JP2002182038A - Light guide plate and backlight system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an edge light type light guide plate which removes a dark line and a bright line appearing in illumination light due to an edge silhouette optical image on the incident side with a simple and inexpensive configuration. SOLUTION: In the light guide plate 2 to be used for the edge light type backlight system, a base region A with a specified width extending from the end face 21 on the incident side in a base reflection plane 22 is formed into a diffusion plane by abrasive blasting treatment or the like. Because the edge silhouette optical image on the incident side is scattered by the diffusion plane, the appearance of the dark line and the bright line in the illuminated region on the incident side of the light guide plate 2 is prevented or suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight system for a liquid crystal panel used in a notebook personal computer, a liquid crystal television and the like, and more particularly, to a light guide plate used in an edge light type backlight system. Things.

[0002]

2. Description of the Related Art A light guide plate used in an edge light type backlight system has a tapered cross section whose thickness gradually decreases from an end face on the light incident side to an end face on the opposite side. In the edge light method, a fluorescent tube (light source) with a reflector is arranged along the light-entering end face of the light guide plate of this shape, and light emitted from the reflector enters the light guide plate from the light-incident side end face, After being reflected at least once by the reflector on the bottom side, the light exits from the upper side and becomes uniform scattered light via the prism sheet, illuminating the liquid crystal panel from the back side.

Here, in the backlight system of the edge light system, an edge contour light image on the light incident side of the light guide plate is multiple-reflected in the light guide plate, and forms dark lines and bright lines on the liquid crystal screen on the light source side. Therefore, the uniformity of the screen luminance is hindered. In particular, when the bottom reflecting surface of the light guide plate is a prism surface composed of narrow grooves extending in a direction perpendicular to the fluorescent tube, the light guide efficiency is increased to increase the screen illuminance. It becomes clearer, dark lines and bright lines appear more clearly, and the brightness unevenness of the screen becomes remarkable.

Conventionally, various proposals have been made to prevent or suppress such adverse effects. For example,
JP-A-6-242322 discloses a light source device in which a large number of hollow particles are mixed in a light guide plate, and the diameter of the hollow particles gradually increases as the distance from the light source increases, and the distribution density also increases. Is disclosed.
Japanese Patent Application Laid-Open No. 6-273759 discloses a configuration in which a plurality of reflective paints distributed and arranged according to the lighting conditions at the spot are printed on the back surface of the light guide plate to prevent uneven illuminance. . Furthermore, a plurality of prism sheets and diffusion sheets are laminated on the exit surface of the light guide plate to make the emitted light uniform scattered light.

[0005]

However, since it is difficult to mix hollow particles having different sizes into the light guide plate so that the distribution density changes gradually, such a light guide plate is easily manufactured. Can not do. Also, a method of printing a plurality of reflective paints according to the lighting conditions at the place is very troublesome. Furthermore, a method of stacking a plurality of prism sheets and diffusion sheets can be expected to be effective in suppressing luminance unevenness. However, since a large number of sheets are stacked, a reduction in screen illuminance is caused and cost is increased. So it is not preferable.

[0006] The object of the present invention is to solve the above problems.
An object of the present invention is to make it possible to reduce or eliminate the occurrence of dark lines and bright lines due to the end face contour on the light incident side of a light guide plate of an edge light system with a simple configuration.

In view of the above, an object of the present invention is to provide a light guide plate of an edge light type that can eliminate or suppress uneven brightness without reducing brightness efficiency by a simple and inexpensive configuration. It is to make.

[0008]

According to the present invention, a dark line / bright line appearing at a light source side on a screen of a liquid crystal panel is defined as:
A diffusion surface is formed only on the portion of the bottom reflection surface of the light guide plate where dark lines and bright lines occur, without disturbing the original bottom reflection surface shape. With this diffusion surface, the end surface contour light image on the light entrance side of the light guide plate is formed. Is diffused so as not to be reflected in a certain direction.

That is, in the present invention, light is scattered only in a portion where a dark line and a bright line are generated without impairing a basic reflecting surface shape of the bottom surface of the light guide plate.
The diffusion process is gradually reduced so that there is no influence of scattered light up to the vicinity of the boundary between the part where dark lines and bright lines occur and the part where it does not, and the original performance of the light guide plate can be exhibited in the part where there is no abnormal light That's how it works.

Here, as a method of diffusion processing of the bottom surface,
There are a method of blasting the surface of a mold for forming a light guide plate, a method of directly blasting the light guide plate, and a method of applying powder to the light guide plate and fixing it with an adhesive.

More specifically, the present invention has a tapered shape in which the top surface is an emission surface, the bottom surface is a reflection surface, and the thickness gradually decreases from the light-incident side end surface to the opposite front-side end surface. In the edge light type light guide plate having a cross section, a bottom surface region in a predetermined range from the light incident side end surface toward the front end side end surface is a diffusion surface, and the unevenness of the diffusion surface is
It is characterized in that the density gradually increases from dense to rough from the light incident side end face toward the front end side end face.

As the form of the diffusion surface, it is possible to form a matte finish surface by blasting or the like, or to form a plurality of line grooves formed so as to be parallel to the end surface on the light incident side. .

In the case of a line groove, its width may be about 15 μm, and its cross section may be triangular, corrugated,
Alternatively, it can be saw-toothed.

In the edge light type backlight system using the light guide plate according to the present invention, the appearance of dark lines and bright lines on the liquid crystal screen due to the contour light image on the light incident side end face of the light guide plate is prevented or suppressed. .

On the other hand, the present invention has a tapered cross section in which the top surface is an emission surface, the bottom surface is a reflection surface, and the thickness is gradually reduced from the light incident side end surface to the opposite end side end surface. In the edge light type light guide plate, the bottom surface is a prism reflecting surface in which narrow grooves extending in a direction perpendicular to the light incident side end surface are formed at a predetermined pitch, and the surface of the prism reflecting surface is The fine grooves extending in a direction orthogonal to the fine grooves are characterized by a fine wave surface or a fine prism surface formed at a predetermined pitch.

Further, the backlight system of the present invention comprises:
The light guide plate having the above configuration is provided.

According to the present invention, the surface of the prism reflecting surface formed on the bottom surface of the light guide plate is a wave surface or a prism surface formed of fine grooves. Therefore, since the diffusivity of the bottom surface of the light guide plate is enhanced, it is possible to form illumination light without luminance unevenness without loss of light quantity.

Here, as the light guide plate, a portion of the bottom surface having a predetermined width from the end surface on the light incident side has a first groove in which narrow grooves extending in a direction parallel to the end surface on the light incident side are formed at a predetermined pitch. The second prism reflecting surface is formed as a prism reflecting surface, and the bottom surface portion other than the first prism reflecting surface is formed with narrow grooves extending at a predetermined pitch in a direction orthogonal to the end surface on the light incident side. In a region of a predetermined width adjacent to the first prism reflection surface in the second prism reflection surface, narrow grooves extending in a direction parallel to the end surface on the light incident side are formed at a predetermined pitch. The third prism is a reflection surface, and the narrow grooves extending in a direction parallel to the end surface on the light incident side are formed at a constant pitch, but the depth thereof increases as the distance from the end surface on the light incident side increases. Use a shallower configuration It is possible.

In this case, the depth of the narrow groove extending in a direction perpendicular to the light incident side end face may be gradually reduced toward the light incident side end face.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An edge light type backlight system to which the present invention is applied will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic structural view showing a main part of a backlight system of the present embodiment, and FIG. 2 is a perspective view showing a light guide plate thereof. As shown in these figures, the backlight system 1 includes a light guide plate 2, a fluorescent tube 3 arranged on an end face 21 on the light incident side of the light guide plate 2, and a reflection plate 4 stacked on a bottom surface 22 of the light guide plate 2. And the upper surface 2 of the light guide plate 2
3 has a prism sheet 5 laminated thereon. Fluorescent tube 3
The portion other than the end face 21 is covered with the reflector 6, and the light emitted from the fluorescent tube 3 enters the light guide plate 2 from the end face 21 of the light guide plate 2 directly or after being reflected by the reflector 6.

The light incident on the light guide plate 2 includes a light component emitted from the upper surface 23 as it is, a light component emitted from the upper surface 23 after being reflected at least once by the bottom reflecting surface 22, and a light component emitted from the bottom reflecting surface 22. A light component which is transmitted, reflected by the lower reflecting plate 4, and emitted from the upper surface 23 via the light guide plate again is included. Most of the light components emitted from the upper surface 23 of the light guide plate 2 are emitted at an angle of about 60 to 65 degrees with the normal to the upper surface 23. The prism sheet 5 corrects such obliquely emitted light so as to be perpendicularly incident on a liquid crystal panel (not shown).
Note that a diffusion sheet may be further laminated on the upper surface of the breath sheet 5 in order to suppress uneven brightness of the emitted light.

The light guide plate 2 is of a 14-inch wedge type, and has a tapered cross section whose thickness gradually decreases from the light incident side end surface 21 to the opposite end side end surface 24.
The bottom surface 22 is a prism reflecting surface having a configuration in which narrow grooves extending in a direction perpendicular to the light incident side end surface 21 are arranged at a constant pitch.

Here, in the bottom surface (prism reflecting surface) 22 of the light guide plate 2 of the present embodiment, a bottom region A having a width of about 10 mm from the light incident side end surface 21 to the opposite end surface 25 is:
It is a diffusion surface in which the surface of the prism reflection surface is subjected to blast processing. The blasting is performed so that the density gradually increases from the density as the distance from the end face 21 increases.

In the backlight system 1 using the light guide plate 2 having this configuration, it was confirmed that almost no dark lines or bright lines appeared on the fluorescent tube side of the illumination light from the upper surface, and illumination light without uneven brightness could be formed. Was done. For example, the light guide plate 2
Was formed by blasting No. 1200, and when a light guide plate not provided with such a diffusion surface was used, a diffusion surface of 15 m on the fluorescent tube side was used.
Almost no dark line / bright line B (see FIG. 1) appearing in the illumination area of about m width was observed.

Also, good results were obtained when a diffusion surface was formed by subjecting a 12-inch light guide plate to a blast treatment of about 1200 in the same manner as described above.

Next, as shown in FIG. 3 and FIG.
Was formed by forming a large number of line grooves having a width of about 15 μm in place of the satin finished surface by blasting. The pitch of the line grooves was formed such that the pitch gradually increased from dense to coarse from the light guide plate end face 21 to the opposite end face 25. As the groove cross-sectional shape, a triangular shape (Pursum shape), a wave shape such as a sine wave, or a saw-tooth shape was formed. In any case, it was confirmed that generation of dark lines and bright lines could be suppressed.

(Second Embodiment) FIG. 5 is a schematic diagram showing another example of a backlight system to which the present invention is applied, and FIG. 6 is a perspective view showing the light guide plate. As shown in these figures, the basic configuration of a backlight system 101 of this example is the same as that of the above-described system 1, and
02, a fluorescent tube 103 disposed on an end face 121 of the light guide plate 102 on the light incident side, a reflecting plate 104 laminated on a bottom surface 122 of the light guide plate 102, and a prism sheet 105 laminated on an upper surface 123 of the light guide plate 102. are doing. Fluorescent tube 103
The light guide plate 102 has a portion other than the end face 121 covered by the reflector 106, and the light emitted from the fluorescent tube 103 is reflected directly or after being reflected by the reflector 106.
From the end face 121 of the light source.

The light guide plate 102 is, for example, a 14-inch wedge type, and has a tapered cross section whose thickness gradually decreases from the light incident side end surface 121 to the opposite end side end surface 124. I have. The bottom surface 122 is the end surface 1 on the light incident side.
The prism reflecting surface has a configuration in which narrow grooves extending in a direction orthogonal to 21 are arranged at a constant pitch.

FIG. 7A is a partially enlarged view showing a part of the prism reflecting surface formed on the bottom surface of the light guide plate 102, and FIG. 7B is cut along the line bb. FIG. 6 is a partial cross-sectional view of a portion illustrated as above. As shown in these figures, the surface of the prism reflecting surface 122, that is, the surfaces of the pair of left and right inclined surfaces 222 and 223 that define the narrow grooves 221 forming the prism reflecting surface, Are formed on a fine prism surface in which fine grooves extending in a direction orthogonal to are arranged at a constant pitch. Instead of the fine prism surface, a fine wave surface having a structure in which fine wavy grooves are formed at a constant pitch can be used.

(Third Embodiment) Next, FIG. 8 is a partial perspective view showing another example of the light guide plate. The overall configuration of the backlight system using the light guide plate 302 of this example is the same as in the above-described first and second embodiments.

In the light guide plate 302 of this embodiment, the bottom surface 322
In the portion from 15 to 20 mm from the end face 321 on the light source side on the light source side, instead of the prism reflecting surface in which the narrow groove extends in the direction orthogonal to the fluorescent tube (not shown), that is, The prism reflection surface 323 has narrow grooves extending in a direction parallel to the tube. In addition, on the bottom surface other than the prism reflecting surface 323, the prism reflecting surface 3 formed of a narrow groove of the same dimension extending in a direction orthogonal to the fluorescent tube is provided.
24 are formed. In addition, the prism reflecting surface 324 adjacent to the prism reflecting surface 323 and having a diameter of 10 to 25 mm is formed as a prism reflecting surface 325 further formed with a narrow groove extending parallel to the fluorescent tube.

Here, the narrow grooves formed on the prism reflecting surfaces 323 and 325 and extending in parallel with the fluorescent tube are formed at regular intervals, but the depth increases as the distance from the end surface 321 on the fluorescent tube side increases. Is shallow.

Even when the light guide plate 302 configured as described above is used, the same operation and effect as those of the above-described examples can be obtained.

Next, FIG. 9 is a partial perspective view showing a modification of the light guide plate 302. Light guide plate 402 shown in FIG.
Also, the end surface 42 on the light source side on the bottom surface 422
In a portion from 1 to 15 to 20 mm, a prism reflecting surface in which a narrow groove extends in a direction parallel to the fluorescent tube instead of a prism reflecting surface in which a narrow groove extends in a direction orthogonal to a fluorescent tube (not shown). 423. On the bottom surface other than the prism reflecting surface 423, there is formed a prism reflecting surface 424 formed of a narrow groove having the same dimensions and extending in a direction orthogonal to the fluorescent tube. In addition to this, the prism surface 424 adjacent to the prism reflection surface 423 and having a diameter of 10 to 25 mm is formed as a prism reflection surface 425 further formed with a narrow groove extending parallel to the fluorescent tube.

In this embodiment, however, the prism reflecting surface 42
The narrow grooves formed on the fluorescent tubes 3 and 425 and extending in parallel with the fluorescent tubes are formed at regular intervals.
As the distance from 21 increases, the depth decreases.
In addition, narrow grooves formed on the prism reflecting surface 424 and extending in a direction perpendicular to the fluorescent tube are formed at regular intervals, but gradually become shallower toward the end surface 421 on the fluorescent tube side. Is formed.

Even when the light guide plate 402 having this configuration is used, the same operation and effect as those of the above embodiments can be obtained.

[0038]

As described above, in the light guide plate of the present invention, the diffusion surface is formed in a region having a predetermined width from the light incident side end surface to the opposite end surface of the bottom reflecting surface.
This diffusion surface prevents or suppresses the appearance of the contour light image of the light guide plate light incident side end face as it is as a dark line or bright line on the exit side.

Therefore, according to the present invention, it is possible to realize a light guide plate and a backlight system capable of suppressing the occurrence of such dark lines and bright lines with a simple and inexpensive configuration.

Further, according to the present invention, the bottom surface of the edge-light type light guide plate is a prism surface, and the surface of the prism surface is a fine prism surface having fine grooves formed at a constant pitch. Or it is a minute wavefront.

Therefore, according to the present invention, since the light diffusing property of the bottom surface of the light guide plate is high, it is possible to emit illumination light without luminance unevenness without loss of light quantity. In addition, since the structure is simpler than the conventional method for suppressing luminance unevenness, there is an advantage that cost is not increased.

Further, by using the light guide plate having such a configuration, a bright backlight system with less luminance unevenness can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a main part showing an edge light type backlight system to which the present invention is applied.

FIG. 2 is a perspective view showing a light guide plate used in the backlight system of FIG. 1 as viewed from the bottom side thereof.

FIG. 3 is a perspective view showing another example of the light guide plate shown in FIG.

4 is an enlarged partial perspective view showing a part of the bottom surface of the light guide plate shown in FIG. 3, a partial end view of the light guide plate seen from the fluorescent tube side,
FIG. 3 is a partial cross-sectional view of a portion cut along line cc.

FIG. 5 is a schematic configuration diagram of a main part in another example of an edge light type backlight system to which the present invention is applied.

FIG. 6 is a perspective view showing a light guide plate used in the backlight system of FIG. 5 when viewed from the bottom side thereof.

7 is a partially enlarged view showing a part of the bottom surface of the light guide plate shown in FIG. 6 in an enlarged manner, and a partial cross-sectional view showing a portion cut along the line bb.

FIG. 8 is a partial perspective view showing another example of the light guide plate according to the present invention.

FIG. 9 is a partial perspective view showing a modification of the light guide plate shown in FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 backlight system 2 light guide plate 21 light-entering end face 22 bottom reflecting surface 23 top surface 24 end face opposite to light-entering end face 3 fluorescent tube 4 reflector 5 prism sheet 6 reflector A bottom surface (diffusion surface) B Area where dark line / bright line appears 101 Backlight system 102 Light guide plate 121 Light-entering side end face 122 Bottom reflection surface 221 Narrow groove 222, 223 Slant surface defining narrow groove 224 Fine groove formed on inclined surface 123 Top surface 124 Input End face opposite to light-side end face 103 Fluorescent tube 104 Reflector 105 Prism sheet 106 Reflector 302, 402 Light guide plate 321, 421 End face 422, 422 Bottom face 323, 324, 325, 423, 424, 425 Prism face

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[Procedure amendment]

[Submission date] December 22, 2000 (200.12.
22)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 8

[Correction method] Change

[Correction contents]

FIG. 8

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Fig. 9

[Correction method] Change

[Correction contents]

FIG. 9

Claims (9)

[Claims] 1. An edge light having an upper surface as an emission surface, a lower surface as a reflection surface, and a tapered cross section having a thickness gradually reduced from a light incident side end surface to an opposite end side end surface. In the light guide plate of the type, a bottom surface region having a predetermined length from the light incident side end surface toward the front end side end surface on the bottom surface is a diffusion surface,
The light guide plate, wherein the unevenness of the diffusing surface is gradually increased from the dense to the rough from the light incident side end surface to the front end side end surface. 2. The light guide plate according to claim 1, wherein the diffusion surface is a matte finish surface. 3. The light guide plate according to claim 1, wherein the diffusion surface is a diffusion surface including a plurality of linear grooves formed so as to be parallel to the end surface on the light incident side. 4. The light guide plate according to claim 3, wherein the width of the line groove is about 15 μm, and a cross-sectional shape thereof is a triangle, a waveform, or a saw-tooth shape. 5. A backlight system comprising the light guide plate according to claim 1. Description: 6. An edge light having a top surface as an emission surface, a bottom surface as a reflection surface, and a tapered cross-section having a thickness gradually reduced from a light incident side end surface to an opposite end side end surface. In the light guide plate of the method, the bottom surface is a prism reflecting surface in which fine grooves extending in a direction perpendicular to the end surface on the light incident side are formed at a predetermined pitch, and the surface of the prism reflecting surface is the fine groove. A light guide plate, wherein fine grooves extending in a direction orthogonal to the above form a fine wave surface or a fine prism surface formed at a predetermined pitch. 7. An edge light having a top surface as an emission surface, a bottom surface as a reflection surface, and a tapered cross section whose thickness gradually decreases from a light incident side end surface to an opposite end side end surface. In the light guide plate of the method, a portion of the bottom surface having a predetermined width from the end surface on the light incident side has a first prism reflecting surface in which narrow grooves extending in a direction parallel to the end surface on the light incident side are formed at a predetermined pitch. The bottom surface portion other than the first prism reflection surface is a second prism reflection surface in which narrow grooves extending in a direction perpendicular to the light incident side end surface are formed at a predetermined pitch. An area of a predetermined width adjacent to the first prism reflection surface in the second prism reflection surface has a third groove in which narrow grooves extending in a direction parallel to the light incident side end face are formed at a predetermined pitch.
The narrow grooves extending in a direction parallel to the light-incident side end face are formed at a constant pitch, but the depth thereof increases with distance from the light-incident side end face. A light guide plate characterized by being shallow. 8. The light guide plate according to claim 7, wherein the narrow groove extending in a direction orthogonal to the light incident side end face gradually decreases in depth toward the light incident side end face. 9. A backlight system comprising the light guide plate according to claim 6. Description: