JP7232432B2 - Display device - Google Patents

Description

The present invention relates to an in-vehicle display device.

A display device such as a liquid crystal display device usually includes a display panel (liquid crystal panel) for displaying images and a backlight (light source) for illuminating the display panel. In such a display device, light from the backlight is emitted not only in the front direction of the display surface of the display panel, but also in various directions inclined from the front direction. Therefore, the light emitted from the display device is emitted in various directions. For example, when the display device is mounted in a car, the emitted light emitted upward is reflected by the windshield of the car, etc. may obstruct the view of the person.

In order to solve this problem, as a conventional technique, for example, in Patent Document 1, an optical member having a prism sheet and a light control sheet (louver film) is provided between a light source and a display panel to limit the traveling direction of light. there is By providing the optical member, it is possible to restrict the incident direction of light incident on the display panel and restrict the direction of light emitted from the display device.

JP 2010-217871 A

However, in the method of controlling the direction of light emitted from a display device using a louver film as in Patent Document 1, light emitted from a light source other than the direction of light emission is absorbed. is used less efficiently, and sufficient brightness cannot be obtained. In order to emit light in a specific direction with high brightness, the output of the light source must be increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a display device capable of effectively improving luminance in a desired direction by improving utilization efficiency of light from a light source. aim.

A first display device of the present invention is an in-vehicle display device having a display surface,
a display panel;
a surface light source device disposed on the back side of the display panel and planarly illuminating the display panel from the back side;
and an adhesive layer that bonds the display panel to the surface light source device,
In the angular distribution of luminance in all directions of the light emitted from the display surface, the luminance in at least one direction inclined by 40° from the direction in which the peak luminance is obtained is 6.5% or less of the peak luminance. there is

A second display device of the present invention is a vehicle-mounted display device having a display surface,
a display panel;
a surface light source device disposed on the back side of the display panel and planarly illuminating the display panel from the back side;
and an adhesive layer that bonds the display panel to the surface light source device,
The surface light source device includes a light guide plate having a light output surface, a back surface arranged to face the light output surface, and a side surface located between the light output surface and the back surface, and arranged to face a part of the side surface. an optical sheet arranged to face the light emitting surface of the light guide plate; and a reflective sheet arranged to face the back surface of the light guide plate;
The diffuse reflectance of the reflecting sheet is 18.3% or less.

In the second display device of the present invention,
the surface of the reflective sheet on the side facing the back surface of the light guide plate has an uneven shape,
The diffuse reflectance of the reflecting sheet may be 1.7% or more.

In the second display device of the present invention,
The reflective sheet has a metal layer and a matte layer laminated on the metal layer,
the metal layer contains silver;
The mat layer may be positioned closer to the light guide plate than the metal layer of the reflective sheet.

According to the present invention, it is possible to effectively improve the luminance in a desired direction by improving the utilization efficiency of light from the light source.

FIG. 1 is a diagram for explaining an embodiment according to the present invention, and is a sectional view showing a schematic configuration of a display device and a surface light source device. 2A and 2B are diagrams for explaining the action of the surface light source device of FIG. FIG. 3 is a diagram showing a reflective sheet. FIG. 4 is a top view showing the surface light source device of FIG. 1 from the light emitting surface side. FIG. 5 is a perspective view showing the light guide plate incorporated in the surface light source device of FIG. 1 from the light exit surface side. FIG. 6 is a perspective view showing the light guide plate incorporated in the surface light source device of FIG. 1 from the rear side. FIG. 7 is a diagram for explaining the action of the light guide plate, and is a diagram showing the light guide plate in a cross section along line VII-VII in FIG. 8 is a perspective view showing an optical sheet incorporated in the surface light source device of FIG. 1. FIG. 9 is a partial cross-sectional view showing the optical sheet of FIG. 8 at its main cross section (cross section along line IX-IX of FIG. 8). FIG. 10 is a diagram for explaining the action of the optical sheet, and is a partial cross-sectional view showing the light guide plate and the optical sheet in the same cross section as in FIG. FIG. 11 is a diagram corresponding to FIG. 10 and showing a modified example of the optical sheet. FIG. 12a is a graph showing the angular distribution of normalized luminance for one example embodiment of the present invention and another example. FIG. 12b is a graph enlarging a portion of FIG. 12a. FIG. 13a is a graph showing the angular distribution of measured luminance for one example embodiment of the invention and another example. FIG. 13b is a graph enlarging a portion of FIG. 13a. FIG. 14 is a table showing the relationship between the diffuse reflectance of the diffusion sheet and the optical adhesion. FIG. 15 is a diagram showing a modified example of the light guide plate and the reflective sheet.

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 12 are diagrams for explaining an embodiment according to the present invention. 1 is a cross-sectional view showing the schematic configuration of a liquid crystal display device and a surface light source device, FIG. 2 is a cross-sectional view for explaining the operation of the surface light source device, and FIG. FIG. 4 is a cross-sectional view showing a reflective sheet, and FIG. 4 is a top view showing a surface light source device. 5 and 6 are perspective views showing the light guide plate included in the surface light source device, and FIG. 7 is a cross-sectional view showing the light guide plate in the main cross section of the light guide plate. FIG. 8 is a perspective view showing an optical sheet included in the surface light source device, FIG. 9 is a cross-sectional view showing the optical sheet at a main cutting plane of the optical sheet, and FIGS. It is a figure for explaining. FIG. 12a is a diagram showing an example of the normalized angular distribution of luminance on the display surface of the display device, and FIG. 12b is an enlarged diagram showing a part thereof. FIG. 13a is a diagram showing an example of the angular distribution of luminance measured on the display surface of the display device, and FIG. 13b is a partially enlarged diagram thereof. FIG. 14 is a table showing the relationship between the diffuse reflectance of the diffusion sheet and the optical adhesion.

As shown in FIG. 1, the display device 10 includes a display panel 15, a surface light source device 20 arranged on the back side of the display panel 15 and planarly illuminating the display panel 15 from the back side, and the display panel 15 and the surface light source device. 20 and an adhesive layer 17 provided between them. The display device 10 has a display surface 11 that displays an image. The 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 . In one example shown in this embodiment, the display device 10 is a liquid crystal display device, and the display panel 15 is a liquid crystal display panel. However, the display panel 15 is not limited to a liquid crystal display panel, and other transmissive display panels can also be used.

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 an electric field is applied. It maintains its polarization direction as it passes through the liquid crystal layer 12 with no voltage 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 display panel 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.

The adhesive layer 17 is provided between the surface light source device 20 and the display panel 15 to bond the surface light source device 20 to the display panel 15 . As the adhesive layer 17, an acrylic adhesive is preferably used. In addition, the thickness of the adhesive layer 17 is preferably 100 μm or less, more preferably 30 μm or less, in consideration of preventing the display device 10 from becoming too thick.

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.

In the example 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 one side (the left side in FIG. 1) of the light guide plate 30 and the light guide plate 30. and an optical sheet (prism sheet) 60 and a reflective sheet 28 which are arranged so as to face the light guide plate 30, respectively. In the illustrated example, the optical sheet 60 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 61 (second light emitting surface) of the optical sheet 60 . Since the light emitting surface 21 of the surface light source device 20 faces the adhesive layer 17, light emitted from the light emitting surface 21 enters the adhesive layer 17 without entering an air layer or the like.

In the illustrated example, the light exit surface 31 (first light exit surface) of the light guide plate 30 has a planar shape (in FIG. 1, is formed in a rectangular shape when viewed from above. As a result, the light guide plate 30 as a whole is configured as a rectangular parallelepiped member having a pair of main surfaces (the light output surface 31 and the back surface 32), and the sides in the thickness direction are relatively smaller than the other sides. The sides defined between the pair of major faces include four faces. Similarly, the optical sheet 60 and the reflective sheet 28 are generally configured as rectangular parallelepiped members having relatively smaller sides in the thickness direction than other sides.

The light guide plate 30 has a light exit surface 31 configured by one principal surface on the liquid crystal display panel 15 side, a back surface 32 composed of the other principal surface facing the light exit surface 31 , and a light exit surface 31 and a back surface 32 . and extending sides. 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 FIGS. 1 and 4, the light source 24 is provided facing the light entrance surface 33 . As shown in FIG. 2, the light incident on the light guide plate 30 from the light incident surface 33 is directed toward the opposite surface 34 facing the light incident surface 33 along the first direction (light guide direction) _d1 . The light is guided through the light guide plate 30 along one direction (light guide direction) _d1 . As shown in FIGS. 1 and 2, the optical sheet 60 is arranged to face the light exit surface 31 of the light guide plate 30, and the reflective sheet 28 is arranged to face the back surface 32 of the light guide plate 30. ing.

The light source 24 can be configured in various forms, 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 dot-like light sources arranged side by side along the longitudinal direction of the light incident surface 33 (in FIG. 1, the direction perpendicular to the plane of the paper, that is, the front and back directions of the plane of the paper). The light emitter 25, specifically, is constituted by a large number of light emitting diodes (LEDs). The light guide plate 30 shown in FIGS. 4 and 5 shows the arrangement positions of 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 rear surface 32 of the light guide plate 30 and allowing the light to enter the light guide plate 30 again. Reflection on the reflection sheet 28 is mainly regular reflection (specular reflection), but includes diffuse reflection. The diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection. The reflecting sheet 28 has a metal layer 28b as a layer forming the reflecting surface from the viewpoint of suppressing the diffuse reflectance of the material forming the reflecting surface. The metal layer 28b preferably contains silver, which has a high specular reflectance. The metal layer 28b may constitute the reflective sheet 28 by itself, or may be provided on the support 28a as shown in FIG.

The diffuse reflectance of the reflective sheet 28 is 18.3% or less. With such a diffuse reflectance, in the angular distribution of luminance in all directions emitted from the display surface 11, the luminance in at least one direction inclined by 40° from the direction in which the peak luminance is obtained is 6 times the peak luminance. .5% or less. As a result of confirmation by the inventors of the present invention, peak luminance can be increased by suppressing luminance in at least one of the directions inclined by 40° according to such luminance characteristics. Specifically, as shown in FIG. 13, which will be described later, the peak luminance can be increased by 17% compared to the case where a conventional white scattering reflective sheet is used as the reflective sheet .

Also, in order to prevent the reflective sheet 28 and the light guide plate 30 from optically coming into close contact with each other and optically forming one layer, as shown in FIG. may have an uneven surface. For example, as shown in FIG. 3, the rugged surface of the reflection sheet 28 is formed by a mat layer 28c containing a transparent binder resin 28c1 and particles 28c2 for forming the rugged surface. If the surface of the reflective sheet 28 is made uneven so as to avoid the optical contact between the reflective sheet 28 and the light guide plate 30, the diffuse reflection due to the uneven shape will result in the diffuse reflectance of the reflective sheet 28 being 1.7% or more. .

The diffuse reflectance is defined by the omnidirectional diffuse reflectance obtained by excluding the light reflectance of the specularly reflected light from the total light reflectance, and is measured using a haze meter (eg, HR-100 Murakami Color Laboratory). be able to.

By the way, in this specification, the “light exit side” refers to the light source 24 , the light guide plate 30 , the optical sheet 60 , 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 (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 adhesive layer 17, the liquid crystal display panel 15, and the constituent elements of the display device 10 without going back, and emitted from the display device 10 toward the viewer.

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 sheet surface (plate surface) of the base portion 40 of the light guide plate 30, which will be described later, the sheet surface of the optical sheet 60, the sheet surface of the reflection sheet 28, and the panel of the liquid crystal display panel. The surface, the display surface 11 of the display device 10, and the light emitting surface 21 of the surface light source device 20 are parallel to each other. Further, 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 nd to the light emitting surface 21 of the surface light source device 20. The line 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 60, the normal direction to the display surface 11 of the display device 10, etc. See Figure 2).

Next, mainly with reference to FIGS. 2 and 4 to 7, the light guide plate 30 will be described in further detail. As best shown in FIGS. 2 and 4 to 7, the light guide plate 30 includes a plate-shaped base portion 40 and one side surface of the base portion 40 (a surface facing the viewer side, a light exit side surface). and a plurality of unit optical elements 50 formed on 41 . The base 40 is configured as a plate-like member having a pair of parallel main surfaces. A back surface 32 of the light guide plate 30 is formed by the other surface 42 of the base portion 40 located on the side facing the reflection sheet 28 .

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.

As shown well in FIG. 6, the other side surface 42 forming the other main surface of the base portion 40 forming the back surface 32 of the light guide plate 30 is formed as an uneven surface. As a specific configuration, the unevenness of the other side surface 42 of the base 40 causes the back surface 32 to have an inclined surface 37, a stepped surface 38 extending in the normal direction nd of the light guide plate 30, and a connection surface extending in the plate surface direction of the light guide plate 30. a surface 39; Light is guided in the light guide plate 30 by total reflection 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 plate surface of the light guide plate 30 so as to approach the light output surface 31 as it goes from the light incident surface 33 side to the opposite surface 34 side. Therefore, the light reflected by the inclined surface 37 has a small incident angle when incident on the pair of main surfaces 31 and 32 . When the incident angle on the pair of main surfaces 31 and 32 becomes less than the critical angle for total reflection due to reflection 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 .

By adjusting the distribution of the inclined surface 37 along the first direction _d1 , which is the light guiding direction, within the back surface 32, 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 examples shown in FIGS. 2 and 4 to 7, the proportion of the inclined surface 37 in the rear surface 32 increases as the incident surface 33 approaches the opposite surface 34 along the light guide direction. According to such a configuration, the emission of light from the light guide plate 30 in the region separated from the incident surface 33 along the light guiding direction is promoted, and the amount of emitted light decreases as the distance from the incident surface 33 increases. can be effectively prevented.

In the illustrated example, the arrangement pitch Ps (see FIG. 4) of the inclined surfaces 37 in the first direction _d1 is constant. In addition, the inclination angle of each inclined surface 37 is the same among the plurality of connecting surfaces 39 . On the other hand, the length of one inclined surface 37 in the first direction _d1 differs among the plurality of inclined surfaces 37 . The length of the inclined surface 37 in the first direction _d1 gradually increases as the arrangement position of the inclined surface 37 moves from one side to the other side in the first direction _d1 . It should be noted that "gradually longer" does not necessarily mean that the two inclined surfaces 37 adjacent to each other in the first direction _d1 have the same length in the first direction _d1 . may be That is, "gradually longer" means that the lengths of the plurality of inclined surfaces 37 in the first direction _d1 are not constant, and the length of one inclined surface 37 in the first direction _d1 is It means that it is not shorter than the length in the first direction _d1 of another inclined surface 37 located on one side of the inclined surface 37 in the first direction _d1 .

Next, the unit optical element 50 provided on one surface 41 of the base 40 will be described. As shown well in FIG. 5, the plurality of unit optical elements 50 are aligned in an arrangement direction that intersects the first direction _d1 and is parallel to the surface 41 on one side of the base 40 (in FIG. ) and arranged on one surface 41 of the base 40 . Each unit optical element 50 linearly extends on one side surface 41 of the base 40 in a direction intersecting the arrangement direction.

Especially in this embodiment, as shown in FIG. 5, the plurality of unit optical elements 50 are arranged on the surface 41 on one side of the base 40 in a second direction ₍ arrangement direction) _d2 orthogonal to the first direction d1. are arranged side by side without gaps. Therefore, the light exit surface 31 of the light guide plate 30 is configured as inclined surfaces 35 and 36 formed by the surfaces of the unit optical elements 50 . Each unit optical element 50 extends linearly along the first direction _d1 perpendicular to the array direction. Furthermore, each unit optical element 50 is formed in a columnar shape and has the same cross-sectional shape along its longitudinal direction. Moreover, in the present embodiment, the plurality of unit optical elements 50 are configured identically to each other. As a result, the light guide plate 30 in this embodiment has a constant cross-sectional shape at each position along the first direction _d1 .

Next, in the cross section shown in FIG. 7, that is, in both directions of the arrangement direction (second direction) _d2 of the unit optical elements and the normal direction nd to one side surface 41 of the base 40 (the plate surface of the light guide plate 30) A cross-sectional shape of each unit optical element 50 in a parallel cross section (hereinafter also simply referred to as a main cross section of the light guide plate) will be described. 7 shows a cross section of the light guide plate 30 along line VII-VII in FIG. As shown in FIG. 7, in the illustrated example, the cross-sectional shape of each unit optical element 50 on the main cut surface of the light guide plate is tapered toward the light output side. In other words, the width of the unit optical element 50 parallel to the surface of the light guide plate 30 on the main cross section of the light guide plate 30 decreases along the normal direction nd of the light guide plate 30 as it separates from the base 40 .

Further, in the present embodiment, the outer contour (corresponding to the light exit surface 31) 51 on the main cutting plane of the unit optical element 50 is formed with respect to one side surface 41 forming one main surface of the base 40. The light output surface angle _θa , which is an angle, extends from the tip 52a on the outer contour 51 of the unit optical element 50 farthest from the base 40 to the base 52b on the outer contour 51 of the unit optical element 50 closest to the base 40. It is changing so that it becomes larger towards. This light exit surface angle _θa can be set as disclosed in Japanese Patent Laid-Open No. 2013-51149, for example.

As described above, the light exit surface angle _θa here is the angle formed by the light exit side surface (outer contour) 51 of the unit optical element 50 with respect to the one side surface 41 of the base 40 on the main cross section of the light guide plate. is. As in the example shown in FIG. 7, when the outer contour (light emitting side surface) 51 on the main cutting plane of the unit optical element 50 is formed in a polygonal line shape, each linear portion constituting the polygonal line and one side surface of the base 40 41 (strictly speaking, the smaller one of the two formed angles (minor angle)) is the light emitting surface angle _θa . On the other hand, when the outer contour (light emitting side surface) 51 on the main cutting plane of the unit optical element 50 is formed by a curved surface, the angle ( Strictly speaking, the smaller angle (minor angle) of the two formed angles is specified as the light exit surface angle _θa .

A unit optical element 50 as a specific example shown in FIG. It has a pentagonal shape with two sides positioned between the end portion 52b, or a shape obtained by chamfering one or more corners of this pentagonal shape. In addition, in the illustrated example, it is possible to effectively improve the luminance at the angle showing the luminance peak, and to impart symmetry to the angular distribution of luminance in the plane along the second direction _d2. For the purpose, the cross-sectional shape of the main cutting plane of the unit optical element 50 has symmetry around the front direction nd. That is, as well shown in FIG. 7, the light output side surface 51 of each unit optical element 50 is composed of a pair of folding surfaces 35 and 36 that are symmetrical about the front direction. The pair of folding surfaces 35 and 36 are connected to each other to define a tip portion 52a. Each folding surface 35, 36 has a first surface 35a, 36a defining the tip portion 52a, and a second surface 35b, 36b connecting to the first surface 35a, 36a from the base 40 side. . The pair of first inclined surfaces 35a, 36a have a symmetrical configuration with respect to the front direction nd, and the pair of second inclined surfaces 35b, 36b also have a symmetrical configuration with respect to the front direction nd.

As the overall configuration of the unit optical element 50, the distance from the base 40 of the unit optical element 50 on the main cross section of the light guide plate 30 to the width W _a in the arrangement direction of the unit optical element 50 on the main cross section of the light guide plate 30 is It is preferable that the ratio (H _a /W _a ) of the projection height H _a along the front direction is 0.3 or more and 0.45 or less. According to the unit optical element 50 as described above, due to refraction and reflection on the light exit side surface 51, an excellent light gathering function is exhibited for the light component along the arrangement direction (second direction) of the unit optical element 50. and effectively suppress the generation of side lobes.

In addition, the “pentagonal shape” in the present specification includes not only a strictly pentagonal shape but also a substantially pentagonal shape that includes limitations in manufacturing technology, errors during molding, and the like. Similarly, terms specifying other shapes and geometrical conditions used herein, such as terms such as "parallel", "perpendicular" and "symmetrical", are not bound by a strict meaning. The same optical function will be interpreted including the degree of error that can be expected.

Here, as an example, the dimensions of the light guide plate 30 can be set as follows. First, as a specific example of the unit optical element 50, the width W _a (see FIG. 7) can be 10 μm or more and 500 μm or less. On the other hand, the thickness of the base 40 can be 0.2 mm to 6 mm.

The light guide plate 30 configured as described above can be produced by molding the unit optical elements 50 on a substrate or by extrusion molding. Various materials can be used as materials for forming the base portion 40 of the light guide plate 30 and the unit optical elements 50 . In particular, 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, polystyrene, polycarbonate, A transparent resin containing one or more of polyethylene terephthalate, polyacrylonitrile, etc. as a main component, and an epoxy acrylate- or urethane acrylate-based reactive resin (ionizing radiation curable resin, etc.) can be suitably used. A diffusion component having a function of diffusing light can be added to the light guide plate 30 as necessary. As an example of the diffusing component, particles made of a transparent material such as silica (silicon dioxide), alumina (aluminum oxide), acryl, polycarbonate, and silicone having an average particle size of about 0.5 to 100 μm can be used.

When the light guide plate 30 is manufactured by curing an ionizing radiation curable resin on a base material, a sheet-like land portion positioned between the unit optical elements 50 and the base material is formed together with the unit optical elements 50. , may be formed on the substrate. In this case, the base portion 40 is composed of a base material and a land portion formed of an ionizing radiation curable resin. Also, as the substrate, a plate made of a resin material that is extruded together with the light diffusion particles can be used. On the other hand, in the light guide plate 30 manufactured by extrusion molding, the base 40 and the plurality of unit optical elements 50 on one side surface 41 of the base 40 can be integrally formed.

Next, mainly with reference to FIGS. 2, 4, and 8 to 11, the optical sheet (prism sheet) 60 will be described in further detail. The optical sheet 60 is a member having a function of changing the traveling direction of transmitted light.

As shown well in FIG. 8, the optical sheet 60 includes a plate-shaped body portion 65 and a plurality of unit prisms (unit shape elements, unit prisms) formed on the light incident side surface 67 of the body portion 65 . and an optical element (unit lens) 70 . The body portion 65 is configured as a plate-like member having a pair of parallel main surfaces. A light exit surface 61 of the optical sheet 60 is formed by the light exit side surface 66 of the body portion 65 located on the side not facing the light guide plate 30 .

Next, the unit prism 70 provided on the light incident side surface of the body portion 65 will be described. 2 and 8, the plurality of unit prisms 70 are arranged side by side on the light incident side surface 67 of the body portion 65. As shown in FIG. Each unit prism 70 is formed in a columnar shape and extends in a direction intersecting the arrangement direction.

In this embodiment, each unit prism 70 extends linearly. Each unit prism 70 is formed in a columnar shape and has the same cross-sectional shape along its longitudinal direction. Furthermore, the plurality of unit prisms 70 are arranged without gaps on the light incident side surface 67 of the main body 65 along the direction orthogonal to the longitudinal direction. Therefore, the light incident surface 62 of the optical sheet 60 is formed by the surfaces (prism surfaces) 71 and 72 of the unit prisms 70 arranged without gaps on the main body portion 65 . As shown in FIG. 8, the plurality of unit prisms 70 are arranged in the third direction _d3 (prism arrangement direction). Each unit prism 70 extends linearly in a fourth direction _d4 orthogonal to the third direction _d3 , which is the arrangement direction.

As described above, the optical sheet 60 is arranged so as to overlap the light guide plate 30 so that the unit prisms 70 of the optical sheet 60 face the light exit surface 31 of the light guide plate 30 . In the example shown in FIG. 4, the optical sheet 60 has the longitudinal direction (fourth direction d ₄ ) of the unit prisms 70 aligned with the light guiding direction of the light guide plate 30 (the light entrance surface 33 of the light guide plate 30 and the light entrance surface). It is positioned with respect to the light guide plate 30 so as to intersect the first direction _d1 connecting the opposing opposite surface 34 . Also, the third direction _d3 , which is the arrangement direction of the unit prisms 70, is arranged parallel to or inclined with respect to the first direction _d1 , which is the light guiding direction. Notably, in the example shown in FIG. 4, the third direction _d3 is inclined at an angle of less than 45° with respect to the first direction _d1 . As will be described later, when such an optical sheet 60 is used, the direction in which the luminance peak occurs can be controlled in various directions by inclining the third direction _d3 with respect to the first direction _d1 . can. However, the arrangement is not limited to this example, and the third direction _d3 , which is the arrangement direction of the unit prisms 70, may be parallel to the first direction _d1 , which is the light guiding direction.

As shown well in FIG. 9, each unit prism 70 has a first prism surface 71 and a second prism surface 71 arranged to face each other along the arrangement direction of the unit prisms 70, that is, along the third direction _d3 . It has a face 72 . The first prism surface 71 of each unit prism 70 is positioned on one side in the third direction _d3 (the left side in the plane of FIG. 9), and the second prism surface 72 is positioned on the other side in the third direction _d3 (FIG. 9). on the right side of the paper). In the cross section of the surface light source device 20 along the main cutting plane of the light guide plate 30 shown in FIGS. 1, 2, 10 and 11, one side of the third direction _{d3 is} one side and the other side in the third direction _d3 becomes the other side in the first direction _d1 .

More specifically, the first prism surface 71 of each unit prism 70 is located on the side of the light source 24 in the third direction _d3 and faces one side (light source side) in the first direction _d1 . The second prism surface 72 of each unit prism 70 is located on the side away from the light source 24 in the third direction _d3 and faces the other side (the side opposite to the light source) in the first direction _d1 . As will be described later, the first prism surface 71 mainly advances into the light guide plate 30 from the light source 24 arranged on one side in the first direction _d1 , and then the light emitted from the light guide plate 30 passes through the optical sheet 60. It functions as an incident surface when incident on. On the other hand, the second prism surface 72 has a function of reflecting the light incident on the optical sheet 60 and correcting the optical path of the light.

As best shown in FIG. 9, the first prism surface 71 and the second prism surface 72 extend from the body portion 65 and are connected to each other. A base end portion 75b of the unit prism 70 is defined at a position where the first prism surface 71 and the second prism surface 72 are connected to the body portion 65, respectively. In addition, a tip (apex) 75a of the unit prism 70 protruding from the main body 65 to the light incident side is defined at the position where the first prism surface 71 and the second prism surface 72 are connected to each other.

As described above, as shown in FIG. 9, the normal direction nd to the sheet surface of the body portion 65 (the light incident side surface 67 of the body portion 65 and the sheet surface of the optical sheet 60) and the arrangement direction of the unit prisms 70 are The cross-sectional shape of each unit prism 70 in a cross-section parallel to both of the third directions _d3 (hereinafter also referred to simply as the main cross-section of the optical sheet) extends linearly in the longitudinal direction of the unit prism 70. direction).

The cross-sectional shape of the unit prism 70 on the main cutting plane of the optical sheet will be described in more detail below. Note that FIG. 9 shows a cross section of the optical sheet along line IX-IX in FIG. 8, which corresponds to the main cross section of the optical sheet. On the other hand, FIGS. 10 and 11 show the light guide plate 30 and the optical sheet 60 in a cross section parallel to the main cutting plane of the light guide plate. As shown in FIG. 9, in the present embodiment, the cross-sectional shape of each unit prism 70 on the main cut surface of the optical sheet tapers toward the light incident side (light guide plate side). there is In other words, the width of the unit prism 70 parallel to the sheet surface of the body portion 65 on the main cutting plane decreases as the distance from the body portion 65 increases along the normal direction nd of the body portion 65 .

In the present embodiment, the second prism surface 72 forming part of the outer contour of the unit prism 70 (the second prism surface 72 forming part of the light incident side surface) on the main cut surface of the optical sheet 60 is oriented in the third direction. Assuming that the angle formed with respect to _d3 is the tilt angle θ _t , the tilt angle θ _t of at least one unit prism 70 is not constant within the second prism surface 72 . As shown in FIG. 9, the inclination angle θ _t ranges from the distal end portion 75a of the unit prism farthest from the main body portion 65 to the proximal end of the unit prism 60 closest to the main body portion 65 in the second prism surface 72. It changes so as to become larger toward the portion 75b. As shown in FIGS. 10 and 11, according to such a unit prism 60, relatively rising light L101 traveling in a direction in which the angle of inclination with respect to the front direction nd of the second prism surface 72 is relatively small. , L111 are mainly incident thereon, and the tip is mainly incident on the relatively oblique lights L102 and L112 traveling in a direction in which the angle of inclination with respect to the front direction nd is very large. An excellent condensing function can be ensured in both regions on the side of the portion 75a. That is, the light emitted from one unit prism 70 travels in a direction within a narrower angular range.

As a specific configuration, the inclination angle θ _t with respect to the third direction _d3 on the main cut surface of the optical sheet gradually increases from the tip end portion 75a side toward the base end portion 75b side of the unit prism 70. It includes n (n is a natural number of 2 or more) element surfaces 73, ie, a plurality of element surfaces. In the illustrated embodiment, the contour of the second prism surface 72 of the unit prism 70 is formed by connecting straight line portions, or by connecting the straight line portions and chamfering the joints on the main cutting surface of the optical sheet. It has a different shape. In other words, the outer contour of the second prism surface 72 of the unit prism 70 is formed in the shape of a polygonal line or in a shape obtained by chamfering the corners of the polygonal line. Especially in the illustrated example, the second prism surface 72 has a first element surface 73a defining the tip portion 75a and a second element surface 73b adjacent to the first element surface 73a from the body portion 65 side. have. As shown in FIG. 9, the inclination angle θ ₁ of the first element surface 73a is smaller than the inclination angle θ ₂ of the second element surface 73b. However, the second prism surface 72 is not limited to this example, and may have three or more element surfaces 73, may be a curved surface, or may be a single flat surface (single element surface). face).

As described above, the inclination angles θ _t , θ ₁ , and θ ₂ are defined so that the light incident side surface (second prism surface 72) of the unit prism 70 is in the third direction _d3 on the main cutting surface of the optical sheet 60. It is the angle to make. The angle formed between each element surface 73 forming the polygonal line and the third direction _d3 (strictly speaking, the smaller angle (minor angle) of the two formed angles) is the inclination angle. θ _t , θ ₁ , θ ₂ .

In the optical sheet 60 having the above configuration, the width W _b (see FIG. 9) of the unit prisms 70 along the arrangement direction of the unit prisms 70 on the main cut surface of the optical sheet is The ratio of the unit prism 70 to the height _Hb along the normal direction nd of the main body 65, that is, the aspect ratio ( _Wb / _Hb ) of the second prism surface 72, and the second prism surface 72 The inclination angle θ _t of each element surface 73 formed affects the light-collecting property of the optical sheet 60 and the direction in which the light should be collected, in other words, the direction in which the luminance peak occurs. As shown in FIG. 10, the directions of travel of emitted light beams L101 and L102, which are emitted from the light exit surface 31 of the light guide plate 30 in a direction inclined from the front direction nd to the first direction _d1 , which is the light guiding direction, are returned to the front direction nd. The aspect ratio (W _b /H _b ) of the unit prism 70 is set to 1.15 or more and 1.5 or less in order to produce the luminance peak in a direction inclined with respect to the first direction _d1 . Furthermore, it is preferable to set the inclination angle θ ₁ of the first element surface 73a to 38° or more and 53° or less and the inclination angle θ ₂ of the second element surface 73b to 43° or more and 57° or less. On the other hand, as shown in FIG. 11, the direction of travel of emitted light beams L111 and L112, which are emitted from the light exit surface 31 of the light guide plate 30 in a direction inclined from the front direction nd to the first direction _d1 , which is the light guiding direction, is defined as the front direction nd. in order to generate the luminance peak in a direction inclined with respect to the first direction _d1 , the aspect ratio (W _b /H _b ) of the unit prism 70 should be 1.1 or more and 1.50 Further, it is preferable that the inclination angle θ ₁ of the first element surface 73a is 53° or more and 68° or less, and the inclination angle θ ₂ of the second element surface 73b is 59° or more and 72° or less.

Therefore, according to the optical sheet 60 having the above configuration, the second prism surface 72 is inclined with respect to the direction perpendicular to the light emitting surface 21, so that the normal direction to the light emitting surface 21 and the prism arrangement direction , the light incident on the first prism surface 71 from the light guide plate 30 and reflected by the second prism surface 72 can be tilted from the direction perpendicular to the light emitting surface 21 and emitted. Further, the prism arrangement direction is inclined with respect to the first direction _d1 , and each unit prism 70 linearly extends in a direction inclined with respect to a direction perpendicular to the first direction _d1 , thereby When the optical sheet 60 is viewed along the normal direction of , the light incident on the first prism surface 71 from the light guide plate 30 and reflected by the second prism surface 72 is tilted from the direction parallel to the first direction _d1 . light can be emitted in the desired direction. As a result, it is possible to emit light with an angular distribution having a peak luminance in an arbitrary direction of the light emitting surface 21 .

As an example, the dimensions of the optical sheet 60 can be set as follows. First, as a specific example of the unit prisms 70 configured as described above, the arrangement pitch of the unit prisms 70 along the prism arrangement direction _d3 (corresponding to the width _Wb of the unit prisms 70 in the illustrated example) is 10 μm. It can be set to 200 μm or more. In recent years, however, the arrangement of the unit prisms 70 is rapidly becoming finer, and it is preferable that the arrangement pitch of the unit prisms 70 along the prism arrangement direction _d3 is 10 μm or more and 35 μm or less. Similarly, the width _Wb2 of the second prism surface 72 of the unit prism 70 along the prism arrangement direction _d3 can be set to 5 μm or more and 100 μm or less, and considering recent trends, it is possible to set it to 5 μm or more and 20 μm or less. can. Further, the projection height _Hb of the unit prisms 70 from the main body 65 along the normal direction nd to the sheet surface of the optical sheet 60 can be set to 5.5 μm or more and 180 μm or less.

The optical sheet 60 configured as described above can be produced by molding the optical sheet 60 on a substrate or by extrusion molding. Various materials can be used as materials for forming the main body portion 65 of the optical sheet 60 and the unit prisms 70 . In particular, 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, polystyrene, polycarbonate, A transparent resin containing one or more of polyethylene terephthalate, polyacrylonitrile, etc. as a main component, and an epoxy acrylate- or urethane acrylate-based reactive resin (ionizing radiation curable resin, etc.) can be suitably used.

When the optical sheet 60 is produced by curing the ionizing radiation curable resin on the base material, the unit prisms 70 and the sheet-like lands positioned between the unit prisms 70 and the base material are placed on the base material. It may be formed on the material. In this case, the body portion 65 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 60 manufactured by extrusion molding, the body portion 65 and the plurality of unit prisms 70 on the light incident side surface 67 of the body portion 65 can be integrally formed.

By the way, in the present embodiment, in the angular distribution of luminance in all directions in which light is emitted from the display surface 11, the luminance in at least one direction inclined by 40° from the direction in which the peak luminance is obtained is 6.5 times the peak luminance. % or less. As confirmed by the inventors of the present invention, the peak luminance can be increased with such luminance characteristics. Further, from the viewpoint of increasing the peak luminance more stably, the luminance in at least one direction inclined by 40° from the direction in which the peak luminance is obtained should be 5.5% or less of the peak luminance. more preferred.

Such luminance characteristics can be realized by changing the shape, each dimension, etc. within the above-described range, for example, in the configuration of the display device described above. That is, it can be realized by providing an adhesive layer for bonding the display panel to the surface light source device, and changing the shape and each dimension within the above range, for example.

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

First, as shown in FIGS. 1 and 2 , light emitted by the light emitter 25 forming the light source 24 enters the light guide plate 30 through the light entrance surface 33 . As shown in FIG. 2, the lights L21 and L22 incident on the light guide plate 30 are reflected at the light exit surface 31 and the back surface 32 of the light guide plate 30, particularly due to the difference in refractive index between the material forming the light guide plate 30 and air. , and travels in the first direction (light guide direction) _d1 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 inclined so as to approach the light exit surface 31 from the light entrance surface 33 toward the opposite surface 34 . The inclined surfaces 37 are connected via a stepped surface 38 and a connecting 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 that travels from the light incident surface 33 side to the opposite surface 34 side in the light guide plate 30 does not enter the step surface 38 of the back surface 32 , and passes through the inclined surface 37 or the connection surface 39 . become reflective. When the light is reflected by the inclined surface 37 of the back surface 32, the traveling direction of the light in the cross section shown in FIG. That is, when the light is reflected by the inclined surface 37 of the back surface 32, the incident angle of the light to the light exit surface 31 and the back surface 32 becomes small thereafter. Therefore, the angle of incidence of light traveling through the light guide plate 30 on the light exit surface 31 and the rear surface 32 gradually decreases due to one or more reflections on the inclined surface 37 of the rear surface 32, and becomes less than the critical angle for total reflection. Become. In this case, the light can be emitted from the light exit surface 31 and the back surface 32 of the light guide plate 30 . Lights L21 and L22 emitted from the light exit surface 31 travel toward the optical sheet 60 arranged on the light exit side of the light guide plate 30 . On the other hand, the light emitted from the rear surface 32 is reflected by the reflective 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 37 in the back surface 32 increases as the opposite surface 34 is approached from the light incident surface 33 along the first direction _d1 , which is the light guiding direction. there is More specifically, the inclined surfaces 37 are arranged at a constant pitch Ps in the first direction _d1 , and the length of each inclined surface 37 along the first direction _{d1 is} It gradually becomes longer from one side to the other. As a result, a sufficient amount of light emitted from the light exit surface 31 of the light guide plate 30 is ensured in a region away from the light entrance surface 33 where the amount of emitted light tends to decrease, and the amount of emitted light is uniform along the light guide direction. can be improved.

By the way, the light exit surface 31 of the light guide plate 30 shown in the figure is composed of a plurality of unit optical elements 50, and the cross-sectional shape of each unit optical element 50 on the main cutting plane is a pentagon or It has a shape obtained by chamfering one or more corners of the pentagonal shape. More specifically, as described above, the light exit surface 31 of the light guide plate 30 is configured as a bent surface inclined with respect to the back surface 32 of the light guide plate 30 (see FIG. 7). The bent surfaces are slanted surfaces 35 and 36 that are slanted in opposite directions with respect to the normal direction nd to the light output side surface 41 of the base 40 . The light traveling through the light guide plate 30 after being totally reflected by the inclined surfaces 35 and 36 and the light emitted from the light guide plate 30 after passing through the inclined surfaces 35 and 36 are divided into the following from the inclined surfaces 35 and 36: It comes to have the effect of explaining. First, the action exerted on the light traveling through the light guide plate 30 after being totally reflected by the inclined surfaces 35 and 36 will be described.

In FIG. 7, the optical paths of the lights L71 and L72 traveling through the light guide plate 30 while repeating total reflection on the light exit surface 31 and the back surface 32 are shown in the main cross section of the light guide plate. As described above, the inclined surfaces 35 and 36 forming the light exit surface 31 of the light guide plate 30 include two types of surfaces inclined in opposite directions across the normal direction nd to the light exit side surface 41 of the base 40. . The two types of inclined surfaces 35 and 36 inclined in opposite directions are alternately arranged along the second direction _d2 . As shown in FIG. 7, in most cases, the light beams L71 and L72 that travel through the light guide plate 30 toward the light exit surface 31 and enter the light exit surface 31 are guided by one of the two types of inclined surfaces 35 and 36. In the main cutting plane of the light plate, the light is incident on an inclined surface inclined in the opposite direction to the traveling direction of the light with reference to the normal direction nd to the light emitting side surface 41 of the base 40 .

As a result, as shown in FIG. 7, the light beams L71 and L72 traveling through the light guide plate 30 are totally reflected by the inclined surfaces 35 and 36 of the light exit surface 31. In many cases, the components along the second direction _d2 are reduced. Furthermore, the direction of travel on the main cutting plane is directed to the opposite side centering on the front direction nd. In this manner, the inclined surfaces 35 and 36 forming the light exit surface 31 of the light guide plate 30 restrict the light emitted radially from a certain light emitting point from continuing to spread in the second direction _d2 . That is, the light emitted from the light emitter 25 of the light source 24 in a direction greatly inclined with respect to the first direction _d1 and entering the light guide plate 30 is also restricted from moving in the second direction _d2 , and is mainly directed to the first direction. It will proceed in direction _d1 . Thereby, the light amount distribution along the second direction _d2 of the light emitted from the light emitting surface 31 of the light guide plate 30 is adjusted by the configuration of the light source 24 (for example, the arrangement of the light emitters 25) and the output of the light emitters 25. It is possible to do

Next, the action exerted on the light emitted from the light guide plate 30 after passing through the light emitting surface 31 will be described. As shown in FIG. 7 , lights L71 and L72 emitted from the light guide plate 30 through the light exit surface 31 are refracted at the light exit side surfaces of the unit optical elements 50 forming the light exit surface 31 of the light guide plate 30 . Due to this refraction, the traveling direction (emission direction) of the light beams L71 and L72 traveling in a direction inclined from the front direction nd on the main cross section is mainly compared to the traveling direction of the light beams passing through the light guide plate 30. It is bent so that the angle formed with respect to the front direction nd becomes smaller. With such an action, the unit optical element 50 can narrow the traveling direction of the transmitted light toward the front direction nd with respect to the light component along the second direction _d2 orthogonal to the light guide direction. That is, the unit optical element 50 exerts a condensing action on light components along the second direction _d2 orthogonal to the light guiding direction. In this way, the emission angle of the light emitted from the light guide plate 30 is narrowed down within a narrow angle range centered on the front direction in the plane parallel to the arrangement direction of the unit optical elements 50 of the light guide plate 30 .

As described above, the emission angle of the light emitted from the light guide plate 30 is narrowed down within a narrow angle range centered on the front direction nd on the plane parallel to the arrangement direction of the unit optical elements 50 of the light guide plate 30. On the other hand, the emission angle of the light emitted from the light guide plate 30 is, as shown in _FIG . (Light guide direction) In a plane parallel to _d1 , a relatively large exit angle _θk is obtained, which 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. 2 )) results in a relatively large angle. In particular, in the present embodiment, the back surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 37 arranged in the first direction _d1 , and each inclined surface 37 extends from one side in the first direction _d1 . It is inclined with respect to the normal direction nd of the light guide plate 30 and the first direction _d1 so as to approach the light exit surface 31 toward the other side. As a result, as shown in FIG. 2, in a plane parallel to the first direction (light guide direction) _d1 , the direction of emission from the light guide plate 30 is inclined at a relatively large angle from the front direction nd. There is a tendency to bias within a narrow angular range of θ _k .

For example, in the light guide plate 30 having the shape and dimensions exemplified above, the light exit 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 , the angle θ _aImax1 at which the direction in which the luminance peak is obtained is inclined from the normal direction nd of the light guide plate 30 to the other side (the opposite surface 34 side) along the first direction d ₁ , and The direction in which half the brightness of the brightness peak located between the normal direction nd of the light guide plate 30 and the direction in which the brightness peak is obtained is _one side ( The angle _θaIα1 inclined toward the light incident surface 33 side) can be set within a range that satisfies the following conditions (1) and (2), more preferably conditions (1′) and (2′).
60°≦ _θaImax1 ≦80° (1)
5°≦ _θaIα1 ≦25° (2)
70°≦ _θaImax1 ≦80° (1′)
5°≦ _θaIα1 ≦15° (2′)

In addition, in the light guide plate 30 having the shape and dimensions exemplified above, a luminance peak is obtained in the angular distribution of luminance on the light exit surface 31 of the light guide plate 30 in each direction within the main cross section of the light guide plate 30. The magnitude of the angle θ _aImax2 that the direction forms with the normal direction nd of the light guide plate 30, and the directions that are located on both sides of the direction in which the luminance peak is obtained and in which half the luminance of the luminance peak is obtained are the directions in which the luminance peak is obtained. The average value θ _aIα2 (=(θ _aIα2x +θ _aIα2y )/2) of the magnitude of the angle tilted from the obtained direction can be set within the following range.
0°≦ _θaImax2 ≦3° (3)
12°≦ _θaIα2 ≦27° (4)

The light emitted from the light guide plate 30 then enters the optical sheet 60 . As described above, the optical sheet 60 has the unit prisms 70 with the tip portions 75a protruding toward the light guide plate 30 side. As shown well in FIG. 4, the longitudinal direction of the unit prism 70 extends in a fourth direction d4 intersecting with the light guiding direction (first direction) _d1 of the light guide plate 30. As shown in FIG. 4, the inclined surface 37 of the light guide plate 30 is indicated by a dotted line, and the unit prisms 70 of the optical sheet 60 are indicated by a chain line.

As a result, the lights L21 and L22 emitted by the light source 24 arranged on one side in the first direction _d1 (the left side in the paper surface of FIG. 2) and traveling to the optical sheet 60 via the light guide plate 30 are connected to each other. The light enters the unit prism 70 through the first prism surface 71 located on one side of the first prism surface 71 and the second prism surface 72 on the light source 24 side in the first direction _d1 . As shown in FIG. 2, the lights L21 and L22 are then totally reflected by the second prism surface 72 located on the other side (the right side in the plane of FIG. ₂ ) opposite to the light source in the first direction d1. to change its direction of travel.

Then, due to total reflection on the second prism surface 72 of the unit prism 70, the main cut surface (first direction (light guide direction) _d1 and front direction nd of the optical sheet shown in FIG. 10 or 11) ), the lights L101, L102, L111, and L112 traveling in directions greatly inclined from the front direction nd are bent so that the angles formed by the traveling directions with respect to the front direction nd become smaller. With such an action, the unit prism 70 can narrow down the traveling direction of the transmitted light along the first direction (light guide direction) _d1 to a direction inclined from the front direction nd. That is, the optical sheet 60 exerts a condensing action on the light component along the first direction _d1 in a direction inclined from the front direction nd.

The light whose traveling direction is greatly changed by the unit prisms 70 of the optical sheet 60 in this way is mainly the component traveling in the first direction _d1 , which is the arrangement direction of the unit prisms 70, and is the unit of the light guide plate 30. It differs from the component traveling in the second direction d ₂ that is focused by the slanted surfaces 35 , 36 of the optical element 50 . Therefore, the optical action of the unit prisms 70 of the optical sheet 60 does not impair the luminance at the angle showing the luminance peak raised by the unit optical elements 50 of the light guide plate 30, and furthermore, at the angle showing the luminance peak brightness can be improved.

In the present embodiment, each unit prism 70 has a first prism surface 71 facing one side in the third direction _d3 and serving as an incident surface for light emitted from the light emitting surface 31 of the light guide plate 30; and a second prism surface 72 that faces the other side of _d3 and totally reflects the light that has passed through the first prism surface 71 and entered the unit prism 70 . The light collection function of the unit prism 70 is based on the total reflection function on the second prism surface 72 . Therefore, the optical sheet 60 can greatly change the traveling direction of light and can adjust the condensing direction with a high degree of freedom. In the example shown in FIG. 10, the direction of travel of the outgoing light beams L101 and L102, which are emitted from the light exit surface 31 of the light guide plate 30 in a direction inclined from the front direction nd to the first direction _d1 , which is the light guiding direction, is set to the front direction nd. The luminance peak is generated in a direction inclined with respect to the first direction _d1 . On the other hand, in the example shown in FIG. 11, the direction of travel of the outgoing light beams L101 and L102 that are emitted from the light exit surface 31 of the light guide plate 30 in a direction inclined from the front direction nd to the first direction _d1 , which is the light guiding direction, is set to the front direction. By varying beyond the direction nd, a luminance peak is produced in a direction oblique to the first direction _d1 . According to the surface light source device 20 having such an optical sheet 60, a luminance peak on the light emitting surface 21 can be generated in a direction other than the front direction with a simple configuration.

The light emitted from the optical sheet 60 forming the light emitting surface 21 of the surface light source device 20 then travels toward the display panel 15 as shown in FIG. One of the polarized light components of the light incident on the liquid crystal display panel 15 is 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, in the present embodiment, an adhesive layer 17 is provided to join the display panel 15 to the surface light source device 20 . In the illustrated example, the adhesive layer 17 joins the display panel 15 and the optical sheet 60 . Therefore, the light emitted from the optical sheet 60 travels through the adhesive layer 17 to the display panel 15 . When the display panel 15 and the surface light source device 20 are bonded by the adhesive layer 17, there is no interface with a large refractive index difference, typically with air, between the display panel 15 and the surface light source device 20. Therefore, the reflection at the interface is reduced. As the interface reflection is reduced, the reflected light passes through the light guide plate 30 and is reflected by the reflection sheet 28, and the light emitted again through the light guide plate 30 and the optical sheet 60 is reduced. The emission angle of the light that is once reflected at the interface and is emitted from the optical sheet 60 again differs from the emission angle of the light that is emitted from the optical sheet 60 without being reflected at the interface. That is, the light that is once reflected at the interface and is emitted from the optical sheet 60 again is emitted from the optical sheet 60 in a direction different from the direction in which the optical sheet 60 is expected to condense the light. Therefore, by reducing interface reflection with the adhesive layer 17, it is possible to avoid large diffusion of the light traveling from the surface light source device 20 to the display panel 15. FIG. Thereby, the peak luminance on the display surface 11 of the display device 10 can be effectively improved, and a bright image can be displayed in a preset desired direction. Particularly, in the display device 10 of the present embodiment, the image light is collected in an intended desired direction by effectively suppressing the diffusion of the image light. In other words, it is possible to brightly observe an image from a desired direction by improving the utilization efficiency of light from the light source without increasing the output of the light source, which is extremely preferable from the viewpoint of energy saving.

As described above, the angle of incidence of the light traveling through the light guide plate 30 on the light exit surface 31 and the back surface 32 decreases each time the light is reflected on the light exit surface 31 or the back surface 32 . The light whose incident angle to the back surface 32 is small is emitted from the back surface 32 and specularly reflected by the reflection sheet 28 . The light that is specularly reflected and travels through the light guide plate 30 again has a small angle of incidence on the rear surface 32 , so the angle of incidence on the light exit surface 31 is also small. Therefore, the light reflected by the reflective sheet 28 and re-entering the light guide plate 30 has a total reflection angle less than the critical angle at the light exit surface 31 and is likely to emerge from the light exit surface 31 . In addition, when the diffuse reflection of the reflection sheet 28 is suppressed, the diffusion of the light re-entering the light guide plate 30 is suppressed. In addition, the diffusion of light emitted from the display surface 11 can be suppressed, and the peak luminance can be increased. In particular, when the diffuse reflectance of the reflective sheet 28 was set to 18.3% or less, the peak luminance could be increased to a visually perceptible level in general display applications.

In addition, in the display device 10 described here, the display panel 15, the surface light source device 20 arranged on the back side of the display panel 15 and planarly illuminating the display panel 15 from the back side, and the display panel 15 as a surface light source. and an adhesive layer 17 that bonds to the device 20 . In the angular distribution of luminance in all directions of the light emitted from the display surface 11 of the display device 10, the luminance in at least one direction inclined by 40° from the direction in which the peak luminance is obtained is 6.5% of the peak luminance. It is below. At a brightness of 6.5% or less of the peak luminance, an image is displayed so dark that it is difficult to recognize it as an image in normal observation, but in normal observation of a display device, the image is displayed. It is rare to change the angle by 40° or more at a time, and therefore, the degree of such diffusion is important not only from the viewpoint of effective use of light from the light source, but also from the perspective of the generation of double images (ghosts) in unintended directions. It is also effective from the viewpoint of prevention.

Here, FIGS. 12a and 13a are graphs obtained by actually manufacturing a plurality of samples of the display device 10 and confirming the performance thereof. The vertical axis in FIG. 12a represents the normalized luminance (relative luminance) when the maximum luminance is 1, and the vertical axis in FIG. 13a represents the measured luminance (absolute luminance). The horizontal axes in FIGS. 12a and 13a represent the angle [°] formed by the direction in which the luminance was measured with respect to the front direction. The measurement angle [°] on the horizontal axis is a negative number when the direction in which the luminance is measured is inclined from the front direction to one side in the first direction d ₁ , and the direction in which the luminance is measured is from the front direction to the first direction d A positive number indicates the case of tilting to the other side in ₁ . A sample of each display device 10 was configured to have the same configuration as the examples of FIGS. 1 to 11 described above. However, the arrangement direction _d3 of the unit prisms 70 and the light guide direction _d1 in the light guide plate 30 were made parallel. The unit prisms 70 of the optical sheet 60 and the surface light source device 20 are designed so that the peak luminance occurs in the front direction. On the other hand, as the display panel 15, a liquid crystal display panel incorporated in the display device 10 mounted on a commercially available automobile is adopted. Therefore, the light emitted from each display device 10 has frontal peak luminance.

The surface light source device 20 and the display panel 15 were common among samples 1 to 5 of the display device 10 . In each sample, the diffuse reflectance was changed by changing the material, surface shape, etc. of the reflection sheet 28 . Specifically, the diffuse reflectance of the reflective sheet 28 is 1.6% (sample 1), 1.7% (sample 2), 18.3% (sample 3), 20% (sample 4), 84.0% (sample 4), 1.6% (sample 1), 1.7% (sample 2), 18.3% (sample 3). 2% (Sample 5). Note that Sample 5 uses a conventional white scattering reflective sheet as the reflective sheet 28 .

FIG. 12b is an enlarged graph showing relative luminance in the vicinity of a direction inclined 40° from the front direction of FIG. 12a. Note that in FIG. 12b the relative luminance of sample 5 is not shown as it is too large. As can be seen from FIG. 12b, the relative luminance of each sample in the direction tilted at an angle of 40° from the front direction is 5.30% for sample 1, 5.37% for sample 2, and 6.47% for sample 3. , 7.12% for sample 4 and 17.5% for sample 5. As understood from each sample, when the diffuse reflectance of the reflection sheet 28 is 18.3% or less, the relative luminance in the direction inclined at an angle of 40° from the front direction is It can be 6.5% or less.

FIG. 13b is an enlarged graph showing the absolute luminance near the maximum luminance in FIG. 13a. Note that in FIG. 13b, the absolute luminances of samples 1 and 2 are shown to match. As can be seen from FIG. 13b, comparing sample 3 and sample 5, sample 3 had a 17% increase in brightness in the front direction.

Further, FIG. 14 shows the relationship between the diffuse reflectance of the diffusion sheet and the optical adhesion. Those with optical contact are marked with x, and those with no optical contact are marked with ◯. As shown in FIG. 14, in sample 1 having a diffuse reflectance of less than 1.7%, the reflection sheet 28 and the light guide plate 30 are optically adhered. In comparison between Sample 1 and Sample 2, if the diffuse reflectance of the reflective sheet 28 is less than 1.7%, uneven brightness occurs or the brightness on the other side of the first direction _d1 is lower than that on the one side. A problem arose. This is probably because, in sample 1, the reflection sheet 28 and the light guide plate 30 are optically adhered to each other, and the light reflected by the optically adhered portion is emitted in a direction outside the original optical design.

The display device 10 according to the present embodiment can be used for various purposes, but it is assumed that the display device 10 is used as an in-vehicle display device. Passengers in a vehicle observe the on-board display device from a generally fixed direction, but due to space limitations within the vehicle, the direction of observation of the on-board display device by the passenger is usually limited to the display surface of the display device. is inclined with respect to the normal direction of Therefore, it is desired that the light is strongly emitted in directions other than the front direction. That is, the display device 10 and the surface light source device 20 of the present embodiment, which can set the direction in which the luminance peak occurs with a simple configuration to a direction other than the front direction, are suitable for vehicle-mounted display devices, more specifically, display devices. It is particularly suitable for an in-vehicle center console using a display device, an in-vehicle rearview mirror using a display device, an in-vehicle side mirror using a display device, an instrument panel and the like. By controlling the emission direction of the image light, it is possible to brightly display the image to the passenger while preventing the passenger from observing the reflection of the image on the windshield or the like due to the light.

However, the display device 10 according to the present embodiment is not limited to an automobile, and can be placed in a place where observation is performed through a transparent plate such as glass, such as when observing the outside from the inside of a vehicle. can be assumed.

As described above, the display device 10 of the present embodiment is a vehicle-mounted display device having the display surface 11, and includes the display panel 15 and the display panel 15 arranged on the back side of the display panel 15. and an adhesive layer 17 for bonding the display panel 15 to the surface light source device 20, and peak luminance is obtained in the angular distribution of luminance in all directions of the light emitted from the display surface 11. The luminance in at least one direction tilted 40° from the direction is 6.5% or less of the peak luminance. According to such a display device 10, in at least one direction, typically the first direction _d1 , the light is sufficiently condensed in the direction in which the peak luminance is obtained, and the direction in which the peak luminance is obtained is the first direction. In a direction inclined by 40° or more to one side in the direction _d1 , the light becomes difficult to be visually recognized. That is, the peak luminance can be increased without increasing the output of the light source. In other words, it is possible to effectively improve the luminance in a desired direction by improving the utilization efficiency of light from the light source.

Further, the display device 10 of the present embodiment is an in-vehicle display device having a display surface 11, and is arranged on the back side of the display panel 15 and the display panel 15, and the display panel 15 is planarly arranged from the back side. A surface light source device 20 for illuminating light and an adhesive layer 17 for bonding the display panel 15 to the surface light source device 20 are provided. A light guide plate 30 having a side surface positioned between a surface 31 and a back surface 32, a light source 24 arranged to face part of the side surface, and an optical sheet arranged to face the light exit surface 31 of the light guide plate 30. 60, and a reflective sheet 28 arranged to face the back surface 32 of the light guide plate 30, and the diffuse reflectance of the reflective sheet 28 is 18.3% or less. According to such a display device 10, a sufficiently high peak luminance can be obtained, and the luminance in a direction deviated from the direction in which the peak luminance can be obtained can be greatly reduced. That is, the peak luminance can be increased without increasing the output of the light source. In other words, it is possible to effectively improve the luminance in a desired direction by improving the utilization efficiency of light from the light source.

Furthermore, in the display device 10 of the present embodiment, the surface of the reflective sheet 28 on the side facing the back surface 32 of the light guide plate 30 is uneven, and the diffuse reflectance of the reflective sheet 28 is 1.7% or more. is. According to such a display device 10 , it is possible to avoid optical contact between the reflection sheet 28 and the light guide plate 30 due to the uneven surface shape of the reflection sheet 28 . Therefore, it is possible to avoid the occurrence of luminance unevenness and the decrease in brightness in areas far from the light source section.

Further, in the display device 10 of the present embodiment, the reflective sheet 28 has a metal layer 28b and a matte layer 28c laminated on the metal layer 28b. The metal layer 28b contains silver and the matte layer 28c is located closer to the light guide plate 30 than the metal layer 28b. According to such a display device 10, the reflective sheet 28 can significantly increase the peak luminance as compared with a conventional white scattering reflective sheet.

Various modifications can be made to the above-described 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 embodiment are used for the portions that can be configured in the same manner as in the above-described embodiment. omit the description.

For example, as shown in FIG. 15, the back surface 32 of the light guide plate 30 may be inclined so as to approach the light output surface 31 from one side to the other side in the first direction _d1 . That is, the connecting surface 39 may be inclined with respect to a plane normal to the front direction nd. In this case, the inclination angle θx of the inclined surface 37, in other words, the angle of the inclined surface 37 with respect to the surface normal to the front direction nd is the inclination angle θy with respect to the surface of the connecting surface 39 normal to the front direction nd. getting bigger. According to such a light guide plate 30 , the incident angle on the light exit surface 31 can be reduced not only on the inclined surface 37 but also on the connection surface 39 , thereby promoting the light output from the light exit surface 31 . Therefore, the light entering from the light entrance surface 33 can be efficiently emitted from the light exit surface 31, and the light emitted from the opposite surface 34 can be reduced. That is, light can be used efficiently. Moreover, not only the inclined surface 37 but also the light reflected at the connection surface 39 has a smaller incident angle to the light exit surface 31 and the back surface 32, and can be emitted from the light exit surface 31 and the back surface 32 of the light guide plate 30. . Therefore, light can be efficiently emitted from the light exit surface 31 .

As the back surface 32 of the light guide plate 30 is inclined, the surface of the reflection sheet 28 is also inclined. In the example shown in FIG. 15 , the front surface of the reflective sheet 28 is provided so as to be parallel to the back surface 32 of the light guide plate 30 . Therefore, the reflecting sheet 28 is generally configured as a trapezoidal columnar member whose side in the thickness direction is relatively smaller than the other side. Alternatively, although not shown, the reflective sheet 28 is configured as a rectangular parallelepiped member whose sides in the thickness direction are smaller than the other sides, and the reflective sheet 28 as a whole is parallel to the back surface 32 of the light guide plate 30 . It may be provided so as to be inclined.

Although an example of the unit prism 70 of the optical sheet 60 has been described in the above-described embodiment, the present invention is not limited to this example, and various modifications are possible. For example, a plurality of unit prisms 70 may have mutually different configurations. Also, although an example in which the second prism surface 72 includes two element surfaces 73 is shown, the present invention is not limited to this, and the second prism surface 72 may include three or more element surfaces 73 . Furthermore, the cross-sectional shape of the unit prism 70 on the main cutting surface is not limited to the specific example shown in FIG. 8, and may be, for example, a pentagonal shape or a hexagonal shape.

A light diffusing layer (mat layer) having light diffusing particles may be formed on the light exit surface 61 opposite to the surface formed by the unit prisms 70 of the optical sheet 60 . Moreover, the adhesive layer 17 may have a light diffusing function by having light diffusing particles.

Furthermore, although an example of the unit optical element 50 of the light guide plate 30 has been described in the above embodiment, the present invention is not limited to this example, and various modifications are possible. For example, a plurality of unit optical elements 50 included in the light guide plate 30 may have mutually different configurations. Also, the cross-sectional shape of the unit optical element 50 on the main cutting plane is not limited to the specific example shown in FIG. 6, and may be triangular or semicircular, for example.

In the illustrated example, the outer contour 51 (corresponding to the light output surface 31) on the main cutting plane of the unit optical element 50 has a light output surface angle _θa increases from the tip 52a on the outer contour 51 of the unit optical element 50 farthest from the base 40 toward the base 52b on the outer contour 51 of the unit optical element 50 closest to the base 40. Was. However, the light emitting surface angle _θa may change so as to decrease from the distal end portion 52a on the outer contour 51 toward the proximal end portion 52b. Moreover, although an example in which the unit optical element 50 is formed as a convex portion protruding from the base portion 40 has been shown, it is not limited to this example, and may be formed as a recessed portion. Furthermore, the convex portion and the concave portion may be formed on a curved surface, or may be formed including a curved surface and a flat surface. Alternatively, the unit optical element 50 may be formed as a prism. Further, a flat surface may be provided between the distal end portion or the proximal end portion of each unit optical element 50 .

Also, although not shown, in the surface light source device 20, between the light emitting surface of the optical sheet 60 (the light emitting surface 21 of the surface light source device in FIG. 1) and the lower polarizing plate 14 of the liquid crystal display panel 15. , a known reflective polarizer (also called a polarization separation film) may be arranged. In such a form, of the light emitted from the optical sheet 60, only the specific polarized component is transmitted, and the polarized component perpendicular to the specific polarized component is reflected without being absorbed. The polarized light component reflected from the reflective polarizer is reflected by the reflecting sheet 28 or the like to be depolarized (state containing both the specific polarized light component and the polarized light component orthogonal to the specific polarized light component), and then reflected again. incident on the type polarizer. Therefore, the polarized component of the re-entering light that has been converted to the specific polarized component is transmitted through the reflective polarizer, and the polarized component orthogonal to the specific polarized component is reflected again. Thereafter, by repeating the same process, about 70 to 80% of the light initially emitted from the optical sheet 60 is emitted as the light source light having the specific polarization component. Therefore, by positioning the polarization direction of the specific polarization component (transmission axis component) of the reflective polarizer and the transmission axis direction of the lower polarizing plate 14 of the liquid crystal display panel 15, all of the emitted light from the surface light source device 20 can be The liquid crystal display panel 15 can be used for image formation. Therefore, even if the light energy input from the light source 24 is the same, it is possible to form a brighter image than when the reflective polarizer is not arranged. of the power source) will also improve.

Further, although not shown, the surface light source device 20 may include a light diffusion sheet for isotropically diffusing or anisotropically diffusing light. As an example, the light diffusing sheet may be arranged on the most light emitting side of the surface light source device to form the light emitting surface 21 .

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.

Industrial field of application

The display device 10 described above can be applied to the following applications in addition to being applied to an in-vehicle display device.
- Application of the display device of an automatic teller machine (ATM) and the application of the display device to a surface light source device It is possible to prevent prying eyes from the side during operation of the ATM.
・Application to digital signage By changing the orientation of the unit prisms of the optical sheet, the optical system is suitable for the installation location and viewer position of digital signage (also known as electronic billboards, electronic billboards, electronic bulletin boards, etc.). properties can be obtained. Such favorable optical characteristics are, for example, matching the direction of the peak brightness of the emitted light to the direction from the display surface of the digital signage toward the expected viewers, and making the angular distribution of brightness match the expected viewers. For example, it may be set to include the range.
- Application to a display device in a train Since the viewer observes the display device from below, it is preferable to display the image toward the viewer (downward from the installation position). Also, when applied to the position of hanging advertisements, since trains are elongated, it is not necessary to widen the viewing angle in the horizontal direction. Therefore, images can be efficiently displayed to the viewer.
- Application to display devices in security rooms, etc. Each of a large number of display devices can have light output characteristics that match the viewer (security guard) positioned in the center.
・Application to table display The viewer is always positioned at the same relative position to the desk with the built-in display. Therefore, it is possible to set the light output characteristics according to the position of the viewer.
・Application to amusement facilities For example, when the display device of a game machine installed in an arcade, etc., where the positional relationship between the installation position and the user is normally constant, a specific user (observer) can be seen from the display surface. The optical characteristic can be such that the luminance peak direction of the emitted light matches the direction toward .
・Application to lighting The light output characteristics can be appropriately set according to the lighting application and lighting installation position, such as indirect lighting and desk lighting.
・Application of display devices for automatic ticket gates and surface light source devices for such display devices Since the line of sight of a person passing through the ticket gate is limited, the direction of the peak brightness of emitted light is aligned with that position (or the direction of the line of sight). It is desirable to make it a characteristic.
・Application to display device for wrist watch To see from the front, it is necessary to twist the arm, and in many cases, observation is performed from the diagonally downward direction of the wrist watch. Therefore, the brightness peak direction and the brightness angular distribution of the emitted light are set so as to cover the range of directions connecting the position of the wristwatch and the position of the observer's eyes, which are usually frequently used. Moreover, since it is often observed under sunlight, it is desirable to have high brightness.
・Other examples include display devices behind the seats of airplanes, display devices used to explain safety equipment on airplanes, etc., display devices near the ceiling of sightseeing buses, display devices for operation guidance at airports and stations, etc. It can also be applied to at least one display device of a game machine having a plurality of screens (for example, a screen in a horizontal plane and a screen in a vertical plane), a liquid crystal operation panel (keyboard, etc.), and the like.

10 Display device 11 Display surface 12 Liquid crystal layer 13 Upper polarizing plate 14 Lower polarizing plate 15 Liquid crystal display panel 17 Adhesive layer 20 Surface light source device 21 Light emitting surface 24 Light source 25 Light emitter 28 Reflective sheet 28a Support 28b Metal layer 28c Matte layer 28c1 Binder Resin 28c2 Particle 30 Light guide plate 31 Light exit surface 32 Back surface 33 Light entrance surface 34 Opposite surface 35 Inclined surface 35a First surface 35b Second surface 36 Inclined surface 36a First surface 36b Second surface 37 Inclined surface 38 Stepped surface 39 Connection surface 40 Base portion 41 One side surface 42 Other side surface 50 Unit optical element 51 Outer contour 52a Tip portion 52b Base end portion 60 Optical sheet 61 Light exit surface 65 Body portion 70 Unit prism 71 First prism surface 72 Second prism surface 73 Element surface 73a First element Surface 73b Second element surface 75a Distal end 75b Base end

Claims (4)

A display device having a display surface,
a display panel;
a surface light source device disposed on the back side of the display panel and planarly illuminating the display panel from the back side;
and an adhesive layer that bonds the display panel to the surface light source device,
The surface light source device includes a light guide plate having a light output surface, a back surface arranged to face the light output surface, and a side surface located between the light output surface and the back surface, and arranged to face a part of the side surface. an optical sheet arranged to face the light emitting surface of the light guide plate; and a reflective sheet arranged to face the back surface of the light guide plate;
the side surface of the light guide plate has a light incident surface facing the light source and an opposite surface facing the light incident surface along a first direction;
The light guide plate has a plate-shaped base, and a plurality of unit optical elements arranged on one side surface of the base in an arrangement direction that intersects the first direction and forming the light output surface,
each unit optical element extends in a direction intersecting with its arrangement direction,
The optical sheet has a plate-like main body, and a plurality of unit prisms arranged on a surface of the main body facing the light guide plate and facing the light guide plate,
each unit prism extends in a direction intersecting with the arrangement direction of the plurality of unit prisms,
the arrangement direction of the unit prisms is parallel to or inclined at an angle of less than 45° with respect to the first direction;
The reflective sheet has a metal layer and a matte layer laminated on the metal layer,
The metal layer contains silver,
The mat layer is positioned closer to the light guide plate than the metal layer,
The mat layer includes a transparent binder resin and particles held by the binder resin, and has convex portions protruding toward the light guide plate due to the arrangement of the particles,
The diffuse reflectance of the reflecting sheet is 18.3% or less,
In the angular distribution of luminance in all directions of the light emitted from the display surface, the luminance in at least one direction inclined by 40° from the direction in which the peak luminance is obtained is 6.5% or less of the peak luminance. There is a display device. the surface of the reflective sheet on the side facing the back surface of the light guide plate has an uneven shape,
2. The display device according to claim 1, wherein said reflecting sheet has a diffuse reflectance of 1.7% or more. In a cross section parallel to both the normal direction to the one side surface of the base and the arrangement direction, the unit optical element has one side located on the one side surface of the base and the one side surface on the outer contour. Claim 1 or the 3. The display device according to 2. Said one side surface of said base of said unit optical element with respect to width W along said arrangement direction of said unit optical element in a cross section parallel to both the normal direction to said one side of said base and said arrangement direction The display device according to any one of claims 1 to 3, wherein the ratio (H/W) of the height H from the edge is 0.3 or more and 0.45 or less.

Images