JP2005235560A - Planar lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a side light type planar lighting device with improved utilization efficiency of light emitted from point light sources. <P>SOLUTION: Point light sources 12a, 12b, 12c are arranged at the side part of a light incident face 11c as a side face of a light guide plate 11, and housed in sections 15a, 15b, 15c composed of concave parts formed on a housing frame 14, and surrounded by a side wall 14a as one side of the housing frame 14 and the light incident face 11c of the light guide plate 11. By the above, a course of the leaked light emitted sideward and backward from a package of the point light sources 12a, 12b, 12c or the like can be changed and made incident on the light incident face 11c. The concave parts forming respective sections may be formed on the light guide plate 11 or on either the housing frame 14 or the light guide plate 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a planar illumination device used as illumination means such as a liquid crystal display device, and more particularly to a sidelight type planar illumination device using a point light source.

  Conventionally, liquid crystal display devices have been widely used as display devices for electronic devices such as personal computers and mobile phones. Since a liquid crystal is not a self-luminous display element unlike a cathode ray tube or the like, for example, in a transmissive liquid crystal display device, illumination means for irradiating light to the liquid crystal panel is indispensable, and reflection using external light is required. In many cases, the liquid crystal display device of the type and the transflective type is also provided with auxiliary illumination means to enable use in a dark place. A sidelight type planar illumination device having a light guide plate and a light source disposed on the side of the light guide plate as main components has an advantage that it can be easily thinned. It is suitably used as an illuminating means, and a cold cathode tube or the like that is a linear light source has been used as the light source. However, in recent years, with the improvement in performance of white light emitting diodes (LEDs), in order to further reduce the size and thickness and reduce power consumption, planar lighting devices using white LEDs as point light sources as light sources have increased. ing.

  FIG. 6 is an exploded perspective view schematically showing, as an example, a configuration in which the above-described sidelight type planar illumination device is applied to a backlight of a liquid crystal display device. In FIG. 6, the planar illumination device 100 includes a light guide plate 101, a point light source 102, a reflection member 103, and optical members 104 and 105. Here, the point light source 102 is a white LED, and the light guide plate 101 is a transparent member formed by injection molding, for example, polycarbonate resin or the like. In general, a pattern for diffusing and reflecting light is formed on the back surface 101 b of the light guide plate 101. The reflection member 103 is a sheet material for regular reflection or diffuse reflection of light leaking from the back surface 101b of the light guide plate, and the optical member usually has a light diffusion sheet 104 for diffusing and uniformizing the light, and The prism sheet 105 etc. for condensing light and improving front luminance are included. In many cases, these components are fixed using a frame-like housing frame 106 to form an integral backlight unit, or a liquid crystal panel (not shown) disposed on the optical members 104 and 105 is also used. A single liquid crystal display device is formed by integrating them (see, for example, Patent Document 1).

  In the planar illumination device 100, the emitted light from the point light source 102 enters the light guide plate 101 from the light incident surface 101c, and is repeatedly reflected between the back surface 101b and the output surface 101a to enter the light guide plate 101. In the process of propagating light, a part thereof is diffusely reflected by the diffuse reflection pattern formed on the back surface 101b and is emitted from the exit surface 101a to irradiate the liquid crystal panel. Therefore, in order to ensure sufficient luminance of the planar illumination device 100, it is important to first improve the utilization efficiency of the emitted light from the point light source 102. In general, the LED used as the point light source 102 is a light emitting element having directivity, and in the planar illumination device 100, the LED is arranged so that the main light emitting direction is the direction of the light incident surface 101c. However, the light emitted from the LED includes light that leaks in a direction different from the direction of the light incident surface 101c through the package or the sealing material (hereinafter referred to as leakage light), and this leakage light is used as illumination light. There is a problem that the light utilization efficiency is lowered because the light cannot be used.

As a means for coping with leakage light from such a light source, it has been proposed to form a reflection surface for light emitted sideways from the LED on a part of the light guide plate (see, for example, Patent Document 2).
JP 2002-98945 A JP 2002-258283 A

  However, the means described in Patent Document 2 is based on the premise that the light guide plate has a specific form, and it cannot be said that the reflection efficiency of leaked light is sufficient.

  In view of the above problems, an object of the present invention is to provide a sidelight type planar illumination device that improves the utilization efficiency of light emitted from a point light source.

  In order to achieve the above object, a planar illumination device according to the present invention includes a light guide plate, a point light source disposed on the side of the light guide plate, and a frame-shaped housing frame that holds the light guide plate. The point light source is housed in a light source housing portion surrounded by a side wall of the housing frame and a light incident surface of the light guide plate.

  In another aspect, the planar illumination device according to the present invention is configured such that the light source housing portion includes one or a plurality of sections including a recess formed in one or both of the housing frame and the light guide plate. The point light source is arranged in each of the sections.

  In another aspect, the planar illumination device according to the present invention is characterized in that a corner portion on the housing frame side of the section is formed in a curved surface shape or a planar shape.

  In another aspect, the planar lighting device according to the present invention has a shape in which the section extends from a side wall side of the housing frame surrounding the light source housing portion toward a light incident surface side of the light guide plate. It is characterized by.

  In another aspect, in the planar illumination device according to the present invention, the point light source is mounted on a flexible printed circuit board, and at least a part of the flexible printed circuit board is fixed to the light guide plate. It is characterized by that.

  According to the planar illumination device according to the present invention, the leakage light emitted from the point light source in the direction different from the light incident surface direction of the light guide plate is reflected by the wall surrounding the light source housing portion, and therefore the path is It becomes possible to change the direction of the light incident surface to enter the light guide plate, and the utilization efficiency of the light emitted from the light source is improved. In particular, by dividing the light source accommodating portion into a plurality of recesses and arranging point-like light sources in each of the compartments, reflection of leakage light occurs at a position close to each point-like light source, so that leakage light is collected more effectively. Light can be reflected. At that time, the shape of the section where the point light source is arranged is formed in a shape in which the corner portion on the housing frame side is curved or planar, or in a shape that spreads from the housing frame side toward the light guide plate side, Alternatively, by performing both of them, it is possible to effectively direct the path of the light leaked to the side and rear of the point light source forward.

  Moreover, in the planar lighting device according to the present invention, the flexible printed circuit board on which the point light source is mounted is directly fixed to the light guide plate, so that each point light source can be easily and against the light incident surface of the light guide plate. Accurate alignment is possible, and utilization efficiency of light emitted from the light source is improved.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig.1 (a) is a top view which shows the principal part of the planar illuminating device 10 in one Embodiment of this invention, FIG.1 (b) is the AA 'sectional view taken on the line. The planar illumination device 10 includes a light guide plate 11, a plurality (three in this embodiment) of point light sources 12 a, 12 b, 12 c, a flexible printed circuit board (FPC) 13, and a housing frame 14. The light guide plate 11 is a plate-like light guide formed by molding a transparent resin material. Suitable transparent resin materials include methacrylic resin, polycarbonate resin, polystyrene resin, polyolefin resin, amorphous polyolefin resin, polyester. Resin, polystyrene resin, transparent fluororesin, epoxy resin and the like are included. The housing frame 14 is a frame-like member having a region for accommodating the light guide plate 11 at the center thereof, and is molded from a resin material mixed with a white pigment and has high light reflectivity. Suitable materials for the housing frame 14 include polycarbonate resin mixed with titanium oxide as a white pigment. In the present embodiment, the light guide plate 11 is fixed by engaging protrusions 11 d formed on two opposite sides with corresponding recesses (not shown) of the housing frame 14. The fixing method with respect to the housing frame 14 is not specifically limited, For example, a double-sided adhesive tape etc. may be used.

  The point light sources 12a, 12b, and 12c are made of white LEDs mounted on the FPC 13. The FPC 13 is attached to one main surface 11b of the light guide plate 11 and the housing frame 14 by, for example, a double-sided adhesive tape (not shown). It is fixed (see FIG. 1B). At this time, the point light sources 12a, 12b, and 12c are arranged on the side of the light incident surface 11c that is one end surface of the light guide plate 11 so that the main light emission direction is the direction of the light incident surface 11c. Regions 15a, 15b, and 15c surrounded by the side wall 14a forming one side of the housing frame 14 and the light incident surface 11c of the light guide plate 11 (hereinafter, these regions are referred to as light source accommodating portions, and 15a, 15b, and 15c are referred to as a whole. In this case, the reference numeral 15 is attached). As shown in FIG. 1, the light source accommodating portion 15 is divided into three compartments 15 a, 15 b, and 15 c that are recessed portions formed in the side wall 14 a, and the point light sources 12 a, 12 b, and 12 c are arranged on the housing frame 14. Surrounded on three sides by light-reflective walls, they are arranged in the sections 15a, 15b and 15c, respectively. Further, the corner 18 on the housing frame side of each of the sections 15a, 15b, and 15c is formed as a curved surface that forms an arcuate curve in FIG. Although the FPC 13 is fixed to the back surface 11b side of the light guide plate 11, the present invention is not limited to such a configuration, and the FPC 13 may be fixed to the emission surface 11a side. .

  Next, the operation of the planar illumination device 10 will be described by taking as an example the case of using it as a backlight that emits light from the back side of the liquid crystal panel. At this time, it is assumed that the light emitting surface is the main surface 11a, and the opposing main surface (back surface) 11b is formed with a reflection pattern that diffuses and reflects light by fine uneven processing or white ink dot printing. Light emitted from the point light sources 12a, 12b, and 12c enters the light guide plate 11 through the light incident surface 11c, and propagates through the light guide plate 11 by repeatedly reflecting between the output surface 11a and the back surface 11b. In the process, a part of the light is diffusely reflected by the reflection pattern formed on the back surface 11b, and emitted from the emission surface 11a to irradiate the liquid crystal panel. At this time, the surface illumination device 10 is emitted not only from the light source forward, that is, in the direction of the light incident surface 11c, but also from the side or rear through the package or sealing material of the point light sources 12a, 12b, and 12c. The leaked light is reflected by the walls 14 a, 16, and 17 that form the light source housing portion 15 to change the course thereof, and is incident on the light incident surface 11 c to be used as illumination light. Further, since the FPC 13 on which the point light sources 12a, 12b, and 12c are mounted is directly fixed to the light guide plate 11, the positional deviation between the point light sources 12a, 12b, and 12c and the light incident surface 11c of the light guide plate 11 is achieved. In this case, the light emitted forward from the light source can be efficiently captured. Further, in the present embodiment, since the FPC 13 covers the light source housing 15 and is also fixed to the housing frame 14, the positional deviation between the point light sources 12a, 12b, 12c and the light incident surface 11c of the light guide plate 11 is prevented. The suppression effect is further increased. In particular, since the partition walls 16 and 17 project from the light source housing 15, the area where the FPC 13 is fixed to the housing frame 14 is increased, and the effect is greatly increased. The inventors of the present invention have confirmed that an improvement in luminance of about 10% to 20% can be seen on average by making the planar lighting device shown in FIG.

  Here, in the planar lighting device 10 shown in FIG. 1, the corner portion 18 on the housing frame 14 side of each section 15a, 15b, 15c has a curved surface forming an arcuate curve in FIG. 1 (a). However, the shape and size of the corner portion 18 are appropriately set in consideration of conditions such as the light emission characteristics of the LED to be used. For example, like the corner portion 22 shown in FIG. Including the case where it is formed as a chamfered portion by a plane, or a corner portion that is not particularly subjected to curved surface or flattening processing, such as a corner portion 24 shown in FIG. Further, each section of the light source housing section is like a section 25a shown in FIG. 2 (c) in order to improve the reflection efficiency of the leaked light from the point light sources 12a, 12b, 12c in the direction of the light incident surface 11c. In addition, the corner portion 26 may be formed so as to expand from the side wall 14a side of the housing frame 14 toward the light incident surface 11c side of the light guide plate 11. In this case, the corner portion 26 is formed as shown in FIGS. It can be formed in the same manner as the corner portion described above based on b).

  Further, in the planar illumination device 10 shown in FIG. 1, the partition walls 16 and 17 are projected between the respective point light sources 12a, 12b, and 12c, and one point is formed in each of the sections 15a, 15b, and 15c formed. The light sources 12a, 12b, and 12c are arranged. This configuration makes the best use of the fact that a plurality of light sources are scattered in the form of dots instead of continuously extending the light source like a linear light source in forming the light source housing 15. This is preferable. However, the present invention is not limited to the number of point light sources arranged in one section, but includes a case where a plurality of point light sources are arranged in one section, and in particular, the light source accommodating portion 31 shown in FIG. As described above, this includes the case where the whole is made into one section and all the point light sources 12a, 12b, 12c are arranged there.

  Furthermore, depending on conditions such as a space that can be used as the light source accommodating portion, the light source accommodating portion of the planar light source device according to the present invention is formed from a recess formed on the light guide plate 11 side as shown in FIG. 4a, or as shown in FIG. 4 (b), the compartments 42a, 42b, 42c are formed of recesses formed on both the housing frame 14 side and the light guide plate side 11. It may have. Even in this case, the shape of each of the partitions 41a, 41b, 41c, 42a, 42b, 42c and the shape of the corner 43 on the housing frame side are the same as those in the case of the light source housing described above with reference to FIGS. Can be formed.

  Here, in the planar illumination device according to the present invention, the utilization efficiency of the emitted light from the light source can be further improved by covering the upper side and the lower side of the light source housing portion with the light reflecting member. Suitable light reflecting members include a sheet material such as a film on which a metal such as silver is vapor-deposited, a white film or a film on which white paint is printed, in addition to a light-reflective resin material that forms a housing frame, or This includes metal plates such as aluminum plates that have been mirror-finished. Although the present invention is not limited to a specific embodiment of this means, for example, a preferred embodiment in the case of using a planar illumination device as a backlight is as follows.

  FIG. 5 shows a planar illumination device in which an optical member 51 and a light reflection member 53 are arranged on the light emitting surface 11a side and the back surface 11b side of the light guide plate 11, respectively, in addition to the configuration of the planar illumination device 10 shown in FIG. It is the figure which showed the structure with sectional drawing similar to FIG.1 (b). Here, the optical member 51 is a light diffusing sheet for diffusing light to make it uniform, or a prism sheet for condensing light to improve the front luminance, and the light reflecting member 53 is a back surface of the light guide plate. It is a light reflecting sheet for reflecting the light leaking from 11 b and re-entering the light guide plate 11. In this case, the light reflecting member 53 is made of the above-described sheet material or metal plate, and covering the lower side of the light source housing portion 15 (see FIG. 1A) with the light reflecting member means that this light reflecting member. This is achieved by extending 23 to the lower side of the light source housing 15. Further, in order to fix the optical member 51 to the housing frame 14, a light-shielding double-sided adhesive tape 52 is usually used. However, covering the upper side of the light source housing 15 with a light reflecting member is used as this double-sided adhesive tape. This is achieved by using a light reflection layer 52a and a light shielding layer 52b having two layers and arranging the light reflection layer 52a so as to face the light source housing 15 side.

  The case where the planar illumination device according to the present invention is mainly used as a backlight has been described above as an example. Unlike the front light, which is required to have no light diffusibility on the surface of the light guide plate in order to irradiate light from the side where the liquid crystal panel is viewed, the backlight is made uniform by means such as a light diffusion sheet. Therefore, the present invention is preferable as an application example of the present invention. However, the present invention is not limited by the configuration of the light guide plate or the light irradiation method from the light guide plate, and therefore any side including the front light. It can be applied to a ride type planar illumination device. In the above description, the point light source is disposed on one end surface of the quadrilateral light guide plate. However, the present invention provides a point light source with respect to a plurality of end surfaces of the light guide plate having an arbitrary shape. It includes the case where it arranges.

It is a figure which shows the principal part of the planar illuminating device in one Embodiment of this invention, (a) is a top view, (b) is the sectional view on the AA 'line of (a). In one Embodiment of this invention, it is a top view which shows the various aspects of the division which makes a light source accommodating part. In one Embodiment of this invention, it is a top view which shows another aspect of a light source accommodating part. In one Embodiment of this invention, it is a top view which shows the light source accommodating part which formed the recessed part in the light-guide plate side. In one Embodiment of this invention, it is sectional drawing similar to FIG.1 (b) which shows the example in the case of covering the upper and lower sides of a light source accommodating part with a light reflection member. It is a disassembled perspective view which shows typically the typical structure of the conventional planar illuminating device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Planar illuminating device 11 Light guide plate 12a, 12b, 12c Point light source 13 Flexible printed circuit board 14 Housing frame 15 Light source accommodating part 15a, 15b, 15c Division

Claims (5)

In a planar lighting device comprising a light guide plate, a point light source arranged on the side of the light guide plate, and a frame-shaped housing frame that holds the light guide plate,
The planar illumination device, wherein the point light source is housed in a light source housing portion surrounded by a side wall of the housing frame and a light incident surface of the light guide plate.   The light source accommodating portion has one or a plurality of sections each formed of a recess formed in one or both of the housing frame and the light guide plate, and each of the sections includes one or a plurality of the points. The planar illumination device according to claim 1, wherein a planar light source is disposed.   The planar illumination device according to claim 1 or 2, wherein a corner portion on the housing frame side of the section is formed in a curved surface shape or a planar shape.   The said division has the shape which spreads toward the light-incident surface side of the said light-guide plate from the side wall side of the said housing frame surrounding the said light source accommodating part, The any one of Claim 1 to 3 characterized by the above-mentioned. The surface illumination device described in 1. The point light source is mounted on a flexible printed circuit board, and at least a part of the flexible printed circuit board is fixed to the light guide plate. Planar lighting device.

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