JP2008262766A - Light guide plate, plane light source device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate which can make a plane light source device which can be manufactured by a simple manufacturing process and has a sufficient luminance of emitted light and has a sufficient color reproducing area and a sufficient and uniform luminance of the emitted light when used in a plane light source device of a side light system. <P>SOLUTION: The light guide pllate 11 is used for a plane light source device 10 of a side light system, and either of side surfaces has an inclined surface 11c so that a width of a light emitting surface 11a is narrower than a width of a rear surface 11b and when t is for a distance between the light emitting surface 11a and the rear surface 11b and L is for a width of the rear surface 11b, an angle θ of a corner between the inclined surface 11c and a straight line α perpendicular to the light emitting surface 11a is close to tan<SP>-1</SP>(t/L) in a cross section in a horizontal direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light guide plate used in a sidelight type surface light source device. The present invention also relates to a surface light source device and a liquid crystal display device having such a light guide plate.

  A schematic configuration of a general sidelight type surface light source device will be described with reference to FIG. FIG. 5 is a horizontal sectional view showing a schematic configuration of a general side light type surface light source device 90.

  The surface light source device 90 includes a light emitting surface 91a, a light guide plate 91 made of acrylic resin, and a back surface 91b on which a light diffusing pattern is formed by blasting or the like, and a side surface 91c; A light source 92 such as a cold-cathode tube or an LED, which is arranged in the vicinity of 91c so that the light emitting portion is parallel to the side surface 91c and the center of the light emitting portion corresponds to the midpoint of the side surface 91c; A reflecting sheet 93 that reflects light; and a light emitting direction correcting element 94 that is formed in the vicinity of the light emitting surface 91a of the light guide plate 91 and that is configured by a prism element or the like. .

  In the surface light source device 90, the light emitted from the light source 92 is incident on the side surface 91 c of the light guide plate 91 after being reflected from the light source 92 directly or by the inner surface of a reflector (not shown) that covers the periphery of the light source 92. The light exit direction is corrected by the light exit direction correcting element 94 after propagating through the interior of 91 and exiting from the light exit surface 91a. Further, the light emitted to the back surface 91b side of the light guide plate 91 is also diffused by a pattern having a light diffusing action formed on the back surface 91b of the light guide plate 91 or reflected by the reflection sheet 93. The light propagates through the light guide plate 91 again.

  The surface light source device 90 has an advantage that power consumption can be reduced as compared with a direct surface light source device. However, the surface light source device 90 has a problem that the luminance of the emitted light becomes insufficient because the central light I from the light source 92 passes through the light guide plate 91 almost as it is. In addition, since the brightness of the emitted light rapidly decreases as the distance from the light source 92 increases, there is a problem that the brightness of the emitted light becomes insufficiently uniform.

  For this reason, in the sidelight type surface light source device, various inventions have been made for the purpose of improving and uniforming the luminance of emitted light, and examples thereof can be seen in Patent Documents 1 to 3.

  In the invention of Patent Document 1, in the side light type surface light source device, the shape of the light guide plate is changed to a wedge shape, thereby improving and uniforming the luminance of the emitted light.

  In the side light type surface light source device using a line light source, the invention of Patent Document 2 is arranged by shifting the line light source to the light emitting surface side and tilting the side surface of the light guide plate on the side where the line light source is disposed. Thus, the brightness of the emitted light is improved.

In the side light type surface light source device, the invention of Patent Literature 3 forms a downward inclined surface on the outer surface of the light guide plate, forms an upward inclined surface on the inner surface of the frame that supports the light guide plate, and faces down the light guide plate. By adopting a configuration in which the inclined surface and the upward inclined surface of the frame are in surface contact with each other, the luminance of the emitted light is made uniform.
Japanese Patent Laid-Open No. 7-036037 JP-A-5-341133 Japanese Patent Laid-Open No. 2004-199930

  However, the surface light source device of Patent Document 1 has a problem in that the production process is complicated because the entire mold needs to be fine and precise in order to produce a wedge-shaped light guide plate.

  In addition, in the surface light source device of Patent Document 2, the luminance of the emitted light varies greatly depending on the shape of the side surface of the light guide plate on the side where the line light source is arranged. There is a problem of becoming. Further, since the line light source is used, there is a problem that the color reproduction range becomes insufficient.

  Further, in the surface light source device of Patent Document 3, most of the light from the light source is emitted directly from the light exit surface without being reflected by the reflector disposed near the back surface of the light guide plate. Thus, there is a problem that the luminance cannot be adjusted sufficiently, and the uniformity of the luminance of the emitted light becomes insufficient.

  In view of the above problems, the present invention can be manufactured by a simple production process, and when used in a side light type surface light source device, the luminance of the emitted light is sufficient, and the color reproduction range. It is an object of the present invention to provide a light guide plate that can provide a surface light source device that is sufficient and the brightness of emitted light is sufficiently uniform. Another object of the present invention is to provide a surface light source device and a liquid crystal display device having such a light guide plate.

In the present invention, the light guide plate is a light guide plate used in a side light type surface light source device, and one side surface is an inclined surface so that the width of the light emitting surface is narrower than the width of the back surface, The distance between the light emitting surface and the back surface is t, the width of the back surface is L, and the angle formed by the inclined surface and a straight line perpendicular to the light emitting surface in a horizontal section. Is characterized by being in the vicinity of tan ^-1 (t / L).

In the present invention, the light guide plate is a light guide plate used in a side light type surface light source device, and one side surface is an inclined surface so that the width of the light emitting surface is narrower than the width of the back surface, The distance between the light emitting surface and the back surface is t, the width of the back surface is L, and the angle formed by the inclined surface and a straight line perpendicular to the light emitting surface in a horizontal section. Is characterized by being tan ^-1 (t / L) or more.

  In the present invention, in the light guide plate having the above-described configuration, it is desirable that an angle formed by a side surface facing the inclined surface and the light emitting surface is approximately 90 degrees in a horizontal section.

  In the present invention, a surface light source device includes the light guide plate having the above-described configuration, and a light source disposed in the vicinity of the inclined surface of the light guide plate so that a light emitting unit is parallel to the inclined surface. And

  In the present invention, in the surface light source device having the above configuration, the light source is preferably an LED in which light emitting elements are arranged in a straight line.

  In the present invention, a liquid crystal display device includes a liquid crystal panel and a surface light source device having the above-described configuration disposed on the back surface of the liquid crystal panel.

In the light guide plate of the present invention, one side surface is an inclined surface so that the width of the light emitting surface is narrower than the width of the back surface, the distance between the light emitting surface and the back surface is t, and the width of the back surface Is L, and the angle between the inclined surface and the straight line perpendicular to the light exit surface in the horizontal cross section is in the vicinity of tan ⁻¹ (t / L). Therefore, in the surface light source device having the light guide plate, when the light source is arranged in the vicinity of the inclined surface of the light guide plate so that the light emitting portion is parallel to the inclined surface, the light guide plate is centered from the light source. Light is received near the middle point in the width direction of the back surface, and the central light from the light source does not pass through the light guide plate almost as it is, so that the loss of light can be suppressed as much as possible. The brightness can be improved. Further, in the surface light source device having the light guide plate, when the light source is arranged in the vicinity of the inclined surface of the light guide plate and the light emitting portion is arranged in parallel with the inclined surface, the light source is formed on the back surface of the light guide plate. The center light from the light source is made as vertical as possible from the back surface of the light guide plate by adjusting the pattern having the light diffusing action and the characteristics of the reflection sheet or the reflection plate arranged near the back surface of the light guide plate. When the light is emitted, light can be used near the center of the surface light source device, and the luminance of the emitted light can be made sufficiently uniform.

In the light guide plate of the present invention, one side surface is an inclined surface so that the width of the light emitting surface is narrower than the width of the back surface, and the distance between the light emitting surface and the back surface is t. In the horizontal section, the angle between the inclined surface and the straight line perpendicular to the light exit surface is tan ⁻¹ (t / L) or more. Therefore, in the surface light source device having the light guide plate, when the light source is arranged in the vicinity of the inclined surface of the light guide plate so that the light emitting portion is parallel to the inclined surface, the light guide plate is centered from the light source. Light is received between the end point on the light source side on the back surface and the center point in the width direction on the back surface, and the central light from the light source does not pass through the light guide plate almost as it is. Loss can be suppressed as much as possible, and the brightness of the emitted light can be improved. Further, in the surface light source device having the light guide plate, when the light source is arranged in the vicinity of the inclined surface of the light guide plate and the light emitting portion is arranged in parallel with the inclined surface, the light source is formed on the back surface of the light guide plate. A pattern having a light diffusing action, a reflective sheet or reflector disposed in the vicinity of the back surface of the light guide plate, and a light exit direction correcting element disposed in the vicinity of the light exit surface of the light guide plate or the light exit surface of the light guide plate The center light from the light source is emitted as vertically as possible from the vicinity of the center of the surface light source device as much as possible by adjusting the characteristics of the pattern having the effect of correcting the light emission direction formed on the surface light source device. Light can be used in the vicinity of the center, and the brightness of the emitted light can be made sufficiently uniform.

  In addition, the light guide plate of the present invention can be manufactured by either processing only the inclined surface in a limited manner or by providing an angle to the side surface so as to have an inclined surface during injection formation. . Therefore, it is possible to manufacture with a simple production process as compared with a wedge-shaped light guide plate that requires fine and precise machining of the entire mold.

  In the light guide plate of the present invention, one side surface is inclined so that the width of the light exit surface is narrower than the width of the back surface. Therefore, in the surface light source device having the light guide plate, when the light source is arranged in the vicinity of the inclined surface of the light guide plate and the light emitting unit is parallel to the inclined surface, the light source is on the back side of the light guide plate. Since the light source is inclined, even when the light source is a point light source, there is no problem that the light does not sufficiently reach the vicinity of the light source side end point on the rear surface of the light guide plate. That is, in the general sidelight type surface light source device 90 shown in FIG. 5, when the light source 92 is a point light source, there is a problem in the vicinity of the end point A on the light source 92 side of the back surface 91b of the light guide plate 91. Therefore, it is possible to suppress the generation of the non-light region at the end of the emitted light due to the fact that the light does not reach the surface sufficiently. For this reason, in the surface light source device having the light guide plate of the present invention, as a light source, an LED in which light emitting elements are arranged in a straight line is arranged near the inclined surface of the light guide plate so that the light emitting portion is parallel to the inclined surface. By doing so, a surface light source device is obtained in which the color reproduction range is wide and the luminance of the emitted light is sufficiently uniform.

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

(First embodiment)
FIG. 1 is a horizontal sectional view showing a schematic configuration of a sidelight type surface light source device 10 according to a first embodiment of the present invention. The surface light source device 10 includes a light emitting surface 11a, a back surface 11b on which a light diffusing pattern is formed by blasting or the like, and one of the light emitting surfaces 11a so that the width of the light emitting surface 11a is smaller than the width of the back surface 11b. A light guide plate 11 made of acrylic resin having an inclined surface 11c formed on a side surface; in the vicinity of the inclined surface 11c of the light guide plate 11, the light emitting portion is parallel to the inclined surface 11c, and the center of the light emitting portion is an inclined surface A light source 12 such as a cold-cathode tube or an LED disposed so as to correspond to the midpoint of 11c; a reflection sheet 13 that reflects light in the vicinity of the back surface 11b of the light guide plate 11; And a light emission direction correcting element 14 composed of a prism element or the like disposed in the vicinity of the emission surface 11a. Here, the side surface of the light guide plate 11 facing the inclined surface 11c is formed perpendicular to the light emitting surface 11a.

  In the surface light source device 10, the light emitted from the light source 12 is incident on the inclined surface 11 c of the light guide plate 11 after being reflected from the light source 12 directly or by the inner surface of a reflector (not shown) covering the periphery of the light source 12. After propagating through the inside of the optical plate 11 and exiting from the light exit surface 11a, the exit direction is corrected by the light exit direction correcting element 14. Further, the light emitted to the back surface 11b side of the light guide plate 11 is also diffused by a pattern having a light diffusing action formed on the back surface 11b of the light guide plate 11 or reflected by the reflection sheet 13. The light propagates again through the light guide plate 11.

Here, in the light guide plate 11, the distance between the light emitting surface 11a and the back surface 11b is t, and the width of the back surface 11b (the end point A on the light source 12 side of the back surface 11b and the end point B on the opposite side of the light source 12). The distance θ between the inclined surface 11c and the straight line α perpendicular to the light emitting surface 11a is in the vicinity of tan ⁻¹ (t / L).

  In the surface light source device 10 configured as described above, the light guide plate 11 receives the central light I from the light source 12 in the vicinity of the center point C in the width direction of the back surface 11b, and the central light I from the light source 12 is received. However, since the light does not pass through the light guide plate 11 as it is, the loss of light can be suppressed as much as possible, and the luminance of the emitted light can be improved. Further, in the surface light source device 10, by adjusting the pattern of the light diffusing action formed on the back surface 11 b of the light guide plate 11 and the characteristics of the reflection sheet 13 disposed in the vicinity of the back surface 11 b of the light guide plate 11, When the center light I from 12 is emitted as vertically as possible from the back surface 11b of the light guide plate 11, the light can be used in the vicinity of the center of the surface light source device 10, and the brightness of the emitted light is sufficiently uniformed. be able to.

  Further, the light guide plate 11 can be manufactured by either processing the inclined surface 11c only in a limited manner, or by providing an angle to the side surface so as to have the inclined surface 11c at the time of injection formation. . Therefore, it is possible to manufacture with a simple production process as compared with a wedge-shaped light guide plate that requires fine and precise machining of the entire mold.

  Moreover, in the surface light source device 10, since the light source 12 is inclined and arranged toward the back surface 11b side of the light guide plate 11, the light source 12 on the back surface 11b of the light guide plate 11 can be used even when the light source 12 is a point light source. There is no problem that light does not reach the vicinity of the end point A on the side. That is, in the general sidelight type surface light source device 90 shown in FIG. 5, when the light source 92 is a point light source, there is a problem in the vicinity of the end point A on the light source 92 side of the back surface 91b of the light guide plate 91. Therefore, it is possible to suppress the generation of the non-light region at the end of the emitted light due to the fact that the light does not reach the surface sufficiently. Therefore, in the surface light source device 10, a surface light source in which the color reproduction range is wide and the luminance of the emitted light is sufficiently uniformed by using an LED in which light emitting elements are linearly arranged as the light source 12. Device 10 is obtained.

(Second Embodiment)
FIG. 2 is a horizontal sectional view showing a schematic configuration of a sidelight type surface light source device 20 according to a second embodiment of the present invention. The surface light source device 20 includes a light emitting surface 21a, a back surface 21b on which a pattern having a light diffusing action is formed by blasting, and the like. A light guide plate 21 made of acrylic resin having an inclined surface 21c formed on a side surface; in the vicinity of the inclined surface 21c of the light guide plate 21, the light emitting portion is parallel to the inclined surface 21c, and the center of the light emitting portion is an inclined surface A light source 22 such as a cold-cathode tube or an LED disposed so as to correspond to the middle point of 21c; a reflection sheet 23 disposed near the back surface 21b of the light guide plate 21; and a light of the light guide plate 21 And a light emission direction correcting element 24 composed of a prism element or the like disposed in the vicinity of the emission surface 21a. Here, the side surface of the light guide plate 21 that faces the inclined surface 21c is formed perpendicular to the light emitting surface 21a.

  In the surface light source device 20, the light emitted from the light source 22 is incident on the inclined surface 21 c of the light guide plate 21 after being reflected from the light source 22 directly or by the inner surface of a reflector (not shown) covering the periphery of the light source 22. After propagating through the inside of the optical plate 21 and emitted from the light emitting surface 21a, the emitting direction is corrected by the light emitting direction correcting element 24. In addition, the light emitted to the back surface 21b side of the light guide plate 21 is also diffused by the light diffusion pattern formed on the back surface 21b of the light guide plate 21 or reflected by the reflection sheet 23. The light propagates again through the light guide plate 21.

Here, in the light guide plate 21, the distance between the light emitting surface 21 a and the back surface 21 b is t, and the width of the back surface 21 b (the end point A on the light source 22 side of the back surface 21 b and the end point B on the opposite side of the light source 22). The distance θ between the inclined surface 21c and the straight line α perpendicular to the light exit surface 21a is equal to or greater than tan ⁻¹ (t / L).

  In the surface light source device 20 configured as described above, the light guide plate 21 transmits the central light I from the light source 22 between the end point A on the light source 22 side of the back surface 21b and the center point C in the width direction of the back surface 21b. Since the center light I from the light source 22 is not transmitted through the light guide plate 21 as it is, the loss of light can be suppressed as much as possible, and the luminance of the emitted light is improved. Can do. Further, in the surface light source device 20, a pattern having a light diffusing action formed on the back surface 21 b of the light guide plate 21, a reflection sheet 23 disposed in the vicinity of the back surface 21 b of the light guide plate 21, and a light emitting surface 21 a of the light guide plate 21. By adjusting the characteristics of the light emission direction correcting element 24 arranged in the vicinity, the center light I from the light source 22 is emitted as vertically as possible from the vicinity of the center of the surface light source device 20 as much as possible. Light can be used in the vicinity of the center of 20, and the luminance of the emitted light can be sufficiently uniformed.

  Further, the light guide plate 21 can be manufactured by either processing the inclined surface 21c only in a limited manner or by providing an angle to the side surface so as to have the inclined surface 21c at the time of injection formation. . Therefore, it is possible to manufacture with a simple production process as compared with a wedge-shaped light guide plate that requires fine and precise machining of the entire mold.

  Moreover, in the surface light source device 20, since the light source 22 is inclined and arranged on the back surface 21b side of the light guide plate 21, the light source 22 on the back surface 21b of the light guide plate 21 even when the light source 22 is a point light source. There is no problem that light does not reach the vicinity of the end point A on the side. That is, in the general sidelight type surface light source device 90 shown in FIG. 5, when the light source 92 is a point light source, there is a problem in the vicinity of the end point A on the light source 92 side of the back surface 91b of the light guide plate 91. Therefore, it is possible to suppress the generation of the non-light region at the end of the emitted light due to the fact that the light does not reach the surface sufficiently. For this reason, in the surface light source device 20, a surface light source in which the color reproduction range is wide and the luminance of the emitted light is sufficiently uniformed by using an LED in which light emitting elements are linearly arranged as the light source 22. Device 20 is obtained.

  In the above description, in the light source 12 (22), the light emitting portion is parallel to the inclined surface 11c (21c) and the center of the light emitting portion is inclined near the inclined surface 11c (21c) of the light guide plate 11 (21). The surface 11c (21c) is arranged so as to correspond to the midpoint. Therefore, a method for realizing this configuration will be specifically described below.

  In FIG. 3, the light source 12 (22) is placed near the inclined surface 11c (21c) of the light guide plate 11 (21), the light emitting part is parallel to the inclined surface 11c (21c), and the center of the light emitting part is the inclined surface 11c. It is horizontal sectional drawing which shows the method of arranging so that it may correspond to the middle point of (21c).

  Here, in FIG. 3A, the light source 12 (22) is arranged on the inclined surface of the triangular cylindrical flexible wiring board 31 whose bottom surface is a right triangle, and two orthogonal side surfaces of the flexible wiring board 31 are This configuration is achieved by bringing the back plate 32 into surface contact. Further, in FIG. 3B, the shape of the light source 12 (22) has two orthogonal surfaces 33 and 34 that are in surface contact with the back plate 32, and the back surface 11b (of the light guide plate 11 (21). This configuration is realized by a shape inclined to the side 21b). Here, the back plate 32 covers the back side of the surface light source device 10 (20), and has a rectangular parallelepiped box shape having a bottom surface parallel to the back surface of the light guide plate 11 (21). It is.

  As the light source 12 (22), as described above, it is desirable to use an LED in which light emitting elements are arranged in a straight line. Therefore, a specific configuration of the LED in which the light emitting elements are arranged in a straight line will be described below.

  FIG. 4 is a horizontal sectional view showing a specific configuration of the LED 12 (22) in which the light emitting elements are linearly arranged. In FIG. 4, the LED 12 (22) covers the LED chips 41, 42, 43 arranged in a straight line, and the side surfaces of the LED chips 41, 42, 43 in the light emission direction X, and faces the light emission direction X. It has plastic light-shielding members 411, 421, and 431 in an expanding shape.

  Here, the distance P between the LED chips 41 and 42 and between the LED chips 42 and 43 is, for example, 7 mm or more, and the width S of the light emission direction X side end of each of the light shielding members 411, 421, and 431 made of plastic is For example, it is desirable to set it to 4 mm or more.

  In addition, this invention is not limited to said embodiment, A various change is possible in the range which does not deviate from the main point of this invention. For example, in the above-described embodiment, the surface light source device 10 or 20 has the light emission direction correcting element 14 or 24 formed of a prism element or the like in the vicinity of the light emission surface 11a or 21a of the light guide plate 11 or 21. It was. However, a pattern having a function of correcting the light emission direction may be formed on the light emission surface 11a or 21a of the light guide plate 11 or 21 by blasting or the like.

  Moreover, in said embodiment, the surface light source device 10 or 20 shall have the reflective sheet 13 or 23 which reflects light in the back surface 11b or 21b vicinity of the light-guide plate 11 or 21. FIG. However, it is good also as having a reflecting plate instead of the reflecting sheet 13 or 23. FIG.

  The present invention is effective as a light guide plate used in a sidelight type surface light source device. Further, the present invention is effective as a surface light source device and a liquid crystal display device having such a light guide plate.

FIG. 2 is a horizontal sectional view showing a schematic configuration of the surface light source device 10. FIG. 3 is a horizontal sectional view showing a schematic configuration of the surface light source device 20. The light source 12 (22) is placed near the inclined surface 11c (21c) of the light guide plate 11 (21), the light emitting portion is parallel to the inclined surface 11c (21c), and the center of the light emitting portion is the inclined surface 11c (21c). FIG. 6 is a horizontal cross-sectional view showing a method for arranging the intermediate points so as to correspond to the middle points. The horizontal sectional view showing the concrete composition of LED12 (22) where the light emitting element was arranged in the shape of a straight line. FIG. 6 is a horizontal sectional view showing a schematic configuration of the surface light source device 90;

Explanation of symbols

10, 20 Surface light source device 11, 21 Light guide plate 11a, 21a Light emission surface 11b, 21b Back surface 11c, 21c Inclined surface 12, 22 Light source 41, 42, 43 LED chip (light emitting element)

Claims (6)

A light guide plate used in a side light type surface light source device,
One side surface is an inclined surface so that the width of the light emitting surface is narrower than the width of the back surface,
The distance between the light exit surface and the back surface is t,
The width of the back surface is L,
A light guide plate characterized in that, in a horizontal section, an angle formed by the inclined surface and a straight line perpendicular to the light emitting surface is in the vicinity of tan ⁻¹ (t / L). A light guide plate used in a side light type surface light source device,
One side surface is an inclined surface so that the width of the light emitting surface is narrower than the width of the back surface,
The distance between the light exit surface and the back surface is t,
The width of the back surface is L,
A light guide plate characterized in that, in a horizontal cross section, an angle formed by the inclined surface and a straight line perpendicular to the light emitting surface is tan ^-1 (t / L) or more.   3. The light guide plate according to claim 1, wherein an angle formed between a side surface facing the inclined surface and the light emitting surface in a horizontal section is about 90 degrees. The light guide plate according to any one of claims 1 to 3,
A light source disposed in the vicinity of the inclined surface of the light guide plate so that a light emitting portion is parallel to the inclined surface;
A surface light source device comprising:   The surface light source device according to claim 4, wherein the light source is an LED in which light emitting elements are linearly arranged. LCD panel,
The surface light source device according to claim 4 or 5 disposed on a back surface of the liquid crystal panel;
A liquid crystal display device comprising:

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