JP2009123361A - Light guide plate and backlight unit for liquid crystal display device - Google Patents

Abstract

A light guide plate capable of further uniforming emitted light (planar light) is provided.
The light guide plate 11 includes a light incident surface 1a for introducing light from a light source 12, and a light emitting surface 1b for emitting light introduced from the light incident surface 1a in a plane shape in a predetermined direction. And a reflection surface 2a for reflecting light leaking from the back surface 1c of the light guide 1 toward the back surface 1c of the light guide 1. And a reflective sheet 2 integrated with the light guide 1 by attaching the reflective surface 2 a to the back surface 1 c of the light guide 1 via the adhesive layer 3. A plurality of bubbles 4 for diffusing light are provided between the light guide 1 and the reflection sheet 2.
[Selection] Figure 2

Description

  The present invention relates to a light guide plate and a backlight unit for a liquid crystal display device.

  Conventionally, lighting devices capable of emitting planar light are known and are used as backlight units for liquid crystal display devices.

  There are two types of conventional backlight units for liquid crystal display devices: a direct type and an edge light type. A direct-type backlight unit for a liquid crystal display device is configured to provide a plurality of light sources on the back side of the liquid crystal display panel and to irradiate the back surface of the liquid crystal display panel with light emitted from the plurality of light sources. It is. On the other hand, the backlight unit for an edge light type liquid crystal display device has a light guide plate disposed on the back side of the liquid crystal display panel and a light source provided so as to face a predetermined side surface of the light guide plate. The light emitted through the light plate is configured to irradiate the back surface of the liquid crystal display panel. In the conventional configuration described above, as the light source, for example, CCFT (cold cathode tube), LED (light emitting diode) or the like is used.

  Among the above-described conventional backlight units for liquid crystal display devices, the edge light type backlight unit for liquid crystal display devices has a light emitting surface of a light guide plate (in order to emit as much light as possible to the liquid crystal display panel ( A reflection sheet is provided on the back side opposite to the surface on the liquid crystal display panel side. By providing such a reflection sheet on the back side of the light guide plate, even if light leaks from the back side of the light guide plate, the leaked light is reflected toward the back side of the light guide plate. Light leaking from the back surface is reintroduced into the light guide plate. That is, since the light leaking from the back surface of the light guide plate can also be used, it is possible to irradiate the liquid crystal display panel with a lot of light.

  Conventionally, an integrated light guide plate in which the above-described reflection sheet is integrated is known (see, for example, Patent Document 1).

  FIG. 5 is a cross-sectional view schematically showing an example of the structure of a conventional integrated light guide plate. Referring to FIG. 5, the conventional integrated light guide plate 110 includes at least a light guide 101 and a reflection sheet 102. The light guide 101 has a function of converting light introduced from the light incident surface 101a into planar light and emitting the light from the light emitting surface 101b. The reflection sheet 102 is provided on the back surface 101 c side of the light guide 101 and has a function of reflecting light leaking from the back surface 101 c of the light guide 101 toward the back surface 101 c of the light guide 101. Yes. In the following description, the surface of the reflective sheet 102 on the light guide body 101 side is referred to as a reflective surface 102a.

  And in the conventional integrated light-guide plate 110 shown in FIG. 5, the light guide 101 and the reflective sheet 102 are united together by bonding together. Specifically, in the conventional integrated light guide plate 110, the back surface 101 c of the light guide 101 and the reflective surface 102 a of the reflective sheet 102 are bonded to each other via the adhesive layer 103. As described above, the conventional integrated light guide plate 110 has a structure in which the light guide body 101 and the reflection sheet 102 are integrated. Therefore, the manufacturing efficiency is improved when the backlight unit for the liquid crystal display device is manufactured. And so on.

JP 2001-228309 A

  By the way, in the conventional liquid crystal display device, in order to improve the display quality, it is necessary to further improve the uniformity of the planar light applied to the liquid crystal display panel from the backlight unit for the liquid crystal display device. That is, in the conventional integrated light guide plate 110 shown in FIG. 5, it is necessary to further improve the uniformity of the planar light emitted from the light exit surface 101 b of the light guide 101. However, the structure of the conventional integrated light guide plate 110 shown in FIG. 5 has a problem that it is difficult to make the planar light emitted from the light emitting surface 101b of the light guide 101 more uniform. It was.

  The present invention has been made to solve the above-described problems, and an object of the present invention is for a light guide plate and a liquid crystal display device capable of further uniforming emitted light (planar light). It is to provide a backlight unit.

  In order to achieve the above object, a light guide plate according to a first aspect of the present invention is a light guide plate that converts light from a light source into planar light, and a light incident surface for introducing light from the light source; A light guide having a light emission surface for emitting light introduced from the light incident surface in a planar shape in a predetermined direction, and a light guide provided on the back side opposite to the light emission surface of the light guide The light guide body has a reflection surface for reflecting light leaking from the back surface of the body toward the back surface of the light guide body, and the reflection surface is bonded to the back surface of the light guide body via an adhesive layer. And an integrated reflection sheet. A plurality of bubbles for diffusing light are provided between the light guide and the reflection sheet.

  In the light guide plate according to the first aspect, since a plurality of bubbles are provided between the light guide and the reflection sheet as described above, a difference in refractive index is generated between the light guide and the bubbles. Light incident on the interface between the light body and the bubble can be refracted and diffused. As a result, the planar light emitted from the light guide plate (light emitting surface of the light guide) can be further uniformized.

  In the light guide plate according to the first aspect, preferably, the back surface of the light guide body is formed with a plurality of recesses whose opening ends are blocked by the adhesive layer, and the bubbles are formed on the back surface of the light guide body. It consists of a space surrounded by a concave portion and an adhesive layer. If comprised in this way, a some bubble can be easily provided between a light guide and a reflective sheet. Further, by uniformly dispersing the plurality of recesses formed on the back surface of the light guide as viewed in a plane, it is possible to easily disperse the plurality of bubbles as viewed in a plane.

  In this case, the concave portion of the light guide is preferably formed so that the cross-sectional shape thereof is hemispherical.

  A backlight unit for a liquid crystal display device according to a second aspect of the present invention includes the light guide plate according to any one of claims 1 to 3. If comprised in this way, the planar light radiate | emitted from the backlight unit for liquid crystal display devices can be achieved further easily. In this case, since the uniformity of the planar light irradiated on the liquid crystal display panel can be further improved, the display quality of the liquid crystal display device can be improved.

  As described above, according to the present invention, it is possible to easily obtain a light guide plate and a backlight unit for a liquid crystal display device capable of further uniforming emitted light (planar light).

  FIG. 1 is an exploded perspective view for explaining the structure of a light guide plate according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the light guide plate according to the embodiment shown in FIG. First, the structure of the light guide plate 11 according to the present embodiment will be described with reference to FIGS. 1 and 2.

  As shown in FIGS. 1 and 2, the light guide plate 11 according to the present embodiment converts the introduced light L into the planar light L and emits it in a predetermined direction after introducing the light L from the light source. It is configured. In addition, the light guide plate 11 of this embodiment is used for a backlight unit for liquid crystal display devices, for example.

  Further, the light guide plate 11 of the present embodiment includes at least the light guide 1 and the reflection sheet 2. The light guide 1 included in the light guide plate 11 is formed of a plate-like member that is a molded product of a transparent resin (for example, polycarbonate resin), and is formed in a quadrangular shape when seen in a plan view. A predetermined side surface 1a among the four side surfaces of the light guide 1 functions as a light incident surface for introducing light L into the light guide 1, and a surface (upper surface) 1b of the light guide 1 is guided. It functions as a light emitting surface for emitting the light L introduced into the light body 1 in a plane in a predetermined direction. In the following description, a predetermined side surface 1a that functions as a light incident surface of the light guide 1 is referred to as a light incident surface 1a, and a surface (upper surface) 1b that functions as a light output surface of the light guide 1 is emitted. This is called surface 1b.

  Further, the reflection sheet 2 included in the light guide plate 11 is provided on the back surface 1 c side opposite to the light emitting surface 1 b of the light guide 1. The reflection sheet 2 is made of a sheet-like member capable of reflecting the light L, and is formed in a quadrangular shape when viewed in plan. The entire back surface 1 c of the light guide 1 is covered with the reflection sheet 2. By providing such a reflection sheet 2, even if the light L leaks from the back surface 1c of the light guide 1, the leaked light L is reflected toward the back surface 1c of the light guide 1. The light L leaking from the back surface 1 c of the light guide 1 is reintroduced into the light guide 1. That is, since the light L leaked from the back surface 1c of the light guide 1 can also be used, the utilization efficiency of the light L can be improved. In the following description, the surface (upper surface) of the reflection sheet 2 on the light guide 1 side is referred to as a reflection surface 2a.

  The light guide 1 and the reflection sheet 2 included in the light guide plate 11 are integrated by bonding the back surface 1c of the light guide 1 and the reflection surface 2a of the reflection sheet 2 to each other via the adhesive layer 3. Yes. The pressure-sensitive adhesive layer 3 used for bonding the light guide 1 and the reflection sheet 2 is made of a material that reduces the difference in refractive index between the light guide 1 and the light guide 1. For example, a transparent double-sided tape or a silicon tape can be used as the adhesive layer 3.

  Here, in the present embodiment, a plurality of bubbles (air layers) 4 for refracting and diffusing the light L introduced from the light incident surface 1 a of the light guide 1 are provided between the light guide 1 and the reflection sheet 2. Is provided. In this embodiment, a plurality of bubbles 4 for refracting and diffusing the light L introduced from the light incident surface 1 a of the light guide 1 are obtained by forming a plurality of recesses 1 d in the light guide 1.

  As a specific structure, the plurality of recesses 1 d described above are formed on the back surface 1 c of the light guide 1. Each of the plurality of concave portions 1d formed on the back surface 1c of the light guide 1 has a hemispherical cross-sectional shape. In addition, each diameter D of the some recessed part 1d of the light guide 1 is about 50 micrometers or about 80 micrometers. Further, the plurality of recesses 1d formed on the back surface 1c of the light guide 1 are uniformly dispersed at a pitch P of about 100 μm when viewed in a plan view. Further, the plurality of recesses 1 d formed on the back surface 1 c of the light guide 1 are in a state in which the respective open ends are closed by the adhesive layer 3. In this embodiment, the light L introduced from the light incident surface 1a of the light guide 1 is refracted and diffused in the space surrounded by the recess 1d formed on the back surface 1c of the light guide 1 and the adhesive layer 3. It is made to function as the bubble 4 for making it.

  In the above-described light guide plate 11 of the present embodiment, since the refractive index of the light guide (polycarbonate resin) 1 is about 1.59 and the refractive index of the bubbles (air) 4 is about 1, the light guide 1 And a difference in refractive index occurs between the bubbles 4. In this case, since the critical angle at the interface between the light guide 1 and the bubble 4 is about 39 °, when the light L is incident on the interface between the light guide 1 and the bubble 4 at an angle larger than that, the light L is Total reflection will occur. In the region where the bubbles 4 do not exist (interface between the light guide plate 1 and the adhesive layer 3), almost no difference in refractive index occurs, so that reflection and refraction that cause light loss are reduced. For this reason, it can suppress that a brightness | luminance falls.

  By the way, when the light guide plate 11 of the present embodiment described above is manufactured, first, the light guide plate 11 is guided so that a plurality of recesses 1d are formed on the front surface (back surface) 1c of the plate-like molded product to be the light guide 1. A polycarbonate resin which is a constituent material of the light body 1 is molded. Thereafter, the back surface 1 c of the light guide 1 and the reflection surface 2 a of the reflection sheet 2 are bonded to each other via the adhesive layer 3. Thereby, the light guide plate 11 in which a plurality of bubbles (space surrounded by the concave portion 1d of the light guide 1 and the adhesive layer 3) 4 is provided between the light guide 1 and the reflection sheet 2 is produced.

  In the present embodiment, as described above, by providing a plurality of bubbles 4 between the light guide 1 and the reflection sheet 2, a difference in refractive index occurs between the light guide 1 and the bubbles 4. The light L incident on the interface between the light body 1 and the bubble 4 can be refracted and diffused. As a result, the planar light L emitted from the light guide plate 11 (the light emission surface 1b of the light guide 1) can be further uniformized.

  In the present embodiment, as described above, a plurality of recesses 1 d are formed on the back surface 1 c of the light guide 1, thereby being surrounded by the recesses 1 d formed on the back surface 1 c of the light guide 1 and the adhesive layer 3. This space can be made to function as a bubble 4 for refracting and diffusing the light L introduced from the light incident surface 1a of the light guide 1. Therefore, a plurality of bubbles 4 for refracting and diffusing the light L introduced from the light incident surface 1 a of the light guide 1 are easily provided between the light guide 1 and the reflection sheet 2. be able to.

  In this case, the plurality of recesses 1d formed on the back surface 1c of the light guide 1 are uniformly dispersed in a plan view, so that the plurality of bubbles 4 are easily dispersed uniformly in a plan view. can do.

  In addition, if the light guide plate 11 of the present embodiment described above is used in a backlight unit for a liquid crystal display device, a backlight unit for a liquid crystal display device that can easily make emitted light (planar light) more uniform can be easily achieved. Can be obtained. In addition, the backlight unit for liquid crystal display devices using the light guide plate 11 of this embodiment is configured, for example, as shown in FIG.

  With reference to FIG. 3, in the backlight unit 10 for a liquid crystal display device using the light guide plate 11 of the present embodiment, the light source 12 is disposed so as to face the light incident surface 1 a of the light guide 1. Then, in a state where the backlight unit 10 for the liquid crystal display device is mounted on the liquid crystal display device, the liquid crystal display panel 20 is disposed so as to face the light emitting surface 1 b of the light guide 1. Thereby, when a display operation is performed in the liquid crystal display device, the liquid crystal display panel 20 is irradiated with the more uniform planar light L emitted from the backlight unit 10 for the liquid crystal display device. As a result, the display quality of the liquid crystal display device can be improved.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the above embodiment, an example in which the present invention is applied to a light guide plate having a flat surface has been described. However, the present invention is not limited to this, and the light guide plate having a curved surface as shown in FIG. Applicable.

  Moreover, although the recessed part was formed in the light guide in the said embodiment, this invention is not limited to this, A recessed part may be formed in an adhesion layer, and a recessed part may be formed in a reflective sheet. .

  Moreover, in the said embodiment, although the cross-sectional shape of the recessed part for obtaining the bubble formed in the light guide was hemispherical, this invention is not restricted to this, It has a cross-sectional shape in which at least one part is spherical. A recess may be formed in the light guide, or a recess having a triangular cross-sectional shape may be formed in the light guide.

It is a disassembled perspective view for demonstrating the structure of the light-guide plate by one Embodiment of this invention. It is sectional drawing of the light-guide plate by one Embodiment shown in FIG. It is sectional drawing of the backlight unit for liquid crystal display devices using the light-guide plate by one Embodiment shown in FIG. It is a perspective view of the light-guide plate by the modification of this embodiment. It is sectional drawing which showed simply an example of the structure of the conventional integrated light-guide plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light guide 1a Light incident surface 1b Light output surface 1c Back surface 1d Recess 2 Reflective sheet 2a Reflective surface 3 Adhesive layer 4 Bubble 10 Backlight unit for liquid crystal display device 11 Light guide plate 12 Light source

Claims (4)

A light guide plate that converts light from a light source into planar light,
A light guide having a light incident surface for introducing light from the light source, and a light emission surface for emitting light introduced from the light incident surface in a planar shape in a predetermined direction;
A reflective surface provided on the back side opposite to the light emitting surface of the light guide, and reflecting light leaking from the back of the light guide toward the back of the light guide; A reflection sheet integrated with the light guide by attaching the surface to the back of the light guide via an adhesive layer;
A plurality of air bubbles for diffusing light are provided between the light guide and the reflection sheet. A plurality of recesses whose opening ends are blocked by the adhesive layer are formed on the back surface of the light guide,
2. The light guide plate according to claim 1, wherein the bubbles are a space surrounded by a recess formed on a back surface of the light guide and the adhesive layer.   The light guide plate according to claim 2, wherein the concave portion of the light guide is formed to have a hemispherical cross-sectional shape.   A backlight unit for a liquid crystal display device, comprising the light guide plate according to claim 1.

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