JP2013076722A - Optical sheet, surface light source device, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet capable of generating excellent visual field characteristics.SOLUTION: An optical sheet 60 includes a body part 65 and unit prisms 70 arranged on the incident side of the body part. Each of the unit prisms includes a first surface 71 and a second surface 72. An incident surface angle θb changes to be larger from an apex 75 of the unit prism toward a base end part 74 of the unit prism. An apex side straight line TEL2 has an angle of 45° or more and 55° or less to a sheet surface of the body part. A base end side straight line DEL2 has an angle of 60° or more and 70° or less to the sheet surface of the body part. A ratio of a maximum clearance Dx2 from a straight line SL2 connecting the apex to the base end part to the second surface and a distance Dy2 between the apex and the base end part is 0.04 or more and 0.06 or less.

Description

  The present invention relates to an optical sheet having a plurality of unit prisms on the light incident side, and relates to an optical sheet that can provide excellent viewing angle characteristics. The present invention also relates to a surface light source device and a display device that exhibit excellent viewing angle characteristics.

  2. Description of the Related Art A surface light source device that irradiates 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.

  A side light type (edge light type) surface light source device has a structural feature that enables the surface light source device to be thinner than a direct type surface light source device. Due to this structural feature, the edge light type surface light source device has been mainly applied to a display device for a notebook personal computer (hereinafter, also simply referred to as “notebook PC”). The sidelight type surface light source device typically includes a light guide plate, a light source disposed on the side of the light guide plate, and a large number of optical sheets disposed on the light output side of the light guide plate. . Examples of the many optical sheets include a light diffusing sheet for diffusing light and a light collecting sheet for deflecting transmitted light.

  In recent years, a combination of a light guide plate having a light exit surface formed by unit-shaped elements extending in the light guide direction and a prism sheet formed so that a unit prism projects toward the light exit surface of the light guide plate is considered. It is being done. According to such a light guide plate, the light component traveling in the direction orthogonal to the light guide direction can be condensed to some extent in the front direction by the unit shape element, so that the separate optical sheet having the same function Can be excluded from the surface light source device. Also,

  The emission direction of the light emitted from such a light guide plate exhibits extremely strong directivity in a plane along the light guide direction. The prism seam disposed on the light condensing side of the light guide plate condenses the light in the front direction very effectively with respect to the light having such strong directivity by total reflection at the unit prism.

  That is, according to the light guide plate having unit-shaped elements extending in the light guide direction and the prism sheet in which the unit prism is formed on the light incident side, the two optical members enable light condensing in two directions, and an excellent front surface. Directional luminance can be ensured.

  Nowadays, along with the rapid spread of mobile terminals typified by mobile phones, application of sidelight type surface light source devices to mobile terminals is rapidly expanding. The sidelight type surface light source device is very suitable for application to a portable terminal in that it can be thinned. Furthermore, according to the sidelight type surface light source device including the light guide plate having the unit shape element and the prism sheet having the unit prism on the light incident side, further thinning is achieved while ensuring excellent front direction luminance. Can be realized.

JP 2004-226503 A

  By the way, the conventional prism sheet having the unit prism on the light incident side can narrow the traveling direction of light to an extremely narrow angle range within the plane along the light guide direction. On the other hand, the light guide plate is required to make the distribution of the emitted light quantity along the light guide direction uniform as a main function. For this reason, the light condensing function by the unit shape element which forms the light exit surface of the light guide plate does not become as strong as the light condensing function of the prism sheet. As a result, the half-value angle (inclination angle from the front direction in the direction in which half the peak luminance is ensured) in the angular distribution of luminance in the plane including the light guide direction on the light emitting surface of the surface light source device is Compared with the half-value angle in the angular distribution of the luminance in the plane including the direction orthogonal to the light guide direction on the light emitting surface of the light source device, it becomes very narrow. Such viewing angle characteristics have been ideal for specific applications, for example, television receivers and display devices for computers in which the vertical viewing angle is narrow and the horizontal viewing angle is set wide.

  On the other hand, when the present inventors applied a side light type surface light source device including a light guide plate having a unit shape element and a prism sheet having a unit prism on the light incident side to a mobile terminal, Although it is very convenient in that the thickness can be reduced, it has been noticed that the visibility is remarkably deteriorated. After further investigation by the inventors of the present invention, it was predicted that this defect was caused by the following.

  That is, 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, the direction in which the user observes each position on the display surface is greatly different. On the other hand, the conventional prism sheet having a unit prism on the light incident side narrows the traveling direction of light from the light guide plate within an extremely narrow angle range, and the half-value angle is also very narrow. For this reason, the brightness of the image observed by the observer is greatly different at each position on the display surface, and as a result, the visibility of the image is significantly deteriorated.

  In addition, in many of recent mobile terminals, the orientation of the image displayed on the display surface changes according to the orientation of the display surface. For this reason, it is preferable that the viewing angle characteristics in each direction on the display surface have the same tendency. As described above, when a conventional prism sheet having a unit prism on the light incident side is used, the half-value angle in the luminance angular distribution in the plane including the light guide direction and the direction orthogonal to the light guide direction are set. The half-value angle in the angular distribution of the luminance in the in-plane is greatly different. Therefore, when an image is observed while changing the orientation of the display surface of the portable terminal, the impression received from the observed image changes greatly before and after the orientation is changed.

  The present invention has been made in view of such points, and an object thereof is to provide an optical sheet that can provide excellent viewing angle characteristics. The present invention also relates to a surface light source device and a display device that exhibit excellent viewing angle characteristics.

The optical sheet according to the present invention is
A sheet-like body,
A plurality of unit prisms arranged side by side on the light incident side of the main body, each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface and a second surface arranged to face each other in a direction parallel to the sheet surface of the main body,
In a main cutting plane parallel to both the normal direction of the main body and the arrangement direction of the unit prisms, an incident surface angle is an angle formed by the second surface of the unit prism with respect to the sheet surface of the main body Then, the light incident surface angle is changed so as to increase 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.
In the main cut surface, the second surface shifted from the top to the base end by a length of 5% of the distance along the sheet surface of the main body between the top and the base end. The top side straight line connecting the upper position and the top portion forms an angle of 45 ° or more and 55 ° or less with respect to the seat surface of the main body portion, and the portion between the top portion and the base end portion is formed. A base end side straight line connecting the base end portion and the position on the second surface shifted from the base end portion to the top side by a length of 5% of the distance along the sheet surface of the main body portion. Is at an angle of 60 ° to 70 ° with respect to the sheet surface of the main body,
In the main cutting plane, the top portion having a separation distance from a straight line connecting the top portion and the base end portion to a position on the second surface that is the farthest from the straight line in a direction orthogonal to the straight line; The ratio (Dx2 / Dy2) to the distance from the base end is 0.04 or more and 0.06 or less.

  In the optical sheet according to the present invention, the difference between the angle formed by the base end side straight line with respect to the sheet surface of the main body portion and the angle formed by the top side straight line with respect to the sheet surface of the main body portion is 12 You may make it be more than °.

  In the optical sheet according to the present invention, the top portion of the unit prism is defined at a position where the first surface and the second surface are connected to each other, and in the main cutting surface, the first surface and the second surface are In addition, symmetry may be provided about an axis that passes through the top and extends in the normal direction of the main body.

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 the one side surface in the first direction of the pair of side surfaces;
Any one of the optical sheets according to the present invention described above, disposed opposite to the light exit surface of the light guide plate,
The arrangement direction of the unit prisms is parallel to the first direction, the first surface of each unit prism is located on one side in the first direction, and the second surface is on the other side in the first direction. The optical sheet and the light guide plate are arranged so as to be positioned.

In the surface light source device according to the present invention,
The light guide plate may include a sheet-like base portion and unit-shaped elements provided on the optical sheet side of the base portion in an arrangement direction intersecting with the first direction.

  In the surface light source device according to the present invention, in the main cut surface of the light guide plate parallel to both the normal direction of the base portion and the arrangement direction of the unit shape elements, the outer contour of the unit shape element is the sheet surface of the base portion. Is a light emitting surface angle, the unit shape element in a region on the outer contour corresponding to 20% to 35% of the width of the unit shape element along the sheet surface of the base portion The light exit surface angle may be 10 ° to 35 °.

  In the surface light source device according to the present invention, the light exit surface angle of the unit shape element may be the outside of the unit shape element closest to the base from the top on the outer contour of the unit shape element farthest from the base. You may change so that it may become large toward the base end part on an outline.

  In the surface light source device according to the present invention, the light exit surface angle may be not less than 10 ° and not more than 60 ° in the entire region on the outer contour of the unit shape element in the main cut surface of the light guide plate.

  In the surface light source device according to the present invention, in the region on the outer contour corresponding to 30% or more and 80% or less of the width of the unit shape element along the sheet surface of the base portion in the main cutting surface of the light guide plate. The light exit surface angle may be greater than 30 ° and 60 ° or less.

  In the surface light source device according to the present invention, the height from the light exit side surface of the base of the unit-shaped element in the main cutting surface with respect to the width Wa along the arrangement direction of the unit-shaped elements in the main cutting surface of the light guide plate. The ratio of Ha (Ha / Wa) may be 0.3 or more and 0.4 or less.

In the surface light source device according to the present invention,
The unit-shaped element includes a top portion of the main cutting surface of the light guide plate, the one side of which is located on the base portion and the most distant from the light exit side surface on the outer contour, and each base end portion connected to the light exit side surface. A pentagonal shape with two sides between them, or a shape formed by chamfering one or more corners of the pentagonal shape,
Of the two sides located between the top and each base end on the outer contour, the light exit surface angle of one side of the top is 10 ° or more and 35 ° or less, and one side of the base end The light exit surface angle may be greater than 30 ° and 60 ° or less.

  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.

  The surface light source device according to the present invention may further include a second light source provided corresponding to the other side surface in the first direction of the pair of side surfaces.

A display device according to the present invention comprises:
Any of the surface light source devices according to the present invention described above;
A transmissive display panel disposed to face 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-shaped 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, excellent viewing angle characteristics can be ensured.

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 perspective view showing a light guide plate incorporated in the surface light source device of FIG. FIG. 4 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 line IV-IV in FIG. 3. FIG. 5 is a cross-sectional view corresponding to FIG. 4 and is a view for explaining the operation of the light guide plate. FIG. 6 is a perspective view showing an optical sheet incorporated in the surface light source device of FIG. FIG. 7 is a diagram for explaining the operation of the optical sheet, and is a partial cross-sectional view of the optical sheet along the line VII-VII in FIG. 6. FIG. 8 is a cross-sectional view corresponding to FIG. 7 and showing a unit prism of the optical sheet. FIG. 9 is a view for explaining a modification of the optical sheet in the same cross section as FIG. FIG. 10 is a view for explaining a modification of the light guide plate in the same cross section as FIG. FIG. 11 is a diagram for explaining another modification of the light guide plate in the same cross section as FIG. 4. FIG. 12 is a diagram corresponding to FIG. 1 and showing a modification of the surface light source device. FIG. 13 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 1. FIG. 14 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 2. FIG. 15 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 3. FIG. 16 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 4. FIG. 17 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 5. FIG. 18 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 6. FIG. 19 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 7. FIG. 20 is a graph showing the luminance distribution on the light emitting surface of the surface light source device according to Sample 8. FIG. 21 is a graph showing the luminance distribution on the light exit surface of the light guide plate of the surface light source device according to Samples 1-8. FIG. 22 is a diagram illustrating a light guide plate incorporated in a surface light source device according to each sample by a main cut surface of the light guide plate, and is a diagram for explaining a cross-sectional shape of a unit shape element of the light guide plate. .

  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.

  FIGS. 1-8 is a figure for demonstrating one Embodiment by this invention. Among these, FIG. 1 is a cross-sectional view showing a schematic configuration of the liquid crystal display device and the 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 perspective view showing a light guide plate included in the surface light source device, and FIGS. 4 and 5 are cross-sectional views showing main cut surfaces of the light guide plate. FIG. 6 is a perspective view showing an optical sheet included in the surface light source device, and FIG. 7 is a cross-sectional view showing a main cut surface of the optical sheet. 1 and 2 correspond to the cross section taken along the line AA in FIG. 3 and the line VII-VII in FIG.

  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.

  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. Among these, the liquid crystal cell 12 includes a pair of support plates made of glass or the like, a liquid crystal disposed between the support plates, and an electrode for controlling the orientation of liquid crystal molecules by an electric field for each region forming one pixel. It is a member having. The control device 18 is configured to control the alignment of liquid crystal molecules for each pixel. As a result, the liquid crystal display panel 15 functions as a shutter that controls transmission and blocking of light from the surface light source device 20 for each pixel, and by selecting and transmitting the planar light from the surface light source device 20, the image is displayed. Will come to form. The details of the liquid crystal display panel 15 are described in various known documents (for example, “Flat Panel Display Dictionary” (supervised by Tatsuo Uchida, Hiraki Uchiike), 2001, Industrial Research Council). Detailed description is omitted.

  Next, the surface light source device 20 will be described. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and illuminates the liquid crystal display panel 15 from the back side. As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device, and includes a light guide plate 30 and light sources 24 a and 24 b disposed on the sides of the light guide plate 30. . 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. Then, at least one light incident surface is formed by a part of the side surface of the light guide plate 30, and the light sources 24a and 24b are arranged to face the light incident surface. In addition, an opposite surface 34 that faces one light incident surface 33 is also formed by a part of the side surface, and the light incident on the light guide plate 30 from the one light incident surface 33 is approximately the light incident surface 33, The light guide plate 30 is guided in the first direction (light guide direction) connecting the opposite surface 34 facing the one light incident surface 33. In addition, the surface light source device 20 further includes a reflection sheet 22 disposed to face the back surface 32 of the light guide plate 30 and an optical sheet 60 disposed to face the light exit surface 31 of the light guide plate 30. ing. The light exit surface of the optical sheet 60 constitutes the light exit surface 21 of the surface light source device 20. The reflection sheet 22 is disposed so as to face the back surface 32 of the light guide plate 30 and covers the light guide plate 30 from the back surface side.

  In the illustrated example, the light exit surface 31 of the light guide plate 30 is formed in a rectangular shape together with the display surface 11 of the liquid crystal display device 10 and the light emitting surface 21 of the surface light source device 20. That is, 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). Therefore, the side surface defined between the pair of main surfaces includes four surfaces. And as shown in FIG. 1, the two surfaces which oppose the 1st direction among the side surfaces comprise the light-incidence surfaces 33 and 34. As shown in FIG. In other words, the one light incident surface described above functions as the first light incident surface 33, and the opposite surface facing the one light incident surface functions as the second light incident surface 34. As shown in FIG. 1, a first light source 24 a is provided to face the first light incident surface 33, and a second light source 24 b is provided to face the second light incident surface 34. In addition, the light guide plate 30 in the present embodiment has a constant cross-sectional shape at each position along the first direction.

  The 1st light source 24a and the 2nd light source 24b can be comprised by various aspects, such as fluorescent lamps, such as a linear cold cathode tube, point-like LED (light emitting diode), and an incandescent lamp, for example. In the present embodiment, each of the first light source 24a and the second light source 24b includes a large number of point light emitters arranged side by side along the longitudinal direction of the corresponding light incident surfaces 33 and 34, specifically, It is comprised by many light emitting diodes (LED). FIG. 3 shows the arrangement positions of a large number of point-like light emitters 25 forming the first light source 24a. 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 22 is a member for reflecting the light emitted from the back surface 32 of the light guide plate 30 so as to enter the light guide plate 30 again. The reflection sheet 22 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.

  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 the present embodiment, the plate surface of the light guide plate 30, the sheet surface of the optical sheet 60, the sheet surface of the reflection sheet 22, the panel surface of the liquid crystal display panel, the display surface 11 of the display device 10, and the surface light source device 20. The light emitting surface 21, the sheet surface of the base 40 of the light guide plate 30 described later, the light exit side surface 41 of the base 40 of the light guide plate 30 described later, the sheet surface of the main body 65 of the optical sheet 60 described later, and the optical sheet 60 described later. The light incident side surfaces 66 and the like of the main body 65 are parallel to each other. Further, in the present specification, the “front direction” is a direction nd of a normal to the light emitting surface 21 of the surface light source device 20 (see, for example, FIG. 2 and FIG. 4), and in the present embodiment, the display device 10. The normal direction to the display surface 11, the normal direction to the plate surface of the light guide plate 30, the normal direction to the sheet surface of the optical sheet 60, and the light exit surface of the light guide plate 30 when viewed globally and globally It also coincides with the normal direction to 31 and so on.

  Further, in this specification, the terms “unit shape element”, “unit optical element”, “unit prism”, and “unit lens” refer to various optical actions (for example, reflection and refraction) on incident light. It means an element (optical element) having a shape that can be exerted. In addition, terms such as “unit shape element”, “unit optical element”, “unit prism”, and “unit lens” are not distinguished from each other based only on the difference in names as optical elements.

  Next, the light guide plate 30 will be described in detail with reference mainly to FIGS. 2 and 3, the light guide plate 30 includes a base portion 40 formed in a plate shape and a plurality of unit shape elements (on a light emitting side surface) 41 formed on one side surface (light emitting side surface) 41 ( Unit optical element, unit prism) 50. The base 40 is configured as a flat member having a pair of parallel main surfaces. And the back surface 32 of the light-guide plate 30 is comprised by the surface 42 of the other side of the base 40 located in the side which does not face the optical sheet 60. FIG.

  As shown in FIG. 2, the base portion 40 has a main portion 44 made of a 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 material containing a gas, and simple bubbles. Note that the diffusion component 45 is omitted in the drawings other than FIGS. 1 and 2.

  Next, the unit shape element 50 provided on the one side surface 41 of the base 40 will be described. As shown well in FIG. 3, the plurality of unit-shaped elements 50 are arranged along the arrangement direction that intersects the first direction and is parallel to one side surface 41 of the base 40 (the sheet surface of the base 40). Are arranged on one side surface 41 of each other. Each unit shape element 50 extends linearly on one side surface 41 of the base 40 so as to intersect the arrangement direction thereof.

  In particular, in the present embodiment, the plurality of unit shape elements 50 are arranged on the one side surface 41 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 constituted by the light exit side surface 51 of the unit shape element 50. Each unit shape element 50 extends linearly along a first direction orthogonal to the second direction. Furthermore, each unit shape element 50 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction. In the present embodiment, the plurality of unit shape elements 50 are configured identically.

  Next, the cross section shown in FIGS. 4 and 5, that is, the arrangement direction of unit shape elements (second direction) and the sheet surface of the base 40 (one side surface 41 of the base 40, the plate surface of the light guide plate 30). A cross-sectional shape of each unit shape element 50 in a cross section parallel to both directions of the normal direction nd (hereinafter, also simply referred to as “main cut surface of the light guide plate”) will be described. In the present embodiment, the outer contour (light-emitting side surface) 51 in the main cutting surface of the unit-shaped element 50 has a light-emitting surface angle θa that is an angle formed by the outer contour with respect to the sheet surface of the base 40 and is 10 ° or more and 35. A region (first region) Z1 that is less than or equal to ° is included. And this 1st area | region Z1 whose light emission surface angle (theta) a is 10 degrees or more and 35 degrees or less is the full width Wa of the unit-shaped element 50 along the sheet | seat surface (more specifically, 2nd direction) of the base 40. Occupies an area on the outer contour 51 corresponding to a width of 20% to 35%.

  That is, the first region Z1 in which the light exit surface angle θa is 10 ° or more and 35 ° or less occupies 20% or more and 35% or less of the entire width of the unit shape element 50 when projected in the front direction nd. It becomes like this. In the example shown in FIG. 4, the width Waa of the first region Z1 of the unit shape elements 50 along the arrangement direction of the unit shape elements 50 is 20% or more and 35% or less with respect to the total width Wa of the unit shape elements 50. It has become. As a result, when the light exit surface 31 of the light guide plate 30 is observed from the front direction nd, in the region of 20% to 35% of the region occupied by the light exit side surface (outer contour) 51 of the unit shape element 50, the unit The light exit surface angle θa of the shape element 50 is not less than 10 ° and not more than 35 °. As described above, by providing the first region Z1 having the light exit surface angle θa of 10 ° to 35 ° on the light exit side surface 51 of the unit-shaped element 50, excellent front direction luminance can be ensured and the unit In the angular distribution of luminance in the plane along the arrangement direction of the shape elements 50, it is effective that the second peak (side lobe) of luminance (brightness) in a direction greatly inclined from the front direction occurs. It becomes possible to prevent.

  Here, the light exit surface angle θa is an angle formed by the light exit side surface (outer contour) 51 of the unit shape element 50 with respect to the sheet surface of the base 40 in the main cut surface of the light guide plate 30 as described above. is there. When the outer contour (light-emitting side surface) 51 in the main cutting surface of the unit-shaped element 50 is formed in a polygonal line shape as in the example shown in FIG. 4, each linear part constituting the polygonal line and the sheet surface of the base part 40 (Strictly speaking, the smaller one of the two formed angles (subordinate angle)) is the light exit surface angle θa. On the other hand, as in a modification described later, the outer contour (light emission side surface) 51 in the main cutting surface of the unit shape element 50 may be configured by a curved surface (see FIGS. 10 and 11). For the outer contour 51 of the curved unit-shaped element 50, an angle formed between the tangent TL to the outer contour and the sheet surface of the base 40 (strictly speaking, of the two formed corners) Is determined as the light exit surface angle θa.

  In the present embodiment, the outer contour (light-emitting side surface) 51 on the main cutting surface of the unit-shaped element 50 further includes a region (second region) Z2 where the light-emitting surface angle θa is greater than 30 ° and equal to or less than 60 °. Contains. And this 2nd area | region Z2 where the light emission surface angle (theta) a is larger than 30 degrees and is 60 degrees or less is along the sheet | seat surface (more specifically, 2nd direction) of the base 40 in the main cut surface of a light-guide plate. The unit shape element 50 occupies a region on the outer contour 51 corresponding to a width of 30% to 80% of the total width Wa. That is, the second region Z2 in which the light exit surface angle θa is greater than 30 ° and less than or equal to 60 ° is projected in the front direction nd, and is 30% to 80% of the full width Wa of the unit shape element 50. Occupy. As a result, when the light exit surface 31 of the light guide plate 30 is observed from the front direction, the unit shape is 30% to 80% of the region occupied by the light exit side surface (outer contour) 51 of the unit shape element 50. The light exit surface angle of the element 50 is greater than 30 ° and 60 ° or less. As described above, by providing the second region Z2 in which the light exit surface angle θa is greater than 30 ° and less than or equal to 60 ° on the light exit side surface 51 of the unit shape elements 50, the unit shape elements 50 are arranged in the arrangement direction (second direction). It is possible to exhibit an excellent light collecting function with respect to the light components along.

  Further, in the present embodiment, the light exit surface angle θa is 10 ° or more and 60 ° or less in the entire region on the outer contour (light exit side surface) 51 in the main cutting surface of the unit shape element 50. By using the light guide plate 30 as described above, it is possible to prevent the occurrence of the second peak of luminance (side lobe) in the direction greatly inclined from the front direction nd, and the arrangement direction of the unit shape elements 50 An excellent light condensing function can be exhibited with respect to light components along the (second direction).

  In addition, in the present embodiment, the light exit surface angle θa of the unit shape element 50 is set so that the unit shape element 50 closest to the base portion 40 from the top 52a on the outer contour 51 of the unit shape element 50 most distant from the base portion 40 is used. It changes so that it may become large toward the base end part 52b on the outer contour 51. According to such a light guide plate 30, the function of preventing the occurrence of the second peak (side lobe) of luminance in the direction greatly inclined from the front direction nd, and the arrangement direction of the unit shape elements 50 (second direction). Both of the functions of condensing the light components along the line are more effectively exhibited.

  Note that changing the light exit surface angle θa from the top 52a on the outer contour 51 of the unit shape element 50 toward the base end portion 52b only means that the light exit surface angle continues to change so as to always increase. Not what you want. As in the example shown in FIG. 4, even if there is a region where the outer contour 51 of the main cutting surface of the unit-shaped element 50 has a polygonal line shape or a shape obtained by chamfering a bent portion of the polygonal line, and the light exit surface angle θa does not change. Good. That is, the shape that changes so that the light exit surface angle θa increases from the top portion 52a on the outer contour 51 of the unit shape element 50 toward the base end portion 52b is based on the light exit surface angle θa at the top portion 52a. In addition, the light output surface angle θa at the base end portion 52b is larger, and a shape that does not include a portion that changes so that the light output surface angle θa decreases from the top portion 52a toward the base end portion 52b is also included.

  Incidentally, the unit shape element 50 as one specific example shown in FIG. 4 and FIG. 5 has an outer contour with one side located on one side surface (light emitting side surface) 41 of the base 40 in the main cut surface of the light guide plate 30. 41 has a pentagonal shape in which two sides are located between the top portion 52a and each base end portion 52b, or a shape formed by chamfering one or more corners of this pentagonal shape. Further, in the illustrated example, the unit shape element 50 is used for the purpose of effectively increasing the luminance in the front direction and imparting symmetry to the angular distribution of the luminance in the plane along the second direction. The cross-sectional shape of the main cutting plane is symmetrical with respect to the front direction nd. That is, as well shown in FIGS. 4 and 5, the light emitting side surface 51 of each unit-shaped element 50 is configured by a pair of bent surfaces 37 and 38 that are configured symmetrically about the front direction. . The pair of folding surfaces 37 and 38 are connected to each other to define a top portion 52a. Each of the folding surfaces 37 and 38 includes first inclined surfaces 37a and 38a that define the top 52a, and second inclined surfaces 37b and 38b that are connected to the first inclined surfaces 37a and 38a from the base 40 side. ing. The pair of first inclined surfaces 37a and 38a have a symmetric configuration with respect to the front direction nd, and the pair of second inclined surfaces 37b and 38b also have a symmetric configuration with respect to the front direction nd.

  And the unit shape element 50 shown by FIG. 4 is the 1st inclined surface 37a of two sides located between the top part 52a and each base end part 52b on the outer contour 51 in a main cut surface. The side on the top 52a side constituted by 38a has a light exit surface angle θa1 of 10 ° or more and 35 ° or less, and the side on the base end portion 52b side constituted by the second inclined surfaces 37b, 38b is from 30 °. It has a light exit surface angle θa2 of 60 ° or less. That is, the above-described first region Z1 of the light emitting side surface 51 of the unit shape element 50 is a region where a pair of first inclined surfaces 37a and 38a configured symmetrically with respect to the front direction nd is disposed, and the unit shape The above-described second region Z2 on the light output side 51 surface of the element 50 is a region where a pair of second inclined surfaces 37b and 38b configured symmetrically with respect to the front direction is disposed.

  In addition, as a whole structure of the unit shape element 50, the method of the base 40 in the main cutting surface of the light guide plate 30 with respect to the width Wa of the unit shape element 50 along the sheet surface of the base 40 in the main cutting surface of the light guide plate 30 is used. It is preferable that the ratio (Ha / Wa) of the protrusion height Ha from the base 40 of the unit-shaped element 50 along the linear direction is 0.3 or more and 0.4 or less. According to such a unit shape element 50, an excellent light collecting function is exhibited with respect to light components along the arrangement direction (second direction) of the unit shape elements 50 due to refraction and reflection at the light exit side surface 51. And generation of side lobes can be effectively suppressed.

  In addition, the “pentagonal shape” in the present specification includes not only a pentagonal shape in a strict sense but also a substantially pentagonal shape including limitations in manufacturing technology, errors in molding, and the like. Similarly, terms used in the present specification to specify other shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, and “symmetric” are not limited to strict meanings. Interpretation will be made including such an error that a similar optical function can be expected.

  Here, the dimension of the light guide plate 30 may be set as follows as an example. First, as a specific example of the unit shape element 50, the width Wa (see FIG. 4) can be set to 0.05 mm or more and 0.5 mm or less. In addition, when the outer contour 51 on the main cutting surface of the unit shape element 50 has a shape formed by chamfering the bent portion of the broken line, the value of the radius of curvature of the chamfered portion on the main cutting surface is the unit shape element 50. The width Wa is preferably equal to or less than the value Wa. This is because when the radius of curvature of the chamfered portion is larger than the value of the width Wa of the unit shape element 50, the unit shape element 50 cannot perform the expected function. On the other hand, the thickness of the base 40 can be set to 0.5 mm to 6 mm.

  The light guide plate 30 having the above configuration can be manufactured by molding the unit shape element 50 on a base material or by extrusion molding. 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 shape element 50. However, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost, such as acrylic, styrene, polycarbonate, Transparent resins mainly composed of one or more of polyethylene terephthalate, acrylonitrile and the like, and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins and the like) 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 portion 40 and the plurality of unit shape elements 50 on one side surface 41 of the base portion 40 can be integrally formed. When the light guide plate 30 is produced by extrusion molding, the unit shape 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 shape 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 optical sheet 60 will be described in detail with reference mainly to FIGS. 2 and 6 to 8. The optical sheet 60 is a member having a function of changing the traveling direction of transmitted light. In particular, the optical sheet 60 described here is a sheet-like member for changing the traveling direction of light incident from the light incident side and emitting the light from the light output side to intensively improve the luminance in the front direction. 2 and 6, the optical sheet 60 includes a main body 65 formed in a plate shape and a plurality of unit prisms (unit shapes) formed on the light incident side surface 66 of the main body 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. And the light emission surface of the optical sheet 60 which comprises the light emission surface 21 of the surface light source device 20 is comprised by the light emission side surface 67 of the main-body part 65 located in the side which does not face the light-guide plate 30. FIG.

  Next, the unit prism 70 provided on the light incident side surface 66 of the main body 65 will be described. As well shown in FIG. 6, the plurality of unit prisms 70 are arranged side by side on the light incident side surface 66 of the main body 65. Each unit prism 70 is formed in a linear shape and extends in a direction intersecting with the arrangement direction.

  In the present embodiment, the plurality of unit prisms 70 are configured identically. In the illustrated example, 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 66 of the main body 65 with no gap along the direction orthogonal to the longitudinal direction.

  As described above, the optical sheet 60 is disposed so as to overlap the light guide plate 30, and the unit prism 70 of the optical sheet 60 faces the light exit surface 31 of the light guide plate 30. As shown in FIGS. 1 and 2, the optical 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 optical sheet 60 is positioned with respect to the light guide plate 30.

  Each unit prism 70 has a first surface 71 and a second surface 72 that are arranged to face each other in a direction parallel to the sheet surface of the main body 65. The first surface 71 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 the other side in the first direction (right side of the paper surface of FIGS. 1 and 2). Is located. The second surface 72 is mainly light emitted from the first light source 24 a disposed on one side in the first direction, travels through the light guide plate 30, and then optically passes through the first surface 71. It deflects the light incident on the sheet 60. On the other hand, the first surface 71 is mainly light emitted from the second light source 24b disposed on the other side in the first direction, travels through the light guide plate 30, and then optically passes through the second surface 72. It deflects the light incident on the sheet 60.

  As well shown in FIGS. 7 and 8, 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. The unit prism illustrated as an embodiment corresponds to the fact that the light sources 24a and 24b and the light guide plate 24 have a symmetric configuration with respect to the center position Pc (see FIG. 2) in the light guide direction. The first surface 71 and the second surface 72 that form 70 are formed symmetrically (line symmetric) about a surface that passes through the top 75 and extends in the normal direction nd of the optical sheet 60.

  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 66 of the main body 65, the sheet surface of the optical 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 “main cutting surface of the light guide plate”) is along the longitudinal direction of the unit prism 70 (direction extending linearly). Is constant. Hereinafter, the cross-sectional shape of the unit prism 70 on the main cut surface of the optical sheet 60 will be described in more detail. 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 optical sheet.

  As shown in FIG. 7, in the present embodiment, the cross-sectional shape of each unit prism 70 on the main cut surface of the optical sheet is a shape that tapers toward the light incident side (light guide plate side). Yes. 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 illustrated embodiment, on the main cut surface of the optical sheet, the outer contour of the unit prism 70 is formed by joining straight portions, or joining straight portions and chamfering joints. have. In other words, the outer contour of the unit prism 70 is formed in a polygonal line shape or a shape formed by chamfering the corners of the polygonal line. In the example shown in FIG. 7 and FIG. 7, the first surface 71 and the second surface 72 of the unit prism 70 are each formed in a polygonal line composed of three linear portions 71a, 71b, 71c, 72a, 72b, 72c. Yes. However, the present invention is not limited to the illustrated example, and the outer contour of the unit prism in the main cutting surface of the optical sheet may be configured to include one or more arcs (arc or elliptic arc), or one or more arcs. (A circular arc or an elliptical arc) and one or more linear portions may be included.

  In the present embodiment, the angle formed by the outer contours of the unit prism 70 (the first surface 71 and the second surface 72 forming the light incident side surface) with respect to the sheet surface of the main body 65 on the main cutting surface of the optical sheet 60. When the light incident surface angle θb is set, the light incident surface angle θb is not constant in the first surface 71 or the second surface 72. As shown in FIGS. 6 and 7, the light incident surface angle θb is closest to the main body 65 from the top 75 of the unit prism farthest from the main body 65 in the first surface 71 and 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. According to such a unit prism 60, the relatively rising light L73 traveling in the direction in which the inclination angle with respect to the front direction nd becomes relatively small out of the first surface 71 and the second surface 72 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.

  The light incident surface angle θb here is the sheet surface of the main body 65 where the light incident side surfaces (first surface 71 and second surface 72) of the unit prism 60 are the main cut surfaces of the optical sheet 60 as described above. It is an angle made with respect to. When the light incident side surfaces (the first surface 71 and the second surface 72) in the main cutting surface of the unit prism 70 are formed in a polygonal line as in the example shown in FIG. And the sheet surface of the main body 65 (strictly speaking, the smaller one of the two formed angles (subordinate angle)) is the light incident surface angle θb. On the other hand, the outer contour (first surface 71 and 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. 9 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 (the minor angle) as the light incident surface angle θb.

  Note that the light incident surface angle θb changes from the top 75 to the base end 74 on the outer contour (the first surface 71 and the second surface 72) of the unit prism 70 so as to increase. It doesn't just mean that it keeps changing to always increase. As shown in the example shown in FIG. 7, the outer contour (first surface 71 and 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. There may be a region where the angle θb does not change. That is, the shape that changes so that the light incident surface angle θb increases from the top 75 to the base end 74 on the outer contour (the first surface 71 and the second surface 72) of the unit prism 70 here. The light incident surface angle θb at the base end portion 74 is larger than the light incident surface angle θb at the top portion 75, and the light incident surface angle θb decreases from the top portion 75 toward the base end portion 74. Also includes shapes that do not include changing locations.

  Further, as shown in FIG. 8, in the main cut surface of the optical sheet 60, 5% of the distances La and Lb along the sheet surface of the main body 65 between the top 75 and the base end 74 of the unit prism 70. Top side straight lines TEL1 and TEL2 connecting the top part 75 and the top vicinity positions Pa1 and Pa2 on the first surface 71 and the second surface 72 shifted from the top part 75 to the base end part 74 side by the lengths La1 and Lb1 respectively. The angle of 45 ° to 55 ° with respect to the sheet surface of the main body 65 (this angle is also referred to as “the top side tilt angle”) θx1 and θx2. In addition, as shown in FIG. 8, 5% of distances La and Lb along the sheet surface of the main body portion 65 between the top portion 75 and the base end portion 74 of the unit prism 70 in the main cut surface of the optical sheet 60. The base end side connecting the base end portion 74 and the base end vicinity positions Pb1 and Pb2 on the first surface 71 and the second surface 72 shifted from the base end portion 74 toward the top portion 75 by the lengths La2 and Lb2 The straight lines DEL1 and DEL2 form an angle θy1 and θy2 of 60 ° or more and 70 ° or less with respect to the sheet surface of the main body 65 (this angle is also referred to as a “base end side inclination angle”). Furthermore, as shown in FIG. 7, along the direction orthogonal to the straight lines SL1 and SL2 from the straight lines SL1 and SL2 connecting the top 75 and the base end 74 of the unit prism 70 on the main cut surface of the optical sheet. The distances Dx1 and Dx2 from the straight lines SL1 and SL2 to the position on the first surface 71 or the second surface 72 farthest from the straight lines SL1 and SL2 with respect to the distances Dy1 and Dy2 between the top 75 and the base end 74 of the unit prism 70 The ratio (Dx1 / Dy1, Dx2 / Dy2) is 0.04 or more and 0.06 or less.

  As a result of extensive research by the present inventors, the top side tilt angles θx1, θx2, the base end side tilt angles θy1, θy2, and the ratios of the distances Dx1, Dx2 to the distances Dy1, Dy2 (Dx1 / Dy1, Dx2 / When Dy2) satisfies the above-described conditions, it has been found that the optical sheet 60 exhibits an excellent light collecting function and can ensure a wide viewing angle in a plane along the arrangement direction of the unit prisms 70. . That is, when the top side inclination angles θx1, θx2, the base end side inclination angles θy1, θy2, and the ratios of the distances Dx1, Dx2 to the distances Dy1, Dy2 (Dx1 / Dy1, Dx2 / Dy2) satisfy the above-mentioned conditions In the angle distribution of the luminance measured on the light emitting surface of the optical sheet 60, relatively high luminance can be secured in the front direction, and measured in the plane along the arrangement direction of the unit prisms 70 and the front direction. The half-value angle can be enlarged.

  Furthermore, the top side inclination angles θx1 and θx2, the base end side inclination angles θy1 and θy2, and the ratio of the distances Dx1 and Dx2 to the distances Dy1 and Dy2 (Dx1 / Dy1, Dx2 / Dy2) satisfy the above-described conditions. In the case where the sheet is used by overlapping the light guide plate having the light exit surface formed by the unit shape elements and the arrangement direction of the unit shape elements 50 and the arrangement direction of the unit prisms being orthogonal to each other, the following can be realized. It was also discovered. First, the angular distribution of luminance on the light exit surface 31 of the light guide plate 30 in the plane along both the light guide direction of the light guide plate 30 and the normal direction of the light guide plate 30 peaks in a direction greatly inclined from the front direction. Has brightness. And when this peak brightness | luminance is 65 degrees or more and 75 degrees or less, it is a half value in the angular distribution of the brightness | luminance measured in the surface along the arrangement direction of the unit prism 70 and the front direction on the light emission surface of the optical sheet 60. The angle and the half-value angle in the angular distribution of the luminance measured in the plane along the longitudinal direction and the front direction of the unit prism 70 can be set to substantially the same size. As a result, when the light guide plate 30 and the optical sheet 60 are incorporated in the display device 10, the image light from the display device can exhibit the same viewing angle characteristics in two orthogonal directions.

  Further, when the inventors further researched, the base end side straight lines DEL1 and DEL2 make base end side inclination angles θy1 and θy2 with respect to the seat surface of the main body 65, and the top side straight lines TEL1 and TEL2 Along the arrangement direction (first direction) of the unit prisms 70 when the difference between the top side inclination angles θx1 and θx2 formed by the main body 65 with respect to the sheet surface is 12 ° or more and 25 ° or less. The half-value angle in the in-plane luminance distribution and the half-value angle in the in-plane luminance distribution along the longitudinal direction (second direction) of the unit prism 70 could be made substantially the same. Then, a display device in which such a light guide plate 30 and the optical sheet 60 are incorporated, in particular, a display device of a mobile terminal, has come to exhibit viewing angle characteristics that cannot be visually recognized in two different directions.

  The dimensions of the optical sheet 60 having the above configuration can be set as follows as an example. First, as a specific example of the unit prism 70, the width Wb (see FIG. 7) along the sheet surface of the optical sheet 60 can be set to 0.02 mm or more and 0.3 mm or less. The height Hb (see FIG. 7) from the light incident side surface 66 of the main body 65 of the unit prism 70 along the line direction nd can be set to 0.02 mm or more and 0.25 mm or less. On the other hand, the thickness of the main body 65 can be 0.1 mm to 0.6 mm.

  The optical sheet 60 having the above-described configuration is formed by, for example, molding the unit prism 70 on the base material using the material used for manufacturing the light guide plate 30 described above, as in the case of manufacturing the light guide plate 30 described above. Or by extrusion molding.

  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 emitters 25 forming the light sources 24 b and 24 b enters the light guide plate 30 through the light incident surfaces 33 and 34. FIG. 2 shows an example in which light enters the light guide plate 30 from the first light source 24a via the first light incident surface 33 as an example. The operation of the surface light source device 20 and the display device 10 will be described below based on the example shown in FIG. However, the light guide plate 30 has a symmetric configuration with the center position Pc in the first direction as the center. The first light source 24a and the second light source 24b are configured symmetrically with the light guide plate 30 sandwiched in the first direction. Further, the other components of the surface light source device 20 such as the optical sheet 60 and the liquid crystal display panel 15 have symmetry as well. Due to the symmetry of such a configuration, the following description applies similarly to the light incident on the light guide plate 30 from the second light source 24b via the second light incident surface 34.

  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, the total reflection is repeated, and the light proceeds to the first direction (light guide direction) connecting the light incident surface 33 and the opposite surface (the other light incident 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. The light L21 and L22 emitted from the light exit surface 31 travels to the optical 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 22 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.

  In particular, as shown in FIG. 4, the cross-sectional shape of the main cutting surface of the unit shape element 50 is a pentagonal shape symmetrically arranged around the front direction or a shape formed by chamfering one or more corners of the pentagonal shape. It has become. More specifically, as described above, the light exit surface 31 of the light guide plate 30 is configured as the bent surfaces 37 and 38 that are inclined with respect to the back surface 32 of the light guide plate 30. The light that is totally reflected by the light exit surface 31 formed by the bent surfaces 37 and 38 and travels through the light guide plate 30 and the light that passes through the light output surface 31 formed by the bent surfaces 37 and 38 and is emitted from the light guide plate 30 are as follows. The light-exiting surface 31 composed of the bent surfaces 37 and 38 has an effect described below. First, the effect exerted on the light traveling through the light guide plate 30 after being totally reflected by the light exit surface 31 including the bent surfaces 37 and 38 will be described.

  In FIG. 4, the optical paths of the lights L41 and L42 that travel in the light guide direction (first direction) 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. ing. As described above, the light exit surface 31 of the light guide plate 30 has a pentagonal shape arranged symmetrically with respect to the front direction or a shape formed by chamfering one or more corners of the pentagonal shape as a cross-sectional shape. More specifically, the unit-shaped element 50 includes two kinds of bent surfaces 37 and 38 that are formed by the light-emitting side surface 51 and are inclined opposite to each other across the normal direction nd to the one side surface 41 of the base 40. Yes. Further, the two types of bent surfaces 37 and 38 that are inclined to the opposite sides are alternately arranged along the second direction. As shown in FIG. 4, the light L41 and L42 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 types of bent surfaces 37 and 38. In the main cutting plane of the optical plate, the light enters the inclined surface inclined to the opposite side to the traveling direction of the light with respect to the normal direction nd to the one side surface 41 of the base 40.

  As a result, as shown in FIG. 4, the light L41 and L42 traveling in the light guide plate 30 is totally reflected by the bent surfaces 37 and 38 of the light exit surface 31, and in many cases, the traveling direction is the main cut surface of the light guide plate. It turns to the opposite side centering on the front direction nd. That is, the component along the second direction of the light is not easily directed to the opposite side due to total reflection at the light exit surface 31. In this manner, the light guided in the first direction (light guide direction) in the light guide plate 30 is easily reversed in the traveling direction in the second direction every time it is totally reflected by the light exit surface 31. As a result, light that is emitted from the light emitters 25 of the light sources 24a and 24b in a direction greatly inclined with respect to the first direction and enters the light guide plate 30 is also mainly controlled in the first direction while being restricted from moving in the second direction. Go on to. 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 sources 24 a and 24 b (for example, the arrangement of the light emitters 25) and the output of the light emitter 25. It becomes possible to do.

  Next, the effect exerted from the folding surfaces 37 and 38 on the light that passes through the folding surfaces 37 and 38 and is emitted from the light guide plate 30 will be described. As shown in FIG. 4, the light L41 and L42 emitted from the light guide plate 30 through the unit shape element 50 are inclined surfaces 37 and 38 forming the light output side surface 51 of the unit shape element 50 forming the light output surface 31 of the light guide plate 30. Refracts at. Due to this refraction, the traveling direction (outgoing direction) of the light L41 and L42 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 when 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 shape element 50 can narrow the traveling direction of the transmitted light to the front direction nd side with respect to the light component along the second direction orthogonal to the light guide direction. That is, the unit shape element 50 has a light condensing effect 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 shape elements 50 of the light guide plate 30.

  The lights L21 and L22 finally emitted from the light exit surface 31 of the light guide plate 30 as described above enter the optical sheet 60 as shown in FIG. Lights L21 and L22 emitted from the first light source 24a located on one side in the first direction are directed from the first light incident surface 33 side to the second light incident surface 34 side in the light guide plate 30. On the way, the light exits from the light exit surface 31 of the light guide plate 30. For this reason, the light L21 and L22 emitted from the first light source 24a are emitted from the light guide plate 30 in the cross section of FIG. 2 along both the front direction nd and the light guide direction (first direction). It inclines from the direction nd to the other side (the second light incident surface 34 side) in the first direction. In the light guide plate 30 that is normally used, the first light of the first light source 24 a emitted from the light output surface 31 of the light guide plate 30 is also affected by the refractive index difference between the material forming the light guide plate 30 and air. The outgoing angle of the direction component (the angle formed by the first direction component of the outgoing light and the normal direction nd to the plate surface of the light guide plate 30) θc tends to be biased within a range of 45 ° to 85 °. Similarly, the emission angle θc from the light guide plate 30 of the first direction component of the light from the second light source 24b located on the other side in the first direction is sandwiched between the light from the first light source 24a and the front direction nd. There is a tendency to deviate within an angle range inclined 45 ° to 85 ° on the opposite side.

  Further, as described above, the optical sheet 60 includes the unit prism 70 from which the top portion 75 projects 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 lights L21 and L22 emitted from the first light source 24a disposed on one side in the first direction (left side in the drawing of FIG. 1) and traveling toward the optical sheet 30 through the light guide plate 30 are connected to each other. Of the first surface 71 and the second surface 72, the light enters the unit prism 70 via the first surface 71 located on one side 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 of the paper surface of FIG. 1). On the other hand, the light traveling from the second light source 24b located on the other side in the first direction to the optical sheet 60 via the light guide plate 30 is the first of the first surface 71 and the second surface 72 connected to each other. The light enters the unit prism 70 via the second surface 72 located on the other side in one direction, and then undergoes total reflection on the first surface 71 located on one side in the first direction to change its traveling direction. Become.

  Then, due to total reflection at the prism surfaces (first surface and second surface) 71 and 72 of the unit prism 70, a cross section parallel to both the cross section (first direction (light guide direction) and front direction nd) of FIG. ), The lights L21 and L22 traveling in the direction inclined from the front direction nd 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). That is, the optical sheet 60 exerts a condensing action on the light component along the first direction.

  The light whose traveling direction is greatly changed by the unit prisms 70 of the optical 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 optical sheet 60.

  As described above, in the surface light source device 20, the distribution of the emitted light amount along the first direction (light guide direction) is made uniform, the front direction luminance is improved, and light is emitted from the light emitting surface 21 in a planar shape. To do. The light emitted from the surface light source device 20 then enters the liquid crystal display panel 15. The liquid crystal display panel 15 selectively transmits light from the surface light source device 20 for each pixel. Thereby, the 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 first direction while being restricted from moving in the second direction by the bent surfaces 37 and 38 that form the light exit side surface 51 of the unit-shaped element 50. become. That is, the light emitted from each of the multiple light emitters 25 constituting the light sources 24a and 24b is located at a predetermined position 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 described above, the conventional prism sheet having the unit prism protruding toward the light incident side. It exhibits an extremely excellent light collecting function. When this conventional prism sheet is used, the half-value angle in the luminance angular distribution measured in the plane along both the arrangement direction of the unit prisms and the normal direction of the prism sheet becomes extremely narrow. On the other hand, according to the above-described optical sheet 60 used in place of the conventional prism sheet, the light incident surface angle θb is the farthest from the main body 65 in the first surface 71 and the second surface 72. The unit prism changes so as to increase from the top 75 of the unit prism toward the base end 74 of the unit prism 60 closest to the main body 65. According to such an optical sheet 60, as described below, the light diffusing function is also appropriately exhibited while the light condensing function is effectively exhibited, and as a result, sufficient front direction luminance is ensured and sufficient. Thus, a sufficiently wide viewing angle can be secured.

  First, the light including more components along the first direction (for example, the light L74 in FIG. 7) is naturally the main body of the light incident side surfaces (the first surface 71 and the second surface 72) of the unit prism 70. It becomes easy to enter the region on the top 75 side close to the portion 60. On the other hand, the light including relatively few components along the first direction (for example, the lights L71, L72, and L73 in FIG. 4) is generally the light incident surface (the first surface 71 and the second surface) of the unit prism 70. It can be uniformly incident on the entire area of the surface 72). Therefore, the light incident on the region including the top portion 75 that is separated from the base end portion 74 of the light incident side surfaces (the first surface 71 and the second surface 72) of the unit prism 70 is the base end portion close to the main body portion 650. In comparison with the light incident on the region including 74, light having a small component along the first direction is included at a higher rate.

  That is, as shown in FIG. 7, the light L73 traveling in a direction that does not significantly tilt with respect to the front direction nd is formed on the prism surface (the first surface 71 and the second surface 72) on the base end portion 74 side of the unit prism 70. Incident light, such light L73 is reflected by prism surfaces 71c and 72c which are relatively inclined with respect to the sheet surface of the optical sheet 60, and changes its traveling direction. Further, light L74 traveling in a direction greatly inclined with respect to the front direction nd is also incident on the prism surface (first surface 71 and second surface 72) on the top 75 side of the unit prism 70, and such light L74 is reflected by the prism surfaces 71a and 72a which are not relatively inclined with respect to the sheet surface of the optical sheet 60, and changes its traveling direction. That is, the light incident surface angle θb at each position of the first surface 71 and the second surface 72 functioning as the reflecting surface of the unit prism 70 changes according to the tendency of the incident direction of light at the position, An excellent condensing function with respect to the incident light on the sheet 60 is exhibited.

  Further, as shown in FIG. 21, for example, the peak angle in the luminance angle distribution in the plane parallel to both the light guide direction and the front direction measured on the light exit surface 31 of the light guide plate 30 is the front direction. There is a tendency to make a very large inclination from nd, for example, an angle of 65 ° to 75 ° with respect to the front direction. In the angular distribution of the brightness, the half-value angle is inevitably small. The conventional prism sheet having the unit prism protruding toward the light incident side has an extremely strong light collecting function as shown in FIG. 20, for example, with respect to the light emitted from the light guide plate having such a strong direction. Was supposed to demonstrate.

  On the other hand, according to the optical sheet 60 described here, the light incident surface angle θb changes in the first surface 71 of the unit prism 70, and the light incident surface angle θb also changes in the second surface 72 of the unit prism 70. . For this reason, the light L71, L72, and L73 that travels in a certain direction and enters the unit prism 70 of the optical sheet 60 is optically dependent on the incident positions in the first surface 71 and the second surface 72 of the unit prism 70. The traveling direction when the light is emitted from the sheet 60 changes. Therefore, according to the optical sheet according to the present embodiment, the half-value angle in the angular distribution of luminance in the plane along the light guide direction (the arrangement direction of the unit prisms 70) measured on the light exit surface of the optical sheet 60. Can be made larger than when a conventional prism sheet is used.

  In other words, according to the optical sheet 10 of the present embodiment, in-plane along the light guide direction (the arrangement direction of the unit prisms 70) measured on the light exit surface of the optical sheet 60 while effectively exhibiting the light collecting function. The half-value angle in the angular distribution of brightness at can be made sufficiently large. Therefore, the peak angle appears in a direction inclined by 65 ° or more and 75 ° or less from the front direction in the luminance angle distribution in a plane parallel to both the light guide direction and the front direction measured on the light exit surface 31. When the optical sheet 60 is incorporated into the display device 10 in combination with the light guide plate 30 that becomes, even if the observation direction when observing each position in the display surface 11 is greatly different, each position on the display surface The brightness of the observed image does not vary greatly. As a result, it is possible to effectively prevent deterioration in visibility due to variations in the brightness of the observed image. For this reason, even if the optical sheet 60 is applied to a display device for a portable terminal and the observer observes the display device 11 from a close position, the visibility deteriorates due to variations in the brightness of the observed image. It can be effectively prevented. In this respect, it can be said that the optical sheet 60 according to the present embodiment and the combination of the optical sheet 60 and the light guide plate 30 according to the present embodiment are suitable for application to the display device 10 for portable terminals.

  In addition, according to the optical sheet described here, as described above, the top side inclination angles θx1 and θx2 that are angles formed by the top side straight lines TEL1 and TEL2 and the sheet surface of the main body 65 are 45 ° or more. It is 55 degrees or less. Further, the base end side inclination angles θy1 and θy2 that are angles formed by the base end side straight lines DEL1 and TEL2 and the sheet surface of the main body 65 are 60 ° or more and 70 ° or less. In addition, the first surface 71 or the first surface 71 farthest from the straight lines SL1 and SL2 along the direction perpendicular to the straight lines SL1 and SL2 with respect to the straight lines SL1 and SL2 connecting the top 75 and the base end portion 74 of the unit prism 70. The ratio (Dx1 / Dy1, Dx2 / Dy2) of the separation distances Dx1, Dx2 to the position on the second surface 72 is set to 0.04 or more and 0.06 or less.

  As a result of extensive research conducted by the inventors of the present invention, as demonstrated in the examples described later, when these three conditions are satisfied at the same time, the unit prism 70 protruding to the light incident side It has been found that the light collecting function corresponding to the light collecting function of the unit shape element 70 is exhibited. According to the experiment results of the present inventors, when the above three conditions are satisfied, the outer contour (the first surface 71 and the second surface 72) of the unit prism 70 on the main cutting surface of the optical sheet is the unit prism 70. From the straight lines SL1 and SL2 connecting the top portion 75 and the base end portion 74, the bulges moderately. Thereby, the optical sheet 60 can correct | amend the advancing direction of the light which has the strong directivity radiate | emitted from the light-guide plate 30, and can diffuse the said light moderately.

As a result, the peak angle in the angular distribution of luminance in a plane parallel to both the light guide direction and the front direction measured on the light exit surface 31 of the light guide plate 30 is inclined by 65 ° or more and 75 ° or less from the front direction. When this optical sheet 60 is provided on the light guide plate 30 that appears in the direction
Viewing angle characteristics in a plane parallel to both the arrangement direction (first direction) of the unit prisms 70 and the front direction nd measured on the light exit surface of the optical sheet 60, and measurement on the light exit surface of the optical sheet 60 The viewing angle characteristics in the plane parallel to both the arrangement direction (second direction) of the unit shape elements 50 to be performed and the front direction nd can be made the same. Therefore, the half-value angle in the angular distribution of luminance in a plane parallel to both the arrangement direction (first direction) of the unit prisms 70 and the front direction nd measured on the light exit surface of the optical sheet 60, and the optical sheet 60. The half-value angles in the angular distribution of luminance in a plane parallel to both the arrangement direction (second direction) of the unit shape elements 50 measured on the light exit surface and the front direction nd are set to substantially the same value. be able to. Furthermore, the angular distribution of luminance in a plane parallel to both the arrangement direction (first direction) of the unit prisms 70 measured on the light exit surface of the optical sheet 60 and the front direction nd, and the light output of the optical sheet 60. The angular distribution of luminance in a plane parallel to both the arrangement direction (second direction) of the unit shape elements 50 measured on the plane and the front direction nd has substantially the same contour on the same graph. It is also possible to have it.

  In this case, in the display device 10 in which the light guide plate 30 and the optical sheet 60 are incorporated, the viewing angle characteristics in two orthogonal directions, for example, the viewing angle in the horizontal direction and the viewing angle in the direction orthogonal to the horizontal direction. It is also possible to have the same characteristics. Therefore, when the light guide plate 30 and the optical sheet 60 described above are applied to a display device for a mobile terminal in which the orientation of the displayed image changes according to the orientation of the display device, the orientation of the mobile terminal is changed. Even if the image is displayed, the image is displayed with the same brightness, and the impression received from the image observed before and after the direction is changed does not change greatly. In this respect, it can be said that the optical sheet 60 according to the present embodiment and the combination of the optical sheet 60 and the light guide plate 30 according to the present embodiment are suitable for application to the display device 10 for portable terminals.

  Further, when the inventors further researched, the base end side straight lines DEL1 and DEL2 make base end side inclination angles θy1 and θy2 with respect to the seat surface of the main body 65, and the top side straight lines TEL1 and TEL2 Along the arrangement direction (first direction) of the unit prisms 70 when the difference between the top side inclination angles θx1 and θx2 formed by the main body 65 with respect to the sheet surface is 12 ° or more and 25 ° or less. The half-value angle in the in-plane luminance distribution and the half-value angle in the in-plane luminance distribution along the longitudinal direction (second direction) of the unit prism 70 can be made more stable and substantially the same. The display device in which the light guide plate 30 and the optical sheet 60 are incorporated, in particular, the display device of the portable terminal is more stable and exhibits viewing angle characteristics that cannot be visually recognized in two different directions. became.

  By the way, as a result of extensive research conducted by the present inventors, when the linear unit-shaped element 50 having a prism surface (inclined surface) inclined by about 45 ° with respect to the front direction is provided on the light guide plate 30, the unit shape It is found that the second brightness peak occurs in the angular range greatly inclined from the front direction nd, that is, so-called side lobes appear in the angular distribution of luminance in the plane along the element arrangement direction. It was done. The light that forms the side lobe is light that travels in a direction greatly inclined from the front direction, and cannot be recognized by the observer as light that effectively forms an image. That is, the occurrence of side lobes is not limited to the fact that the image is brightly observed in a direction that is largely inclined from the front direction, but does not form an image that can be effectively observed by an observer. It cannot be said that the emitted light is used effectively. That is, the generation of side lobes is not preferable in terms of energy efficiency.

  The cause of the occurrence of side lobes is estimated as follows. As already described with reference to FIG. 4, the light L41 and L42 that travel in the light guide plate 30 toward the light exit surface 31 and enter the light exit surface 31 are often out of the two types of bent surfaces 37 and 38. In the main cut surface of the light guide plate, the light enters the inclined surface inclined to the side opposite to the traveling direction of the light with reference to the normal direction nd to the one side surface 41 of the base 40. However, as shown in FIG. 5, when the angle formed by the traveling direction of the light L51 and the front direction nd is small, the light L51 is inclined to the same side as the traveling direction of the light with respect to the normal direction nd. It can also enter the inclined surface. In this case, the light L51 can be totally reflected by the incident prism surface (inclined surface 37 in FIG. 5), and in many cases, the opposite inclined surface (inclined surface 38 in FIG. 7) facing the prism surface. ).

  At this time, when the light exit surface angle θa of the inclined surface on the opposite side is a relatively large angle that is considered suitable for light collection, it is particularly about 45 ° that is considered to exhibit the most excellent light collection function. In this case, the incident angle of the light on the opposite inclined surface is relatively small. As a result, like the light L51a in FIG. 5, the light is refracted and emitted from the unit shape element without being reflected by the opposite inclined surface. And in the main cut surface of a light-guide plate, the emission angle of the said light L51a becomes very large. In order to correct the traveling direction of the light L51a, an optical sheet having unit shape elements arranged in the second direction or a light diffusing sheet having a light diffusing function is arranged on the light output side of the light guide plate. Unless it is not corrected, the direction of travel is not corrected. And it is estimated that such light L51a is a cause which forms a side lobe.

  On the other hand, according to the present embodiment, as described above, the outer region corresponding to the width region of 20% or more and 35% or less of the total width Wa of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. In the region on the contour (first region Z1), the light output that is an angle formed by the light output side surface 51 of the unit-shaped element 50 or the tangent to the light output side surface 51 on the main cut surface of the light guide plate 30 with respect to the side surface 41 of the base 40 The surface angle θa1 is 10 ° to 35 °.

  As a result of extensive research conducted by the present inventors, according to the light emitting side surface 51 of the unit-shaped element 50 having a relatively small light emitting surface angle θa of 10 ° or more and 35 ° or less, as shown in FIG. Light that has traveled in a direction that is not significantly inclined with respect to the front direction nd on the main cutting plane, and that is then totally reflected by an inclined surface that is inclined to the same side as the traveling direction with respect to the normal direction nd as a reference, and is incident on the surface L51 can be totally reflected. In other words, the first region Z1 in which the light exit surface angle θa is relatively small at 10 ° to 35 ° is effective in that the light L51 is emitted in a direction greatly inclined from the front direction nd forming the side lobe. Can be prevented. The light totally reflected by the first region Z1 of the unit shape element 50 then proceeds again toward the light exit side by reflection on the back surface 32 of the light guide plate 30 or the reflection sheet 22. That is, it is possible to correct the traveling direction of the light that has been formed by wasting side lobes so far and use the light as light for effectively forming an image.

  As a result of extensive research conducted by the present inventors, the light exit surface angle θa is a region on the outer contour 51 corresponding to 20% or more of the total width Wa of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. Is 10 ° or more and 35 ° or less, in the display device having the configuration shown in FIG. 1, that is, the optical sheet for correcting the traveling direction of light along the second direction is a light guide plate. In the display device that is not arranged on the light-emission side, the luminance angle distribution in the plane along the second direction is such that the occurrence of side lobes on the display surface 11 of the display device 10 cannot be visually detected. The second peak at could be made inconspicuous.

  Further, according to the research results of the present inventors, a region on the outer contour (first region) corresponding to a width region of 35% or less of the total width Wa of the unit shape elements 50 along the arrangement direction of the unit shape elements 50 In Z1), if the light exit surface angle θa1 is 10 ° or more and 35 ° or less, the luminance in the front direction is substantially the same as the case where the first region Z1 in which the light exit surface angle θa1 is 10 ° or more and 35 ° or less is not provided. It was confirmed that it could be secured. Such a phenomenon is predicted based on the fact that light that has been wasted by forming side lobes so far can be effectively used. Such an effect exceeds the range predicted from the state of the art, where the unit shape element having a right-angled isosceles triangular cross-sectional shape was considered to be able to exhibit the most excellent light collecting function. It can be said that it is remarkable.

  In particular, in the present embodiment, in the region (second region) Z2 on the outer contour corresponding to 30% to 80% of the total width Wa of the unit shape elements 50 along the arrangement direction of the unit shape elements 50. The light exit surface angle θa2 is greater than 30 ° and 60 ° or less. As a result of extensive studies by the present inventors, when such a light guide plate 30 is used, the unit-shaped element 50 of the light guide plate 30 has a light exit surface angle θa of 10 ° to 35 ° as described above. It was confirmed that the light condensing function can be effectively exhibited along the arrangement direction (second direction) of the unit shape elements 50 even if the light emitting side surface 51 (light emitting surface 31) is included.

  Further, in the present embodiment, the light exit surface angle is 10 ° or more and 60 ° or less in the entire region on the outer contour 51 in the main cutting surface of the unit shape element 50. Thereby, it is possible to prevent light from being emitted from the light guide plate 30 without having any light collecting action on the components along the arrangement direction (second direction) of the unit shape elements 50.

  According to the present embodiment as described above, the top side inclination angles θx1, θx2, the base end side inclination angles θy1, θy2, and the ratio of the distances Dx1, Dx2 to the distances Dy1, Dy2 (Dx1 / Dy1, Dx2 / With the optical sheet 60 configured so that Dy2) satisfies a predetermined condition, it is possible to ensure excellent viewing angle characteristics. Further, in the light guide plate 30 having the unit-shaped element 50 that protrudes toward the light incident side and extends in the light guide direction, and particularly in a plane parallel to both the light guide direction and the front direction measured on the light exit surface 31. In the luminance angle distribution, the light guide plate 30 whose peak angle appears in a direction inclined by 65 ° or more and 75 ° or less from the front direction, top side inclination angles θx1, θx2, base end side inclination angles θy1, θy2, In the combination with the optical sheet 60 configured such that the ratio (Dx1 / Dy1, Dx2 / Dy2) of the distances Dx1, Dx2 to the distances Dy1, Dy2 satisfies the predetermined condition, the unit shape element of the light guide plate 30 The viewing angle characteristics along the arrangement direction of 50 and the viewing angle characteristics along the arrangement direction of the unit prisms 60 of the optical sheet 60 have the same tendency to the extent that visual identification is impossible. Door can be. Such excellent viewing angle characteristics are mainly realized by the two components of the light guide plate 30 and the optical sheet 60. Therefore, by manufacturing the display device 10 using these two members, excellent viewing angle characteristics can be obtained. Thinning can also be realized while ensuring. In particular, in the display device 10 for a mobile terminal in which the direction in which the video is displayed changes in accordance with the orientation of the display device 10, for example, the brightness of the observed video varies depending on the position where the video is displayed. Can be prevented, and the same image can be observed with the same brightness while changing its direction.

  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.

  In the above-described embodiment, the top side inclination angles θx1, θx2, the base end side inclination angles θy1, θy2, and the ratio of the distances Dx1, Dx2 to the distances Dy1, Dy2 (Dx1 / Dy1, Dx2 / Dy2) are predetermined. Although an example of the optical sheet configured to satisfy the conditions has been shown, the present invention is not limited to this. For example, the shape of the unit prism 70 on the main cutting surface of the optical sheet can be changed. As already described, as shown in FIG. 9, the cross-sectional shape of the unit prism 70 at the main cutting surface of the optical sheet may include a curve. In such a modification, as shown in FIG. 9, the light incident surface angle θb includes the tangent line TL to the outer contour (the first surface 71 and the second surface 72) on the main cutting surface of the unit prism 70, and the main body portion. It is specified as a value of an angle formed by 65 sheet surfaces, more strictly, a smaller angle (subordinate angle) of two formed angles. Also in such a modification, the top side inclination angles θx1 and θx2, the base end side inclination angles θy1 and θy2, and the ratio of the distances Dx1 and Dx2 to the distances Dy1 and Dy2 (Dx1 / Dy1, Dx2 / Dy2) are described above. If the above conditions are satisfied, the same effects as those of the above-described embodiment can be obtained. When the first surface 71 and the second surface 72 of the unit prism 70 on the main cutting surface of the optical sheet are configured as curves, the top side straight lines TEL1, TEL2 and the base end side straight lines DEL1, DEL2 are A string for a curve.

  In the above-described embodiment, the example in which the unit prisms 70 of the optical sheet 60 are arranged adjacent to each other has been described. However, the present invention is not limited to this. For example, as shown in FIG. 9, a flat portion 68 may be formed between two adjacent unit prisms 70, or between two adjacent unit prisms 70 as indicated by a two-dot chain line in FIG. A recess 69 may be formed.

  Furthermore, the optical 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.

  Moreover, the structure mentioned above of the unit shape element 50 of the light-guide plate 30 is only an illustration. 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. As already described, when the cross-sectional shape of the unit-shaped element 50 at the main cutting surface of the light guide plate includes a curve, the light exit surface angle θa is set to be equal to that of the unit-shaped element 50 as shown in FIGS. The angle formed by the tangent TL to the outer contour 51 in the main cut surface and the sheet surface of the base 40, more precisely, the smaller one of the two formed angles (subordinate angle)) Specified as the value of. Also in such a modification, it is preferable that the unit shape element 50 has the above-described configuration.

  In the above-described embodiment, the example in which the unit shape elements 50 of the light guide plate 30 are disposed adjacent to each other has been described, but the present invention is not limited thereto. For example, as shown in FIG. 10, a flat portion 58 may be formed between two adjacent unit shape elements 50, or as shown in FIG. May be formed.

  Furthermore, in the above-described embodiment, an example in which the unit shape element 50 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. You may make it change along the longitudinal direction of an element.

  Further, in the above-described embodiment, the example in which the two opposing surfaces 33 and 34 among the side surfaces of the light guide plate 30 form the light incident surface is shown, but the present invention is not limited thereto. For example, as in the modification shown in FIG. 12, only one of the side surfaces 33 of the light guide plate 30 may function as a light incident surface. In such a modification, the emission direction of the emitted light emitted from the light guide plate 30 in the cross section parallel to both the normal direction nd to the light emitting surface 21 of the surface light source device 20 and the first direction is the front direction. It is inclined to only one side with respect to nd. That is, when the light source 24a is disposed only on one side in the first direction (light guide direction), the first surface 71 of the unit prism 70 located on one side in the first direction (light guide direction) It does not function as a reflecting surface for deflecting the traveling direction. Therefore, only the second surface 72 needs to satisfy the above-mentioned conditions of the top side inclination angle θx2, the base end side inclination angle θy2, and the ratio of the distance Dx2 to the distance Dy2 (Dx2 / Dy2).

  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. In such a light guide plate 30, the peak angle is usually 65 ° or more and 75 from the front direction in the angular distribution of luminance in a plane parallel to both the light guide direction and the front direction measured on the light exit surface 31. Appears in an inclined direction of less than °. However, the present invention is not limited to the above example, and as an example, as shown in FIG. 12, the light output surface 31 and the back surface 32 of the light guide plate 30 may be inclined with respect to each other. Also in the light guide plate 30 shown in FIG. 12, the peak angle is usually 65 degrees from the front direction in the angular distribution of luminance in a plane parallel to both the light guide direction and the front direction measured on the light exit surface 31. It appears in a direction inclined by not less than ° and not more than 75 °.

  In the example shown in FIG. 12, the back surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 32 a that are inclined so as to approach the light exit surface 32 as it goes from the light incident surface 33 to the opposite surface 34, and two adjacent two surfaces. And a step surface 32b connecting the inclined surfaces 32a. Among these, the step surface 32 b extends in the normal direction nd of the plate surface of the light guide plate 30. Therefore, most of the light traveling in the light guide plate 30 from the light incident surface 33 side to the opposite surface 34 side is reflected by the inclined surface 32 a without entering the step surface 32 b of the back surface 32. Become. For this reason, as shown in FIG. 12, when the light L111 is reflected by the light exit surface 31 and the back surface 32 and travels through the light guide plate 30, the incident angle of the light L111 on the light exit surface 31 and the back surface 32 is the back surface 32. It becomes smaller every time it is reflected, and becomes less than the critical angle for total reflection after repeating total reflection. As a result, the light L111 traveling in the light guide plate 30 is emitted from the light guide plate 30 in a region separated from the light incident surface 33 without colliding with the light scattering agent 45 in the base 40. Thereby, the emitted light quantity along the first direction can be made uniform.

  Furthermore, the present invention is not limited to the example in the above-described embodiment or the example illustrated in FIG. 12, and another configuration (another light extraction configuration) for emitting light incident on the light guide plate 30 from the light guide plate 30 is described above. Instead of the above configuration or in addition to the above-described configuration, it can be adopted.

  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.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to this Example.

  A surface light source device according to Samples 1 to 8 described below and a display device using the surface light source device were manufactured. The viewing angle characteristics were compared for each of the produced samples.

[Configuration of surface light source device and display device]
A display device having a surface light source device and a liquid crystal display panel was produced. The surface light source device is a device in which a light guide plate, a light source, a reflection sheet, and an optical sheet are arranged in the same positional relationship as in the above-described embodiment. However, the second light source was not provided. As components other than the optical sheet and the light guide plate, that is, the liquid crystal display panel, and the light source and the reflection sheet of the surface light source device, those incorporated in a commercially available liquid crystal display device were used. And between samples, the thing from which only an optical sheet mutually differs was used, and the same thing was used about the liquid crystal display panel, the light guide plate of a surface light source device, a light source, and a reflective sheet.

(Optical sheet)
The optical sheet has a sheet-like main body portion and a large number of linear unit prisms protruding from the light incident side surface of the main body portion. Many unit prisms were arranged without gaps in a direction perpendicular to the longitudinal direction. The cross-sectional shape of each unit prism is constant along the longitudinal direction of the unit prism. The outer contour of the cross-sectional shape on the main cutting surface of the unit prism was changed between the optical sheets incorporated in each sample. The width Wb (see FIG. 7) and the height Hb (see FIG. 7) of the unit prism are the same between the optical sheets incorporated in each sample.

  For samples 1, 4, 5, and 6, as in the example shown in FIGS. 7 and 8, the first surface and the second surface of the unit prism have three straight portions (on the top side) on the main cutting surface of the optical sheet. A straight line portion, an intermediate portion straight portion, and a base end portion side straight portion). For Samples 2, 3, and 7, the first and second surfaces of the unit prism are arranged on the main cutting surface of the optical sheet with four straight portions (a straight portion on the top side, two straight portions on the middle portion, and a base portion). It was made into the shape of a polygonal line consisting of the end side straight part). In samples 1 to 7, the light incident surface angle was increased from the top side toward the base end side. For sample 8, the unit prism was formed in an isosceles triangle shape on the main cut surface of the optical sheet. Further, in Samples 1 to 8, the first surface and the second surface of the unit prism are configured to be line symmetric about the axis extending through the top of the unit prism in the front direction on the main cutting surface of the optical sheet. did.

  Table 1 shows the shape of the main prism of the unit prism of the optical sheet incorporated in each sample. The “width ratio” in Table 1 means that the symmetric linear portion of the main cutting surface of the optical sheet occupies the first surface or the second surface in the direction along the sheet surface of the main body. The percentage is shown as a percentage. Further, in the “value” column of “Dx / Dy” in Table 1, the straight line SL1, SL2 connecting the top and the base end of the unit prism on the main cut surface of the optical sheet, Distances Dy1, Dy2 between the top and base ends of the unit prisms of the separation distances Dx1, Dx2 from the straight lines SL1, SL2 to the position on the first surface or the second surface that are farthest from the straight lines SL1, SL2 along the orthogonal direction (Dx1 / Dy1, Dx2 / Dy2) are shown (see FIG. 7). In the “Satisfaction” column of “Dx / Dy” in Table 1, “O” is added when the value of “Dx / Dy” is 0.04 or more and 0.06 or less, and 0.04 When it was not 0.06 or less, “X” was given.

(Light guide plate)
The light guide plate includes a base and a plurality of unit shape elements arranged side by side in the second direction on one side surface of the base with no gap, as in the above-described embodiment. The cross-sectional shape of the unit shape element on the main cut surface of the light guide plate was as shown in FIG. The plurality of unit shape elements included in one light guide plate were configured identically. The base was formed as a rectangular plate having a main part formed in a flat plate shape with a constant thickness and a diffusion component (light diffusion particles) dispersed in the main part. In the light guide plate, only one of the pair of side faces facing the light guide direction forms a light incident surface. That is, the light source described later is arranged so as to face only one of the pair of side surfaces.

(light source)
As in the above-described embodiment, a light source is configured from a point light emitter. Specifically, a configuration is adopted in which LED chips are arranged at intervals of 2 mm along the second direction at positions facing one of a pair of side surfaces facing the light guide direction of the light guide plate.

(Reflective sheet)
A mirror sheet was used as the reflection sheet.

<Evaluation results>
The angular distribution of luminance on the light emitting surface of the surface light source device according to each sample, that is, on the light emitting surface of the optical sheet was measured. The angular distribution of the brightness is in a plane parallel to both the first direction (unit prism arrangement direction) and the front direction, and in a plane parallel to both the second direction (unit shape element arrangement direction) and the front direction. , Measured by. FIGS. 13 to 21 show the angular distribution of the measured luminance. 13 to 20, the solid line indicates the angular distribution of luminance in a plane parallel to both the first direction (unit prism arrangement direction) and the front direction, and the dotted line indicates the second direction (unit shape). The angular distribution of luminance in a plane parallel to both the element arrangement direction and the front direction is shown. FIG. 21 shows an angular distribution of luminance in a plane parallel to both the first direction (longitudinal direction of the unit shape element) and the front direction, measured on the light exit surface of the light guide plate. The angular distribution of luminance on the light exit surface of the light guide plate shown in FIG. 21 is a result common to the samples 1-8.

  In Samples 1 to 3, the luminance angular distribution in a plane parallel to both the first direction (unit prism arrangement direction) and the front direction, and both the second direction (unit shape element arrangement direction) and the front direction. The angle distribution of the luminance in the plane parallel to the curve shows the same contour on the graph, and the half-value angle is substantially the same. In Samples 4 to 8, the angular distribution of luminance in a plane parallel to both the first direction (unit prism arrangement direction) and the front direction, and both the second direction (unit shape element arrangement direction) and the front direction are used. The angular distribution of luminance in a plane parallel to the image was significantly different.

  Moreover, the image | video displayed by the display apparatus which concerns on each sample was observed from the position 30 cm away from the display surface in the front direction. In samples 1 to 3, an image displayed in a display area of 10 cm × 15 cm was observed with a uniform brightness distribution. On the other hand, in samples 4 to 8, the image observed at the outer edge of the 10 cm × 15 cm display area was felt darker than the image observed at the center of the display area.

DESCRIPTION OF SYMBOLS 10 Display apparatus 15 Liquid crystal display panel 18 Control apparatus 20 Surface light source device 22 Reflection sheet 24a, 24b Light source 25 Light emitter 26 Optical sheet 30 Light guide plate 31 Light emission surface 32 Back surface 33 Light incident surface (1st light incident surface)
34 Opposite surface (second light entrance surface)
37 Folded surface 37a First inclined surface 37b Second inclined surface 38 Folded surface 38a First inclined surface 38b Second inclined surface 40 Base 41 One side, light exit side 44 Main part 45 Diffusion component 50 Unit shape element 51 Light exit side (outer contour) )
52a Top portion 52b End portion 60 Optical sheet 65 Main body portion 66 Light incident side surface 67 Light exit side surface 70 Unit prism 71 First surface 72 Second surface 74 Base end portion (end portion)
75 Top (tip)

Claims (13)

A sheet-like body,
A plurality of unit prisms arranged side by side on the light incident side of the main body, each extending linearly in a direction intersecting the arrangement direction,
Each unit prism has a first surface and a second surface arranged to face each other in a direction parallel to the sheet surface of the main body,
In a main cutting plane parallel to both the normal direction of the main body and the arrangement direction of the unit prisms, an incident surface angle is an angle formed by the second surface of the unit prism with respect to the sheet surface of the main body Then, the light incident surface angle is changed so as to increase 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.
In the main cut surface, the second surface shifted from the top to the base end by a length of 5% of the distance along the sheet surface of the main body between the top and the base end. The top side straight line connecting the upper position and the top portion forms an angle of 45 ° or more and 55 ° or less with respect to the seat surface of the main body portion, and the portion between the top portion and the base end portion is formed. A base end side straight line connecting the base end portion and the position on the second surface shifted from the base end portion to the top side by a length of 5% of the distance along the sheet surface of the main body portion. Is at an angle of 60 ° to 70 ° with respect to the sheet surface of the main body,
In the main cutting plane, the top portion having a separation distance from a straight line connecting the top portion and the base end portion to a position on the second surface that is the farthest from the straight line in a direction orthogonal to the straight line; The ratio with respect to the distance between the said base end parts is an optical sheet which is 0.04 or more and 0.06 or less.   The difference between the angle formed by the base end side straight line with respect to the seat surface of the main body portion and the angle formed by the top side straight line with respect to the seat surface of the main body portion is 12 ° or more. The optical sheet according to 1. The top of the unit prism is defined at a position where the first surface and the second surface are connected to each other;
In the main cut surface, the first surface and the second surface have symmetry about an axis passing through the top and extending in a normal direction of the main body.
The prism sheet according to claim 1 or 2, wherein 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 the one side surface in the first direction of the pair of side surfaces;
The optical sheet according to any one of claims 1 to 3, disposed opposite the light exit surface of the light guide plate,
The arrangement direction of the unit prisms is parallel to the first direction, the first surface of each unit prism is located on one side in the first direction, and the second surface is on the other side in the first direction. A surface light source device in which the optical sheet and the light guide plate are arranged so as to be positioned. The light guide plate is
A sheet-like base;
5. The surface light source device according to claim 4, further comprising unit-shaped elements arranged in an arrangement direction intersecting the first direction and provided on the optical sheet side of the base.   In the main cutting surface of the light guide plate parallel to both the normal direction of the base and the arrangement direction of the unit shape elements, the light exit surface forms an angle formed by the outer contour of the unit shape elements with respect to the sheet surface of the base In terms of an angle, in the region on the outer contour corresponding to 20% to 35% of the width of the unit shape element along the sheet surface of the base, the light exit surface angle of the unit shape element is 10 °. The surface light source device according to claim 5, wherein the surface light source device is at least 35 °.   The light exit surface angle of the unit shape element is directed from the top on the outer contour of the unit shape element farthest from the base to the base end on the outer contour of the unit shape element closest to the base. The surface light source device according to claim 5, wherein the surface light source device changes so as to increase.   The ratio of the height Ha from the light emission side surface of the base of the unit-shaped element in the main cutting surface to the width Wa along the arrangement direction of the unit-shaped elements in the main cutting surface of the light guide plate is 0.3. The surface light source device according to claim 5, which is 0.4 or more and 8 or less. The unit-shaped element includes a top portion of the main cutting surface of the light guide plate, the one side of which is located on the base portion and the most distant from the light exit side surface on the outer contour, and each base end portion connected to the light exit side surface. A pentagonal shape with two sides between them, or a shape formed by chamfering one or more corners of the pentagonal shape,
Of the two sides located between the top and each base end on the outer contour, the light exit surface angle of one side of the top is 10 ° or more and 35 ° or less, and one side of the base end The surface light source device according to claim 5, wherein the light exit surface angle is greater than 30 ° and 60 ° or less.   The surface light source device according to any one of claims 5 to 9, wherein the base includes a main portion made of resin and a diffusion component dispersed in the main portion.   The surface light source device according to any one of claims 4 to 10, further comprising a second light source provided corresponding to the other side surface in the first direction of the pair of side surfaces. A surface light source device according to any one of claims 4 to 11,
A transmissive display panel disposed to face 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-shaped 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 12, 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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