JP2001093317A - Backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a problem such that a light guide plate has poor emission efficiency when using a light source having high directivity. SOLUTION: An end face facing an incident plane is tilted to the direction of approaching backside facing an emission plane, whereby a light reaching the end face is reflected to the center of the backside and effectively emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for illuminating a display panel of a transmission type liquid crystal display device from the back.

[0002]

2. Description of the Related Art An example of a conventional backlight device is shown in FIG.

[0003] In the drawing, reference numeral 11 denotes a light guide plate having excellent translucency such as an acrylic resin; 21, a tubular light source; It is a reflector for taking in. At a certain angle into the light guide plate 11, the light incident from the incident surface 111 is:
The light travels in the light guide plate 11 toward the front end surface 114 while reflecting between the lower back surface 112 and the upper emission surface 113. The tip surface 114 is opposed to the incident surface 111 in parallel and perpendicular to the back surface 112.

[0004] In the light guide plate 11, a light scattering material 41 is provided on the back surface 112 so as to reflect light traveling in the light guide plate 11 to the exit surface 113 side. The light scattering members 41 are arranged with a certain distribution so as to emit light almost uniformly to the exit surface of the light guide plate 11.
The light scattering material 41 is obtained by screen printing white ink. Numeral 511 denotes light rays that are reflected by the light scattering material 41 while traveling in the light guide plate 11 and exit from the exit surface 113.

[0005] A reflection sheet 61 made of a high-reflectance white synthetic resin film is provided on the rear surface 112 side and the front end surface 114 side of the light guide plate 11. The diffusion sheet 71 is disposed on the light guide plate 11 on the light exit surface 113 side, and the liquid crystal display panel 81 is disposed on the diffusion sheet 71.

In this figure, a light beam 512 horizontally incident from the tubular light source 21 is mainly vertically reflected on the tip end surface 114 side and returns to the tubular light source 21 side, so that it is emitted to the liquid crystal display panel 81 side. There are few components to do.

As an improvement of FIG. 4, a technique having the configuration shown in FIG. 5 is disclosed in Japanese Utility Model Laid-Open Publication No. 6-16943.

In FIG. 5, 12 is a light guide plate, 22 is a tubular light source, 32 is a reflector, 121 is an entrance surface, 122 is a back surface, 123 is an exit surface, 124 is a tip surface, and 42 is a light guide plate 1.
This is a light scattering material provided on the back surface 122 side so as to reflect from the emission surface 123 side light traveling in the interior 2 while reflecting between the back surface 122 and the emission surface 123. The reflection sheet 62 is provided on the back surface 122 side and the front end surface 124 side of the light guide plate 12. Outgoing surface 12 on light guide plate 12
A diffusion sheet 72 is disposed on the third side, and a liquid crystal display panel 82 is further disposed thereon.

In FIG. 5, the front end face 124 faces the incident face 121 but is not parallel, but is inclined at an angle. Further, the front end surface 124 is not perpendicular to the back surface 122 but is inclined at an angle.
The angle of the inclination is such that the light beam 513 traveling rightward horizontally in the light guide plate 12 is reflected in the direction of the upper display panel 82 on the exit surface 123 side of the light guide plate 12. The inward normal of the light guide plate 12 of the tip end surface 124 is the emission surface 1
23, ie, the inner surface of the distal end surface 124 is open upward. In this case, the angle between the front end surface 124 and the back surface 122 is an obtuse angle.

In the configuration shown in FIG. 5, the light is reflected toward the liquid crystal display panel 82, which is in front of the light guide plate 12, by tilting the front end surface 124 in the direction shown in the drawing.
2 is characterized by improving the luminance. Further, the light scattering material 42 on the inclined distal end surface 124 prevents this portion from being locally brightened.

[0011]

By the way, in recent years, there has been a demand for a thinner and lighter backlight device as a whole of a liquid crystal display device has been made thinner and lighter. Have a problem. One is that an inverter circuit is necessary for driving the fluorescent tube at an AC high voltage, and the other is that there is a certain limit to the narrowing of the tube due to the mechanical strength of the fluorescent tube. As a light source replacing the fluorescent tube, a white LED is promising. The white LED element has a feature that it can be made into a small chip, and does not require an inverter circuit, and can be driven by a DC at a relatively low voltage.

However, white LED elements usually have strong directivity. FIG. 6 shows an example of a characteristic curve diagram representing the directional characteristics of the white LED element. In the figure, the curve is farthest from the origin 0 in the 0 ° direction and the direction perpendicular to the element surface, indicating that the light intensity is the strongest. Also, 90
°, the origin becomes 0 as approaching the element surface and the horizontal direction.
And the curve become closer, indicating that the light intensity becomes weaker. In FIG. 7, a white LE is used instead of the tubular light source 22 of FIG.
The case where D231 is used is shown. The drawing is the same as FIG. 5 except for the light source and the light beam.

When the white LED 231 having a high directivity is used, a component such as a light ray 521 that travels horizontally in the light guide plate 12 increases. Therefore, although the light is scattered by the light scattering material 42, the light traveling forward near the distal end surface 124 is
More. That is, it becomes locally bright. Normally, light guide plate 1
Since the brightness is likely to be non-uniform in the vicinity of the end face of No. 2, the effective display area of the liquid crystal display panel 82 is slightly smaller than the size of the light guide plate 12 so as to avoid the influence of that portion. Therefore, when a lot of light is emitted near the front end surface 124,
Light that leaks outside the effective display area, for example, the light beam 522, increases, and the light output efficiency of the light guide plate 12 decreases.

[0014] Also, in a configuration in which the front end surface 114 is parallel to the incident surface 111 as shown in FIG.
When a light source having high directivity is used, the light is mainly vertically reflected on the tip end surface 114 side and returns to the light source side, so that a component emitted to the liquid crystal display panel 81 side is small, and the emission efficiency is poor.

An object of the present invention is to solve the above-mentioned problems of the prior art, that is, to solve the problem that, when a light source having high directivity is used, the emission efficiency of the light guide plate is poor.

[0016]

Means for Solving the Problems To solve the above problems, the present invention has the following features. The invention according to claim 1 is characterized in that an angle formed between a front surface facing an incident surface on which light from a light source having a spatial intensity distribution is incident and a back surface facing the emitting surface is acute. And

The invention according to claims 2 and 3 is characterized in that a reflection film is formed on the above-mentioned front end surface, or a member on which the reflection film is formed is arranged substantially parallel to the front end surface. The invention described in claim 4 is characterized in that the angle formed between the front end surface and the back surface is an angle larger than 45 degrees and smaller than 90 degrees.

Further, the invention according to claim 5 is characterized in that the front end surface is a curved surface, and the entire curved surface is inclined in a direction approaching the back surface.

The invention according to claims 6 and 7 is characterized in that a reflection film is formed on the end surface of the curved surface, or a member having the reflection film is arranged substantially parallel to the end surface. I do.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a backlight device according to a first embodiment of the present invention.

In the figure, reference numeral 13 denotes a light guide plate having excellent translucency such as acrylic resin, 232 denotes a white LED having high directivity,
Reference numeral 33 denotes a reflector for efficiently taking in light other than directly entering the light guide plate 13 from the white LED 232 into the light guide plate 13. The tip surface 134 faces the incident surface 131 and is inclined with respect to the back surface 132 as shown in the figure.
On the back surface 132, light traveling in the light guide plate 13
The light scattering material 43 is provided so as to reflect the light toward the emission surface 133 side. The light scattering members 43 are arranged with a certain distribution so as to emit light almost uniformly to the exit surface of the light guide plate 13. The light scattering material 43 is obtained by screen printing white ink.

On the back side 132 of the light guide plate 13, a reflection sheet 63 is provided. This reflection sheet 63
Is a high reflectance white synthetic resin film. Exit surface 1
A diffusion sheet 73 is disposed on the 33 side, and a liquid crystal display panel 83 is disposed further thereon.

As compared with the conventional structure, in FIG.
34 has a different inclination direction with respect to the back surface 132. The inclination angle is such that the light beam 531 traveling rightward horizontally in the light guide plate 13 is reflected on the rear surface 132 side of the light guide plate 13 and the surface side facing the display panel 83. In other words, the normal to the light guide plate 13 inward of the front end surface 134 is inclined in a direction intersecting the rear surface 132, that is, in a direction in which the inner surface of the front end surface 134 faces the rear surface 132 in the figure. in this case,
The angle formed by the tip surface 134 and the back surface 132 is an acute angle.

By inclining the front end surface 134 toward the rear surface 132, the light beam 531 traveling horizontally rightward in the light guide plate 13 can be reflected in the light guide plate 13 toward a region near the center of the rear surface 132. In this area, the emission surface 13
By further reflecting the light toward the third side, light such as the light ray 532 can be increased, and the luminance in the effective display range near the center of the liquid crystal display panel 83 can be increased.

Further, the total reflection film 44 is provided on the front end surface 134 to prevent light scattering near the front end surface 134.

In this way, it is possible to prevent the light from leaking at the ends, collect the light at the center, and increase the light output efficiency of the light guide plate.

FIG. 2 is a detailed explanatory diagram of FIG. Thickness t
In the light guide plate 130, the front end surface 1341 is inclined at an angle θ from the vertical with respect to the back surface 1321 as shown in the figure. The light beam 5331 has a height t within the light guide plate 130.
/ 2 is horizontal and parallel to the back surface 1321 toward the front end surface 1341. Then, the tip surface 1341
The light is totally reflected by the total reflection film 440 provided on the substrate. The incident light beam 5331 and the reflected light beam 5332 form an angle of 2θ. Further, at a horizontal distance L from the point of reflection, the light is reflected by the light scattering material 431 on the back surface 1321, and the light exit surface 1
Go to 331 side. Here, the relationship of tan (2θ) = (t / 2) / L holds. Therefore, by adjusting the inclination angle θ, the horizontal distance L can be set, and the position where the reflected light beam 5332 is guided to the back surface 1321 can be appropriately determined.

In the figure, when the inclination angle θ is 45 °, 2θ becomes 90 ° and L becomes 0, so that light is not reflected from the center of the light guide plate 130. Therefore, the inclination angle θ needs to be smaller than 45 °. At this time, the angle α between the front end surface 1341 and the back surface 1321 is
The angle is larger than 45 ° and smaller than 90 °.

In the above description, the total reflection film is provided directly on the front end surface of the light guide plate. However, a similar effect can be obtained by disposing a member having the total reflection film outside the front end surface and parallel to the front end surface. Can be.

FIG. 3 is a diagram showing a configuration of a backlight device according to a second embodiment of the present invention. In the figure, 14 is a light guide plate, 233 is a white LED, 34 is a reflector, 141 is an incident surface of the light guide plate 14, 142 is a back surface,
143 is an emission surface, and 144 is a tip surface. A diffusion sheet 74 is disposed on the light guide plate 14 on the light exit surface 143 side, and a liquid crystal display panel 84 is disposed thereon. Light guide plate 14
The reflection sheet 64 is provided on the back surface 142 side of. On the back surface 142 side, a plurality of V-shaped grooves 14
21 are provided. The V-grooves 1421 have a triangular cross section perpendicular to the plane of the paper, and are parallel to each other at appropriate intervals. Reference numeral 540 denotes a light beam that collides with the V-groove 1421 while traveling in the light guide plate 14, changes its direction, and exits from the exit surface 143 side.

Unlike FIG. 1, the front end surface 144 is
It has a curved surface that is convex toward the side, and
A reflection film 441 is provided. Thereby, the tip surface 1
The light that has reached the 44 side is dispersed and reflected on the back surface 142 side, and can be broadly emitted on the emission surface 143 side as shown by light rays 541, 542, and 543 in the figure. This increases the luminance of a wide area of the liquid crystal display panel 84.

The present invention is not limited to the above embodiment. For example, in the light guide plate of the above embodiment, the concave shape on the back surface may be a conical hole instead of the V-groove.

[0034]

As described above, according to the present invention, when a light source having a high directivity is used, the emission efficiency of the light guide plate can be increased, and the luminance of the backlight device can be increased. In addition, if the luminance is the same as the conventional one, the power consumption of the light source can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating details of the embodiment.

FIG. 3 is a diagram showing a second embodiment.

FIG. 4 is a diagram showing a conventional technique.

FIG. 5 is a diagram showing another conventional technique.

FIG. 6 is a diagram illustrating an example of a directional characteristic of a white LED.

FIG. 7 is a diagram showing a conventional example using a white LED.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 Light guide plate 131 Incident surface of light guide plate 132 Back surface of light guide plate 133 Outgoing surface of light guide plate 134 Tip surface of light guide plate 130 Light guide plate 1321 Back surface of light guide plate 1331 Exit surface of light guide plate 1341 Tip surface of light guide plate 14 Light guide plate 141 Incident surface of light guide plate 142 Back surface of light guide plate 1421 V-groove on back surface of light guide plate 143 Exit surface of light guide plate 144 Tip surface of light guide plate 232 White LED 33 Reflector 43 Light scattering material 44 Total reflection film 440 Total reflection film 441 Total reflection Film 83 LCD panel

 ──────────────────────────────────────────────────の Continued on the front page (72) Toshio Ito 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Masato Yamada 2-5-5 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Yasuko Teragaki 2-5-5 Keihanhondori, Moriguchi-shi, Osaka F-term in Sanyo Electric Co., Ltd. 2H038 AA55 BA06 2H091 FA23Z FB02 FC17 FD06 LA03 LA17 LA18

Claims (7)

[Claims] 1. A light source having a spatial distribution of the intensity of emitted light, an incident surface on one side close to the light source, an exit surface on one side substantially orthogonal to the incident surface, and facing the exit surface. A backlight device comprising: a light guide plate having a front surface as a back surface and a side surface opposite to the incident surface as a front surface, wherein the angle between the front surface and the back surface is an acute angle. . 2. The backlight device according to claim 1, wherein a reflection film is formed on the front end surface. 3. The backlight device according to claim 1, wherein a member having a reflection film formed on the light guide plate side is disposed substantially in parallel with the front end surface. 4. An angle formed between the front end surface and the back surface,
The backlight device according to any one of claims 1 to 3, wherein the angle is larger than 45 degrees and smaller than 90 degrees. 5. A light source having a spatial distribution of the intensity of emitted light, an incident surface on one side close to the light source, an exit surface on one side substantially orthogonal to the incident surface, and facing the exit surface. In a backlight device including a light guide plate having a surface as a back surface and a side surface opposite to an incident surface as a front surface, the front surface is a curved surface, and is inclined in a direction approaching the rear surface. Backlight device. 6. The backlight device according to claim 5, wherein a reflection film is formed on the front end surface. 7. The backlight device according to claim 5, wherein a member having a reflection film formed on the light guide plate side is disposed substantially parallel to the front end surface.