KR100634079B1 - Light plate, surface light source device and display device - Google Patents

Abstract

The surface light source device 13 for illuminating the liquid crystal display panel 2 of the liquid crystal display device 11 includes a light guide plate 16, an LED 18, and a reflective sheet 5. The inclined end surface 16C is formed in the thick side, and the recessed part 16E is formed there. The cross-sectional shape of the recessed part 16E is substantially circular arc shape, and gradually becomes shallow toward the exit surface 16B. The emitted light of the LED 18 is introduced into the light guide plate 16 through the incident surface 16D and is internally incident on the inner surface of the concave portion 16E corresponding to each LED 18. Some are leaked but trapped with black tape 19. By internal reflection in the recessed part 16E, the light propagating in the light guide plate 16 in various directions is produced | generated. Thereby, light is supplied to the light guide plate 16 without any gap, and the emission intensity from the emission surface 16B is also uniformed. The luminance non-uniformity in the periphery of the inclined cross section 16C is also remarkably alleviated. For example, a high quality display screen is obtained by applying to the liquid crystal display device of a cellular phone.

Light guide plate, surface light source device, display device

Description

Light guide plate, surface light source device and display device {LIGHT PLATE, SURFACE LIGHT SOURCE DEVICE AND DISPLAY DEVICE}

1 is an exploded perspective view schematically showing an entire arrangement of a liquid crystal display according to an exemplary embodiment of the present invention.

Fig. 2 is a view showing an exemplary optical path as an arrow group with respect to the light guide plate employed in the embodiment, with the concave portion and its periphery viewed from the emission surface side.

3 is a cross-sectional view showing a cross-sectional structure around a primary light source with respect to the liquid crystal display shown in FIG.

4 is a view for explaining a modification of the recessed portion formed on the inclined end surface of the light guide plate.

5 is a cross-sectional view illustrating a modification of the light guide plate.

6 is an exploded perspective view schematically showing the entire arrangement of a liquid crystal display device using a conventional surface light source device using a local light source.

FIG. 7 is a cross-sectional view showing a cross-sectional structure around a primary light source with respect to the liquid crystal display shown in FIG. 6; FIG.

8 is a plan view for explaining luminance unevenness in the prior art;

Explanation of symbols on the main parts of the drawings                 

1, 11: liquid crystal display device 2: liquid crystal display panel

4: frame 5: reflective sheet

6, 16: light guide plate 6A, 16A: back side

6B, 16B: exit face 6C, 16C: inclined cross section

6D, 16D: incident face 8, 18: LED (light emitting diode)

16E: recess 19: black tape (shielding member)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate, a surface light source device and a display device, and more particularly, to a light guide plate improved to be suitable for light input from a light source having a local light emitting area such as a point light source, and a light guide plate thus improved. A display device using the surface light source device and the same surface light source device for illumination of a liquid crystal display panel. The present invention is applied to, for example, a display device attached to a cellular phone, a surface light source device and a light guide plate used therein.

It is already known to illuminate the liquid crystal display panel of the liquid crystal display device by the surface light source device. In general, the surface light source device includes a light guide plate and a primary light source for supplying primary light thereto. Conventionally, rod-shaped fluorescent lamps (cold cathode tubes) have been widely used as primary light sources, but in recent years, those using point-like or local light emitting sources such as LEDs (light emitting diodes) have been adopted.                         

In particular, in a relatively small display device attached to a cellular phone, it has become mainstream.

6 shows an exploded perspective view of an example of a liquid crystal display device in which a liquid crystal display panel is illuminated in a conventional surface light source device using a local light emitting source. 7, the cross-sectional structure around the primary light source is shown.

Referring to the drawing, the liquid crystal display device 1 has a liquid crystal display panel 2 illuminated by the surface light source device 3. The surface light source device 3 includes a light guide plate 6, an LED (point light source 8), and a reflection sheet 5. The light guide plate 6 has a substantially wedge shaped cross section, one measuring surface providing an exit surface 6B, and the other measuring surface providing a back surface 6A. The thick end face 6C is inclined approximately 45 degrees with respect to the exit face 6B. Hereinafter, in the present specification, such a cross section is referred to as an "inclined cross section".

The reflective sheet 5 is made of, for example, a white PET film, reflects light leaked from the back surface 6A and returns to the light guide plate 6 to prevent loss of light. In addition, the diffuse reflection generates light in various propagation directions to promote the emission from the emission surface 6B.

One or more LEDs 8 are arranged according to the required brightness, and constitute the primary light source as a whole. In this example, four LEDs are arranged at equal intervals. As is apparent from FIG. 7, these LEDs 8 are disposed directly below the inclined end surface 6C, and supply primary light toward the inclined end surface 6C through the incident surface 6D.                         

Here, the incidence surface 6D is a band-shaped partial region of the back surface 6A, and the inclined end surface 6C and the incidence surface 6D have a relationship of sharing one edge.

The box-shaped frame 4 is formed of a molded body of white resin, and accommodates and supports the reflective sheet 5, the light guide plate 6, and the liquid crystal display panel 2 in a laminated state.

As shown in FIG. 7, the frame 4 has an opening 4A at a position corresponding to the incident surface 6D. The primary light supplied by the LED 8 is incident on the incident surface 6D through this opening 4A. Further, the mouth wall 4B is formed so as to surround the opening portion 4A. The inner surface of the wall 4B is a highly reflective diffused reflection surface (white surface) or a regular reflection surface, and as shown by the arrow group, the light emitted from the LED 8 is efficiently introduced into the incident end surface 6D. .

The LED 8 is mounted on the printed wiring board 7 together with the driving circuit so that electric power is supplied from the driving circuit. All the above elements are housed and supported in a housing (for example, a cellular phone) partially depicted by reference numeral 9.

When the LED 8 is turned on, light is introduced into the light guide plate 6 through the incident surface 6D directly or via reflection by the entrance wall 4B. Most of the light introduced is internally incident on the inclined end surface 6C. Most of the internal incident light is internally reflected at the inclined end surface 6C, is turned in the substantially inward direction of the light guide plate 6 (direction falling from the inclined end surface 6C), and propagates in the light guide plate 6.

As is widely known, in this process, exiting while experiencing the back reflection 6A, the internal reflection by the exit surface 2B, the reflection by the reflection sheet 5 (after leakage from the back 6A), and the like. Light emission gradually occurs from the surface 6B, and the output light (light output) is used for illumination of the liquid crystal display panel 2.

The problem in the conventional liquid crystal display device or the surface light source device described above is that the uniformity of the luminance distribution on the emission surface 6B is low. This is because the light source (LED 8) which has a local light emitting area is used as a primary light source. That is, the light emitting area of the point light source such as the LED 8 is very small in proportion to the total area of the incident surface even if summed with respect to the total number (four here), so that the width direction of the light guide plate 6 ( A large nonuniformity of light supply occurs with respect to the long axis direction of the inclined end surface 6A.

In particular, as shown in FIG. 8, in the vicinity of the inclined end surface 6C, excessively bright bright lines (dashed lines) are generated on the emission surface corresponding to the position of the LED 8. On the contrary, between the list and the list, a relatively dark portion occurs in correspondence with the point light source member section. If the liquid crystal display device is applied in such a state that the contrast of the contrast remains, a high quality display image cannot be obtained. In particular, in the case of color display, the screen looks dirty, and the commodity value is significantly reduced.

In the prior art shown in FIGS. 6 and 7, the direction change by the internal reflection in the inclined cross section 6C is substantially inward of the light guide plate 6 (the direction perpendicular to the long axis of the inclined cross section 6C). It is limited to thing. Therefore, it is hardly helpful for alleviating and eliminating light and shade unevenness as shown in FIG.

By increasing the number of point light sources (LED) 8 and densely arranging along the long axis direction of the inclined end surface 6C, the unevenness is alleviated. However, such an arrangement is not economically advantageous and also results in an increase in the weight of the device. In recent years, a point-shaped light source (LED) having a large light output per unit can be obtained inexpensively, and in view of this, using a few point-shaped light sources, it is desirable to use a surface light source device in which luminance unevenness is inconspicuous. Is rising. In particular, there is a strong demand for a device having a relatively small display screen such as a cellular phone or a portable personal computer.

The present invention has been proposed under the above background. It is an object of the present invention to provide a display device for illuminating a liquid crystal display panel with a light guide plate, a surface light source device using the same, and a coplanar light source device, which are improved so as not to cause the above problems. Specifically, the present invention provides a light guide plate capable of obtaining output light having high uniformity with respect to light input from a relatively small number of local light emitting sources.

Furthermore, by forming this in the surface light source device, a surface light source device can be obtained in which high uniformity illumination output can be obtained without high density arrangement of the local light emission primary light source. In addition, the use of the coplanar light source device for illumination of a liquid crystal display panel provides a display device capable of obtaining high display quality.

The present invention is first applied to a light guide plate having an emission surface for outputting light, a rear surface opposite to the emission surface, and an inclined cross section inclined with respect to the emission surface. An improvement of the present invention is to form at least one concave portion for light input on the inclined end surface of the light guide plate of this type. The light input to the recess is performed by a light source having at least one local light emitting region in the vicinity of the inclined cross section toward the inner surface of the recess via the edge of the rear surface.

In a typical example, the cross-sectional contour parallel to the exit surface of the recess is substantially arc-shaped. Moreover, it is preferable that the said recessed part is formed so that a depth may become small gradually with distance from the said back surface.

Next, the surface light source device according to the present invention includes a light guide plate and a primary light source having one or more local light emitting regions, and the end shape of the light guide plate is defined in relation to the arrangement of the primary light source.

That is, the light guide plate has an emission surface for outputting light, a rear surface opposite to the emission surface, and an inclined end surface inclined with respect to the exit surface, and at least one recess is formed in the inclined end surface. The primary light source is arranged such that the primary light is introduced into the light guide plate from the edge of the rear surface in the vicinity of the inclined cross section, and then internally reflected by the inner surface of the recess.

In a typical example, the cross-sectional contour parallel to the exit surface of the recess is substantially arc-shaped. Moreover, it is preferable that the said recessed part is formed so that a depth may become small gradually with distance from the said back surface.

When the improved surface light source device is arranged for illumination of the liquid crystal display panel as described above, the liquid crystal display device according to the present invention is obtained.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described with reference to FIGS. In addition, in each figure, in order to make understanding easy, the dimension, shape, etc. of each element are shown to exaggerate suitably. In addition, about the element used in common with FIG. 6, FIG. 7, the common code | symbol is attached | subjected and overlapping description is abbreviate | omitted suitably.

First, referring to FIGS. 1 and 3, a schematic structure of a liquid crystal display according to the present invention is shown in an exploded perspective view and a partial sectional view. In the liquid crystal display device 11 according to the present invention, the surface light source device 13 is disposed to illuminate the liquid crystal display panel 2 from behind.

The surface light source device 13 includes a light guide plate 16, an LED (point light source) 18, and a reflection sheet 5. The light guide plate 16 is a translucent member made of, for example, acrylic resin (PMMA resin), and has a substantially wedge-shaped cross section, one measuring surface providing an exit surface 16B, and the other measuring surface is a rear surface ( 16A).

The thick end face 16C provides an inclined cross section inclined approximately 45 degrees with respect to the exit face 16B, where one or more concave portions 16E are formed according to the features of the present invention ( See partially enlarged A). It is preferable that the inclined end surface 16C including the recessed part 16E be a mirror surface.

The cross-sectional shape (cross-section along the exit surface 16B) of the recessed part 16E has a smooth curved outline which forms substantially circular arc shape. The concave portion 16E is provided with a contour shape that draws a smooth curved ridge line between the flat surface and the concave surface. Such contour smoothness of the recessed portion 16E prevents the occurrence of so-called "illumination" by forming the recessed portion 16E.

Here, "illumination" is a phenomenon where, when there is a portion lacking in the contour smoothness in the vicinity of the primary light source, it is locally strongly reflected, and it is observed as a linear luminance unevenness from the exit surface 16B side. . If the smoothness is insufficient in the contour of the concave portion 16E, a portion that is strongly reflected by the light of the LED 18 occurs, and it is easily observed from the exit surface 16B side.

In response to the inclined end surface 16C in which the recessed part 16E was formed as mentioned above, black tape (light shielding member) 19 is formed in the width rather wider than the incident surface 16D. The black tape 19 functions as a trap for absorbing light leakage in the vicinity of the inclined end surface 16C.

This light leakage may include a component escaping from the light guide plate 16 at or near the recessed portion 16E, and a component passing through the valley space created by the recessed portion 16E without being introduced into the light guide plate 16. have. If such light leakage reaches the liquid crystal display panel 2, it causes the display to be disturbed. The black tape 19 prevents this.

What is noteworthy here is that the concave portion 16E is formed to gradually become shallow toward the exit surface 16B. In the present embodiment, the edge where the exit surface 16B meets the inclined end surface 16C forms a straight line over the entire width of the light guide plate 16. That is, the depth of the recessed part 16E becomes zero at the position of the exit surface 16B immediately. As a result, light shielding by the black tape 19 is facilitated.

If the recessed part 16E is formed so that the edge of the exit surface 16B can be cut off, a risk of light leakage will arise unless the black tape 19 is formed so that this cut | covered part may be covered and reliably covered.

The reflective sheet 15 is made of, for example, a white PET film, reflects the light leaked from the back surface 16A and returns it to the light guide plate 16 to prevent loss of light. In addition, the diffuse reflection generates light in various propagation directions to promote the emission from the emission surface 16B. In addition to or instead of this, other means may be applied to facilitate the emission from the emission surface 16B.

For example, the light scattering pattern of the light guide plate 16 may be formed on one or both of the back surface 16A and the exit surface 16B of the light guide plate 16. The light scattering pattern is composed of light scattering elements arranged according to a predetermined distribution. The light scattering element is provided by, for example, a small rough surface area or a white ink printed in a minute dot shape.

The light scattering pattern (distribution of light scattering elements) may be designed to uniform the luminance on the emission surface 16B. For example, the density (covering rate) of the light scattering element may be increased or decreased in accordance with the perspective from the LED 18. In addition, the arrangement of the light scattering elements is preferably designed so as not to have high regularity. The arrangement of light scattering elements with high regularity is easy to see, and may cause moiré pattern in relation to other regular arrangement elements (for example, liquid crystal cell arrays of liquid crystal display panels).

One to several LEDs 18 are arranged depending on the required brightness, and two LEDs are arranged in this embodiment. Each LED 18 is disposed just below each recessed portion 16E formed in the inclined end surface 16C, and supplies primary light toward the inner surface (dashed line) of the recessed portion 16E via the incident surface 16D. do. The incident surface 16D is a partial region of the rear surface 16A, and geometrically represented, corresponds to the band portion in which the inclined cross section 16C is projected on the rear surface 16A.

The frame 4 which accommodates and supports the reflective sheet 5, the light guide plate 16, and the liquid crystal display panel 2 in a laminated state may be the same as that shown in Figs. That is, the frame 4 is formed of a box-shaped molded body of white resin, and an opening 4A is formed at a position corresponding to the incident surface 16D, and the primary light supplied by the LED 18 is this opening 4A. Is incident on the incident surface 16D through ().

The mouth wall 4B is formed so as to surround the opening part 4A. The inner surface of the wall 4B becomes a high reflectance diffuse reflection surface (white surface) or a regular reflection surface, and as shown by the arrow group, the light emitted from the LED 18 is efficiently introduced into the entrance surface 16D.

The LED 18 is mounted on the printed wiring board 7 together with the drive circuit, and electric power is supplied from the same drive circuit. All of the above elements are housed and supported in a housing (for example in the case of a cellular phone) as partially depicted by reference numeral 9.

When the LED 18 is turned on, light is introduced into the light guide plate 16 directly or via reflection by the entrance wall 4B through the incident surface 16D.

Most of the light introduced is internally incident on the inner surface of the recessed part 16E corresponding to each LED 18. The function of the recessed part 16E can be easily understood with reference to FIG. With reference to FIG. 2, the typical optical path is input to the group of arrows for the partial description which looked at the recessed part 16E and its periphery from the emission surface 16B side.                     

As indicated by the arrow group, most of the light introduced from the incident surface 16D into the light guide plate 16 is internally incident on the inner surface of the concave portion 16E corresponding to each LED 18, and most of the light is internally reflected. . Some are leaked out, but trapped with black tape 19. How much light leakage occurs depends mainly on the distribution of the internal incident angle with respect to the inner surface (mirror surface) of the recessed part 16E.

Generally speaking, the higher the ratio which satisfies the total reflection condition among the internal incident light on the inner surface of the concave portion 16E, the smaller the light leakage. Therefore, the inner surface of the recess 16E is preferably designed to form such a curved surface.

Needless to say, the internal reflection in the recessed part 16E is a reflection in the "convex surface." Therefore, as shown in FIG. 2, light propagates in the light guide plate 16 in various directions.

By this action, light is supplied to every corner in the light guide plate 16, whereby the emission intensity (luminance) from the emission surface 16B is also equalized. The luminance non-uniformity (see Fig. 8 and related description above), which is particularly problematic in the prior art, is also alleviated significantly.

The mechanism by which the internal propagation light of the light guide plate 16 is output from the emission surface 16B is the same as in the case of the prior art described above. That is, the internally propagated light is emitted from the exit surface 16B while experiencing the back reflection 16A, the internal reflection by the exit surface 12B, the reflection by the reflective sheet 5 (after leakage from the back 16A), and the like. The opportunity for internal recruitment to                     

As is already known, if the exit surface 16B is specular, a component that is small enough to break the total reflection condition upon internal incidence of the internally radiated light to the exit surface 16B can cause emission from the exit surface 16B. have. Moreover, when the above-mentioned light scattering pattern is formed in the emission surface 16B, emission from the emission surface 16B will occur more easily.

As described above, the surface light source device 13 emits light because the light is supplied to every corner of the light guide plate as compared with the conventional surface light source device 3 (Fig. 6) due to the presence of the concave portion 16E. The uniformity of the luminance distribution on the surface 16B can be easily increased.

In particular, even if the arrangement of the LEDs 18 (typically a light source having a local emission region) is limited to a small number (for example, one to several), the resulting luminance unevenness (in particular, the luminance around the inclined section) Non-uniformity) does not occur.

In addition, the liquid crystal display panel 2 is uniformly illuminated by the output illumination light of the surface light source device 13. As a result, high display quality is obtained.

For example, when the present invention is applied to a liquid crystal display device such as a cellular phone or a portable personal computer employing color liquid crystal display, no display deterioration due to unevenness of contrast is observed on the screen, and the product value is significantly increased.

In addition, the above-mentioned embodiment does not mean limiting the scope of the present invention. For example, the following modifications are allowed.

(a) In the said embodiment, the recessed part formed in the inclined cross section of the light guide plate forms the valley which consists of a smooth curved surface. However, the shape of the recess is not limited to this. For example, as shown in Fig. 4, a concave portion (V-shaped concave portion) having a triangular cross-sectional outline composed of a pair of flat slopes may be employed. However, it is preferable to form the bottom part of a V-shaped valley so that both surfaces may be connected in a smooth surface. This is because the sharp bottom shape is likely to cause a luminance non-uniformity on the linear line by the above-described "lighting".

Also in this case, the depth is preferably reduced toward the exit surface.

(b) In the above-described embodiment, the incident surface 16D is formed at the same level on a part of the back surface 16A. However, the formation mode of the incident surface 16D is not limited to this. For example, as shown in FIG. 5, you may employ | adopt the light guide plate which has a cross-sectional shape which extended the part just under a slope cross section, and may make the front end surface of this extension part into an incident surface.

(c) The light guide plate 16 in the above embodiment has a wedge-shaped cross section, but this does not limit the present invention. For example, you may employ | adopt the light guide plate which has uniform thickness in the whole, and may form a recessed part in the above-mentioned method in the one end surface or two or more end surfaces.

(d) The present invention may be applied to a surface light source device used for a use other than illumination of a liquid crystal display panel of a liquid crystal display device such as a cellular phone or a laptop computer and a light guide plate used therein. For example, the present invention can be widely applied to lighting devices, display devices, and light guide plates used for other electronic devices such as liquid crystal televisions.

 As described above, in the surface light source device of the present invention, since light is supplied to every corner of the light guide plate as compared with the conventional surface light source device due to the presence of the concave portion, the uniformity of the luminance distribution on the emission surface can be easily increased. do. In particular, even when the LED arrangement is limited to a small number (for example, one to several), there is no significant luminance nonuniformity (in particular, luminance nonuniformity around the inclined cross section).

In addition, since the liquid crystal display panel 2 is uniformly illuminated with the output illumination light of the surface light source device 13, high display quality is obtained.

Claims (9)

A light guide plate having an emission surface for outputting light, a rear surface opposite to the emission surface, and an inclined cross section inclined with respect to the emission surface, At least one concave portion for light input is formed on the inclined end surface, And a light input is performed by a light source having at least one local light emitting area from an edge portion of the back surface to an inner surface of the concave portion in the vicinity of the inclined end surface. The light guide plate according to claim 1, wherein the concave section has a substantially circular cross section along a cross section parallel to the exit surface. The light guide plate according to claim 1 or 2, wherein the concave portion is formed such that the depth gradually decreases in accordance with the distance from the back surface. A surface light source device comprising a primary light source having at least one local emission region and a light guide plate, The light guide plate has an emission surface for outputting light, a rear surface opposite to the emission surface, and an inclined cross section inclined with respect to the emission surface, At least one recess is formed in the inclined cross section, And said primary light source is arranged so that primary light is introduced into said light guide plate from an edge of said back surface near said inclined end surface, and is then internally reflected by an inner surface of said recess. 5. The surface light source device according to claim 4, wherein the concave section has a substantially circular cross section along a cross section parallel to the exit surface. 6. The surface light source device according to claim 4 or 5, wherein the concave portion is formed so that the depth gradually decreases with distance from the rear surface. A display device for illuminating a liquid crystal display panel using a surface light source device, The surface light source device includes a primary light source having one or more local light emitting regions, and a light guide plate, The light guide plate has an emission surface for outputting light, a rear surface opposite to the emission surface, and an inclined cross section inclined with respect to the emission surface, At least one recess is formed in the inclined cross section, And the primary light source is arranged so that primary light is introduced into the light guide plate from an edge portion of the rear surface near the inclined end surface, and then internally reflected by an inner surface of the concave portion. 8. The display device according to claim 7, wherein the concave portion has a cross-sectional outline along a cross section parallel to the exit surface, in a substantially arc shape. The display device according to claim 7 or 8, wherein the concave portion is formed such that the depth gradually decreases with distance from the back surface.

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