JP2004213921A - Flat illuminator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat illuminator obtaining sufficient average brightness and using a point light source eliminating uneven brightness such as an abnormally bright part on a light source side. <P>SOLUTION: Light absorbing layers 7a and 7b are provided in a part facing LED 3a of the point light source in an outer periphery part of a light emitting area Ae set on a front surface 2c emitting the light in a light guide plate 2. A front surface light reflecting film 6 is attached in a light incident area Ai between a light incident end plane 2a3 in which the LED3a is installed and the light emitting area Ae, covering the light absorbing layers 7a and 7b. Here, the distance from each incident end plane part to the light emitting area Ae in an orthogonal direction to each of the light incident end planes 2a3 and 2a4 of the light guide plate 2 is L. When each width in the orthogonal direction of the light absorbing layers 7a and 7b are W, 1/6≤W/L≤1/2 is preferable. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sidelight type planar lighting device using a point light source.
[0002]
[Prior art]
Conventionally, as a backlight for a liquid crystal display device, a light source is disposed opposite to one end surface of a rectangular light guide plate, and light emitted from this light source is guided into the light guide plate and is opposed to the back surface of the liquid crystal display device. 2. Description of the Related Art A sidelight type planar illumination device that emits a planar light from a light emitting area of a main surface is often used. In this case, as a light source, a point light source such as a light emitting diode (hereinafter, referred to as an LED) is often used in order to promote a reduction in size and thickness of a liquid crystal display module including a backlight. (For example, see Patent Document 1)
[0003]
[Patent Document 1]
JP-A-8-313902 (2 pages, FIGS. 1 and 4)
[0004]
[Problems to be solved by the invention]
In the case of the planar lighting device using the above-mentioned point light source, if the output of the LED is increased to increase the average luminance of the entire light emitting area, luminance unevenness occurs, and both improvement of luminance and reduction of luminance unevenness are realized. It was difficult. In particular, an abnormally bright portion (hereinafter, referred to as a light source side abnormally bright portion) tends to be generated at a light source side edge portion of a light emitting area, and eliminating the light source side abnormally bright portion is an urgent need for a planar lighting device using a point light source. Was an issue.
[0005]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a planar lighting device using a point light source in which a sufficient average luminance is obtained and the occurrence of luminance unevenness such as a light source side abnormal bright portion is eliminated.
[0006]
[Means for Solving the Problems]
The spread illuminating apparatus according to the present invention includes a point light source that radially emits light, and light emitted from the point light source, which is incident from an end face opposed to the point light source and is divided and set on one main surface. A planar illumination device comprising a light guide plate that emits light from an area in a planar manner, wherein an outer peripheral portion of the light emitting area of the light guide plate, at least in a portion facing the point light source, a light absorbing layer having a predetermined width. It is characterized by being arranged.
[0007]
According to the planar lighting device of the present invention configured as described above, a light absorption layer is provided over a predetermined width at least in a portion facing the point light source at an outer peripheral portion of the light emitting area of the light guide plate. Therefore, light reflected on the outer peripheral portion of the light emitting area, which is a main factor for generating the light source side abnormal bright portion, is absorbed by the light absorbing layer, and the occurrence of the light source side abnormal bright portion can be prevented. In addition, since the light absorbing layer is selectively arranged only on the outer peripheral portion of the light emitting area, excessive light absorption by the light absorbing layer is suppressed, and the necessary average luminance in the light emitting area is ensured while the luminance of the light source side abnormal bright portion and the like is maintained. Good planar irradiation light without unevenness can be obtained.
[0008]
In the spread illuminating device of the present invention, as described in claim 2, a light incident area on a light emitting surface from an end face of the light guide plate where light enters to the light emitting area, at least the It is preferable that a light reflecting film is applied to an area where the light absorbing layer is not applied, whereby light loss in a light input area of the light guide plate is reduced, and the average luminance in the light emitting area is further improved. I do.
[0009]
In this case, as described in claim 3, the distance from the incident end face to the light emitting area in a direction perpendicular to the incident end face of the light guide plate facing the point light source is L, and the light absorbing layer is provided. When the width in the perpendicular direction is W,
1/6 ≦ W / L ≦ 1/2
It is thus preferable to obtain better surface irradiation light in which the required average luminance in the light emitting area is sufficiently ensured and the luminance unevenness such as the abnormal light portion on the light source side is surely eliminated.
[0010]
In the spread illuminating apparatus according to the present invention, the light absorbing layer is preferably a black ink layer provided by printing, thereby providing a sufficient light absorbing ability. The light absorbing layer can be easily laminated with a small thickness, and the light reflecting layer can be laminated almost flat on the light absorbing layer. In addition, since the light absorbing layer can be easily laminated to an optimum layer thickness and shape according to the shape of the light emitting area and the light guide plate, a planar lighting device having a required average luminance and having no luminance unevenness is inexpensive regardless of the shape. Can be manufactured.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
A backlight device for a liquid crystal display device as one embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a plan view showing a state in which the backlight device of the present example is housed in a storage case 1. In the storage case 1 having a rectangular planar outer shape, a light guide plate storage room Rg, which is surrounded on three sides by side walls 1a to 1c, and a light source storage room Rs in which a point light source and its attached members are stored are defined. .
[0012]
The light guide plate 2 is housed in the light guide plate housing room Rg. The light guide plate 2 is formed of a transparent acrylic resin or the like, and is housed in such a state that three flat end surfaces thereof are along the inner surfaces of the flat side walls 1a to 1c of the light guide plate housing chamber Rg. The end 2 a of the light guide plate 2 in the remaining direction is formed as a light entrance for introducing light into the light guide plate 2.
[0013]
That is, in this example, two projections 2a1 and 2a2 are formed in the upper writing light end 2a of the light guide plate in line symmetry with respect to the center line of the end 2a. LEDs 3a and 3b as point light sources are installed on the tip surfaces 2a3 and 2a4 of these convex portions 2a1 and 2a2, respectively.
[0014]
FIG. 2 is a cross-sectional view taken along line AA of FIG. 1 and shows a configuration of a light source side portion of the backlight device. On the rear surface 2b of the light guide plate 2, which is placed on the bottom 1d of the storage case 1, fine irregularities (not shown) are formed, and the light that propagates through the light guide plate becomes a light emitting surface. The light is reflected toward the front surface 2c, and emitted from the front surface 2c toward the rear surface of the liquid crystal display element (not shown) to be irradiated. On the rear surface 2b, a rear light reflection film 4 is adhered. The rear light reflecting film 4 is provided to reflect light propagating in the light guide plate 2, which is not reflected by the uneven surface of the rear surface 2 b and is going to be emitted outside, into the light guide plate 2. The rear light reflection film 4 of this example is formed by depositing silver on a PET (polyethylene terephthalate) film and has a high light reflectance. The rear light reflection film 4 has an unillustrated light incident side end bonded to the light guide plate rear surface 2b with a double-sided tape.
[0015]
A light emitting area Ae is sectioned on the front surface 2c of the light guide plate 2. The light-emitting area Ae is set so as to correspond to the display area of the liquid crystal display element to be irradiated by the backlight device. In this example, substantially the entire area of the front surface 2c excluding the light-entering section described above is a light-emitting area Ae. Is set to In this case, the diffusion film 5 is applied to the light emitting area Ae, and the front light reflection film 6 is applied to the light incident area Ai, which is the remaining area of the front surface 2c. That is, the light emitting area Ae is defined by the boundary between the diffusion film 5 and the front light reflection film 6.
[0016]
The diffusion film 5 attached to the light emitting area Ae is provided for diffusing light emitted from the light emitting area Ae to make the luminance distribution uniform. The light-incident side end of the diffusion film 5 is adhered to the front surface 2c of the light guide plate by a double-sided tape, similarly to the rear light reflection film 4.
[0017]
The front light reflection film 6 attached to the light entrance area Ai reflects light entering from the convex end surfaces 2a2 and 2a4 of the light entrance end 2a of the light guide plate 2 and going to exit from the front surface 2c to the inside. It is provided for. The front light reflection film 6 of this example is also formed of a silver-evaporated PET film of the same material as the rear light reflection film 4.
[0018]
Light absorbing layers 7a and 7b are disposed on the light-emitting area Ae side end of the surface (reflection surface) 6a of the front light reflection film 6 on the side of the light guide plate front surface 2c. As shown in FIG. 1, the light absorbing layers 7a and 7b are selectively provided at respective portions facing the LEDs 3a and 3b of the point light source. That is, the light absorbing layers 7a and 7b are arranged in a band shape along the edge of the light emitting area Ae at the outer peripheral portion of the light emitting area Ae and at each of the opposing portions with the LEDs 3a and 3b of the point light source. Note that the light absorbing layer of the present invention may be provided at least in the outer peripheral portion of the light emitting area Ae at a portion facing the point light source. Therefore, when two point light sources are used as in this example, the light absorbing layer One light-absorbing layer may be provided in a continuous range including each facing portion of the point light source.
[0019]
Here, in a direction perpendicular to each of the incident end faces 2a3, 2a4 of the light guide plate 2, a distance from each of the incident end faces to the light emitting area Ae is L, and each width of the light absorbing layers 7a, 7b in the perpendicular direction is W. If
1/6 ≦ W / L ≦ 1/2
Is preferred. This is because, when W / L is larger than 1/2, the ratio of incident light absorbed by the light absorbing layer becomes too large, and it becomes impossible to secure the average luminance required for the lighting device. This is because when the value is smaller than 6, the light source side abnormal bright portion in the light emitting area Ae starts to occur.
[0020]
Further, the light absorbing layers 7a and 7b of this example are formed by printing using black ink. By setting the color of the light absorbing layers 7a and 7b to black as in this example, the necessary light absorbing ability can be easily secured. However, the color of the light absorbing layers 7a and 7b is not limited to black and may be other colors such as gray. Or the like. That is, the light absorbing layer of the present invention absorbs at least half of the light incident thereon.
[0021]
Also, by forming the light absorbing layer by printing as in this example, the light absorbing layer can be easily laminated to an optimum layer thickness and shape according to the specifications of the lighting device such as the light emitting area and the shape of the light guide plate. That is, the light absorbing layers 7a and 7b of the present example have an extremely thin layer thickness of about 10 μm and are selectively disposed at the portion facing the point light source as described above. Can also be easily laminated by a printing method.
[0022]
The front light reflecting film 6 on which the light absorbing layers 7a and 7b are laminated as described above is bonded to the front surface 2c at the light incident end 2a of the light guide plate 2 by the adhesive layer 8 applied to the reflecting surface 6a. Have been. As shown in FIG. 3 in which part Q of FIG. 2 is enlarged, the adhesive layer 8 has a thickness t2 such that the thickness t1 can sufficiently cover the light absorbing layers 7a and 7b as thin as about 10 μm. Are stacked relatively thickly at about 27 μm. As described above, by forming the light absorbing layers 7a and 7b thinly and forming the adhesive layer 8 sufficiently thicker, the front light reflecting film 6 can be formed with the light absorbing plate 7a and 7b interposed therebetween. It becomes possible to adhere flatly to the front surface 2c.
[0023]
In FIG. 2, two refraction films 9 and 10 are superposed on the diffusion film 5 in the light emitting area Ae. These refraction films 9 and 10 are provided for condensing the light emitted from the light guide plate 2 diffused by the diffusion film 5 toward the liquid crystal display element to be irradiated. The refraction films 9 and 10 of this example are prism sheets in which a plurality of ridges (not shown) are formed in parallel on one main surface, and the surfaces on which the ridges are provided are directed toward the light guide plate. It is installed so that the extending direction of each ridge is orthogonal. The light source side end of the front refraction film 10 extends over a predetermined length, and the extension 10a covers the end of the front light reflection film 6 on the light emitting area Ae side. In this case, the thickness of each member is set such that the thickness of the rear refraction film 9 on the diffusion film 5 is equal to the total thickness of the front light reflection film 6 and the adhesive layer 8. Thus, the whole of the front refraction film 10 including the extended portion 10a can be set flat.
[0024]
As described above, LEDs 3a and 3b as point light sources are provided on the incident end surfaces 2a3 and 2a4 of the light incident end 2a of the light guide plate 2 (see FIG. 1). The LEDs 3a and 3b are installed such that the light emitting surfaces 3a1 and 3b1 are in close contact with the incident end surfaces 2a3 and 2a4, respectively. The LEDs 3 a and 3 b are mounted on a flexible printed circuit board 11, and one end of the flexible printed circuit board 11 is fixed to a rear surface of the light guide plate 2 via a rear light reflection film 4. Then, the flexible printed circuit board 11 is placed on the bottom surface of the light source accommodating chamber Rs formed to be substantially deeper by the thickness than the light guide plate accommodating chamber Rg. Thereby, the LEDs 3a, 3b and the flexible printed circuit board 11 are arranged such that the flexible printed circuit board 11 extends along the bottom surface of the light source member accommodating chamber Rs and the light emitting surfaces 3a1, 3b1 of the LEDs 3a, 3b are connected to the light guide plate, as shown in the drawing. 2 are kept in close contact with the incident end faces 2a3 and 2a4.
[0025]
In the planar lighting device configured as described above, of the light emitted from the LEDs 3a and 3b, a light ray that enters the front surface 2c or the rear surface 2b of the light guide plate 2 at an angle θ smaller than the total reflection angle (hereinafter, referred to as “light”). For example, the light ray a) travels toward the light emitting area Ae side while being regularly reflected by the reflection surfaces of the front and rear light reflection films 6 and 4, and enters the light absorption layers 7a and 7b. Is absorbed. Here, if the light absorbing layers 7a and 7b are not provided, the light ray b is regularly reflected by the rear light reflecting film 4 and then emitted from the light source side edge of the light emitting area Ae, and the light source side abnormal bright part May cause it to occur. However, according to the spread illuminating device of the present invention, most of the specularly reflected light rays such as the light rays b, which cause the light source side abnormal bright part, enter the light absorbing layers 7a and 7b and are absorbed. The generation of the abnormal light portion on the light source side is prevented.
[0026]
In addition, since the installation width W of the light absorbing layers 7a and 7b is limited to the appropriate range as described above, the specular reflected light other than the specular reflected light that causes the above-described light source side abnormal bright portion, such as the light ray b, Since the light is not absorbed by the light absorbing layers 7a and 7b and travels to the corresponding area of the light emitting area Ae and is emitted as irradiation light, it sufficiently contributes to the improvement of the average brightness of the irradiation light.
[0027]
Then, the light totally reflected by the front surface 2c or the rear surface 2b of the light guide plate 2, such as the light ray C, travels to the area corresponding to the light emitting area Ae regardless of the presence or absence of the light absorbing layers 7a and 7b, and is irradiated from the light emitting area Ae. It is emitted as light. The regular reflection light beam used as the above-mentioned irradiation light is combined with the total reflection light beam, so that the necessary luminance in the planar irradiation light is sufficiently ensured. Further, with this planar irradiation light, as described above, the occurrence of the abnormal light portion on the light source side is prevented and the light diffusion effect of the diffusion film 5 is exerted, so that there is no luminance unevenness.
[0028]
Note that the present invention is not limited to the above embodiment.
For example, instead of forming the light absorbing layer by ink printing, a black film may be attached to the light guide plate at the same position as the light absorbing layers 7a and 7b in the above embodiment.
[0029]
Further, in the above-described embodiment, the front light reflection film 6 having the mirror reflection surface is disposed on the outer peripheral portion to partition the light emitting area Ae. However, the invention is not limited to this. It may be provided instead of the front light reflection film 6.
[0030]
【The invention's effect】
The spread illuminating apparatus of the present invention has a point light source that radially emits light, and light emitted from the point light source is incident on an end face facing the point light source and is sectioned on one main surface. A planar lighting device comprising a light guide plate that emits light from a light emitting area in a planar manner, wherein the light absorbing plate has a light absorbing layer over a predetermined width at least at a portion facing the point light source at an outer peripheral portion of the light emitting area. Since it is provided, the light reflected on the outer peripheral portion of the light emitting area, which is a main factor for generating the light source side abnormal bright portion, is absorbed by the light absorbing layer, thereby preventing the light source side abnormal bright portion from occurring. be able to. In addition, since the light absorbing layer is selectively disposed only on the outer peripheral portion of the light emitting area, excessive light absorption due to the provision of the light absorbing layer over a wide area is suppressed, and the light source side abnormalities are secured while maintaining the necessary average luminance in the light emitting area. Good planar irradiation light without luminance unevenness such as a bright portion can be obtained.
[0031]
In the spread illuminating apparatus according to the present invention, at least the light absorption area is provided at a light incident area on a light emitting surface from an end face of the light guide plate where light is incident to the light emitting area. By applying the light reflecting film to the area where the layer is not applied, light loss in the light entering area of the light guide plate is reduced, and the average luminance in the light emitting area can be further improved.
[0032]
In this case, as described in claim 3, the distance from the incident end face to the light emitting area in a direction perpendicular to the incident end face of the light guide plate facing the point light source is L, and the light absorbing layer is provided. When the width in the perpendicular direction is W, W / L is
1/6 ≦ W / L ≦ 1/2
As a result, the required average luminance in the light emitting area is sufficiently ensured, and the better planar irradiation light in which the luminance unevenness such as the abnormal light portion on the light source side is surely eliminated can be obtained.
[0033]
In the spread illuminating apparatus of the present invention, as described in claim 4, the light absorbing layer is a black ink layer provided by printing, so that the light absorbing layer having a sufficient light absorbing ability is provided. A thin layer can be easily formed with a thin layer, and a light reflecting layer can be stacked substantially flat on the light absorbing layer. In addition, since the light absorbing layer can be easily laminated to an optimum layer thickness and shape according to the shape of the light emitting area and the light guide plate, a planar lighting device having a required average luminance and having no luminance unevenness is inexpensive regardless of the shape. Can be manufactured.
[Brief description of the drawings]
FIG. 1 is a plan view showing a backlight device for a liquid crystal display element as one embodiment of the present invention.
FIG. 2 is a sectional view taken along line AA of the backlight device of FIG.
FIG. 3 is a partially enlarged sectional view showing a portion Q in FIG. 2 in an enlarged manner.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Storage case 2 ... Light guide plate 3a, 3b ... LED (light emitting diode)
4 Back light reflection film 5 Diffusion film 6 Front light reflection films 7a and 7b Light absorption layer 8 Adhesive layer 9 Back refraction film 10 Front refraction film 11 Flexible wiring circuit board

Claims (4)

A point light source that emits light radially,
A light guide plate for causing light emitted from the point light source to enter from an end face facing the point light source and emitting the light in a planar manner from a light emitting area defined on one main surface. hand,
A spread illuminating device, wherein a light absorbing layer having a predetermined width is disposed at least at a portion facing the point light source at an outer peripheral portion of the light emitting area of the light guide plate. A light-reflecting film is applied to at least an area where the light-absorbing layer is not applied, which is a light-entering area on a light-emitting surface from the incident end surface of the light guide plate where light enters to the light-emitting area. The spread illuminating apparatus according to claim 1, wherein: When the distance from the incident end face to the light emitting area in the direction perpendicular to the incident end face of the light guide plate facing the point light source is L, and the width of the light absorbing layer in the perpendicular direction is W,
1/6 ≦ W / L ≦ 1/2
The planar illumination device according to claim 2, wherein: 4. The spread illuminating apparatus according to claim 1, wherein the light absorption layer is a black ink layer provided by printing.

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