JP2004302443A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the luminance unevenness which occurs on the screen of a main liquid crystal display panel of a liquid crystal display device which respectively irradiates the main liquid crystal display panel on one of the major faces of a light guide plate equipped with a light source at one end and a sub-liquid crystal display panel of the screen smaller than the screen of the main liquid crystal display panel on the other of the major faces. <P>SOLUTION: The reflectivity of an undulating structure which is formed on the second major face of the light guide plate having a portion facing the sub-liquid crystal display panel and reflects the light propagated by the light guide plate toward the first major face facing the main liquid crystal display panel of the light guide plate is corrected by changing the shape (a height difference to the second major faces, the area or density within the second major face) of the undulating structure in the portion where the second major face opposes the sub-liquid crystal display panel to suppress the local degradation in the luminance of the first main face by the light radiation from the portion of the second main face which is the cause for the luminance unevenness. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device (double-sided liquid crystal display device) including a main liquid crystal display panel suitable for mounting on a foldable mobile phone and the like and a sub liquid crystal display panel having a smaller screen than the main liquid crystal display panel. The present invention relates to a liquid crystal display device provided with a lighting device suitable for reducing luminance unevenness on a screen.

  With the downsizing of mobile phones and personal digital assistants equipped with liquid crystal display panels, mobile phones and personal digital assistants are designed so that the keypad part and the liquid crystal display panel can be folded so as to overlap with each other during non-calls (standby). Was commercialized. In recent years, a product in which a small panel capable of displaying information even when such a foldable mobile phone or portable information terminal is folded (when not in a call) is arranged behind the above-mentioned liquid crystal display panel has appeared. Was. In addition to such a conventional liquid crystal display panel (also referred to as a main liquid crystal display panel or a main panel), a mobile phone or a portable information terminal equipped with a second liquid crystal display panel (also referred to as a sub liquid crystal display panel or a sub panel). As a suitable liquid crystal display device (liquid crystal display module), two liquid crystal display panels are arranged on both sides of one lighting device (also called a backlight system), and each of the liquid crystal display panels is irradiated with light by this lighting device. A product called a double-sided liquid crystal display has been developed. Such a double-sided liquid crystal display device and a mobile phone equipped with the same are described, for example, in Patent Document 1 below.

On the other hand, an illuminating device that radiates light from both sides thereof (a two-sided light emitting planar light source device) is described in Patent Document 2 below, and a light guide plate (light guide, light guide) suitable for designing an optical system of the flat light source device is disclosed. ) Are disclosed in Patent Document 3 below.
Japan: JP-A-2002-287144 Japan: Patent No. 3332654 Japan: JP-A-2000-310777

  In the double-sided liquid crystal display device as described in Patent Literature 1, one flat light source is shared by a main liquid crystal display panel and a sub liquid crystal display panel having different display screen sizes. On the other hand, mobile phones and personal digital assistants are required to have downsizing and reduced power consumption. Therefore, a double-sided liquid crystal display device mounted on the mobile phone or portable information terminal has a light emitting diode (semiconductor light emitting element) and a light guide plate combined. A flat light source (illumination device) as described in Patent Document 2 is widely used.

  In such a lighting device (a two-sided light emitting flat light source), a main liquid crystal display panel is disposed on one of the main surfaces of a light guide plate disclosed in Patent Document 2, and a sub liquid crystal display panel is disposed on the other side thereof, Light incident on the light guide plate from a light source (the above-described light emitting diode) disposed opposite to one of the side surfaces of the light guide plate is radiated to each main surface to display an image on the main liquid crystal display panel and the sub liquid crystal display panel. Do.

  Light incident on one of the side surfaces of the light guide plate propagates along the main surface inside the light guide plate, and light reflected on one of the main surfaces is reflected from the other side on the other of the main surfaces. The emitted light is radiated from one of them, and enters each of the sub liquid crystal display panel and the main liquid crystal display panel. In order to uniformly correct the radiation intensity of light from each of the main surfaces, which decreases with the distance from the light source (the side surface of the light guide plate facing the light emitting diode), at least one of the light guide plate main surfaces has A pattern of grooves and projections as shown in Patent Document 3 is formed, and the size and interval thereof can be changed according to the distance from the light source.

  However, the other area of the main surface of the light guide plate facing the sub liquid crystal display panel is smaller than the area of one side of the main surface of the light guide plate facing the main liquid crystal display panel, and one of the main surfaces of the light guide plate faces the other. Since the light guide plate opposes each other, the intensity of light radiated from one of the light guide plate main surfaces is equal to a part of the light guide plate main surface facing a region of the light guide plate main surface facing the other sub liquid crystal display panel. It is lower than the peripheral part surrounding a part. As a result, in the image displayed on the main liquid crystal display panel, so-called luminance unevenness that darkens according to the region of the main surface of the light guide plate facing the other sub liquid crystal display panel occurs.

  According to the present invention, in a liquid crystal display device called a double-sided liquid crystal display device, it is possible to suppress the above-described luminance unevenness occurring in a main liquid crystal display panel and display an image with uniform luminance over practical use over the entire screen. A lighting device is provided.

  An example of a typical structure of a liquid crystal display device (also called a double-sided liquid crystal display device or a liquid crystal display module) provided with the above-described lighting device provided by the present invention is described as follows.

  A first liquid crystal display panel, a second liquid crystal display panel having a smaller main surface than the first liquid crystal display panel, a first main surface and a second main surface opposed to each other, and the first main surface and the second main surface. A light guide plate having a plurality of side surfaces separating the light guide plate, and a light source including at least one light emitting element disposed opposite to one of the plurality of side surfaces of the light guide plate (for example, a light emitting diode or an optically coupled light source) A liquid crystal display panel provided separately from the light guide plate), and a first liquid crystal display panel is disposed with its main surface facing the first main surface of the light guide plate. A liquid crystal display device assembled by arranging a second liquid crystal display panel with its main surface facing a part of the second main surface of the light guide plate, wherein the second main surface of the light guide plate has an undulating structure. It is provided.

  This undulating structure controls the reflection of light propagated in the light guide plate by the second main surface. Further, at least one of the height and depth of the undulating structure with respect to the second main surface, and the density and area within the second main surface are different from each other in the portion of the second main surface and the peripheral portion adjacent thereto. It may be different.

  Further, in these structures, at least one of the height, the depth, the density, and the area of the relief structure on the second main surface of the light guide plate is at least one of the side faces of the light guide plate facing the light source. The height, the depth, the density, and the area of the relief structure in the portion of the second main surface (the portion that irradiates light to the second liquid crystal display panel) are increased according to the distance. Along one (extending direction) of the side surfaces of the light plate, it is larger than that of the peripheral portion adjacent to the portion. The direction in which one of the side surfaces of the light guide plate extends can also be referred to as the direction in which the light emitting elements are juxtaposed when a plurality of light emitting elements are arranged so as to face one of the side surfaces.

  In addition, the undulation structure protrudes higher from the second main surface, is deeply depressed from the second main surface, and has a higher density (shorter) in the second main surface than in the peripheral portion adjacent to the second main surface. And at least one of the first and second surfaces is arranged at intervals.

  Further, the undulating structure on the second main surface of the light guide plate is a plurality of grooves formed on the second main surface.

  Further, a housing (for example, a frame-shaped case) is added to the liquid crystal display device. A first concave portion for holding a first liquid crystal display panel, a light guide plate, and a light source is provided on one side of the housing, and a second concave portion is provided on the other side of the housing facing the one side. The second recess holding the liquid crystal display panel is formed, for example, in a frame shape. The housing also has an opening between the first concave portion and the second concave portion for irradiating the main surface of the second liquid crystal display panel with light radiated from the second main surface of the light guide plate. It is formed. The aperture faces or is projected onto a second major surface of the light guide plate to define the portion within the second major surface.

  Further, the reflectance of a part of the second main surface of the light guide plate and the reflectance of a peripheral portion adjacent to a part of the second main surface along one of the side surfaces of the light guide plate facing the light source are the light guide plate. In itself, the reflectance of a part is higher than the reflectance of the peripheral part, and the difference between these reflectances is reduced by housing the light guide plate in the housing. That is, when light is incident from one side surface of the light guide plate in a single state, the radiation intensity of the light from the first main surface increases in the region of the first main surface facing a part of the second main surface. Is made uniform by incorporating this light guide plate into the above-described housing. As a result, in the liquid crystal display device, the intensity of light radiated from the first main surface of the light guide plate does not drop in a region facing a part of the second main surface, and thus occurs in the first liquid crystal display panel. The luminance unevenness is eliminated.

  According to another embodiment of the present invention, a first liquid crystal display panel, a second liquid crystal display panel having a smaller main surface than the first liquid crystal display panel, a first main surface, and a first main surface. A liquid crystal display device comprising: a light guide plate having an opposing second main surface; and a side surface separating the first main surface and the second main surface; and a liquid crystal display device having a light source disposed on a side surface of the light guide plate. The panel is arranged with its main surface facing the first main surface of the light guide plate, and the second liquid crystal display panel is arranged with its main surface facing a part of the second main surface of the light guide plate. A groove is formed in the second main surface of the light guide plate.

  In this case, a configuration in which the groove of the second main surface of the light guide plate is deeper at least from the light source to a part of the second main surface as the distance from the light source increases is also conceivable. Further, the groove on the second main surface of the light guide plate may be configured such that the groove farthest from the light source is deeper than the groove closest to the light source. Further, the groove on the second main surface of the light guide plate may have a depth of a groove on a side of the part of the second main surface remote from the light source, and a depth of a groove adjacent to a part of the second main surface. A configuration that is deeper than that is also conceivable.

  According to another embodiment of the present invention, a first liquid crystal display panel, a second liquid crystal display panel having a smaller main surface than the first liquid crystal display panel, a first main surface, and a first main surface. A liquid crystal display device comprising: a light guide plate having an opposing second main surface; and a side surface separating the first main surface and the second main surface; and a liquid crystal display device having a light source disposed on a side surface of the light guide plate. The panel is arranged with its main surface facing the first main surface of the light guide plate, and the second liquid crystal display panel is arranged with its main surface facing a part of the second main surface of the light guide plate. In the second main surface of the light guide plate, at least one of a height, a depth, a density and an area in the second main surface with respect to the second main surface is the part of the second main surface. And a peripheral portion adjacent thereto.

  Note that the present invention is not limited to the above configuration, and various modifications can be made without departing from the technical idea of the present invention.

  According to the present invention, the first liquid crystal display panel (main liquid crystal display panel) on one side of the main surface of the light guide plate having a light source at one end and the second liquid crystal display panel on the other side having a smaller screen than the first liquid crystal display panel. In a liquid crystal display device (double-sided liquid crystal display device) mounted so as to irradiate the liquid crystal display panel (sub-liquid crystal display panel), respectively, according to the other part of the main surface of the light guide plate facing the second liquid crystal display panel. A local decrease in the intensity of light radiation on one of the main surfaces of the light guide plate is compensated for, and luminance unevenness occurring on the screen of the first liquid crystal display panel is suppressed. Thereby, the display quality of each screen of the first liquid crystal display panel and the second liquid crystal display panel is improved. In a foldable mobile phone or a portable information terminal equipped with the liquid crystal display device, the visibility of images (information) displayed on the main screen and the sub-screen is improved.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings referred to in the following description, those having the same functions are denoted by the same reference numerals, and overlapping description will be omitted as much as possible.

  FIG. 1A shows an example of a liquid crystal display device (double-sided liquid crystal display device) according to the present invention including a main liquid crystal display panel PNL1 and a sub liquid crystal display panel PNL2 having a smaller screen than the main liquid crystal display panel PNL1. 2 shows a planar structure drawn from FIG. FIG. 1B shows a cross-sectional structure when the liquid crystal display device is cut along the line Ib-Ib 'shown in FIG. In the planar structure shown in FIG. 1A, the sub liquid crystal display panel PNL2 is drawn so as not to be accommodated in the casing CAS in order to explain the connection between the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2. However, when this liquid crystal display device is completed, the sub liquid crystal display panel PNL2 is also housed in the casing CAS as shown in FIG. 1B. The coordinate axes shown in FIGS. 1A and 1B, respectively, assist in the description of the shape and layout of the liquid crystal display device of this embodiment and the components mounted thereon. (Light-emitting diode LED) or the direction away from the side surface (left end surface in FIG. 1B) of the light guide plate GLB facing the light source along the light guide plate GLB, and the y-axis indicates the extension of the side surface of the light guide plate GLB facing the light source. Each direction is shown.

  Each of the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 shown in FIGS. 1A and 1B has an active matrix structure in which an active element (such as a thin film transistor) is arranged in each pixel. . The main liquid crystal display panel PNL1 fixes a pair of substrates (a glass substrate or a plastic substrate) SUB1m and SUB2m having optical transparency with their main surfaces facing each other, and a liquid crystal layer LCm is provided in a gap between these substrates. The display screen. Similarly to the main liquid crystal display panel PNL1, the sub liquid crystal display panel PNL2 also fixes a pair of substrates SUB1s and SUB2s having light transmittance with their main surfaces facing each other, and a liquid crystal layer LCs is provided in a gap between these substrates. Provided on the display screen. As a casing CAS for holding the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2, for example, a molded case made of a molded resin material is used.

  The casing CAS has a first concave portion that opens on one side (Side A shown in FIG. 1B) and another opposite side (Side B shown in FIG. 1B) opposite to the one side. And a second concave portion that opens to the outside. The first concave portion accommodates a light emitting diode LED, a light source substrate LSB on which the light emitting diode LED is mounted, and a light guide plate GLB, and a main liquid crystal is provided at an entrance thereof (at the top of the casing CAS shown in FIG. 1B). The substrate SUB1m of the display panel PNL1 is fitted. On the other hand, the substrate SUB1s of the sub liquid crystal display panel PNL2 is fitted into the second concave portion (the lower surface of the casing CAS shown in FIG. 1B). At the entrance of the first concave portion, a terrace-like surface fitted to the periphery of the main liquid crystal display panel PNL1 (substrate SUB1m) is formed in a frame shape, and the periphery of the main surface of the main liquid crystal display panel PNL1 has adhesiveness. It is fixed to the terrace-shaped surface by the light shielding spacer LSSm. In the second concave portion, a terrace-like surface fitted to the periphery of the sub liquid crystal display panel PNL2 (substrate SUB1s) is formed in a frame shape, and the periphery of the main surface of the sub liquid crystal display panel PNL2 has an adhesive light shielding spacer. It is fixed to the terrace surface by LSSs. An opening OPN extending from the bottom of the first recess to the bottom of the second recess is formed in the housing CAS, and the second main surface (the lower surface in FIG. 1B) of the light guide plate GLB is formed through the opening OPN. Irradiates the main surface of the sub liquid crystal display panel PNL2 (substrate SUB1s). The area of the opening OPN is smaller than the bottom of the first recess and the bottom of the second recess.

  On the other hand, between the first main surface of the light guide plate GLB and the main surface of the main liquid crystal display panel PNL1 (substrate SUB1m), light radiated from the first main surface is uniformly diffused into the main surface of the substrate SUB1m. An optical sheet (light diffusing sheet) OPS1m to be transmitted and an optical sheet (light collecting sheet) OPS2m having a function of condensing the traveling direction of the light along the normal line of the main surface of the substrate SUB1m are inserted. Further, between the second main surface of the light guide plate GLB and the main surface of the sub liquid crystal display panel PNL2 (substrate SUB1s), the light radiated from the second main surface (a portion facing the opening OPN) is supplied to the substrate SUB1s. Optical sheet (light diffusing sheet) OPS1s for uniformly diffusing the light into the main surface of the substrate, and an optical sheet (light collecting sheet) OPS2s having a function of condensing the traveling direction of the light along the normal to the main surface of the substrate SUB1s. Is inserted. These optical sheets are provided in the first concave portion of the casing CAS from the bottom thereof in the form of a light-collecting sheet OPS2s (two sheets), a light-diffusing sheet OPS1s, a light guide plate GLB, a light-diffusing sheet OPS1m, and a light-collecting sheet OPS2m (two sheets). Are stacked in this order. As the light condensing sheets OPS2s and OPS2m, for example, a prism sheet having prism-like protrusions formed on one main surface is used.

  The light-condensing sheet OPS2s and the light-diffusing sheet OPS1s have the same or larger area as the screen of the main liquid crystal display panel PNL1, and are arranged so as to straddle the above-mentioned opening OPN on the bottom surface of the first concave portion. When the casing CAS is formed of a material that does not allow light to pass therethrough, in the region of the light-collecting sheet OPS2s facing the bottom surface of the first concave portion (not facing the opening OPN), the second main surface of the light guide plate GLB is used. Is returned to the inside of the light guide plate GLB, and is radiated from the first main surface to the main surface of the main liquid crystal display panel PNL1. The optical characteristics of the light diffusion sheet and the condensing sheet may be common to those of the main liquid crystal display panel PNL1 and those of the sub liquid crystal display panel PNL2, and according to the optical characteristics of the light guide plate GLB. It is not necessary to use one or both of the light-collecting sheet and the light-collecting sheet.

  Since both the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 of this embodiment shown in FIG. 1A have an active matrix type structure, their screens (image display areas) are arranged along the x-axis. A plurality of video signal lines DL extending along the y-axis intersecting the x-axis and a plurality of scanning signal lines GL extending along the y-axis and juxtaposed along the x-axis. Is provided. In FIG. 1A, the illustration of the video signal lines DL and the scanning signal lines GL arranged in the respective screens of the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 is omitted, and they are arranged outside thereof. Only a part is shown.

  A video signal driving circuit VDR and a scanning signal driving circuit SDR are mounted on the periphery of the main surface of the substrate SUB1m protruding from the substrate SUB2m of the main liquid crystal display panel PNL1. The video signal driving circuit VDR outputs video signals to a plurality of video signal lines DL provided on respective screens of the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2, and the scanning signal driving circuit SDR outputs the main liquid crystal display panel PNL1 and A scanning signal is output to a plurality of scanning signal lines GL provided on each screen of the sub liquid crystal display panel PNL2. Each of the pixels provided on the respective screens of the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 fetches a video signal from one of the plurality of video signal lines DL through an active element provided therein, Is controlled by a scanning signal input to the active element from one of the plurality of scanning signal lines GL.

  On the screen of the main liquid crystal display panel PNL1 of this embodiment, 176 video signal lines transmitting a red video signal, a green video signal, and a blue video signal are repeated in the order of red, green, and blue in the order of y. It is juxtaposed along the axis. Therefore, a total of 528 video signal lines are juxtaposed on the screen of the main liquid crystal display panel PNL1. Further, 240 scanning signal lines intersecting these video signal lines are arranged in parallel along the x-axis, and a color image is displayed by a total of 42,240 pixels.

  On the other hand, on the screen of the sub liquid crystal display panel PNL2 of this embodiment, 120 video signal lines transmitting a red video signal, a green video signal, and a blue video signal are repeated in the order of red, green, and blue in order of 120 lines. Are arranged along the y-axis. Therefore, a total of 360 video signal lines are juxtaposed on the screen of the main liquid crystal display panel PNL2. Further, 64 scanning signal lines crossing these video signal lines are arranged in parallel along the x-axis, and a color image is displayed by a total of 7,680 pixels.

  On the other hand, the video signal drive circuit VDR has 528 (176 for each color) video signal lines provided on the screen of the main liquid crystal display panel PNL1 and 360 video signal lines provided on the screen of the sub liquid crystal display panel PNL2. Video signals are output to (120 lines for each color) video signal lines. The video signal drive circuit VDR receives the video data from the external circuit of the liquid crystal display device through the flexible printed circuit board FPC1. Therefore, the periphery of the main surface of the substrate SUB1m to which one end of the flexible printed circuit board FPC1 is connected (FIG. 1A) Is installed on the left). At the other end of the flexible printed circuit board FPC1, a plurality of terminals TM connected to an external circuit (not shown in FIG. 1) of the liquid crystal display device are provided. The output of the video signal from the video signal driving circuit VDR arranged as described above to the video signal line provided on the screen of the sub liquid crystal display panel PNL2 is performed among the video signal lines provided on the screen of the main liquid crystal display panel PNL1. (120 lines for each color), and these 360 image signal lines DL are extended to the main surface of the substrate SUB1s of the flexible printed circuit board FPC2 and the sub liquid crystal display panel PNL2.

  On the other hand, the scanning signal drive circuit SDR also has 240 scanning signal lines provided on the screen of the main liquid crystal display panel PNL1 in response to a clock signal input thereto from an external circuit of the liquid crystal display device through the flexible printed circuit board FPC1. And the scanning signals are sequentially output to 64 scanning signal lines provided on the screen of the sub liquid crystal display panel PNL2. The output of the scanning signal from the scanning signal drive circuit SDR mounted on the periphery (the upper end in FIG. 1A) of the main surface of the substrate SUB1m to the 64 scanning signal lines provided on the sub liquid crystal display panel PNL2 is the sub liquid crystal. Each of the 64 scanning signal lines drawn to the periphery (the upper end in FIG. 1A) of the main surface of the substrate SUB1s of the display panel PNL2 is transferred to the main surface of the flexible printed circuit board FPC2 and the substrate SUB1m of the main liquid crystal display panel PNL1. The extension is performed.

The image (information) generated on the screen of the main liquid crystal display panel PNL1 and the screen of the sub liquid crystal display panel PNL2 in each frame period in this manner is a light emitting diode disposed to face one of the side surfaces of the light guide plate GLB. (Light Emitting Element) Light from an LED is propagated into the light guide plate GLB and radiated from its first main surface (upper surface in FIG. 1B) and second main surface (lower surface in FIG. 1B). By irradiating the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2, the user perceives.
<Correction of reflectance on main surface of light guide plate GLB>

  The above-described liquid crystal display device (double-sided liquid crystal display device) is mounted on a foldable mobile phone such that the keypad portion and the main liquid crystal display panel PNL1 face each other in a folded state. Therefore, in the state where the foldable mobile phone is folded (for example, at the time of standby), only the image of the sub liquid crystal display panel PNL2 is perceived by the user of the foldable mobile phone, and the foldable mobile phone is opened. In the state (for example, during a call), each image of the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 is perceived by the user of the foldable mobile phone.

  In a so-called edge-light type liquid crystal display device having an illumination device including a light guide plate and a light source arranged on the side surface thereof, a reflection structure for returning light radiated from this to the inside of the light guide plate is provided on one of the main surfaces of the light guide plate. Even when the light guide plate is formed, light is emitted from one main surface of the light guide plate. Therefore, even if such a reflection structure is provided on the second main surface of the light guide plate GLB mounted on the liquid crystal display device of the present embodiment, light of sufficient intensity is radiated toward the sub liquid crystal display panel PNL2. . For this reason, the sub-liquid crystal display panel PNL2 of the foldable mobile phone equipped with the liquid crystal display device of the present embodiment receives sufficient light irradiation even when the foldable mobile phone is folded or opened. The image generated thereby is perceived by the user of the foldable mobile phone.

  On the other hand, main liquid crystal display panel PNL1 mounted on such a foldable mobile phone is irradiated with light radiated from the first main surface of light guide plate GLB. However, the first main surface partially faces the second main surface facing the sub liquid crystal display panel PNL2, and the main liquid crystal display panel PNL1 provides an image to the user with the foldable mobile phone opened. Therefore, the image displayed on the main liquid crystal display panel PNL1 has uneven brightness.

  The cause of the uneven brightness that occurs on the screen of the main liquid crystal display panel PNL1 will be described as follows. As described above, when an image is generated on both the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 for each frame period, at least a part of the screen of the sub liquid crystal display panel PNL2 has a light transmitting area. Further, even if the image display on the sub-liquid crystal display panel PNL2 is stopped during the image display period on the main liquid crystal display panel PNL1, the sub-liquid crystal display panel PNL2 becomes the maximum when the electric field applied to the liquid crystal layer LCs is the minimum. When driven in the normally white mode showing the light transmittance of, the entire screen of the sub liquid crystal display panel PNL2 transmits light well. Therefore, even if the above-described reflection structure is provided on the second main surface of the light guide plate GLB, a part of the light to be reflected toward the first main surface by this is transferred to the opening OPN and the auxiliary opening provided in the housing CAS. The light is emitted to the outside of the foldable mobile phone (in an open state) through the screen of the liquid crystal display panel PNL2.

  On the other hand, since the part other than the above-mentioned part of the second main surface of the light guide plate GLB which faces the sub-liquid crystal display panel PNL2 faces the inner wall of the housing CAS, light to be radiated from there is more efficiently due to the above-mentioned reflection structure. The light is reflected toward the first main surface. Accordingly, a dark portion corresponding to a portion of the second main surface of the light guide plate GLB facing the sub liquid crystal display panel PNL2 is formed on the screen of the main liquid crystal display panel PNL1. For example, on the screen of the main liquid crystal display panel PNL1 shown in FIG. 1A (which roughly corresponds to the main surface of the substrate SUB2m), the brightness of the display image is reduced within the dashed frame marked as the sub panel illumination area. It is lower than other surrounding areas. As shown in FIG. 1B, the sub-panel illumination region includes a region where the second main surface of the light guide plate GLB faces the sub-liquid crystal display panel PNL2 (the “partial portion”) and the first main surface of the light guide plate GLB. It is defined by projecting it on a surface. Further, the main liquid crystal display panel PNL1 is provided on one surface (Side A) of the housing CAS having the opening OPN as shown in FIG. 1B, and the sub-surface of the second main surface is provided on the other surface (Side B). When each of the liquid crystal display panels PNL2 is mounted, it is also specified that a “part” of the second main surface of the light guide plate GLB facing the opening OPN is projected on the first main surface of the light guide plate GLB.

  Even if the casing CAS is formed of a material having a high light transmittance, the difference in luminance between the sub panel illumination area and the other area on the screen (substrate SUB2m) of the main liquid crystal display panel PNL1 is reduced. As long as the housing (at least the image display unit) of the foldable mobile phone in which the liquid crystal display device is incorporated is made of a material that does not easily transmit light, the above-mentioned uneven brightness cannot be eliminated.

  Under such circumstances, the present invention provides the light guide plate GLB shown in FIG. 2 to a liquid crystal display device (double-sided liquid crystal module) as shown in FIG. In FIG. 2A, a planar structure viewed from the second main surface of an example of the light guide plate GLB according to the present invention has three light emitting element LEDs arranged to face one of the side surfaces and a light source equipped with these. It is drawn with the substrate LSB. Therefore, the plan view of FIG. 2A is drawn so as to look up the second main surface of the light guide plate GLB and the light emitting element LED from the bottom surface of the first concave portion of the housing CAS shown in FIG. 1B. . A colored region surrounded by a pair of solid lines shown on the second main surface of the light guide plate GLB indicates a plurality of grooves GRV formed on the second main surface, and a dashed line shown at the center of each of the colored regions is respectively. Of the groove GRV with respect to the second main surface. The width of these grooves GRV gradually expands as one moves away from one of the side surfaces of the light guide plate GLB facing the three light emitting elements LED along the x-axis, so that light propagated by the light guide plate GLB is reduced. The light is strongly reflected toward the first main surface. By expanding the width of the groove in accordance with the distance from one side of the light guide plate GLB facing the light source (light emitting element LED), the first light guide plate GLB attenuates as the distance from one side of the light guide plate GLB increases. Compensates the radiation intensity of light from the main surface. The attenuation of the light radiated from the first main surface of the light guide plate GLB occurs even when the reflection structure is not provided on the second main surface of the light guide plate GLB.

  In the planar structure of the light guide plate GLB shown in FIG. 2A, the feature of the present invention is a “sub-panel illuminated region” surrounded by a broken line (the sub-liquid crystal display panel PNL2 on the second main surface of the light guide plate GLB). This is represented by the difference in the width of the groove GRV between the above-described “part” and a region (hereinafter, referred to as a “peripheral portion”) between the broken line frame and the dotted frame surrounding the broken line frame. In a region other than the “sub-panel irradiation region” of the second main surface of the light guide plate GLB (including the “peripheral portion”), the width of the groove GRV is from the light source side of the light guide plate GLB (the left end in FIG. 2A). Although the width gradually increases as the distance increases, the width of the groove GRV rapidly increases in the “sub-panel irradiation area”, and includes a groove GRV wider than the groove GRV farther from the light source than the “sub-panel irradiation area”. . The difference in the reflection structure between the “sub-panel irradiation region” and the other region on the second main surface of the light guide plate GLB is such that the “sub-panel irradiation region” and the above-mentioned “peripheral portion” adjacent thereto are guided. It is described in comparison with the extending direction of the side surface of the light plate GLB facing the light source. In the planar structure of the light guide plate GLB shown in FIG. 2A, the area (groove) in the second main surface of the undulating structure (groove) that controls the reflection of the light propagated in the light guide plate GLB by the second main surface. The width is different between the “sub-panel irradiation region” and the “peripheral portion” adjacent thereto, and the area of the undulating structure in the former is larger than that in the latter.

  A plurality of grooves formed in the second main surface of the light guide plate GLB shown in FIG. 2A were cut along the line AA ′ shown in FIG. 2 and drawn in FIG. 2B. As shown in the cross-sectional structure of the light guide plate GLB, the “sub-panel illuminated area” is different from the other areas in the change of the depth according to the distance from the light source. FIG. 2B shows a light source (only the light emitting element LED) facing one of a plurality of side surfaces separating the light guide plate GLB shown in FIG. 1B and the first main surface and the second main surface thereof. And are excerpted. The groove GRV formed on the second main surface (the lower surface in FIG. 2B) of the light guide plate GLB is formed gradually deeper according to the distance from one side surface of the light guide plate GLB facing the light source. Such a change in the depth of the grooves GRV juxtaposed in the x-axis direction is obtained by changing the groove indicated by the solid line from the groove indicated by the dotted line in the “sub-panel irradiation area” of FIG. ) Is replaced with a cross-sectional shape along the line BB ′ indicated as “no reflectance correction”. By increasing the depth of the groove GRV as the distance from the light source increases, the radiation intensity of light from the first main surface of the light guide plate GLB attenuating according to the distance from the light source is compensated. When the cross-sectional shape of a plurality of grooves GRV arranged along the line AA 'including the "sub panel irradiation region" is made similar to that along the line BB', radiation from the first main surface of the light guide plate GLB is performed. The intensity of the light (the luminance of the main liquid crystal display panel PNL1 displaying the entire screen white) is indicated by the “sub panel illuminated area” (the sub liquid crystal display on the second main surface) as shown by a broken line in FIG. (Part facing the panel PNL2). Such a local drop in the brightness of the first main surface causes the above-described uneven brightness on the screen of the main liquid crystal display panel PNL1. Note that the vertical axis in FIG. 2C is the luminance (Side A) of the main liquid crystal display panel PNL1, and the horizontal axis is the distance from the light source.

  On the other hand, when the cross section of the groove GRV in the “sub-panel irradiation region” is changed to a shape indicated by a solid line indicated as “reflectance correction” in FIG. 2B, a broken line in FIG. The drop in luminance near the center of the first main surface (the screen of the main liquid crystal display panel PNL1) of the light guide plate GLB, which is indicated by, is resolved as shown by the solid line labeled "after reflectance correction", and the main liquid crystal display panel PNL1 It is difficult for the user of the mobile phone equipped with the liquid crystal display device of the present embodiment to perceive the luminance unevenness on the screen.

  The cross-sectional shape of the groove GRV indicated by a solid line (along the line AA ′) and the cross-sectional shape of the groove GRV indicated by a dotted line (the line BB ′) are shown in the “sub-panel irradiation region” of FIG. As is clear from the comparison with the above, the depth of the groove GRV gradually increasing in accordance with the distance from the light source sharply increases as drawn by a solid line in the “sub-panel irradiation area”. On the other hand, the groove GRV formed in the “peripheral portion” adjacent to the “sub-panel irradiation region” along the extending direction (the y-axis in FIG. 2A) of the side surface of the light guide plate GLB facing the light source. The depth still increases gradually with the distance from the light source, as depicted by the dotted line. For this reason, the grooves GRV formed in the “sub-panel irradiation area” include those deeper than the grooves GRV formed farther from the light source than the “sub-panel irradiation area”.

  The reflection structure of the “sub-panel irradiation region” and the reflection structure of the “peripheral portion” adjacent to the second main surface of the light guide plate GLB described above with reference to FIG. When compared along the extending direction of the opposing side surfaces, the difference is described as follows. In the cross-sectional structure of the light guide plate GLB shown in FIG. 2B, the depth of the undulating structure (groove) for controlling the reflection of the light propagated in the light guide plate GLB by the second main surface with respect to the second main surface. However, the difference between the “sub-panel irradiation region” and the “peripheral portion” adjacent thereto is different, and the height difference (Peak-to-Valley) of the relief structure in the former is larger than that in the latter.

  FIG. 2C showing the effect of the light guide plate GLB according to the present invention referred to in the above description. FIG. 2C shows the light guide plate GLB provided on the casing CAS as shown in FIG. The result measured in the state mounted with panel PNL2 is shown. In this experiment, the entire screen of each of the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 is displayed white (maximizing the light transmittance of each screen), and the screen of the main liquid crystal display panel PNL1 (FIG. The intensity of the light emitted from the upper surface of the substrate SUB2m in b) was measured. Based on the measurement results of the light intensity (the luminance of the main liquid crystal display panel PNL1), the distribution of the radiation intensity of light on the first main surface of the light guide plate GLB was discussed.

  However, the light guide plate GLB according to the present invention is not mounted on the casing CAS as described above, and a light source is arranged on one of its side faces in a bare state as shown in FIGS. 2 (a) and 2 (b). In this case, the distribution of the radiation intensity of the light on the first main surface (change along the x-axis direction) is different from that shown in FIG. When the intensity of light radiated from the first main surface of the light guide plate GLB is measured in a single product state, the light intensity before the reflectance correction indicated by a broken line in FIG. The light intensity after the reflectance correction indicated by the solid line locally increases in the “sub-panel irradiation area”. Therefore, the brightness of the first main surface of the light guide plate GLB itself is corrected by correcting the reflection structure of the second main surface at a part facing the sub liquid crystal display panel PNL2 (the “sub panel irradiation area”). (A part of the first main surface opposite to a part of the second main surface). The local increase in brightness on the first main surface of the light guide plate GLB itself is caused by excessive light from a part of the second main surface to the sub liquid crystal display panel PNL2 generated when the light guide plate GLB is mounted on the casing CAS. Suppress leaks. Thus, in the liquid crystal display device assembled by arranging the main liquid crystal display panel PNL1 on the first main surface of the light guide plate GLB and the sub liquid crystal display panel PNL2 on the second main surface according to the present invention, the main liquid crystal display panel PNL1 is assembled. Of the sub-liquid crystal display panel PNL2 can be displayed with practically usable luminance.

In the light guide plate GLB described in the above-described embodiment, the width (area) and depth of the groove formed in the second main surface is equal to the “sub-panel irradiation region” (a portion facing the sub-liquid crystal display panel PNL2). The other parts were different. However, the effect shown in FIG. 2C can be obtained even if only one of the width and the depth of the groove is different between the “sub-panel irradiation region” and the other portion. Further, the same effect can be obtained by completely replacing the plurality of grooves (concave portions) formed on the second main surface with the plurality of protrusions (convex portions) protruding from the second main surface. In the light guide plate GLB having the second main surface in which a plurality of protrusions are juxtaposed from the light source side, the second undulating structure (projection) for controlling the reflection of the light propagated in the light guide plate GLB by the second main surface is provided. The height with respect to the main surface is different from each other in the “sub-panel irradiation region” and the “peripheral portion” adjacent thereto.
<Another embodiment related to reflectance correction on light guide plate GLB main surface>

  The light guide plate suitable for the so-called double-sided liquid crystal display device according to the present invention is not limited to the structure described above with reference to FIGS. 2 (a) and 2 (b). It can be embodied in the planar structure shown. In each of FIGS. 3A and 3B, similarly to FIG. 2A, the planar structure viewed from the second main surface of the light guide plate GLB is arranged to face one side surface. (The details of which differ from one another).

  On the second main surface of the light guide plate GLB shown in FIG. 3A, a plurality of grooves GRV or protrusions PRO indicated by a pair of curves are sequentially arranged along the x-axis direction from the light source side of the light guide plate GLB. . A dashed line sandwiched between each of the pair of curves indicates a valley when the pair of curves indicates the groove GRV, and indicates a ridge when the pair of curves indicates the protrusion PRO. In the embodiment shown in FIG. 3A, a light source having two light emitting elements LEDs arranged side by side along one side surface of the light guide plate GLB is used. For this reason, in order to reduce the bias of light generated because the light emitting element LED is a point light source, the width of the groove GRV or the protrusion PRO indicated by the interval between the pair of curves is narrowed at a position facing the light emitting element LED, The depth of the GRV or the height of the protrusion PRO is also suppressed at a position facing the light emitting element LED.

  The width of the plurality of grooves GRV formed on the second main surface of the light guide plate GLB in FIG. 3A is the same along the y-axis direction regardless of the position (distance from the light source side) where each is formed. Changes to When the plurality of grooves GRV are replaced with the plurality of protrusions PRO, the width of each protrusion PRO also changes along the y-axis direction regardless of the position where the protrusions PRO are formed. Further, the depth of each groove GRV similarly changes along the y-axis direction, and the height of each projection PRO also changes similarly along the y-axis direction. However, when the plurality of grooves GRV and the plurality of protrusions PRO are provided side by side on the second main surface of the light guide plate GLB, the distance between the grooves GRV or the protrusions PRO becomes narrower as the distance from the light source side increases. In this way, by gradually narrowing the distance between the groove GRV or the protrusion PRO on the second main surface of the light guide plate GLB, the first main surface of the light guide plate GLB attenuates as it moves away from one side surface of the light guide plate GLB facing the light source. The radiation intensity of the light from is compensated.

  However, as shown in FIG. 3A, the “sub-panel irradiation area” on the second main surface of the light guide plate GLB has a new groove in the gap between the grooves GRV formed in the “peripheral portion” adjacent thereto. The GRV is formed, or a new protrusion PRO is formed in a gap between the protrusions PRO formed in the “peripheral portion”. Therefore, the interval between the grooves GRV or the protrusions PRO along the x-axis direction is smaller in the “sub-panel irradiation region” than in the “peripheral portion” adjacent thereto. Further, in the “sub-panel irradiation area”, there is a portion where the grooves GRV or the protrusions PRO are arranged at intervals smaller than the intervals between the grooves GRV or the protrusions PRO formed apart from the light source. As described above, the interval between the grooves GRV or the protrusions PRO formed in a portion (the “sub-panel irradiation region”) of the second main surface of the light guide plate GLB facing the sub-liquid crystal display panel is changed to the “peripheral portion” adjacent thereto. Even if the distance between the grooves GRV or the protrusions PRO formed on the main liquid crystal display panel PNL1 is reduced, as described with reference to FIG.

  The reflection structure of the “sub-panel irradiation area” and the reflection structure of the “peripheral portion” adjacent to the second main surface of the light guide plate GLB described above with reference to FIG. When compared along the extending direction (y-axis) of the opposing side surfaces, the difference is described as follows. The density (density and interval along the x-axis) of the undulating structure (groove GRV or protrusion PRO) for controlling the reflection of light propagated in the light guide plate GLB by the second main surface in the second main surface is “sub-panel”. The “irradiation region” and the “peripheral portion” adjacent thereto are different from each other, and the density of the relief structure in the former is higher than that in the latter.

  On the other hand, on the second main surface of the light guide plate GLB of FIG. 3B, a plurality of dots DOT indicated by small squares are formed, and the density (the number of dots per unit area of the second main surface) depends on the light source. The height gradually increases as the distance from one side surface of the light guide plate GLB that faces the light guide plate increases. As described above, by sequentially increasing the density of the plurality of dots DOT formed on the second main surface of the light guide plate GLB according to the distance from the light source, the attenuation increases as the distance from one side of the light guide plate GLB facing the light source increases. The radiation intensity of light from the first main surface of the light guide plate GLB is compensated. In the second main surface of the light guide plate GLB of FIG. 3B, a quadrangular pyramid depression (recess) or a quadrangular pyramid projection (pyramid-shaped projection) is formed for each quadrangle indicating each dot DOT. . Further, the quadrangular pyramids of the dots DOT formed as depressions or protrusions on the second main surface have the same depth or height and the same bottom area regardless of the position of the dot DOT in the second main surface. .

  The shape of the depression or projection formed on the second main surface of the light guide plate GLB as a dot is not limited to the above-described quadrangular pyramid, but may be a polygonal pyramid such as a triangular pyramid or a pentagonal pyramid, a cone, or a vertex of the polygonal pyramid or the cone. May be replaced with a truncated pyramid or a truncated cone. The plurality of dots DOT formed as the plurality of depressions or the plurality of protrusions on the second main surface of the light guide plate GLB cause an undulating structure to appear on the second main surface, and the light guide plate GLB does not depend on its individual shape. The reflection of the propagated light by the second main surface is controlled.

  The light source facing one end of the light guide plate GLB shown at the left end of FIG. 3B includes an auxiliary light guide plate SGL and two light emitting elements LEDs arranged at both ends thereof. The auxiliary light guide plate SGL is formed of a light transmissive material such as an acrylic resin like the light guide plate GLB, and has a light exit surface facing one side surface of the light guide plate GLB and a reflection surface facing the light exit surface. The light emitting surface and the reflecting surface extend in the y-axis direction, and the reflecting surface has a wavy uneven structure along the y-axis. The light exit surface and the reflection surface are joined to the light entrance surface at both ends thereof, and each light entrance surface is optically connected to the light emitting element LED. Light incident on the auxiliary light guide plate SGL from both light entrance surfaces travels along the y-axis in the auxiliary light guide plate SGL while being gradually reflected on the light exit surface side by the wavy reflection surface. Therefore, the light source shown in FIG. 3B radiates light with substantially uniform intensity from the light exit surface of the auxiliary light guide plate SGL while using a point light source called a light emitting element LED, and one side of the light guide plate GLB. Function as a so-called surface light source for irradiating light.

  As shown in FIG. 3B, the density (the number of dots per unit area) of the dots DOT formed on the second main surface of the light guide plate GLB is equal to the “peripheral edge” adjacent to the “sub panel irradiation area”. Higher than "parts". The density of the dots DOT in the “sub-panel irradiation area” is higher than the density of the dots DOT in the peripheral portion farther from the light source (to the right of the “sub-panel irradiation area” in FIG. 3B). Therefore, the brightness of the first main surface of the light guide plate GLB shown in FIG. 3B is locally increased in the “sub-panel irradiation area” in a single state. However, when the light guide plate GLB is mounted on the casing CAS together with the main liquid crystal display panel PNL1 and the sub liquid crystal display panel PNL2 as shown in FIG. 1B, the local brightness of the screen of the main liquid crystal display panel PNL1 is reduced. The drop is suppressed as shown in FIG. 2C, and as a result, the occurrence of uneven brightness on the screen of the main liquid crystal display panel PNL1 is suppressed.

  The reflection structure of the “sub-panel irradiation region” and the reflection structure of the “peripheral portion” adjacent to the second main surface of the light guide plate GLB described above with reference to FIG. When compared along the extending direction (y-axis) of the opposing side surfaces, the difference is described as follows. The density (number per unit area) of the relief structure (dot DOT) for controlling the reflection of the light propagated in the light guide plate GLB by the second main surface in the second main surface is referred to as “sub-panel irradiation region”. Is different from the “peripheral portion” adjacent thereto, and the density of the relief structure in the former is higher than that in the latter.

  In the light guide plate GLB in which the plurality of dots DOT are formed on the second main surface, the density of the dots DOT formed in the “sub-panel irradiation area” is set along the y axis in the area adjacent to both sides of the “sub-panel irradiation area”. The following structure may be adopted in place of the structure shown in FIG. In this structure, dots “DOT” are formed at the same density in each of the “sub-panel irradiation region” and the regions adjacent on both sides along the y-axis, and the dots DOT formed in the “sub-panel irradiation region” are placed in the adjacent regions. Larger than that formed. When the dot DOT is formed as a depression on the second main surface, at least one of the bottom area and the depth of the dot DOT in the sub panel irradiation area is set to be larger than that of the dot DOT in the adjacent area. When the dot DOT is formed as a protrusion on the second main surface, at least one of the bottom area and the height of the dot DOT in the sub panel irradiation area is set to be larger than that of the dot DOT in the adjacent area.

  In this way, in the “sub-panel irradiation area” on the second main surface of the light guide plate GLB, the dots DOT are formed with the same density as the dots DOT in the other areas and with a size larger than that of the other areas. By doing so, the height or depth of the undulating structure (dot DOT) for controlling the reflection of the light propagated in the light guide plate GLB by the second main surface with respect to the second main surface, and the area of the area within the second main surface At least one is different in the “sub-panel irradiation region” and the “peripheral portion” adjacent to the sub-panel irradiation region along the extending direction (y-axis) of the side surface of the light guide plate GLB facing the light source. In one example, the area in the second main surface of the undulating structure in the “sub-panel irradiation region” is wider than that in the “peripheral portion”, and the “sub-panel irradiation region” has the “sub-panel irradiation region”. The reflectance of the second main surface in the “panel irradiation area” is corrected.

  Further, in an example in which the dots DOT are formed as depressions on the second main surface, the undulating structure in the “sub panel irradiation area” is formed deeper than that in the “peripheral portion”, and the dots DOT are formed as projections on the second main surface. In the example formed, the undulating structure in the “sub-panel irradiation region” is formed higher than that in the “peripheral portion”. In each of these two examples, the height difference (peak-to-valley) of the undulating structure in the “sub-panel irradiation region” is larger than that in the “peripheral portion”. Similarly to the light plate GLB, the reflectance of the second main surface in the “sub panel irradiation area” is corrected.

FIG. 1A shows an example of a liquid crystal display device (double-sided liquid crystal display device) according to the present invention, and FIG. 1B shows a planar structure of the liquid crystal display device as viewed from a mounting side of a main liquid crystal display panel, and FIG. 2) shows the cross-sectional structure of the liquid crystal display device along the line Ib-Ib ′ shown in FIG. 2A shows an example of a light guide plate suitable for the liquid crystal display device shown in FIG. 1, FIG. 2A shows a planar structure of the light guide plate viewed from a main surface facing the sub liquid crystal display panel, and FIG. FIG. 2C shows a cross-sectional structure of the light guide plate along the line AA ′ and the line BB ′ shown in FIG. 2A, and FIG. 2C shows a liquid crystal display in which the light guide plate is mounted as shown in FIG. The luminance profile (Profile) of the main liquid crystal display panel of the device is shown respectively. FIG. 3A shows another example of a light guide plate suitable for the liquid crystal display device shown in FIG. 1, and FIG. 3A shows a planar structure of a light guide plate having a plurality of grooves or projections formed on a main surface facing the sub liquid crystal display panel. FIG. 3B shows a planar structure of a light guide plate in which a plurality of dots (dents or protrusions) are formed on a main surface facing the sub liquid crystal display panel.

Explanation of reference numerals

PNL1: main liquid crystal display panel, PNL2: sub liquid crystal display panel, CAS: housing, LED: light emitting element (light emitting diode), GLB: light guide plate, OPN: (housing CAS) aperture, GRV groove, PRO protrusion, DOT dot, SGL auxiliary light guide plate.

Claims (14)

A first liquid crystal display panel;
A second liquid crystal display panel having a main surface smaller than that of the first liquid crystal display panel;
A light guide plate having a first main surface, a second main surface facing the first main surface, and a plurality of side surfaces separating the first main surface and the second main surface;
A light source including at least one light emitting element disposed opposite to one of the plurality of side surfaces of the light guide plate,
The first liquid crystal display panel is disposed such that a main surface thereof is opposed to a first main surface of the light guide plate,
The second liquid crystal display panel is disposed such that a main surface thereof faces a part of a second main surface of the light guide plate,
A liquid crystal display device, wherein an undulating structure is provided on the second main surface of the light guide plate.   The liquid crystal display device according to claim 1, wherein the undulating structure controls reflection of light propagated in the light guide plate by the second main surface.   The undulating structure may be configured such that at least one of a height and a depth with respect to the second main surface, and a density and an area in the second main surface are in the portion of the second main surface and a peripheral portion adjacent thereto. The liquid crystal display device according to claim 1, wherein the liquid crystal display devices are different from each other.   In the undulating structure, at least one of a height and a depth with respect to the second main surface, and a density and an area in the second main surface are determined according to a distance of the light guide plate from one of the side surfaces to the light source. And at least one of the height, depth, density and area of the relief structure in the portion of the second main surface is adjacent to the portion along one of the side surfaces of the light guide plate. 2. The liquid crystal display device according to claim 1, wherein the number is larger than that at a peripheral portion.   The liquid crystal display device according to claim 1, wherein the undulating structure is a plurality of grooves formed in the second main surface.   The first liquid crystal display panel, the light guide plate, and a first concave portion for holding the light source are formed on one side thereof, and the second liquid crystal display panel is formed on the other side opposite to the one side. A housing provided with a second recess for holding the housing, wherein the housing is provided with light radiated from the second main surface of the light guide plate between the first recess and the second recess. An opening for irradiating the main surface of the second liquid crystal display panel is formed, and the portion of the light guide plate in the second main surface is defined as a portion of the second main surface facing the opening. The liquid crystal display device according to claim 1.   The reflectance of the portion of the second main surface of the light guide plate and the peripheral portion adjacent to the portion along one of the side surfaces of the light guide plate facing the light source is the light guide plate itself. The liquid crystal display device according to claim 6, wherein the reflectance is higher at the portion, and the difference in reflectance between the portion and the peripheral portion is reduced by housing the light guide plate in the housing. A first liquid crystal display panel;
A second liquid crystal display panel having a main surface smaller than that of the first liquid crystal display panel;
A light guide plate having a first main surface, a second main surface facing the first main surface, and a plurality of side surfaces separating the first main surface and the second main surface;
Arranging a light source on the side of the light guide plate,
The first liquid crystal display panel is arranged such that a main surface thereof faces the first main surface of the light guide plate,
The second liquid crystal display panel is arranged such that a main surface thereof faces a part of a second main surface of the light guide plate,
The liquid crystal display device according to claim 6, wherein a groove is formed in the second main surface of the light guide plate.   9. The liquid crystal display device according to claim 8, wherein the groove of the second main surface of the light guide plate is deeper at least from the light source to a part of the second main surface as being farther from the light source. 10.   9. The liquid crystal display device according to claim 8, wherein the groove on the second main surface of the light guide plate is a groove that is farthest from the light source than a groove that is closest to the light source.   The groove of the second main surface of the light guide plate is such that the depth of the groove on the side away from the light source among the grooves of a part of the second main surface is greater than the depth of the groove adjacent to a part of the second main surface. The liquid crystal display device according to claim 8, wherein the liquid crystal display device is deepened.   The first liquid crystal display panel, the light guide plate, and a first concave portion for holding the light source are formed on one side thereof, and the second liquid crystal display panel is formed on the other side opposite to the one side. A housing provided with a second recess for holding the housing, wherein the housing is provided with light radiated from the second main surface of the light guide plate between the first recess and the second recess. An opening for irradiating the main surface of the second liquid crystal display panel is formed, and the portion of the light guide plate in the second main surface is defined as a portion of the second main surface facing the opening. The liquid crystal display device according to claim 8, wherein A first liquid crystal display panel;
A second liquid crystal display panel having a main surface smaller than that of the first liquid crystal display panel;
A light guide plate having a first main surface, a second main surface facing the first main surface, and a side surface separating the first main surface and the second main surface;
Arranging a light source on the side of the light guide plate,
The first liquid crystal display panel is arranged such that a main surface thereof faces the first main surface of the light guide plate,
The second liquid crystal display panel is disposed such that a main surface thereof faces a part of a second main surface of the light guide plate,
In the second main surface of the light guide plate, at least one of a height and a depth with respect to the second main surface, a density and an area in the second main surface are the same as the part of the second main surface. A liquid crystal display device which is different from a peripheral portion adjacent to the liquid crystal display device. The first liquid crystal display panel, the light guide plate, and a first concave portion for holding the light source are formed on one side thereof, and the second liquid crystal display panel is formed on the other side opposite to the one side. A housing provided with a second recess for holding the housing, wherein the housing is provided with light radiated from the second main surface of the light guide plate between the first recess and the second recess. An opening for irradiating the main surface of the second liquid crystal display panel is formed, and the portion of the light guide plate in the second main surface is defined as a portion of the second main surface facing the opening. The liquid crystal display device according to claim 13, wherein:

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