JP3776658B2 - Light guide plate, lighting device, and liquid crystal display device including the lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light guide plate used for irradiating light to a desired planar region, an illumination device using the light guide plate, and a liquid crystal display device including the illumination device.
[0002]
[Prior art]
In recent years, various liquid crystal display devices employing a front light system have been proposed as liquid crystal display devices. Unlike the transflective liquid crystal display device employing the backlight method, this reflective liquid crystal display device does not use a transflective plate that causes the light transmitted through the liquid crystal panel to be attenuated. It is known that the display screen can be brightened and the contrast can be increased, and the power consumption required for illumination can be suppressed.
[0003]
Conventionally, as an example of an illuminating device used for such a reflective liquid crystal display device, there is one described in Japanese Patent Laid-Open No. 10-188636. The one described in this publication is a combination of a light guide plate 9 made of a transparent member and a point light source 3e such as an LED lamp, as shown in FIG. The light guide plate 9 is formed with a plurality of cylindrical protrusions 90 on the back surface 9b. When light from the point light source 3e is incident on one end surface 91 as a light incident surface of the light guide plate 9, the light guide plate 9 The light travels in a certain direction while being totally reflected by the front and back surfaces 9 a and 9 b of the light guide plate 9. However, when the light reaches each projection 90 of the light guide plate 9, the light passes through each projection 90 and is emitted to the outside, and the back surface 9 b of the light guide plate 9 is a light emitting surface. Therefore, in such an illuminating device, it is possible to irradiate light on a planar region of an object 99 such as a liquid crystal panel of a liquid crystal display device. Further, since the point light source 3e is used as the light source, the component cost can be reduced as compared with the case where a so-called linear light source extending in a certain direction such as a cold cathode tube is used, and further, illumination. This is advantageous in reducing the size of the entire apparatus.
[0004]
[Problems to be solved by the invention]
However, the conventional means has the following problems.
[0005]
That is, as shown in FIG. 10, when a conventional illumination device is viewed in plan, light is emitted radially from the point light source 3e, and this light enters the light guide plate 9 while traveling in a radial shape. For this reason, the light flux density in the front region Sa of the point light source 3 e can be increased in the light guide plate 9, but the light flux density in the other regions Sb is decreased, and the light is uniformly distributed to various places in the light guide plate 9. I can't let you go around. Such unevenness of light increases as the number of point light sources 3e decreases, and becomes most noticeable when only one point light source 3e is used as shown. Conventionally, due to this, the amount of light emitted to the outside from various places on the back surface 9b of the light guide plate 9 has also become uneven. In this case, when the illumination device is used as a front light of a reflective liquid crystal panel, for example, the brightness of the liquid crystal screen varies.
[0006]
In the prior art, in the configuration shown in FIG. 10, there is also a means for emitting light to the outside only from the back surface 9 b of this region S, with a constant region S separated by an appropriate distance La from the point light source 3 e as a light emitting region. is there. In this way, the light flux density of the light traveling in the light exit area S can be made uniform to some extent by the distance between the point light source 3e and the light exit area S, and variations in the emitted light quantity can be reduced. It is. However, in order to make the above-mentioned light beam density uniform in such means, it is necessary to make the distance La quite long. Therefore, with such a means, the overall size of the light guide plate 9 becomes considerably large, and the advantage of using the point light source 3e that is smaller than the linear light source is impaired.
[0007]
The present invention has been conceived under such circumstances, and even when a small number of point light sources are used as the light source, while suppressing an increase in the size of the light guide plate, a desired surface can be obtained. The problem is to make it possible to uniformly irradiate light on the region.
[0008]
DISCLOSURE OF THE INVENTION
In order to solve the above problems, the present invention takes the following technical means.
[0009]
The light guide plate provided by the first aspect of the present invention comprises a transparent member having front and back surfaces, and a part of the surface of the transparent member is a light incident surface. The fixed region of the transparent member is a light emitting plate that emits light incident on the transparent member from the light incident surface and emits the light from either the front or back surface to the outside of the transparent member. The light incident surface is provided near the center of the first width direction perpendicular to the direction in which the front and back surfaces are separated from each other, and the light emitting region is formed in the direction in which the front and back surfaces are separated from each other and the first In the second width direction orthogonal to any of the width directions of the first light source and the second light source. The second light width direction is spaced from the light incident surface. And the first width direction A plurality of recesses are spaced apart from each other, and each of which forms a light incident into the transparent member from said light incident surface, a first light-reflecting surface capable of reflecting toward the first width direction in Alternatively, a through hole is provided, and the plurality of concave portions or the through holes are arranged so as to be sandwiched in the first width direction, and the first light reflecting surface advances from the plurality of first light reflecting surfaces in the first width direction. It is characterized by comprising a pair of second light reflecting surfaces that reflect the light that has been transmitted in the second width direction .
[0010]
In the light guide plate having such a configuration, at least part of the light incident from the light incident surface into the transparent member is sequentially reflected by the first light reflecting surface and the second light reflecting surface, thereby the first light reflecting surface. Light can travel from the two light reflecting surfaces toward the light emitting region. For this reason, even when a point light source is used as the light source and light is incident on the transparent member from the light incident surface so as to spread radially, a part of the light is converted into a light beam that does not spread radially. It can be made to advance to the desired location of the emission area. Therefore, it is possible to prevent a large variation in the amount of light reaching each part of the light emission region, as compared with the conventional means in which light travels radially from the light incident surface toward the light emission region. it can. As a result, the amount of light emitted from each part of the light emission region can be made uniform, and light can be evenly applied to a desired planar region. Further, in the present invention, it is not necessary to increase the distance between the light incident surface and the light emitting region, and the size of the light guide plate can be suppressed. In addition, the first light reflection surface and the second light reflection surface can be easily provided on the light guide plate without increasing the size of the transparent member.
[0013]
The illumination device provided by the second aspect of the present invention includes a light guide plate provided by the first aspect of the present invention, a point light source provided to face the light incident surface of the light guide plate, It is characterized by having.
[0014]
According to the illuminating device having such a configuration, the same effect as described above with respect to the light guide plate provided by the first aspect of the present invention can be obtained. It becomes possible to uniformly irradiate the planar region with light.
[0015]
A liquid crystal display device provided by the third aspect of the present invention includes a liquid crystal panel, an illumination device that irradiates light to the liquid crystal panel via a light guide plate disposed in front of the liquid crystal panel, and the liquid crystal panel A reflection plate that is provided behind and reflects light that has passed through the liquid crystal panel from the light guide plate toward the liquid crystal panel. The illumination device provided by the second aspect is used.
[0016]
According to the liquid crystal display device having such a configuration, it is possible to uniformly irradiate light on various portions of the liquid crystal panel, and it is possible to improve the image quality of the liquid crystal display image. In addition, since the lighting device can be made not to be large and bulky, it is advantageous in manufacturing the entire liquid crystal display device in a small size.
[0017]
Other features and advantages of the present invention will become more apparent from the following description of embodiments of the invention.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be specifically described with reference to the drawings.
[0019]
1 to 4 show an example of a lighting device according to the present invention. As clearly shown in FIG. 1, the illumination device A according to the present embodiment includes a light guide plate 2 and an LED light source 3 as an example of a point light source.
[0020]
The LED light source 3 is configured using, for example, a white LED. For example, an LED chip (LED bare chip) is resin-sealed, so that the whole is a surface-mounted chip light source device. It is. However, instead of this, an LED lamp type having a lead terminal can also be used. Furthermore, the LED bare chip can be used as it is, for example, by directly mounting the LED bare chip on an appropriate substrate not shown.
[0021]
The light guide plate 2 includes a substantially flat transparent member 20. However, in the present embodiment, the light guide plate 2 is configured only by the transparent member 20, and the configuration of the transparent member 20 and the configuration of the light guide plate 2 are the same. As a specific material of the transparent member 20, polycarbonate having excellent transparency or PMMA (polymethyl methacrylate (methacrylic resin)) is preferably used. The transparent member 20 has a front surface 20a, a back surface 20b, a first end surface 20c, a second end surface 20d, and a pair of side surfaces 20e, and these surfaces and a first light reflecting surface 24 and a second surface to be described later. Each of the light reflecting surfaces 25 is a smooth surface (mirror surface). In the present embodiment, the direction in which the first and second end faces 20c, 20d extend is defined as the first width direction, and the direction orthogonal thereto is defined as the second width direction.
[0022]
A part of the first end surface 20 c is a light incident surface 21, and the LED light source 3 is provided facing the light incident surface 21. The light incident surface 21 is a substantially arc-shaped concave surface that defines a concave portion 22 in which the LED light source 3 can be disposed. In this way, as clearly shown in FIG. 2, the light incident angles when the light emitted radially from the LED light source 3 reaches the light incident surface 21 are reduced, and the transparent member 20 is reduced. It is possible to facilitate the light to travel inside. Further, it is useful for increasing the light spreading angle when the light travels through the transparent member 20 after entering the light incident surface 21. However, the present invention is not limited to this, and the light incident surface 21 may be planar.
[0023]
In the vicinity of the light incident surface 21 of the transparent member 20, a plurality of first light reflecting surfaces 24 are formed by providing a plurality of recesses 23. That is, each concave portion 23 plays a role similar to a prism by being a hollow portion in which air resides. Each first light reflecting surface 24 is an inner wall surface of each recess 23. When light incident on the transparent member 20 from the light incident surface 21 is received, the first light reflecting surface 24 indicates the light as indicated by the arrow Na. 1 is a surface that totally reflects in the width direction. The plurality of recesses 23 are spaced from each other at an appropriate interval so as to reflect only a part of the light traveling from the light incident surface 24 into the transparent member 20 in the direction of the arrow Na and not the other light. Is provided. In the present embodiment, each recess 23 is in a hollow state, but the present invention is not limited to this, and each recess 23 is filled with a substance having a refractive index different from that of the transparent member 20. You can also.
[0024]
As shown in FIG. 3, each recess 23 is provided so as not to penetrate the transparent member 20, but the present invention is not limited to this. For example, as shown in FIG. The first light reflecting surface 24 may be formed by providing a hole 23 </ b> A that penetrates the transparent member 20. In this way, the area of the first light reflecting surface 24 can be increased, and the amount of reflected light in the direction of the arrow Na can be increased. Moreover, in this invention, as shown in FIG. 6, it is set as the structure which formed the 1st light reflection surface 24 by providing the transparent member 20 with the recessed part 23B of the cross-sectional triangle shape which becomes narrow as it goes to the bottom part. You can also
[0025]
As clearly shown in FIGS. 1 and 2, a pair of second light reflecting surfaces 25 as side surfaces of the transparent member 20 are formed at both ends of the first end surface 20 c. Each of the second light reflecting surfaces 25 is connected to both ends of the first end surface 20c so as to be inclined. When the light reflected from the first light reflecting surface 24 in the arrow Na direction is received, the light is reflected. Total reflection is possible so that the light travels in the direction of the arrow Nb toward the second end face 20d.
[0026]
Of each part of the transparent member 20, a region S1 closer to the second end face 20d than the formation portion of the plurality of recesses 23 is a light emitting region that allows the light to be emitted to the outside while traveling the light into the transparent member 20. It is said that. The surface 20a of the transparent member 20 in the light emission region S1 is formed in an uneven shape. More specifically, as shown in FIG. 4, the surface 20a of the transparent member 20 has a plurality of convex portions 26 that have two types of inclined surfaces 26a and 26b having different inclination directions and angles, as viewed from the side. Is formed continuously in the second width direction of the transparent member 20. Each protrusion 26 extends uniformly in the first width direction of the transparent member 20. The pitch of the plurality of convex portions 26 in the second width direction of the transparent member 20 is, for example, about a few hundreds of μm.
[0027]
Unlike the surface 20a, the entire surface of the back surface 20b of the transparent member 20 is flat, and a portion facing the uneven region of the surface 20a is a light emitting surface 27. As shown in FIG. 4, when light enters the transparent member 20 from the light incident surface 21, the light travels toward the second end surface 20d while repeating total reflection by the front surface 20a and the back surface 20b. When the light traveling in the transparent member 20 reaches the inclined surface 26a of the surface 20a, the incident angle of light with respect to the inclined surface 26a is increased by the amount that the inclined surface 26a is inclined in a predetermined direction. The incident angle is larger than a predetermined total reflection critical angle determined by the refractive index of the transparent member 20, and the possibility of total reflection is high. Therefore, the possibility that light is emitted from the surface 20a of the transparent member 20 can be reduced. On the other hand, the inclined surface 26b of the front surface 20a plays a role of reflecting received light so as to enter the back surface 20b of the transparent member 20 at a small incident angle. Therefore, the light that has reached the back surface 20b after passing through the inclined surface 26b is more likely to be transmitted through the back surface 20b as its incident angle becomes smaller than the total reflection critical angle. The light is efficiently emitted downward.
[0028]
In the illuminating device A having the above configuration, as shown in FIGS. 1 and 2, the light emitted radially from the LED light source 3 travels into the light guide plate 2 (transparent member 20) via the light incident surface 21. . Then, a part of the light reaches the plurality of recesses 23 and is sequentially totally reflected by the first light reflecting surface 24 and the second light reflecting surface 26, thereby proceeding to the light emitting region S <b> 1. In this case, each light reflected by the second light reflecting surface 26 can be made into a bundle of rays that are parallel or substantially parallel to each other. On the other hand, the light passing between the plurality of recesses 23 can be directly advanced in the light guide plate 2 as it is. For example, a part of the light traveling in the front direction of the LED light source 3 is the second light. The light can be caused to travel to the light exit region S1 as a light bundle substantially parallel to the light reflected by the reflecting surface 26.
[0029]
Thus, in this illuminating device A, the light emitted from the LED light source 3 does not travel to the light emission region S1 so that all of the light spreads radially around the LED light source 3, but the light emission region. Light can travel from a wide area on one side of S1, that is, a region where the light incident surface 21 and the second light reflecting surface 25 are formed, toward the light emitting region S1. Moreover, all or part of the light can be parallel or substantially parallel to each other. Therefore, light can be made to travel evenly or substantially uniformly to each part of the light emitting region S1, and the amount of light emitted downward from each part of the light emitting surface 27 can be made uniform. Although a plurality of recesses 23 are provided between the light incident surface 21 of the light guide plate 2 and the light emission region S1, the plurality of recesses 23 can be formed in a small size. In addition, since each first light reflecting surface 24 reflects light in the first width direction of the light guide plate 2, each first light reflecting surface 24 and each second light reflecting surface 25. Can be provided so as to overlap in the second width direction of the light guide plate 2. Therefore, the distance from the light incident surface 21 to the light emitting region S1 in the second width direction of the light guide plate 2 can be shortened, and the overall size of the light guide plate 2 can be reduced.
[0030]
FIG. 7 shows an example of a liquid crystal display device configured to include the illumination device A having the above-described configuration. The illustrated liquid crystal display device B is a reflective liquid crystal display device adopting a front light system, and the light guide plate 2 of the illumination device A described above is provided on the front surface (above) of the liquid crystal panel 1. However, a polarizing plate 4 a is provided between the light guide plate 2 and the liquid crystal panel 1. A polarizing plate 4 b and a reflecting plate 5 are provided on the back surface of the liquid crystal panel 1.
[0031]
The liquid crystal panel 1 is configured to be capable of color display, for example, and includes a liquid crystal 12 sealed in a region surrounded by a pair of glass transparent substrates 10a and 10b and a seal member 11. The transparent substrate 10a is provided with color filters 6 (6R, 6G, 6B) of R, G, and B colors in a matrix, and a black matrix 60 is provided between the color filters 6. ing. The transparent substrates 10a and 10b are also provided with alignment films 13a and 13b and transparent electrodes 14a and 14b for twisting the liquid crystal molecules. The liquid crystal panel 1 employs an active matrix driving method, and a thin film transistor (TFT) 15 for holding a voltage applied to the liquid crystal cell is disposed in one liquid crystal cell. Yes. More specifically, as clearly shown in FIG. 8, a plurality of transparent electrodes 14b (cross-hatched portions) having a constant area are provided in a matrix on one side of the transparent substrate 10b. In the gap region between the transparent electrodes 14b, a plurality of wiring portions 15a, 15b called lines or data lines are provided extending vertically and horizontally, and these wiring portions 15a, 15b and the transparent electrodes 14b are It is configured to conduct through the thin film transistor 15. The transparent electrode 14a of the transparent substrate 10a is a common electrode, and is provided over a wide area on one side of the transparent substrate 10a.
[0032]
In the liquid crystal display device B configured as described above, when the liquid crystal panel 1 is irradiated with light from the light reflecting surface 27 of the light guide plate 2 of the illumination device A via the polarizing plate 4a, the light is emitted from the liquid crystal panel 1 and the polarizing plate 4b. Is transmitted downward and then reflected upward by the reflector 5. Then, the light passes through the polarizing plate 4b and the liquid crystal panel 1 again, then passes through the polarizing plate 4a and the light guide plate 2, and is emitted to the front surface of the liquid crystal display device B. By such an action, the display of the image by the liquid crystal panel 1 can be viewed from the front through the light guide plate 2. In the case where the LED light source 3 of the illumination device A is not driven, an image display using external light can be performed. That is, when using external light, the external light is sequentially transmitted downward through the light guide plate 2, the polarizing plate 4a, the liquid crystal panel 1 and the polarizing plate 4b, and then reflected upward by the reflecting plate 5, thereby the light. However, the light passes through the respective parts in the opposite direction and is emitted to the front surface of the liquid crystal display device B. In the reflection type liquid crystal display device B, the light transmitted through the liquid crystal panel 1 downward is highly reflected by the reflection plate 5 in both cases of using light from the illumination device A and using external light. Therefore, the liquid crystal screen can be brightened as compared with a transflective liquid crystal display device using a transflective plate.
[0033]
In the above-described liquid crystal display device B, when the illumination device A is used to irradiate the liquid crystal panel 1 with light, as can be understood from the operation described above, the light emission surface 27 of the light guide plate 2 allows the liquid crystal panel 1 to Light can be uniformly irradiated to each part. Therefore, the brightness of the display image on the liquid crystal panel 1 can be prevented from being uneven and the image quality can be improved. Since only one LED light source 3 is used as the light source of the illumination device A, the power consumption can be reduced. Furthermore, since the light guide plate 2 can be formed relatively small, the overall size of the liquid crystal display device B can be prevented from becoming large.
[0034]
The present invention is not limited to the contents of the above-described embodiment, and the specific configuration of each part can be varied in design in various ways.
[0035]
For example, the specific number, size, position, formation method, and the like of the first light reflection surface and the second light reflection surface according to the present invention can be variously changed. As a light guide plate according to the present invention, as in the conventional light guide plate shown in FIG. Various forms can be used for emitting incident light to the outside. In the illumination device according to the present invention, the type of point light source is not limited, and the number of point light sources is not limited to one, and a plurality of point light sources may be used. The use of the light guide plate and the illumination device according to the present invention is not necessarily used only for the illumination application of the liquid crystal display device, and can be used for various applications for irradiating the planar area with light. The specific application is not limited. Furthermore, the liquid crystal display device according to the present invention may be either a color image display or a monochrome image display, and the type of liquid crystal and its driving method are not limited.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a lighting device according to the present invention.
FIG. 2 is a plan view of the main part of FIG.
3 is a cross-sectional view taken along the line III-III in FIG.
4 is a cross-sectional view taken along the line IV-IV in FIG.
FIG. 5 is a cross-sectional view showing another example of the present invention.
FIG. 6 is a cross-sectional view showing another example of the present invention.
FIG. 7 is a cross-sectional view showing an example of a liquid crystal display device according to the present invention.
8 is a perspective view of a main part showing a transparent substrate and a transparent electrode used in the liquid crystal display device of FIG. 7;
FIG. 9 is an explanatory diagram showing a conventional example.
FIG. 10 is an explanatory plan view showing a conventional example.
[Explanation of symbols]
A Illuminating device B Liquid crystal display device S1 Light emission area 1 Liquid crystal panel 2 Light guide plate 3 LED light source (point light source)
5 reflector 20 transparent member 20a surface (transparent member)
20b Back side (transparent material)
20c 1st end surface (of a transparent member)
21 Light incident surface 23 Recess 24 First light reflecting surface 25 Second light reflecting surface 27 Light emitting surface

Claims (3)

A transparent member having front and back surfaces is configured, and a part of the surface of the transparent member is a light incident surface, and a certain area of the transparent member is transparent from the light incident surface. A light guide plate that is a light emission region that emits light incident on the member to the outside of the transparent member from any one of the front and back surfaces while traveling,
The light incident surface is provided near the center of the first width direction perpendicular to the direction in which the front and back surfaces are separated from each other,
The light emitting region is provided at a position separated from the light incident surface in a direction in which the front and back surfaces are separated and a second width direction orthogonal to both of the first width directions.
In the second width direction, the transparent member is located between the light incident surface and the light emitting region and spaced apart from each other in the first width direction, and each of the transparent members is separated from the light incident surface. the light incident on the inside, a plurality of recesses or through-holes are provided to form a first light-reflecting surface capable of reflecting toward the first width direction,
The plurality of recesses or through holes are arranged to be sandwiched in the first width direction, and light traveling in the first width direction from the plurality of first light reflecting surfaces is the second width. A light guide plate comprising a pair of second light reflecting surfaces that reflect in a direction . An illumination device comprising: the light guide plate according to claim 1; and a point light source provided to face a light incident surface of the light guide plate. A liquid crystal panel, an illuminating device that irradiates light to the liquid crystal panel via a light guide plate disposed in front of the liquid crystal panel, and a liquid crystal panel that is provided behind the liquid crystal panel and passes through the liquid crystal panel. A reflective plate that reflects the reflected light toward the liquid crystal panel,
A liquid crystal display device, wherein the lighting device according to claim 2 is used as the lighting device.

Images