JP4701926B2 - Surface light source device - Google Patents

Description

  The present invention relates to a sidelight type surface light source device using a point light source.

  Conventionally, as a backlight for a flat panel display module such as a liquid crystal display module, a light source is disposed opposite to one end surface of a rectangular light guide plate, and light emitted from the light source is guided into the light guide plate and the back of the display panel A so-called side light type surface light source device that emits in a planar shape from a light emitting area of one main surface opposed to the light source is often used. As a light source in this case, a point light source such as a light emitting diode (hereinafter referred to as an LED (Light Emitting Diode)) is often employed in order to promote a reduction in size and thickness of a display module including a backlight.

In recent years, liquid crystal display modules using the above-mentioned side light type surface light source device using a point light source as a backlight have been widely used as a display for mobile devices such as mobile phones. Is done. As a surface light source device that is extremely advantageous for promoting a particularly small and thin liquid crystal display module, an LED is directly mounted on a flexible wiring board (hereinafter referred to as FPC (Flexible Printed Circuit Board)). Such a sidelight type surface light source device is known.
JP-A-2005-17964

  In the surface light source device in which the above-described LEDs are directly mounted on the FPC, since the LEDs are supported by the flexible FPC, the plurality of LEDs are accurately and reliably positioned at predetermined positions with respect to the light incident end surface of the light guide plate. Difficult to position.

  If the positions of the plurality of LEDs with respect to the respective light guide plates are shifted, it becomes impossible to emit planar irradiation light having a uniform luminance distribution, which causes display defects such as luminance unevenness in the display of the liquid crystal display panel.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a surface light source device that is convenient for downsizing and thinning, in which a plurality of point light sources are accurately and reliably supported at a predetermined position with respect to a light guide plate and can stably emit irradiation light having a uniform luminance distribution. Is to provide.

The surface light source device of the present invention has a belt-like portion on which a light emitting element is mounted, and a plurality of slits opened toward one of the two long sides of the belt-like portion are formed in the belt-like portion. A predetermined distance between the one long side of each of the flexible wiring board and the predetermined mounting section defined by the slit, and the light exit surface is the one of the two long sides. The light emitted from the light emitting surface is formed in a plate shape having a plurality of light emitting elements mounted one by one, a first main surface and a second main surface so as to face the long side. A light guide plate that is incident from a side surface, and the flexible wiring board is configured so that the light emitting surface of the light emitting element mounted on the mounting section is in close contact with the side surface of the light guide plate. The end of the belt-like portion on the long side of the one of the long sides is the front Wherein while being adhered to the first major surface for each mounting compartment, that end of the belt portion of the other long side of said two long sides is bonded to the second major surface It is what.

According to the present invention, there is provided a surface light source device that is convenient for miniaturization and thinning, in which a plurality of point light sources are accurately and reliably supported at a predetermined position with respect to a light guide plate and can stably emit irradiation light having a uniform luminance distribution. can get.

  FIG. 1 is a schematic cross-sectional view showing a liquid crystal display module using a surface light source device as one embodiment of the present invention.

  The housing of the present liquid crystal display module is covered with a storage case 1 in which a top plate of a box having a flat outer shape is removed and a cover case 2 having the same outer shape from which a bottom plate is removed in a fitted state. Being done. The storage case 1 is formed in a structure having a two-stage storage space using a resin material by, for example, an injection molding method. That is, two spaces of a lower space and an upper space wider than the step 1c by an area of the step 1c are formed at a predetermined height position of the side wall 1b erected on the peripheral edge of the bottom plate 1a. The storage space is formed in two stages. The cover case 2 is provided with a display window 2a.

  A liquid crystal display panel 3 is stored in the upper space of the storage case 1. The liquid crystal display panel 3 is joined to a pair of glass substrates 4 and 5 on which electrodes (not shown) are formed, with a predetermined gap maintained by a frame-shaped sealing material (not shown) with the respective electrode forming surfaces facing each other. The liquid crystal is sealed between the glass substrates 4 and 5 surrounded by the frame-shaped sealing material. A pair of front and rear polarizing plates 6 and 7 are attached to the outer surfaces of the glass substrates 4 and 5, respectively. The liquid crystal display panel 3 of the present embodiment is an active matrix type liquid crystal display panel, and a plurality of pixel electrodes (not shown) are arranged in a matrix arrangement on the inner surface of one of the pair of glass substrates 4 and 5, for example, the glass substrate 5. A single-layered counter electrode (not shown) is provided on the inner surface of the other glass substrate 4 opposite to the glass substrate 4.

  One glass substrate 5 out of the glass substrates 4 and 5 is formed with an extending portion 5 a by extending an edge portion outward from a corresponding end surface of the other glass substrate 4. On the surface of the extension portion 5a (extension surface of the electrode forming surface), wirings connected to the electrodes of both the substrates 4 and 5 are routed, and connection terminals (not shown) of these wirings are provided. Are arranged side by side.

  A driving circuit element 8 for driving the liquid crystal is directly mounted on the extending portion 5a in which the above-described lead wiring and connection terminal row are formed by a COG (Chip On Glass) method. A flexible wiring board 9 for electrically connecting a driving control circuit board (not shown) for controlling the driving of the entire liquid crystal display module provided outside and the driving circuit element 8 is provided at the edge of the extending part 5a. Are conductively joined.

  A backlight unit 10 is stored in a lower space of the storage case 1. The backlight unit 10 of the present embodiment generally includes a light guide plate 11, LEDs 12 as a plurality of point light sources, an FPC 13 mounted with these, a light reflection sheet 14 that prevents light leakage, and an optical sheet for adjusting irradiation light It consists of a laminate 15.

  The light guide plate 11 is formed in a substantially rectangular plate shape using a transparent resin material such as acrylic resin, and one end surface of the four side end surfaces is an incident end surface 11a on which light is incident, and is perpendicular to the incident end surface 11a. One main surface 11b of the pair of main surfaces extending in the direction is a light emitting surface (front surface) from which light is emitted, and a main surface (rear surface) 11c opposite to the light emitting surface 11b has a plurality of fine surfaces. A groove 11d is formed. The fine groove 11d is formed in a pattern in which three concentric circles each centering on each LED 12 intersect. When light propagating through the light guide plate 11 enters the micro grooves 11d formed in the concentric pattern, the incident light is internally reflected to the front surface 11b side serving as a light output surface, and the liquid crystal display panel that is an irradiation target from the front surface 11b. 3 is emitted toward the back surface.

  In the present embodiment, three LEDs 12 are installed at equal intervals on the incident end surface 11a of the light guide plate 11 with the light emitting surfaces 121 in close contact with each other. These LEDs 12 are directly mounted on the FPC 13 in which energization wiring and the like are patterned by a COF (Chip On Film) method, and a part of the FPC 13 extends out of the storage case 1, and the drive control circuit board. Is electrically connected.

  2 (a) to 2 (c) show an FPC 13 in which three LEDs 12a to 12c are mounted with COF, (a) is a developed view thereof, (b) is a sectional view taken along line BB of (a), (C) is a side view which shows an installation state. FIG. 3 is a partial perspective view showing an installation state of the LED 12c among the three LEDs 12a to 12c.

  As shown in the development view of FIG. 2A, the FPC 13 of this embodiment includes a strip-shaped LED mounting portion 131 and a lead wiring portion 132 in which one end portion extends at a right angle. In the LED mounting portion 131, three LEDs 12a to 12c are arranged at equal intervals. Slits 13a and 13b are formed between the adjacent LEDs 12a and 12b and between the LEDs 12b and 12c of the LED mounting portion 131, and a slit 13c is formed between the lead wiring portion 132 and the adjacent LED 12c. These slits 13a to 13c are formed in the same shape, and the length L thereof is set to 3/4 to 4/5 of the width W of the LED mounting portion 131 as shown in FIG. The positions of the slits 13a to 13c are the same as the mounting sections 131a to 131c of the LEDs 12a to 12c divided by the slits 13a to 13c, and the LEDs 12a to 12c are mounted to the mounting sections 131a to 131c. It is set so that it may be arranged in the center of the tip part. Note that a connection terminal portion 133 is formed at the leading end portion of the lead wiring portion 132 by exposing the leading end portion of the wiring without depositing an insulating protective film.

Here, the dimension e, that is, the distance from the base of each of the slits 13a to 13c to the light exit surface 121 of each of the LEDs 12a to 12c, the depth, width, and height of each of the LEDs 12a to 12c is a, b, c, and the light guide plate 11, respectively. E> 2a + t (1)
Is set to

  Then, the FPC 13 on which the above-described LEDs 12a to 12c are mounted is curved so that the LED 12a to 12c mounting surface is inside, as shown in FIG. 2 (c) and FIG. 3, and the light emission surfaces of the respective LEDs 12a to 12c The light guide plate 11 is installed at the light incident side end of the light guide plate 11 in a state where the entire 121 is in close contact with the light incident end surface 11a of the light guide plate. In this case, the end portion 131d of the LED mounting portion 131 of the FPC 13 where the slits 13a to 13c are not drilled is bonded to the light incident side end portion of the rear surface 11c of the light guide plate by an adhesive member such as a double-sided adhesive sheet (not shown), and The LED 12a to 12c mounting side end portion 131e is a light incident side end portion of the light guide plate front surface 11b, a double-sided pressure-sensitive adhesive sheet (not shown) or the like so that the entire light exit surface 121 of each LED 12a to 12c is in close contact with the light incident end surface 11a of the light guide plate It is bonded by an adhesive member.

  By installing the plurality of LEDs 12 a to 12 c with respect to the light guide plate 11 as described above, the respective LEDs 12 a to 12 c have the entire light emission surface 121 of the light guide plate 11 by the elasticity (restoring force) of the curved FPC 13 itself. It is stably supported in a state where it is in close contact with the light incident end face 11a with an appropriate pressure (hereinafter referred to as an appropriate pressure contact state). Here, even if the mounting position of any of the LEDs 12a to 12c is slightly deviated from the normal position, the mounting sections 131a and 131b, each of the LEDs 12a to 12c can be independently deformed by the slits 13a to 13c, respectively. Since each dimension is set as shown in the above equation (1), the LEDs 12a to 12c are adjusted by deforming the mounting sections 131a, 131b, and 131c and adjusting the attaching position of the end 131d. Each misalignment is easily corrected.

For example, as shown in FIG. 4A, when the mounting position of the LED 12b is shifted toward the slit base by Δd1, the amount of deviation Δd1 is Δd1 <e− (2a + t).
Then, as shown in FIG. 4B, the FPC of the LED 12b mounting section 131b is deformed so as to have a small curvature (large curvature radius) by its own elasticity, and the above-described proper pressure contact state is obtained. At this time, since the mounting section 131b of the LED 12b is separated from the mounting sections 131a and 131c of the adjacent LEDs 12a and 12c by the slits 13a and 13b on both sides, the self-correction by the elastic deformation described above is easily performed. The shift amount Δd1 is Δd1 ≧ e− (2a + t).
4C, the adhesion width of the FPC 13 to the rear surface 11c of the light guide plate is slightly reduced by an amount Δp as compared to the case of normal mounting shown in FIG. 3C. That is, the FPC end 131d protrudes from the light incident end face 11a by Δp. This protrusion amount Δp is set according to the shift amount Δd1 so that the proper pressure contact state can be obtained.

  On the other hand, as shown in FIG. 5A, when the mounting position of the LED 12b is shifted to the tip side of the mounting section 131b on the contrary by Δd2, the FPC of the mounting section 131b is changed as shown in FIG. In a curved shape with a larger curvature (smaller radius of curvature) than when placed in the normal position (see adjacent LED placement section 131a), it is elastically deformed by being separated from the adjacent LED mounting sections 131a and 131c. Thus, the proper pressure contact state is obtained. In this case as well, when the amount of deviation Δd2 is large, it can be dealt with by increasing the adhesion width of the FPC 13 to the rear surface 11c of the light guide plate. However, if there is room in the storage space (see FIG. 1) of the curved FPC 13 in the storage case 1. The adhesive width need not be changed.

  In this way, by separating the mounting sections 131a to 131c of the three LEDs 12a to 12c in the FPC 13 by the slits 13a to 13c, all the three LEDs 12a to 12c are always in the proper pressure contact state regardless of the mounting position on the FPC 13. Can be installed. As a result, irradiation light having a uniform luminance distribution is stably emitted from the light emission surface 11b of the light guide plate 11.

  Returning to FIG. 1, the light reflecting film 14 is provided on the rear surface 11 c of the light guide plate 11. The light reflecting film 14 is provided to reflect the light propagating through the light guide plate 11 and reflected outside without being internally reflected by the minute grooves 11 d on the rear surface 11 c and reentering the light guide plate 11. . The light reflecting film 14 of this example is formed by depositing silver on a PET (Poly-Ethylene Terephthalate) film, and has a high light reflectance.

  On the front surface 11b of the light guide plate 11, an optical sheet laminate 15 is installed. The optical sheet laminate 15 is formed by laminating a diffusion sheet 16 and two prism sheets 17 and 18 in order from the light guide plate 11 side.

  The diffusion sheet 16 is provided for diffusing and transmitting the light emitted from the light emitting surface 11b to make the luminance distribution of the planar emitted light uniform, and is used as the light emitting side of a transparent base sheet such as PET. A light diffusion layer is laminated on the surface.

  The prism sheets 17 and 18 are provided for condensing the emitted light from the light guide plate 11 diffused by the diffusion sheet 16 toward the normal direction of the liquid crystal display panel 3 to be irradiated. The prism sheets 17 and 18 of this example are prism sheets in which a plurality of protrusions (not shown) are formed in parallel on one main surface, and are installed with the extending directions of the protrusions orthogonal to each other. .

  In the backlight unit 10 configured as described above, the light emitted from the LEDs 12 a to 12 c is uniformly incident from the light incident end surface 11 a into the light guide plate 11 and propagates through the light guide plate 11. Is incident on the fine groove 11d and reflected from the inner surface toward the front surface 11b or emitted to the outside of the light guide plate 11. The light emitted to the outside of the light guide plate 11 is reflected by the light reflection film 14, reenters the light guide plate 11, and travels toward the front surface 11b.

  The light emitted from the front surface 11b of the light guide plate is emitted so as to be substantially aligned in the normal direction of the front surface 11b because the fine grooves 11d are formed concentrically around the LEDs 12a to 12c. In addition, since the three LEDs 12a to 12c are arranged on the light incident end face 11a evenly and in an appropriate pressure contact state, the distribution of light emitted from the front face 11b is made uniform. Furthermore, since each LED 12a-12c is covered with FPC13, even if it inject | emits from each LED12a-12c, the malfunction which the leak light which did not enter in the light-guide plate 11 will be scattered and it becomes stray light is prevented. As a result, planar light having a uniform luminance distribution and high front luminance emitted from the front surface 11 b of the light guide plate 11 and transmitted through the optical laminate 15 is irradiated toward the liquid crystal display panel 3.

  As described above, in the liquid crystal display module of the present embodiment, the plurality of LEDs 12a to 12c are individually separated by the slits 13a to 13c and mounted on the FPC 13, so that even if the mounting positions are shifted, the individual LEDs 12a to 12c are individually separated. The FPC of the mounting section of the LED flexibly self-corrects its curvature without being affected by the other LED mounting sections separated by the elasticity of the material itself, and all the LEDs 12a to 12c always have their light emitting surfaces 121 guided to the light guide plate. The light incident end face 11a is held in close contact with the light incident end face 11a. Therefore, by directly mounting the point light source LEDs 12a to 12c on the FPC 13 having the wiring circuit, the surface light source device can be reduced in size and thickness, and all the LEDs 12a to 12c can be guided regardless of the mounting position on the FPC 13. It can always be easily installed in an appropriate pressure contact state at an accurate position with respect to the light plate light incident end face 11a. As a result, a planar illumination light having a uniform luminance distribution and high front luminance can be emitted, and a surface light source device that is easy to manufacture and facilitates downsizing and thinning can be obtained. .

In addition, this invention is not limited to said embodiment.
For example, as shown in FIGS. 6A and 6B, a flexible wiring board 22 on which a plurality of, for example, three LEDs 21a to 21c are mounted is straightly extended without being inverted as in the above embodiment. In this state, the light emitting surfaces 211 of the LEDs 21a to 21c may be in close contact pressure contact with the light guide plate light incident end surface 11a. In this case, the displacement of the mounting positions of the LEDs 21a to 21c is absorbed by bending the FPC 22 of each LED mounting section as indicated by a two-dot chain line, and the light emission surfaces 211 of all the LEDs 21a to 21c are guided. The optical plate can be brought into close contact with the light incident end face 11a. Also here, each LED mounting section is separated from the adjacent portion by the slits 22a and 22b, so that each LED 21a to 21c can be flexibly bent individually, and each of the LEDs 21a to 21c can absorb elasticity by using the elasticity of the FPC 22 itself. Is played smoothly.

  The present invention is also effectively applied to a case where the point light source is held by a dedicated holder at a position separated by a predetermined distance without being brought into pressure contact with the light incident end face of the light guide plate.

  Furthermore, the present invention is not limited to a surface light source device using a light emitting diode as a point light source, but is also effectively applied to a surface light source device using other various point light sources such as a micro light bulb.

  In addition, the present invention is not limited to the liquid crystal display module, and can naturally be applied to other various flat panel display modules including a surface light source device using a point light source.

It is a typical sectional view showing the whole liquid crystal display module composition to which the surface light source device as one embodiment of the present invention is applied. (A) is a top view which expands and shows FPC with which LED which is a main member of the liquid crystal display module shown in FIG. 1 was mounted, (b) is the BB sectional drawing, (c) is the installation state. FIG. It is a fragmentary perspective view which expands and shows the installation state of the said FPC. 4A and 4B are explanatory diagrams showing an LED mounting position deviation correcting action by the FPC, where FIG. 5A is a state before installation, FIG. 5B is a state after installation when the mounting position deviation is small, and FIG. The state after installation of each is shown. It is explanatory drawing which shows the other LED mounting position shift correction effect | action by said FPC, (a) shows the state before installation, (b) has shown the state after installation. It is explanatory drawing which shows the LED mounting position shift correction effect | action in the modification of the said embodiment, (a) shows the state before installation, (b) has shown the state after installation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Storage case 2 Cover case 3 Liquid crystal display panel 4, 5 Glass substrate 6, 7 Polarizing plate 10 Surface light source device 11 Light guide plate 12a, 12b, 12c
21a, 21b, 21c LED (light emitting diode)
13, 22 FPC (flexible wiring board)
13a, 13b, 13c
22a, 22b Slit 14 Light reflection sheet 15 Optical sheet laminate 16 Diffusion sheet 17, 18 Prism sheet

Claims (4)

A flexible wiring board having a belt-like portion on which the light-emitting element is mounted, and a plurality of slits opened toward one long side of the two long sides of the belt-like portion ;
A predetermined distance is provided between each of the predetermined mounting sections defined by the slit and the one long side so that the light emission surface faces the one long side of the two long sides. A plurality of light emitting elements mounted one by one,
A light guide plate that is formed in a plate shape having a first main surface and a second main surface, and in which light emitted from the light emitting surface is incident from a side surface;
With
The flexible wiring board is arranged on the one long side of the two long sides such that the light emitting surface of the light emitting element mounted on the mounting section is in close contact with the side surface of the light guide plate. The end of the band-shaped portion is bonded to the first main surface for each mounting section, and the end of the band-shaped portion on the other long side of the two long sides is the second main surface. A surface light source device that is adhered to the surface light source device. 2. The surface light source device according to claim 1, wherein the belt-like portion is folded in a curved shape so as to enclose the light emitting element . 3. The surface light source device according to claim 1 , wherein the light guide plate is formed such that the first main surface is an exit surface of light from the light emitting element incident on the light guide plate . 4. 4. The slit according to claim 1, wherein the slit has a length extending from the one long side toward the other long side and reaching an adhesion region to the second main surface. 5. The surface light source device described in 1.

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