JP2005321586A - Surface light source unit and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce loss of light quantity brought about in the case of directly fixing an FPC substrate with an LED mounted thereon and a light guide plate to each other with a fixing tape. <P>SOLUTION: A construction of a surface light source unit is provided with: an LED 1; the FPC substrate 7 with the LED 1 mounted thereon; the light guide plate 2 to guide light emitted from the LED 1; a reflection sheet 4 disposed and superposed on a second surface 22 of the light guide plate 2 opposite to a first surface 21 and reflecting light, guided to the second surface 22 side with the light guide plate 2, to the first surface 21 side; and a double-sided adhesion tape 8 fixing the FPC substrate 7 and the light guide plate 2 on a position opposite to the reflection sheet 4 and making the surface opposite to the reflection sheet 4 be a light reflection surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface light source unit that generates planar light and a liquid crystal display device using the surface light source unit.

  2. Description of the Related Art In recent years, liquid crystal display devices have been mounted on various electronic devices ranging from personal computers, PDAs (Personal Digital Assistants), portable information terminals such as mobile phones, and home appliances such as video cameras and digital cameras. In general, in a liquid crystal display device, since the liquid crystal itself does not emit light, a backlight unit or a front light unit is used as a surface light source unit for displaying an image brightly.

  Backlight units are roughly divided into an area light system (direct system) in which a light source is arranged directly under the liquid crystal panel unit, and an edge light system (light guide plate system) in which a light source is arranged at the end (edge) of the light guide plate. It is properly used according to the purpose. In particular, the edge light method has advantages in that the backlight unit can be made thinner than the area light method, heat from the light source is not easily transmitted to the liquid crystal panel unit, and uniform surface emission can be obtained.

  An edge-light type backlight unit includes a plurality of light sources, a light guide plate that guides light incident from the plurality of light sources, and emits the light to the first surface side (liquid crystal panel unit side). The optical sheet includes a plurality of optical sheets arranged in a laminated state on the first surface side, and a reflection sheet disposed in close proximity to and opposed to the second surface opposite to the first surface of the light guide plate. As such an edge light type backlight unit, one in which a light source such as an LED (Light Emitting Diode) is mounted on a flexible printed wiring board (hereinafter referred to as an FPC board) is known (for example, Patent Documents 1 to 3 below). 4).

JP 2001-117093 A Japanese Patent Laid-Open No. 2003-92020 JP 2003-90993 A JP 2002-330377 A

  By the way, when the planar light is uniformly irradiated from the backlight unit to the liquid crystal panel unit, the positional relationship between each light source and the light guide plate is important. This is because if the positional relationship between each light source and the light guide plate is inconsistent, the distribution of light applied to the liquid crystal panel unit varies, which appears due to uneven brightness on the liquid crystal screen. In order to eliminate such luminance unevenness, it is necessary to accurately align each light source mounted on the FPC board and the light guide plate in the manufacturing process of the backlight unit.

  In such a case, since the light source and the light guide plate cannot be directly fixed by bonding or the like, both are fixed via some intermediate member. At that time, in order to maintain the positional relationship between the light source and the light guide plate with high accuracy, it is effective to directly fix the FPC board on which the light source is mounted to the light guide plate. In view of the labor for manufacturing the backlight unit, it is desirable to fix the FPC board and the light guide plate with double-sided tape.

  However, when the FPC board and the light guide plate are fixed with the double-sided tape, a part of the light incident from the light source to the light guide plate is absorbed by the fixing part by the double-sided tape, and therefore the light quantity loss there The brightness will be lowered.

  A surface light source unit according to the present invention includes a light source, a mounting substrate on which the light source is mounted, a light guide plate that guides light emitted from the light source, and a second surface opposite to the first surface of the light guide plate. And a reflection sheet that reflects the light guided to the second surface side by the light guide plate to the first surface side, and the mounting substrate and the light guide plate are fixed at a position facing the reflection sheet. In addition, a fixing tape having a surface facing the reflection sheet as a light reflection surface is provided. The liquid crystal display device according to the present invention uses the surface light source unit having the above-described configuration.

  In the surface light source unit and the liquid crystal display device according to the present invention, the mounting substrate and the light guide plate are fixed by a fixing tape at a position facing the reflection sheet disposed to overlap the second surface of the light guide plate, and the fixing is performed. By making the surface of the tape facing the reflection sheet a light reflection surface, a part of the light taken from the light source to the light guide plate is reflected by the fixed tape, and this reflected light is reflected by the second light guide plate. The light is reflected by the reflection sheet on the surface and emitted from the first surface of the light guide plate.

  According to the present invention, it is possible to reduce the light amount loss when the mounting substrate on which the light source is mounted and the light guide plate are directly fixed by the fixing tape, thereby improving the luminance.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. The liquid crystal display device according to the present invention is mainly composed of a liquid crystal panel unit and a surface light source unit. The liquid crystal panel unit, for example, sandwiches a liquid crystal layer in which color filters, transparent electrodes, alignment films, liquid crystals, alignment films, transparent electrodes, etc. are stacked in order between two panel substrates (glass substrates) and deflects them outside An optical film such as a film or an antireflection film is arranged. In this liquid crystal panel unit, only light amount modulation of light passing therethrough is performed in the liquid crystal cell, so that the liquid crystal panel unit itself does not emit light. Therefore, in order to display an image (image) on the liquid crystal panel, a surface light source unit that emits planar light is required. In the present embodiment, a backlight unit will be described as an example of a surface light source unit, but the present invention is also applicable to a front light unit.

  FIG. 1 is an exploded view showing a configuration example of a backlight unit used in a liquid crystal display device according to an embodiment of the present invention. The illustrated backlight unit employs an edge light system, and is roughly divided into a plurality of white LEDs (light sources) 1, a light guide plate 2, a plurality of optical sheets 3, a reflection sheet 4, and a case. 5 and a holding frame 6.

  The LED 1 is mounted on an FPC board (mounting board) 7 using solder. On the FPC board 7, a plurality of LEDs 1 are mounted in a line at equal intervals in the depth direction of the figure (see FIG. 2). Each LED 1 is arranged to abut against (or in close proximity to) the end surface 20 of the light guide plate 2 as a primary light source for obtaining planar light. The FPC board 7 is provided with a connection terminal portion (not shown) integrally therewith, and the power for LED emission is supplied from the outside through this connection terminal portion. In addition, about the number of LED1, each size of the light-guide plate 2, the optical sheet 3, and the reflective sheet 4, it can change suitably according to the magnitude | size (panel size) of the liquid crystal panel unit used as light irradiation object.

  The light guide plate 2 is for uniformly emitting the light incident from the end face 20 of the light guide plate 2 to the outside while guiding the inside of the light guide plate 2. The light guide plate 2 is formed of a resin molded product having optical transparency. The light guide plate 2 includes a first surface (light emitting surface) 21 that emits light toward a liquid crystal panel unit (not shown) (upper side in FIG. 1), and a first surface (lower side in FIG. 1) opposite to the first surface 21. Two surfaces 22.

  The plurality of optical sheets 3 diffuses and collects light incident on the optical sheet 3 to form a surface light source. For example, a combination of a lens sheet (prism sheet) and a diffusion sheet, or a brightness enhancement sheet Consists of a combination of Each optical sheet 3 is arranged on the first surface 21 side of the light guide plate 2 in a stacked state.

  The reflection sheet 4 is a thin sheet having a high reflectance, and is disposed so as to overlap the second surface 22 opposite to the first surface 21 of the light guide plate 2. The reflection sheet 4 directs the light guided from the end surface 20 of the light guide plate 2 to the second surface 22 side of the light guide plate 2 toward the first surface 21 side of the light guide plate 2. reflect.

  The case 5 accommodates the LED 1, the light guide plate 2, the optical sheet 3, and the reflection sheet 4. The presser frame 6 presses and holds each member accommodated in the case 5. The case 5 is made of, for example, aluminum, and the holding frame 6 is made of, for example, resin.

  The FPC board 7 is directly fixed to the light guide plate 2 in a state where the board surface on which the LED 1 is mounted is attached to the first surface 21 of the light guide plate 2 with a double-sided tape (fixed tape) 8. In contrast, the plurality of optical sheets 3 overlap the first surface 21 of the light guide plate 2 at a position (a position adjacent to the fixed position) where the FPC board 7 is fixed by the double-sided tape 8. Be placed. The reflection sheet 4 is disposed so as to overlap the end surface of the LED 1 and the second surface 22 of the light guide plate 2. Therefore, the double-sided tape 8 is disposed in a state of facing the reflection sheet 4 through the light guide plate 2.

  2A and 2B show an attached state of the FPC board on which the LED is mounted and the light guide plate, where FIG. 2A is a plan view thereof and FIG. 2B is a cross-sectional view taken along line EE of FIG. In FIG. 2, six LEDs 1 are mounted on the FPC board 7. The light emission surface of each LED 1 is disposed in a state of abutting against the end surface of the light guide plate 2. Further, in the vicinity of the end face of the light guide plate 2, a part of the first surface 21 of the light guide plate 2 faces the LED mounting surface of the FPC board 7 in a band shape in plan view, and a belt-like double-sided tape 8 is interposed in this facing portion. Has been. In this double-sided tape 8, the surface facing the reflection sheet 4, that is, the surface attached to the first surface 21 of the light guide plate 2 is used as a light reflection surface (mirror surface).

  More specifically, as shown in FIG. 3, for example, the double-sided tape 8 includes a tape base material 81 made of a resin such as PET (polyethylene terephthalate), a reflective layer 82 sequentially laminated on one surface of the tape base material 81, and The adhesive layer 83 includes a colored layer 84 and an adhesive layer 85 that are sequentially laminated on the other surface of the tape substrate 80. Among these, the reflective layer 82 is formed by a vapor deposition layer or a coating layer of a metal such as aluminum, silver, or platinum, and the colored layer 84 is colored white, for example. The adhesive layers 83 and 85 are formed using an adhesive material having high light transmittance (for example, a transparent adhesive material). The colored layer 84 may be provided as necessary.

  When manufacturing the backlight unit 1 having the above-described configuration, as shown in FIG. 4A, after mounting a plurality (six in the illustrated example) of LEDs 1 on the FPC board 7, as shown in FIG. 4B. Thus, the double-sided tape 8 is affixed on the board | substrate surface (LED mounting surface) of the FPC board | substrate 7 in the light-projection surface side of each LED1. At this time, the double-sided tape 8 is attached to the substrate surface of the FPC substrate 7 using the adhesive layer 85 (see FIG. 3).

  Next, as shown in FIG. 5, the light guide plate 2 is attached to the FPC board 7 with a double-sided tape 8 in accordance with the light emission surface of each LED 1 mounted on the FPC board 7. At this time, the double-sided tape 8 is attached to the first surface 21 of the light guide plate 2 using the adhesive layer 83 (see FIG. 3). As a result, the light guide plate 2 and the FPC board 7 are directly fixed by the double-sided tape 8. Moreover, the reflective layer 82 of the double-sided tape 8 is in a state of being arranged facing the first surface 21 side of the light guide plate 2.

  Thereafter, these components are housed in the case 5 in a state where a plurality of separately prepared optical sheets 3 and reflection sheets 4 are superimposed on the first surface 21 and the second surface 22 of the light guide plate 2, respectively. Next, each holding component is held in the case 5 by attaching the holding frame 5 to the opening of the case 5.

  In the backlight unit having the above-described configuration, when light is emitted from each LED 1 mounted on the FPC board 7, a part of the light taken from the LED 1 to the light guide plate 2 as shown in FIG. The light is reflected by the double-sided tape 8, and the reflected light is reflected by the reflection sheet 4 on the second surface 22 of the light guide plate 2 and emitted from the first surface 21 of the light guide plate 2. Thereby, when the light guide plate 2 and the FPC board 7 are fixed with the double-sided tape 8, it is possible to reduce a light amount loss due to light absorption by the double-sided tape 8. Further, the light incident on the double-sided tape 8 can be efficiently reflected inside the light guide plate 2 and emitted from the first surface 21 of the light guide plate 2. As a result, the luminance of the backlight unit can be improved.

  By the way, the substrate surface of the double-sided tape 8 attached to the second surface 22 of the light guide plate 2 in a backlight unit for a liquid crystal panel unit with a screen size of 2.88 inches (6 LEDs mounted) When the luminance change was measured for the “white” surface, the “aluminum” reflecting surface, and the “silver” reflecting surface, and the respective center luminances were compared, the following results were obtained. That is, when the center brightness when the “white” surface is normalized as “1”, the center brightness when the “aluminum” reflecting surface is “1.082”, the “silver” reflecting surface In this case, the center luminance is “1.175”. From this result, when the base surface of the double-sided tape 8 is set as a “white” surface, when the “aluminum” reflecting surface is used, an increase in luminance of about 8% in the central luminance is confirmed. In the case of the “silver” reflecting surface, a luminance increase of about 17% was confirmed at the center luminance.

It is an exploded view which shows the structural example of the backlight unit used for the liquid crystal display device which concerns on embodiment of this invention. It is a figure which shows the attachment state of the FPC board in which LED was mounted, and a light-guide plate. It is a figure which shows the cross-section of a double-sided tape. It is FIG. (1) explaining an example of the manufacturing method of a surface light source unit. It is FIG. (2) explaining an example of the manufacturing method of a surface light source unit. It is a figure which shows the advancing direction of the light within a light-guide plate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... LED, 2 ... Light guide plate, 4 ... Reflection sheet, 7 ... FPC board, 8 ... Double-sided tape, 21 ... 1st surface, 22 ... 2nd surface, 82 ... Reflection layer

Claims (2)

A light source;
A mounting substrate on which the light source is mounted;
A light guide plate for guiding light emitted from the light source;
A reflective sheet that is arranged on the second surface opposite to the first surface of the light guide plate and reflects light guided to the second surface side by the light guide plate to the first surface side,
A surface light source unit comprising: a fixing tape that fixes the mounting substrate and the light guide plate at a position facing the reflection sheet, and has a surface facing the reflection sheet as a light reflection surface. . A light source;
A mounting substrate on which the light source is mounted;
A light guide plate for guiding light emitted from the light source;
A reflective sheet that is arranged on the second surface opposite to the first surface of the light guide plate and reflects light guided to the second surface side by the light guide plate to the first surface side,
The mounting substrate and the light guide plate are fixed at a position facing the reflection sheet, and a surface light source unit including a fixing tape having a surface facing the reflection sheet as a light reflection surface is used. A liquid crystal display device.

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