JP2002270024A - Surface light source device and liquid crystal display device having the same - Google Patents

Abstract

(57) [Summary] An object of the present invention is to provide a surface light source device capable of suppressing luminance unevenness and preventing occurrence of display defects, and a liquid crystal display device including the surface light source device. A backlight unit includes a light source.
And an incident surface 26d facing the light source 33 and the incident surface 2
Light guide 26 having an emission surface 26c substantially orthogonal to 6d
And a reflector 48 surrounding the light source 33.
The reflector 48 is a diffusion unit 5 that diffuses the light emitted from the emission surface 26e located on the incident surface 26d side of the light guide 26.
It has 0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device and a liquid crystal display device provided with the surface light source device, and more particularly to a structure for preventing luminance unevenness of light emitted from the surface light source device.

[0002]

2. Description of the Related Art A liquid crystal display device includes a surface light source device for illuminating a transmission type liquid crystal display panel from the back. Electronic devices such as portable personal computers equipped with such a liquid crystal display device are desired to be small and light in weight due to their properties, and are required to have high strength. In order to respond to these conflicting demands, improvements have been made to the driving circuit, mounting technology, and structure of the liquid crystal display device.

[0003] Against this background, the thickness of the entire liquid crystal display device is also required to be thin, and a liquid crystal display device that meets the requirement that the total thickness is 5 mm or less has been put to practical use.

A surface light source device applied to such a liquid crystal display device has a light guide having a wedge-shaped cross section, a reflection sheet disposed on the back of the light guide, and an end face of a thick portion of the light guide. And a reflector surrounding the light source. The reflector is assembled by sandwiching the thick portion of the light guide and the reflection sheet.

In recent years, a light guide having a prism-shaped groove on the back surface has been proposed in Japanese Patent Application Laid-Open No. 2000-294019 for the purpose of achieving high luminance, thinness, and light weight.

[0006]

In a surface light source device using a light guide having a prism-shaped groove on the back surface as described above, uneven brightness such as a bright line or a dark line occurs near the light source of the light guide. It will be easier. That is, as the light incident on the light guide, the light incident from the thick portion of the light guide, the light incident from the edge portion of the light guide, and the light incident from the thick portion of the light guide are reflected by the reflector. There is reflected light.

[0007] These lights are emitted directly from the emission surface, or emitted from the emission surface after being reflected by a prism-shaped groove formed on the back surface of the light guide. Due to the intensity of light incident on the light guide, light reflected on the back surface of the light guide and emitted from the light exit surface near the light source of the light guide generates uneven brightness.

As described above, when luminance unevenness occurs in a part of the surface light source device, there is a possibility that a display defect may occur in a liquid crystal display panel illuminated by the surface light source device.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide a surface light source device and a surface light source device capable of suppressing luminance unevenness and preventing occurrence of display defects. Liquid crystal display device provided with the same.

[0010]

According to a first aspect of the present invention, there is provided a surface light source device, comprising: a light source; an incident surface facing the light source; and a light source substantially perpendicular to the incident surface. In a surface light source device comprising: a light guide having an emission surface; and a reflector surrounding the light source, the reflector diffuses light emitted from the emission surface located on the incident surface side of the light guide. It is characterized by having a diffusing portion that performs the following.

According to a fifth aspect of the present invention, there is provided a liquid crystal display device comprising: a transmission type liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates;
A surface light source device for illuminating the liquid crystal display panel, wherein the surface light source device has a light guide having a light source, an incident surface facing the light source, and an emission surface substantially orthogonal to the incident surface. And a reflector surrounding the light source, wherein the reflector has a diffusing portion for diffusing light emitted from the light exit surface located on the light incident surface side of the light guide.

[0012] According to a sixth aspect of the present invention, there is provided a surface light source device comprising: a light source;
A light guide having an entrance surface facing the light source and an exit surface substantially perpendicular to the entrance surface; a reflector surrounding the light source; and a predetermined optical property given to light emitted from the exit surface of the light guide. An optical sheet provided with the light guide, wherein the optical sheet has a diffusing portion for diffusing light emitted from the light exit surface located on the light incident surface side of the light guide. .

According to a ninth aspect of the present invention, there is provided a liquid crystal display device comprising: a transmission type liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates;
A surface light source device for illuminating the liquid crystal display panel, wherein the surface light source device has a light guide having a light source, an incident surface facing the light source, and an emission surface substantially orthogonal to the incident surface. And a reflector surrounding the light source; and an optical sheet for giving predetermined optical characteristics to light emitted from the light exit surface of the light guide, wherein the optical sheet comprises the light incident surface of the light guide. And a diffusing portion for diffusing light emitted from the emission surface located on the side.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface light source device of the present invention and a liquid crystal display device provided with the surface light source device will be described below with reference to the drawings.

As shown in FIG. 1, the liquid crystal display device includes a transmissive liquid crystal display panel 10, an edge light type surface light source device that illuminates the liquid crystal display panel 10 from the back side, that is, a backlight unit 12, and a rectangular frame. Are laminated.

The liquid crystal display panel 10 controls a rectangular array substrate 100 and a counter substrate 200, a twisted nematic liquid crystal layer 300 sealed between these substrates via an alignment film, respectively, and the liquid crystal display panel 10. The control circuit boards 510 and 520, the drive integrated circuit 600 for electrically connecting the liquid crystal display panel 10 to the control circuit boards 510 and 520, and supplying drive signals to the liquid crystal display panel 10 are provided. The array substrate 100 includes a sealing material 331.
Is bonded to the opposing substrate 200 via the. The outer surface of each of the substrates 100 and 200 is covered by a deflecting plate arranged so that its polarization axis is orthogonal to each other.

The array substrate 100 is, for example, 1024 × 3
The signal line 115 includes 768 scanning lines 113 arranged to be orthogonal to each other. In the vicinity of the intersection between each signal line 115 and each scanning line 113, a thin film transistor or TFT using an amorphous silicon film or polysilicon in a channel region is provided.
117 are arranged. The gate electrode of the TFT 117 is electrically connected to the scanning line 113. TFT
The drain electrode 117 is electrically connected to the signal line 115. The source electrode of the TFT 117 is electrically connected to a pixel electrode 119 formed of a transparent conductive member, for example, ITO (indium-tin-oxide).

The drive integrated circuit 600 for electrically connecting the array substrate 100 and the control circuit substrate 510 includes the signal line 11
And a signal line driving integrated circuit 610 electrically connected to the signal line driving integrated circuit 610. The array substrate 100 and the control circuit substrate 52
0 is electrically connected to the scanning line driving integrated circuit 620 which is electrically connected to the scanning line 113.
It has.

The signal line driving integrated circuit 610 converts a digital image signal input from the outside into a desired analog signal voltage based on a control signal and outputs the analog signal voltage. It is composed of a buffer circuit and the like. Further, the scanning line driving integrated circuit 620 includes a shift register, a buffer circuit, and the like so as to sequentially transfer and output scanning pulses based on a control signal input from the outside.

The counter substrate 200 includes a color filter layer disposed for each pixel region, and a counter electrode 217 formed of a transparent conductive member, for example, ITO. The color filter layer is formed of, for example, a colored resin colored red, green, and blue, respectively.

Next, the structure of a surface light source device applied to the liquid crystal display device, that is, a backlight unit will be described.

As shown in FIGS. 1 and 2, the backlight unit 12 includes a rectangular plate-like holding frame 24, a light guide 26, and a plurality of sheet members, for example, three optical sheets 2
8, 30, 32, and an elongated tubular cold cathode ray tube 33 as a light source.

The holding frame 24 is formed of, for example, a synthetic resin, and has a rectangular storage recess 36 for storing the light guide 26.

The optical sheet 28 is a reflection sheet made of, for example, milky white polyimide resin, and is formed in a rectangular shape having substantially the same size as the storage recess 36 of the holding frame 24.

The light guide 26 is formed of, for example, an acrylic resin, and is formed in a rectangular shape having substantially the same size as the storage recess 36 of the holding frame 24. This light guide 26
Has a thick portion 26a on one side thereof, a thin portion 26b on a side facing the thick portion 26a, and has a wedge-shaped cross section. One side surface 26d of the thick portion 26a of the light guide 26 is disposed to face the cold cathode ray tube 33, and serves as an incident surface on which light emitted from the cold cathode ray tube 33 enters.

On the back surface 26e side of the light guide 26, as shown in FIG. 3, a prism-shaped groove is formed. Light guide 2
6, one main surface substantially orthogonal to the incident surface 26d, that is, the main plane 2 facing the back surface 26e on which the reflection sheet 28 is provided.
Reference numeral 6c denotes an exit surface from which light incident from the entrance surface 26d exits.

The light guide 26 is accommodated in the accommodating recess 36 of the holding frame 24 so that the back surface 26e is disposed on the above-mentioned reflection sheet 28.

The optical sheet 30 is, for example, a diffusion sheet and is formed in a rectangular shape having substantially the same size as the storage recess 36. The optical sheet 30 is laminated on the light exit surface 26c of the light guide 26. The optical sheet 32 is a prism sheet and is formed in a rectangular shape having substantially the same size as the storage recess 36. The optical sheet 32 is laminated on the diffusion sheet 30.

In the vicinity of the side wall 24a of the holding frame 24, an elongated lamp accommodating groove 40 extending over the entire length in the width direction is formed. A rib 41 having substantially the same height as the side wall 24a is provided upright at a central portion in the longitudinal direction of the lamp accommodating groove 40, and extends along the longitudinal direction of the lamp accommodating groove 40 and a predetermined distance from the inner surface of the side wall 24a. It extends at intervals.

In the lamp accommodating groove 40, a cold cathode ray tube 33 is accommodated in a region of the rib 41 on the side of the accommodating recess 36. That is, the cold cathode ray tube 33 is assembled integrally with the reflector 48 in a state where both ends are supported by the holder 42 in a predetermined positional relationship. As shown in FIG. 3, the reflector 48 has a substantially rectangular cross-section, and is arranged so as to surround the peripheral surface of the cold cathode ray tube 32 other than the peripheral surface facing the light guide 26. The cold cathode ray tube 33 is disposed at a predetermined position facing the thick portion 26 a of the light guide 26.

From the pair of holders 42, the cold cathode ray tubes 33
The connection cables 44a and 44b for supplying a voltage to are connected to each other. The connection cable 44a is routed to the other holder 42 side through the region between the rib 41 and the side wall 24a in the lamp housing groove 40, and is drawn out together with the other connection cable 44b. The two connection cables 44a and 44b pulled out are as shown in FIG.
Are connected to the lamp drive circuit 46 as shown in FIG.

As shown in FIG. 1, the liquid crystal display panel 10
Is the backlight unit 12 configured as described above.
And is adjacently opposed to the optical sheet 32. The bezel 14 is formed in a rectangular shape having an opening exposing an effective area of the liquid crystal display device, and the backlight unit 1 is overlapped with the periphery of the liquid crystal display panel 10.
2 with the holding frame 24. Then, by fixing the bezel 14 to the holding frame 24 by screwing or the like, the liquid crystal display panel 10 is fixed to the holding frame 24 while being sandwiched between the bezel 14.

During operation of the liquid crystal display device, part of the light emitted from the cold cathode ray tube 33 directly enters the light guide 26 from the incident surface 26d of the light guide 26, and the remaining light is reflected by the reflector 48. After being reflected by the light guide 26, the light enters the light guide 26 through the incident surface 26d. The incident light propagates through the entire inside of the light guide 26, and the light exit surface 26 of the light guide 26
The light exits from c toward the diffusion sheet 30.

The light leaking from the light guide 26 to the reflection sheet 28 is reflected by the reflection sheet 28 and enters the light guide 26 again. Light emitted from the emission surface 26c of the light guide 26 is diffused by the diffusion sheet 30 and guided to the entire surface of the liquid crystal display panel 10 by the prism sheet 32.

In the liquid crystal display panel 10, transmission and non-transmission of the light guided for each pixel is selectively controlled, and an image is displayed.

Next, the structure of the reflector 48 applied to the backlight unit 12 according to the first embodiment will be described in more detail.

The reflector 48 is formed of a metal plate having a thickness of about 0.1 to 0.2 mm. As shown in FIG. 3, a part of the reflector 48 is a part of the light guide 2.
6 is disposed so as to cover the exit surface 26c located on the side of the entrance surface 26d. Reflector 48 covering emission surface 26c
Has a diffusing portion 50 for diffusing the light emitted from the exit surface 26c located on the incident surface 26d side of the light guide 26.

The diffusion section 50 is a diffusion tape attached to the reflector 48. This diffusion tape 50
It is colored gray or white and has the property of diffusing transmitted light. As shown in FIG. 3 and FIG.
Reference numeral 0 denotes a first tape portion 50a which is attached so as to cover the surface of the reflector 48, and a portion which is folded back along the folding line 51 to cover the back surface of the reflector 48 (the surface covering the emission surface 26c of the light guide 26). And a second tape portion 50b attached to the second tape portion 50b.

As shown in FIG. 4, the diffusion tape 50 has a positioning portion 52 for positioning with respect to the reflector 48. The positioning portion 52 is provided to stabilize the dimension of the tape that is folded back from the tip of the reflector 48. That is, the diffusion tape 5
Numeral 0 has a notch portion as the positioning portion 52, which is adapted to the shape of the holder 42 supporting the cold cathode ray tube 33.

The diffusion tape 50 has a slit 54 arranged along the folding line 51. The slit 54 functions as a positioning portion for stabilizing the size of the tape folded from the front end of the reflector 48, like the notch portion.

By providing such a positioning portion, the amount of winding of the second tape portion 50b can be made substantially constant.

The reflector 4 to which the diffusion tape 50 is attached
8 is assembled together with the cold cathode ray tube 33, and then assembled by sandwiching the thick portion 26a of the light guide 26 and the reflection sheet 28. At this time, the diffusion tape 50 affixed to the reflector 48 is assembled so as to cover the exit surface 26c of the light guide 26 near the light source 33.

The light reflected by the reflector 48 among the light directly incident from the incident surface 26 d of the light guide 26 is diffused by the diffusion tape 50. For this reason,
Thereafter, the back surface 26e of the light guide 26 or the reflection sheet 28
The light reflected from the light guide 26 and emitted from the emission surface 26c of the light guide 26 has a dispersed luminance, and can suppress the occurrence of bright lines and dark lines.

As a result, in the backlight unit 12, luminance unevenness does not occur in the vicinity of the light source 33, and display defects on the liquid crystal display panel 10 illuminated by the backlight unit 12 are prevented. It becomes possible.

Next, the structure of the optical sheet applied to the backlight unit 12 according to the second embodiment will be described in more detail.

An optical sheet for giving predetermined optical characteristics to the light emitted from the light exit surface 26c of the light guide 26, that is, the diffusion sheet 30 disposed on the light exit surface 26c, is provided on the light incident surface 26d of the light guide 26. It has a diffusion part 31 for diffusing light emitted from the emission surface 26c located on the side.

The diffusion section 31 is a gradation pattern printed on the diffusion sheet 30. As shown in FIG. 6, the gradation pattern 31 is printed at a position where a bright line easily occurs, and has a property of diffusing transmitted light.

The diffusion sheet 30 having the gradation pattern 31 is placed on the light guide 26 after the reflector 48 integrated with the cold cathode ray tube 33 sandwiches the thick portion 26a of the light guide 26 and the reflection sheet 28. Outgoing surface 26c of
It is arranged to cover.

Of the light directly incident from the incident surface 26d of the light guide 26, the light reflected by the back surface 26e of the light guide 26 is the gradation pattern 31 of the diffusion sheet 30.
Is spread by. Therefore, after that, the light is reflected by the back surface 26e of the light guide 26 or the reflection sheet 28, and
The light emitted from the emission surface 26c of No. 6 is dispersed in luminance, and it is possible to suppress the occurrence of bright lines and dark lines.

As a result, in the backlight unit 12, uneven brightness is not generated in the vicinity of the light source 33, and a display defect on the liquid crystal display panel 10 illuminated by the backlight unit 12 is prevented. It becomes possible.

The first embodiment and the second embodiment described above may be combined. That is, in the backlight unit 12 configured by combining the reflector 48 on which the diffusion tape 50 is stuck and the diffusion sheet 30 on which the gradation pattern 31 is printed, it is possible to obtain the same effects as those of the above-described embodiment. .

[0052]

As described above, according to the present invention, there is provided a surface light source device capable of suppressing luminance unevenness and preventing occurrence of display defects, and a liquid crystal display device provided with the surface light source device. can do.

[Brief description of the drawings]

FIG. 1 is an exploded view schematically showing a structure of a liquid crystal display device provided with a surface light source device of the present invention.

FIG. 2 is an exploded view schematically showing the structure of the surface light source device of the present invention.

FIG. 3 is a diagram showing a part of the surface light source device shown in FIG.
FIG. 2 is a cross-sectional view of the structure according to the first embodiment when cut along a line A.

FIG. 4 is a plan view schematically showing an example of a diffusion tape applied to the surface light source device shown in FIG.

FIG. 5 is a diagram showing a part of the surface light source device shown in FIG.
It is sectional drawing of the structure which concerns on 2nd Embodiment when cut | disconnected along the A line.

FIG. 6 is a plan view schematically showing an example of a diffusion sheet applied to the surface light source device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal display panel 12 ... Surface light source device 100 ... Array substrate 200 ... Counter substrate 300 ... Liquid crystal layer 26 ... Light guide 26a ... Thick part 26b ... Thin part 26c ... Outgoing surface 26d ... Incident surface 26e ... Back surface 30 ... Diffusion Sheet 31: gradation pattern 33: cold cathode ray tube 48: reflector 50: diffusion tape

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13357 G02F 1/13357 G09F 9/00 336 G09F 9/00 336J // F21Y 103: 00 F21Y 103: 00 F term (reference) 2H038 AA52 AA55 BA06 2H089 HA40 QA11 QA16 TA17 TA18 2H091 FA14Z FA21Z FA23Z FA31Z FA42Z GA01 LA11 LA18 5G435 AA01 BB12 BB15 DD14 EE27 FF03 FF06 FF08 GG24

Claims (9)

[Claims] 1. A surface light source device comprising: a light source; a light guide having an incident surface facing the light source and an exit surface substantially orthogonal to the incident surface; and a reflector surrounding the light source. And a diffusing portion for diffusing light emitted from the light exit surface located on the light incident surface side of the light guide. 2. The surface light source device according to claim 1, wherein the diffusion unit is a diffusion tape attached to the reflector. 3. The surface light source device according to claim 1, wherein the diffusing section has a positioning section for the reflector. 4. The surface light source device according to claim 1, wherein the light guide has a prism-shaped groove on a surface facing the light exit surface. 5. A liquid crystal display device comprising: a transmissive liquid crystal display panel that sandwiches a liquid crystal layer between a pair of substrates; and a surface light source device that illuminates the liquid crystal display panel. And a light guide having an incident surface facing the light source and an emission surface substantially orthogonal to the incident surface; and a reflector surrounding the light source, wherein the reflector is provided on the incident surface side of the light guide. A liquid crystal display device, comprising: a diffusing portion for diffusing light emitted from the light exit surface located. 6. A light source, a light guide having an entrance surface facing the light source and an exit surface substantially orthogonal to the entrance surface, a reflector surrounding the light source, and a light emitted from the exit surface of the light guide. An optical sheet for providing predetermined optical characteristics to the light, wherein the optical sheet diffuses light emitted from the light exit surface located on the light incident surface side of the light guide. A surface light source device having a portion. 7. The surface light source device according to claim 6, wherein the diffusing portion of the optical sheet is a gradation pattern printed on the optical sheet. 8. The surface light source device according to claim 6, wherein the light guide has a prism-shaped groove on a surface facing the emission surface. 9. A liquid crystal display device comprising: a transmissive liquid crystal display panel that sandwiches a liquid crystal layer between a pair of substrates; and a surface light source device that illuminates the liquid crystal display panel. A light guide having an entrance surface facing the light source and an exit surface substantially orthogonal to the entrance surface; a reflector surrounding the light source; and a predetermined optical element for light emitted from the exit surface of the light guide. A liquid crystal display device, comprising: an optical sheet that imparts characteristics; and wherein the optical sheet includes a diffusion unit that diffuses light emitted from the light exit surface located on the light incident surface side of the light guide. .