mm) at both ends of the longitudinal direction, 12mm from the end length
A tube in which a long cold cathode tube of 4.1 mm diameter (4.8 mm diameter normal tube manufactured by Harrison Electric Co., Ltd.) is arranged, and the outer periphery of the tube is provided with a silver-evaporated film on the inner surface having a 3 mm slit. It was arranged so that light emitted from the slits would 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 is formed by screen printing circular dot patterns at a pitch of 1.0 mm. Under the screen plate, the light diffusing substance is formed by CAD. Drawing was performed so that the coverage was constant at 32%. The haze value of the light diffusing ability of the light diffusing element of the light guide was 45% when measured according to JIS-K7105.

Further, one light diffusion film (D-204, Tsujimoto Electric Co., Ltd.) was arranged on the light exit surface side of the light guide plate. Then, a surface other than the light entrance surface and the light exit surface of the light guide plate is covered with a light diffusion reflector film (MTN-W20 manufactured by Tsujimoto Electric Co., Ltd.).
0).

FIG. 7A shows the surface luminance measured by a luminance meter (Topcon BM-8) when the cold cathode tube was driven at a constant current by applying an alternating voltage of 30 KHz from the inverter. 5 ). FIG. 7A shows that the luminance distribution is uniform.

The measurement was carried out in the same manner as in the above example except that the coating ratio of the light diffusing substance was kept constant at 40%, and the results are shown in FIG. 7B (Comparative Example 4). The haze value of the light diffusing ability of the light diffusing element of the light guide was 56% when measured according to JIS-K7105. FIG. 7b shows that the luminance distribution is non-uniform.

[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 of a backlight according to one embodiment of the present invention.

FIG. 4 is a diagram of a backlight according to one embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a distance from a light source on a light guide plate and luminance.

FIG. 6 is a diagram showing a relationship between a distance from a light source on a light guide plate and luminance.

FIG. 7 is a diagram illustrating a relationship between a distance from a light source on a light guide plate and luminance.

FIG. 8 is a diagram showing luminance measurement points on the light guide plate.

[Explanation of symbols]

 1: Light guide plate 2: Light diffusion plate 3: Light reflection plate 4: Linear light source 5: Light reflector 6: Light scattering material 7: Distance from light source

Claims (2)

(57) [Claims] 1. A edge which on one or both of the end face portion of the light guide plate made of a translucent material, to have a linear light source in proximity thereto
It is a backlight of a gillight type, wherein one of the light guide plates is
Has a higher refractive index than the material of the light guide plate.
Light-diffusing material with high diffuse reflectance
By fabric, becomes substantially constant at any value in the range haze value in the sheet plane of the wide surface of the light guide plate is 0.5% to 50% by a value measured in accordance with JIS-K7105 Backlight for a panel consisting of a light guide plate having such a light diffusion function. 2. The panel backlight according to claim 1, wherein a light guide plate is used in which a side end of the side surface of the light guide plate other than the side close to the linear light source unit is covered with a light reflection plate or a light reflection film.