JP2003045212A - Plane illumination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plane illumination device for a front light which can be made small size and in which the image display is easily viewed without having bright lines or a Moire fringe on the light-guiding plate. SOLUTION: The illumination device comprises a light guiding plate 1 formed with micro prisms on the viewing face side, a light introducing plate 2 that is arranged along one side of the outer frame of this light guiding plate 1, and a light source 3 that is arranged opposed to one end side of this light introducing plate 2, and the light source 3 is contained in the outer frame of the light guiding plate 1, and also the direction of the pitch of the waveform of the micro prisms 1a is formed so as to be in acute angle to the optical axis of the light from the light source 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface illuminator used for a front light or the like which can be suitably used for a reflective color liquid crystal display.

[0002]

2. Description of the Related Art Recently, a color liquid crystal display has been used for a display portion of a mobile phone or the like, but a backlight is eliminated and a reflection type liquid crystal panel is used in order to reduce power consumption and reduce weight and thickness. There is a movement to cope with the combination of the front light type surface lighting device. This front-light type surface illumination device is basically the same in that the surface emission is performed similarly to the conventional backlight, and there is, for example, the one described in JP-A-11-184386. The front light type surface lighting device described in this publication has chip type LEDs arranged facing one end surface of a light guide plate for surface light emission, and light from these LEDs is incident from the end face of a light introducing plate. Then, the light reflected and refracted by the light introducing plate is made incident on the light guide plate, and the light is irradiated to the liquid crystal panel side by the micro prism formed on the light emission observation surface side.

FIG. 5 shows a conventional example having basically the same structure as the surface illumination device described in the above publication, (a) is a partially enlarged front view, and (b) is (a). It is sectional drawing by the CC line arrow.

The surface illuminating device is a combination of a light introducing plate 51 having a prism 51a formed on the lower surface side and a light guiding plate 52 which is arranged with its lower end facing the light introducing plate 51 and emits light as a front light source. . On the front surface side of the light guide plate 52, a micro prism 52a having a predetermined cross-sectional shape is formed in a wave shape so as to be parallel to the lower end. The light introducing plate 51 is covered with a metal reflection case 53, and chip LEDs 54 and 55 are arranged as light sources at positions slightly apart from both ends as shown in FIG.
Light from these chip LEDs 54, 55 is applied to the light introducing plate 51, reflected and refracted in the light introducing plate 51, and applied to the light guide plate 52. Then, in the light guide plate 52, light is emitted to the back surface side of the light guide plate 52 by refraction and reflection of light by the micro prism 52a formed on the front surface side thereof, and the liquid crystal display panel 56 arranged on the back surface side of the light guide plate 52.
The side is illuminated. A reflection plate 57 is arranged on the back surface side of the liquid crystal display panel 56 to reflect the light from the light guide plate 52 to the liquid crystal display panel 56 side, whereby the liquid crystal display panel 56 can be illuminated.

Here, it is necessary to dispose the chip LEDs 54 and 55 slightly apart from the end face of the light introducing plate 51.
This is one condition in which no bright line is generated in 2. That is, when the chip LEDs 54 and 55 come into contact with the end face of the light introducing plate 51 or are incorporated inside, the direct light of the LED chips easily enters the light guide plate, and the direct light of the LED light causes a bright line on the light guide plate 52. Occur. This bright line becomes an obstacle when viewing the image display of the liquid crystal display panel 56, and the image quality is significantly deteriorated. On the other hand, chip LEDs 54, 5
If 5 is positioned so as to be slightly separated from the end face of the light introducing plate 51, the direct light from the chip LEDs 54 and 55 is guided by the light guiding plate 52.
It becomes difficult for the light guide plate 52 to enter, and the occurrence of bright lines on the light guide plate 52 can be prevented.

[0006]

In a mobile phone or the like equipped with a front-light type surface lighting device, miniaturization is considered to be the greatest design issue, and accordingly, the surface lighting device is also downsized. At the same time, it is necessary to prevent bright lines from being generated on the light guide plate 52.

However, as shown in the example of FIG.
If the EDs 54 and 55 are not separated from the end surface of the light introducing plate 51, the generation of bright lines on the light guide plate 52 cannot be prevented. Therefore, the chip LEDs 54 and 55 are connected to the light introducing plate 51.
Since it can only be placed at a position projecting from the end face of the device, the width dimension of the surface lighting device cannot be shortened. Therefore, it is not possible to reduce the size of mobile phones and other electronic devices, and when the chip LEDs 54 and 55 are to be incorporated into the light introducing plate 51, bright lines are generated in the light guide plate 52 and the liquid crystal display panel 5 is produced.
6 images will be affected.

As described above, the conventional surface lighting device used as a front light of a liquid crystal display panel or the like has a problem that it is impossible to achieve both miniaturization and prevention of generation of bright lines.

Therefore, an object of the present invention is to provide a surface illuminating device for a front light, which can be further miniaturized and which is easy to view an image display without generation of bright lines or moire fringes on a light guide plate.

[0010]

The surface lighting device of the present invention comprises:
A light guide plate having micro prisms formed on the observation surface side, a light introduction plate arranged along one side of the outer contour of the light guide plate, and a light source unit arranged facing one end surface side of the light introduction plate. The light source unit is included in the outer shape of the light guide plate, and the waveform pitch direction of the microprisms is formed in a relationship that makes an acute angle with the optical axis of the light from the light source unit.

According to the present invention, it is possible to obtain a surface illumination device for a front light which can be made smaller and which is easy to view an image display without generating bright lines or moire fringes on the light guide plate.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a light guide plate having a micro prism formed on the observation surface side, a light introducing plate arranged along one side of the outline of the light guide plate, and the light guide plate. And a light source section arranged facing the one end surface side of the introduction plate,
While including the light source unit in the outer contour of the light guide plate,
A surface illuminating device characterized in that the waveform pitch direction of the microprisms is formed in a relationship that makes an acute angle with the optical axis of the light from the light source unit, and the surface is obtained by including the light source unit in the outer shell of the light guide plate. The illuminating device can be miniaturized as a whole, and the light from the light introducing plate is well two-dimensionally diffused by the microprisms of the light guide plate, so that no bright line is generated.

According to a second aspect of the present invention, the angle formed by the waveform pitch direction of the micro prism and the optical axis of the light from the light source section is about 22.5 °. It is a surface illuminating device described, by optimizing the angle formed by the waveform pitch direction of the micro prism and the optical axis of the light from the light source, it is possible to obtain a light emitting form without the occurrence of bright lines or moire fringes on the light guide plate. Have an effect.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing an example in which the surface lighting device of the present invention is provided as a front light of a reflection type liquid crystal display panel, FIG. 2 is a sectional view taken along the line AA of FIG. 1, and FIG. It is an enlarged front view of a part.

In the figure, the surface illuminating device is a combination of a light guide plate 1 and a light introducing plate 2, and a light source section having two LEDs (light emitting diodes) 3a, 3b facing the left end face of the light introducing plate 2. 3 is arranged. Then, as shown in FIG. 2, a liquid crystal display panel 21 and a reflection plate 22 are arranged on the back surface side of the light guide plate 1, and the light from the light guide plate 1 is reflected by the reflection plate 22.
The liquid crystal display panel 21 can be illuminated by being reflected by. That is, the light guide plate 1 functions as a front light of the liquid crystal display panel 21.

Both the light guide plate 1 and the light guide plate 2 are made of a transparent acrylic plate or the like. As shown in FIG. 3, the light guide plate 1 receives light from the light source section 3 on the lower surface side of the light guide plate 2. A prism 2a for reflecting and refracting is formed on the side. The length of the light guide plate 2 in the width direction (the left-right direction in FIG. 1) is shorter than the width dimension of the light guide plate 1, and the right end of the light guide plate 1 is aligned with the right end of the light guide plate 1, and the left end of the light guide plate 2 is aligned. The light source unit 3 is incorporated at a position recessed from the left end of the light guide plate 1. That is, the light source unit 3 is arranged at a position that fits within the width dimension of the light guide plate 1, and the width dimension of the surface lighting device is determined by the width of the light guide plate 1.

The light introducing plate 2 and the light source section 3 are covered with a reflection case 4 made of metal having a sectional shape as shown in FIG. By providing this reflection case 4, the light from the light source unit 3 and the light introducing plate 2 enter the prism 2a.
All the light reflected and refracted by the light is irradiated to the light guide plate 1 side.

A micro prism 1a for reflecting and diffusing light from the light source section 3 and the light introducing plate 2 to the liquid crystal display panel 21 side is formed on the surface side of the light guide plate 1. As shown in FIG. 4 (enlarged cross-sectional view of the main part at the position of arrow BB in FIG. 1), the micro prism 1a has, for example, an apex angle of about 135 ° and a height of a mountain. The shape is a scalene triangular wave shape with a pitch of about 7 μm and a pitch of about 300 μm.

Here, in the conventional example, the microprism is parallel to the light introduction direction of the light introduction plate 2 from the light source section 3, that is, the horizontal direction in FIG. 5, but in the present invention, the waveform pitch direction of the microprism 1a is as shown in FIG. As shown in FIG. 1, it is inclined by an angle α. That is, the waveform of the micro-prism 1a is not orthogonal to the light emitting direction of the light introducing plate 2, but is a pattern inclined obliquely to the upper right from the light source 3 side. The angle α intersecting the optical axis of the light source unit 3 of the micro prism 1a is about 22.5 °.

In the above structure, the light from the light source section 3 is introduced into the light introducing plate 2 from the left end to the right end in FIG. 1, and the prism 2a formed on the light introducing plate 2 directs the light beam in the direct upward direction in FIG. Is reflected and refracted by. On the other hand, the micro prism 1 a of the light guide plate 1 is formed so that its waveform pitch direction forms an acute angle with the optical axis of the light from the light source unit 3. Therefore, the light emitted from the light introducing plate 2 in the vertical direction of the light guide plate 1 is a direct light as compared with the case where the waveform pitch direction is parallel to the optical axis of the light from the light source unit 3 as in the conventional example. Even if it enters, it is hard to become a bright line. That is, in FIG. 1, since the light traveling directly above the light introducing plate 2 travels in a direction nearly orthogonal to the waveform pitch direction of the microprism, the light is transmitted through the light guide plate with little attenuation, but is guided directly from the LED chip. It is possible to prevent the occurrence of bright lines by utilizing the fact that the direction of travel of the light incident on the optical plate is close to being parallel to the waveform pitch direction of the microprism, and the light is likely to be attenuated.

Further, by inclining the micro-prism, it is possible to prevent interference with the dot pitch of the liquid crystal, which leads to measures against moire fringes. For this reason, when used as a front light of the liquid crystal display panel 21, the image on the liquid crystal display panel 21 is not affected because bright lines are not generated on the light guide plate 1 and moire fringes are less likely to be generated.

Further, the light emitting section 3 including the two LEDs 3a and 3b is included in the outer shell of the light guide plate 1 as shown in FIG. Therefore, the width dimension of the surface lighting device can be matched with the width of the light guide plate 1, and the overall width dimension can be shortened as compared with the conventional example shown in FIG. Therefore, the size can be reduced, and the size reduction of a mobile phone or the like can be sufficiently achieved.

[0024]

According to the present invention, since the waveform pitch direction of the micro prisms provided on the light guide plate is arranged so as to form an acute angle with the optical axis of the light from the light source section, it is easy to attenuate the direct light from the light source section. Bright lines will not enter the light guide plate,
In addition, the moire fringes generated by the interference with the dot pitch of the liquid crystal are less likely to occur, and even if the light guide plate is used as the front light of the liquid crystal display panel, the image on the liquid crystal display panel is not damaged. In addition, since the light source unit is arranged so as to be included in the outline of the light guide plate, the entire width of the surface lighting device can be made to be the size occupied by the light guide plate, which is significantly smaller than the conventional example. It will be possible.

[Brief description of drawings]

FIG. 1 is a front view showing an example in which a surface lighting device of the present invention is arranged as a front light of a liquid crystal display panel.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an enlarged front view showing a main part of a light source unit arranged so as to be included in an outer contour of a light guide plate.

FIG. 4 is a cross-sectional view of the shape of the microprisms of the light guide plate taken along the line BB of FIG. 1 as viewed in the waveform pitch direction.

FIG. 5A is an enlarged front view showing a part of a conventional surface lighting device, and FIG. 5B is a cross-sectional view taken along line CC of FIG.

[Explanation of symbols]

1 Light guide plate 1a Micro prism 2 Light introduction plate 2a prism 3 light source 3a, 3b LED 4 reflective case 21 Liquid crystal display panel 22 Reflector

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Claims (2)

[Claims] 1. A light guide plate having micro prisms formed on the observation surface side, a light introducing plate arranged along one side of the outer contour of the light guide plate, and one end surface side of the light introducing plate facing each other. And a light source part included in the outer shape of the light guide plate, and the waveform pitch direction of the microprisms is formed in a relationship that makes an acute angle with the optical axis of the light from the light source part. Characteristic surface lighting device. 2. The angle formed by the waveform pitch direction of the micro prism and the optical axis of the light from the light source unit is about 22.5.
The surface illuminator according to claim 1, wherein the surface illuminator is set at 0 °.