JP7178003B2 - Light guide plate, surface light source device and display device - Google Patents

Description

The present invention relates to a light guide plate, a surface light source device and a display device.

2. Description of the Related Art A surface light source device having a light-emitting surface that emits light in a planar manner is widely used as a backlight that is incorporated in, for example, a liquid crystal display device to illuminate the liquid crystal display panel from the back side. Patent Literature 1 discloses an edge light type surface light source device. In the edge light type surface light source device, a light source such as a light emitting diode faces a light incident surface which is a part of the side surface of the light guide plate. Therefore, the edge light type surface light source device has the advantage of being able to be made thinner. Edge-light type surface light source devices that can be made thinner are used in mobile devices such as smartphones, tablets, and personal computers.

Japanese Patent Application Laid-Open No. 2004-46076

These days, there is a demand for narrowing the bezel width of display devices and surface light source devices, that is, narrow bezels. This demand is particularly strong for surface light source devices that are applied to display devices for mobile devices. Here, the bezel is a portion that separates the display surface of the display device and the light emitting surface of the surface light source device from the surroundings. By narrowing the width of the bezel, the size of the display device and the surface light source device can be reduced without reducing the size of the display surface and the light emitting surface.

The inventors of the present invention have confirmed that if the width of the bezel is narrowed in an edge-light type surface light source device, the presence of the end face of the light guide plate can be perceived under the bezel when the light-emitting surface is obliquely observed. Further investigation revealed that light emitted from the end surface of the light guide plate was diffused by a frame or the like, and thus the vicinity of the end surface of the light guide plate was observed to be locally bright. This local brightness causes the end face of the light guide plate to be grasped. As a solution to such problems, it is conceivable to impart light absorption performance to the frame or the like. However, this solution means a decrease in the energy efficiency of the surface light source device. Improving energy efficiency has become an important technical issue, along with the narrowing of bezels, especially in applications to mobile devices.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above points, and an object of the present invention is to provide a surface light source device with a narrow bezel while effectively utilizing light.

The light guide plate according to the present invention is
a light guide plate body including a light incident surface and a facing surface facing the light incident surface;
and a reflective layer provided on the facing surface of the light guide plate main body.

In the light guide plate according to the present invention, the facing surface may have a surface roughness Ra of 0.01 μm or more and 0.3 μm or less.

In the light guide plate according to the present invention, the total light reflectance Rt[%] and the diffuse reflectance Rd[%] of the reflective layer may satisfy the following relationship.
20<((Rt−Rd)/Rt)×100

The light guide plate according to the present invention is
including, as a pair of main surfaces, a light emitting side surface divided into an active area and a non-active area located around the active area, and a rear side surface facing the light emitting side surface;
The width Wa [mm] of the non-active area located on the opposite surface side of the light output side surface along the first direction in which the light incident surface and the opposite surface face each other is the height H [mm] of the opposite surface ] and the following relationship may be satisfied.
Wa<1.73×H

The surface light source device according to the present invention is
any of the light guide plates according to the invention described above;
a light emitter disposed facing the light incident surface of the light guide plate;
a bonding layer provided on the reflective layer of the light guide;
a frame bonded to the light guide plate via the bonding layer;
The bonding layer is positioned between the reflective layer and the frame in a first direction in which the light incident surface and the opposing surface face each other.

In the surface light source device according to the present invention, the bonding layer may have a thickness of 200 μm or more and 800 μm or less along the first direction.

The surface light source device according to the present invention may further include a main frame that supports the light emitter, the light guide plate and the frame.

A display device according to the present invention comprises:
any of the surface light source devices according to the present invention described above;
and a liquid crystal display panel illuminated by the surface light source device.

ADVANTAGE OF THE INVENTION According to this invention, the narrow bezel-ization of a surface light source device can be implement|achieved, aiming at effective utilization of light.

FIG. 1 is a diagram for explaining an embodiment according to the present invention, and is a longitudinal sectional view showing a schematic configuration of a display device and a surface light source device. 2 is a top view of the surface light source device of FIG. 1. FIG. 3A and 3B are diagrams for explaining the action of the surface light source device of FIG. FIG. 4 is a perspective view showing the light guide plate incorporated in the surface light source device of FIG. 1 from the rear side. FIG. 5 is a perspective view showing the optical sheet incorporated in the surface light source device of FIG. 1 from the light incident surface side. 6 is a partially enlarged cross-sectional view showing a main part of the surface light source device of FIG. 1. FIG. FIG. 7 is a graph showing an example of the angular distribution of luminance on the light exit surface of the light guide plate measured from each direction within a plane parallel to both the front direction and the first direction. FIG. 8 is a graph showing the front direction luminance distribution on the light exit surface of the optical sheet measured at each position along the first direction. FIG. 9(a) is a diagram for explaining a method of observing the opposite surface through the light exit surface of the light guide plate, and FIG. 9(b) is an observation of the opposite surface through the light exit surface of the light guide plate. It is a photograph showing the results. FIG. 10 is a diagram corresponding to FIG. 6 and showing a reference example of a surface light source device. FIG. 11 is a diagram corresponding to FIG. 11(a) is a diagram for explaining a method of observing the opposite surface through the light exit surface of the light guide plate shown in FIG. 10, and FIG. It is a photograph showing the result of observing the opposite surface through the light exit surface of the light plate.

An embodiment of the present invention will be described below with reference to the drawings. In the drawings attached to this specification, for the convenience of illustration and ease of understanding, the scale and the ratio of vertical and horizontal dimensions are changed and exaggerated from those of the real thing.

1 to 9 are diagrams for explaining an embodiment according to the present invention. 1 is a longitudinal sectional view showing a schematic configuration of a liquid crystal display device and a surface light source device, and FIG. 2 is a plan view showing the surface light source device with some components omitted. FIG. 3 is a longitudinal sectional view for explaining the action of the surface light source device. FIG. 4 is a perspective view showing a light guide plate included in the surface light source device, and FIG. 5 is a perspective view showing an optical sheet included in the surface light source device. FIG. 6 is a vertical cross-sectional view of the surface light source device showing the opposite surface of the light guide plate and its surroundings. 7 and 8 are graphs showing luminance characteristics of the surface light source devices shown in FIGS. 1 to 6, and FIG. 9 shows observation results of the opposite surface of the light guide plate shown in FIGS. It is a figure for explaining.

As shown in FIG. 1, the display device 10 includes a liquid crystal display panel 15 and a surface light source device 20 arranged on the rear side of the liquid crystal display panel 15 and planarly illuminating the liquid crystal display panel 15 from the rear side. . The display device 10 has a display surface 11 that displays an image. 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 .

A region that becomes the display surface 11 of the display device 10 is partitioned by a frame member 18 . The frame member 18 is a member made of a visible light impermeable material. A frame member 18 is provided on a portion surrounding the liquid crystal display panel 15 . The frame member 18 hides the area where the wiring of the liquid crystal display panel 15 is formed and the area where uneven brightness of the surface light source device 20 is visible. In this display device 10, the area overlapping the display surface 11 in projection in the front direction nd is the active area Aa, and the area overlapping the frame member 18 in projection in the front direction nd is the non-active area Ab. In the illustrated example, the non-active area Ab is adjacent to the active area Aa and circumferentially surrounds the active area Aa.

The illustrated liquid crystal display panel 15 includes an upper polarizing plate 13 arranged on the light exit side, a lower polarizing plate 14 arranged on the light entering side, and a liquid crystal display panel 15 arranged between the upper polarizing plate 13 and the lower polarizing plate 14 . and a liquid crystal layer 12 . The polarizing plates 14 and 13 decompose the incident light into two orthogonal polarized components (P wave and S wave), and convert the linearly polarized component (for example, P wave ) and absorbs a linearly polarized component (for example, S wave) vibrating in the other direction (direction parallel to the absorption axis) perpendicular to the one direction.

An electric field can be applied to each region forming one pixel in the liquid crystal layer 12 . 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, the polarization component in a specific direction transmitted through the lower polarizing plate 14 arranged on the light incident side rotates its polarization direction by 90° when passing through the liquid crystal layer 12 to which no electric field is applied. It maintains its polarization direction when passing through the liquid crystal layer 12 to which an electric field is applied. In this case, depending on whether or not an electric field is applied to the liquid crystal layer 12, the polarized light component that has passed through the lower polarizing plate 14 and oscillates in a specific direction is further transmitted through the upper polarizing plate 13 arranged on the light output side of the lower polarizing plate 14. , or whether the light is absorbed and blocked by the upper polarizing plate 13 can be controlled.

In this manner, the liquid crystal 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 known documents (for example, "Flat Panel Display Comprehensive Dictionary (supervised by Tatsuo Uchida and Heiki Uchiike)" published by the Industrial Research Institute in 2001). The above detailed description 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 for illuminating the liquid crystal display panel 15 from the rear side in the present embodiment.

As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device, and is arranged on the side of a light guide plate 30 and one side (the left side in FIG. 1) of the light guide plate 30. and an optical sheet (prism sheet) 50 and a reflective sheet 28 arranged to face the light guide plate 30, respectively. In the illustrated example, the optical sheet 50 is arranged facing the liquid crystal display panel 15 . The light emitting surface 21 of the surface light source device 20 is defined by the light emitting surface 51 of the optical sheet 50 . Further, the surface light source device 20 includes a frame 55 that protects the light guide plate 30 and the optical sheet 50, and a main frame 60 that houses the light source 24, the light guide plate 30, the optical sheet 50, the reflection sheet 28, and the frame 55. have more.

In the illustrated example, the light emitting side surface 31 of the light guide plate 30 has a planar shape (in FIG. ) is formed in a rectangular shape. As a result, the light guide plate 30 as a whole is configured as a flattened rectangular parallelepiped member having a pair of main surfaces (the light output side surface 31 and the back side surface 32) and having relatively smaller sides in the thickness direction than the other sides. and the sides defined between the pair of major faces include four faces. As shown in FIG. 2, the side surfaces extend in a _first direction d1 and a _second direction d2 orthogonal to each other. Similarly, the optical sheet 50 and the reflective sheet 28 are generally configured as a flattened rectangular parallelepiped member whose sides in the thickness direction are relatively smaller than the other sides. In the plan view shown in FIG. 2, illustration of the optical sheet 50 and the main frame 60 is omitted.

The light guide plate 30 has a light output side surface 31 configured by one main surface on the liquid crystal display panel 15 side, a back side surface 32 composed of the other main surface opposite to the light output side surface 31 , and the light output side surface 31 and the back side surface 32 . and a side surface extending therebetween. One side surface of the two surfaces facing the first direction d ₁ among the side surfaces forms the light incident surface 33 . As shown in FIG. 1 , the light source 24 is provided facing the light entrance surface 33 . Light entering the light guide plate 30 from the light incident surface 33 is directed toward the opposite surface 34 opposite to the light incident surface 33 along the _first direction (light guiding direction) d1, and travels approximately in the first direction (light guiding direction) d1. _The light is guided through the light guide plate 30 along the direction d1. As shown in FIGS. 1 and 3, the optical sheet 50 is arranged to face the light exit side surface 31 of the light guide plate 30, and the reflection sheet 28 is arranged to face the back side surface 32 of the light guide plate 30. It is

The light source can be configured in various ways, for example, a fluorescent lamp such as a linear cold-cathode tube, a point-like LED (light-emitting diode), an incandescent lamp, or the like. In this embodiment, the light source 24 is composed of a large number of point-like light emitters 25, specifically a large number of light emitting diodes (LEDs) arranged side by _side along the longitudinal direction d2 of the light incident surface 33. It is It should be noted that the light guide plate 30 shown in FIG. 4 shows positions facing a large number of point-like light emitters 25 forming the light source 24 .

The reflective sheet 28 is a member for reflecting the light leaked from the back side surface 32 of the light guide plate 30 and allowing the light to enter the light guide plate 30 again. The reflective sheet 28 is composed of a white scattering reflective sheet, a sheet made of a material having a high reflectance such as metal, a sheet including a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, or the like. obtain. The reflection on the reflection sheet 28 may be regular reflection (specular reflection) or diffuse reflection. When the reflection on the reflection sheet 28 is diffuse reflection, the diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection.

By the way, in this specification, the “light exit side” refers to the light source 24 , the light guide plate 30 , the optical sheet 50 , the liquid crystal display panel 15 , and the light source 24 , the light source 24 , the liquid crystal display panel 15 , and the components of the display device 10 . It means the downstream side (the observer side, for example, the upper side of the paper surface in FIG. 1) in the traveling direction of the light emitted toward the observer. , the upstream side in the traveling direction of the light emitted from the display device 10 and traveling between the constituent elements of the liquid crystal display panel 15 and the display device 10 without turning back to the observer.

Also, in this specification, terms such as "sheet", "film", and "plate" are not to be distinguished from each other based only on the difference in designation. Therefore, for example, "sheet" is a concept that includes members that can also be called films and plates.

Furthermore, in the present specification, the term “sheet surface (plate surface, film surface)” corresponds to the planar direction of the target sheet-shaped member when the target sheet-shaped member is viewed as a whole and from a broad perspective. refers to the face In the present embodiment, the plate surface of the light guide plate 30, the plate surface of the light guide plate main body 40 described later, the sheet surface of the optical sheet 50, the sheet surface of the reflection sheet 28, the panel surface of the liquid crystal display panel, and the display device 10 and the light emitting surface 21 of the surface light source device 20 are parallel to each other. Furthermore, in this specification, the normal direction of the sheet-shaped member refers to the normal direction to the sheet surface of the target sheet-shaped member. Furthermore, in this specification, the term "front direction" refers to the normal direction to the light emitting surface 21 of the surface light source device 20. In the present embodiment, the normal direction to the light emitting surface 21 of the surface light source device 20 is It also matches the direction, the normal direction to the plate surface of the light guide plate 30, the normal direction to the sheet surface of the optical sheet 50, the normal direction to the display surface 11 of the display device 10, and the like.

Next, mainly with reference to FIGS. 1, 3, 4 and 6, the light guide plate 30 will be described in further detail. As described above, the light guide plate 30 is a plate-like member including the light exit side surface 31 and the back side surface 32 as a pair of main surfaces. One of the four side surfaces connecting the light emitting side surface 31 and the back side surface 32 forms a light entering surface 33 facing the light source 24 . The light incident surface 33 faces the opposite surface 34 in the _first direction d1. The light exit side 31 can be divided into an active area Aa and a non-active area Ab. It is preferable that the active area Aa is set in a region on the light emitting side surface 31 in which unevenness in brightness is not visually recognized, for example, even when viewed from various directions. In the illustrated example, the active area Aa is a rectangular area occupying the center of the light exit side surface 31 (see FIG. 2). The non-active area Ab is an area including the periphery of the light output side surface 31 and is a circumferential area extending along the four sides of the light output side surface 31 .

As shown in FIGS. 1, 2, 4 and 6, in the present embodiment, the light guide plate 30 includes a plate-like light guide plate main body 40 and a reflective layer 38 laminated on the light guide plate main body 40. have. As shown in FIG. 4 , the light guide plate main body 40 occupies most of the light guide plate 30 and substantially defines the outer contour of the light guide plate 30 . The light guide plate main body 40 has a light exit surface 41 and a back surface 42 forming a pair of main surfaces, and a side surface connecting the light exit surface 41 and the back surface 42 . The light exit surface 41 of the light guide plate main body 40 forms most of the light exit side surface 31 of the light guide plate 30 . A rear surface 42 of the light guide plate body 40 forms most of the rear surface 32 of the light guide plate 30 . In the illustrated example, the light guide plate main body 40 has four sides. A light incident surface 43 , which is one of the four side surfaces, forms the light incident surface 33 of the light guide plate 30 . Further, the side surface of the light guide plate main body 40 includes a facing surface 44 as a surface facing the light incident surface 43 in the _first direction d1. A reflective layer 38 is formed on the facing surface 44 . Especially in the illustrated example, the reflective layer 38 is formed so as to cover the entire surface of the opposing surface 44 . A reflective layer 38 forms the opposite surface 34 of the light guide plate 30 .

The light guide plate main body 40 is a part that guides light incident from the light incident surface 43 mainly in the _first direction d1. Therefore, the light guide plate main body 40 can be made of a material having visible light transmittance, such as a transparent resin material as a specific example.

As shown well in FIG. 4, the rear surface 42 of the light guide plate main body 40 forming the rear side surface 32 of the light guide plate 30 is formed as an uneven surface. As a specific configuration, the unevenness of the back surface 42 of the light guide plate main body 40 causes the back side surface 32 to have an inclined surface 47, a stepped surface 48 extending in the normal direction nd of the light guide plate 30, and a and an extending connecting surface 49 . Light is guided in the light guide plate main body 40 by total reflection on the pair of main surfaces 41 and 42 of the light guide plate main body 40 . On the other hand, the inclined surface 47 is inclined with respect to the plate surface of the light guide plate main body 40 so as to approach the light output surface 41 as it goes from the light incident surface 43 side toward the opposing surface 44 side. Therefore, the light reflected by the inclined surface 47 has a small incident angle when it enters the pair of main surfaces 41 and 42 . When the incident angle on the pair of main surfaces 41 and 42 becomes less than the critical angle for total reflection due to reflection on the inclined surface 47 , the light is emitted from the light guide plate 30 . That is, the inclined surface 47 functions as a light extraction element for extracting light from the light guide plate 30 .

As shown in FIGS. 3 and 4, the inclined surface 47 has its longitudinal direction extending in the light guiding direction of the light guide plate 30 (the direction connecting the light incident surface 33 of the light guide plate 30 and the opposite surface 34 opposite to the light incident surface). It is positioned with respect to the light guide plate 30 so as to intersect ₁ direction) d1. More strictly, the longitudinal direction of the inclined surface 47 is orthogonal to the light guiding direction (that is, the _first direction) d1 of the light guide plate 30, and the arrangement direction of the inclined surface 47 is the light guiding direction _d1 of the light guide plate 30. is parallel to

By adjusting the distribution of the inclined surface 47 along the _first direction d1, which is the light guiding direction, within the back surface 42, the distribution of the amount of light emitted from the light guide plate 30 along the _first direction d1 can be adjusted. can. In the illustrated example, the proportion of the inclined surface 47 in the rear surface 42 increases as the light entrance surface 43 approaches the opposing surface 44 along the light guide direction _d1 . According to such a configuration, the emission of light from the light guide plate 30 in the region separated from the light entrance surface 43 along the light guide direction is promoted, and the amount of emitted light decreases as the distance from the light entrance surface 43 increases. It is possible to effectively prevent it from being put away.

Here, as an example, the dimensions of the light guide plate 30 and the light guide plate body 40 can be set as follows. The thickness H of the light guide plate 30 and the light guide plate body 40 can be, for example, 300 μm or more and 800 μm or less. Further, the inclination angle of the inclined surface 47 with respect to the plate surface of the light guide plate main body 40 can be, for example, 0.1° or more and 5° or less, and further 0.1° or more and 2.0° or less.

The light guide plate main body 40 configured as described above can be manufactured by, for example, extrusion molding. Various materials can be used as the material for the light guide plate main body 40 . However, materials that are widely used as materials for optical sheets incorporated in display devices, have excellent mechanical properties, optical properties, stability, workability, etc., and are available at low cost, such as acrylic resins, polystyrene resins, A transparent resin containing one or more of polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc. as a main component can be suitably used. A diffusive component having a function of diffusing light can be added into the light guide plate main body 40 as necessary. As an example of the diffusion component, particles made of a transparent substance such as silica (silicon dioxide), alumina (aluminum oxide), acrylic resin, polycarbonate resin, silicone resin, etc. having an average particle size of about 0.5 to 100 μm may be used. can be done.

On the other hand, the reflective layer 38 directs the light guided in the _first direction d1 from the light incident surface 43 to the opposing surface 44 in the light guide plate main body 40 toward the light incident surface 43 side in the _first direction d1. It is a reflective layer. The light reflected by the reflective layer 38 can be emitted from the light guide plate 30 by being reflected or transmitted by the back surface 42 . That is, by providing the reflective layer 38 , leakage of light from the light source from the opposite surface 34 of the light guide plate 30 is prevented. As a result, the light from the light source can be used efficiently, and the luminance on the light emitting side surface 31 of the light guide plate 30 can be improved without increasing the output of the light source 24 .

The reflective layer 38 is produced by forming a film on the facing surface 44 of the light guide plate main body 40 by coating, vapor deposition, printing, or the like with a reflective material. More specifically, by spray coating aluminum or silver on the opposing surface 44, by depositing aluminum or silver on the opposing surface 44, or by coating a resin composition containing metal particles on the opposing surface 44. The reflective layer 38 can be produced by printing and drying.

From the viewpoint of preventing the opposite surface 34 of the light guide plate 30 from being seen, the reflection on the reflective layer 38 is preferably specular reflection rather than diffuse reflection. From the viewpoint of preventing visibility of the opposite surface 34 of the light guide plate 30, the ratio R [%] of the specularly reflected light in the total reflected light in the reflective layer 38 for visible light having a wavelength of 380 nm or more and 780 nm or less is It is preferably larger than 20[%], more preferably larger than 40[%], and even more preferably larger than 60%. Here, the ratio R [%] of the specularly reflected light in the total reflected light on the reflective layer 38 is calculated using the total light reflectance Rt [%] and the diffuse reflectance Rd [%] of the reflective layer as follows: specified by the formula
R = ((Rt-Rd)/Rt) x 100
Here, the total light reflectance Rt [%] is the ratio of all reflected light to incident light. All this reflected light then contains both diffuse and specular reflection components. Diffuse reflectance Rd [%] is the ratio of diffusely reflected light to incident light. Total light reflectance Rt [%] and diffuse reflectance Rd [%] are calculated according to the procedure described in JIS A 5759 by measuring the reflection spectrum in the measurement wavelength range of 380 nm to 780 nm under the condition of a light incident angle of 45 degrees. be.

From the viewpoint of preventing diffusion at the interface between the light guide plate main body 40 and the reflective layer 38, the surface roughness of the facing surface 44 of the light guide plate main body 40 is the arithmetic mean roughness Ra [μm] specified by ISO 25178. , it is preferably 0.3 [μm] or less, more preferably 0.2 [μm] or less, and even more preferably 0.15 [μm] or less. On the other hand, from the viewpoint of improving the adhesion between the light guide plate main body 40 and the reflective layer 38, the surface roughness of the facing surface 44 of the light guide plate main body 40 should be the arithmetic mean roughness Ra [μm] specified by ISO 25178. is preferably 0.01 [μm] or more, more preferably 0.03 [μm] or more, and still more preferably 0.05 [μm] or more. The arithmetic mean roughness Ra [μm] is a value measured in accordance with ISO 25178 using a VK8700 shape measuring laser microscope manufactured by Keyence Corporation.

The surface roughness Ra of the facing surface 44 of the light guide plate main body 40 can be set to about 0.2 μm to 0.3 μm by ordinary tool finishing, and the surface roughness Ra of the facing surface 44 can be reduced to 0.2 μm by mirror surface tool finishing. It can be about 1 μm. Furthermore, by performing finishing such as buffing, the surface roughness Ra of the facing surface 44 can be reduced to about 0.05 μm.

Next, mainly with reference to FIGS. 3 and 5, the optical sheet (prism sheet) 50 will be described in further detail. The optical sheet 50 is a member having a function of changing the traveling direction of transmitted light.

As shown well in FIG. 5, the optical sheet 50 includes a plate-shaped main body portion 53 and a plurality of unit prisms (unit shaped elements, unit optical elements, unit lenses, etc.) provided on the main body portion 53 . ) 54 and . The body portion 53 is configured as a plate-like member and has a light exit side surface 53a and a light entrance side surface 53b as a pair of parallel main surfaces. A plurality of unit prisms 54 are formed on the light incident side surface 53 b of the body portion 53 . A light exit surface 51 of the optical sheet 50 is configured by the light exit side surface 53 a of the main body portion 53 located on the side not facing the light guide plate 30 .

In this specification, "unit prism", "unit shape element", "unit optical element" and "unit lens" refer to optical effects such as refraction and reflection on light to change the traveling direction of the light. Refers to elements that have a changing function and are not distinguished from each other based solely on a difference in designation.

Next, the unit prism 54 provided on the light incident side surface of the body portion 53 will be described. As well shown in FIGS. 3 and 5, the plurality of unit prisms 54 are arranged side by side on the light incident side surface 53b of the body portion 53. As shown in FIG. Each unit prism 54 is formed in a columnar shape and extends in a direction intersecting the arrangement direction.

In the illustrated example, each unit prism 54 extends linearly. Each unit prism 54 is formed in a columnar shape and has the same cross-sectional shape along its longitudinal direction. A plurality of unit prisms 54 included in the optical sheet 50 are configured identically to each other. Further, the plurality of unit prisms 54 are arranged without gaps on the light incident side surface 53b of the main body 53 along the direction orthogonal to the longitudinal direction. Therefore, the light incident surface 52 of the optical sheet 50 is formed by the surfaces (prism surfaces) 54a and 54b of the unit prisms 54 arranged without gaps on the main body portion 53 .

As described above, the optical sheet 50 is arranged so as to overlap the light guide plate 30 so that the unit prisms 54 of the optical sheet 50 face the light exit side surface 31 of the light guide plate 30 . In addition, as shown in FIG. 1, the optical sheet 50 is such that the longitudinal direction of the unit prisms 54 is the light guiding direction of the light guide plate 30 (the light entrance surface 33 of the light guide plate 30 and the opposite surface 34 opposite to the light entrance surface). It is positioned with respect to the light guide plate 30 so as to cross the _first connecting direction d1. More strictly, the longitudinal direction of the unit prisms 54 is orthogonal to the light guiding direction (that is, the _first direction) d1 of the light guide plate 30, and the arrangement direction of the unit prisms 54 is the light guiding direction _d1 of the light guide plate 30. The optical sheet 50 is positioned with respect to the light guide plate 30 so as to be parallel. Therefore, each unit prism 54 extends in the second direction d ₂ parallel to the longitudinal direction of the inclined surface 47 .

As shown well in FIG. 3, each unit prism 54 has a first prism surface 54a and a second prism surface 54a which are arranged to face each other along the arrangement direction of the unit prisms 54, that is, along the _first direction d1. It has a surface 54b. The first prism surface 54a of each unit prism 54 is located on one side in the _first direction d1 (the left side in the paper surface of FIGS. 1 and 3), and the second prism surface 54b is located on the other side in the _first direction d1. (on the right side of the page of FIGS. 1 and 3). More specifically, the first prism surface 54a of each unit prism 54 is located on the side of the light source 24 in the _first direction d1 and faces _one side in the first direction d1. The second prism surface 54b of each unit prism 54 is located on the side away from the light source 24 in the _first direction d1 and faces the other side in the _first direction d1. As will be described later, the first prism surface 54 a mainly advances into the light guide plate 30 from the light source 24 arranged on one side in the first direction d ₁ , and then the light emitted from the light guide plate 30 passes through the optical sheet 50 . It functions as an incident surface when incident on. On the other hand, the second prism surface 54b has a function of reflecting the light incident on the optical sheet 50 and correcting the optical path of the light.

As shown in FIG. 3, the first prism surface 54a and the second prism surface 54b extend from the body portion 53 and are connected to each other. At the position where the first prism surface 54a and the second prism surface 54b are connected to each other, a tip portion (apex portion) 54c of the unit prism 54 protruding from the main body portion 53 to the light incident side is formed.

As described above and as shown in FIGS. 5 and 6, the normal direction nd to the sheet surface of the main body 53 (the light incident side surface 53b of the main body 53 and the sheet surface of the optical sheet 50) and the direction of the unit prism 54 The cross-sectional shape of each unit prism 54 in a cross section parallel to both the _first direction d1, which is the arrangement direction, is constant along the longitudinal direction (the direction in which the unit prisms 54 extend linearly). In this cross section, each unit prism 54 has a shape that tapers toward the light incident side (light guide plate side). That is, in this cross section, the width of the unit prism 54 parallel to the sheet surface of the body portion 53 decreases along the normal direction nd of the body portion 53 as it separates from the body portion 53 .

As an example, the dimensions of the optical sheet 50 can be set as follows. First, as a specific example of the unit prisms 54 configured as described above, the arrangement pitch of the unit prisms 54 along the _first direction d1 (corresponding to the width of the unit prisms 54 in the illustrated example) is 10 μm to 200 μm. can be: In recent years, however, the arrangement of the unit prisms 54 has been rapidly becoming finer, and it is preferable that the arrangement pitch of the unit prisms 54 along the _first direction d1 is 10 μm or more and 50 μm or less. Further, the height of the unit prisms 54 protruding from the main body portion 53 along the normal direction nd to the sheet surface of the optical sheet 50 can be set to 5.5 μm or more and 180 μm or less.

The optical sheet 50 configured as described above can be produced by molding the unit prisms 54 on the substrate or by extrusion molding. Various materials can be used as materials for forming the main body portion 53 and the unit prisms 54 of the optical sheet 50 . However, materials that are widely used as materials for optical sheets incorporated in display devices, have excellent mechanical properties, optical properties, stability, workability, etc., and are available at low cost, such as acrylic resins, polystyrene resins, Transparent resins mainly composed of one or more of polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc., and reactive resins such as epoxy acrylate resins and urethane acrylate resins (ionizing radiation curable resins, etc.) can be preferably used.

When the optical sheet 50 is produced by curing the ionizing radiation curable resin on the base material, the unit prisms 54 and the sheet-like lands positioned between the unit prisms 54 and the base material are placed on the base material. It may be formed on the material. In this case, the body portion 53 is composed of a base material and a land portion formed of an ionizing radiation curable resin. On the other hand, in the optical sheet 50 produced by extrusion molding, the body portion 53 and the plurality of unit prisms 54 on the light incident side surface 53b of the body portion 53 can be integrally formed.

Next, the frame 55 and the main frame 60 are described. First, the main frame 60 supports the components of the surface light source device 20 , such as the light source 24 , the reflection sheet 28 , the light guide plate 30 and the optical sheet 50 . In addition, the main frame 60 protects the supported components of the surface light source device 20 from the outside. The light source 24 , reflective sheet 28 , light guide plate 30 and optical sheet 50 are positioned with respect to the main frame 60 . The liquid crystal display panel 15 described above is positioned with respect to the main frame 60 . However, the reflecting sheet 28 , the light guide plate 30 and the optical sheet 50 heat up and expand during use of the surface light source device 20 . Therefore, the reflective sheet 28, the light guide plate 30 and the optical sheet 50 are supported by the main frame 60 so that they can expand and contract. Typically, the light source 24 is fixed to the main frame 60, and the reflective sheet 28, the light guide plate 30 and the optical sheet 50 are attached to the main frame 60 on one side close to the light source 24 in the _first direction d1. Fixed. The reflecting sheet 28, the light guide plate 30, and the optical sheet 50 can be extended to the other side away from the light source 24 in the _first direction d1 when thermally expanded. Such a main frame 60 is formed using metal such as aluminum, stainless steel, and iron.

The frame body 55 is provided between the reflection sheet 28 , the light guide plate 30 and the optical sheet 50 and the main frame 60 . The frame 55 prevents the reflection sheet 28, the light guide plate 30, and the optical sheet 50 from coming into contact with each other. The frame 55 has a function of protecting the reflection sheet 28 , the light guide plate 30 and the optical sheet 50 from the main frame 60 . 1, the frame 55 supports the liquid crystal display panel 15 in the front direction nd. The frame 55 forms a gap between the liquid crystal display panel 15 and the optical sheet 50 . Thereby, the optical sheet 50 is prevented from coming into contact with the liquid crystal display panel 15 .

In the illustrated example, the frame 55 is supported so as to be relatively movable with respect to the main frame 60 . The frame 55 is fixed to the opposite surface 34 of the light guide plate 30 via the bonding layer 58 . That is, the reflective layer 38 of the light guide plate 30 and the frame 55 are connected by the reflective layer 38 along the _first direction d1. As the light guide plate 30 thermally expands, the frame 55 moves relative to the main frame 60 . As the bonding layer 58, various adhesive layers and adhesive layers used in display devices can be employed.

In the example shown in FIG. 1, a gap S that allows thermal expansion of the light guide plate 30 is formed between the frame 55 and the main frame 60 in the _first direction d1. However, at least part of the thermal expansion of the light guide plate 30 may be absorbed by the bonding layer 58 . In this case, the width Ws [μm] of the gap S between the frame 55 and the main frame 60 along the _first direction d1 can be made shorter than the assumed thermal expansion length of the light guide plate 30 . As a result, the width of the non-active area Ab of the light guide plate 30 can be narrowed, and the width of the bezel can be narrowed. The assumed thermal expansion length [μm] of the light guide plate 30 is the length [μm] along the _first direction d1 of the light guide plate 30, the thermal expansion coefficient [1/° C.] of the light guide plate 30, and , can be specified by multiplying the assumed temperature difference [°C]. The temperature difference [°C] assumed here can typically be 40°C, assuming that the ambient temperature changes between 20°C and 60°C. In order to absorb the expansion of the light guide plate 30 with the bonding layer 58, the thickness Wj [μm] of the bonding layer 58 along the _first direction d1 is preferably set large. Assuming display devices such as tablets, display devices for smartphones, etc., the thickness is preferably 100 μm or more and 700 μm or less, more preferably 200 μm or more and 600 μm or less, and further preferably 300 μm or more and 500 μm or less. preferable. Furthermore, setting the thickness Wj [μm] of the bonding layer 58 along the _first direction d1 to be longer than the expected thermal expansion length of the light guide plate 30 also allows the expansion of the light guide plate 30 to be caused by the bonding layer 58. effective in absorption.

In the example shown in FIG. 2, the frame 55 faces the reflective sheet 28, the light guide plate 30 and the optical sheet 50 from three sides. More specifically, the frame 55 faces the reflection sheet 28, the light guide plate 30, and the optical sheet 50 from the other side opposite to the light source 24 in the _first direction d1, and faces the _second direction d2. facing the reflective sheet 28, the light guide plate 30 and the optical sheet 50 from both sides of the . The frame 55 is formed using resin, for example. The frame 55 made of resin material has sufficient flexibility.

In addition, in the example shown in FIG. 2, the bonding layer 58 is linearly provided on the opposite surface 34 of the light guide plate 30 along the _second direction d2, but is not limited to this example. The bonding layer 58 may be provided only in a partial region along the _second direction d2 on the opposite surface 34 of the light guide plate 30 to bond the light guide plate 30 and the frame 55 together. Also, the bonding layer 58 may be provided in a plurality of regions spaced apart along the _second direction d2 on the opposite surface 34 of the light guide plate 30 to bond the light guide plate 30 and the frame 55 together. Furthermore, the bonding layer 58 is provided on the pair of side end faces 35 and 36 of the light guide plate 30 facing in the _second direction d2, and joins the side end faces 35 and 36 of the light guide plate 30 and the frame 55. may

Next, the operation of the display device 10 configured as described above will be described.

First, as shown in FIG. 3, light emitted by the light emitter 25 forming the light source 24 enters the light guide plate main body 40 of the light guide plate 30 via the light incident surface 33 . As shown in FIG. 3, the lights L31 and L32 incident on the light guide plate main body 40 are reflected on the light exit surface 41 and the back surface 42 of the light guide plate main body 40, and in particular, the difference in refractive index between the material forming the light guide plate main body 40 and air. , the light travels in the _first direction (light guide direction) d1 connecting the light incident surface 43 and the opposing surface 44 of the light guide plate main body 40 .

The back surface 42 of the light guide plate main body 40 has an inclined surface 47 inclined so as to approach the light exit surface 41 from the light entrance surface 43 toward the opposing surface 44 . The inclined surface 47 forms the back surface 42 together with the stepped surface 48 and the connecting surface 49 . Among them, the step surface 48 extends in the normal direction nd of the plate surface of the light guide plate main body 40 . Therefore, most of the light that travels from the light incident surface 43 side to the opposing surface 44 side in the light guide plate main body 40 does not enter the stepped surface 48 of the back surface 42 , but reaches the inclined surface 47 or the connection surface 49 . will be reflected. When the light is reflected by the inclined surface 47 of the back surface 42, the traveling direction of the light in the cross section shown in FIG. That is, when the light is reflected by the inclined surface 47 of the back surface 42, the incident angle of the light to the light exit surface 41 and the back surface 42 becomes small thereafter. Therefore, the angle of incidence of the light traveling through the light guide plate body 40 on the light output surface 41 and the rear surface 42 gradually decreases due to one or more reflections on the inclined surface 47 of the rear surface 42, and is less than the critical angle for total reflection. becomes. In this case, the light passes through the light exit side 31 or the back side 32 of the light guide plate 30 formed by the light exit surface 41 or the back surface 42 of the light guide plate main body 40 and can be emitted from the light guide plate 30 . Lights L31 and L32 emitted from the light exit side surface 31 travel toward the optical sheet 50 arranged on the light exit side of the light guide plate 30 . On the other hand, the light emitted from the rear side surface 32 is reflected by the reflection sheet 28 arranged on the rear surface 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 47 in the rear surface 42 increases as the light guide direction approaches the opposing surface 44 from the light incident surface 43 . As a result, in a region away from the light entrance surface 33 of the light guide plate 30 where the amount of emitted light tends to decrease, a sufficient amount of light emitted from the light exit side surface 31 of the light guide plate 30 is ensured, Emission light quantity can be made uniform.

By the way, in the illustrated _example , the emission angle of the light emitted from the light guide plate 30 is as shown in FIG. , the plane parallel to the _first direction (light guide direction) d1 has a relatively large outgoing angle θ _k that is relatively greatly inclined from the front direction nd. That is, the emission angle of the _first direction component d1 of the light emitted from the light guide plate 30 (the angle θ _k formed by the first direction component of the emitted light and the normal direction nd to the plate surface of the light guide plate 30 (see FIG. 3 )) tend to be biased within a narrow angular range resulting in relatively large angles.

Here, FIG. 7 shows an example of the angular distribution of luminance measured at the light exit side surface 31 of the light guide plate 30 . The luminance distribution shown in FIG. 7 is the result of actually investigating the luminance on the light exit side surface 31 in each direction in a plane parallel to both the _first direction d1 and the front direction nd. In the graph shown in FIG. 7, the value of the angle inclined from the front direction to the other side along the first direction is positive.

For example, in the light guide plate 30 having the above-described shape and dimensions, on the light exit side surface 31 of the light guide plate 30 in each direction in a plane parallel to both the normal direction nd of the light guide plate 30 and the _first direction d1 In the angular distribution of luminance, the angle θmax at which the direction in which the peak luminance Lmax is obtained is inclined from the normal direction nd of the light guide plate 30 to the other side (the side of the opposite surface 34) along the _first direction d1, and the light guide plate 30 and the direction in which the peak luminance Lmax is obtained is along the _first direction d1 from the direction in which the peak luminance is obtained. The angle θα inclined to one side (the light incident surface 33 side) should be set within a range that satisfies the following conditions (1) and (2), more typically conditions (3) and (4). can be done.
60° ≤ θmax ≤ 85° (1)
5°≦θα≦25° (2)
70° ≤ θmax ≤ 80° (3)
5°≦θα≦15° (4)

The light emitted from the light guide plate 30 then enters the optical sheet 50 . As described above, the optical sheet 50 has the unit prisms 54 with the tip portions 54c protruding toward the light guide plate 30 side. As well shown in FIG. 3, the longitudinal direction of the unit prisms 54 is a direction intersecting the light guiding direction ( _first direction) d1 by the light guide plate 30, particularly perpendicular to the light guiding direction in the illustrated example. It is parallel to the _second direction d2.

As a result, as shown in FIG. 3, lights L31 and L32 are emitted from the light source 24 arranged on one side (the left side in the plane of FIG. 3) in the _first direction d1 and travel through the light guide plate 30 toward the optical sheet 50. is incident on the unit prism 54 via the first prism surface 54a located on the side of the light source 24 in the _first direction d1, of the first prism surface 54a and the second prism surface 54b connected to each other. do. As shown in FIG. 3, the lights L31 and L32 are then totally reflected by the second prism surface 54b located on the other side (right side in FIG. 3) opposite to the light source in the _first direction d1. to change its direction of travel.

3 (a cross section parallel to both the _first direction (light guide direction) d1 and the front direction nd) of the optical sheet shown in FIG. The lights L31 and L32 traveling in the direction are bent with high precision by total reflection on the second prism surface 54b of the unit prism 54 so that the angle formed by the traveling direction with respect to the front direction nd becomes small. With such an action, the unit prism 54 can narrow down the traveling direction of the transmitted light toward the front direction nd with respect to the light component along the _first direction (light guide direction) d1. That is, the optical sheet 50 exerts a converging effect on the light component along the _first direction d1. In particular, in combination with the light guide plate 30 that satisfies the above conditions (1) and (2), the optical sheet 50 can exhibit an excellent light-condensing function, and further satisfies the above conditions (3) and (4). In combination with the light guide plate 30, the optical sheet 50 can exhibit a better light collecting function.

Light of one polarization component emitted from the optical sheet 50 forming the light emitting surface 21 of the surface light source device 20 is then incident on the liquid crystal display panel 15 and transmitted through the lower polarizing plate 14 . The light transmitted through the lower polarizing plate 14 is selectively transmitted 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 the light from the surface light source device 20 for each pixel, so that the viewer of the liquid crystal display device 10 can observe an image.

By the way, as explained in the Background Art column, these days, there is a demand for narrowing the bezel width of a display device or a surface light source device, that is, narrowing the bezel. If the width of the bezel can be reduced, the size of the display device and surface light source device can be reduced without reducing the size of the display surface and the light emitting surface. At present, it is necessary to narrow the non-active area Ab of the light guide plate 30 in order to promote narrow bezel display devices and surface light source devices.

Here, FIG. 10 shows a surface light source device 20 as a reference example developed by the applicant of the present application. In the example shown in FIG. 10 , the surface light source device 120 has a reflective sheet 128 , a light guide plate 130 , an optical sheet 150 , a frame 155 and a main frame 160 . Of these, the light guide plate 130 is composed only of the light guide plate main body 40 of the present embodiment described above, and does not include the reflective layer 38 . Other components of the surface light source device 120, that is, the reflective sheet 128, the optical sheet 150, the frame 155 and the main frame 160 are configured in the same manner as the corresponding components of the above-described embodiments.

When the periphery of the opposite surface 134 of such a surface light source device 120 was confirmed through the light exit surface 131, it was locally observed brighter than other portions. As a result of further intensive studies on such a phenomenon, it was found that the cause of the local brightness was that the light L101 emitted from the light guide plate 130 via the opposite surface 134 was diffused by the frame 155 . That is, the light diffused by the frame 155 was observed brightly as the opposite surface 134 .

Such non-uniformity in brightness becomes conspicuous when the emitted light from the light guide plate 30 has directivity. In particular, the local brightness is viewed from a direction inclined from the front direction nd to one side (light source 24 side) in the _first direction d1. Therefore, as described with reference to FIG. 7, the light guide plate 30 in which the luminance peak on the light exit side surface 31 appears in a direction inclined from the front direction nd to the other side in the _first direction d1, more specifically, the above-described light guide plate 30 When the light guide plate 30 that satisfies the above conditions (1) and (2) is used, unevenness in brightness becomes remarkable. The problem becomes serious.

The area where such a localized brightness change occurs, in other words, the area on the light emitting side surface 31 where the opposite surface 134 is confirmed cannot ensure the uniformity of brightness, so it is used as the active area Aa. I can't. That is, the area on the light output side surface 31 where the opposite surface 134 is confirmed needs to be hidden by a member having a light shielding property such as the frame member 18 as the non-active area Ab. This is the reason why the size of the non-active area Ab and the bezel cannot be reduced.

Here, FIG. 11 explains the result of observing the surface light source device 120 shown in FIG. FIG. 11A shows an observation method of the surface light source device 120. FIG. As shown in FIG. 11A , with the optical sheet 150 removed, the luminous body of the light source was turned on, and the periphery of the opposite surface 134 of the light guide plate 130 was observed through the light exit surface 131 . FIG. 11(b) is a photograph showing the result of observation, in which the opposite surface 134 and its periphery are observed to be bright.

In order to avoid such a problem, it is considered effective not to use the frame 155 to diffuse the light. For example, by forming the frame 155 from a black resin material, the frame 155 can be given light absorption. However, as shown in FIG. 10, when the light L102 that has passed through the opposite surface 134 and is emitted from the light guide plate 130 is absorbed by the frame 155, another problem arises that the utilization efficiency of the light from the light source is lowered.

Here, FIG. 8 shows the distribution along the first direction of the front luminance measured on the optical sheet 150 of the surface light source device 120 shown in FIG. The surface light source device 120 to be measured was used for a 14-inch display device incorporated in a notebook computer. The display surface of this surface light source device 120 had a length of approximately 180 mm along the _first direction d1. In the luminance distribution shown in FIG. 8, the horizontal axis indicates the position along the _first direction d1, and "0" indicates the central luminance value of the display surface in the _first direction d1. . In the surface light source device shown as sample B in FIG. 8, the frame 155 is white and has light diffusion properties. Note that the sample B is also the surface light source device that is the object of observation in FIG. 11 . Further, in the surface light source device shown as sample C in FIG. 8, the frame 155 is black and has light absorption properties. In the measurement result of sample B, the brightness in the front direction increased sharply in the area farthest from the light source. On the other hand, according to the measurement results of sample C, no local increase in the front direction luminance occurred in the area farthest from the light source. However, the front luminance of sample C is lower than that of sample B over substantially the entire area along the _first direction d1, especially in the half area opposite the light source in the _first direction d1. , the luminance in the front direction was significantly lower than that of sample B.

On the other hand, in the present embodiment, as shown in FIG. 6, the opposite surface 34 of the light guide plate 30 is formed with a reflective layer 38 . As shown in FIG. 6, the reflective layer 38 reflects lights L61 and L62 that travel in the _first direction d1 in the light guide plate main body 40 and reach the opposing surface 44 . The optical paths of the lights L61 and L62 reflected by the reflective layer 38 are turned back in the _first direction d1. Such lights L61 and L62 travel through the light guide plate main body 40 toward the light incident surface 43 in the _first direction d1. The light beams L61 and L62 are emitted from the light guide plate 30 via the light emitting surface 41 or the back surface 42 by bending the optical paths at the inclined surface 47 and the stepped surface 48 .

Therefore, in the surface light source device 20 according to the present embodiment, even when the luminance characteristic has strong directivity, that is, when the above-described conditions (1) and (2) are satisfied, or when the above-described To effectively prevent the periphery of an opposite surface 34 of a light guide plate 30 from being locally brightly observed through a light exit side surface 31 even when conditions (3) and (4) are satisfied. can be done. Therefore, the width Wa along the _first direction d1 of the non-active area Ab located on the opposite surface 34 (reflective layer 38) can be narrowed to the extent that the reflective layer 38 is not directly visible from the front direction nd. .

Conventionally, the width Wa along the _first direction d1 of the non-active area Ab of the light guide plate 130 located on the opposite surface 134 is the length obtained by multiplying the height (thickness) H of the light guide plate 130 by 1.73. was considered necessary. Here, 1.73 corresponds to a value of tan60°, that is, in the conventional art, the area on the light output surface 131 crossed by the straight line segment LS that is inclined by 60° from the front direction nd and intersects the opposite surface 134 is inactive. It was supposed that it should be Area Ab. Compared with such a conventional non-active area Ab, in the present embodiment, the width of the non-active area Ab can be significantly narrowed.

9 illustrates the result of observation of the surface light source device 120 shown in FIG. FIG. 9A shows an observation method of the surface light source device 120. FIG. As shown in FIG. 9A, with the optical sheet 50 removed, the light emitter 25 of the light source 24 is turned on, and the periphery of the opposite surface 34 of the light guide plate 30 is observed through the light exit side surface 31. As shown in FIG. 9B, no locally bright regions were observed around the opposite surface 34 .

8 shows, as the measurement result of sample A, the distribution along the _first direction d1 of the front luminance measured on the optical sheet 50 of the surface light source device 20 shown in FIG. The dimensions and measurement conditions of sample A were the same as those of sample B described above. That is, sample A and sample B are measured under the same conditions, except for the differences shown in FIGS. Sample A is also the surface light source device that is the object of observation in FIG. As shown in FIG. 8 , in the measurement results of sample A, unlike the measurement results of sample B, no local increase in the front luminance occurred in the region farthest from the light source. On the other hand, the front-direction luminance of sample A was generally higher than the front-direction luminance of sample B, except for the local region farthest from the light source.

By the way, in the surface light source device 120 shown in FIG. 10 , the bonding layer 158 is not provided on the opposite surface 134 of the light guide plate 130 . This is because if the bonding layer 158 is provided on the opposite surface 134 of the light guide plate 130 , the light guided through the light guide plate 130 and reaching the opposite surface 134 is absorbed or diffused by the bonding layer 158 . . The joining layer 158 shown in FIG. 10 joins the main frame 160 and the end of the back surface 132 of the light guide plate 30 on the side opposite to the surface 134 in the _first direction d1. In this surface light source device 120 , the light guide plate 130 can expand by shearing and compressing the bonding layer 158 . A gap is provided between the reflective sheet 128 and the bonding layer 158 along the _first direction d1, and this gap allows the reflective sheet 128 to expand in the _first direction d1.

In the surface light source device 120 shown in FIG. 10, it has been confirmed that a dark area with reduced luminance is generated as an elongated area along the _second direction d2 on the light exit surface 131 . As a result of repeated studies by the inventors of the present invention, such a dark region is thought to be caused by the fact that a part of the back surface 132 of the light guide plate 130 does not face the reflective sheet 128 as shown in FIG. was taken. Even in the vicinity of the opposite surface ₁₃₄ of the light guide plate 130 shown in FIG. Proceed toward the face side. Light L103 traveling toward the light exit surface 131 from a region of the back surface 132 of the light guide plate 130 where the reflective sheet 128 does not exist on the back side is emitted from the area where the reflective sheet 128 exists on the back surface side of the back surface 132 of the light guide plate 130 . The amount of light is remarkably low compared to the light L104 directed toward the light exit surface 131 from the area where the light exits. A dark region is generated in a region on the light exit surface 131 from which such light L103 can exit. Therefore, in the surface light source device 120 shown in FIG. 10, it is necessary to set the region where the dark region is formed on the light emitting surface 131 as the non-active area Ab. becomes larger.

Regarding this point, in the present embodiment, the opposite surface 34 of the light guide plate 30 is formed of a reflective layer 38 with low transmittance. Therefore, even if the bonding layer 58 is provided on the opposite surface 34, problems such as absorption and diffusion due to the bonding layer 58 cannot occur. As a result, as shown in FIG. 6, the reflective sheet 28 can be arranged so as to face the entire area of the back surface 32 of the light guide plate 30 . Thereby, it is possible to avoid the occurrence of a dark area on the light exit side surface 31 due to the presence or absence of the reflection sheet 28 on the back side of the light guide plate 30 . Therefore, in the light guide plate 30 of the surface light source device 20 illustrated, the width Wa of the non-active area Ab located on the opposite surface 34 side is effectively narrowed, and the surface light source device 20 and the display device 10 are made narrow bezels. be able to.

In the embodiment described above, the light guide plate 30 includes a light guide plate main body 40 including a light incident surface 43 and an opposing surface 44 facing the light incident surface 43 , and a reflector provided on the opposing surface 44 of the light guide plate main body 40 . a layer 38; According to such a light guide plate 30 , the lights L 61 and L 62 reaching the facing surface 44 of the light guide plate body 40 are reflected by the reflective layer 38 . The lights L61 and L62 reflected by the reflective layer 38 travel through the light guide plate main body 40 in the opposite direction to the direction before being reflected by the reflective layer 38 . Therefore, the lights L61 and L62 traveling through the light guide plate main body 40 are effectively prevented from reaching the opposite surface 34 of the light guide plate 30, exiting from the light guide plate 30, and being absorbed by the frame 55 and the main frame 60. can do. That is, according to the present embodiment, it is possible to improve the utilization efficiency of the light from the light source, and to effectively avoid the reduction in brightness particularly in the vicinity of the opposite surface 34 . In addition, it is possible to effectively prevent the lights L61 and L62 traveling through the light guide plate 30 from reaching the opposite surface 34, being emitted from the light guide plate 30, and being diffused by the frame 55 and the main frame 60. Therefore, it is possible to effectively prevent a local luminance increase in the vicinity of the opposite surface 34 of the light guide plate 30 . As a result, the opposite surface 34 of the light guide plate 30 is made invisible, and the non-active area Aa on the opposite surface 34 side of the light guide plate 30 can be effectively reduced. can be realized.

In the specific example of one embodiment described above, the surface roughness Ra of the facing surface 44 is 0.01 μm or more and 0.3 μm or less. According to the light guide plate 30 as described above, since the surface roughness Ra is 0.01 μm or more, the reflective layer 38 can sufficiently adhere to the facing surface 44 of the light guide plate main body 40 . Further, since the surface roughness Ra is 0.3 μm or less, light diffusion at the interface between the light guide plate main body 40 and the reflective layer 38 and diffuse reflection at the reflective layer 38 are effectively suppressed. be able to. As a result, it is possible to effectively prevent a local increase in brightness due to light diffusion in the vicinity of the opposite surface 34 of the light guide plate 30, and realize a narrow bezel.

In the specific example of the embodiment described above, the ratio R [%] of the specularly reflected light in the total reflected light on the reflective layer 38 is greater than 20. With such a light guide plate 30, diffuse reflection at the reflective layer 38 can be effectively suppressed. As a result, it is possible to effectively prevent a local increase in brightness due to light diffusion in the vicinity of the opposite surface 34 of the light guide plate 30, and realize a narrow bezel.

In one embodiment described above, the light guide plate 30 includes the light exit side surface 31 and the back side surface 32 facing the light exit side surface 31 as a pair of main surfaces. The light emitting side surface 31 is divided into an active area Aa and a non-active area Ab located around the active area Aa and finally covered by the light-shielding frame member 18 . The width Wa [mm] along the _first direction d1 of the non-active area Ab located on the facing surface 44 side of the light output side surface 31 is less than 1.73 times the height H [mm] of the facing surface 44. It's becoming Conventionally, in order to prevent the opposite surface 34 of the light guide plate 30 from being seen, the width Wa of the non-active area Ab on the opposite surface 34 side has been set so that Wa≧1.73×H. However, when the light guide plate 30 with the reflective layer 38 is used, the opposite surface 34 can be made sufficiently invisible. Therefore, by setting the width Wa of the non-active area Ab on the opposite surface 34 side of the light guide plate 30 so that Wa<1.73×H, a narrow bezel can be realized.

In the specific example of the embodiment described above, the surface light source device 20 includes the light guide plate 30 having the light guide plate main body 40 and the reflective layer 38, and the light emitters arranged to face the light entrance surface 33 of the light guide plate 30. 25 , a bonding layer 58 provided on the reflective layer 38 of the light guide plate 30 , and a frame body 55 bonded to the light guide plate 30 via the bonding layer 58 . The bonding layer 58 is positioned between the reflective layer 38 and the frame 55 in the _first direction d1. In such a surface light source device 20 , an end surface (opposite surface) 34 of the light guide plate 30 on the side opposite to the light source 24 side in the first direction d ₁ is formed of a reflective layer 38 . Therefore, the bonding layer 58 can be directly bonded to the end surface 34 . Compared to the surface light source device 120 in which a bonding layer is provided on the back surface 132 of the light guide plate 130, the width Wa of the non-active area Ab on the opposite surface 34 side of the light guide plate 30 can be effectively narrowed, and a narrow bezel can be achieved. can be realized.

In the specific example of the embodiment described above, the thickness of the bonding layer 58 along the _first direction d1 is 200 μm or more and 800 μm or less. According to such a surface light source device 20 , the thermal expansion of the light guide plate 30 can be effectively absorbed at least partially by the compression of the bonding layer 58 . Therefore, it is also possible to effectively prevent displacement of relative positions of the constituent elements of the surface light source device 20 due to thermal expansion of the light guide plate 30 . Thereby, the expected optical performance of the surface light source device 20 can be stably exhibited.

Although an embodiment has been described through several specific examples, these specific examples are not intended to limit an embodiment. The embodiment described above can be implemented in various other specific examples, and various omissions, replacements, and modifications can be made without departing from the spirit of the embodiment.

An example of modification will be described below with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding portions in the above-described specific example are used for the portions that can be configured in the same manner as in the above-described specific example, and redundant description is given. omitted.

In the specific example described above, the reflective layer 38 is provided only on the facing surface 44 of the light guide plate main body 40, but the present invention is not limited to this example. The reflective layer 38 may be provided on the pair of side end surfaces 35 and 36 of the light guide plate 30 facing in the _second direction d2. According to this example, it is possible to effectively prevent light from leaking from the light guide plate 30 via the side end surfaces 35 and 36 . As a result, the width Wb (see FIG. 2) of the non-active area Ab on the side end surfaces 35 and 36 of the light guide plate 30 can be narrowed to realize a narrow bezel. Light leakage from the side end surfaces 35 and 36 is likely to occur on the light incident surface 33 side of the side end surfaces 35 and 36 in the _first direction d1. Therefore, the reflective layer 38 may be provided on a part of the side end faces 35 and 36 that faces the light incident surface 33 in the _first direction d1.

Further, various modifications can be made to the light guide plate main body 40 and the optical sheet 50 of the light guide plate 30 described above. For example, the first prism surface 54a and the second prism surface 54b of the optical sheet 50 may be formed as folded surfaces. Further, as shown in FIG. 6, for the lights L61 and L62 reflected by the reflecting layer 38, the second prism surface 54b functions as a light incident surface, and the first prism surface 54a functions as a reflecting surface. Therefore, the first prism surface 54a and the second prism surface 54b may be configured symmetrically with the normal direction nd of the optical sheet 50 as a reference. Alternatively, the configuration of the unit prism 54 may be changed according to the position in the _first direction d1. Further, in the above-described specific example, the inclined surface 47 was adopted as the light extraction element of the light guide plate 30, but instead of the inclined surface 47 or in addition to the inclined surface 47, another light extraction element such as a diffusing material or the like may be used. may be included in the light guide plate 30 .

Furthermore, various changes are possible for the overall configurations of the surface light source device 20 and the display device 10 described above. For example, the surface light source device 20 may further include a prism sheet projecting on the light output side instead of or in addition to the optical sheet 50, or may further include a reflective polarization separation sheet.

Although several modifications of the above-described embodiment have been described above, it is of course possible to apply a plurality of modifications in appropriate combination.

Aa Active area Ab Non-active area S Gap 10 Display device 11 Display surface 12 Liquid crystal cell 13 Upper polarizing plate 14 Lower polarizing plate 15 Liquid crystal display panel 18 Frame member 20 Surface light source device 21 Light emitting surface 24 Light source 25 Emitter 28 Reflective sheet 30 Conductor Light plate 31 Light output side surface 32 Back side surface 33 Light input surface 34 Opposite surface 35 Side end surface 36 Side end surface 38 Reflective layer 40 Light guide plate main body 41 Light output surface 42 Back surface 43 Light input surface 44 Opposing surface 47 Inclined surface 48 Stepped surface 49 Connection surface 50 Optics Sheet 51 Light output surface 52 Light input surface 53 Body portion 53a Light output side surface 53b Light input side surface 54 Unit prism 54a First prism surface 54b Second prism surface 54c Tip portion 55 Frame 58 Bonding layer 60 Main frame 120 Surface light source device 128 Reflection sheet 130 light guide plate 131 light exit surface 132 back surface 134 opposite surface 150 optical sheet 155 frame body 158 bonding layer 160 main frame

Claims (7)

a light guide plate body including a light incident surface and an opposing surface facing the light incident surface in a first direction ;
a reflective layer provided on the facing surface of the light guide plate main body;
As a material forming the light guide plate main body, a transparent resin containing one or more of acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, and polyacrylonitrile resin as a main component is used,
The light guide plate, wherein the surface roughness Ra of the facing surface linearly extending in the second direction perpendicular to the first direction when observed from the normal direction of the light guide plate main body is 0.01 μm or more and 0.3 μm or less. . a light guide plate body including a light incident surface and an opposing surface facing the light incident surface in a first direction;
a reflective layer provided on the facing surface of the light guide plate main body;
As a material forming the light guide plate main body, a transparent resin containing one or more of acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, and polyacrylonitrile resin as a main component is used,
The surface roughness Ra of the facing surface is 0.01 μm or more and 0.3 μm or less,
The light guide plate according to claim 1, wherein the total light reflectance Rt[%] and the diffuse reflectance Rd[%] of the reflective layer satisfy the following relationship.
20<((Rt−Rd)/Rt)×100 including, as a pair of main surfaces, a light emitting side surface divided into an active area and a non-active area located around the active area, and a rear side surface facing the light emitting side surface;
The width Wa [mm] of the non-active area located on the opposite surface side of the light output side surface along the first direction in which the light incident surface and the opposite surface face each other is the height H [mm] of the opposite surface and the light guide plate according to claim 1 or 2, wherein the following relationship is satisfied.
Wa<1.73×H a light guide plate according to any one of claims 1 to 3;
a light emitter disposed facing the light incident surface of the light guide plate;
a bonding layer provided on the reflective layer of the light guide plate;
a frame bonded to the light guide plate via the bonding layer;
The surface light source device, wherein the bonding layer is positioned between the reflective layer and the frame in a first direction in which the light incident surface and the opposing surface face each other. 5. The surface light source device according to claim 4, wherein a thickness of said bonding layer along said first direction is 200 [mu]m or more and 800 [mu]m or less. 6. The surface light source device according to claim 4, further comprising a main frame supporting said light emitter, said light guide plate and said frame. a surface light source device according to any one of claims 4 to 6;
A display device comprising: a liquid crystal display panel illuminated by the surface light source device.

Images