JP2008123915A - Surface light source and liquid crystal display device using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device capable of realizing thinness without causing luminance unevenness, and a liquid crystal display device. <P>SOLUTION: The surface light source device 1 includes a light source (LED chip 2), a light guide plate 4 which guides light from the light source in a prescribed direction, and an optical film group 6 superposed on the light guide plate 4. As an optical film constituting the optical film group 6, a prism film 62 and a prism-integrated reflection type polarizing film 64 in which the prism film and a reflection type polarizing film are integrated are provided. The prism-integrated reflection type polarizing film 64 is laminated on the prism film 62 by having the reflection type polarizing sheet side opposed to the prism film 62, and an intermediate sheet (diffusion sheet 63) is interposed between the prism-integrated reflection type polarizing film 64 and the prism film 62. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface light source device in which an optical film group is disposed on a light guide plate, and further relates to a liquid crystal display device in which the surface light source device is incorporated.

  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.

  By the way, for example, in the case of the edge light type backlight unit, the light from the light source is converted into a surface light source by the light guide plate so as to be irradiated in a predetermined direction, but the light uniformity is improved and the luminance is improved. For this purpose, an optical film group is widely installed on a light guide plate.

  FIG. 4 shows an example of a conventional surface light source device. In the surface light source device shown in FIG. 4, the LED 101 that is a light source is installed facing the end face of the light guide plate 102, and light emitted from the LED 101 is irradiated upward by the light guide plate 102. A reflective sheet 103 is installed on the lower surface of the light guide plate 102 to minimize light loss. Further, a diffusion sheet 104 is installed on the upper surface side of the light guide plate 102, and an optical film group for improving luminance is further arranged.

  Here, the optical film group is composed of two brightness enhancement films (prism films) 105 and 106 and a reflective polarizing film 107, on which a liquid crystal panel 109 is installed via a frame-shaped shading tape 108. Is done. The liquid crystal panel 109 includes, for example, an array substrate 110, a counter substrate 111, and polarizing films 112 and 113.

  Further, for the purpose of reducing the thickness of the surface light source device, the optical film is being combined. For example, as described in paragraph No. 0013 of Patent Document 1, the prism film and the reflective polarizing film are integrated. A prism-integrated reflective polarizing film has been developed. This prism-integrated reflective polarizing film 114 is obtained by laminating and integrating a prism portion 114b on a reflective polarizing film portion 114a. When the prism film and the reflective polarizing film are formed separately, respectively. Compared to this, a significant reduction in thickness can be realized.

Therefore, by using the prism-integrated reflective polarizing film 114 as described above, for example, as shown in FIG. 5, the optical film group has a two-layer configuration of a prism film 105 and a prism-integrated reflective polarizing film 114. Compared with the configuration shown in FIG. 3, the surface light source device can be made thinner.
JP 2001-281424 A

  However, when the prism-integrated reflective polarizing film 114 is directly superimposed on the prism film 105, the prism film is formed on the surface of the prism-integrated reflective polarizing film 114 on the reflective polarizing film side (the reflective polarizing film portion 114a). The unevenness on the surface 105 is transferred, which is visually recognized as streaky luminance unevenness on the liquid crystal panel 109, and there is a problem that display quality is remarkably deteriorated.

  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 realizing a reduction in thickness without causing luminance unevenness. An object is to realize a display device.

  In order to achieve the above 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 stacked on the light guide plate, The optical film constituting the optical film group includes a prism film, and a prism-integrated reflective polarizing film in which the prism film and the reflective polarizing film are integrated. The reflective polarizing sheet is laminated on the prism film with the reflective polarizing sheet facing the prism film, and an intermediate sheet is interposed between the prism-integrated reflective polarizing film and the prism film. Further, the liquid crystal display device of the present invention has a liquid crystal panel and has the above-described surface light source device incorporated therein.

  In the present invention, since the prism-integrated reflective polarizing film is used, the configuration of the optical film group is simplified and the thickness is reduced. In addition, since the intermediate sheet is interposed between the prism film and the prism-integrated reflective polarizing film, the surface unevenness of the prism film is not transferred to the prism-integrated reflective polarizing film, resulting in uneven brightness. It will be resolved.

  According to the present invention, it is possible to provide a surface light source device that is thin and has no luminance unevenness, and further, it is possible to provide a thin liquid crystal display device that is excellent in 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.

  FIG. 1 shows a basic configuration of a surface light source device (backlight unit) 1 to which the present invention is applied. As shown in FIG. 2, the backlight unit 1 of this embodiment includes a flexible substrate 3 on which an LED chip 2 that is a point light source device is mounted, a light guide plate 4, a reflective sheet 5, and an optical film group 6. The light of the LED chip 2 that is a point light source is converted into a surface light source 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 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. . Hereinafter, the optical film which comprises the optical film group 6 is demonstrated.

  In this embodiment, the optical film group 6 includes a first diffusion sheet 61 for making light uniform, a prism film 62 that is a brightness enhancement film, and a second diffusion sheet 63 for preventing the transfer of the prism film 62. The prism-integrated reflective polarizing film 64, which is an integrated prism film and reflective polarizing film, is composed of four optical films.

  Among these optical films, the diffusion sheets 61 and 63 play a role of diffusing and uniformizing the light transmitted through the light guide plate 4. For example, light diffusing particles in a light transmissive resin film. A film in which is dispersed is used. As the resin film, for example, a film such as polyethylene terephthalate or polycarbonate is used.

  The prism film 62 plays a role of improving luminance by condensing light in one direction, and is a film having 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 film 62, and the light is efficiently irradiated. As a result, the luminance is improved. Figured.

  The prism-integrated reflective polarizing film 64 is obtained by integrating a prism film portion 64a and a reflective polarizing film 64b. Here, the prism film portion 64 b has the same form and function as the previous prism film 62, and contributes to luminance improvement together with the prism film 62. The reflective polarizing film 64b was developed based on the reflective polarizing technology, and selectively reflects light from the light source (LED chip 2) without causing the lower polarizing film of the liquid crystal panel to absorb the light, for example. The liquid crystal panel can be reused over the entire viewing angle. For example, when the lower polarizing film of the liquid crystal panel absorbs S waves, the reflective polarizing film 64b reflects the S waves to the light source side (light guide plate 4 side) and reproduces them. As a result, the number of P waves transmitted through the liquid crystal panel increases, and a luminance increase of 60% or more can be obtained by increasing the integrated light quantity.

  As the prism-integrated reflective polarizing film 64, a commercially available film can be used, and specific examples thereof include a product name DBEF manufactured by Sumitomo 3M Limited. The prism-integrated reflective polarizing film 64 can be made much thinner than the case where a prism film and a reflective type performance film are used separately, and the surface light source device can be made thinner, and further the liquid crystal This is useful for reducing the thickness of the display device.

  However, when the prism-integrated reflective polarizing film 64 is used, when the prism-integrated reflective polarizing film 64 is directly stacked on the prism film 62, the surface of the prism film 62 has unevenness on the surface of the prism-integrated reflective polarizing film. It may be transferred to the back side (the reflective polarizing film 64b portion) of the film 64 and cause uneven brightness. In the film-integrated reflective polarizing film 64, the reflective polarizing film portion is soft, and the surface irregularities of the prism film 62 are easily transferred.

  Therefore, in the surface light source device of this embodiment, a diffusion sheet 63 is interposed between the prism film 62 and the prism-integrated reflective polarizing film 64 so as to prevent the surface irregularities of the prism film 62 from being transferred. Yes. By interposing the diffusion sheet 63, the prism film 62 is not in direct contact with the back surface of the prism-integrated reflective polarizing film 64, and the transfer of the surface irregularities is reliably prevented.

  Here, the diffusion sheet 63 is formed of polyethylene terephthalate, polycarbonate, or the like as described above, and even when the diffusion sheet 63 is in contact with the prism film 62, the surface unevenness is hardly transferred. Further, even if the surface irregularities of the prism film 62 are transferred to the diffusion sheet 63, the diffusion sheet 63 has a light diffusion effect, so that there is no influence such as luminance unevenness. Further, the diffusion sheet 63 has a thin thickness of, for example, 0.038 mm (38 μm), and the increase in the thickness of the optical film group 6 can be minimized. For example, even if the diffusion sheet 63 is used as an intermediate sheet, the overall thickness can be significantly reduced as compared with a case where a prism film and a reflective polarizing film formed separately are used in an overlapping manner.

  The intermediate sheet interposed between the prism film 62 and the prism-integrated reflective polarizing film 64 is not limited to the diffusion sheet 63, and any sheet can be used. Moreover, although the thickness is arbitrary if it is not zero, it is preferable to use a sheet having a thickness as thin as possible in consideration of thinning of the surface light source device 1.

  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. 2 is an exploded view of a liquid crystal display device incorporating a surface light source device (backlight unit). As shown in FIG. 2, the liquid crystal display device of this embodiment includes a liquid crystal panel 11 and the surface light source device 1 described above, and a periphery of these is held by a frame 12 so as to be integrated. The frame is usually made of a resin material, but there is no problem even if it is made of a metal material.

  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 13 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.

  The frame 12 is usually formed of a resin material, and has an outer frame portion that is substantially perpendicular to the main surfaces of the liquid crystal panel 11 and the light guide plate 4, and the outer periphery of the liquid crystal panel 11 and the light guide plate 4 is formed by the outer frame portion. Hold. The constituent material of the frame is not limited to a resin material, and a metal material such as stainless steel may be used.

  A plurality of optical film groups 6 (here, four optical sheets) are interposed between the light guide plate 4 and the liquid crystal panel 11 and are fixed to the frame 12 in a state where they are overlapped. Note that a frame-shaped double-sided adhesive sheet 14 is used for fixing the liquid crystal panel 11, and the optical sheet group 6, the light guide plate 4, A flexible substrate 3 or the like on which the LED chip 2 is mounted is sandwiched between the liquid crystal panel 11 and the frame 12 and fixed.

  FIG. 3 shows an arrangement state of each element in the liquid crystal display device. The configuration of the surface light source device 1 is as described above, and is the same as the configuration shown in FIG. In the case of a liquid crystal display device, the liquid crystal panel 11 is arranged on the optical film group 6, but the peripheral portion is fixed by a frame-like double-sided adhesive sheet 14. Polarizing films 15 and 16 are attached to the front and back surfaces of the liquid crystal panel 11, respectively.

  In the liquid crystal display device having the above-described configuration, since the prism-integrated reflective polarizing film 64 of the optical film group 6 of the surface light source device 1 is used, the thickness of the surface light source device 1 can be suppressed and the liquid crystal display device can be thinned. Is done. Further, in the optical film group 6 of the surface light source device 1, since the diffusion sheet 63 is interposed between the prism film 62 and the prism-integrated reflective polarizing film 64, luminance unevenness due to transfer of surface irregularities of the prism film 62 is caused. It is eliminated and high quality display is possible.

It is a schematic side view which decomposes | disassembles and shows the arrangement | positioning state of the component of the surface light source device to which this invention is applied. It is a disassembled perspective view which shows an example of a liquid crystal display device. It is a schematic side view which decomposes | disassembles and shows the arrangement | positioning state of the component in a liquid crystal display device. It is a schematic side view which decomposes | disassembles and shows the arrangement | positioning state of the component in an example of the conventional surface light source device. It is a schematic side view which decomposes | disassembles and shows the arrangement | positioning state of the component in the other example of the conventional surface light source device.

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, 11 Liquid crystal panel, 12 Frame, 13 LSI, 14 Double-sided adhesive sheet, 15, 16 Polarizing film, 61 Diffusion sheet 62 prism film 63 diffusion sheet 64 prism integrated reflective polarizing film

Claims (6)

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,
As an optical film constituting the optical film group, a prism film, and a prism-integrated reflective polarizing film in which the prism film and the reflective polarizing film are integrated,
The prism-integrated reflective polarizing film is laminated on the prism film with the reflective polarizing sheet side facing the prism film,
A surface light source device comprising an intermediate sheet interposed between the prism-integrated reflective polarizing film and the prism film.   The surface light source device according to claim 1, wherein the intermediate sheet is a diffusion sheet.   The surface light source device according to claim 1, wherein the intermediate sheet is made of polyethylene terephthalate or polycarbonate.   The diffusion sheet is arranged on one surface of the light guide plate, the reflection sheet is arranged on the other surface, and the optical film group is overlaid on the diffusion sheet. The surface light source device according to claim 1.   The surface light source device according to claim 1, wherein the light source is an LED, and is disposed to face an end surface of the light guide plate.   6. A liquid crystal display device comprising a liquid crystal panel and the surface light source device according to claim 1 incorporated therein.

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