JP2009080947A - Surface light source device and liquid crystal display device using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of a luminance decrease due to attachment of an adhesive tape to a light guide plate for providing a surface light source and a liquid crystal display device that offer high luminance. <P>SOLUTION: The surface light source includes a light source (LED chip 2), the light guide plate 4 which guides light from the light source in a given direction, an optical film group 6 overlaid on the light guide plate 4, and a liquid crystal panel 11 fixed by a shading adhesive tape 8. For example, a diffusion sheet 61 making up the optical film group 6 is extended and is interposed between the shading adhesive tape 8 and the light guide plate 4. As a result, an adhesive surface of the shading adhesive tape 8 is not brought into contact with the light guide plate 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface light source device that irradiates light from a light source in a planar manner through a light guide plate, and further relates to a liquid crystal display device incorporating such a surface light source device.

  In recent years, liquid crystal display devices having features such as light weight, thinness, and low power consumption are widely used as display devices for information devices such as personal computers and word processors, and display devices for video devices such as televisions, video movies, and car navigation systems. . In many cases, such a liquid crystal display device adopts a configuration in which a backlight unit (surface light source device) for applying illumination light from behind the liquid crystal panel is incorporated in order to realize a bright display screen.

  Here, the backlight unit is classified into an edge light system and a direct system according to the location of the light source. For example, the edge light system is a system in which a point light source device such as an LED is disposed on the edge of a light guide plate facing a liquid crystal panel. The direct method is a method in which a plurality of straight tubular light sources such as fluorescent discharge tubes are arranged on the back surface of the liquid crystal panel, and a diffusion plate is arranged between the liquid crystal panel and the light source. Among these methods, the edge light method is advantageous in terms of thinning, and can be said to be a method suitable for a display device of a portable electronic device or a notebook personal computer, for example.

  Incidentally, for example, in the case of the edge light type backlight unit, light from a light source is usually converted into planar light by a light guide plate so as to be irradiated in a predetermined direction. Therefore, it is necessary to arrange the liquid crystal panel so as to overlap the light guide plate, and the outer periphery of the surface light source device and the liquid crystal panel is fixed using a light-shielding adhesive tape (for example, Patent Document 1). reference).

The invention described in Patent Document 1 mainly relates to a double-sided pressure-sensitive adhesive tape having light reflectivity and light-shielding property. A liquid crystal display panel and a backlight sandwiched between flexible printed circuit boards using the double-sided pressure-sensitive adhesive tape. A liquid crystal display module unit having a housing fixed thereto is disclosed.
JP 2006-10931 A

  By the way, since a polarizing film is usually attached to both surfaces of a liquid crystal panel and this forms a step, in the combined surface light source device, the end portion of the light guide plate is inclined according to the step. Etc. are applied. By forming the inclined surface, a step between the polarizing film and the glass substrate of the liquid crystal panel can be absorbed, and a space for accommodating the polarizing film can be formed on the effective light emitting region.

  However, in this case, since light leakage from the inclined surface becomes a problem, a structure is adopted in which a light shielding adhesive tape is attached to the inclined surface portion of the light guide plate to prevent light leakage. If the region between the end portion (light incident portion) of the light guide plate and the effective light emitting region is covered with a light-blocking adhesive tape, light does not leak from this portion, and no problem in appearance occurs.

  However, if a light-shielding adhesive tape is directly attached to the light guide plate for light shielding, the performance of the light guide plate is impaired due to the influence of the adhesive, which causes a decrease in luminance. For example, backlights for liquid crystal modules for mobile use and the like are required to have higher luminance, and the reduction in luminance is a serious problem.

  The present invention has been proposed in view of such a conventional situation, and an object of the present invention is to provide a surface light source device capable of eliminating a decrease in luminance due to adhesion of an adhesive tape to a light guide plate. Furthermore, it aims at providing a liquid crystal display device.

  In order to achieve the above-described object, a surface light source device according to the present invention includes a light source, a light guide plate that guides light from the light source in a predetermined direction, and an optical film group that is stacked on the light guide plate. A surface light source device in which a liquid crystal panel is fixed by an adhesive tape, wherein an adhesive surface of the light-shielding adhesive tape is connected to the light guide plate in a region between a light incident portion where light from the light source is incident and an effective light emission region. It is characterized by not touching.

  Further, the liquid crystal display device of the present invention includes a light shielding adhesive tape on a surface light source device including a light source, a light guide plate that guides light from the light source in a predetermined direction, and an optical film group superimposed on the light guide plate. A liquid crystal display device in which the liquid crystal panel is fixed by the method, wherein an adhesive surface of the light-shielding adhesive tape is not in contact with the light guide plate in a region from a light incident portion of a light source to an effective light emitting region. And

  If the light-shielding adhesive tape is not in direct contact with the light guide plate in the region from the light incident portion of the light source to the effective light emission region, the light guide plate is not affected by the adhesive, and a decrease in luminance can be avoided.

  However, in the light guide plate, it is necessary to shield the area between the light incident part of the light source and the effective light emitting area. Specific configurations for realizing light shielding without directly attaching the light shielding adhesive tape to this region are the inventions according to claims 3 to 5 and the inventions according to claims 7 to 11.

  For example, by enlarging a part of the optical film constituting the optical film group to the light incident part of the light source and interposing between the light shielding adhesive tape and the light guide plate, without directly attaching the light shielding adhesive tape to the light guide plate Shading is realized. Similarly, a light-shielding tape that is not coated with an adhesive or a pressure-sensitive adhesive layer only on the surface facing the liquid crystal panel in the area between the light incident part of the light source of the light guide plate and the effective light-emitting area By providing the adhesive tape, light shielding is realized without directly attaching the light shielding adhesive tape to the light guide plate.

  ADVANTAGE OF THE INVENTION According to this invention, the surface light source device without a brightness fall by sticking of the adhesive tape to a light-guide plate can be provided, Furthermore, it is possible to provide the liquid crystal display device excellent in the display quality.

  Hereinafter, a surface light source device according to the present invention and a liquid crystal display device using the same will be described.

(First embodiment)
In the surface light source device of this embodiment, a part of the optical film constituting the optical film group is expanded to the light incident part of the light source, and interposed between the light shielding adhesive tape and the light guide plate, whereby the adhesive surface of the light shielding adhesive tape is guided. It is the example comprised so that it might not contact with an optical plate directly.

  First, FIG. 1 shows a basic configuration of a surface light source device (backlight unit) 1. As shown in FIG. 1, the backlight unit 1 includes a flexible substrate 3 on which an LED chip 2 as a point light source device is mounted, a light guide plate 4, a reflection sheet 5, and an optical film group 6. Light from a certain LED chip 2 is converted into planar light by the light guide plate 4.

  The LED chip 2 is, for example, a so-called side-view type LED chip in which a light-emitting diode element (LED) is embedded in a sealing resin, and irradiates light parallel to the mounting surface of the flexible substrate 3 from the side surface. is there. In the case of this example, a plurality of LED chips 2 are arranged along the longitudinal direction of the flexible substrate 3, and the LED chips 2 are arranged at substantially equal intervals.

  The LED chip 2 emits light from one side surface (side surface on the light guide plate 4 side). That is, the side surface is a light exit surface. And the light emitted from the LED chip 2 is guided to the light guide plate 4 by the end face of the light guide plate 4 and the light exit surface of the LED chip 2, and is converted into planar light.

  In the light guide plate 4, the end surface 4 a facing the LED chip 2 is a light incident part, and effective light emission from the light incident part (end surface 4 a) in order to absorb a step of a polarizing film provided in a liquid crystal panel described later. A region between the regions is an inclined surface 4b.

  In addition, a reflective sheet 5 is attached to the back side of the light guide plate 4 to prevent light from the LED chip 2 from leaking from the back side of the light guide plate 4 and to minimize light loss. It is configured.

  On the other hand, on the surface side (light irradiation surface side) of the light guide plate 4, an optical film group 6 composed of a plurality of optical films is installed for the purpose of improving the uniformity of the irradiated light and improving the brightness. . In the case of this example, the optical films constituting the optical film group 6 are a diffusion sheet 61 for making light uniform, and two prism films (lens films) 62 and 63.

  Among these optical films, the diffusion sheet 61 plays a role of diffusing and uniformizing the light transmitted through the light guide plate 4. For example, the light diffusion particles are dispersed in a light transmissive resin film. Film etc. are used. As the resin film, for example, a film such as polyethylene terephthalate or polycarbonate is used. The prism films 62 and 63 play a role of improving luminance by condensing light in one direction, and have a form in which prisms having a condensing function are arranged. The light transmitted through the light guide plate 4 and the diffusion film 61 is aligned in a predetermined direction (a direction substantially perpendicular to the film surface) by the prism films 62 and 63, and the light is efficiently irradiated, resulting in luminance. Improvement is achieved.

  Each of the above-described components is incorporated in the resin frame 7, and a frame-shaped light-blocking adhesive tape 8 having a black upper surface and a white lower surface is attached to the outer periphery thereof. As shown in FIG. 2, the light-shielding adhesive tape 8 is attached so as to cover the outer peripheral portion of the light guide plate 4. Correspondingly, the area is enlarged and it is also affixed on the inclined surface 4b. This is to prevent light leakage in a region between the light incident portion (end surface 4a) of the light guide plate 4 and the effective light emitting region.

  However, as shown in FIG. 3A, when the light shielding adhesive tape 8 is directly attached onto the inclined surface 4b of the light guide plate 4, the light guide plate 4 comes into direct contact with the adhesive surface of the light shielding adhesive tape 8, There is a problem that the function of the light guide plate 4 is impaired due to the influence of the adhesive applied to the adhesive surface, leading to a decrease in luminance.

  Therefore, in this embodiment, the area of the diffusion sheet 61 in the optical film group 6 is enlarged so as to cover the inclined surface 4 and is interposed between the light guide plate 4 and the light shielding adhesive tape 8. By interposing the diffusion sheet 61, the adhesive surface (adhesive) of the light-shielding adhesive sheet 8 does not come into contact with the surface of the light guide plate 4, and luminance reduction is prevented.

  The optical film interposed between the light guide plate 4 and the light shielding adhesive tape 8 is not limited to the diffusion sheet 61, and any optical film can be selected. However, when the prism films 62 and 63 are enlarged and interposed, incident light is scattered due to the function of the prism, and light leakage may occur inadvertently. Therefore, the diffusion sheet 61 may be interposed. preferable. In addition, the optical film whose area is increased and interposed between the light guide plate 4 and the light shielding adhesive tape 8 needs to be part of the optical film group 6. When all the optical films are enlarged, there is a risk of hindering the accommodation of the polarizing film attached to the liquid crystal panel.

  The surface light source device having the above configuration is incorporated as a backlight unit in a liquid crystal display device. Next, a liquid crystal display device incorporating the above-described surface light source device will be described.

  FIG. 4 is an exploded view of a liquid crystal display device in which a surface light source device (backlight unit) is incorporated. As shown in FIG. 4, the liquid crystal display device of this embodiment includes a liquid crystal panel 11 and the surface light source device 1 described above, and the periphery of these is held and integrated with the resin frame 7 described above.

  The liquid crystal panel 11 is configured, for example, by enclosing a liquid crystal material between an array substrate and a counter substrate, and pixel electrodes and switching elements (thin film transistors) corresponding to display pixels are formed in a matrix on the array substrate. . In addition, a signal line for sending an electric signal to the pixel electrode and a gate line for supplying a switching signal to the thin film transistor, which is a switching element, are wired on the array substrate at right angles to each other. On the other hand, on the counter substrate, the counter electrode is formed on almost the entire surface with a transparent electrode material (for example, ITO), and a color filter layer is formed corresponding to each pixel. Further, polarizing plates are bonded to the outer surfaces of the array substrate and the counter substrate so that the polarization axes are orthogonal to each other.

  An LSI 12 for supplying a drive signal is mounted on the liquid crystal panel 11, and an image is displayed by driving the switching element based on the drive signal from the external circuit board. A region where this image display is performed is a display region, and the liquid crystal panel 11 has a display region in which a large number of pixels are arranged.

  The surface light source device 1 used as the backlight unit emits light from the back side of the liquid crystal panel 11 to make the display on the liquid crystal panel 11 bright and easy to see. And as described above, as the main components, the light guide plate 4 for irradiating the light from the LED chip 2 as the light source to the back surface of the liquid crystal panel 11 and the back surface side of the light guide plate 4 are arranged. The reflection sheet 5 and the optical film group 6 disposed on the surface side of the light guide plate 4 are provided. The LED chip 2 as a light source is provided along at least one side of the light guide plate 4. In the case of this embodiment, the flexible substrate 3 on which the LED chip 2 is mounted is installed on the short side of the light guide plate 4. ing.

  Light emitted from the LED chip 2 that is a light source is reflected directly or by the reflection sheet 5 and guided to the light guide plate 4, passes through the light guide plate 4 and the optical film group 6, and is then irradiated to the liquid crystal panel 11. The irradiated light is transmitted through the liquid crystal panel 11, and images such as characters and videos are displayed with a predetermined brightness.

  For fixing the liquid crystal panel 11, a frame-shaped light shielding adhesive sheet 8 is used, and the liquid crystal panel 11 and the surface light source device 1 are integrated by fixing the liquid crystal panel 11 to the resin frame 7 with the light shielding adhesive sheet 8. Assembled into. FIG. 5 shows an arrangement when the liquid crystal panel 11 is fixed to the surface light source device 1. Polarizing films 13 and 14 are attached to both surfaces of the liquid crystal panel 11, but a stepped portion by attaching the polarizing film 14 is accommodated in a space formed by forming the inclined surface 4 b on the light guide plate 4. It has become a form.

  In the liquid crystal display device of the present embodiment, as described above, the area of the light-shielding adhesive tape 8 is enlarged corresponding to the region from the light incident part (end surface 4a) of the light guide plate 4 to the effective light emitting region, It is affixed through the diffusion sheet 61 on the inclined surface 4b. Therefore, a decrease in luminance due to the adhesive having an adverse effect on the light guide plate 4 is prevented. Actually, when the present inventors assembled and confirmed the liquid crystal display device, a luminance improvement of about 7% was recognized as compared with the case where the light shielding adhesive tape 8 was directly attached to the light guide plate 4. Further, since the light-shielding adhesive tape 8 is also arranged on the inclined surface 4b of the light guide plate 4, light from the region between the light incident part (end surface 4a) of the light guide plate 4 and the effective light emitting region is formed. Leakage is also reliably prevented.

(Second Embodiment)
The present embodiment is an example in which a part of the light shielding adhesive tape 8 is replaced with a non-adhesive sheet. Since other configurations are the same as those of the surface light source device and the liquid crystal display device of the first embodiment, only the configuration of the light-shielding adhesive tape 8 used in this embodiment will be described here.

  The light-shielding adhesive tape 8 used in the surface light source device and the liquid crystal display device of this embodiment is arranged corresponding to the frame-like double-sided adhesive tape portion 8a and the inclined surface 4b of the light guide plate 4 as shown in FIG. Non-adhesive tape piece 8b. The non-adhesive tape piece 8b is a strip-shaped member formed separately from the double-sided adhesive tape portion 8a, and has a light shielding function, but no adhesive layer is formed on any surface thereof. Moreover, the non-adhesive tape piece 8b has its both ends bonded to the double-sided adhesive tape portion 8a.

  FIG. 7 shows a state where the light-shielding adhesive tape 8 is attached to the surface light source device 1. A double-sided adhesive tape portion 8a is affixed on the resin frame 7, and the liquid crystal panel 11 can be fixed thereon. On the other hand, the non-adhesive tape piece 8 b is placed on the inclined surface 4 b of the light guide plate 4. Here, an adhesive layer is not formed on the non-adhesive tape piece 8b, and a decrease in luminance due to the adhesive contacting the light guide plate 4 is prevented. In addition, since the non-adhesive tape piece 8b has a light shielding function, light leakage does not occur from a region between the light incident portion (end surface 4a) of the light guide plate 4 and the effective light emitting region.

(Third embodiment)
The present embodiment is an example in which a part of the light shielding adhesive tape 8 is a single-sided adhesive tape. Since other configurations are the same as those of the surface light source device and the liquid crystal display device of the first embodiment, only the configuration of the light-shielding adhesive tape 8 used in this embodiment will be described here.

  The light-shielding adhesive tape 8 used in the surface light source device and the liquid crystal display device of the present embodiment is formed as a frame-like double-sided adhesive tape as shown in FIG. A portion (a shaded portion in the drawing) 8c facing the light guide plate 4 between the light incident portion and the effective light emitting region) is a single-sided adhesive tape, and an adhesive layer is provided on the surface facing the light guide plate 4 Not formed.

  The inclined surface 4b of the light guide plate 4 comes into contact with the portion 8c formed as a single-sided adhesive tape, and the adhesive does not come into contact with the light guide plate 4, thereby preventing a decrease in luminance. Moreover, since the part 8c made into the single-sided adhesive tape also has a light-shielding function, light leakage does not occur from a region between the light incident part (end surface 4a) of the light guide plate 4 and the effective light emitting region.

It is a schematic side view which decomposes | disassembles and shows the arrangement | positioning state of the component of a surface light source device. It is a schematic sectional drawing in the xx line | wire of FIG. It is the schematic sectional drawing in the y-y line | wire of FIG. 1, (a) is the state in which the light shielding adhesive tape was affixed directly to the light-guide plate, (b) was the diffusion sheet interposed between the light-shielding adhesive tape and the light guide plate. Indicates the state. It is a disassembled perspective view which shows an example of a liquid crystal display device. It is a schematic side view which shows the arrangement state of the liquid crystal panel on a surface light source device. It is a schematic perspective view which shows the other structural example of a light shielding adhesive tape. It is a schematic sectional drawing which shows the affixed state of the light-shielding adhesive tape shown in FIG. It is a schematic perspective view which shows the other structural example of a light shielding adhesive tape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface light source device, 2 LED chip, 3 Flexible substrate, 4 Light guide plate, 5 Reflective sheet, 6 Optical film group, 7 Resin frame, 8 Light-shielding adhesive tape, 8a Double-sided adhesive tape part, 8b Non-adhesive tape piece, 11 Liquid crystal panel , 12 LSI, 13, 14 Polarizing film, 61 Diffusion sheet, 62, 63 Prism film

Claims (11)

A surface light source device comprising a light source, a light guide plate that guides light from the light source in a predetermined direction, and an optical film group superimposed on the light guide plate, wherein the liquid crystal panel is fixed by a light shielding adhesive tape,
A surface light source device, wherein an adhesive surface of the light-shielding adhesive tape is not in contact with the light guide plate in a region between a light incident portion where light from a light source is incident and an effective light emitting region.   2. The surface light source device according to claim 1, wherein a part of the optical film constituting the optical film group is enlarged to a light incident portion of the light source and is interposed between the light shielding adhesive tape and the light guide plate.   2. The surface light source device according to claim 1, wherein a light shielding tape to which an adhesive is not applied is disposed in a region between a light incident portion and an effective light emitting region of the light source.   2. A light-shielding single-sided adhesive tape having an adhesive layer formed only on a surface facing a liquid crystal panel is disposed in a region between a light incident part and an effective light-emitting region of the light source. The surface light source device described.   5. The surface according to claim 1, wherein a region between the light incident portion and an effective light emitting region is an inclined surface corresponding to a step of the liquid crystal panel. Light source device. A liquid crystal display in which a liquid crystal panel is fixed by a light-shielding adhesive tape on a surface light source device having a light source, a light guide plate for guiding light from the light source in a predetermined direction, and an optical film group superimposed on the light guide plate A device,
A liquid crystal display device, wherein an adhesive surface of the light-shielding adhesive tape is not in contact with the light guide plate in a region between a light incident part of a light source and an effective light emitting region.   The liquid crystal display device according to claim 6, wherein a part of the optical film constituting the optical film group is enlarged to a light incident portion of the light source and is interposed between the light shielding adhesive tape and the light guide plate.   The liquid crystal display device according to claim 6, wherein a light shielding tape to which an adhesive is not applied is disposed in a region between a light incident portion of the light source and an effective light emitting region.   7. The light-shielding single-sided adhesive tape having an adhesive layer formed only on the surface facing the liquid crystal panel is disposed in a region between the light incident part and the effective light-emitting region of the light source. The liquid crystal display device described. The outer periphery of the surface light source device and the liquid crystal panel is supported by a resin frame,
The liquid crystal according to claim 9, wherein the light-shielding single-sided adhesive tape has an adhesive layer formed on a surface facing the light guide plate only at a portion facing the resin frame, and is adhesively fixed to the resin frame. Display device.   11. The liquid crystal according to claim 6, wherein the light guide plate has an inclined surface corresponding to a step of the liquid crystal panel in a region between the light incident portion and the effective light emitting region. Display device.

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