JP3608412B2 - Planar light emitter, front light, liquid crystal device, and light guide plate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a planar light emitter, a front light , a liquid crystal device, and a light guide plate , and more particularly to a structure of a planar light emitter suitable for use as a front light of a liquid crystal display device.
[0002]
[Prior art]
Conventionally, reflective liquid crystal display panels with low power consumption have been used for portable devices and the like, but there is a problem that the display cannot be seen in a dark place such as at night. On the other hand, the transmissive liquid crystal display panel is equipped with a backlight, so the display can be seen even in the dark. However, the backlight consumes a lot of power. There is a problem that it is difficult to see the display.
[0003]
In order to solve the above problems, a light guide plate is installed on the front surface of the reflective liquid crystal display panel, and light from a light source such as a cold cathode tube arranged near the end of the light guide plate is introduced into the light guide plate. A liquid crystal display device having a front light which is a planar light emitter that can be viewed in a dark place by irradiating light from the surface of the light guide plate toward the liquid crystal display panel has been proposed. . In a liquid crystal display device equipped with a front light, the liquid crystal display panel can be visually recognized through a light guide plate in the daytime, so that it can be used as a normal reflection type liquid crystal display panel. The display can be made visible.
[0004]
[Problems to be solved by the invention]
By the way, in the above conventional front light, a linear light source such as a cold cathode tube is used to introduce light almost uniformly into the light guide plate and illuminate the liquid crystal display panel. In such a small device, it may be impossible to use a cold cathode tube from the viewpoint of cost and volume, and there is a problem that power consumption is too large in the cold cathode tube.
[0005]
For this reason, for example, it is conceivable that the device can be reduced in cost, size, and power consumption by using an inexpensive and low power consumption point light source such as a light emitting diode. However, in this case, since the light emitting diode is a point light source and has directivity in the light emission direction, the light emission to the light guide plate becomes non-uniform, resulting in a liquid crystal display. There is a problem that the light intensity distribution (in-plane distribution) of the illumination light to the panel is biased and the visibility in a dark place is hindered.
[0006]
In the case of providing a front light 10 using a light guide plate 12 formed by arranging convex portions having a stripe shape in a plan view composed of a gentle slope 12a and a steep slope 12b and a triangular cross section as shown in FIG. In order to increase the effective brightness of the display at the time of illumination, it is often set to be viewed from the F direction shown in the figure slightly inclined from the normal of the plate surface of the light guide plate 12. When the linear light source is used, a number of bright lines are visually recognized as horizontal lines as shown in FIG. 6 due to light leaking from the steep slope 12b. In this case, when a point light source 13 such as a light-emitting diode is used as the light source, unlike the case of a linear light source such as a cold cathode tube, short bright lines are formed along the light guide direction from the light source as shown in FIG. Therefore, the visibility is further deteriorated as compared with the case of a linear light source.
[0007]
Therefore, the present invention solves the above-described problems, and an object thereof is to provide a planar light-emitting body such as a front light that does not deteriorate in visibility even when a point light source such as a light-emitting diode is used.
[0008]
[Means for Solving the Problems]
The means taken by the present invention to solve the above problems is a light guide plate having translucency configured to emit light propagating through the inside in a predetermined direction along the plate surface from the plate surface. And a light source that is disposed near the end of the light guide plate and that introduces light into the light guide plate in a different direction from the predetermined direction, and is different from a side of the light guide plate on which the light source is disposed. A planar light-emitting body, characterized in that a reflection layer that reflects light propagating in the light guide plate in the other direction toward the predetermined direction in the light guide plate is provided at an end portion. .
[0009]
According to this means, the light introduced from the light source into the light guide plate travels through the light guide plate, is reflected by the reflection plate, and travels in a predetermined direction, and is emitted from the plate surface of the light guide plate. Since the optical path length from the light source to the emission position can be increased, the light source has directivity, the shape of the light source is a point light source, or the light introduction distribution from the light source to the light guide plate is biased In some cases, the in-plane uniformity of emitted light can be improved. In addition, when used as a front light arranged on the front side of various display bodies, it is possible to alleviate the uneven distribution of leakage light that leaks to the front side, so that visibility can be improved. The other direction may be, for example, a direction along the plate surface of the light guide plate and a direction opposite to the predetermined direction.
[0010]
Moreover , it is preferable to arrange | position a light-scattering layer between the said light-guide plate and the said reflection layer. Since the light scattering layer is disposed in front of the reflecting surface, the light is scattered before and after the reflection, so that the in-plane uniformity of the emitted light can be further improved.
[0011]
The light source may have directivity in the direction of light emission in the light guide plate, and the light source may be a point light source. In these cases, the present invention is particularly effective.
[0012]
The light source is preferably a light emitting diode. By using a light emitting diode, it is possible to reduce the size and weight of a device incorporating a planar light emitter, and to reduce the manufacturing cost.
[0013]
Further, the light guide plate is desirably above the light traveling in the other direction before reaching the reflective layer is configured so as not to release from the plate surface. The light guide plate is formed so as not to emit light traveling in the other direction among the light introduced from the light source, so that the optical path length of the light emitted from the plate surface of the light guide plate is all the distance from the light source to the reflection layer Since it can take above, the in-plane uniformity of emitted light can be improved.
[0014]
Moreover , it is preferable that a convex portion or a concave portion having a slope for emitting light from the plate surface is formed on the surface of the light guide plate. Furthermore, this said convex portion or concave portion, is formed so as to face the other direction as viewed from the inside of the light guide plate, and a gentle slope having a gentle angle with respect to the plate surface of the light guide plate, said guide It is desirable to provide a steep slope formed so as to face the predetermined direction when viewed from the inside of the optical plate and having a steep angle with respect to the plate surface of the light guide plate. In this case, the surface is preferably composed of only a gentle slope and a steep slope, and is a convex portion having a triangular cross section and a stripe shape in plan view. At this time, when the convex portion is formed on the plate surface opposite to the light emitting direction, and the predetermined direction and the other direction are opposite to each other, the steep slope is the convex portion. On the light source side, the gentle slope is formed on the side opposite to the light source.
[0015]
On the other hand , it is desirable that the light source and the light guide plate are configured as a front light disposed on the front side of the panel surface of the liquid crystal device. Such front lights include those described below.
[0016]
A light guide plate having translucency configured to emit light propagating through the inside in a predetermined direction along the plate surface, and the light guide plate disposed near an end of the light guide plate A light source for introducing light toward the other direction different from the predetermined direction, and the light guide plate is configured to be seen through, at an end portion different from the side where the light source is disposed in the light guide plate. The front light is characterized in that a reflection layer is provided that reflects light propagating in the light guide plate in the other direction toward the predetermined direction in the light guide plate.
[0017]
According to this means, light introduced from the light source into the light guide plate propagates in the light guide plate in a predetermined direction, is reflected by the reflective layer, propagates in the other direction, and is emitted from the plate surface of the light guide plate. . Therefore, since the optical path length from the light source to the light guide plate before being emitted can be made large, even if there is directivity in the light emission direction of the light source, this can be mitigated. It is possible to improve the in-plane uniformity and reduce the bias of leaked light, and to reduce the deterioration of visibility due to the directivity of the light source.
[0018]
Moreover , it is preferable to arrange | position a light-scattering layer in front of the reflective surface of the said reflective layer. According to this front light, since the light scattered by the light scattering layer away from the light source is emitted from the light guide plate, even if the light emission direction of the light source has directivity, the same effect as a light source with less directivity is obtained. Thus, visibility can be further improved. In particular, compared with a conventional front light structure in which a scattering plate is disposed on the incident surface of the light guide plate, a large directivity mitigating action can be expected in a region near the light source. In addition, this relaxation action allows the use of a light scattering plate having a relatively low scattering intensity, thereby reducing light loss.
[0019]
The front light is characterized in that the light source has directivity in the light emission direction in the light guide plate.
[0020]
The present invention is particularly effective when the light source is a point light source, and the light source is preferably a light emitting diode. Further, it is particularly effective that the light guide plate is configured not to emit light traveling in the other direction from the plate surface before reaching the reflection layer.
[0021]
A reflective liquid crystal device having the above-described front lights on the front side of the liquid crystal panel can be configured. In this case, good visibility can be obtained in a bright place or a dark place.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the planar light emitter and the liquid crystal device according to the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view showing a schematic structure of a planar light emitter 20 according to the present invention. In the present embodiment, a point light source 21 such as a light emitting diode, a light guide plate 22 having translucency made of acrylic resin or polycarbonate resin formed by injection molding, and the point light source 21 in the light guide plate 22 It is composed of a transmissive light scattering plate 23 attached to the end surface 22d opposite to the arranged end surface 22c, and a reflection plate 24 attached to the surface of the light scattering plate 23. The light scattering plate 23 and the reflection plate 24 may be held by another member such as a case body only by contacting the end surface 22d of the light guide plate 22, and may be physically or on the end surface 22d. It may be formed by a chemical method.
[0023]
On the surface of the light guide plate 22, a large number of stripe-shaped convex portions each including a gentle slope 22 a and a steep slope 22 b are formed in parallel. Here, in FIG. 1, the number of convex portions is limited to three, and the shape of the convex portions is schematically enlarged and drawn so that the shape of the convex portions can be easily understood. The light propagating along the plate surface of the light guide plate 22 is totally reflected by the high light refractive index of the light guide plate and does not leak to the outside even if it hits the back surface or the gentle slope 22a of the light guide plate, and the change in the propagation direction is small. The light again propagates along the plate surface, but when the incident angle to the steep slope 22b is smaller than the critical angle among the light impinging on the steep slope 22b, it is emitted as leaked light 22B to the surface side of the light guide plate 22 and steep slope 22b. When the incident angle to the is larger than the critical angle, total reflection is performed. When this reflected light reaches the back surface of the light guide plate 22, if the incident angle on the back surface is larger than the critical angle, it is totally reflected and propagates through the light guide plate again. On the other hand, when the incident angle to the back surface is larger than the critical angle, it is not reflected and is emitted downward from the back surface of the light guide plate 22 as illumination light 22A. In this case, as the steep slope 22b is steeper, the average emission direction of the illumination light 22A approaches the normal direction of the plate surface of the light guide plate 22, so that the illumination efficiency is improved. At the same time, the incident angle to the steep slope 22b is the critical angle. Since the proportion of light that becomes smaller increases, leakage light 22B that is emitted from the steep slope 22b without being totally reflected also increases. As the amount of the leaked light 22B increases, the visibility becomes worse. Therefore, the steep slope 22b is set to an appropriate inclination angle, for example, about 30 to 50. Note that the light emission structure for emitting light from the back surface of the light guide plate 22 in the light guide plate 22 is not limited to the convex portion.
[0024]
In the present embodiment, the light emitted from the point light source 21 once travels to the left side of the drawing along the plate surface of the light guide plate. Here, part of the light hits the gentle slope 22 a and the back surface, but most of the light is totally reflected by the gentle slope 22 a and the back surface and propagates while remaining in the light guide plate 22. The inclination angle of the gentle slope 22a is such that the light emitted from the point light source 21 and hits the gentle slope 22a does not leak to the outside without being totally reflected, but viewed in the light traveling direction of the gentle slope 22a. The length of the hypotenuse in the cross section at the time is increased so that the formation pitch of the convex portions is increased and the number and area of the steep slopes 22b are not reduced.
[0025]
Eventually, when the light reaches the left end face 22d of the light guide plate 22, the light passes through the light scattering plate 23 and is reflected by the reflection plate 24, and proceeds inside the light guide plate 22 to the right side of the drawing. Then, since the steep slope 22b is formed on the surface side in the traveling direction of the reflected light, most of the light hitting the steep slope 22b becomes illumination light 22A emitted from the back surface of the light guide plate 22 due to total reflection, and partly Passes through the steep slope 22b and becomes leaked light 22B.
[0026]
FIG. 2 shows a schematic configuration of a liquid crystal display device provided with the planar light emitter 20 as a front light. This liquid crystal display device is configured by disposing a light guide plate 22 of a planar light emitter 20 on the front side of a reflective liquid crystal display panel 30 having a reflective layer 31. When the outside is bright, the planar light-emitting body 20 transmits external light to guide the light into the reflective liquid crystal display panel 30, and the display area of the reflective liquid crystal display panel 30 is reflected by the light reflected by the reflective layer 31. The display content formed on V can be visually recognized. On the other hand, when the outside is dark, the illumination light 22A can be irradiated from the lower surface of the light guide plate 22 toward the reflective liquid crystal display panel 30 by turning on the point light source 21, and therefore reflected by the illumination light 22A. The display contents formed on the liquid crystal display panel 30 can be visually recognized.
[0027]
FIG. 3 is a partial cross-sectional plan view of the planar light emitter 20 described above. The three point light sources 21 are arranged substantially evenly along one end face 22 c of the light guide plate 22. Each point light source 21 has a light emitting characteristic having directivity so that the illuminance in the front direction is the highest as shown by the arrows in the figure, and the illuminance decreases rapidly as it deviates from the front direction. Accordingly, when illumination is performed using light traveling along the plate surface of the light guide plate 12 from the light source 11 as in the conventional front light shown in FIG. In the display area V shown in FIG. 4, sufficient in-plane uniformity of illumination light cannot be obtained in the light source vicinity area Va near the point light source 21 of the light guide plate 22. In this case, a method of obtaining sufficient in-plane uniformity of illumination light even in the light source vicinity region Va by disposing light by arranging a light scattering plate or the like between the point light source 21 and the light guide plate 22. There is also. When the scattering plate is disposed on the incident surface of the light guide plate, the scattered light on the scattering plate surface is equivalent to the linear light source by arranging the point light source 21 at a location sufficiently away from the light guide plate to ensure a sufficient optical path length. Therefore, in-plane uniformity can be obtained. At this time, the scattering plate may be a light scattering plate having a low scattering intensity, but there is a structural problem because it is necessary to provide a sufficient distance between the light guide plate and the point light source. Therefore, if the same effect is to be obtained in the state where the point light source 21 is adjacent to the light guide plate, it is necessary to use a light scattering plate having a high scattering intensity. Therefore, light loss is large and it is difficult to obtain sufficient brightness. On the contrary, there is a problem that the power consumption becomes too large to obtain sufficient brightness.
[0028]
In this embodiment, as shown in FIG. 3, when light is introduced from the point light source 21 into the light guide plate 22, most of the light arrives at the opposite end 22d, and the light formed at the opposite end 22d. The light after being scattered and reflected by the scattering plate 23 and the reflecting plate 24 is irradiated downward as the illumination light 22A from the steep slope 22b. Since the optical path length from the point light source 21 to the light scattering plate 23 can be made long, even if the scattering intensity of the light scattering plate 23 is small, the scattered light by the light scattering plate 23 becomes the same light as the linear light source. It is possible to obtain sufficient in-plane uniformity of the illumination light 22A, and to reduce the bias of the leakage light 22B as shown in FIG.
[0029]
Here, if the directivity of the point light source 21 is not so strong, a certain degree of in-plane uniformity of illumination light and uniformity of leakage light can be secured without the light scattering layer 23. Further, instead of using the light scattering plate 23, the surface (reflection surface) of the reflection plate 24 is formed into a rough surface, or another material is selectively attached to the surface of the reflection plate 24 to form fine irregularities. For example, the light scattering effect may be obtained. Further, fine irregularities may be formed on the end face portion 22d of the light guide plate to form a light scattering portion.
[0030]
In this embodiment, when the density or shape of the light emitting structure such as the convex portion is gradually changed along the light traveling direction in order to make the in-plane distribution of the illumination light uniform as a planar light emitter The in-plane uniformity of the illumination light 22A is obtained by changing the density and shape of the light emitting structure along the traveling direction of reflected light reflected from the reflecting surface of the reflecting layer such as the plate 24 (that is, the right direction in FIG. 1). Can increase the sex.
[0031]
【The invention's effect】
As described above, according to the present invention, the light introduced from the light source into the light guide plate travels through the light guide plate, is reflected by the reflection plate, and travels in a predetermined direction. Since the light source is emitted from the light source, the optical path length from the light source to the emission position can be increased, so that the light source has directivity, the shape of the light source is a point light source, or the light from the light source to the light guide plate In the case where the introduction distribution is biased, the in-plane uniformity of the emitted light can be improved. In addition, when used as a front light arranged on the front side of various display bodies, it is possible to alleviate the uneven distribution of leakage light that leaks to the front side, so that visibility can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of an embodiment of a planar light emitter (front light) according to the present invention.
FIG. 2 is a schematic configuration diagram showing a schematic configuration of a liquid crystal display device using the embodiment.
FIG. 3 is a partial cross-sectional schematic plan view for illustrating a planar light distribution state according to the embodiment;
FIG. 4 is a schematic plan view showing a schematic plan configuration of a liquid crystal display device using the same embodiment.
FIG. 5 is a schematic cross-sectional view for illustrating a schematic structure of a conventional front light.
FIG. 6 is an external explanatory diagram for illustrating an external appearance when a linear light source is used as a light source in a conventional front light.
FIG. 7 is an external explanatory diagram for showing an external appearance when a point light source is used as a light source in a conventional front light.
[Explanation of symbols]
20 planar light emitter 21 point light source 22 light guide plate 22a gentle slope 22b steep slope 22c, 22d end face 22A illumination light 22B leaked light 23 light scattering plate 24 reflector 30 liquid crystal display panel 31 reflective layer

Claims (10)

A light guide plate having translucency configured to emit light propagating through the plate surface in a predetermined direction along the plate surface, and the light guide plate disposed near an end of the light guide plate A light source that introduces light in a different direction different from the predetermined direction, and in the light guide plate toward the other direction at an end different from the side where the light source is disposed in the light guide plate. In the planar light-emitting body provided with a reflective layer that reflects the propagated light toward the predetermined direction in the light guide plate.
The planar light emitter, wherein the light guide plate is configured not to emit light traveling in the other direction from the plate surface before reaching the reflection layer. The planar light-emitting body according to claim 1, wherein the light source has directivity in a light emission direction in the light guide plate. 2. The planar light emitter according to claim 1, wherein the light source is a point light source. 4. The planar light emitter according to claim 2, wherein the light source is a light emitting diode. A light guide plate having translucency configured to emit light propagating through the plate surface in a predetermined direction along the plate surface, and the light guide plate disposed near an end of the light guide plate A light source for introducing light toward the other direction different from the predetermined direction, the light guide plate is configured to be seen through, and at an end portion different from the side where the light source is disposed in the light guide plate In the front light provided with a reflective layer that reflects the light propagating in the light guide plate toward the other direction, generally in the predetermined direction in the light guide plate,
The light guide plate is configured so that light traveling in the other direction is not emitted from the plate surface before reaching the reflection layer. 6. The front light according to claim 5, wherein the light source has directivity in a light emission direction in the light guide plate. 6. The front light according to claim 5, wherein the light source is a point light source. 8. The front light according to claim 6, wherein the light source is a light emitting diode. A liquid crystal device comprising the front light according to any one of claims 5 to 8 on a front side of a liquid crystal panel. It has translucency and is configured to emit light propagating through the inside in a predetermined direction along the plate surface from the plate surface,
A reflection layer that reflects light propagating through the interior toward the other direction generally reflects toward the predetermined direction at an end where the light propagating through the interior toward the other direction is different from the predetermined direction. In the light guide plate provided,
A light guide plate configured to prevent light traveling in the other direction from being emitted from the plate surface before reaching the reflection layer.

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