JP2009008784A - Back light unit, display device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back light unit inexpensively and easily improved in luminance, and a liquid crystal display device or the like mounted therewith. <P>SOLUTION: A light guide plate 11 is provided with a prism piece 15 for deflecting light included in a top surface 12 and a grain pattern for diffusing light included in a bottom surface 13. A permeable sheet group GR includes a plurality of optical sheets 21, 31 and 41 each having one prism surface by including each sheet prism piece 25, 35 or 45 for deflecting light. The main first optical sheet 21 transmitting light from the top surface 12 of the light guide plate 11 is disposed with the reverse side of a prism surface 21p being turned to the top surface 12, and the sub-optical sheet 41 transmitting light from the bottom surface 13 is disposed with a prism surface 41p being turned to the bottom surface 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a backlight unit that emits light (backlight light) in two directions, a display device on which the backlight unit is mounted, and an electronic device on which the display device is mounted.

  In recent years, foldable mobile phones that can fold a main body have become widespread. Such a mobile phone includes a sub display screen for displaying auxiliary information and a main display screen for displaying main information. The sub display screen is located at a place where the mobile phone can be viewed from the outside even when the cellular phone is folded, and displays the reception state of the radio wave, the remaining battery level, and the like. On the other hand, the main display screen is located at a place where the mobile phone can be viewed with the mobile phone opened, and displays the telephone number to be transmitted.

  Then, as an example of an efficient arrangement of the sub display screen and the main display screen, there is a mobile phone in which the back side of the sub display screen and the back side of the main display screen face each other. In particular, if the sub display screen and the main display screen are two liquid crystal display panels, a liquid crystal display including both the liquid crystal display panels and a backlight unit that supplies light (backlight light) to the two liquid crystal display panels. A mobile phone equipped with the device is desirable. This is because such a liquid crystal display device contributes to the thinness of the mobile phone because only one backlight unit is included.

  An example of this is a liquid crystal display device 189 equipped with a backlight unit 181 as shown in FIG. 12 (see Patent Document 1). In the liquid crystal display device 189, the polarization separation element 191 that reflects one of two different polarization components and transmits the other is positioned so as to face the bottom surface 113 of the light guide plate 111.

  More specifically, the polarization separation element 191 has a reflection axis 191a and a transmission axis 191b that are orthogonal to each other. Therefore, the polarization separation element 191 reflects linearly polarized light components having a vibration surface parallel to the reflection axis 191a and travels toward the first liquid crystal display panel 182, while linearly polarized light having a vibration surface parallel to the transmission axis 191b. The component is transmitted and travels toward the second liquid crystal display panel 183.

  In addition, in the liquid crystal display device 189, the diffusion sheet 152, the prism sheet 121, and the prism sheet 131 are interposed between the light guide plate 111 and the first liquid crystal display panel 182, while the light guide plate 111 and the second liquid crystal display panel 182 are interposed. Between the liquid crystal display panel 183, a prism sheet 141, a prism sheet 149, and a diffusion sheet 153 are interposed.

  The prism sheets 121, 131, 141, and 149 emit light from the light guide plate 111 in a direction perpendicular to the display surfaces of the first liquid crystal display panel 182 and the second liquid crystal display panel 183 in order to improve luminance. Make it progress.

Japanese Patent Laying-Open No. 2004-354751 (see FIG. 1)

  However, such prism sheets 121, 131, 141, and 149 and the polarization separation element 191 are expensive members. Therefore, the cost of the backlight unit 181 may be increased. Further, it is extremely difficult to control the light to travel with an appropriate amount of light while being divided into the top surface 112 side and the bottom surface 113 side of the light guide plate 111 by the polarization separation element 191. Therefore, it cannot be said that such a liquid crystal display device 189 has sufficiently improved luminance.

  The present invention has been made in view of the above situation. An object of the present invention is to provide a backlight unit that realizes an improvement in luminance, a liquid crystal display device and the like mounted thereon, inexpensively and easily.

  The backlight unit internally transmits the light from the light source entering from the light receiving surface and emits the light to the outside through the opposed first and second emission surfaces, and the light emitted from the light guide plate. And a transmissive sheet group to be transmitted.

  In such a backlight unit, the light guide plate includes the first light guide plate prism prism for refracting light in the first output surface, and the second output surface includes a texture pattern for diffusing light. The transmissive sheet group includes a plurality of deflection sheets that include a prism piece for a sheet that refracts light so that one surface is a prism surface.

  Further, in this backlight unit, when the deflection sheet that transmits light from the first emission surface is the first deflection sheet, the first deflection sheet has the back surface of the prism surface facing the first emission surface, If the deflection sheet that transmits light from the two emission surfaces is the second deflection sheet, the second deflection sheet has the prism surface facing the second emission surface.

  However, the light guide plate in the backlight unit is not limited to the one in which the first prism piece for the light guide plate is included in the first emission surface and the texture pattern is included in the second emission surface. For example, the light guide plate may include a first prism piece for a light guide plate that refracts light in the first emission surface and a second prism piece for the light guide plate in the second emission surface.

  In addition, the backlight unit preferably includes a first diffusion sheet that diffuses light traveling from the first emission surface while transmitting the light and guides it to the first deflection sheet.

  Further, in the backlight unit, when the deflection sheet that transmits light traveling from the first deflection sheet is the third deflection sheet, the third deflection sheet preferably has the rear surface of the prism surface facing the first deflection sheet. .

  In the backlight unit, the prism pieces for the sheet in the first deflection sheet are linear and arranged in parallel, and the parallel direction is the F1 direction, and the prism piece for the sheet in the third deflection sheet is linear. If the parallel direction is the F2 direction, it is desirable that the F1 direction and the F3 direction in the third deflection sheet are orthogonal to each other.

  In addition, in the backlight unit, it is preferable that a second diffusion sheet that diffuses while transmitting light traveling from the second deflection sheet is included behind the prism surface of the second deflection sheet.

By the way, in the backlight unit, the first prism piece for the light guide plate located on the first emission surface is linear, and the linear direction is the D2 direction, and the first emission surface is orthogonal to the light receiving surface. Is a reference direction, it is desirable that at least one light guide plate first prism piece satisfying the following conditional expression (1) exists.
0 ° ≦ θ1 ≦ 10 ° ... Conditional expression (1)
However,
θ1: The minimum angle formed by the D2 direction and the reference direction M.

In the backlight unit, the prism pieces for sheet included in the first deflection sheet are linear and arranged in parallel. When the parallel direction is the F1 direction, the following conditional expression (2) is applied to the first deflection sheet. It is desirable that at least one sheet prism piece satisfying the above condition exists.
80 ° ≦ θ2 ≦ 90 ° Conditional expression (2)
However,
θ2: The first prism pieces for the light guide plate located on the first emission surface are linear and arranged in parallel.
If the parallel direction is D1 direction, the D1 direction on the first deflection sheet, the F1 direction,
The minimum angle formed by.

In the backlight unit, the prism pieces for sheet included in the first deflection sheet are linear and arranged in parallel. When the parallel direction is F1 direction, the following conditional expression (3) is applied to the first deflection sheet. It is desirable that at least one sheet prism piece satisfying the above condition exists.
35 ° ≦ θ2 ≦ 55 ° Conditional expression (3)
However,
θ2: The first prism pieces for the light guide plate located on the first emission surface are linear and arranged in parallel.
If the parallel direction is D1 direction, the D1 direction on the first deflection sheet, the F1 direction,
The minimum angle formed by.

In the backlight unit, the prism pieces for sheet included in the second deflection sheet are linear and arranged in parallel. When the parallel direction is F3 direction, the following conditional expression (4) is applied to the second deflection sheet. It is desirable that at least one sheet prism piece satisfying the above condition exists.
80 ° ≦ θ3 ≦ 90 ° Conditional expression (4)
However,
θ3: The first prism pieces for the light guide plate located on the first emission surface are linear and arranged in parallel.
If the parallel direction is D1 direction, the D1 direction on the second deflection sheet, the F3 direction,
The minimum angle formed by.

  In the backlight unit, the first emission surface and the second emission surface are surfaces that sandwich the light receiving surface, and the surface relationship between the first emission surface and the light receiving surface is in an intersecting relationship (for example, an orthogonal relationship), and The surface relationship between the second emission surface and the light receiving surface is preferably in a cross relationship (for example, an orthogonal relationship).

  Further, in the backlight unit, it is preferable that the plurality of first light guide plate prism pieces are arranged in parallel with each other, and a planar first emission surface is exposed between the first light guide plate prism pieces. .

  Further, in the backlight unit, if a plurality of first light guide plate prism pieces arranged in parallel is a large group, the large group includes a small group of light guide plate first prism pieces having different arrangement pitches. It is desirable.

  In the backlight unit, the light source is preferably a light emitting element.

  The backlight unit as described above, the first display panel that modulates by receiving the light traveling from the first emission surface, and the modulation by receiving the light traveling from the second emission surface. A display device including the second display panel to be operated can also be said to be the present invention.

  Further, an electronic device that houses such a display device can also be said to be the present invention.

  According to the backlight unit of the present invention, the first light exit surface and the second light exit surface of the light guide plate are subjected to processing for deflecting the optical path (prism processing or embossing), and further from the first light exit surface. A first deflection sheet that allows light to pass through while deflecting light and a second deflection sheet that allows light from the second exit surface to pass while deflecting are also included. Therefore, such a backlight unit improves the luminance of the emitted light from both surfaces of the light guide plate without having an expensive special member that separates the polarized light.

[Embodiment 1]
The following describes one embodiment with reference to the drawings. In addition, although a member code | symbol, hatching, etc. may be abbreviate | omitted for convenience for some drawings, in such a case, other drawings shall be referred to. Moreover, the black circle on the drawing means a direction perpendicular to the paper surface.

  As shown in FIG. 11, the liquid crystal display device (display device) 89 includes a backlight unit 81, a first liquid crystal display panel (first display panel) 82, and a second liquid crystal display panel (second display panel) 83. It is out.

  The backlight unit 81 generates planar light that irradiates the first liquid crystal display panel 82 and the second liquid crystal display panel 83. That is, the backlight unit 81 is an illumination device that emits light (backlight light) in two directions. Therefore, such a backlight unit 81 is also referred to as a double-sided light emitting illumination device.

  As shown in FIGS. 11 and 1 (enlarged view of the backlight unit 81), the backlight unit 81 includes an LED (Light Emitting Diode) 51, a light guide plate 11, a diffusion sheet 52, an optical sheet 21, an optical sheet 31, The optical sheet 41 and the diffusion sheet 53 are included (the diffusion sheets 52 and 53 and the optical sheets 21, 31, and 41 are referred to as a transmission sheet group GR).

  An LED (light source, light emitting element) 51 is a point light source, and emits light toward the side surface of the light guide plate 11. Further, in order to secure the light amount, the plurality of LEDs 51 are arranged in parallel (note that the parallel direction of the parallel LEDs 51 is defined as a parallel direction D1). However, only some of the LEDs 51 are shown in the drawing.

  The LED 51 is driven by a current supplied through the FPC board 54. Further, the light source of the backlight unit 81 is not limited to the LED 51, and may be another type of light source such as a fluorescent tube (Cold Cathode Fluorescent Tube). However, from the viewpoint of reducing the size and thickness of the backlight unit 81, the LED 51 is desirable.

  1 and 11, the light of the LED 51 is incident on only one side surface 14 of the four side surfaces 14... Of the light guide plate 11. However, the present invention is not limited to this. That is, the LEDs 51 may be disposed in all four side surfaces 14 of the light guide plate 11 or in front of the two or three side surfaces 14.

  The light guide plate 11 receives the light from the LED 51 by making the side surface 14 face the light emitting surface of the LED 51. The received light is mixed inside the light guide plate 11 and is emitted as planar light from the top surface (first emission surface) 12 and the bottom surface (second emission surface) 13 (details will be described later). In the following description, a member located on the top surface 12 side may be referred to as “main” and a member located on the bottom surface 13 side as “sub”.

  The main diffusion sheet (first diffusion sheet) 52 is positioned so as to cover the top surface 12 of the light guide plate 11, diffuses the planar light traveling from the top surface 12, and spreads over the entire area of the first liquid crystal display panel 82. Stir light.

  The main first optical sheet (first deflection sheet) 21 is positioned so as to cover the main diffusion sheet 52, thereby transmitting light traveling from the main diffusion sheet 52. In addition, the main first optical sheet 21 includes a plurality of linear prism pieces (linear prisms) 25 that refract light on a surface (surface 21p) facing the back surface with respect to the top surface 12 of the light guide plate 11. Contains.

  Therefore, these parallel prism pieces (prism pieces for main first optical sheet) 25 deflect the radiation direction of the light traveling through the main first optical sheet 21, thereby causing light emission per unit area. Brightness is improved.

  In addition, the parallel direction of the prism pieces 25 is a direction that intersects (for example, orthogonal to) the parallel direction D1 that is the parallel direction of the LEDs 51, and is hereinafter referred to as a parallel direction F1. Further, since the prism piece 25 extends in a direction intersecting (for example, orthogonal to) the parallel direction F1, this direction is referred to as a linear direction S1.

  The main second optical sheet (third deflection sheet) 31 is positioned so as to cover the main first optical sheet 21, thereby transmitting light traveling from the main first optical sheet 21. In addition, like the main first optical sheet 21, the main second optical sheet 31 is a linear prism that refracts light on a surface (surface 31p) facing the back side with respect to the top surface 12 of the light guide plate 11. A plurality of pieces 35 are included.

  Therefore, these parallel prism pieces (prism pieces for the main second optical sheet) 35 deflect the radiation direction of the light traveling through the main first optical sheet 21, and as a result, emit light per unit area. Brightness is improved.

  The parallel direction of the prism pieces 35 is the same as the parallel direction D1 that is the parallel direction of the LEDs 51, and is hereinafter referred to as a parallel direction F2. Therefore, the parallel direction F2 intersects the parallel direction F1 that intersects the parallel direction D1.

  In addition, since the prism piece 35 extends in a direction intersecting (for example, orthogonal to) the parallel direction F2, this direction is referred to as a linear direction S2. Therefore, the linear direction S2 and the linear direction S1 are in an intersecting relationship.

  The sub optical sheet (second deflection sheet) 41 is positioned so as to be covered with the bottom surface 13 of the light guide plate 11 and transmits light traveling from the bottom surface 13. In addition, the sub optical sheet 41 includes a plurality of linear prism pieces 45 that refract light on the surface (surface 41 p) facing the bottom surface 13 of the light guide plate 11.

  Therefore, these parallel prism pieces (sub-optical sheet prism pieces) 45 deflect the radiation characteristics of the light traveling through the bottom surface 13 of the light guide plate 11, resulting in the emission luminance per unit area. improves.

  The parallel direction of the prism pieces 45 is a direction that intersects (for example, orthogonal to) the parallel direction D1 that is the parallel direction of the LEDs 51, and is hereinafter referred to as a parallel direction F3. Further, since the prism piece 45 extends in a direction intersecting (for example, orthogonal to) the parallel direction F3, this direction is referred to as a linear direction S3.

  The sub-diffusion sheet (second diffusion sheet) 53 is positioned so as to be covered by the sub-optical sheet 41, diffuses the light traveling from the sub-optical sheet 41, and transmits the light to the entire area of the second liquid crystal display panel 83. Scatter.

  Next, the liquid crystal display panel will be described. As shown in FIG. 11, both the first liquid crystal display panel 82 and the second liquid crystal display panel 83 are panels that perform display functions by receiving light (backlight light) from the backlight unit 81. The first liquid crystal display panel 82 and the second liquid crystal display panel 83 include active matrix substrates 71 and 71, counter substrates 72 and 72, and polarizing plates 73.

  The active matrix substrates 71 and 71 are substrates including switching elements such as TFTs (Thin Film Transistors) that control liquid crystal, source lines, gate lines, pixel electrodes, and the like. On the other hand, the counter substrates 72 and 72 are substrates facing the active matrix substrates 71 and 71, and include color filters and the like necessary for color display (note that TFTs, color filters and the like are not shown). And the periphery vicinity of these board | substrates 71 * 72 (71 * 72) is bonded together via a frame-shaped sealing member (not shown), and a liquid crystal (not shown) is inject | poured into these clearance gaps.

  The polarizing plates 73... Sandwich the active matrix substrate 71 and the counter substrate 72 and limit the vibration of the backlight light supplied from the backlight unit 81 in a specific direction.

  The first liquid crystal display panel 82 and the second liquid crystal display panel 83 are TFTs under the control of an IC (Integrated Circuit; drain driver, gate driver, etc.) mounted on an FPC (Flexible Printed Circuits) substrate (not shown). The display image is adjusted by controlling the voltage applied to the liquid crystal and changing the transmittance of the backlight that transmits the liquid crystal.

  Here, the light guide plate 11 will be described in detail with reference to FIGS. The light guide plate 11 has a plate shape. Therefore, on the surface of the light guide plate 11, a bottom surface 13, a top surface 12 that faces the bottom surface 13, and a side surface 14 that is positioned between the bottom surface 13 and the top surface 12 are positioned. .

  The light emitting surface of the LED 51 faces one surface of the side surfaces 14. Therefore, the side surface 14 becomes a light receiving surface (incident surface) 14a. Then, the surface relationship between the light receiving surface 14a and the top surface 12 is a cross relationship (for example, orthogonal relationship), and the surface relationship between the light receiving surface 14a and the bottom surface 13 is also a cross relationship (for example, orthogonal relationship).

  2 is a perspective view showing the top surface 12 of the light guide plate 11, and FIG. 3 is a cross-sectional view taken along the line A-A 'in FIG. As shown in these drawings, a prism piece (first prism piece for light guide plate) 15 extending in a triangular prism shape is arranged in parallel on the top surface 12 in the same direction as the parallel direction D1 of the LEDs 51.

  Further, since this prism piece 15 extends in a direction intersecting (for example, orthogonal to) the parallel direction D1, this direction is referred to as a linear direction D2. Furthermore, a direction (eg, a perpendicular direction) intersecting the parallel direction D1 and the linear direction D2 is referred to as a direction D3 (note that this direction D3 is also the overlapping direction of the sheets in the transmissive sheet group GR. ).

  When the prism piece 15 as described above is formed on the top surface 12, the light (planar light) traveling through the top surface 12 is aligned in the parallel direction D1 due to refraction at the side surfaces of the parallel prism pieces 15. Without proceeding excessively, that is, so as to approach the direction D3. Thereafter, the planar light traveling in this manner is diffused by the main diffusion sheet 52 and passes through the main first optical sheet 21.

  With this configuration, the planar light that travels in the direction D3 while being diffused by the main diffusion sheet 52 is refracted by the side surfaces of the prism pieces 25 that are arranged in parallel in the main first optical sheet 21. It proceeds without excessively spreading in the parallel direction F1. Then, the planar light travels so as not to spread excessively in the intersecting (for example, orthogonal) parallel direction D1 and parallel direction F1.

  Therefore, such planar light travels very close to the direction D3 intersecting (for example, orthogonal) with respect to both the parallel direction D1 and the parallel direction F1 (that is, condensing), resulting in it. Thus, the light emission luminance per unit area of the planar light is improved.

  In addition, after passing through the main first optical sheet 21, the planar light passes through the main second optical sheet 31 in which the prism pieces 35 are arranged in the parallel direction F2 intersecting (for example, orthogonal to) the parallel direction F1. Then, such planar light travels very close to a direction D3 that intersects (for example, is orthogonal to) the three directions of the parallel direction D1, the parallel direction F1, and the parallel direction F2. As a result, the emission luminance per unit area of the planar light is surely improved.

  The light passing through the top surface 12 of the light guide plate 11 (the prism surface 12 of the light guide plate 11) is shown in an optical path diagram of FIG. 5 described later (an optical path diagram seen from a cross section taken along line BB ′ in FIG. 2). As described above, the light diffused by the raised pieces 17 on the bottom surface 13 of the light guide plate 11, in particular, diffused and progressed toward the top surface 12, reaches the top surface 12 directly from the light receiving surface 14 a of the light guide plate 11 and is totally reflected. And light that is refracted and transmitted without any problem.

  On the other hand, as shown in FIG. 4 which is a perspective view showing the bottom surface 13 of the light guide plate 11 and FIG. 3, a plurality of convex raised pieces 17 for diffusing light are scattered on the bottom surface 13 (the bottom surface 13). A wrinkle pattern is formed on the surface). More specifically, as the distance from the light receiving surface 14a of the light guide plate 11 deviates, the raised pieces 17 are scattered so as to increase the distribution density.

  When the protruding pieces 17 are scattered in this way, as shown in the optical path diagram of FIG. 5 (the one-dot chain line is the optical path), after entering the light guide plate 11 from the light receiving surface 14a, the top surface 12 totally reflects. A large amount of light reaching the bottom surface 13 that is relatively far away from the light receiving surface 14a is diffused efficiently. Of the light that diffuses in this way, the light that travels through the bottom surface 13 (planar light) passes through the sub optical sheet 41 and the sub diffusion sheet 53.

  Further, as shown in FIG. 6 (an optical path diagram seen from the cross-section taken along the line CC ′ in FIG. 5), each of the two side surfaces of the prism piece 15 is not refracted and transmitted through the top surface 12 of the light guide plate 11. The light (planar light) that travels through the bottom surface 13 among the light that is totally reflected and travels through the refraction is also transmitted through the sub optical sheet 41 and the sub diffusion sheet 53.

  More specifically, the light refracting from the prism piece 15 on the top surface 12 travels through the bottom surface 13 without excessively spreading in the parallel direction D1 of the prism piece 15 (the point H is from the light receiving surface 14a). This is the center point of light traveling along the linear direction D2 while radiating).

  Then, the planar light passing through the bottom surface 13 as described above proceeds without excessively spreading in the parallel direction F3 due to refraction at the side surfaces of the prism pieces 45 arranged in parallel in the sub optical sheet 41, and further, It is diffused by the diffusion sheet 53.

  In particular, as shown in FIG. 6, light that does not spread excessively in the parallel direction D1 by the prism piece 15 on the top surface 12 further travels without being excessively spread in the parallel direction F3 by the prism piece 45 of the sub optical sheet 41. Therefore, it proceeds very close to a direction D3 that intersects (for example, is orthogonal to) both the parallel direction D1 and the parallel direction F3. Therefore, the light emission luminance per unit area of the planar light is improved.

  That is, the light guide plate 11 in the backlight unit 81 as described above includes a prism piece 15 that refracts light on the top surface 12 and a texture pattern that diffuses light on the bottom surface 13. Further, the transmission sheet group GR includes a plurality of optical sheets 21, 31, and 41 having prism surfaces 21 p, 31 p, and 41 p as one surface by including prism pieces 25, 35, and 45 for refracting light. Yes.

  The main first optical sheet 21 that transmits light from the top surface 12 of the light guide plate 11 has the rear surface of the prism surface 21p directed to the top surface 12, and the sub optical sheet 41 that transmits light from the bottom surface 13 is The prism surface 41 p faces the bottom surface 13.

  In this way, the planar light passing through the top surface 12 is the prism piece 15 of the top surface 12 and the main first optical sheet that are parallel to each other (parallel direction D1 and parallel direction F1). By refraction by the prism piece 25 of 21, the direction D3 (for example, the direction perpendicular to the top surface 12) comes closer. As a result, the emission luminance per unit area of the planar light is improved (light use efficiency is improved).

  Further, the planar light passing through the bottom surface 13 travels outside while being diffused by the raised pieces 17 located on the bottom surface 13 itself. In addition, the refraction at the side surfaces of the prism pieces 45 arranged in parallel in the sub optical sheet 41 proceeds without excessively spreading in the parallel direction F3 (for example, proceeds in the direction perpendicular to the bottom surface 13). As a result, the planar light is diffused into uniform light while improving the light emission luminance per unit area.

  That is, the backlight unit 81 improves the emission luminance of the emitted light in two directions.

  As shown in FIG. 1, if the main diffusion sheet 52 is interposed between the top surface 12 of the light guide plate 11 and the main first optical sheet 21, diffusion of light reaching the main first optical sheet 21. The degree is relatively high. Therefore, when such light passes through the main first optical sheet 21, luminance unevenness does not occur in the light (as a result, the illumination angle dependency is improved).

  Further, when the main second optical sheet 31 that transmits light traveling from the main first optical sheet 21 has the back surface of the prism surface 31p facing the main first optical sheet 21, the planar light from the top surface 12 is The light is refracted by the prism pieces 15, 25, and 35. Furthermore, it is desirable that the parallel direction F1 of the prism pieces 25 superimposed on the main second optical sheet 31 and the parallel direction F2 of the prism pieces 35 in the main second optical sheet 31 are orthogonal to each other.

  In this case, in the parallel direction D1, the parallel direction F1, and the parallel direction F2 of the prism pieces 15, 25, and 35, the parallel directions D1 and F2 intersect the parallel direction F1. Therefore, the light passing through the prism pieces 15, 25, and 35 travels very close to the direction D3 that is also a crossing direction with respect to the parallel direction D1 and the parallel direction F1 and also a crossing direction with respect to the parallel direction F2 and the parallel direction F1. become. As a result, the light emission luminance per unit area of the planar light is surely improved (for example, luminance is not insufficient or luminance unevenness does not occur even by a perspective view).

  Further, a sub-diffusion sheet 53 that diffuses light traveling from the sub optical sheet 41 is included on the back side of the prism surface 41 p of the sub optical sheet 41. With this configuration, the light emitted from the bottom surface 13 of the light guide plate 11 with a relatively high degree of uniformity passes through the sub-diffusion sheet 53, thereby further increasing the degree of uniformity. Further, such a backlight unit 81 includes only one optical sheet on the bottom surface 13 side of the light guide plate 11 (only the sub optical sheet 41 is included). Therefore, the cost of the backlight unit 81 can be reduced.

[Embodiment 2]
A second embodiment will be described. In addition, about the member which has the same function as the member used in Embodiment 1, the same code | symbol is attached and the description is abbreviate | omitted. In the second embodiment, a desirable position of the prism piece will be described.

  For example, the prism pieces 15 located on the top surface 12 of the light guide plate 11 are juxtaposed in the parallel direction D1 and extend in the linear direction D2 intersecting the parallel direction D1. Therefore, when the orthogonal direction from the light receiving surface 14a on the top surface 12 is a reference direction M, as shown in FIGS. 7A to 7C, at least one prism piece 15 that satisfies the following conditional expression (1) exists. (It is noted that FIG. 7A is a plan view of the top surface 12 of the light guide plate 11).

0 ° ≦ θ1 ≦ 10 ° ... Conditional expression (1)
However,
θ1: The minimum angle formed by the linear direction D2 and the reference direction M.

  Conditional expression (1) means that the prism piece 15 is located within an error range of 10 ° with respect to the reference direction M. More specifically, as shown in FIG. 7B, the rotation angle (θ1) from the reference direction M to the G1 direction clockwise is within 10 ° (referred to as + 10 ° for convenience), or as shown in FIG. 7C. The rotation angle (θ1) from the reference direction M to the G1 direction counterclockwise is within 10 ° (referred to as −10 ° for convenience).

  When θ1 exceeds the upper limit value or less than the lower limit value in the conditional expression (1), most of the light traveling from the light receiving surface 14a of the light guide plate 11 is substantially the side surface of the prism piece 15. In this case, the light is refracted to the outside without being totally reflected, and the amount of light mixed inside the light guide plate 11 is reduced. However, this problem does not occur if θ1 is within the range of conditional expression (1).

  Further, the relationship between the parallel direction D1 of the prism pieces 15 of the light guide plate 11 and the parallel direction F1 of the prism pieces 25 of the main first optical sheet 21 is shown in FIG. 8 (plan view of the prism surface 21p of the main first optical sheet 21). ) Is desirable.

  More specifically, the prism pieces 25 included in the main first optical sheet 21 are linear and arranged in parallel. When the parallel direction is a parallel direction F1, the following conditional expression (2) is applied to the main first optical sheet 21. It is desirable that at least one prism piece 25 satisfying the above condition exists.

80 ° ≦ θ2 ≦ 90 ° Conditional expression (2)
However,
θ2: The prism pieces 15 located on the top surface 12 of the light guide plate 11 are linear and arranged in parallel.
When the parallel direction is the parallel direction D1, the parallel direction in the main first optical sheet 21
D1 (the parallel direction D1 superimposed on the main first optical sheet 21) and the parallel direction F1
This is the minimum angle formed.

  The main first optical sheet 21 allows light traveling through the prism pieces 15 on the top surface 12 of the light guide plate 11 to pass therethrough. However, the prism pieces 15 on the top surface 12 are arranged in parallel along the parallel direction D1. Therefore, the light traveling through the top surface 12 travels without excessively spreading in the parallel direction D1.

  Then, the main first optical system having the prism surface 21p in which the prism pieces 25 extending in the same direction (linear direction S1) as the parallel direction D1 are arranged in parallel in the direction intersecting the parallel direction D1 (parallel direction F1). Sheet 21 would be desirable. In this case, the light that travels without being excessively spread in the parallel direction D1 passes through the main first optical sheet 21, and is further parallel to the parallel direction D1. This is because it does not spread to F1.

  However, in such a case, interference may occur between the prism piece 25 of the main first optical sheet 21 and the prism piece 15 of the light guide plate 11. Further, between the prism piece 25 of the main first optical sheet 21 and the prism piece 45 of the sub optical sheet 41 or the prism piece 25 of the main first optical sheet 21 and the first liquid crystal display panel 82 and the second liquid crystal display panel. Interference may also occur between the 83 pixels.

Therefore, when it is desired to avoid such a situation of interference, θ2 satisfies the conditional expression (2). However, the angle θ2 that is desirable from the viewpoint of preventing interference as described above is not limited to the conditional expression (2), and may be the following conditional expression (3) (desired: Is preferable that θ2 is 45 °).
35 ° ≦ θ2 ≦ 55 ° Conditional expression (3)

  In the conditional expressions (2) and (3), the angle is defined by the parallel direction D1 and F1 of the prism pieces 15 and 25, but is defined by the linear direction (ridge line direction) D2 and S1 of the prism pieces 15 and 25. It doesn't matter. That is, the prism piece 25 included in the main first optical sheet 21 is linear, and when the linear direction is a linear direction S1, the following conditional expression (2) ′ is applied to the main first optical sheet 21. It is desirable that at least one prism piece 25 satisfying (3) ′ is present.

80 ° ≦ θ′2 ≦ 90 ° Conditional expression (2) ′
35 ° ≦ θ′2 ≦ 55 ° Conditional expression (3) ′
However,
θ′2: The prism piece 15 located on the top surface 12 of the light guide plate 11 is linear, and its linear direction is
The linear direction D2 is the minimum angle formed by the linear direction D2 (the linear direction D2 superimposed on the main first optical sheet 21) on the main first optical sheet 21 and the linear direction S1.

  Further, the relationship between the parallel direction D1 of the prism pieces 15 of the light guide plate 11 and the parallel direction F3 of the prism pieces 45 of the sub optical sheet 41 is as shown in FIG. 9 (plan view of the prism surface 41p of the sub optical sheet 41). It is desirable that

  More specifically, the prism pieces 45 included in the sub optical sheet 41 are linear and arranged in parallel, and when the parallel direction F3 is set, the prism piece 45 satisfying the following conditional expression (4) is provided on the sub optical sheet 41. Desirably, at least one is present.

80 ° ≦ θ3 ≦ 90 ° Conditional expression (4)
However,
θ3: The prism pieces 15 located on the top surface 12 of the light guide plate 11 are linear and arranged in parallel.
When the parallel direction is the parallel direction D1, the parallel direction D1 in the sub optical sheet 41
(The parallel direction D1 superimposed on the sub optical sheet 41) and the minimum angle formed by the parallel direction F3.

  The light that passes through the bottom surface 13 of the light guide plate 11 includes light that is refracted and propagated totally by the two side surfaces of the prism piece 15 without being refracted and transmitted by the top surface 12 of the light guide plate 11. It is. Such light comes toward the bottom surface 13 without spreading excessively in the parallel direction D1 of the prism pieces 15. Therefore, in order to increase the degree of further deflection (condensation) of such light, it is desirable that θ3 in conditional expression (4), which is an angle close to orthogonal to the parallel direction D1, is satisfied.

  In this case, the light that does not spread excessively in the parallel direction D1 by the prism piece 15 on the top surface 12 further travels without being excessively spread in the parallel direction F3 by the prism piece 45 of the sub optical sheet 41. is there. That is, light is easily collected in a direction D3 intersecting (for example, orthogonal to) both the parallel direction D1 and the parallel direction F3, and the light emission luminance per unit area of the planar light is improved.

  In the conditional expression (4), the angle is defined by the parallel directions D1 and F3 of the prism pieces 15 and 45, but may be defined by the linear directions (ridge line directions) D2 and S3 of the prism pieces 15 and 45. . That is, the prism piece 45 included in the sub optical sheet 41 is linear, and when the linear direction is S3, the prism piece 45 satisfying the following conditional expression (4) ′ is provided on the sub optical sheet 41. Desirably, at least one is present.

80 ° ≦ θ′3 ≦ 90 ° Conditional expression (4) ′
However,
θ′3: The prism piece 15 located on the top surface 12 of the light guide plate 11 is linear, and its linear direction is
The linear direction D2 is the minimum angle formed by the linear direction D2 in the secondary optical sheet 41 (the linear direction D2 superimposed on the secondary optical sheet 41) and the linear direction S3.

  It is most desirable that only prism pieces 15, 25, and 45 satisfying the above conditional expressions (1) to (4) are gathered to form a prism surface, but a prism that satisfies the conditions (1) to (4). Even if there are at least one piece 15, 25, or 45, it can be said that the effects according to the conditional expressions (1) to (4) can be obtained.

[Other embodiments]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, the plurality of prism pieces 15 on the top surface 12 of the light guide plate 11 do not need to be arranged in parallel without a gap. For example, the prism pieces 15 may be arranged in parallel while being separated from each other, and the planar top surface 12 may be exposed between the prism pieces 15 and 15.

  This is because the planar portion (flat portion) between the prism pieces 15 and 15 refracts light in a direction different from that of the prism piece 15, and thus the degree of freedom of light amount adjustment in the light guide plate 11. This is because of the increase. That is, the light guide plate 11 can perform various light amount adjustments by appropriately changing the occupation ratio of the prism pieces 15 and the occupation ratio of the flat portion on the top surface 12 of the light guide plate 11.

  Further, the arrangement pitch of the prism pieces 15 need not be constant. In other words, when a plurality of prism pieces 15 arranged in parallel on the top surface 12 is a large group, the large group may include a small group of a plurality of prism pieces 15 having different arrangement pitches.

  Because, if the arrangement pitch of the prism pieces 15 is not constant (if it is random), the interference between the light guide plate 11 and the main first optical sheet 21, the main second optical sheet 31, or the sub optical sheet 41 This is because it becomes difficult to occur.

  Further, the arrangement pitch of the prism pieces 15 located on the top surface 12 where a large amount of light reaches, for example, the top surface 12 near the point H in FIG. 6 is larger than the arrangement pitch of the prism pieces 15 in other portions. It may be wide. This is because the small group of prism pieces 15 having a relatively wide arrangement pitch refracts so as to spread a large amount of light.

  10A (enlarged perspective view of main first optical sheet 21 and main second optical sheet 31 in FIG. 1; see broken line portion) and FIG. 10B (enlarged perspective view of sub optical sheet 41 in FIG. 1; see broken line portion). The prism angles δ1, δ2, and δ3 (angles formed by the side surfaces of the prism pieces) of the prism pieces 25, 35, and 45 are not particularly limited.

  However, δ1 and δ2 are desirably 80 ° or more and 100 ° or less (80 ° ≦ δ1 ≦ 100 °, 80 ° ≦ δ2 ≦ 100 °), and the most desirable angle can be said to be 90 °. Further, δ3 is desirably 50 ° or more and 90 ° or less (50 ° ≦ δ3 ≦ 90 °), and the most desirable angle is 70 °.

  In particular, when the prism angle is relatively large (for example, an obtuse angle), the light tends to be refracted so as to spread on the side surface of the prism piece. Therefore, the light may be spread more widely by relatively increasing the prism angle of the prism piece corresponding to the portion where the light tends to concentrate.

  In addition, there are many types of embossed patterns formed on the bottom surface 13 of the light guide plate 11 and the present invention is not limited thereto. For example, the embossed pattern may be a convex raised piece 17 (see FIG. 3) or a concave recessed piece. Moreover, it may be a spherical raised piece 17 or a hollow piece by having a curved surface, or may be a polygonal solid raised piece 17 or a hollow piece. In short, various patterns are formed by a mold for molding the light guide plate 11 (such as a blasted mold) or by machining the light guide plate 11.

  In addition, although the embossing pattern was given to the bottom face 13 of the light-guide plate 11, it is not limited to this. That is, a texture pattern may be formed on the top surface 12. The embossed pattern may be used in combination with the prism piece 15.

  That is, at least one of the top surface 12 and the bottom surface 13 may be a prism surface that has been subjected to graining. However, the top surface 12 that emits light so as to pass through the main first optical sheet 21 and the main second optical sheet 31 is not a prism surface subjected to a textured process, but is subjected only to a textured process (textured pattern). It may also be a surface).

  In FIG. 4, the distribution density of the embossed pattern increases as it deviates from the light receiving surface 14 a of the light guide plate 11, but is not limited thereto. For example, if the luminance near the center of the first liquid crystal display panel 82 needs to be high, the vicinity of the center of the bottom surface 13 of the light guide plate 11 corresponding to the vicinity of the center is a portion where the distribution density of the wrinkle pattern is relatively high. It only has to be.

  In addition, a texture pattern may be formed on the light receiving surface 14a of the light guide plate 11 corresponding to between the LEDs 51 and 51. Since it corresponds between LED51 * 51 in this way, a part of light-receiving surface 14a which only a small amount of light reaches | attains has a wrinkle pattern. For this reason, due to the diffusion of the light due to the embossed pattern, the backlight light does not include a dark part (the luminance unevenness of the backlight light disappears).

  The liquid crystal display device 89 as described above is mounted on an electronic device such as a mobile phone or a PDA (Personal Digital Assistant). However, it is not limited to this. However, as an effective example, in a foldable mobile phone, the first liquid crystal display panel 82 is displayed on a main display screen for displaying main information, the second liquid crystal display panel 83 is displayed on a sub display screen for displaying auxiliary information, It is desirable to correspond.

  Finally, it goes without saying that embodiments obtained by appropriately combining the techniques disclosed above are also included in the technical scope of the present invention.

These are the enlarged views of the backlight unit in a liquid crystal display device. FIG. 4 is a perspective view showing the top surface of the light guide plate in the backlight unit. FIG. 3 is a cross-sectional view taken along line A-A ′ of FIG. 2. FIG. 5 is a perspective view showing the bottom surface of the light guide plate in the backlight unit. These are the optical path views seen from the B-B 'arrow cross section of FIG. FIG. 6 is an optical path diagram viewed from a cross-section taken along line C-C ′ in FIG. 5. Then, (A) is a top view of the top surface of the light guide plate, (B) is an example of an explanatory view showing an intersecting state of the reference direction M and the linear direction D2, and (C) is (B) and Is an example of an explanatory diagram showing a crossing state between different reference directions M and linear directions D2. These are the top views of the prism surface of a main 1st optical sheet. These are the top views of the prism surface of a sub optical sheet. (A) is an enlarged perspective view of the main first optical sheet and the main second optical sheet, and (B) is an enlarged perspective view of the sub optical sheet. FIG. 3 is an exploded perspective view of a liquid crystal display device. FIG. 6 is an exploded perspective view of a conventional liquid crystal display device.

Explanation of symbols

11 Light guide plate 12 Top surface of light guide plate (first emission surface)
13 Bottom surface of light guide plate (second exit surface)
14 Side surface of light guide plate 14a Light receiving surface of light guide plate 15 Prism piece included in light guide plate (first prism piece for light guide plate)
GR transmission sheet group 21 Main first optical sheet (first deflection sheet)
21p Prism surface of main first optical sheet 25 Prism piece (prism piece for sheet) included in main first optical sheet
31 Main second optical sheet (third deflection sheet)
31p Prism surface of main second optical sheet 35 Prism piece (prism piece for sheet) included in main second optical sheet
41 Sub optical sheet (second deflection sheet)
41p Prism surface of sub optical sheet 45 Prism piece (prism piece for sheet) included in sub optical sheet
51 LED (light source)
52 Main diffusion sheet (first diffusion sheet)
53 Sub-diffusion sheet (second diffusion sheet)
71 active matrix substrate 72 counter substrate 73 polarizing plate 81 backlight unit 82 first liquid crystal display panel (first display panel)
83 Second liquid crystal display panel (second display panel)
89 Liquid crystal display device (display device)
D1 LED parallel direction, prism piece included in the light guide plate parallel direction (D1 direction)
D2 Linear direction of the prism piece included in the light guide plate (D2 direction)
D3 Direction perpendicular to parallel direction D1 and linear direction D2 (D3 direction)
M Orthogonal direction from the light receiving surface on the top (reference direction M)
F1 Parallel direction of prism pieces (F1 direction) included in the main first optical sheet
S1 Linear direction (S1 direction) of prism pieces included in the main first optical sheet
F2 Parallel direction of prism pieces (F2 direction) included in the main second optical sheet
S2 Linear direction of the prism piece included in the main second optical sheet (direction S2)
F3 Parallel direction of prism pieces included in the sub optical sheet (F3 direction)
S3 Linear direction of the prism piece included in the sub optical sheet (S3 direction)

Claims (16)

The light from the light source that enters from the light receiving surface is internally transmitted, and the first emission surface and the second light emitting device arranged opposite to each other
A light guide plate that emits to the outside via the exit surface;
A transmission sheet group that transmits light emitted from the light guide plate;
In the backlight unit including
The light guide plate includes a first prism piece for a light guide plate that refracts the light in the first emission surface, and a texture pattern that diffuses the light is included in the second emission surface.
The transmission sheet group includes a plurality of deflection sheets having a prism surface as a surface by including a prism piece for a sheet that refracts the light,
When the deflection sheet that transmits light from the first emission surface is the first deflection sheet, the first deflection sheet has the back surface of the prism surface facing the first emission surface,
When the deflection sheet that transmits light from the second emission surface is the second deflection sheet, the second deflection sheet has the prism surface facing the second emission surface.
Backlight unit. The light from the light source that enters from the light receiving surface is internally transmitted, and the first emission surface and the second light emitting device arranged opposite to each other
A light guide plate that emits to the outside via the exit surface;
A transmission sheet group that transmits light emitted from the light guide plate;
In the backlight unit including
The light guide plate includes a first prism piece for a light guide plate that refracts the light in the first emission surface, and includes a second prism piece for the light guide plate on the second emission surface,
The transmission sheet group includes a plurality of deflection sheets having a prism surface as a surface by including a prism piece for a sheet that refracts the light,
When the deflection sheet that transmits light from the first emission surface is the first deflection sheet, the first deflection sheet has the back surface of the prism surface facing the first emission surface,
When the deflection sheet that transmits light from the second emission surface is the second deflection sheet, the second deflection sheet has the prism surface facing the second emission surface.
Backlight unit.   3. The backlight unit according to claim 1, wherein the backlight unit includes a first diffusion sheet that diffuses light traveling from the first emission surface while transmitting the light and guides the light to the first deflection sheet.   The deflection sheet that transmits light traveling from the first deflection sheet is a third deflection sheet, and the third deflection sheet has the rear surface of the prism surface facing the first deflection sheet. The backlight unit according to item 1. The prism pieces for the sheet in the first deflection sheet are linear and parallel, and the parallel direction is the F1 direction,
The sheet prism pieces in the third deflection sheet are linear and parallel, and the parallel direction is the F2 direction.
The backlight unit according to claim 4, wherein the F1 direction and the F2 direction on the third deflection sheet are orthogonal to each other.   6. The second diffusion sheet according to claim 1, wherein a second diffusion sheet that diffuses light traveling from the second deflection sheet while transmitting the light is transmitted behind the prism surface of the second deflection sheet. Backlight unit. The first prism piece for the light guide plate located on the first emission surface is linear, and its linear direction is the D2 direction,
In the first emission surface, a direction orthogonal to the light receiving surface is a reference direction M.
The backlight unit according to any one of claims 1 to 6, wherein at least one first prism piece for a light guide plate that satisfies the following conditional expression (1) exists:
0 ° ≦ θ1 ≦ 10 ° ... Conditional expression (1)
However,
θ1: The minimum angle formed by the D2 direction and the reference direction M. The sheet prism pieces included in the first deflection sheet are linear and parallel, and the parallel direction is the F1 direction.
The backlight unit according to any one of claims 1 to 7, wherein at least one sheet prism piece that satisfies the following conditional expression (2) is present in the first deflection sheet:
80 ° ≦ θ2 ≦ 90 ° Conditional expression (2)
However,
θ2: The first prism pieces for the light guide plate located on the first emission surface are linear and arranged in parallel.
When the parallel direction is the D1 direction, the D1 direction in the first deflection sheet is
This is the minimum angle formed with the F1 direction. The sheet prism pieces included in the first deflection sheet are linear and parallel, and the parallel direction is the F1 direction.
The backlight unit according to any one of claims 1 to 7, wherein at least one sheet prism piece that satisfies the following conditional expression (3) is present in the first deflection sheet;
35 ° ≦ θ2 ≦ 55 ° Conditional expression (3)
However,
θ2: The first prism pieces for the light guide plate located on the first emission surface are linear and arranged in parallel.
When the parallel direction is the D1 direction, the D1 direction in the first deflection sheet is
This is the minimum angle formed with the F1 direction. The sheet prism pieces included in the second deflection sheet are linear and parallel, and the parallel direction is the F3 direction.
The backlight unit according to any one of claims 1 to 9, wherein at least one sheet prism piece that satisfies the following conditional expression (4) is present in the second deflection sheet:
80 ° ≦ θ3 ≦ 90 ° Conditional expression (4)
However,
θ3: The first prism pieces for the light guide plate located on the first emission surface are linear and arranged in parallel.
When the parallel direction is the D1 direction, the D1 direction in the second deflection sheet is
This is the minimum angle formed with the F3 direction. The first emission surface and the second emission surface are surfaces that sandwich the light receiving surface,
The backlight according to any one of claims 1 to 10, wherein a surface relationship between the first emission surface and the light-receiving surface is an intersection relationship, and a surface relationship between the second emission surface and the light-receiving surface is an intersection relationship. unit. The plurality of first prism pieces for the light guide plate are arranged in parallel while being separated from each other,
The backlight unit according to any one of claims 1 to 11, wherein a planar first emission surface is exposed between the first prism pieces for the light guide plate. When the plurality of first prism pieces for the light guide plate arranged in parallel is a large group,
The backlight unit according to any one of claims 1 to 12, wherein the large group includes a small group of a plurality of first prism pieces for light guide plates having different arrangement pitches.   The backlight unit according to claim 1, wherein the light source is a light emitting element. The backlight unit according to any one of claims 1 to 13,
A first display panel that modulates light by receiving light traveling from the first emission surface;
A second display panel that modulates light received from the second light exit surface;
Display device.   An electronic device containing the display device according to claim 15.

Images