JP2016194988A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device capable of suppressing leakage light at a side opposite to a light source and a stripe-shaped dark color pattern extending in a light guide direction on a light emission surface.SOLUTION: A surface light source device comprises: a light guide plate having a light emission surface, a back surface and a side surface, the back surface including a plurality of inclined faces arranged in a first direction on the back surface, and applying a part positioned at one side in the first direction of the side surface as an incident surface; a light source disposed in opposition to the incident surface; and a housing including a front surface portion surrounding the light emission surface, a back surface portion opposite to the front surface portion, and a side surface portion, and accommodating the light guide plate and the light source. A fixing member is disposed in a region positioned between the back surface of the light guide plate and the back surface portion of the housing, and including at least a part of a region at the other side along the first direction with respect to the light emission surface and overlapped with the front surface portion of the housing along a normal direction of the light guide plate. The fixing member connects the light guide plate and the back surface portion of the housing to fix the light guide plate to the housing. The fixing member has a reflecting property for mirror-reflecting the light incident from the light guide plate or a transmitting property for transmitting the light incident from the light guide plate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an edge light type surface light source device.

  2. Description of the Related Art A surface light source device having a light emitting surface that emits light in a planar shape is widely used as a backlight that is incorporated in, for example, a liquid crystal display device and illuminates a liquid crystal display panel from the back side. Surface light source devices for liquid crystal display devices can be broadly classified into a direct type in which a light source is arranged directly under an optical member and an edge light type in which a light source is arranged on a side of the optical member (also referred to as a side light type). being classified. The edge light type surface light source device is superior to the direct type surface light source device in that the thickness can be reduced.

  An edge-light type surface light source device disclosed in Patent Document 1 includes a resin substrate formed of a highly translucent acrylic resin, a light source lamp disposed facing a side end surface of the resin substrate, and a resin substrate And a scattering pattern disposed on the back surface of the resin substrate containing a light diffusive reflection material such as titanium oxide. In this surface light source device, the emitted light emitted from the light source lamp enters the resin substrate from its side end surface. The emitted light incident on the resin substrate travels from the light source lamp side to the opposite side of the light source lamp while repeating total reflection at the interface between the front or back surface of the resin substrate and the air layer. When the emitted light enters the scattering pattern disposed on the back surface of the resin substrate, the emitted light is reflected and diffused to the surface side of the resin substrate by the light diffusing and reflecting material included in the scattering pattern, and from the surface of the resin substrate. The light is emitted toward the diffusion plate.

JP-A-9-178952

  On the other hand, the inventors of the present invention have, as the light guide plate, a light exit surface, a back surface disposed to face the light exit surface, and a side surface located between the light exit surface and the back surface, and the back surface is in the first direction. A portion located on one side in the first direction among the side surfaces forms a light incident surface, and each inclined surface is a light exit surface as it goes from one side to the other side in the first direction. The light guide plate that is inclined with respect to the normal direction of the light guide plate and the first direction is considered. In the surface light source device using this light guide plate, the light incident on the light incident surface of the light guide plate from the light source repeats total reflection at the interface between the light exit surface or back surface of the light guide plate and the adjacent layer (for example, air layer) The light guide plate travels from one side (light incident surface side) to the other side in the first direction. At this time, the light reflected by the inclined surface on the back surface has a small incident angle when entering the light exit surface. When the incident angle when entering the light exit surface becomes less than the total reflection critical angle by reflecting on the inclined surface, this light is emitted from the light exit surface of the light guide plate. And the advancing direction of the emitted light is bent by an optical sheet having a plurality of linear prisms protruding toward the light guide plate so as to go in the normal direction to the light output surface of the light guide plate. This surface light source device has an advantage that high front luminance can be obtained as compared with the surface light source device disclosed in Patent Document 1 that emits diffused light from the surface of the resin substrate.

  The inventors of the present invention have studied the surface light source device using this light guide plate. In this surface light source device, leakage light is visually recognized on the opposite side of the light source on the light emitting surface, or the light guiding direction ( It has been found that there is a problem that a streak-like dark color pattern extending in the first direction is visually recognized. The inventors of the present invention diligently investigated the cause of this problem, and when the back surface of the light guide plate and the case were fixed with a light colored fixing member (adhesive tape, etc.) on the opposite side of the light source. Furthermore, it has been found that the scattered light is emitted on the opposite side of the light source on the light emitting surface due to the irregular reflection of the light incident on the fixing member. On the other hand, when the back surface of the light guide plate and the housing are fixed with a dark fixing member such as black on the opposite side of the light source, light from the fixing member is caused by uneven sticking of the fixing member to the light guide plate. It has been found that there are relatively high and low absorptivity absorption points, whereby a streak-like dark color pattern extending in the light guide direction is visually recognized on the light emitting surface.

  In the surface light source device of the type that emits diffused light from the surface of the resin substrate disclosed in Patent Document 1, since the diffused light is emitted from the surface of the resin substrate, unintended scattered light is generated at any part of the resin substrate. Even if it occurred, it was difficult for the observer to visually recognize the scattered light. Moreover, even if a portion where the light absorption rate by the fixing member is relatively higher than that of the surrounding area is generated, the dark color pattern is difficult to be visually recognized by the observer due to the diffused light generated in the surrounding area. That is, in the surface light source device of the type that emits diffused light from the surface of the resin substrate, the above-described problems have not been recognized in the first place. Therefore, the problem that the leaked light is visually recognized on the light source side of the light exit surface is the light guide plate of the surface light source device between the light exit surface, the back surface disposed opposite to the light exit surface, and the light exit surface and the back surface. And the back surface includes a plurality of inclined surfaces arranged in the first direction, a portion located on one side in the first direction of the side surfaces forms a light incident surface, and each inclined surface is The light guide plate that is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction. It can be said that this is a problem.

  The present invention has been made in consideration of the above points. Leakage light is generated on the light exit surface opposite to the light source, and a stripe-like dark pattern extending in the light guide direction is generated on the light output surface. An object of the present invention is to provide a surface light source device capable of suppressing the above.

A surface light source device according to the present invention comprises:
A surface light source device having a light emitting surface for emitting light,
A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, wherein the back surface is a plurality of inclined surfaces arranged in a first direction. A portion of the side surface located on one side in the first direction forms a light incident surface, and a light guide plate,
A light source disposed opposite the light incident surface;
A housing that houses the light guide plate and the light source, including a front surface that surrounds the light emitting surface, a back surface that faces the front surface, and a side surface that connects the front surface and the back surface. With
Each inclined surface is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction,
It is between the back surface of the light guide plate and the back surface portion of the housing, and is on the other side along the first direction with respect to the light emitting surface and along the normal direction of the light guide plate. A fixing member is provided in a region including at least a part of a region overlapping the front portion of the housing,
The fixing member joins the light guide plate and the back portion of the housing to fix the light guide plate to the housing,
The fixing member has a reflection characteristic that specularly reflects light incident from the light guide plate or a transmission characteristic that transmits light incident from the light guide plate.

  In the surface light source device according to the present invention, the fixing member has a reflection characteristic of specularly reflecting light incident from the light guide plate, and the fixing member may include a metal layer.

  In the surface light source device according to the present invention, the surface of the metal layer may have a reflectance of 90% or more.

  In the surface light source device according to the present invention, the fixing member may have a transmission characteristic of transmitting light incident from the light guide plate, and the fixing member may have a light transmittance of 80% or more.

  A display device according to the present invention includes the above-described surface light source device and a display panel disposed to face the surface light source device.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that leak light arises on the opposite side of the light source in a light-emitting surface, and the streak-like dark color pattern extended in a light guide direction in a light-emitting surface.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device and a surface light source device for explaining an embodiment according to the present invention. FIG. 2 is a cross-sectional view corresponding to the line II-II of the surface light source device of FIG. FIG. 3 is a perspective view showing the surface light source device cut along line II in FIG. FIG. 4 is a perspective view showing the light guide plate, the optical sheet, and the light source of the surface light source device as seen from the back side of the light guide plate. FIG. 5 is an enlarged view of the light guide plate, the optical sheet, and the light source of FIG. FIG. 6 is a cross-sectional view showing an example of a fixing member of the surface light source device. FIG. 7 is a cross-sectional view for explaining the operation when a specular reflection member is used as a fixing member of the surface light source device. FIG. 8 is a cross-sectional view for explaining the operation when a light transmissive member is used as a fixing member of the surface light source device.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product.

  As used in this specification, shapes and geometric conditions and their degree are specified. For example, terms such as “parallel”, “orthogonal”, “identical”, length and angle values, etc. are strictly Without being bound by meaning, it should be interpreted including the extent to which similar functions can be expected.

  In the present specification, the “light exit side” refers to the light source 24, the light guide plate 30, the optical sheet 40, the liquid crystal display panel 15, and the components of the display device 10 without reversing, for example, in the illustrated example. 24, the light guide plate 30, the optical sheet 40, and the liquid crystal display panel 15 in this order, and the downstream side in the traveling direction of the light emitted from the display device 10 toward the observer (the observer side, for example, the upper side of the paper surface in FIG. The “light incident side” means that the light source 24, the light guide plate 30, the optical sheet 40, the liquid crystal display panel 15, and the components of the display device 10 are advanced without going back to each other. It is the upstream side in the traveling direction of the light emitted and directed to the observer.

  Further, in the present specification, terms such as “sheet”, “film”, “plate”, and “panel” are not distinguished from each other based only on the difference in names. Therefore, for example, “sheet” is a concept that includes members that can also be referred to as “film”, “plate”, and “panel”.

  1-8 is a figure for demonstrating one Embodiment by this invention. Among these, FIG. 1 is a cross-sectional view showing a schematic configuration of the display device and the surface light source device, and is a cross-sectional view corresponding to line II in FIG. FIG. 2 is a cross-sectional view corresponding to the line II-II of the surface light source device of FIG. FIG. 3 is a perspective view showing the surface light source device cut along line II in FIG. FIG. 4 is a perspective view showing the light guide plate, the optical sheet, and the light source of the surface light source device as seen from the back side of the light guide plate. FIG. 5 is an enlarged view of the light guide plate, the optical sheet, and the light source of FIG.

  As shown in FIG. 1, the display device 10 includes a liquid crystal display panel 15 and a surface light source device 20 that is disposed on the back side of the liquid crystal display panel 15 and illuminates the liquid crystal display panel 15 in a planar shape from the back side. . The display device 10 has a display surface 11 for displaying an image. The liquid crystal display panel 15 includes a display area 15A that can display an image, and a non-display area (also referred to as a frame area) 15B that is disposed outside the display area 15A so as to surround the display area 15A. Yes. In the illustrated example, the display area 15 </ b> A of the liquid crystal display panel 15 defines the display surface 11 of the display device 10. The liquid crystal display panel 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel, and is configured to display an image on the display surface 11 (display region 15A).

  The illustrated liquid crystal display panel 15 includes an upper polarizing plate 13 disposed on the light output side, a lower polarizing plate 14 disposed on the light incident side, an upper polarizing plate 13 and a lower polarizing plate 14 in the display region 15A. And a liquid crystal layer cell 12 disposed therebetween. The polarizing plates 14 and 13 decompose the incident light into two orthogonal polarization components (P wave and S wave) and vibrate in one direction (direction parallel to the transmission axis) (for example, P wave). ) And absorbs a linearly polarized light component (for example, S wave) that vibrates in the other direction (direction parallel to the absorption axis) perpendicular to the one direction.

  An electric field can be applied to the liquid crystal layer 12 for each region where one pixel is formed. Then, the alignment direction of the liquid crystal molecules in the liquid crystal layer 12 changes depending on whether or not an electric field is applied. As an example, a polarization component in a specific direction that has passed through the lower polarizing plate 14 disposed on the light incident side rotates the polarization direction by 90 ° when passing through the liquid crystal layer 12 to which an electric field is applied. When passing through the liquid crystal layer 12 that is not applied, the polarization direction is maintained. In this case, depending on whether or not an electric field is applied to the liquid crystal layer 12, does the polarized light component that vibrates in a specific direction transmitted through the lower polarizing plate 14 further pass through the upper polarizing plate 13 disposed on the light output side of the lower polarizing plate 14? Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 13.

  In this way, the liquid crystal display panel (liquid crystal display unit) 15 can control transmission or blocking of light from the surface light source device 20 for each pixel. The details of the liquid crystal display panel 15 are described in various publicly known documents (for example, “Flat Panel Display Dictionary (supervised by Tatsuo Uchida, Hiraki Uchiike)” published in 2001 by the Industrial Research Council). The detailed description above is omitted.

  Next, the surface light source device 20 will be described. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and is used as a device that illuminates the liquid crystal display panel 15 from the back side in the present embodiment.

  As shown in FIGS. 1 to 5, the surface light source device 20 is configured as an edge light type surface light source device, and includes a housing 22, a light guide plate 30 disposed in the housing 22, and one of the light guide plates 30. 1 (the left side in FIG. 1), the light source 24 disposed on the side, the optical sheet (prism sheet) 40 disposed so as to face the light exit surface 31 of the light guide plate 30, and the back surface of the light guide plate 30. 32 and a fixing member 60 provided between the back surface portion 22 b of the housing 22. In the illustrated example, the optical sheet 40 is disposed facing the liquid crystal display panel 15. The light emitting surface 21 of the surface light source device 20 is defined by the light exit surface 41 of the optical sheet 40.

  The housing 22 is a member that houses the light source 24 and the light guide plate 30. The housing 22 has a function of holding the light source 24, the light guide plate 30, and the optical sheet 40 at predetermined relative positions. The housing 22 also has a function of shielding outside light. As shown in FIGS. 1 to 3, the housing 22 includes a front portion 22 a that faces the light exit surface 31 of the light guide plate 30, a back portion 22 b that faces the back surface 32 of the light guide plate 30, and a front portion 22 a. And a plurality of side surface portions 22c connecting the back surface portion 22b. In the illustrated example, the front surface portion 22a and the back surface portion 22b are parallel to each other, the side surface portion 22c has a frame shape including four side surfaces, and the two opposing side surfaces of the side surface portion 22c are parallel to each other. There is no. That is, the housing | casing 22 is comprised as a rectangular parallelepiped member as a whole. Such a housing | casing 22 can be formed with aluminum, iron, stainless steel, titanium, etc., for example.

  The front portion 22 a of the housing 22 has an opening 221 through which light emitted from the light exit surface 31 of the light guide plate 30 passes toward the display panel 15. Therefore, the front portion 22a of the housing 22 is formed in a frame shape (frame shape) so as to surround the periphery of the opening 221. In the example shown in FIGS. 1 and 3, the optical sheet 40 is disposed in the opening 221 of the front portion 22a. As will be described later, the light exit surface 41 of the optical sheet 40 forms the light emitting surface 21 of the surface light source device 20. That is, the front portion 22 a of the housing 22 surrounds the light emitting surface 21 of the surface light source device 20. In particular, in the illustrated example, the outer surface of the front portion 22a, that is, the surface facing the display panel 15, and the light emitting surface 41 of the optical sheet 40 (the light emitting surface 21 of the surface light source device 20) are flush with each other. In addition, the optical sheet 40 is not limited to this, and the optical sheet 40 is formed larger than the opening 221 of the housing 22 so that at least a part of the peripheral edge of the optical sheet 40 faces the front portion 22 a of the housing 22. The light may be disposed on the light incident side or the light exit side of the front portion 22a.

  The front part 22a, the side part 22c, and the rear part 22b of the housing 22 do not need to be formed integrally. For example, the front part 22a is formed separately from the side part 22c and the rear part 22b, The portion 22a may be detachable from the side surface portion 22c. Alternatively, the front part 22a and the side part 22c may be formed separately from the back part 22b, and the front part 22a and the side part 22c may be detachably attached to the back part 22b. According to such a case 22, it is easy to house the light source 24 and the light guide plate 30 in the case 22.

  Further, a frame member (mold frame) may be attached to the housing, and the light source 24 and the light guide plate 30 may be disposed on the frame member. As such a frame member, a material made of a resin material such as an epoxy resin or a metal material such as aluminum can be preferably used. By using such a frame member, the housing 22, the light source 24, the light guide plate 30, and the optical sheet 40 can be accurately and easily aligned with each other. It is possible to prevent the optical plate 30 from moving.

  As shown in FIG. 2, the light exit surface 31 of the light guide plate 30 is formed in a square shape in plan view, like the display surface 11 of the liquid crystal display device 10 and the light emitting surface 21 of the surface light source device 20. Yes. As a result, the light guide plate 30 is generally configured as a rectangular parallelepiped member having a pair of main surfaces (the light exit surface 31 and the back surface 32) in which the sides in the thickness direction are smaller than the other sides. A side surface defined between the pair of main surfaces includes four surfaces.

The light guide plate 30 includes a light output surface 31 constituted by one main surface on the liquid crystal display panel 15 side, a back surface 32 formed of the other main surface facing the light output surface 31, and a space between the light output surface 31 and the back surface 32. And a side surface extending. One side surface of the two surfaces facing the first direction d ₁ of the side surfaces forms the light incident surface 33. As shown in FIG. 1, a light source 24 is provided facing the light incident surface 33. The light that has entered the light guide plate 30 from the light incident surface 33 is directed substantially along the first direction d ₁ toward the opposite surface 34 that faces the light incident surface 33 along the first direction (light guide direction) d _1. Light is guided through the light guide plate 30. As shown in FIGS. 1, 3, and 4, the optical sheet 40 is disposed so as to face the light exit surface 31 of the light guide plate 30.

  The light source 24 may be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), an incandescent lamp, and the like. In the present embodiment, the light source 24 is configured by a large number of point-like light emitters 25, specifically, a large number of LEDs, arranged side by side along the longitudinal direction of the light incident surface 33.

  In addition, although illustration is abbreviate | omitted, in this Embodiment, the reflection sheet is arrange | positioned so that the back surface 32 of the light-guide plate 30 may be faced. The reflection sheet is a member for reflecting the light leaking from the back surface 32 of the light guide plate 30 and entering the light guide plate 30 again. The reflection sheet may be composed of a white scattering reflection sheet, a sheet made of a material having a high reflectance such as metal, a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, and the like. . The reflection on the reflection sheet may be specular reflection (regular reflection) or diffuse reflection. The reflection sheet can be attached to the inner surface of the housing 22 via an adhesive or an adhesive, for example.

  By the way, in this specification, the “sheet surface (film surface, plate surface, panel surface)” means the planar direction of the target sheet-like member when the target sheet-like member is viewed as a whole and globally. Refers to the face that matches. In the present embodiment, the plate surface of the light guide plate 30, the sheet surface of the optical sheet 40, the panel surface of the liquid crystal display panel 15, the display surface 11 of the display device 10, the light emitting surface 21 of the surface light source device 20, and The light exit surfaces 41 of the optical sheet 40 are parallel to each other. Furthermore, in this specification, the normal line direction of a sheet-like member refers to the normal line direction to the sheet | seat surface of the sheet-like member used as object. Further, in the present specification, the “front direction” is a normal direction to the light emitting surface 21 of the surface light source device 20, and in this embodiment, the normal to the light emitting surface 21 of the surface light source device 20. The normal direction to the plate surface of the light guide plate 30, the normal direction to the sheet surface of the optical sheet 40, the normal direction to the display surface 11 of the display device 10, and the like (for example, see FIG. 1). .

  Next, the light guide plate 30 will be described in more detail with reference to FIGS. As shown in FIGS. 1 to 5, the light guide plate 30 is configured as a flat plate-like member having a pair of parallel main surfaces (light-emitting surface 31 and back surface 32).

As shown in FIGS. 1 and 3 to 5, the back surface 32 of the light guide plate 30 is formed as an uneven surface. As a specific configuration, the back surface 32 includes an inclined surface 37, a step surface 38 extending in the normal direction nd of the light guide plate 30, and a connection surface 39 extending in the plate surface direction of the light guide plate 30. The light guide in the light guide plate 30 is based on the total reflection action on the pair of main surfaces 31 and 32 of the light guide plate 30. On the other hand, the inclined surface 37 is inclined with respect to the normal direction nd and the plate surface of the light guide plate 30 so as to approach the light exit surface 31 from the light incident surface 33 side toward the opposite surface 34 side. In other words, the inclined surface 37 is inclined with respect to the normal direction nd of the light guide plate and the light guide direction (first direction) d ₁ . Therefore, the incident angle when the light reflected by the inclined surface 37 enters the pair of main surfaces 31 and 32 becomes small. When the incident angle on the pair of main surfaces 31 and 32 is less than the total reflection critical angle by reflecting on the inclined surface 37, the light is emitted from the light guide plate 30. That is, the inclined surface 37 functions as an element for extracting light from the light guide plate 30.

The distribution of the amount of light emitted from the light guide plate 30 along the light guide direction (first direction) d ₁ is adjusted by adjusting the distribution of the inclined surface 37 along the first direction d ₁ that is the light guide direction. Can be adjusted. In the example shown in FIG. 1 and FIGS. 3 to 5, the inclined surface 37 of the back surface 32 becomes closer to the opposite surface 34 from the light incident surface 33 along the light guide direction (first direction) d _1. The share is high. According to such a configuration, the emission of light from the light guide plate 30 in the region separated from the light incident surface 33 along the light guide direction (first direction) d ₁ is promoted and separated from the light incident surface 33. As a result, it is possible to effectively prevent the amount of emitted light from decreasing.

  Such a light guide plate 30 can be produced, for example, by forming irregularities on the surface of the substrate by extrusion molding, injection molding or the like, or by shaping the irregular surface on the substrate. Various materials can be used as the material of the light guide plate 30. However, it is widely used as a material for optical members incorporated in display devices, and has excellent mechanical properties, optical properties, stability, workability, etc. and is available at low cost, such as acrylic resin, polystyrene, polycarbonate, etc. Transparent resins mainly composed of one or more of polyethylene terephthalate, polyacrylonitrile, etc., and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins, etc.) can be suitably used.

  Next, the optical sheet (prism sheet) 40 will be described mainly with reference to FIG. The optical sheet 40 is a member having a function of changing the traveling direction of transmitted light.

  As shown in FIG. 5, the optical sheet 40 includes a main body portion 45 formed in a plate shape and a plurality of unit prisms 50 formed on the light incident side surface 47 of the main body portion 45. Yes. The main body 45 is configured as a flat plate-like member having a pair of parallel main surfaces. The light output surface 41 of the optical sheet 40 is configured by the light output side surface 46 of the main body 45 located on the side not facing the light guide plate 30.

  Next, the unit prism 50 provided on the light incident side surface 47 of the main body 45 will be described. As shown in FIG. 5, the plurality of unit prisms 50 are arranged side by side on the light incident side surface 47 of the main body 45. Each unit prism 50 is formed in a column shape and extends in a direction intersecting with the arrangement direction.

  In the present embodiment, each unit prism 50 extends linearly. Each unit prism 50 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction thereof. Further, the plurality of unit prisms 50 are arranged on the light incident side surface 47 of the main body 45 without any gap along the direction orthogonal to the longitudinal direction. Therefore, the light incident surface 42 of the optical sheet 40 is formed by the surfaces (prism surfaces) 51 and 52 of the unit prisms 50 arranged on the main body 45 without any gaps.

As described above, the optical sheet 40 is disposed so as to overlap the light guide plate 30, and the unit prism 50 of the optical sheet 40 faces the light exit surface 31 of the light guide plate 30. Further, as shown in FIGS. 1 and 3 to 5, in the optical sheet 40, the longitudinal direction of the unit prism 50 is the light guide direction by the light guide plate 30 (the light incident surface 33 of the light guide plate 30 faces the light incident surface). so as to intersect with the first direction) d ₁ connecting the opposite surface 34 which is positioned relative to the light guide plate 30. Preferably, the longitudinal direction of the unit prisms 50 intersects the light guide direction (first direction) d ₁ by the light guide plate 30 at an angle of 80 ° to 100 °, and the arrangement direction of the unit prisms 50 is the light guide plate 30. so as to intersect with parallel or 10 ° angle of less than a light guiding direction d ₁ by the optical sheet 40 is positioned with respect to the light guide plate 30.

As shown in FIG. 5, each unit prism 50 includes a first prism surface 51 and a second prism surface that are arranged to face each other along the arrangement direction of the unit prisms 50, that is, the first direction d _1. 52. The first prism surface 51 of each unit prism 50 is located on one side in the first direction (left side of the paper surface of FIG. 5), and the second prism surface 52 is on the other side in the first direction (right side of the paper surface of FIG. 5). ). More specifically, the first prism surface 51 of each unit prism 50 faces the one side in the first direction d ₁ positioned on the side of the light source 24 in the first direction d _1. The second prism surface 52 of each unit prism 50 is located on the side away from the light source 24 in the first direction d _1, it faces the other side in the first direction d _1. As will be described later, the first prism surface 51 mainly travels from the light source 24 disposed on one side in the first direction d ₁ into the light guide plate 30, and then the light emitted from the light guide plate 30 is converted into the optical sheet 40. It functions as an incident surface when entering the lens. On the other hand, the second prism surface 52 has a function of reflecting light incident on the optical sheet 40 and correcting the optical path of the light.

  For example, the dimensions of the optical sheet 40 can be set as follows. First, as a specific example of the unit prism 50 configured as described above, the arrangement pitch of the unit prisms 50 (corresponding to the width W of the unit prism 50 in the illustrated example) can be set to 10 μm or more and 200 μm or less. However, in recent years, the arrangement of the unit prisms 50 has been rapidly refined, and the arrangement pitch of the unit prisms 50 is preferably 10 μm or more and 40 μm or less. Further, the projection height H of the unit prism 50 from the main body 45 along the normal direction nd to the sheet surface of the optical sheet 40 can be set to 5.5 μm or more and 180 μm or less.

  The optical sheet 40 having the above-described configuration can be manufactured by molding the unit prism 50 on a base material or by extrusion molding. Various materials can be used as the material forming the main body 45 and the unit prism 50 of the optical sheet 40. However, it is widely used as a material for optical members incorporated in display devices, and has excellent mechanical properties, optical properties, stability, workability, etc. and is available at low cost, such as acrylic resin, polystyrene, polycarbonate, etc. Transparent resins mainly composed of one or more of polyethylene terephthalate, polyacrylonitrile, etc., and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins, etc.) can be suitably used.

  When the optical sheet 40 is produced by curing an ionizing radiation curable resin on a base material, a sheet-like land portion that is positioned between the unit prism 50 and the base material is used together with the unit prism 50. You may make it form on a material. In this case, the main body 45 is composed of a base and a land formed by an ionizing radiation curable resin. On the other hand, in the optical sheet 40 manufactured by extrusion molding, the main body 45 and the plurality of unit prisms 50 on the light incident side surface 47 of the main body 45 can be integrally formed.

Next, the fixing member 60 will be described with reference to FIGS. 1, 3, and 6. An example of the arrangement of the fixing members 60 of the surface light source device 20 is shown in FIGS. 1 and 3. The fixing member 60 has a function of fixing the light guide plate 30 to the back surface portion 22 b of the housing 22. In the example shown in FIG. 1 and FIG. 3, it is between the back surface 32 of the light guide plate 30 and the back surface portion 22 b of the housing 22, and is first with respect to the light emitting surface 21 (the light exit surface 41 of the optical sheet 40). The fixing member 60 is provided in a region S that is at the other side along the direction d ₁ and includes at least a part of a region that overlaps the front portion 22 a of the housing 22 along the normal direction nd of the light guide plate 30. . In particular, in the example shown in FIGS. 1 and 3, the fixing member 60 is on the other side of the light emitting surface 21 along the first direction d ₁ and along the normal direction nd of the light guide plate 30. It is provided in a region overlapping with the front part 22 a of the body 22.

In the example shown in FIGS. 1 and 3, the fixing member 60 is in the light guide direction (first direction) d _{1 of} the light guide plate 30 and the normal direction nd of the light guide plate 30 (normal direction of the light exit surface 31). It extends in a straight line (band shape) in a direction perpendicular to both (in FIG. 1, a direction perpendicular to the paper surface). The fixing member 60 has the same cross-sectional shape along the longitudinal direction.

  As such a fixing member 60, a fixing member 60 a having a reflection characteristic that specularly reflects (regular reflection) light incident from the light guide plate 30, or a fixing member having a transmission characteristic that transmits light incident from the light guide plate 30. 60b is used.

  As an example of the fixing member 60a having a reflection characteristic of specularly reflecting light incident from the light guide plate 30, a fixing member 60a including a metal layer can be given. FIG. 6A shows an example of a fixing member 60a including a metal layer. In the illustrated example, the fixing member 60a includes a base material 61, a metal layer 62 provided on the base material 61, a covering layer 63 provided on the metal layer 62, and a metal layer 62 of the base material 61. It has the joining layer 64 provided on the surface on the opposite side, and the joining layer 65 provided on the surface on the opposite side to the metal layer 62 of the coating layer 63.

  As the base material 61, for example, polyethylene terephthalate (PET), triacetyl cellulose (TAC), acrylic (PMMA), polycarbonate (PC) or the like can be used. The substrate 61 preferably has a thickness of 5 μm or more and 200 μm or less.

  As the metal layer 62, for example, one or more of aluminum, silver, platinum, chromium, nickel, tin, and alloys thereof can be used. The metal layer 62 can be formed by a known method. For example, a physical vapor deposition method (PVD method) such as a vacuum deposition method, a sputtering method, or an ion plating method, a chemical vapor deposition method (CVD method), a liquid phase growth method such as a plating method, or these two methods. A method combining the above can be employed.

  The metal layer 62 preferably has a high reflectance on the surface thereof. Specifically, the regular reflectance (specular reflectance) of the surface of the metal layer 62 is preferably 80% or more. Furthermore, it is more preferable that the total reflectance of the surface of the metal layer 62 is 90% or more and the diffuse reflectance is 10% or less. In the present embodiment, the total reflectance, diffuse reflectance, and regular reflectance are each measured at an incident angle of 45 ° using a reflectometer (“HR-100” manufactured by Murakami Color Research Laboratory). It is specified as total reflectance, diffuse reflectance, and regular reflectance obtained from the total reflectance and diffuse reflectance, measured using incident light. Moreover, it is preferable that the metal layer 62 has a thickness of 0.5 μm or more and 2 μm or less.

  As the coating layer 63, a base material layer or a coating layer can be illustrated. As this coating layer 63, for example, polyethylene terephthalate (PET), triacetyl cellulose (TAC), acrylic (PMMA), polycarbonate (PC) or the like can be used. However, it is preferable to use a coating layer 63 having a high light transmittance. Specifically, the light transmittance is preferably 80% or more. In this embodiment, the light transmittance is measured within a measurement wavelength range of 380 nm to 780 nm using a spectrophotometer (“UV-3100PC” manufactured by Shimadzu Corporation, JIS K 0115 compliant product). Of the transmittance at each wavelength. The covering layer 63 preferably has a thickness of 5 μm to 200 μm.

  As the bonding layers 64 and 65, layers made of materials having various adhesiveness or tackiness can be used. However, it is preferable to use a bonding layer 65 provided on the surface of the coating layer 63 opposite to the metal layer 62 with a high light transmittance. Specifically, the light transmittance is preferably 80% or more. Each of the bonding layers 64 and 65 preferably has a thickness of 1 μm or more and 50 μm or less.

  As an example of the fixing member 60b having a transmission characteristic of transmitting light incident from the light guide plate 30, a fixing member 60b including a light transmitting member can be given. The fixing member 60b is preferably a member having a light transmittance of 80% or more. More preferably, the member has a light transmittance of 80% or more. FIG. 6B shows an example of the fixing member 60b. In the illustrated example, the fixing member 60 b includes a light-transmitting base material 67 and bonding layers 68 and 69 formed on two main surfaces of the base material 67, respectively.

  As the light transmissive substrate 67, for example, polyethylene terephthalate (PET), triacetyl cellulose (TAC), acrylic (PMMA), polycarbonate (PC), or the like can be used. The substrate 67 preferably has a light transmittance of 80% or more. Moreover, it is preferable that the base material 67 has a thickness of 5 μm to 100 μm.

  As the bonding layers 68 and 69, layers made of materials having various light adhesion properties or adhesive properties having high light transmittance can be used. Specifically, a bonding layer having a light transmittance of 90% or more is preferable. Each of the bonding layers 68 and 69 preferably has a thickness of 1 μm or more and 200 μm or less.

  The fixing member 60b is not limited to the one having the light-transmitting base material 67 and the bonding layers 68 and 69 described above. For example, the fixing member 60b may be configured by a layer that does not include the base material 67, that is, a layer that includes only a bonding layer.

  When the fixing member 60b having a transmission characteristic that transmits light incident from the light guide plate 30 is used as the fixing member 60, the inner surface of the back surface portion 22b of the housing 22, that is, the fixing member 60b on the surface facing the light guide plate 30 is used. The area facing the area or the area facing the fixing member 60b of the reflection sheet disposed so as to face the back surface 32 of the light guide plate 30 in the housing 22 is specularly reflected (regular reflection). It is preferable to have a reflective characteristic. Specifically, the surface preferably has a reflectance of 90% or more.

  Next, the operation of the display device 10 having the above configuration will be described.

First, as shown in FIG. 1, the light emitted from the light emitter 25 constituting the light source 24 enters the light guide plate 30 via the light incident surface 33. The light L incident on the light guide plate 30 is reflected on the light output surface 31 and the back surface 32 of the light guide plate 30, particularly the material forming the light guide plate 30, and the layer adjacent to the light guide plate 30 through the light output surface 31 or the back surface 32. The total reflection is repeated due to the difference in refractive index with (for example, the air layer), and proceeds in the first direction (light guide direction) d ₁ connecting the light incident surface 33 and the opposite surface 34 of the light guide plate 30.

  The back surface 32 of the light guide plate 30 has an inclined surface 37 that is inclined so as to approach the light exit surface 31 from the light incident surface 33 toward the opposite surface 34. The inclined surface 37 is connected via a step surface 38 and a connection surface 39. Among these, the step surface 38 extends in the normal direction nd of the plate surface of the light guide plate 30. Therefore, most of the light traveling in the light guide plate 30 from the light incident surface 33 side to the opposite surface 34 side is not incident on the step surface 38 of the back surface 32, but is incident on the inclined surface 37 or the connection surface 39. To reflect. When reflected by the inclined surface 37 of the back surface 32, the traveling direction of the light in the cross section shown in FIG. 1 increases the inclination angle with respect to the plate surface of the light guide plate 30. That is, when the light is reflected by the inclined surface 37 of the back surface 32, the incident angle of the light on the light output surface 31 and the back surface 32 in the following becomes small. Therefore, the incident angle of the light traveling on the light guide plate 30 to the light exit surface 31 and the back surface 32 is gradually reduced by one or more reflections on the inclined surface 37 of the back surface 32, and is less than the total reflection critical angle. Become. At this time, the light can be emitted from the light exit surface 31 or the back surface 32 of the light guide plate 30. The light L emitted from the light exit surface 31 travels to the optical sheet 40 disposed on the light exit side of the light guide plate 30. On the other hand, the light emitted from the back surface 32 is reflected by the reflection sheet disposed facing the back surface 32 of the light guide plate 30, enters the light guide plate 30 again, and travels through the light guide plate 30.

  In particular, in the illustrated example, the proportion of the inclined surface 37 in the back surface 32 increases as the distance from the incident surface 33 approaches the opposite surface 34 along the light guide direction. This ensures a sufficient amount of light emitted from the light exit surface 31 of the light guide plate 30 in a region separated from the light incident surface 33 where the amount of emitted light tends to decrease, and the amount of emitted light uniform along the light guide direction. Can be achieved.

The light L emitted from the light exit surface 31 of the light guide plate 30 then enters the optical sheet 40. As described above, the optical sheet 40 includes the unit prism 50 that protrudes toward the light guide plate 30 side. The longitudinal direction of the unit prism 50 intersects the light guide direction (first direction) d ₁ by the light guide plate 30 and the normal direction nd of the plate surface of the light guide plate 30. In particular, in the present embodiment, the longitudinal direction of the unit prism 50 is orthogonal to both the light guide direction (first direction) d ₁ by the light guide plate 30 and the normal direction nd of the plate surface of the light guide plate 30.

As a result, the light L emitted from the light source 24 arranged on one side in the first direction d ₁ and traveling toward the optical sheet 40 through the light guide plate 30 is connected to the first prism surface 51 and the second prism surface 52. of, incident on the unit prisms 50 through the first prism surface 51 which is positioned on one side of the light source 24 side in the first direction d _1. As shown in FIGS. 1 and 5, the light L is then totally reflected by the second prism surface 52 located on the other side opposite to the light source in the first direction d ₁ to change its traveling direction. It becomes like this.

Then, by total reflection at the second prism surface 52 of the unit prisms 50, the main cross (first direction (light guide direction of the light guide plate 30 of the optical sheet 40 shown in FIGS. 1 and 5) d ₁ and the front The light L traveling in the direction inclined from the front direction nd in the direction (cross section parallel to both directions) with respect to the direction (normal direction of the plate surface of the light guide plate 30) has a small angle formed by the traveling direction with respect to the front direction nd. And is emitted from the light exit surface 41 of the optical sheet 40. Such action, the unit prism 50, the component of light along the first direction d _1, the traveling direction of the transmitted light can be narrowed down in the front direction nd side. That is, the optical sheet 40, the component of light along the first direction d _1, it will exert a light condensing effect.

  The light of one polarization component emitted from the light exit surface 41 of the optical sheet 40 that forms the light emitting surface 21 of the surface light source device 20 is then incident on the liquid crystal display panel 15 and is transmitted through the lower polarizing plate 14. The light transmitted through the lower polarizing plate 14 selectively passes through the upper polarizing plate 13 according to the state of electric field application to each pixel. In this manner, the liquid crystal display panel 15 selectively transmits light from the surface light source device 20 for each pixel, so that an observer of the liquid crystal display device 10 can observe an image.

  Next, the operation of the fixing member 60 will be described with reference to FIGS. FIG. 7 is a diagram for explaining the operation when a fixing member 60 a having a reflection characteristic of specularly reflecting light incident from the light guide plate 30 is used as the fixing member 60. FIG. 8 is a diagram for explaining the operation when a fixing member 60 b having a transmission characteristic of transmitting light incident from the light guide plate 30 is used as the fixing member 60. In FIGS. 7 and 8, for the sake of simplicity of illustration, the uneven surface, that is, the inclined surface 37 and the step surface 38 of the back surface 32 of the light guide plate 30 are omitted.

As described above, the light L that has entered the light guide plate 30 from the light source 24 through the light incident surface 33 is reflected on the light exit surface 31 or the back surface 32 of the light guide plate 30, particularly totally reflected to enter the light guide plate 30. Proceed in a first direction (light guide direction) d ₁ connecting the light surface 33 and the opposite surface 34. At this time, of the light L that enters the light guide plate 30 from the light incident surface 33 and travels toward the opposite surface 34, a part of the light L that has not exited from the light exit surface 31 is as shown in FIGS. 7 and 8. Then, the light enters the fixing member 60 joined in the vicinity of the opposite surface 34 on the back surface 32 of the light guide plate 30.

  Here, when the fixing member is a light-colored fixing member such as white, the light incident on the fixing member is irregularly reflected, so that the light emitting surface of the light guide plate is near the opposite surface on the opposite side of the light source. Scattered light is generated. Thereby, leakage light can be visually recognized on the light-emitting surface of the surface light source device on the opposite side of the light source. Further, when the fixing member is a dark fixing member such as black, due to uneven sticking of the fixing member to the light guide plate, there are places where the light absorption rate by the fixing member is relatively high and low. As a result, a streak-like dark color pattern extending in the light guide direction can be visually recognized on the light emitting surface of the surface light source device.

On the other hand, in the example shown in FIG. 7, it is between the back surface 32 of the light guide plate 30 and the back surface portion 22 b of the housing 22, and is along the first direction d ₁ with respect to the light emitting surface 21 of the surface light source device 20. The fixing member 60a is provided in a region S that is on the other side and includes at least a part of the region overlapping the front portion 22a of the housing 22 along the normal direction nd of the light guide plate 30. It has a reflection characteristic of specularly reflecting (regularly reflecting) the light L incident from the light plate 30.

In the example shown in FIG. 7, the light L incident on the fixing member 60 a is specularly reflected (regular reflection) by the metal layer 62 of the fixing member 60 a and travels toward the opposite surface 34 side of the light guide plate 30. That is, since the irregular reflection of the light L incident on the fixed member 60a is suppressed, the emission of the scattered light from the light exit surface 31 of the light guide plate 30 due to the irregular reflection of the light incident on the fixed member 60a is suppressed. Therefore, it is possible to effectively prevent leakage light from being visually recognized on the light emitting surface 21 of the surface light source device 20 on the side opposite to the light source 24. In addition, since the difference in light absorption at the interface between the light guide plate 30 and the fixing member 60a that may be caused by uneven sticking of the fixing member 60a to the light guide plate 30 is extremely small, the light emitting surface 21 of the surface light source device 20 is used. in the stripe-like dark markings extending in the light guiding direction (first direction) d ₁ is viewed it can be effectively prevented.

Further, in the example shown in FIG. 8, it is between the rear surface 32 of the light guide plate 30 and the rear surface portion 22 b of the housing 22, and is along the first direction d ₁ with respect to the light emitting surface 21 of the surface light source device 20. The fixing member 60b is provided in a region S that is at the other side and includes at least a part of the region overlapping the front portion 22a of the housing 22 along the normal direction nd of the light guide plate 30. It has a transmission characteristic that transmits the light L incident from the light plate 30.

In the example shown in FIG. 8, the light L incident on the fixing member 60 b passes through the fixing member 60 b and is the inner surface of the back surface portion 22 b of the housing 22, that is, the surface facing the light guide plate 30, or the housing 22. The light is incident on the reflection sheet disposed so as to face the back surface 32 of the light guide plate 30. The light L incident on the inner surface or the reflection sheet of the back surface portion 22 b is reflected by the inner surface or the reflection sheet, passes through the fixing member 60 b again, and returns into the light guide plate 30 through the back surface 32 of the light guide plate 30. In particular, when the region facing the fixing member 60b on the inner surface of the back surface portion 22b or the region facing the fixing member 60b on the reflection sheet has a reflection characteristic of specularly reflecting light incident on the region, the back surface portion 22b The light L incident on the inner surface or the reflection sheet is specularly reflected by the inner surface or the reflection sheet, passes through the fixing member 60 b again, and returns into the light guide plate 30 through the back surface 32 of the light guide plate 30. Thereby, since the irregular reflection of the light L incident on the fixing member 60b is suppressed, the emission of the scattered light from the light exit surface 31 of the light guide plate 30 due to the irregular reflection of the light incident on the fixing member 60b is suppressed. Therefore, it is possible to effectively prevent leakage light from being visually recognized on the light emitting surface 21 of the surface light source device 20 on the side opposite to the light source 24. In addition, since the difference in light absorption at the interface between the light guide plate 30 and the fixing member 60 b that may be caused by uneven sticking of the fixing member 60 b to the light guide plate 30 is extremely small, the light emitting surface 21 of the surface light source device 20. in the stripe-like dark markings extending in the light guiding direction (first direction) d ₁ is viewed it can be effectively prevented.

  Note that various modifications can be made to the above-described embodiment.

In the above-described embodiment, the fixing member 60 (60 a, 60 b) is on the other side along the first direction d ₁ with respect to the light emitting surface 21 and along the normal direction nd of the light guide plate 30. of showed that provided in the front portion 22a and the overlapping area is not limited to this, the fixing member 60 (60a, 60b), on the other side along the first direction d ₁ with respect to the light emitting surface 21 There may be provided from a region overlapping the front portion 22a of the housing 22 along the normal direction nd of the light guide plate 30 to a region overlapping the light emitting surface 21 along the normal direction nd of the light guide plate 30. .

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Display surface 15 Display panel 20 Surface light source device 21 Light emission surface 22 Case 22a Front part 22b Back surface part 22c Side surface part 221 Opening part 24 Light source 25 Point-like light-emitting body 28 Light-diffusion member 30 Light guide plate 31 Light emission surface 32 Back surface 33 Light entrance surface 34 Opposite surface 37 Inclined surface 38 Step surface 39 Connection surface 40 Optical sheet 41 Light exit surface 42 Light entrance surface 45 Main body portion 46 Light exit side surface 47 Light entrance side surface 50 Unit prism 51 First prism surface 52 Second prism surface 60 Fixing member 61 Base material 62 Metal layer 63 Cover layer 64 Joining layer 65 Joining layer 67 Base material 68 Joining layer 69 Joining layer

Claims (5)

A surface light source device having a light emitting surface for emitting light,
A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, wherein the back surface is a plurality of inclined surfaces arranged in a first direction. A portion of the side surface located on one side in the first direction forms a light incident surface, and a light guide plate,
A light source disposed opposite the light incident surface;
A housing that houses the light guide plate and the light source, including a front surface that surrounds the light emitting surface, a back surface that faces the front surface, and a side surface that connects the front surface and the back surface. With
Each inclined surface is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction,
It is between the back surface of the light guide plate and the back surface portion of the housing, and is on the other side along the first direction with respect to the light emitting surface and along the normal direction of the light guide plate. A fixing member is provided in a region including at least a part of a region overlapping the front portion of the housing,
The fixing member joins the light guide plate and the back portion of the housing to fix the light guide plate to the housing,
The surface light source device, wherein the fixing member has a reflection characteristic that specularly reflects light incident from the light guide plate or a transmission characteristic that transmits light incident from the light guide plate. The fixing member has a reflection characteristic of specularly reflecting light incident from the light guide plate,
The surface light source device according to claim 1, wherein the fixing member includes a metal layer.   The surface light source device according to claim 2, wherein the metal layer has a reflectance of 90% or more on a surface thereof. The fixing member has a transmission characteristic of transmitting light incident from the light guide plate,
The surface light source device according to claim 1, wherein the fixing member has a light transmittance of 80% or more.   A display device comprising: the surface light source device according to claim 1; and a display panel disposed to face the surface light source device.

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