JP6008241B2 - Surface light source device and display device - Google Patents

Description

  The present invention relates to a prism sheet, a surface light source device, and a display device, and more particularly to a surface light source device and a display device that can effectively uniformize the in-plane distribution of perceived brightness.

  2. Description of the Related Art A surface light source device having a light emitting surface that emits light in a planar shape is widely used as a backlight that is incorporated in, for example, a liquid crystal display device and illuminates a liquid crystal display panel from the back side (eg, Patent Document 1). Surface light source devices for liquid crystal display devices can be broadly classified into a direct type in which a light source is arranged directly under an optical member and an edge light type in which a light source is arranged on a side of the optical member (also referred to as a side light type). being classified.

  In the edge light type surface light source device, the light source is provided on the side of the light guide plate, and light from the light source enters the light guide plate from the side surface (light incident surface) of the light guide plate. The light incident on the light guide plate is repeatedly reflected on a pair of opposing main surfaces of the light guide plate, and travels in the light guide plate in a direction substantially perpendicular to the light incident surface (light guide direction). The light traveling in the light guide plate receives an optical action from the light guide plate, and is gradually emitted from the pair of main surfaces as it travels in the light guide plate. As an example of a specific configuration of the light guide plate, diffusion components are dispersed in the light guide plate, and each direction of the light guide plate along the light guide direction is changed by changing the traveling direction of the light traveling in the light guide plate by the diffusion component. Light can be emitted little by little from the position.

  Such a surface light source device has been required to ensure high front direction luminance and to make the in-plane distribution of front direction luminance more uniform. That is, it has been considered ideal that the angular distribution of luminance measured at each position on the light emitting surface of the surface light source device has the highest luminance in the front direction and exhibits substantially the same distribution. For example, a display device has been expected to display an image brightly in the front direction by using such a surface light source device.

JP 2007-227405 A

  By the way, in recent years, along with the development of LEDs and the like that can achieve energy saving and high linearity, the size of edge light type surface light source devices has increased, and it is also used in combination with a display surface having a large display surface. It became so. When observing such a display device, the observation angle for observing each position on the display surface of the display device changes greatly. Specifically, the observation angle when observing the central portion of the display surface is relatively small, and the observation angle when observing the peripheral portion of the display surface is relatively large. For this reason, when the surface light source device that has been considered to be ideal is used, there arises a problem that the in-plane distribution of brightness perceived by the observer varies greatly.

  Such inconveniences have also occurred in display devices for portable terminals that have recently become increasingly popular in civic life. Since the mobile terminal is held by the user's hand, the user observes the display surface of the mobile terminal from a close position. For this reason, although the display surface of a portable terminal is comparatively small, the direction in which a user observes each position on the display surface is greatly different. As a result, the in-plane distribution of brightness perceived by the observer varies greatly.

  Accordingly, the present invention has been made in consideration of such points, and provides a prism sheet, a surface light source device, and a display device that can make the in-plane distribution of perceived brightness more uniform. Objective.

The first prism sheet according to the present invention is:
A sheet-like body,
A plurality of unit prisms arranged on the main body and each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface located on one side in the arrangement direction, and a second surface located on the other side opposite to the one side in the arrangement direction,
In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit prisms, the angle formed by the second surface of the unit prism with respect to the sheet surface of the main body portion is a surface angle. The surface angle of at least one unit prism changes from the top of the unit prism farthest away from the main body to the base end of the unit prism closest to the main body, and increases.
The outline of the second surface of the main cutting surface of at least one unit prism is a part including the apex, and the main cutting of at least one other unit prism located on one side of the prism in the arrangement direction. The contour of the second surface in the surface is included.

The second prism sheet according to the present invention is:
A sheet-like body,
A plurality of unit prisms arranged on the main body and each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface located on one side in the arrangement direction, and a second surface located on the other side opposite to the one side in the arrangement direction,
In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit prisms, the angle formed by the second surface of the unit prism with respect to the sheet surface of the main body portion is a surface angle. The surface angle of at least one unit prism changes from the top of the unit prism farthest away from the main body to the base end of the unit prism closest to the main body, and increases.
The cross-sectional shape of the main cutting surface of at least one unit prism is a cross-sectional shape of the main cutting surface of at least one other unit prism located on one side of the prism in the arrangement direction as a part including the top. Is included.

The third prism sheet according to the present invention is:
A sheet-like body,
A plurality of unit prisms arranged on the main body and each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface located on one side in the arrangement direction, and a second surface located on the other side opposite to the one side in the arrangement direction,
In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit prisms, the angle formed by the second surface of the unit prism with respect to the sheet surface of the main body portion is a surface angle. The surface angle of at least one unit prism changes from the top of the unit prism farthest away from the main body to the base end of the unit prism closest to the main body, and increases.
The separation length along the sheet surface of the main body between the tops of at least two adjacent unit prisms is at a position that is one side in the arrangement direction with respect to the two unit prisms. It is longer than the separation length along the sheet surface of the main body portion between the top portions of at least one of the other two unit prisms provided adjacent to each other.

The fourth prism sheet according to the present invention is:
A sheet-like body,
A plurality of unit prisms arranged on the main body and each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface located on one side in the arrangement direction, and a second surface located on the other side opposite to the one side in the arrangement direction,
In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit prisms, the angle formed by the second surface of the unit prism with respect to the sheet surface of the main body portion is a surface angle. The surface angle of at least one unit prism changes from the top of the unit prism farthest away from the main body to the base end of the unit prism closest to the main body, and increases.
The height along the normal direction of the main body portion of at least one unit prism is the height of the main body portion of at least one other unit prism positioned on one side in the arrangement direction with respect to the one unit prism. It is higher than the height along the normal direction.

The fifth prism sheet according to the present invention is:
A sheet-like body,
A plurality of unit prisms arranged on the main body and each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface located on one side in the arrangement direction, and a second surface located on the other side opposite to the one side in the arrangement direction,
In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit prisms, the angle formed by the second surface of the unit prism with respect to the sheet surface of the main body portion is a surface angle. The surface angle of at least one unit prism changes from the top of the unit prism farthest away from the main body to the base end of the unit prism closest to the main body, and increases.
The width along the sheet surface of the main body portion of at least one unit prism is the sheet surface of the main body portion of at least one other unit prism positioned on one side in the arrangement direction with respect to the one unit prism. It is wider than the width along.

  In the first to fifth prism sheets according to the present invention, the contour of the second surface of the main cutting surface of at least one unit prism is a part including the top portion, and is on one side of the prism in the arrangement direction. The contour of the second surface in the main cutting surface of at least one other unit prism positioned may be included. Further, in the first to fifth prism sheets according to the present invention, the outline of the second surface of the main cutting surface of the unit prism located on the most other side in the arrangement direction is defined as a part including the top portion as the arrangement. An outline of the second surface of the main cutting surface of the unit prism located on the most side in the direction may be included.

  In the first to fifth prism sheets according to the present invention, the outline of the second surface of the main cutting surface of any one unit prism is located on one side in the arrangement direction with respect to the one unit prism. The contour of the second surface in the main cutting surface of one unit prism is included as a part including the top, or the contour of the second surface in the main cutting surface of the other unit prism. You may make it the same.

  In the first to fifth prism sheets according to the present invention, the cross-sectional shape of the main cutting surface of at least one unit prism is at least one located on one side of the prism in the arrangement direction as a part including the top. A cross-sectional shape of the main cutting plane of two other unit prisms may be included. Further, in the first to fifth prism sheets according to the present invention, the cross-sectional shape of the unit prism located on the most other side in the arrangement direction is the most in the arrangement direction as a part including the top. The cross-sectional shape of the main cutting surface of the unit prism located on the side may be included.

  In the first to fifth prism sheets according to the present invention, the cross-sectional shape of the main cutting plane of any one unit prism is one other unit located on one side in the arrangement direction than the one unit prism. The cross-sectional shape of the prism at the main cutting surface may be included as a part including the top, or may be the same as the cross-sectional shape at the main cutting surface of the other unit prism.

  In the first to fifth prism sheets according to the present invention, the separation length along the sheet surface of the main body between the tops of at least any two adjacent unit prisms is the two units. From the separation length along the sheet surface of the main body portion between the top portions of at least one of the two adjacent unit prisms provided at one side in the arrangement direction with respect to the prism. May be longer. Further, in the first to fifth prism sheets according to the present invention, along the sheet surface of the main body portion between the top portions of the two unit prisms positioned adjacent to the position on the most other side in the arrangement direction. The separation length may be longer than the separation length along the sheet surface of the main body portion between the top portions of the two unit prisms located adjacent to the position closest to the one side in the arrangement direction. .

  In the first to fifth prism sheets according to the present invention, the separation length along the sheet surface of the main body between the tops of any two unit prisms positioned adjacent to each other is more than that of the two unit prisms. Alternatively, the distance may be equal to or longer than the separation length along the sheet surface of the main body portion between the top portions of the two adjacent unit prisms located adjacent to each other in the arrangement direction.

  In the first to fifth prism sheets according to the present invention, a height along the normal direction of the main body portion of at least one unit prism is positioned on one side in the arrangement direction with respect to the one unit prism. The height of the main body portion of at least one other unit prism may be higher than the height along the normal direction. In the first to fifth prism sheets according to the present invention, the height along the normal direction of the main body portion of the unit prism located on the most other side in the arrangement direction is the one side most in the arrangement direction. You may make it become higher than the height along the said normal line direction of the said main-body part of the unit prism located in.

  In the first to fifth prism sheets according to the present invention, the height along the normal direction of the main body portion of any one unit prism is positioned on one side in the arrangement direction with respect to the one unit prism. You may make it more than the height along the said normal line direction of the said main-body part of the other one unit prism to do.

  In the first to fifth prism sheets according to the present invention, the width of the main body portion of at least one unit prism along the sheet surface is at least one positioned on one side in the arrangement direction with respect to the one unit prism. The width | variety along the said sheet surface of the said main-body part of one other unit prism may be wider. In the first to fifth prism sheets according to the present invention, the width along the sheet surface of the main body portion of the unit prism located on the most other side in the arrangement direction is located on the most side in the arrangement direction. You may make it become wider than the width | variety along the said sheet surface of the said main-body part of the unit prism to perform.

  In the first to fifth prism sheets according to the present invention, the width along the sheet surface of the main body portion of any one unit prism is located on one side in the arrangement direction with respect to the one unit prism. The unit prism may have a width equal to or greater than the width of the main body portion along the sheet surface.

A surface light source device according to the present invention comprises:
A light guide plate having a light exit surface and a pair of side surfaces disposed opposite to each other in the first direction;
A light source provided corresponding to one of the pair of side surfaces;
Any one of the first to fifth prism sheets according to the present invention, comprising: a prism sheet disposed so that the light exit surface of the light guide plate and the unit prism face each other;
The prism sheet is arranged such that the arrangement direction of the unit prisms is parallel to the first direction, and the one side of the arrangement direction of the unit prisms is the side where the light source is provided in the first direction. And the light guide plate is disposed.

In the surface light source device according to the present invention,
The second surface of the unit prism located at the most other side in at least the arrangement direction includes a first portion that is the farthest from the main body, a second portion that is adjacent to the first portion from the main body, and Have
When the angular distribution of luminance in a plane parallel to the main cutting surface of the prism sheet is measured on the light exit surface of the light guide plate, the light guide plate has the light source caused by the light emitted from the light source. Light traveling in a direction parallel to the peak angle that gives the highest luminance in the angular distribution of luminance on the light exit surface,
After being incident on the unit prism of the prism sheet and reflected by the first portion of the second surface of the unit prism, the main body portion is inclined in the direction inclined from the normal direction to the other side in the arrangement direction. Proceed,
After being incident on the unit prism of the prism sheet and reflected by the second portion of the second surface of the unit prism, the main body portion is inclined in a direction inclined to one side in the arrangement direction from the normal direction. You may make it go.

  In the surface light source device according to the present invention, the light guide plate includes a sheet-like base and unit optical elements arranged in a direction intersecting the first direction and provided on the prism sheet side of the base. It may be.

  In the surface light source device according to the present invention, the base portion may include a main portion made of resin and a diffusion component dispersed in the main portion.

A display device according to the present invention comprises:
Any surface light source device according to the present invention;
A transmissive display panel illuminated by the surface light source device.

The display device according to the present invention further comprises a control device connected to the light source,
The light guide plate includes a base and a plurality of linear unit optical elements arranged in one direction on a surface on one side of the base to form the light exit surface,
The light source includes a plurality of point-like light emitters arranged in the one direction,
The said control apparatus may be comprised so that the output of each point-like light-emitting body may be adjusted according to the image | video which should be displayed.

  According to the present invention, the in-plane distribution of perceived brightness can be effectively made uniform.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device and a surface light source device for explaining an embodiment according to the present invention. FIG. 2 is a diagram for explaining the operation of the surface light source device of FIG. FIG. 3 is a diagram for explaining the operation of the display device and the surface light source device when the display device of FIG. 1 is observed. 4 is a perspective view showing a light guide plate incorporated in the surface light source device of FIG. FIG. 5 is a view for explaining the operation of the light guide plate, and is a view showing the light guide plate in a cross section taken along the line V-V in FIG. 4. FIG. 6 is a perspective view showing a prism sheet incorporated in the surface light source device of FIG. FIG. 7 is a partial cross-sectional view showing the prism sheet of FIG. 6 in its main cut surface, and is a view showing the unit prisms located in one side region in the arrangement direction of the unit prisms. FIG. 8 is a graph showing an example of an angular distribution of luminance that can be measured at one end along the arrangement direction of the unit prisms on the light emitting surface of the surface light source device of FIG. FIG. 9 is a partial cross-sectional view showing the prism sheet of FIG. 6 in its main cut surface, and is a view showing the unit prism located in the central region in the arrangement direction of the unit prisms. FIG. 10 is a graph showing an example of the angular distribution of luminance that can be measured at the center position along the arrangement direction of the unit prisms on the light emitting surface of the surface light source device of FIG. FIG. 11 is a partial cross-sectional view showing the prism sheet of FIG. 6 in its main cut surface, and is a view showing the unit prisms located in the other side region in the arrangement direction of the unit prisms. 12 is a graph showing an example of an angular distribution of luminance that can be measured at the other end along the arrangement direction of the unit prisms on the light emitting surface of the surface light source device of FIG. FIG. 13 is a diagram for explaining a mold manufacturing method capable of producing the prism sheet of FIG. 6. FIG. 14 is a view for explaining a modification of the prism sheet in the same cross section as FIG. FIG. 15 is a view for explaining another embodiment of the present invention, and is a cross-sectional view showing a schematic configuration of a display device and a surface light source device.

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

  1 to 15 are diagrams for explaining one embodiment of the present invention. Among these, FIG. 1 is a perspective view showing a schematic configuration of a liquid crystal display device and a surface light source device, and FIG. 2 is a cross-sectional view for explaining the operation of the surface light source device. FIG. 3 is a diagram for explaining the operation during observation of the surface light source device and the display device. FIG. 4 is a perspective view showing a light guide plate included in the surface light source device, and FIG. 5 is a cross-sectional view showing the light guide plate in the main cut surface of the light guide plate. FIG. 6 is a perspective view showing a prism sheet included in the surface light source device, and FIGS. 7, 9, and 11 are cross-sectional views showing the prism sheet on the main cut surface of the prism sheet. 8, 10, and 12 are graphs showing the angular distribution of luminance measured at each position on the light emitting surface (the effective region of the most light-emitting side surface) of the surface light source device of FIG. 1.

  As shown in FIG. 1, the display device 10 includes a liquid crystal display panel 15, a surface light source device 20 that is disposed on the back side of the liquid crystal display panel 15 and illuminates the liquid crystal display panel 15 in a planar shape from the back side, and the liquid crystal display panel 15. And a control device 18 for controlling the surface light source device 20. The display device 10 has a display surface 11 as an effective screen (effective area) that can display an image effectively without being covered by a housing or the like. The liquid crystal display panel 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel, and is configured to display an image on the display surface 11.

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

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

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

  Next, the surface light source device 20 will be described. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and is used as a device that illuminates the liquid crystal display panel 15 from the back side in the present embodiment. The light emitting surface 21 here is a surface that is not covered with a housing or the like and can emit light effectively according to the use, that is, an effective region of the most light emitting side surface of the surface light source device 20. It is. Therefore, when the surface light source device 20 is used as a backlight for illuminating the liquid crystal display panel 15 from the back side to form the display device 10 as in the present embodiment, the light emitting surface 21 is the outermost surface of the surface light source device 20. It means an area facing the area forming the display surface 11 of the display device 10 (facing in the front direction nd) on the light exit side surface.

  As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device, and faces the light guide plate 30, the light source 24 disposed on the side of the light guide plate 30, and the light guide plate 30. The prism sheet (optical sheet) 60 and the reflection sheet 28 are arranged. In the illustrated example, the prism sheet 60 is arranged facing the liquid crystal display panel 15. The light emitting surface 21 is defined by a region facing the region forming the display surface 11 of the light exit surface 61 of the prism sheet 60.

  In the illustrated example, the light exit surface 31 of the light guide plate 30 is formed in a quadrangular shape, similar to the display surface 11 of the liquid crystal display device 10 and the light emitting surface 21 of the surface light source device 20. As a result, the light guide plate 30 is generally configured as a quadrangular plate-like member having a pair of main surfaces (light-emitting surface 31 and back surface 32), and the side surfaces defined between the pair of main surfaces are four. Includes two aspects. Similarly, the prism sheet 60 and the reflection sheet 28 are configured as quadrilateral plate-like members as a whole.

  The light guide plate 30 includes a light output surface 31 constituted by a main surface on the liquid crystal display panel 15 side, a back surface 32 formed of the other main surface facing the light output surface 31, and a side surface extending between the light output surface 31 and the back surface 32. And have. Of the two side surfaces, one of the two surfaces facing the first direction forms a light incident surface 33. As shown in FIG. 1, a light source 24 is provided facing the light incident surface 33. The light incident on the light guide plate 30 from the light incident surface 33 is directed substantially along the first direction (light guide direction) toward the opposite surface 34 facing the light incident surface 33 along the first direction (light guide direction). Light is guided through the light guide plate 30. As shown in FIGS. 1 and 2, the prism sheet 60 is disposed so as to face the light output surface 31 of the light guide plate 30, and the reflection sheet 28 is disposed so as to face the back surface 32 of the light guide plate 30. ing.

  The light source may be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), an incandescent lamp, and the like. In the present embodiment, the light source 24 is constituted by a large number of point-like light emitters 25, specifically a large number of light emitting diodes (LEDs) arranged side by side along the longitudinal direction of the light incident surface 33. Yes. In FIG. 4, arrangement positions of a large number of point-like light emitters 25 forming the light source 24 are shown. The control device 18 determines the output of each point light emitter 25, that is, the brightness at the time of turning on and off each point light emitter 25 and / or the lighting of each point light emitter 25, as another point light emission. It is configured to be adjusted independently of the body output.

  The reflection sheet 28 is a member for reflecting the light leaking from the back surface 32 of the light guide plate 30 so as to enter the light guide plate 30 again. The reflection sheet 28 is composed of a white scattering reflection sheet, a sheet made of a material having a high reflectance such as metal, a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, and the like. obtain.

  By the way, in this specification, the “light exit side” means the downstream side in the traveling direction of light from the light source 24 toward the observer through the light guide plate 30 or the prism sheet 60 without wrapping the traveling direction (observer side, For example, the upper side of the paper surface in FIG. 1, and “light incident side” refers to light that travels from the light emitting body 25 of the light source 24 to the observer through the light guide plate, the prism sheet 60, and the like without being folded back in the traveling direction. It is the upstream side in the direction of travel.

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

  Further, in this specification, the “sheet surface (plate surface, film surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed as a whole and globally. Refers to the surface. In this embodiment, the plate surface of the light guide plate 30, the sheet surface (plate surface) of the base portion 40 described later of the light guide plate 30, the sheet surface of the prism sheet 60, and the sheet of the main body portion 65 described later of the prism sheet 60. The surface, the sheet surface of the reflection sheet 28, the panel surface of the liquid crystal display panel, 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 the present specification, the “front direction” is a normal direction to the light emitting surface 21 of the surface light source device 20, and in this embodiment, a normal direction to the plate surface of the light guide plate 30, a prism sheet. This also coincides with the normal direction to the sheet surface of 60, the normal direction to the display surface 11 of the display device 10, and the like (see, for example, FIG. 2).

  Next, the light guide plate 30 will be described in more detail with reference mainly to FIGS. 2, 4 and 5. As shown well in FIGS. 2, 4, and 5, the light guide plate 30 includes a base 40 formed in a plate shape and a surface on one side of the base 40 (a surface facing the viewer side, a light exit side). A plurality of unit optical elements 50 formed on 41. The base 40 is configured as a flat member having a pair of parallel main surfaces. The back surface 32 of the light guide plate 30 is configured by the surface 42 on the other side of the base 40 located on the side facing the reflection sheet 28.

  The “unit prism”, “unit shape element”, “unit optical element”, and “unit lens” in the present specification refer to the optical action such as refraction and reflection on the light, and indicate the traveling direction of the light. It refers to an element having a function to be changed, and is not distinguished from each other based only on a difference in designation.

  As shown in FIG. 1 and FIG. 2, the base portion 40 has a main portion 44 made of resin and a diffusion component 45 dispersed in the main portion 44. The diffusion component 45 referred to here is a component that can exert an action of changing the traveling direction of the light traveling in the base 40 by reflection or refraction. Such a light diffusing function (light scattering function) of the diffusing component 45 can be achieved, for example, by configuring the diffusing component 45 from a material having a refractive index different from that of the material forming the main portion 44 or with respect to light. It can be applied by constructing the diffusing component 45 from a material that can exert a reflective action. Examples of the diffusion component 45 having a refractive index different from that of the material forming the main portion 44 include a metal compound, a porous substance containing gas, and simple bubbles. Note that the diffusion component 45 is omitted in the drawings other than FIGS. 1 and 2.

  Next, the unit optical element 50 provided on the surface 41 on one side of the base 40 will be described. As shown well in FIG. 4, the plurality of unit optical elements 50 are arranged in an arrangement direction that intersects the first direction and is parallel to the surface 41 on one side of the base 40. Arranged on the surface 41. Each unit optical element 50 extends linearly on the surface 41 on one side of the base 40 in a direction intersecting with the arrangement direction.

  In particular, in the present embodiment, the plurality of unit optical elements 50 are arranged on the surface 41 on one side of the base 40 side by side in the second direction (arrangement direction) orthogonal to the first direction without a gap. Therefore, the light exit surface 31 of the light guide plate 30 is configured as inclined surfaces 37 and 38 formed by the surface of the unit optical element 50. Each unit optical element 50 extends linearly along a first direction orthogonal to the arrangement direction. Further, each unit optical element 50 is formed in a column shape and has the same cross-sectional shape along the longitudinal direction thereof. In the present embodiment, the plurality of unit optical elements 50 are configured identically. As a result, the light guide plate 30 in the present embodiment has a constant cross-sectional shape at each position along the first direction.

  The cross section shown in FIG. 5, that is, a cross section parallel to both the normal direction nd to the arrangement direction (second direction) of the unit optical elements 50 and the surface 41 (plate surface of the light guide plate 30) on one side of the base 40 ( In the following, each unit optical element 50 has a triangular shape in which one side is located on the surface 41 on one side of the base 40 in the “main cut surface of the light guide plate (main cut surface related to the light guide plate)”. Alternatively, the apex angle protruding from the triangular base 40 is chamfered. In the illustrated example, the cross-sectional shape of each unit optical element 50 at the main cut surface is a shape obtained by chamfering the apex angle 56 of a triangle protruding from the base 40 (see FIG. 5).

  In the example shown in FIG. 5, the light guide plate is used for the purpose of effectively increasing the luminance in the front direction and providing symmetry to the angular distribution of the luminance in the plane along the second direction. The cross-sectional shape of the unit optical element 50 at the main cutting plane is symmetrical about the front direction nd. Accordingly, the two base angles θa1 and θa2 (see FIG. 5) having a triangular cross section on the main cut surface are equal to each other.

  The “triangular shape” in the present specification includes not only a triangular shape in a strict sense but also a substantially triangular shape including limitations in manufacturing technology, errors in molding, and the like. Similarly, terms used in this specification to specify other shapes and geometric conditions, for example, terms such as “parallel” and “orthogonal” are not limited to strict meanings, Interpretation will be made including errors to the extent that functions can be expected.

  The dimensions of the light guide plate 30 having the above-described configuration can be set as follows as an example. First, as a specific example of the unit optical element 50, the width Wa (see FIG. 5) along the plate surface of the light guide plate 30 can be 5 μm or more and 500 μm or less, and the normal direction nd to the plate surface of the light guide plate 30 is nd. The height Ha from one side surface 41 of the base portion 40 of the unit optical element 50 can be 1 μm or more and 250 μm or less. When the cross-sectional shape of the unit optical element 50 is a triangular shape or a shape formed by chamfering the apex angle of the triangular shape, the angle θa3 (see FIG. 5) of the apex angle 56 is 90 ° or more and 145 ° or less. can do. When the cross-sectional shape of the unit optical element 50 is a shape formed by chamfering a triangular apex angle 56, the top 52 of the unit optical element 50 has a radius of curvature of the unit optical element 50 in the main cutting plane. It is preferably formed as a curve that is equal to or less than the value of the width Wa. On the other hand, the thickness of the base 40 can be set to 0.5 mm to 6 mm.

  The shape and dimensions of the light guide plate 30 are such that the amount of light emitted from the light exit surface 31 of light emitted from the light emitter 25 of the light source 24 and incident on the light guide plate 30 is in the first direction (light guide direction). Furthermore, it can be designed to be uniform so that it does not vary greatly at each position. On the other hand, as already described, the configuration of the light guide plate 30 in the present embodiment (for example, the cross-sectional shape of the main cut surface) is constant at each position along the first direction. Therefore, the luminance angle on the light exit surface 31 of the light guide plate 30 measured in a plane including the front direction nd and the first direction (light guide direction) (that is, in a plane orthogonal to the main cut surface of the light guide plate). The distribution exhibits substantially the same distribution shape at each position along the first direction. According to the size and shape of the illustrated light guide plate 30, the angle when tilted from the front direction nd toward the light incident surface 33 side (one side) in the first direction is a negative value, and the first direction from the front direction nd When the angle when tilted toward the second light incident surface 34 (the other side) in one direction is defined as a positive value, the angle distribution of the brightness is between 65 ° and 80 °. The peak angle at which the luminance is maximized can be obtained, and the peak angle at which the luminance is maximized can be obtained between 65 ° and 75 ° by narrowing the range of the exemplified dimensions.

  The light guide plate 30 having the above-described configuration can be manufactured by extrusion molding or by molding the unit optical element 50 on a base material. Various materials can be used as the material forming the main portion 44 of the base portion 40 of the light guide plate 30 and the unit optical element 50. However, it is widely used as a material for an optical sheet (optical member) incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability and the like, and can be obtained at low cost, for example, acrylic, A transparent resin mainly composed of one or more of styrene, polycarbonate, polyethylene terephthalate, acrylonitrile, or the like, or an epoxy acrylate or urethane acrylate-based reactive resin (such as ionizing radiation curable resin) can be suitably used. On the other hand, the diffusion component 45 includes particles made of a transparent material such as silica (silicon dioxide), alumina (aluminum oxide), acrylic resin, polycarbonate resin, and silicone resin having an average particle diameter of about 0.5 to 100 μm. Can be used.

  When the light guide plate 30 is produced by curing the ionizing radiation curable resin on the base material, the sheet-shaped land portion that is positioned between the unit shape element 50 and the base material is provided together with the unit shape element 50. It may be formed on a substrate. In this case, the base 40 is composed of a base material and a land portion formed of an ionizing radiation curable resin. Moreover, the board | plate material which consists of a resin material extrusion-molded with the diffusion component as a base material 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. When the light guide plate 30 is manufactured by extrusion molding, the unit optical element 50 is composed of the same resin material as the material forming the main portion 44 of the base portion 40 and particles forming the diffusion component 45 of the base portion 40. Also good. Alternatively, the light guide plate 30 is manufactured by so-called coextrusion, and the base portion 40 is composed of a main portion 44 made of a resin material and a diffusion component 45 dispersed in the main portion 44, while a unit optical element 50 may be composed of the same resin material as the material forming the main portion 44 of the base portion 40, and particles having a separate function as the diffusion component 45 of the base portion 40, or You may comprise only the same resin material as the material which forms the part 44. FIG.

  Next, the prism sheet (optical sheet) 60 will be described in further detail with reference mainly to FIGS. 2, 6, 7, 9, and 11. The prism sheet 60 is a member having a function of changing the traveling direction of transmitted light. In particular, the prism sheet 60 described here determines the traveling direction of light incident from the light incident side according to the distance along the first direction between the incident position of the light on the prism sheet 60 and the light source 24. , And has a function of changing the light beam in an appropriate direction and emitting it from the light output side.

  2 and 6, the prism sheet 60 includes a main body portion 65 formed in a plate shape and a plurality of unit prisms (unit shapes) formed on the light incident side surface 67 of the main body portion 65. Element, unit optical element, unit lens) 70. The main body portion 65 is configured as a flat plate-like member having a pair of parallel main surfaces. The light exit surface 61 of the prism sheet 60 that forms the light emitting surface 21 of the surface light source device 20 is configured by the light exit side surface 66 of the main body 65 located on the side not facing the light guide plate 30.

  Next, the unit prism 70 provided on the light incident side surface 67 of the main body 65 will be described. As well shown in FIGS. 2 and 6, the plurality of unit prisms 70 are arranged side by side on the light incident side surface 67 of the main body 65. Each unit prism 70 is formed in a columnar shape and extends in a direction intersecting with the arrangement direction.

  In the present 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 the longitudinal direction. Further, the plurality of unit prisms 70 are arranged on the light incident side surface 67 of the main body 65 with no gap along the direction orthogonal to the longitudinal direction. Therefore, the light incident surface 62 of the prism sheet 60 is formed by the surfaces 71 and 72 of the unit prisms 70 arranged on the main body portion 65 without a gap.

  As described above, the prism sheet 60 is disposed so as to overlap the light guide plate 30, and the unit prism 70 of the prism sheet 60 faces the light output surface 31 of the light guide plate 30. As shown in FIGS. 1 and 2, the prism sheet 60 has a longitudinal direction of the unit prism 70 in the light guide direction by the light guide plate 30 (the light incident surface 33 of the light guide plate 30 and the opposite surface facing the light incident surface). 34 is positioned with respect to the light guide plate 30 so as to intersect the first direction). More precisely, the longitudinal direction of the unit prisms 70 is orthogonal to the light guide direction by the light guide plate 30 (that is, the first direction), and the arrangement direction of the unit prisms 70 is parallel to the light guide direction by the light guide plate 30. Further, the prism sheet 60 is positioned with respect to the light guide plate 30.

  As shown well in FIG. 2, the unit prisms 70 are arranged to face each other in the direction parallel to the sheet surface of the main body 65 along the arrangement direction of the unit prisms 70, that is, the first direction. A first surface 71 and a second surface 72 are provided. The first surface 71 of each unit prism 70 is located on one side in the first direction (left side of the paper surface of FIGS. 1 and 2), and the second surface 72 is on the other side in the first direction (FIGS. 1 and 2). On the right side of the paper. More specifically, the first surface 71 of each unit prism 70 is located on the light source 24 side in the first direction, and the second surface 72 of each unit prism 70 is on the side away from the light source 24 in the first direction. positioned. The first surface 71 mainly proceeds from the light source 24 arranged on one side in the first direction into the light guide plate 30, and then the light emitted from the light guide plate 30 is incident on the prism sheet 60. Functions as a surface. On the other hand, the second surface 72 has a function of reflecting light incident on the prism sheet 60 and correcting the optical path of the light.

  As shown well in FIGS. 2, 7, 9, and 11, the first surface 71 and the second surface 72 extend from the main body portion 65 and are connected to each other. A base end portion 74 of the unit prism 70 is defined at a position where the first surface 71 and the second surface 72 are respectively connected to the main body portion 65. In addition, at the position where the first surface 71 and the second surface 72 are connected to each other, a top portion (tip portion) 75 of the unit prism 70 that protrudes most from the main body portion 65 toward the light incident side is defined.

  As described above and as shown in FIG. 6, the normal direction nd to the sheet surface of the main body 65 (the light incident side surface 67 of the main body 65, the sheet surface of the prism sheet 60) and the arrangement direction of the unit prisms 70. The cross-sectional shape of each unit prism 70 in a cross section parallel to both (hereinafter, also simply referred to as “principal sheet main cutting surface”) is along the longitudinal direction of the unit prism 70 (direction extending linearly). Is constant. On the other hand, the cross-sectional shape at the main cutting surface of the prism sheet is not constant among the plurality of unit prisms 70 provided on the main body 65. The plurality of unit prisms 70 has any one of a plurality of cross-sectional shapes smaller than the plurality, or all the unit prisms 70 have different cross-sectional shapes. The cross-sectional shape of each unit prism 70 at the main cut surface of the prism sheet changes according to the distance along the first direction between the position of the unit prism 70 in the main body 65 and the light source 24. ing.

  Hereinafter, the cross-sectional shape of the unit prism 70 on the main cut surface of the prism sheet will be described in more detail. 7, 9, and 11 show the main cutting surface of the prism sheet, and FIGS. 1 and 2 show the surface light source device 20 (display device 10) in a cross section parallel to the main cutting surface of the prism sheet. It is shown. In particular, FIGS. 7, 9, and 11 show unit prisms 70 arranged in one side region in the arrangement direction (first direction) of unit prisms 70, and the central region in the arrangement direction (first direction) of unit prisms 70. The cross-sectional shapes of the main prisms of the unit prisms 70 arranged on the side and the unit prisms 70 arranged on the other side region in the arrangement direction (first direction) of the unit prisms 70 are shown.

  As shown in FIG. 7, FIG. 9, and FIG. 11, in the present embodiment, the cross-sectional shape of each unit prism 70 on the main cut surface of the prism sheet is tapered toward the light incident side (light guide plate side). It has a shape that goes on. In other words, the width of the unit prism 70 parallel to the sheet surface of the main body 65 on the main cut surface decreases as the distance from the main body 65 increases along the normal direction nd of the main body 65.

  In the present embodiment, the second surface 72 that forms part of the outer contour of the unit prism 70 on the main cutting surface of the prism sheet 60 (the second surface 72 that forms part of the light incident side surface) is the sheet of the main body 65. Assuming that the angle formed with respect to the surface is the surface angle θb, the surface angle θb of at least one unit prism 70 is not constant in the second surface 72. More specifically, the surface angle θb varies with respect to the unit prism 70 that is located at the most other side (that is, the side opposite to the light source 24) in at least the arrangement direction of the unit prisms (that is, the first direction). As shown in FIGS. 7, 9, 11 and 2, in particular, in the illustrated example, the surface angle θb of the second surface is not constant for all the unit prisms 70.

  As shown in FIGS. 2, 7, 9, and 11, the surface angle θb is the closest to the main body 65 from the top 75 of the unit prism farthest from the main body 65 in the second surface 72. It changes so that it may become large toward the base end part 74 of the said unit prism 60 concerned. As shown in FIG. 7, according to such a unit prism 60, the relatively rising light L <b> 73 traveling in the direction in which the inclination angle with respect to the front direction nd of the second surface 72 becomes relatively small is mainly incident. Excellent in both the region on the base end 74 side and the region on the top 75 side where the relatively sleeping light L74 traveling in a direction in which the inclination angle with respect to the front direction nd becomes very large is mainly incident. The light condensing function can be secured.

  As a specific configuration, in the illustrated embodiment, the outline of the second surface 72 of the unit prism 70 is formed by joining the straight portions on the main cut surface of the prism sheet, or joining the straight portions. In addition, it has a shape formed by chamfering joints. In other words, the outer contour of the second surface 72 of the unit prism 70 is formed in a polygonal line shape or a shape formed by chamfering the corners of the polygonal line. More specifically, the second surface 72 includes a flat surface that forms a first portion 72a that defines the top portion 75, and a second portion 72b that is adjacent to the first portion 72a from the body portion 65 side. ing. The surface angle θb of the second portion 72b is larger than the surface angle θb of the first portion 72a.

  In combination with the sectional shape of the unit prism 70 described below, the surface angle θb of the first portion 72a and the surface angle θb of the second portion 72b are preferably set as follows. That is, as shown in FIGS. 7, 9, and 11, the peak luminance is obtained when the angular distribution of luminance in a plane parallel to the main cutting surface of the prism sheet 60 is measured on the light exit surface 31 of the light guide plate 30. The light L71, L91, L111 traveling in a direction parallel to the direction exhibiting the incident light enters the unit prism 70 of the prism sheet 60 and then is reflected by the first portion 71 on the top 75 side of the second surface 70 of the unit prism 70. Then, the process proceeds in a direction inclined from the normal direction nd of the main body 65 to the other side (counterlight source side) in the arrangement direction (first direction) of the unit prisms 70. Further, as shown in FIGS. 7, 9, and 11, the peak luminance is obtained when the angular distribution of luminance in a plane parallel to the main cutting surface of the prism sheet 60 is measured on the light exit surface 31 of the light guide plate 30. When light L72, L92, L112 traveling in a direction parallel to the direction exhibiting the light is incident on the unit prism 70 of the prism sheet 60 and then reflected by the second portion 72b of the second surface 72 of the unit prism 70, the main body portion The direction proceeds from the normal direction nd of 65 toward one side (light source side) in the arrangement direction of the unit prisms 70. When the surface angle θb of the first portion 72a and the surface angle θb of the second portion 72b are set in this way, an observer who observes the display device 10 in which the surface light source device 20 is incorporated is on the display surface 11. In addition to the image displayed in the central region, the images displayed on both edges along the first direction (the arrangement direction of the unit prisms 70) can be observed brightly.

  The surface angle θb is an angle formed by the light incident side surface (second surface 72) of the unit prism 60 with respect to the sheet surface of the main body 65 in the main cut surface of the prism sheet 60 as described above. When the second surface 72 of the main cutting surface of the unit prism 70 is formed in a polygonal line as in the examples shown in FIGS. 2, 7, 9, and 11, each linear part constituting the polygonal line The angle formed between the main body 65 and the sheet surface (strictly speaking, the smaller one of the two formed angles (subordinate angle)) is the surface angle θb. On the other hand, the second surface 72 of the main cutting surface of the unit prism 70 may be formed of a curved surface as in a modification described later (see FIG. 14 described later). For the outer contour (the first surface 71 and the second surface 72) of the curved unit prism 70, an angle formed between the tangent TL to the outer contour and the sheet surface of the main body 65 (strictly, Is to specify the smaller one of the two angles to be formed (a minor angle) as the surface angle θb.

  Further, changing the surface angle θb from the top 75 on the second surface 72 of the unit prism 70 toward the base end portion 74 only means that the surface angle θb keeps changing so as to always increase. It is not a thing. As shown in FIGS. 2, 7, 9, and 11, the second surface 72 of the main cutting surface of the unit prism 70 has a polygonal line shape or a shape formed by chamfering a bent portion of the polygonal line, and the surface angle θb. There may be a region where does not change. That is, the shape that changes so that the surface angle θb increases from the top portion 75 on the second surface 72 of the unit prism 70 toward the base end portion 74 is based on the surface angle θb at the top portion 75. A shape that does not include a portion where the surface angle θb at the end portion 74 is larger and the surface angle θb decreases from the top portion 75 toward the base end portion 74 is also included.

  In addition, in the prism sheet 60 described here, the outline of the second surface 72 in the main cutting surface of the unit prism 70 located on the most other side in the arrangement direction (first direction) of the unit prisms 70 is the one unit. The part including the apex 75 of the prism 70 includes the entire outline of the second surface 72 of the main cutting surface of the unit prism 70 located on the most side in the arrangement direction of the unit prisms 70. Furthermore, as shown in FIGS. 7, 9, and 11, the outline of the second surface 72 in the main cutting surface of any one unit prism 70 is the arrangement direction of the unit prisms 70 rather than the one unit prism 70. The contour of the second surface 72 of the main cutting plane of another unit prism located on one side of the unit prism is included as a part including the top 75 of the one unit prism 70, or the contour of the other unit prism is included. This is the same as the contour of the second surface 72 in the main cut surface.

  As described above, in the illustrated example, the second surface 72 of the unit prism 70 is formed of the first portion 72a disposed on the top side and the second portion 72b disposed on the base end side. ing. Therefore, the configuration of the first portion 72a located on the base end side of the second surface 72 among all the unit prisms 70, regardless of the arrangement position along the arrangement direction of the unit prisms 70, more specifically. The first portion 72a has the same surface angle θb and the same dimension.

  In the illustrated example, the first surface 71 of each unit prism 70 is configured as follows, similarly to the second surface 72. That is, the outline of the first surface 71 on the main cutting surface of the unit prism 70 located on the most other side in the arrangement direction (first direction) of the unit prisms 70 is a part including the top 75 of the one unit prism 70. The entire outline of the first surface 71 in the main cutting surface of the unit prism 70 located on the most side in the arrangement direction of the unit prisms 70 is included. Furthermore, as shown in FIGS. 7, 9, and 11, the outline of the first surface 71 in the main cut surface of any one unit prism 70 is the arrangement direction of the unit prisms 70 rather than the one unit prism 70. The contour of the first surface 71 in the main cutting plane of another unit prism located on one side of the unit prism is included as a part including the apex 75 of the one unit prism 70, or This is the same as the contour of the second surface 72 in the main cut surface. In particular, in the illustrated example, the first surface 71 of the unit prism 70 is composed of a single surface, and forms one straight line on the main cutting surface of the prism sheet 60. Accordingly, the first surfaces 71 of the unit prisms 70 included in the prism sheet 60 are parallel to each other although the sizes thereof are different from each other.

  In the illustrated example, the cross-sectional shape at the main cutting surface of the unit prism 70 located on the most other side in the arrangement direction of the unit prisms 70 is the arrangement of the unit prisms 70 as a part including the apex 75 of the unit prisms 70. The entire cross-sectional shape of the main cutting surface of the unit prism located on the most side in the direction is included. In other words, a part of the main cut surface of the unit prism 70 located on the most other side in the arrangement direction of the unit prisms 70 including the top 75 is the unit prism 70 located on the most side in the arrangement direction of the unit prisms 70. It is the same as the cross-sectional shape in the main cut surface. Furthermore, as shown in FIGS. 7, 9, and 11, the cross-sectional shape of the main cutting surface of any one unit prism 70 is one side in the arrangement direction of the unit prisms 70 relative to the one unit prism 70. The cross-sectional shape at the main cutting plane of the other one unit prism is included as a part including the top 75 of the single unit prism 70, or the same as the cross-sectional shape at the main cutting plane of the other unit prism. It has become.

  In the illustrated example, the height Hb along the normal direction nd of the main body portion 65 of the unit prism 70 located on the most other side in the arrangement direction of the unit prisms 70 is the most in the arrangement direction of the unit prisms 70. It is higher than the height along the normal direction nd of the main body portion 65 of the unit prism 70 located on the side. Furthermore, as shown in FIGS. 7, 9, and 11, the height Hb along the normal direction nd of the main body 65 of any one unit prism 70 is higher than that of the unit prism 70. The height is equal to or higher than the height along the normal direction nd of the main body portion 65 of the other unit prism located on one side in the 70 arrangement direction.

  Further, in the illustrated example, the width Wb along the sheet surface of the main body 65 of the unit prism 70 located on the most other side in the arrangement direction of the unit prisms 70 is located on the most side in the arrangement direction of the unit prisms 70. The unit prism 70 is wider than the width Wb of the main body 65 along the sheet surface. Furthermore, as shown in FIGS. 7, 9, and 11, the width Wb along the sheet surface of the main body portion 65 of any one unit prism 70 is an arrangement of the unit prisms 70 rather than the one unit prism 70. The width is equal to or larger than the width Wb along the sheet surface of the main body 65 of the other unit prism 70 located on one side in the direction.

  In the illustrated example, the plurality of unit prisms 70 are arranged on the main body 65 without any gap. The separation length (pitch) Pb along the sheet surface of the main body 65 between the tops 75 of the two unit prisms 70 adjacent to the position on the most other side in the arrangement direction of the unit prisms 70 is expressed in units. It is longer than the separation length (pitch) Pb along the sheet surface of the main body 65 between the tops 75 of the two unit prisms 70 that are adjacent to the position closest to the one side in the arrangement direction of the prisms 70. . Furthermore, as shown in FIGS. 7, 9 and 11, the separation length (pitch) Pb along the sheet surface of the main body 65 between the tops 75 of any two unit prisms 70 located adjacent to each other is as follows. The separation length along the sheet surface of the main body 65 between the apexes 75 of the other two unit prisms adjacent to each other at a position closer to the one side in the arrangement direction of the unit prisms 70 than the two unit prisms 70. It is over Pb.

  In the prism sheet 60 having the above-described configuration, the width Wbx of the second surface 72 of the unit prism 70 along the arrangement direction of the unit prisms 70 on the main cutting surface of the prism sheet (see FIGS. 7, 9, and 11). ) In the main cut surface of the prism sheet along the normal direction nd of the main body portion 65, the ratio of the height Hb of the unit prism 70 (Hb / Wbx) is determined by the light collecting property and diffusion of the prism sheet 60. Affects sex. In this embodiment, in order to secure the effects described later, the ratio (Hb / Wbx) of the height Hb of the unit prism 70 to the width Wbx of the second surface 72 of the unit prism 70 is 1.2. It is preferably 2.0 or less and more preferably 1.50 or more and 1.55 or less. Further, the surface angle θb at the first portion 72a of the second surface 72 can be set to 45 ° or more and 60 ° or less, and the surface angle θb at the second portion 72b of the second surface 72 is set to 50 ° or more and 70 ° or less. It can be.

  Moreover, the other dimension of the prism sheet 60 can be set as follows as an example. First, as a specific example of the unit prism 70 configured as described above, the width Wb of the unit prism 70 can be set to 10 μm to 200 μm, and the second surface 72 width Wbx of the unit prism 70 can be set to 5 μm to 100 μm. can do. Further, the projection height Hb of the unit prism 70 from the light exit side surface 67 of the main body 65 along the normal direction nd to the sheet surface of the prism sheet 60 can be set to 7 μm or more and 150 μm or less. On the other hand, the thickness of the main body 65 can be set to 0.01 mm to 1 mm.

  Such a prism sheet 60 can be manufactured by using the same material as the above-described material that can be used for manufacturing the light guide plate 30 and the same method as the above-described light guide plate manufacturing method. That is, the prism sheet 60 can be manufactured by extrusion molding or by molding the unit optical element 50 on a base material.

  By the way, in the extrusion molding and other molding processes, a molding die 90 having a mold surface 91 in which a groove having a shape complementary to the cross-sectional shape of the unit prism 70 of the prism sheet 60 is used. FIG. 13 shows an example of a method for manufacturing the mold 90. In the method shown in FIG. 13, a roll-shaped mold 90 is produced.

  In the example shown in FIG. 13, an annular groove 91 is formed in the base 94 using the cutting tool 95 while rotating the cylindrical base 94 around the central axis CA of the base 94. . The cutting edge 95a of the cutting tool 95 includes, as a part, the cross-sectional shape of the unit prism 70 located on the othermost side in the arrangement direction of the unit prisms 70 among the many unit prisms 70 included in the prism sheet 60 to be manufactured. It is a shape that includes. Then, as shown in FIG. 13, by changing the feed amount of the cutting tool 95 along the center axis CA of the base material 94 and the cutting amount of the cutting tool 95 into the base material 94 for each groove 91 to be manufactured. An annular groove 91 having a different pitch and depth can be formed on the base 94 to produce the mold 90.

  The mold 90 manufactured in this way has a large number of grooves 91 formed using the same cutting tool 95. Therefore, even if the depths of the plurality of grooves 91 are different from each other, the cross-sectional shapes in the deepest portion are common to each other. As a result, the prism sheet 60 including the unit prism 70 described above with reference mainly to FIGS. 2, 7, 9, and 11 can be manufactured.

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

  First, as shown in FIG. 2, the light emitted from the light emitter 25 constituting the light source 24 enters the light guide plate 30 via the light incident surface 33. As shown in FIG. 2, the light L21 and L22 incident on the light guide plate 30 is reflected on the light output surface 31 and the back surface 32 of the light guide plate 30, particularly due to a difference in refractive index between the material forming the light guide plate 30 and air. Then, total reflection is repeated, and the light advances to the first direction (light guide direction) connecting the light incident surface 33 and the opposite surface 34 of the light guide plate 30.

  However, the diffusion component 45 is dispersed in the base 40 of the light guide plate 30. For this reason, as shown in FIG. 2, the light L21 and L22 traveling in the light guide plate 30 has their traveling directions irregularly changed by the diffusion component 45, and the light exit surface 31 and the back surface 32 at an incident angle less than the total reflection critical angle. May be incident. 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 to the prism sheet 60 disposed on the light exit side of the light guide plate 30. On the other hand, the light emitted from the back surface 32 is reflected by the reflection sheet 28 disposed on the back surface of the light guide plate 30, enters the light guide plate 30 again, and travels through the light guide plate 30.

  The collision between the light traveling in the light guide plate 30 and the diffusion component 45 dispersed in the light guide plate 30 occurs in each area along the light guide direction in the light guide plate 30. For this reason, the light traveling in the light guide plate 30 is gradually emitted from the light exit surface 31. Thereby, the light quantity distribution along the light guide direction (first direction) of the light emitted from the light exit surface 31 of the light guide plate 30 can be made uniform.

  The amount of light emitted from each position of the light guide plate 30 is measured by the illuminometer in a state where a commercially available illuminometer sensor is in contact with the position on the light output surface 31 of the light guide plate 30 to be measured. It can be evaluated by the magnitude of the illuminance value.

  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 at the main cutting surface is formed by chamfering a triangular shape or a triangular apex angle 56. It has a shape. That is, the light exit surface 31 is configured as inclined surfaces 37 and 38 that are inclined with respect to the back surface 32 of the light guide plate 30 (see FIG. 5). The light that is totally reflected by the inclined surfaces 37 and 38 and travels through the light guide plate 30 and the light that passes through the inclined surfaces 37 and 38 and is emitted from the light guide plate 30 are transmitted from the inclined surfaces 37 and 38 to the following. It comes to have an effect to explain. First, the effect exerted on the light traveling through the light guide plate 30 after being totally reflected by the inclined surfaces 37 and 38 will be described.

  In FIG. 5, the optical paths of the lights L51 and L52 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 cut surface of the light guide plate. As described above, the inclined surfaces 37 and 38 forming the light exit surface 31 of the light guide plate 30 are formed by the outer surface of the unit optical element 50 having a cross-sectional shape formed by chamfering a triangular apex angle. The base 40 includes two types of surfaces that are inclined in opposite directions with respect to the normal direction nd to the light exit side surface 41. In addition, the two types of inclined surfaces 37 and 38 that are inclined opposite to each other are alternately arranged along the second direction. As shown in FIG. 5, the light L51 and L52 that travel in the light guide plate 30 toward the light exit surface 31 and enter the light exit surface 31 are often guided out of the two kinds of inclined surfaces 37 and 38. The light enters the inclined surface inclined to the opposite side of the traveling direction of the light with reference to the normal direction nd to the light exit side surface 41 of the base 40 on the main cut surface of the optical plate.

  As a result, as shown in FIG. 5, the light L51 and L52 traveling in the light guide plate 30 is totally reflected by the inclined surfaces 37 and 38 of the light exit surface 31, and the component along the second direction is reduced in many cases. Furthermore, the traveling direction of the main cut surface is directed to the opposite side with respect to the front direction nd. In this way, the inclined surfaces 37 and 38 forming the light exit surface 31 of the light guide plate 30 restrict the light emitted radially at a certain light emitting point from continuing to spread in the second direction as it is. That is, light that is emitted from the light emitter 25 of the light source 24 in a direction greatly inclined with respect to the first direction and enters the light guide plate 30 also travels mainly in the first direction while being restricted from moving in the second direction. become. Thereby, the light quantity distribution along the second direction of the light emitted from the light exit 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 emitter 25. It becomes possible.

  Next, the effect exerted on the light that passes through the light exit surface 31 and exits from the light guide plate 30 will be described. As shown in FIG. 5, the lights L51 and L52 emitted from the light guide plate 30 through the light output surface 31 are refracted on the light output side surface of the unit optical element 50 that forms the light output surface 31 of the light guide plate 30. Due to this refraction, the traveling direction (outgoing direction) of the lights L51 and L52 traveling in the direction inclined from the front direction nd on the main cut surface is mainly compared with the traveling direction of the light passing through the light guide plate 30. Thus, it is bent so that the angle formed with respect to the front direction nd is small. By such an action, the unit optical element 50 can narrow the traveling direction of the transmitted light to the front direction nd side for the light component along the second direction orthogonal to the light guide direction. That is, the unit optical element 50 exerts a condensing action on the light component along the second direction orthogonal to the light guide direction. In this way, the emission angle of the light emitted from the light guide plate 30 is narrowed down to a narrow angle range centering on the front direction in a 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 to a narrow angle range centering on the front direction on a 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 a surface parallel to the first direction (light guide direction) due to the fact that it has traveled mainly in the first direction in the light guide plate 30 until then. In FIG. 5, the emission angle θk is relatively large and is relatively inclined with respect to the front direction nd. Specifically, the emission angle of the first direction component of the light emitted from the light guide plate 30 (the angle θk 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). )) Tends to be biased within a narrow angular range with relatively large angles. For example, as already described, in the light guide plate having the above-described exemplary shape and size, 65 ° to 80 ° (and 65 ° to 75 ° relative to the normal direction nd to the plate surface of the light guide plate 30). The peak luminance can be set to occur in the following range.

  The light emitted from the light guide plate 30 then enters the prism sheet 60. As described above, the prism sheet 60 has the unit prism 70 with the top portion 75 protruding toward the light guide plate 30 side. As shown in FIG. 2, the longitudinal direction of the unit prism 70 intersects with the light guide direction (first direction) by the light guide plate 30, particularly in the present embodiment, the second direction orthogonal to the light guide direction. It is parallel to the direction.

  As a result, the light L21 and L22 emitted from the light source 24 arranged on one side in the first direction (left side in FIG. 2) and directed to the prism sheet 30 via the light guide plate 30 are connected to each other. The light enters the unit prism 70 via the first surface 71 located on one side of the first surface 71 and the second surface 72 in the first direction. As shown in FIG. 2, the lights L21 and L22 are then totally reflected by the second surface 72 located on the other side in the first direction (the right side in the drawing of FIG. 2) to change the traveling direction thereof. Become.

  Then, due to total reflection on the second surface 72 of the unit prism 70, in a direction inclined from the front direction nd in the cross section of FIG. 2 (a cross section parallel to both the first direction (light guide direction) and the front direction nd). The traveling lights L21 and L22 are bent so that the angle formed by the traveling direction with respect to the front direction nd is small. By such an action, the unit prism 70 can narrow the traveling direction of the transmitted light to the front direction nd side with respect to the light component along the first direction (light guide direction). In other words, the prism sheet 60 exerts a condensing action on the light component along the first direction.

  The light whose traveling direction is largely changed by the unit prisms 70 of the prism sheet 60 is mainly a component that travels in the first direction, which is the arrangement direction of the unit prisms 70, and is a unit shape element of the light guide plate 30. It is different from the component traveling in the second direction that is collected by the 50 inclined surfaces 37 and 38. Therefore, the front direction luminance can be further improved without harming the front direction luminance raised by the unit shape element 50 of the light guide plate 30 by the optical action of the unit prism 70 of the prism sheet 60.

  The light emitted from the prism sheet 60 enters the lower polarizing plate 14 of the liquid crystal display panel 15. The lower polarizing plate 14 transmits one polarization component (P wave in the present embodiment) of incident light and absorbs the other polarization component (S wave in the present embodiment). The light transmitted through the lower polarizing plate 14 selectively passes through the upper polarizing plate 13 according to the state of electric field application to each pixel. In this manner, the liquid crystal display panel 15 selectively transmits light from the surface light source device 20 for each pixel, so that an observer of the liquid crystal display device 10 can observe an image.

  As described above, the light that has entered the light guide plate 30 travels in the second direction by the light output surface 31, mainly the light output surface 31 of the light guide plate 30 formed by the light output side surface (prism surface) of the unit optical element 50. The movement proceeds in the first direction while being restricted. In other words, the light emitted from each of the multiple light emitters 25 that constitute the light source 24 is located within a predetermined range in the second direction on the light exit surface 31 of the light guide plate 30 and extends in the first direction. The light is mainly emitted from within the region. Therefore, the control device 18 may adjust the output of each light emitter 25 in accordance with the image displayed on the display surface 11 of the display device 10.

  For example, when nothing is displayed in a certain area within the display surface 11 of the display device 10, in other words, when black is displayed in a certain region within the display surface 11 of the display device 10, this corresponds to the region of the display surface 10. The point light emitter 25 that supplies light to the region of the light exit surface 31 of the light guide plate 30 may be turned off. In this case, it is possible to eliminate conventional problems such as a decrease in contrast caused by the illumination light from the surface light source device 20 being not completely blocked by the display panel 15. Further, the amount of electricity used can be saved, which is preferable from the viewpoint of energy saving.

  Furthermore, the display is not limited to the example of displaying black, and the display level is not dependent on only the display panel 15 by adjusting the output level of each point-like light emitter 25 corresponding to the image displayed on the display surface 11. You may make it adjust the brightness in each area | region of the image | video to be performed. Even in such an example, the contrast of the displayed image can be improved and energy saving can be realized.

  By the way, as mentioned in the section of the prior art, the conventional edge light type surface light source device has an angular distribution of luminance in a plane parallel to both the front direction nd and the light guide direction (first direction). It is adjusted to have the same tendency at each position in the light guide direction. In particular, the angular distribution of luminance in a plane parallel to both the front direction nd and the light guide direction (first direction) is such that the highest luminance appears in the front direction nd at any position in the light guide direction. It was adjusted.

  However, when the display surface 11 of the display device 10 and the light emitting surface 21 of the surface light source device 20 are enlarged accordingly, the observer O1 observes the image displayed on the display surface 11 as shown in FIG. The observation angle θx at the time of doing so is greatly different at each position on the display surface 11. For example, there may be a difference of 10 ° or more between the observation angle at which the central position Pc of the display surface 11 is observed and the angle at which the end positions Pe1, Pe2 of the display surface 11 are observed.

  Further, not only when observing the large display device 10 but also when observing the display device 10 of the portable terminal, similarly, the observation angle for observing the central position Pc of the display surface 11 and the edge of the display surface 11 are also observed. There may be a difference of 10 ° or more in the angle at which the part positions Pe1 and Pe2 are observed. The portable terminal is used by being held by an observer's hand. As a result, the display surface 11 of the portable terminal is arranged near the observer's head, and the observation angle when observing each position on the display surface changes greatly.

  Note that the observation angle θx here refers to the observation direction for observing each position on the display surface 11 with respect to the front direction (normal direction to the display surface 11) nd of the display device 10, as shown in FIG. It is the size of the angle to be made.

  Therefore, as in a display device incorporating a conventional surface light source device, the luminance angle distribution in a plane parallel to the front direction and the light guide direction is different from each other on the display surface in the direction parallel to the light guide direction. When the position shows a symmetric and generally constant tendency (distribution mode) about the front direction, the brightness of the image at the center position Pc which is the center in the light guide direction of the display surface 11 and the display surface 11 The brightness of the image at the end positions Pe1 and Pe2 that are the ends in the light guide direction is greatly different. In other words, in such a surface light source device and a display device, the distribution of luminance in the front direction along the light guide direction is substantially uniform, but the brightness actually sensed by the observer is along the light guide direction. Will vary greatly.

  On the other hand, in the prism sheet 60 according to the present embodiment, the cross-sectional shape of the unit prism 70 at the main cutting surface of the prism sheet is not constant. In the illustrated example, the cross-sectional shape of the unit prism 70 at the main cutting surface of the prism sheet changes depending on the arrangement position of the unit prisms in the first direction (the arrangement direction of the unit prisms 70). On the other hand, as described above, the light distribution characteristics of the light incident on the prism sheet 60 can be adjusted to some extent depending on the configuration (shape and dimensions) of the light guide plate 30. Specifically, the light amount distribution of the light emitted from each position along the first direction on the light output surface 31 of the light guide plate 30 and directed to the prism sheet 60 is made uniform to some extent. Further, the angular distribution of the luminance in the plane along the first direction and the front direction nd at each position along the first direction on the light output surface 31 of the light guide plate 30 also shows a similar distribution to some extent. It becomes like this. Therefore, according to the prism sheet 60 having the unit prism 70 whose cross-sectional shape changes as follows according to the arrangement position along the first direction, the angular distribution of luminance at each position along the first direction is Can be adjusted.

  First, in the prism sheet 60 described above, the cross-sectional shape of the unit prism 70 at the main cutting surface of the prism sheet is configured as follows. The outline of the second surface 72 of the main cutting surface of the unit prism 70 located on the most other side in the first direction is located on the most side in the first direction as a part including the top 75 of the one unit prism 70. The entire outline of the second surface 72 in the main cutting surface of the unit prism 70 is included. The cross-sectional shape of the main cutting surface of the unit prism 70 located on the most other side in the first direction is the main cutting surface of the unit prism located on the most side in the first direction as a part including the top 75 of the unit prism 70. The entire cross-sectional shape is included. The height Hb along the normal direction nd of the main body portion 65 of the unit prism 70 located on the most other side in the first direction is the normal line of the main body portion 65 of the unit prism 70 located on the most side in the first direction. It is higher than the height along the direction nd. The width Wb along the sheet surface of the main body portion 65 of the unit prism 70 located on the most other side in the first direction is along the sheet surface of the main body portion 65 of the unit prism 70 located on the most side in the first direction. It is wider than the width Wb. The separation length (pitch) Pb along the sheet surface of the main body portion 65 between the top portions 75 of the two unit prisms 70 adjacent to each other in the first direction is the most in the first direction. It is longer than the separation length (pitch) Pb along the sheet surface of the main body portion 65 between the top portions 75 of the two unit prisms 70 located adjacent to each other on the side.

  Furthermore, as shown in FIGS. 7, 9, and 11, the cross-sectional shape of the unit prism 70 at the main cutting surface of the prism sheet is configured as follows. The contour of the second surface 72 of the main cutting surface of any one unit prism 70 is the second contour of the main cutting surface of another unit prism located on one side of the one unit prism 70 in the first direction. The contour of the surface 72 is included as a part including the top 75 of the one unit prism 70, or is the same as the contour of the second surface 72 in the main cutting surface of the other unit prism. The cross-sectional shape of the main cutting surface of any one unit prism 70 is the same as the cross-sectional shape of the main cutting surface of another unit prism located on one side of the one unit prism 70 in the first direction. It is included as a part including the top 75 of one unit prism 70, or it is the same as the cross-sectional shape of the main cutting surface of another unit prism. The height Hb along the normal direction nd of the main body portion 65 of any one unit prism 70 is the main body portion of another unit prism located on one side in the first direction with respect to the one unit prism 70. The height is not less than 65 along the normal direction nd. The width Wb along the sheet surface of the main body 65 of any one unit prism 70 is the width of the main body 65 of the other unit prism 70 located on one side in the first direction with respect to the one unit prism 70. The width is equal to or greater than the width Wb along the sheet surface. The separation length (pitch) Pb along the sheet surface of the main body portion 65 between the top portions 75 of any two unit prisms 70 positioned adjacent to each other is one side in the first direction with respect to the two unit prisms 70. The separation length Pb along the sheet surface of the main body 65 between the tops 75 of the other two unit prisms adjacent to each other is equal to or longer than the separation length Pb.

  In the prism sheet 60 in which the unit prisms 70 arranged on the main body 65 are configured as described above, the arrangement position of the unit prisms 70 is from the light source 24 along the first direction (the arrangement direction of the unit prisms 70). When separated, the light incident on the unit prism 70 arranged at the arrangement position enters the portion of the second surface 72 far away from the top 75 along the normal direction nd of the main body 65. Can do. As described above, between the plurality of unit prisms 70, the first portion 72a of the second surface 72 is formed to have the same size. Therefore, as the arrangement position of the unit prism 70 moves away from the light source 24 along the first direction, the amount of light incident on the second portion 72b of the unit prism 70 arranged at the arrangement position increases. On the other hand, depending on the arrangement position of the unit prism 70 along the first direction, the amount of light incident on the first portion 72a of one unit prism 70 does not vary greatly. As a result, the traveling direction of light emitted from one side region located on one side in the first direction of the light emitting surface 21 of the surface light source device 20 is corrected by the first portion 72 a of the second surface 72. Will contain a relatively large amount of light. Conversely, the light emitted from the other side region located on the other side in the first direction of the light emitting surface 21 of the surface light source device 20 is corrected in the traveling direction by the second portion 72 b of the second surface 72. Will contain a relatively large amount of light.

  Further, the surface angle θb of the second surface 72 changes so as to increase from the top portion 75 side toward the base end portion 74 side. For this reason, the direction in which the light incident on the prism sheet 60 from the light guide plate 30 is reflected by the second surface 72 varies depending on the incident position on the prism sheet 60 along the arrangement direction of the unit prisms 70. Show a tendency to

  In particular, the surface angle θb at the first portion 72 a of the second surface 72 is smaller than the surface angle θb at the second portion 72 b of the second surface 72. Therefore, the light that enters the prism sheet 60 from the light guide plate 30 and travels to the second surface 72 of the unit prism 70, that is, the other side in the first direction from the front direction nd in a plane parallel to the first direction and the front direction nd. The light traveling in the direction inclined to the second surface 72 can change its traveling direction more greatly by the second portion 72b than by the first portion 72a. For this reason, the angle of the luminance measured at the first end position Pe1 that is one end in the first direction on the light emitting surface 21 of the surface light source device 20 and the second end position Pe2 that is the other end. The direction showing the peak luminance in the distribution can be directed to each other.

  In particular, in the example shown in FIGS. 7, 9, and 11, when the angular distribution of luminance in a plane parallel to the main cutting surface of the prism sheet 60 is measured on the light exit surface 31 of the light guide plate 30. Lights L71, L91, and L111 traveling in a direction parallel to the direction exhibiting the peak luminance are incident on the unit prism 70 of the prism sheet 60 and then reflected by the first portion 71 on the top 75 side of the second surface 70 of the unit prism 70. Then, the process proceeds in a direction inclined from the normal direction nd of the main body 65 to the other side (counterlight source side) in the arrangement direction (first direction) of the unit prisms 70. Further, in the examples shown in FIGS. 7, 9, and 11, when the angular distribution of luminance in a plane parallel to the main cutting surface of the prism sheet 60 is measured on the light exit surface 31 of the light guide plate 30. When light L72, L92, L112 traveling in a direction parallel to the direction exhibiting the peak luminance is incident on the unit prism 70 of the prism sheet 60 and then reflected by the second portion 72b of the second surface 72 of the unit prism 70, The process proceeds in a direction inclined from the normal direction nd of the main body 65 to one side (light source side) in the arrangement direction of the unit prisms 70. According to such an example, the angular distribution of luminance shown in FIGS. 8, 10 and 12 can be realized at each position along the first direction of the light emitting surface 21 of the surface light source device 20. It becomes possible.

  8, 10, and 12 are obtained by actually simulating the surface light source device 20 having the above-described configuration by adopting one of the shapes and dimensions within the specific range illustrated. The obtained angular distribution of luminance is shown by a solid line. 8, 10, and 12, the calculation result of the angular distribution of the luminance on the light emitting surface 21 caused by the light component reflected by the first portion 72 a of the second surface 72 is indicated by a one-dot chain line. The calculation result of the angular distribution of the luminance on the light emitting surface 21 caused by the light component reflected by the second portion 72b of the second surface 72 is indicated by a dotted line.

  FIG. 8 shows the angular distribution of luminance at the first end position Pe1 of the light emitting surface 21 that is one end in the direction parallel to the first direction. FIG. 10 shows the angular distribution of luminance at the central position Pc that is the center of the light emitting surface 21 in the direction parallel to the first direction. FIG. 12 shows an angular distribution of luminance at the second end position Pe2 of the light emitting surface 21 which is the other end in the direction parallel to the first direction. In the luminance angle distribution shown in FIGS. 8, 10, and 12, the front direction is set to 0 ° and one side in the direction parallel to the first direction from the front direction nd (the light source side, the light source is arranged). The angle when it is inclined toward the other side (anti-light source side, the side away from the light source) in the direction parallel to the first direction from the front direction nd Is defined to be a positive value.

  In the example shown in FIGS. 8, 10, and 12, the angular distribution of luminance on the light emitting surface 21 due to the reflected light component from the first portion 72a of the second surface 72 is in the first direction. At each position along it, it has a substantially constant shape. The direction showing the peak luminance in the angular distribution of the luminance on the light emitting surface 21 due to the reflected light component from the first portion 72a is inclined from the front direction to the other side in the first direction at each position in the first direction. ing. That is, the direction indicating the peak luminance in the angular distribution of the luminance on the light emitting surface 21 due to the reflected light component from the first portion 72a (distribution indicated by the alternate long and short dash line in FIGS. 8, 10, and 12) is A positive angle is formed with respect to the front direction. On the other hand, the angular distribution of luminance on the light emitting surface 21 due to the reflected light component from the second portion 72b of the second surface 72 also exhibits a substantially constant shape at each position along the first direction. Yes. However, the direction showing the peak luminance in the angular distribution of the luminance on the light emitting surface 21 due to the reflected light component from the second portion 72b is from one direction in the first direction to one side in the first direction at each position in the first direction. Inclined. That is, in the angular distribution of the luminance on the light emitting surface 21 due to the reflected light component from the second portion 72b (distribution indicated by the dotted line in FIGS. 8, 10, and 12), the direction indicating the peak luminance is the front surface. A negative angle with respect to the direction.

  Further, the ratio of the amount of reflected light from the first portion 72a to the total amount of emitted light and the ratio of the amount of reflected light from the second portion 72b to the total amount of emitted light vary at each position along the first direction. doing. The ratio of the amount of reflected light from the first portion 72a to the total amount of emitted light is from the first end position Pe1 to the second end position Pe2, that is, from one side to the other side along the first direction. is decreasing. On the other hand, the ratio of the amount of reflected light from the second portion 72b to the total amount of emitted light is from the first end position Pe1 to the second end position Pe2, that is, from one side along the first direction. It is increasing toward the side. In particular, in the example shown in FIG. 10, the light emitted from the central position Pc in the first direction on the light emitting surface 21 has substantially the same reflected light component at the first portion 72a and reflected light component at the second portion 72b. The amount is adjusted to be included.

  Due to the above-mentioned tendency regarding the angular distribution of luminance caused by the reflected light component at the first portion 72a and the angular distribution of luminance caused by the reflected light component at the second portion 72b, it is defined due to the total emitted light component. The angular distribution of luminance on the light emitting surface 21 of the surface light source device 20 exhibits the following tendency. The angular distribution of luminance at the first end position Pe1 of the light emitting surface 21 has a shape similar to the angular distribution of luminance due to the reflected light component at the first portion 72a, and the luminance at the first end position Pe1. The peak angle θya of the angle distribution takes a positive value. Conversely, the angular distribution of luminance at the second end position Pe2 of the light emitting surface 21 has a shape that is very similar to the angular distribution of luminance caused by the reflected light component at the second portion 72b. The peak angle θyb of the luminance angular distribution at the end position Pe2 takes a negative value.

In addition, the peak in the angular distribution of luminance at the central position Pc of the light emitting surface 21 where the reflected light component at the first portion 72a and the reflected light component at the second portion 72b are included in the emitted light by substantially the same amount. The angle θyc is an angular distribution of luminance at the first end position Pe1 on the light emitting surface 21 that is more strongly governed by the reflected light component at the first portion 72a than at the second portion 72b. The luminance at the second end position Pe2 on the light emitting surface 21 is smaller than the peak angle θya and is more strongly governed by the reflected light component at the second portion 72b than the reflected light component at the first portion 72a. It takes a larger value than the peak angle θyb of the angle distribution. That is, as shown in FIGS. 8, 10, and 12, the peak angle θya that provides the highest luminance in the angular distribution of luminance at the first end position Pe <b> 1 on the light emitting surface 21 and the second end on the light emitting surface 21. The peak angle θyb that provides the highest luminance in the angular distribution of luminance at the part position Pe2 and the peak angle θyc that provides the highest luminance in the angular distribution of luminance at the central position Pc on the light emitting surface 21 are expressed by the following equation (1). Satisfies the relationship.
θyb <θyc <θya (1)

  FIG. 3 shows the display device 10 using the surface light source device 20 shown in FIGS. 8, 10, and 12 and having a luminance characteristic satisfying the expression (1). In the surface light source device 20 having the luminance characteristics shown in FIGS. 8, 10 and 12 and satisfying the formula (1), the image displayed at the center position Pc on the display surface 11 is as shown in FIG. It can be observed brightest from the front direction.

  In addition, the image displayed at the first end position Pe1 on the display surface 11 is more than the position O11 facing the first end position Pe1 from the front direction nd (the position of O11 in FIG. 3). Is observed brightest at a position shifted from the center to the center position Pc along the first direction. Specifically, the image displayed at the first end position Pe1 on the display surface 11 can be observed brightest from the direction inclined from the front direction nd by the peak angle θya shown in FIG. . Therefore, when the display surface 11 is observed from a position facing the center position Pc in the front direction nd (position of the observer O1 in FIG. 3), an image displayed at the first end position Pe1 on the display surface 11 Can be observed relatively brightly. That is, it is possible to prevent the brightness of the image projected at the first end position Pe1 from being significantly darker than the brightness of the image projected at the center position Pc.

  Furthermore, the image displayed at the second end position Pe2 on the display surface 11 is at the position O12 rather than the position facing the second end position Pe1 from the front direction nd (position O12 in FIG. 3). Is observed brightest at a position shifted from the center to the center position Pc along the first direction. Specifically, the image displayed at the second end position Pe2 on the display surface 11 can be observed brightest from the direction inclined from the front direction nd by the peak angle θyb shown in FIG. . Therefore, when the display surface 11 is observed from a position facing the center position Pc in the front direction nd (the position of the observer O1 in FIG. 3), an image displayed at the second end position Pe2 on the display surface 11 Can be observed relatively brightly. That is, it is possible to prevent the brightness of the video displayed at the first end position Pe2 from being significantly darker than the brightness of the video displayed at the center position Pc. In this way, the unevenness in brightness perceived by the observer can be effectively made inconspicuous.

  With respect to the luminance angular distribution on the light emitting surface 21 of the surface light source device 20 according to the present embodiment as described above, in the prism sheet incorporated in the conventional display device, at each position along the arrangement direction of the unit prisms. The front direction brightness is intensively improved. For example, as shown by a two-dot chain line at the first end position Pe in FIG. 3, the peak luminance is formed in the front direction with a narrow half-value angle. However, in such a conventional display device, when the display surface is observed from the position facing the front direction nd (the position of the observer O1 in FIG. 3) with respect to the center position Pc, the center position Pc of the large display surface 11 is observed. Compared with the image projected on the image, the image projected on the end positions Pe1 and Pe2 is observed to be extremely dark. That is, the in-plane variation in brightness is increased, and the image displayed on the display surface is significantly deteriorated.

  Further, as shown by a two-dot chain line in FIG. 3, the second end along the first direction (light guide direction) from the position where the observer O2 faces the front direction nd with respect to the center position Pc. When the display surface 11 is observed at a position shifted toward the part position Pe2, the observation angle of the first end position Pe becomes very large. As can be understood from the angular distribution of the emitted light quantity (brightness angular distribution) at each position along the first direction on the display surface 11 indicated by the solid line in FIG. 3, FIG. 8, FIG. 10, and FIG. When the surface light source device 20 having the luminance characteristics shown in FIG. 6 is used, the brightness is slightly dark overall, but an image displayed on the entire area of the display surface 11 can be observed. On the other hand, in the example of the conventional display device indicated by a two-dot chain line in FIG. 3, it is no longer possible to observe an image in a part of the area including the first end position Pe1 on the display surface.

  According to the present embodiment as described above, the unevenness in brightness sensed by the observer can be effectively made inconspicuous. In addition, since the brightness of an image that can be observed by an observer can be effectively increased, effective use of light from the light source is realized and energy efficiency is improved.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above-described embodiment are used, and redundant descriptions are omitted.

  The cross-sectional shape of the unit prism 70 on the main cutting surface of the prism sheet described in the above embodiment is merely an example, and can be variously changed. As already described, as shown in FIG. 14, the contour of the second surface 72 of the unit prism 70 at the main cutting surface of the prism sheet may include a curve. In such a modification, the surface angle θb is an angle formed by a tangent TL to the second surface 72 in the main cutting surface of the unit prism 70 and the sheet surface of the main body 65, as shown in FIG. More precisely, it is specified as the value of the smaller one of the two formed corners (the minor angle). Similarly, it is not essential that the first surface 71 of the unit prism 70 is a flat surface. For example, the unit prism 70 may have a configuration symmetrical to the second surface 72 as shown in FIG.

  In the above-described embodiment, the example in which the unit prisms 70 of the prism sheet 60 are disposed adjacent to each other has been described. However, the present invention is not limited to this. For example, as shown in FIG. 14, a flat portion 68 may be formed between two adjacent unit prisms 70, or between two adjacent unit prisms 70 as shown by a two-dot chain line in FIG. A recess 69 may be formed.

  Furthermore, the prism sheet 60 may contain a diffusing component that diffuses transmitted light, and may exhibit an isotropic diffusion function or an anisotropic diffusion function. According to such a modification, the viewing angle characteristic in each direction can be adjusted with a higher degree of freedom.

  Further, the above-described configuration of the unit shape element 50 of the light guide plate 30 is merely an example. As an example, the outer contour 51 of the unit shape element 50 may include a curve on the main cut surface of the light guide plate.

  Further, in the above-described embodiment, the example in which the unit shape element 50 of the light guide plate 30 has a constant cross-sectional shape along the longitudinal direction thereof is shown, but the present invention is not limited thereto, and the cross-sectional shape of the unit shape element 50 is The unit shape element may change along the longitudinal direction.

  Furthermore, in the above-described embodiment, an example in which the light incident on the light guide plate 30 can be emitted from the light guide plate 30 by dispersing the diffusion component 45 in the base portion 40 has been described. However, the present invention is not limited to the above example, and as an example, as shown in FIG. 15, the light output surface 31 and the back surface 32 of the light guide plate 30 may be inclined with respect to each other. According to the example shown in FIG. 15, the diffusion component 45 is dispersed in the light guide plate 30, and the inclined surface 32 a is supplementarily provided on the back surface 32 of the light guide plate 30. In particular, in the example shown in FIG. 15, as the incident surface 33 approaches the opposite surface 34 along the light guide direction, the proportion of the inclined surface 32 a in the back surface 32 increases. According to such a configuration, emission of light from the light guide plate 30 in a region separated from the incident surface 33 along the light guide direction is promoted, and the amount of emitted light decreases as the distance from the incident surface 33 increases. Can be effectively prevented. Further, another configuration (another light extraction configuration) for causing the light incident on the light guide plate 30 to be emitted from the light guide plate 30 may be adopted instead of the above-described configuration or in addition to the above-described configuration. it can.

  Furthermore, the configurations of the surface light source device 20 and the display device 10 described above are merely examples, and various modifications can be made. For example, a light diffusion sheet having a function of diffusing transmitted light, a polarization separation sheet having a polarization separation function of transmitting only a specific polarization component and reflecting other polarization components, etc. You may make it provide in the side.

  In addition, although the some modification with respect to embodiment mentioned above was demonstrated above, naturally, it is also possible to apply combining a some modification suitably.

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Display surface 15 Liquid crystal display panel 18 Control apparatus 20 Surface light source device 21 Light emission surface 24 Light source 25 Light emitter 28 Reflecting sheet 30 Light guide plate 31 Light emission surface 32 Back surface 33 Light incident surface 34 Opposite surface 37 Inclination surface 38 Inclination surface 40 Base 44 Main part 45 Diffusing component 50 Unit shape element, unit optical element, unit lens, unit prism 60 Prism sheet, optical sheet 61 Light exit surface 65 Main body part 70 Unit prism, unit optical element, unit shape element, unit lens 71 1st Surface 72 Second surface 72a First portion 72b Second portion 74 Base end portion 75 Top portion

Claims (14)

A light guide plate having a light exit surface and a pair of side surfaces disposed opposite to each other in the first direction;
A light source provided corresponding to a side surface located on one side in the first direction of the pair of side surfaces;
A sheet-like main body portion, is arranged on the main body portion, each extending linearly in a direction intersecting the array direction, comprising: a plurality of unit prisms, and a prism sheet having a,
The prism sheet is arranged such that the light exit surface of the light guide plate and the unit prism face each other.
Each unit prism has a first surface located on one side in the arrangement direction, and a second surface located on the other side opposite to the one side in the arrangement direction,
In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit prisms, the angle formed by the second surface of the unit prism with respect to the sheet surface of the main body portion is a surface angle. The surface angle of at least one unit prism changes from the top of the unit prism farthest away from the main body to the base end of the unit prism closest to the main body, and increases.
The outline of the second surface of the main cutting surface of at least one unit prism is a part including the apex of at least one other unit prism located on one side of the one unit prism in the arrangement direction. look including the contour of the second side of said main cutting plane,
The arrangement direction of the unit prisms is parallel to the first direction, and the one side of the arrangement direction of the unit prisms is the one side where the light source in the first direction is provided, The prism sheet and the light guide plate are arranged,
The second surface of the unit prism located at the most other side in at least the arrangement direction includes a first portion that is the farthest from the main body, a second portion that is adjacent to the first portion from the main body, and Have
When the angular distribution of luminance in a plane parallel to the main cutting surface of the prism sheet is measured on the light exit surface of the light guide plate, the light guide plate has the light source caused by the light emitted from the light source. Light traveling in a direction parallel to the peak angle that gives the highest luminance in the angular distribution of luminance on the light exit surface,
After being incident on the unit prism of the prism sheet and reflected by the first portion of the second surface of the unit prism, the main body portion is inclined in the direction inclined from the normal direction to the other side in the arrangement direction. Proceed,
After being incident on the unit prism of the prism sheet and reflected by the second portion of the second surface of the unit prism, the main body portion is inclined in a direction inclined to one side in the arrangement direction from the normal direction. Advance, surface light source device . The outline of the second surface of the main cutting surface of any one unit prism is the second contour of the main cutting surface of another unit prism located on one side of the unit direction with respect to the unit prism. 2. The surface light source device according to claim 1, wherein the surface light source device includes a contour of two surfaces as a part including the top portion, or is identical to a contour of the second surface in the main cutting surface of the other unit prism. . The cross-sectional shape of the main cutting surface of at least one unit prism is a part including the top, and the main cutting surface of at least one other unit prism located on one side of the one unit prism in the arrangement direction. The surface light source device according to claim 1, comprising the cross-sectional shape of The cross-sectional shape at the main cutting plane of any one unit prism is the cross-sectional shape at the main cutting plane of another unit prism located on one side in the arrangement direction with respect to the one unit prism. The surface light source device according to any one of claims 1 to 3, wherein the surface light source device includes, as a part including, or the same cross-sectional shape of the other one unit prism in the main cut surface. The separation length along the sheet surface of the main body between the tops of at least two adjacent unit prisms is at a position that is one side in the arrangement direction with respect to the two unit prisms. It is longer than the separation length along the said sheet surface of the said main-body part between the said top parts of the other two unit prisms located at least adjacent to each other at any one of Claims 1-4. The surface light source device described in 1. The separation length along the sheet surface of the main body portion between the top portions of any two unit prisms positioned adjacent to each other is adjacent to a position that is one side in the arrangement direction with respect to the two unit prisms. 6. The surface light source device according to claim 1, wherein the surface light source device is at least a separation length along the sheet surface of the main body portion between the top portions of the other two unit prisms positioned together. The height along the normal direction of the main body portion of at least one unit prism is the height of the main body portion of at least one other unit prism positioned on one side in the arrangement direction with respect to the one unit prism. The surface light source device according to claim 1, wherein the surface light source device is higher than a height along a normal direction. The height along the normal direction of the main body portion of any one unit prism is the height of the main body portion of one other unit prism located on one side in the arrangement direction than the one unit prism. The surface light source device as described in any one of Claims 1-7 which is more than the height along a normal line direction. The width along the sheet surface of the main body portion of at least one unit prism is the sheet surface of the main body portion of at least one other unit prism positioned on one side in the arrangement direction with respect to the one unit prism. The surface light source device according to claim 1, wherein the surface light source device is wider than the width along the surface . The width along the sheet surface of the main body portion of any one unit prism is the sheet surface of the main body portion of one other unit prism located on one side in the arrangement direction than the one unit prism. The surface light source device as described in any one of Claims 1-9 which is more than the width | variety along. The light guide plate is
A sheet-like base;
Having a unit optical element provided on the prism sheet side of the base are arranged in a direction intersecting the first direction, the surface light source device according to any one of claims 1 to 10. The surface light source device according to claim 11 , wherein the base portion includes a main portion made of a resin and a diffusion component dispersed in the main portion. A surface light source device according to any one of claims 1 to 12 ,
A transmissive display panel illuminated by the surface light source device. A controller connected to the light source;
The light guide plate includes a base and a plurality of linear unit optical elements arranged in one direction on a surface on one side of the base to form the light exit surface,
The light source includes a plurality of point-like light emitters arranged in the one direction,
The display device according to claim 13 , wherein the control device is configured to adjust an output of each point light emitter in accordance with an image to be displayed.

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