JP6939372B2 - Surface light source device and display device - Google Patents

Description

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

A surface light source device having a light emitting surface that emits light in a planar shape is widely used, for example, as a backlight that illuminates a liquid crystal display panel from the back side (for example, Patent Document 1). A surface light source device for a liquid crystal display device is roughly 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 portion of the optical member. The edge light type surface light source device is superior to the direct type surface light source device in that it can be made thinner, cost lower, and consume less power.

The edge light type surface light source device of Patent Document 1 includes a light guide plate, a light deflection element arranged to face the light emitting surface of the light guide plate, and a light source arranged to face one side surface of the light guide plate. have. The light guide plate distributes the light from the light source so that the amount of light along the light guide direction is uniform. The specific shape of the light deflection element is shown in FIG. 6, and the surface of the light deflection element on the incident side facing the light guide plate is a plurality of inclinations arranged in a direction parallel to the light guide direction of the light guide plate. The surface on the exit side, which has a surface and is opposite to the side of the light guide plate of the light deflection element, has a plurality of lens surfaces arranged in a direction parallel to the light guide direction of the light guide plate. In this light deflection element, the light emission direction is controlled by a combination of the refraction of the surface on the incident side and the refraction of the surface on the exit side.
Further, Patent Document 2 discloses a method of shifting the emission peak with a lens or the like in the azimuth angle direction or the elevation angle direction of the screen, such as multi-view or 3D display.

Special Fair 7-66122 Gazette Japanese Unexamined Patent Publication No. 2005-78078

Recently, a liquid crystal display device provided with an edge light type surface light source device has been applied to various devices. In many applications, a liquid crystal display device ideally has a luminance peak in the normal direction of the display surface.
However, depending on the application, it may be preferable that the display surface has a luminance peak in a direction inclined from the normal direction. For example, a liquid crystal display applied to a center console of an automobile will be observed by the driver of the automobile from diagonally above. Therefore, in such a liquid crystal display device, it is preferable that the peak of brightness appears diagonally upward.

The liquid crystal display device of Patent Document 1 describes that the peak of the luminance is aligned with the center of the viewing angle characteristic of the liquid crystal display element by the configuration of the surface on the incident side and the surface on the light emitting side of the light deflection element.
However, in Patent Document 1, only the matching of the luminance peaks is examined, and the luminance distribution centered on the peak is not examined at all. Further, although light is emitted in various directions, Patent Document 1 does not study any brightness distribution in multiple directions.
Further, in the first place, as shown in FIG. 6 of Patent Document 1, when the peak direction of the brightness is adjusted by a combination of the refraction on the surface on the incident side of the light deflection element and the refraction on the surface on the exit side of the light deflection element. Since it is necessary to align the positions on the front and back sides, it is not possible to design a fine pattern, which makes it difficult to design a multifaceted brightness distribution, complicates the configuration, and lowers the yield.
In Patent Document 2, it is possible to provide a luminance peak in a desired direction, but the spread in the azimuth and elevation directions is not controlled.

The present invention has been made in consideration of the above points, and a peak of luminance can be generated in a direction other than the normal direction by a simple configuration, and an azimuth of the luminance distribution centered on the direction showing the peak. It is an object of the present invention to provide a surface light source device and a display device having improved symmetry in the direction and the elevation angle direction.

In order to solve the above problems, the present invention provides the following surface light source device and display device.
(1) A light guide plate having a light emitting surface, a back surface facing the light emitting surface, and a side surface located between the light emitting surface and the back surface, and any side surface of the side surfaces is an incoming light surface. A surface light source device including a light source arranged to face the light entering surface and an optical sheet arranged to face the light emitting surface of the light guide plate, wherein the optical sheet has a sheet shape. The main body portion and a plurality of structural rows provided on the surface of the main body portion on the light source plate side, the direction perpendicular to the light source surface of the light guide plate is the first direction d ₁ , and the arrangement of the structural rows. When the direction is the third direction d ₃ , the first direction d ₁ and the third direction d ₃ are non-parallel, and the brightness of the light emitted from the center of the surface of the optical sheet opposite to the light source plate. A surface light source device that satisfies the following conditions 1-1 and 2-1 when measured.
<Condition 1-1>
The maximum brightness when the brightness distribution of the light emitted from the center of the surface of the optical sheet opposite to the light guide plate is measured in a matrix at every 0.5 ° elevation and 0.5 ° azimuth is P _max. And. Here, when the surface light source device is viewed from the normal direction, the direction of the perpendicular line drawn from the center to the light entry surface side is "azimuth angle 0 °", and the surface of the optical sheet opposite to the light guide plate. The direction from to the normal direction is defined as "elevation angle 0 °".
When the elevation angle indicating _{P max is EA max} and the azimuth indicating _{P max is DA max} , the EA _max indicates a value other than 0 °.
<Condition 2-1>
Based on the brightness of each angle measured under the condition 1-1, a brightness distribution map A for each azimuth angle at the _{elevation angle EA max is created.} In the luminance distribution diagram A, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The integral value of the brightness in the range of the azimuth angle "(DA _max −45 °) to (DA _{max + 45 °)" of the luminance distribution map A is DA −45 / + 45} , and the azimuth angle “(DA _{max + 45 °) of the luminance distribution map A”.} The integrated value of the brightness in the range of -20 °) to DA _max to (DA _{max + 20 °) is set to DA -20 / + 20} .
Based on the brightness of each angle measured under condition 1-1, a brightness distribution map B for each elevation _{angle at the azimuth angle DA max is created.} In the luminance distribution diagram B, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The integrated value of the luminance in the range of the elevation angle "(EA _max −45 °) to (EA _{max + 45 °)” of the luminance distribution diagram B is EA −45 / + 45} , and the azimuth angle “(EA _max −” of the luminance distribution diagram A is The integrated value of the luminance in the range of "20 °) to (EA _{max + 20 °)" is defined as EA-20 / + 20} .
In the above, 0.77 ≦ (DA _{-20 / + 20} / DA _{−45 / + 45} ) / (EA _{-20 / + 20} / EA _{−45 / + 45} ) ≦ 1.30 is satisfied.
(2) The surface light source device according to (1) above, wherein the condition 1-1 further _{satisfies the condition of 27 ° ≤ EA max ≤ 60 °.}
(3) Further, the surface light source device according to (1) or (2) above, which satisfies the following conditions 1-2.
<Condition 1-2>
DA _max indicates a value other than 0 ° or 180 °.
(4) The surface light source device according to (3) above, which satisfies the condition of 240 ° ≤ DA _{max ≤ 310 ° under the above conditions 1-2.}
(5) The surface light source device according to any one of (1) to (4) above, which satisfies the following conditions 2-3.
<Condition 2-3>
Based on the brightness of each angle measured under the condition 1-1, a brightness distribution map A for each azimuth angle at the _{elevation angle EA max is created.} In the luminance distribution diagram A, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
With the azimuth DA _max as the reference azimuth, the angle of the azimuth that first shows the brightness that is 1/3 or less _{of P max} in the azimuth on the minus direction side from the reference azimuth of the _{brightness distribution map A is −βDA max} . _{Let + βDA max be} the angle of the azimuth that first shows the brightness that is 1/3 or less _{of P max} in the azimuth on the plus direction side from the reference azimuth.
_{Let β D1} be the angle interval between the reference azimuth and −βDA _{max, and β D2} be the angle interval between the reference elevation angle and + βDA _max.
In the above, the condition of 20 ° ≦ (β _D1 + β _D2 ) / 2 ≦ 60 ° is satisfied.
(6) The surface light source device according to any one of (1) to (5) above, which satisfies the following conditions 2-4.
<Condition 2-4>
Based on the brightness of each angle measured under condition 1-1, a brightness distribution map B for each elevation _{angle at the azimuth angle DA max is created.} In the luminance distribution diagram B, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The elevation angle EA _max is used as a reference elevation angle, and the elevation angle inclined toward the normal direction is defined as the "minus direction elevation angle", and the elevation angle inclined toward the side away from the normal direction is defined as the "plus direction side elevation angle".
The elevation angle showing brightness that is 1/3 or less _{of P max} first at the elevation angle on the minus direction side from the reference elevation angle of the _{brightness distribution diagram B is −βEA max , and P max} is first at the elevation angle on the plus direction side from the reference elevation angle. _{Let + βEA max be} the angle of elevation that indicates the brightness that is 1/3 or less of.
The spacing angle between the reference elevation angle and the -βEA _max β _E1, the spacing angle between the reference elevation angle and the + βEA _max and beta _E2.
In the above, the condition of 20 ° ≦ (β _E1 + β _E2 ) / 2 ≦ 30 ° is satisfied.
(7) The surface light source device according to any one of (1) to (6) above, wherein the angle θ _{d1 d3} formed by the first direction d ₁ and the third direction d ₃ satisfies 15 ° ≤ θ _{d1 d3 ≤ 50 °.} ..
(8) The surface light source device according to any one of (1) to (7) above, which further satisfies the following conditions 1-3.
<Condition 1-3>
In the surface light source device, the surface light source device in which the first direction d ₁ and the third direction d ₃ are parallel is referred to as a comparative surface light source device. When the brightness of the light emitted in the normal direction from the center of the surface of the optical sheet of the comparative surface light source device opposite to the light guide plate is measured and the brightness is set to Ref, 1.0 ≦ P _max / Ref. Meet.
(9) Under the condition 2-1 above, the DA- _{20 / + 20} / DA- _{45 / + 45} is 0.55 or more, and the EA- _{20 / + 20} / EA- _{45 / + 45} is 0.70 or more ( 1) The surface light source device according to any one of (8) (10) The surface light source device according to any one of (1) to (9) above, and a display panel arranged facing the surface light source device. A display device comprising.

The surface light source device and the display device of the present invention can generate a peak of luminance in a direction other than the normal direction by a simple configuration, and are symmetrical in the azimuth and elevation directions of the luminance distribution centered on the direction showing the peak. The sex can be improved.

It is sectional drawing which shows one Embodiment of the surface light source device and the display device of this invention. It is sectional drawing of the surface light source apparatus of FIG. 1, and is the figure for demonstrating the operation of the surface light source apparatus. It is a top view from the light emitting surface side of the surface light source device of FIG. It is a perspective view from the light emitting surface side of the light guide plate incorporated in the surface light source device of FIG. It is a perspective view from the back surface side of the light guide plate incorporated in the surface light source device of FIG. It is sectional drawing of the light guide plate along the VI-VI line of FIG. 4, and is the figure for demonstrating the operation of the light guide plate. It is a perspective view from the surface of the optical sheet incorporated in the surface light source device of FIG. 1 from the surface on the light receiving side. It is a partially enlarged view of the cross section of the optical sheet along the line VIII-VIII of FIG. It is the figure which enlarged the cross section similar to FIG. 2 to a part of an optical sheet, and is the figure for demonstrating the operation of an optical sheet. It is a figure for demonstrating the operation of the optical sheet when the optical sheet of FIG. 9 is changed to another optical sheet. In the normal direction and the first direction d ₁ of both the plane parallel is a graph showing the angular distribution of luminance on the light exit surface of the light guide plate. In the normal direction and the second direction d a plane parallel to both ₂ is a graph showing the angular distribution of luminance on the light exit surface of the light guide plate. It is a graph which shows the angular distribution of the brightness on the light emitting surface of an optical sheet when the bias angle of an optical sheet is set to 0 °. It is a graph which shows the angular distribution of the brightness on the light emitting surface of an optical sheet when the bias angle of an optical sheet is 10 °. It is a graph which shows the angular distribution of the brightness on the light emitting surface of an optical sheet when the bias angle of an optical sheet is set to 20 °. It is a graph which shows the angular distribution of the brightness on the light emitting surface of an optical sheet when the bias angle of an optical sheet is set to 30 °. It is a graph which shows the angular distribution of the brightness on the light emitting surface of an optical sheet when the bias angle of an optical sheet is 40 °. It is a graph which shows the luminance distribution for each azimuth angle in _{elevation angle EA max} when the bias angle of an optical sheet is set to 0 °. It is a graph which shows the luminance distribution for each azimuth angle _{at the elevation angle EA max} when the bias angle of an optical sheet is 10 °. It is a graph which shows the luminance distribution for each azimuth angle in _{elevation angle EA max} when the bias angle of an optical sheet is set to 20 °. It is a graph which shows the luminance distribution for each azimuth angle in _{elevation angle EA max} when the bias angle of an optical sheet is set to 30 °. It is a graph which shows the luminance distribution for each azimuth angle in _{elevation angle EA max} when the bias angle of an optical sheet is 40 °. It is a graph which shows the luminance distribution for each elevation _{angle at the azimuth angle DA max} when the bias angle of an optical sheet is set to 0 °. It is a graph which shows the luminance distribution for each elevation _{angle at the azimuth angle DA max} when the bias angle of an optical sheet is 10 °. It is a graph which shows the luminance distribution for each elevation _{angle at the azimuth angle DA max} when the bias angle of an optical sheet is set to 20 °. It is a graph which shows the luminance distribution for each elevation _{angle at the azimuth angle DA max} when the bias angle of an optical sheet is set to 30 °. It is a graph which shows the luminance distribution for each elevation _{angle at the azimuth angle DA max} when the bias angle of an optical sheet is 40 °.

Hereinafter, embodiments of the surface light source device and display device of the present invention will be described mainly with reference to the drawings.
In the drawings attached to the present specification, the aspect ratio and the like may be changed from the actual ones from the viewpoint of ease of illustration.

Further, in the present specification, the “light emitting side” refers to the light emitted from the surface light source device and directed toward the observer by traveling through the components of the surface light source device such as the light source, the light guide plate, and the optical sheet without reversing. It means the downstream side in the traveling direction, and the "light source side" means the upstream side in the traveling direction.
Further, in the present specification, terms such as "sheet", "film", and "board" are not distinguished from each other. For example, a sheet is a concept that includes a member that can also be called a film or a plate.

Further, in the present specification, the "sheet surface (plate surface, film surface)" coincides with the plane direction of the target sheet-like member when the target sheet-like member is viewed as a whole and in a broad view. Refers to a plane. In the present embodiment, the plate surface of the light guide plate, the sheet surface of the optical sheet, the sheet surface of the reflective sheet, the panel surface of the display panel, the display surface of the display device, and the light emitting surface of the surface light source device are substantially parallel to each other. It has become.
Further, in the present specification, the "normal direction" is the normal direction to the light emitting surface of the surface light source device, and in the present embodiment, the normal direction and guidance to the light emitting surface of the surface light source device. It also matches the normal direction to the plate surface of the optical plate, the normal direction to the sheet surface of the optical sheet, the normal direction to the display surface of the display device, and the like.

Further, in the present specification, "pentagon" and "quadrangle" are not only pentagons and quadrangles in a strict sense, but also substantially pentagons and abbreviations in consideration of the limit of accuracy in manufacturing technology and errors during molding. Includes a rectangle. Similarly, other terms used herein that specify shape and geometric conditions (eg, parallel, orthogonal, symmetric, etc.) can be expected to have equivalent optical functionality without being bound by strict meaning. Interpretation shall include some error.

[Surface light source device]
The surface light source device of this embodiment is
A light guide plate having a light emitting surface, a back surface facing the light emitting surface, and a side surface located between the light emitting surface and the back surface, and any side surface of the side surface is an incoming light surface.
A light source arranged facing the incoming light surface and
A surface light source device including an optical sheet arranged to face the light emitting surface of the light guide plate.
The optical sheet has a sheet-shaped main body portion and a plurality of structural rows provided on the surface of the main body portion on the light guide plate side.
When the direction perpendicular to the light entering surface of the light guide plate is the first direction d ₁ and the arrangement direction of the structural rows is the third direction d ₃ , the first direction d ₁ and the third direction d ₃ are non-parallel. And
When the brightness of the light emitted from the center of the surface of the optical sheet opposite to the light guide plate is measured, the following conditions 1-1 and 2-1 are satisfied.
The arrangement direction of the plurality of structural rows is usually perpendicular to the extending direction of the structural rows in the sheet surface. The extending direction of the structural row is usually linear, but it is the same regardless of whether it is curved, meandering, or a mixture of them.

<Condition 1-1>
The maximum brightness when the brightness distribution of the light emitted from the center of the surface of the optical sheet opposite to the light guide plate is measured in a matrix at every 0.5 ° elevation and 0.5 ° azimuth is P _max. And. Here, when the surface light source device is viewed from the normal direction, the direction of the perpendicular line drawn from the center to the light entry surface side is "azimuth angle 0 °", and the surface of the optical sheet opposite to the light guide plate. The direction from to the normal direction is defined as "elevation angle 0 °".
When the elevation angle indicating _{P max is EA max} and the azimuth indicating _{P max is DA max} , the EA _max indicates a value other than 0 °.

<Condition 2-1>
Based on the brightness of each angle measured under the condition 1-1, a brightness distribution map A for each azimuth angle at the _{elevation angle EA max is created.} In the luminance distribution diagram A, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The integral value of the brightness in the range of the azimuth angle "(DA _max −45 °) to (DA _{max + 45 °)" of the luminance distribution map A is DA −45 / + 45} , and the azimuth angle “(DA _{max + 45 °) of the luminance distribution map A”.} The integrated value of the brightness in the range of -20 °) to DA _max to (DA _{max + 20 °) is set to DA -20 / + 20} .
Based on the brightness of each angle measured under condition 1-1, a brightness distribution map B for each elevation _{angle at the azimuth angle DA max is created.} In the luminance distribution diagram B, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The integrated value of the luminance in the range of the elevation angle "(EA _max −45 °) to (EA _{max + 45 °)” of the luminance distribution diagram B is EA −45 / + 45} , and the azimuth angle “(EA _max −” of the luminance distribution diagram A is Let _{EA-20 / + 20} be the integrated value of the luminance in the range of "20 °) _{to EA max} to (EA _{max + 20 °)".}
In the above, 0.77 ≦ (DA _{-20 / + 20} / DA _{−45 / + 45} ) / (EA _{-20 / + 20} / EA _{−45 / + 45} ) ≦ 1.30 is satisfied.
When (DA- _{20 / + 20} / DA- _{45 / + 45} ) / (EA- _{20 / + 20} / EA- _{45 / + 45} ) is less than 0.77 or more than 1.30, the direction showing the peak is centered. The brightness distribution is less likely to be symmetrical in the azimuth and elevation directions.
It is preferable that 0.80 ≦ (DA _{-20 / + 20} / DA _{−45 / + 45} ) / (EA _{-20 / + 20} / EA _{−45 / + 45} ) ≦ 1.25 is satisfied, and 0.83 ≦ (DA _{-20 /). +20} / DA _{−45 / + 45} ) / (EA- _{20 / + 20} / EA _{−45 / + 45} ) ≦ 1.20 is more preferable, and 0.91 ≦ (DA- _{20 / + 20} / DA _{−45 / + 45} ) / (EA _{−20 / + 20} / EA _{−45 / + 45} ) ≦ 1.10 is more preferable.

Satisfying condition 1-1 means that the peak of luminance occurs in a direction other than the normal direction.
Satisfying condition 2-1 means that the luminance distribution centered on the direction showing the peak has good symmetry in the azimuth direction and the elevation angle direction.

The surface light source device of the present embodiment further preferably satisfies the following conditions 1-2.
<Condition 1-2>
DA _max indicates a value other than 0 ° or 180 °.

Satisfying the conditions 1-2, which means that the peak of luminance is generated in a direction other than the first direction d _1.
However, in the present specification, " _{a value other than 0 ° or 180 ° for DA max} " depends not only on 0 ° or 180 ° but also on the type of light source, stability, measurement error, etc. in a strict sense. However, in consideration of the measurement point of the azimuth angle (every 0.5 °) and the measurement condition of the brightness described later, the DA _max is 0 ° ≤ DA _max <2.0 °, 358.0 ° <DA _max ≤ 360. It means that it shows a value other than ° (DA _max is assumed that 360 ° and 0 ° are the same) or 178.0 ° <DA _{max <182.0 °.}

The surface light source device of the present embodiment further preferably satisfies the following conditions 1-3.
<Condition 1-3>
The first direction d ₁ of the surface light source device and the third direction d ₃ is the comparison surface light source device a surface light source device are parallel. When the brightness of the light emitted in the normal direction from the center of the surface of the optical sheet of the comparative surface light source device opposite to the light guide plate is measured and the brightness is set to Re, 1.0 ≦ P _max / Re. Meet.

Satisfying the conditions 1-3 while satisfying the condition 1-1 means that the peak of the brightness is generated in a direction other than the normal direction while maintaining a peak of the constant brightness.

Under the above conditions 1-1, the EA _max is preferably 27 ° ≤ EA _max ≤ 60 °, more preferably 29 ° ≤ EA _max ≤ 50 °, and even more preferably 31 ° ≤ EA _max ≤ 45 °.

Under the above conditions 1-2, the DA _max is more preferably 240 ° ≦ DA _max ≦ 310 °, further preferably 250 ° ≦ DA _max ≦ 290 °.

The surface light source device of the present embodiment further preferably satisfies the following conditions 2-3.
<Condition 2-3>
Based on the brightness of each angle measured under the condition 1-1, a brightness distribution map A for each azimuth angle at the _{elevation angle EA max is created.} In the luminance distribution diagram A, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
With the azimuth DA _max as the reference azimuth, the angle of the azimuth that first shows the brightness that is 1/3 or less _{of P max} in the azimuth on the minus direction side from the reference azimuth of the _{brightness distribution map A is −βDA max} . _{Let + βDA max be} the angle of the azimuth that first shows the brightness that is 1/3 or less _{of P max} in the azimuth on the plus direction side from the reference azimuth.
_{Let β D1} be the angle interval between the reference azimuth and −βDA _{max, and β D2} be the angle interval between the reference elevation angle and + βDA _max.
In the above, it is preferable to satisfy the condition of 20 ° ≦ (β _D1 + β _D2 ) / 2 ≦ 60 °, more preferably 20 ° ≦ (β _D1 + β _D2 ) / 2 ≦ 50 °, and 20 ° ≦ ((β _D1). + Β _D2 ) / 2 ≦ 40 ° is more preferable.
When (β _D1 + β _D2 ) / 2 is in the above range, it becomes easy to satisfy the conditions 1-2, 1-3 and 2-1.

The surface light source device of the present embodiment further preferably satisfies the following conditions 2-4.
<Condition 2-4>
Based on the brightness of each angle measured under condition 1-1, a brightness distribution map B for each elevation _{angle at the azimuth angle DA max is created.} In the luminance distribution diagram B, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The elevation angle EA _max is used as a reference elevation angle, and the elevation angle inclined toward the normal direction is defined as the "minus direction elevation angle", and the elevation angle inclined toward the side away from the normal direction is defined as the "plus direction side elevation angle".
The elevation angle showing brightness that is 1/3 or less _{of P max} first at the elevation angle on the minus direction side from the reference elevation angle of the _{brightness distribution diagram B is −βEA max , and P max} is first at the elevation angle on the plus direction side from the reference elevation angle. _{Let + βEA max be} the angle of elevation that indicates the brightness that is 1/3 or less of.
The spacing angle between the reference elevation angle and the -βEA _max β _E1, the spacing angle between the reference elevation angle and the + βEA _max and beta _E2.
In the above, it is preferable to satisfy the condition of 20 ° ≦ (β _E1 + β _E2 ) / 2 ≦ 30 °, more preferably 20 ° ≦ (β _E1 + β _E2 ) / 2 ≦ 27 °, and 20 ° ≦ ((β _E1). + Β _E2 ) / 2 ≦ 24 ° is more preferable.
When (β _E1 + β _E2 ) / 2 is in the above range, it becomes easy to satisfy the conditions 1-3 and 2-1.

FIG. 1 is a cross-sectional view of a display device 10 including the surface light source device 20 of the present embodiment.
The surface light source device 20 of FIG. 1 is configured as an edge light type surface light source device, and faces the light guide plate 30, the light source 24 arranged on the light incoming surface 33 of the light guide plate, and the light emitting surface 31 of the light guide plate. It has an arranged optical sheet 60 and a reflective sheet 28 arranged so as to face a surface opposite to the light emitting surface of the light guide plate. Further, the surface light source device 20 of FIG. 1 has a light emitting surface 21 that emits light in a planar shape, and the light emitting surface (the surface opposite to the light guide plate of the optical sheet) 61 of the optical sheet serves as the light emitting surface 21. Is forming.
As shown in FIG. 1, such a surface light source device 20 is installed on the back surface of a display panel 15 such as a liquid crystal display panel 15A, and has a role of illuminating the display panel 15 from the back surface.

<Light source>
Examples of the light source 24 include a linear light source such as a cold cathode tube, a point light source such as an LED, and the like. The light source 24 in FIG. 3 is a point light source. Further, in FIG. 3, the light source 24 is formed by a large number of point-shaped light sources 25 arranged along the longitudinal direction of the light entry surface of the light guide plate.
In the light guide plate shown in FIGS. 4 and 5, the arrangement positions of a large number of point-shaped light sources forming the light source 24 are indicated by “+” marks.

<Reflective sheet>
The reflective sheet 28 is arranged so as to face the back surface 32 of the light guide plate. Such a reflective sheet 28 is a member for reflecting the light leaked from the back surface 32 of the light guide plate 30 and causing it to enter the light guide plate 30 again.
Examples of the reflective sheet 28 include a sheet having a reflective layer containing high reflectance particles, a sheet having a layer having a large number of air holes, a sheet having a metal thin film layer, and the like.
The reflection on the reflective sheet 28 may be specular reflection or diffuse reflection. Further, the diffuse reflection may be an isotropic diffuse reflection or an anisotropic diffuse reflection.
From the viewpoint of maintaining the directivity, that is, making it easier for the reflected light leaked from the back surface 32 to be efficiently reflected in the light guide plate 30 again, a sheet provided with a metal thin film layer in which specular reflection is easily obtained is provided. preferable.

<Light guide plate>
In the present embodiment, the light guide plate 30 is formed between a pair of main surfaces and a pair of main surfaces composed of an light emitting surface 31 which is a surface on the display panel 15 side and a back surface 32 on the side opposite to the light emitting surface. Includes four sides.
Further, in the present embodiment, one of the four side surfaces forms the light entering surface 33. Direction perpendicular to the light incident surface 33 is the first direction _{d 1.} As shown in FIG. 2, when the light incident on the light guide plate 30 from the light entry surface 33 travels in the light _{guide plate 30 along the first direction d 1} (light guide direction) and becomes less than the critical angle. Light is emitted from the light emitting surface 31.

Examples of the light guide plate 30 include those in which a dot-shaped reflection pattern is printed on the back surface 32, those in which a concavo-convex pattern is formed on the back surface 32, and the like. From the viewpoint of facilitating the satisfaction of conditions 1-1, 2-1 and the like by combining with an optical sheet described later, it is preferable that a concavo-convex pattern is formed on the back surface 32.

Hereinafter, embodiments of the light guide plate 30 will be described in detail with reference to FIGS. 2 to 6.
The light guide plate 30 of FIGS. 2 to 6 has a plate-shaped base 40 and a plurality of optical elements formed on one side surface (observer side surface, light emitting side surface) 41 of the base portion 40. Has 50 and. The base 40 is configured as a flat plate-like member having a pair of parallel main surfaces. The back surface 32 of the light guide plate is formed by the other surface of the base 40 (the surface facing the reflective sheet 28).

The uneven pattern formed on the back surface 32 of the light guide plate will be described with reference to FIGS. 2 and 5.
The uneven pattern of FIGS. 2 and 5 has an inclined surface 37, a stepped surface 38 extending in the normal direction nd of the light guide plate, and a connecting surface 39 connecting the inclined surface and the stepped surface.
In the light guide plate 30, light is guided from the light entry surface side to the side opposite to the light entry surface by the total reflection action of the pair of main surfaces 31 and 32 of the light guide plate. On the other hand, the inclined surface 37 is inclined with respect to the plate surface of the light guide plate so as to approach the light emitting surface 31 from the light entering surface 33 side to the opposite surface 34 side. Therefore, the incident angle at which the light reflected by the inclined surface 37 is incident on the pair of main surfaces 31 and 32 gradually becomes smaller, and when the incident angle becomes less than the total reflection critical angle, the light is emitted from the light guide plate. Become. That is, the inclined surface 37 functions as an element for extracting light from the light guide plate.

_{By adjusting the distribution of the inclined surface 37 along the first direction d 1} which is the light guide direction on the back surface 32, the distribution of the amount of light emitted from the light guide plate 30 _{along the first direction d 1} can be adjusted. ..
In the example shown in FIGS. 2 to 6, the inclined surface of the back surface 32 as the distance from the light entering surface 33 along the light guide direction (as the approach to the opposite surface 34 opposite to the light entering surface) increases. The proportion of 37 is high. According to such a configuration, the emission of light from the light guide plate 30 in a region away from the light entry surface 33 along the light guide direction is promoted, and it is possible to suppress a decrease in the amount of emitted light as the distance from the light entry surface 33 increases. ..

In one example shown, the arrangement pitch Ps of the inclined surface 37 in the first direction d ₁ (FIG. 3) is constant. Further, the angles of the inclined surfaces 37 are the same among the plurality of connecting surfaces 39. On the other hand, the length in the first direction d ₁ of one of the inclined surface 37 is different between a plurality of connecting surfaces 39. Specifically, the length of the inclined surface 37 in the first direction d ₁ gradually increases as the arrangement position of the connecting surface 39 goes from one side (the side having the light source) in _{the first direction d 1 to the other side.} Become.
Note that "gradually longer", not always necessary to continue to change as long, the length in the first direction d ₁ of the two inclined surfaces 37 adjacent in the first direction d ₁ are identical to each other May be good. That is, the "gradually longer", rather than the length in the first direction d ₁ of the plurality of inclined surfaces 37 is constant, and the length in the first direction d ₁ of one of the inclined surfaces, from the inclined surface means that does not become shorter than the length in the first direction d ₁ of the other inclined surface located on the light source side.

The arrangement pitch Ps of the inclined surface 37 is preferably 20 μm to 500 μm, and more preferably 50 μm to 300 μm.
The angle between the inclined surface 37 and the seat surface (horizontal plane) is 0.5 to 5.0 °, preferably 1.0 to 3.0 °.
The ratio of the length of the first direction _{d 1} of the inclined surface 37 with respect to the array pitch Ps is preferably 10-50% by near the light source side (light incident surface 33 side), and more preferably 20 to 50%. 50 to 90% is preferable, and 50 to 80% is more preferable on the side far from the light source (opposite surface 34 side).

Next, an embodiment of a plurality of optical elements 50 provided on the surface 41 on one side of the base 40 will be described.
As shown in FIG. 4, the plurality of optical elements 50 are arranged on the surface 41 on one side of the base 40 without any gap in the second direction d _{2 orthogonal to the first direction d 1.} Therefore, in FIG. 4, the light emitting surface 31 of the light guide plate is formed by the inclined surfaces 35 and 36 of the optical element 50. The optical element 50, extends in a straight line along the first direction d ₁ perpendicular to the orientation direction d _2. Further, the optical element 50 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction thereof.
Further, the plurality of optical elements 50 of FIG. 4 are configured to be identical to each other.

FIG. 6 shows a cross section parallel to both the arrangement direction of the optical elements 50 (second direction d ₂ ) and the normal direction nd of the light guide plate 30 to the plate surface (light guide plate along the VI-VI line of FIG. 4). The cross-sectional shape of the optical element 50 in (hereinafter, may be referred to as "main cut surface of the light guide plate") is shown.
In FIG. 6, the cross-sectional shape of each optical element 50 on the main cut surface of the light guide plate is a shape that tapers toward the light emitting side. That is, on the main cut surface of the light guide plate, the width of the optical element 50 parallel to the plate surface of the light guide plate decreases as the distance from the base 40 increases along the normal direction nd of the light guide plate.

Further, in FIG. 6, the outer contour 51 on the main cut surface of each optical element 50 has an emission surface angle θ _{a, which} is an angle formed by the outer contour with respect to the surface 41 on one side of the base 40, at the tip of the outer contour. It changes from (outer contour at the position farthest from the base 40) toward the base end 52b (outer contour at the position closest to the base 40). The light emitting surface angle θ _a can be set, for example, as disclosed in Japanese Patent Application Laid-Open No. 2013-51149.

The light emitting surface angle θ _a is an angle formed by the light emitting side surface (outer contour) 51 of the optical element 50 with respect to the one side surface 41 of the base 40 on the main cut surface of the light guide plate.
As shown in FIG. 6, when the outer contour (the surface on the light emitting side) on the main cut surface of each optical element 50 is formed in a polygonal line shape, each straight portion forming the polygonal line and one side surface of the base 40 The angle formed between the angle 41 and the angle (strictly speaking, the smaller angle of the two formed angles (the angle of the inferior angle)) is the light emitting surface angle θ _a .
When the outer contour of the main cut surface of the optical element has a curved surface, the angle formed between the tangent of the curved surface and the base 40 is the emission surface angle θ _a .

The optical element of FIG. 6 is a pentagon in which one side is located on the surface 41 on one side of the base 40 and two sides are located between the tip 52a and each base end 52b on the main cut surface of the light guide plate. It has a shape or a shape in which one or more corners of the pentagonal shape are chamfered.
Further, in the optical element of FIG. 6, the cross-sectional shape of the optical element 50 on the main cut surface has symmetry about the normal direction nd. That is, as shown in FIG. 6, the outer contour 51 of each optical element 50 is composed of a pair of bent surfaces 35 and 36 symmetrically formed about the normal direction. The pair of bent surfaces 35 and 36 are connected to each other to form a tip portion 52a. Each bent surface has first surfaces 35a and 36a forming the tip portion 52a and second surfaces 35b and 36b connecting the first surface and the base portion 40. The pair of first inclined surfaces 35a and 36a have a symmetrical configuration centered on the normal direction nd, and the pair of second inclined surfaces 35b and 36b also have a symmetrical configuration centered on the normal direction nd. ing.

In the main cut surface of the light guide plate, the width W _a in the arrangement direction of the optical element, the height (protruding height along the normal direction from the base portion 40) of the optical elements H ratio of _a (H a _/ W _a ) is preferably 0.30 or more and 0.45 or less.
According to the optical element 50, the refraction and reflection on the surface 51 on the light emitting side exert an excellent light-collecting action on the light component along _{the arrangement direction (second direction d 2) of each optical element 50.} It can be exerted and the generation of side lobes (leakage light) can be suppressed. In addition, the light-collecting action makes it easier to satisfy conditions 1-3.

Width _{W a} it is preferably set to 10 m to 500 m. The thickness of the base 40 is preferably 0.2 mm to 6.0 mm.
Further, the plurality of optical elements 50 may have a concave shape, and may have a curved surface or a flat surface (horizontal plane).

In the present embodiment, it is preferable that the brightness of the light emitted from the center of the light emitting surface 31 of the light guide plate 30 satisfies the following condition 3-1. Satisfying the conditions 3-1, the angle indicating the maximum luminance of the light exiting from the light guide plate, the more deviated from the normal direction in the first direction d _1. By satisfying the condition 3-1, the above conditions 1-1 and 1-2 can be easily satisfied.
Condition 3-1 can be satisfied, for example, by a light guide plate having the above-exemplified shape.

<Condition 3-1>
The luminance of light emitted from the center of the light exit surface of the light guide plate, a maximum luminance when measured every elevation 0.5 ° in a direction along the first direction d ₁ and P _d1max. Here, the direction of the light emitted from the light emitting surface of the light guide plate in the normal direction is defined as "elevation angle 0 °", and the elevation angle inclined from the normal direction toward the light input surface side of the light guide plate is defined as "minus direction elevation angle". ..
When the angle indicating the maximum brightness P _{d1max is EA d1max} , and the angle of elevation indicating the brightness that _{is first 1/2 or less of P d1max} at the elevation angle on the minus direction side from _{EA d1max is −αEA d1max} , 60 ° ≦ EA _{The condition of d1max} ≦ 80 °, 5 ° ≦ EA _d1max − (−αEA _d1max ) ≦ 25 ° is satisfied.

In condition 3-1, it is more preferable to satisfy the condition of _{70 ° ≦ EA d1max} ≦ 80 °, 5 ° ≦ EA _d1max − (−αEA _{d1max) ≦ 15 °.}

In the present embodiment, it is preferable that the brightness of the light emitted from the center of the light emitting surface 31 of the light guide plate 30 satisfies the following condition 3-2. Satisfying the conditions 3-2, the angle indicating the maximum luminance of the light exiting from the light guide plate, which means that no deviated from the normal direction in the second direction d _2. By satisfying the condition 3-2, the above conditions 1-3 and 2-1 can be easily satisfied.
Condition 3-2 can be satisfied by, for example, a light guide plate having the above-exemplified shape.

<Condition 3-2>
The luminance of light emitted from the center of the light exit surface of the light guide plate, a maximum luminance when measured every elevation 0.5 ° in a direction along the second direction d ₂ and P _D2max. Here, the direction of the light emitted from the light emitting surface of the light guide plate in the normal direction is "elevation angle 0 °", and the elevation angle inclined to the left side in the normal direction when viewed from the light input surface side of the light guide plate is "minus direction side". The "elevation angle" and the elevation angle inclined to the right in the normal direction when viewed from the light receiving surface side of the light guide plate are defined as the "elevation angle on the plus direction side".

An absolute value of an angle showing the maximum intensity _{P D2max} a _{| EA d2max |, | EA d2max} | First the absolute value of the angle of elevation showing the luminance is 1/2 or less of _{P D2max} in the elevation of the minus direction from | - When the absolute value of the elevation angle indicating the brightness that _{is first 1/2 or less of P d2max} at the elevation angle on the plus direction side from _{αEA d2max} |, | EA _{d2max | is | + αEA d2max} | _{The conditions of d2max} | ≤3 ° and 12 ° ≤ (|-αEA _d2max | + | + αEA _d2max |) / 2≤27 ° are satisfied.
In condition 3-2, it is more preferable to satisfy the condition of 0 ° ≦ | EA _d2max | ≦ 5 °, 10 ° ≦ (| − αEA _d2max | + | + αEA _{d2max |) / 2 ≦ 30 °.}

The light guide plate 30 having the above configuration can be manufactured by imposing a back surface pattern or an optical element 50 on a light transmissive base material, or by extrusion molding or the like.
Various materials can be used as the material of the base 40 of the light guide plate and the optical element 50, but a material having excellent mechanical properties, optical properties, stability, and workability is preferable. Examples of such a material include thermoplastic resins such as acrylic resin, polystyrene resin, polycarbonate resin, polyester resin and polyacrylonitrile, and transparent resins such as ionizing radiation curable resins such as epoxy acrylate resin and urethane acrylate resin.
If necessary, a light diffusing component can be added to the light guide plate. Examples of the light diffusing component include inorganic particles and organic particles having an average particle diameter of about 0.5 to 100 μm.

When an optical element or an uneven pattern is formed on a light-transmitting base material, a sheet-like layer (hereinafter referred to as a "land portion") is formed between the base material and the optical element or between the base material and the uneven pattern. The "land portion" is made of the same material as the optical element or the uneven pattern, and may be formed at the same time as the optical element or the uneven pattern is formed. In this case, the base 40 is composed of a light-transmitting base material and a land portion. On the other hand, in the optical sheet manufactured by extrusion molding, the base portion 40, the plurality of optical elements 50 on one surface of the base portion, and the uneven pattern on the other side surface of the base portion are integrally formed.

<Optical sheet>
As shown in FIG. 1, the optical sheet 60 is arranged so as to face the light emitting surface 31 of the light guide plate.
As shown in FIG. 7, such an optical sheet 60 has a sheet-shaped main body portion 65 and a plurality of structural rows 70 provided on the light guide plate side surface (light receiving side surface) 67 of the main body portion. It consists of a basic configuration. The main body 65 is configured as a flat plate-like member having a pair of parallel main surfaces. The light emitting surface 61 of the optical sheet 60 is formed by the light emitting side surface 66 of the main body portion located on the side not facing the light guide plate 30.
Further, as shown in FIG. 3, the optical sheet 60 has a direction perpendicular to the light entry surface of the light guide plate as the first direction d ₁ , and an arrangement direction of the structural rows of the optical sheet as the third direction d ₃ . The first direction d ₁ and the third direction d ₃ are arranged so as to be non-parallel.

First, a plurality of structural rows 70 provided on the surface of the main body 65 on the light receiving side will be described.
As shown in FIGS. 2 and 7, the structural rows 70 are arranged side by side on the light guide plate side surface (light receiving side surface) 67 of the main body portion 65. Each structural row 70 is formed in a columnar shape and extends in a direction intersecting the arrangement direction of the structural rows.

In this embodiment, each structural row 70 extends linearly. Further, each structural row 70 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction thereof. Further, the plurality of structural rows 70 are arranged without gaps on the surface 67 on the light receiving side of the main body portion along the direction orthogonal to the longitudinal direction thereof. As described above, the light entry surface of the optical sheet is formed by the surfaces of the structural rows 70 arranged without gaps on the main body 65.
Further, as shown in FIG. 7, a plurality of structural columns 70 are arranged in the third direction d _3. Each structure column 70 extends in the fourth direction _{d 4} perpendicular to the third direction _{d 3.}
As described above, by forming the structure of the surface of the optical sheet on the light guide plate side into a linearly extending structure row, the condition 2-1 can be easily satisfied. In the case where the structure arranged on the surface of the optical sheet on the light guide plate side is a non-structural row that does not extend linearly (for example, a pyramid type), it becomes difficult to satisfy the condition 2-2.

As shown in FIG. 7, a plurality of structural columns 70 of the present embodiment, the first structured surface 71 of the arrangement direction of the structure column 70, i.e. along a third direction d _3, are arranged opposite to each other And has a second structured surface 72.
The first structured surface 71 of each structural column is located on one side in the third direction d _3, second structured surface 72 is positioned on the other side in the third direction d _3. Further, in FIG. 1, FIG. 2, in the cross section of the surface light source device along the main cut surface of the light guide plate shown in FIGS. 9 and 10, one side in the third direction d _3, the first direction d ₁ becomes one side, the other side in the third direction d ₃ is a other side in the first direction d _1.

Accordingly, in the surface light source device 20, a first structured surface 71 of each structural column is positioned on the side of the light source 24 in the third direction d _3, facing one side in the first direction d _1. The second structured surface 72 of each structural column is located on the side away from the light source 24 in a third direction d _3, facing the other side in the first direction d _1. As will be described later, the first structured surface 71 functions as an incident surface when the light emitted from the light guide plate 30 is incident on the optical sheet 60. On the other hand, the second structured surface 72 has a function of reflecting the light incident on the optical sheet 60 and correcting the optical path of the light.

As shown in FIG. 8, the first structured surface 71 and the second structured surface 72 each extend from the main body portion 65 and are connected to each other. The base end portion 75b of the structural row is formed at a position where the first structured surface 71 and the second structured surface 72 are connected to the main body portion 65, respectively. Further, at a position where the first structured surface 71 and the second structured surface 72 are connected to each other, a tip portion (apex portion) 75a of each structural row is formed.
8 shows, the third parallel to both the direction d ₃ cross-section that is the arrangement direction of the normal direction nd and structure column to the seat surface of the main body (hereinafter, simply referred to as "main cross of the optical sheet" In some cases), the cross-sectional shape of the structural row 70 is shown.

The cross-sectional shape of the structural row 70 described above is a quadrangle, but the cross-sectional shape of the structural row 70 is not limited to a quadrangle and may be a polygon such as a triangle or a pentagon. Further, the cross-sectional shape of the structural row 70 may have a curved surface shape at least in part. For example, at least a part of any one or both of the first structured surface 71 and the second structured surface 72 may be a curved surface.

In the present embodiment, as shown in FIG. 3, in the optical sheet 60, the direction perpendicular to the light entering surface of the light guide plate is set to the first direction d ₁ , and the arrangement direction of the structural rows of the optical sheet is set to the third direction d ₃ . At this time, the first direction d ₁ and the third direction d ₃ are arranged so as to be non-parallel.
By arranging the optical sheets so that _{the first direction d 1} and the third direction d ₃ are non-parallel in the display device, it becomes easy to set the elevation angle EA _{max indicating the maximum brightness P max} to a value other than 0 °. , The above condition 1-1 can be easily satisfied. Further, by arranging the optical sheet as described above, the azimuth angle DA _{max indicating the maximum brightness P max} can be easily set to a value other than 0 ° or 180 °, and the above conditions 1-2 can be easily satisfied. Further, by arranging the optical sheets so that the first direction d ₁ and the third direction d ₃ are non-parallel, the brightness distribution of each azimuth angle at the _{elevation angle EA max} is positive in the negative direction with respect _{to the DA max.} It becomes easy to be symmetrical in the direction, and the brightness distribution of each elevation angle at the _{azimuth angle DA max tends to be symmetrical in the minus direction and the plus direction with respect to the EA max} , so that the condition 2-1 can be easily satisfied.
Of the angles formed by the first direction d ₁ and the third direction d ₃ , the narrower angle (hereinafter, may be referred to as “optical sheet bias angle”), that is, the optical sheet bias angle θ _{d1 d3} is 15 ° ≦. (Θ _d1d3 ) ≦ 50 ° is preferable, 18 ° ≦ (θ _d1d3 ) ≦ 45 ° is more preferable, and 20 ° ≦ (θ _d1d3 ) ≦ 40 ° is further preferable. When the bias angle of the optical sheet is within the above range, it becomes easy to satisfy the conditions 1-1 and 1-3.
Furthermore, in order to facilitate satisfying the above conditions 1-1 and conditions 2-1, the first direction d ₁ and the third direction d ₃ not only in non-parallel, is exiting from the light exit surface of the light guide plate It is preferable that the brightness distribution satisfies the above condition 3-2 and the shape of the structural row of the optical sheet is in the range described later.

Hereinafter, the cross-sectional shape of each structural row 70 on the main cut surface of the optical sheet will be described in more detail.
FIG. 8 shows a cross section of the optical sheet along the line VIII-VIII of FIG. 7 (a cross section corresponding to the main cut surface of the optical sheet). On the other hand, in FIGS. 9 and 10, a cross section obtained by cutting the light guide plate and the optical sheet in a direction parallel to both _{the first direction (light guide direction) d 1 and the normal direction nd of the plate surface of the light guide plate.} The shape is shown.
As shown in FIG. 8, in the present embodiment, the cross-sectional shape of each structural row 70 on the main cut surface of the optical sheet is a shape that tapers toward the light entry side (light guide plate side). There is. That is, on the main cut surface of the optical sheet, the width of the structural row 70 becomes narrower as it is separated from the main body 65 along the normal direction nd of the main body 65.

The angle formed by the second structured surface 72, which forms a part of the outer contour of the structural row 70 of the optical sheet, with respect to the surface parallel to the sheet surface of the optical sheet (for example, the surface parallel to the broken line in FIG. 8). Assuming that the "tilt angle θ _t " is set, in the illustrated example, the tilt angle θ _t is not constant in the second structured surface 72. In FIG. 8, the inclination angle θ _t is set from the tip end portion 75a of the structure row closest to the main body portion 65 toward the base end portion 75b of the structure row closest to the main body portion 65 in the second structured surface 72. It is changing to be larger.

In FIGS. 9 and 10, L91 and L101, which are light traveling in a direction in which the inclination angle with respect to the normal direction nd is relatively small, are incident on the region of the second structured surface 72 near the base end portion 75b. It will be easier. Further, L92 and L102, which are light traveling in a direction in which the inclination angle with respect to the normal direction nd becomes relatively large, are likely to be incident on the region of the second structured surface 72 near the tip portion 75a. _{Then, by changing the inclination angle θ t} in the second structured surface 72, the light entering the light entering surface of the optical sheet (light emitted from the light emitting surface of the light guide plate) is formed on the second structured surface 72. As a result, the degree of light collection that has passed through the light emitting surface of the optical sheet can be adjusted by changing the reflected light of.

Further, although FIG. 8 shows only the case where n is 2, which will be described later, the inclination angle θ _t is directed from the side of the tip portion 75a of the structural row to the side of the base end portion 75b on the main cut surface of the optical sheet. It may include n element surfaces (n is a natural number of 2 or more) arranged so as to gradually increase, that is, a plurality of element surfaces 73.
In FIG. 8, the contour of the second structured surface 72 of the structural row 70 has a shape in which straight lines are joined together, or the straight lines are joined together and the joints are chamfered. In other words, the outer contour of the second structured surface 72 of the structural row 70 is formed in a polygonal line shape or in a shape formed by chamfering the corners of the polygonal line. In particular, in the illustrated example, the second structured surface 72 has a first element surface 73a forming the tip portion 75a and a second element surface 73b adjacent to the first element surface 73a from the side of the main body portion 65. ing. Then, as shown in FIG. 8, the inclination angle θ ₂ of the second element surface 73b is larger than _{the inclination angle θ 1} of the first element surface 73a.
However, the present invention is not limited to this example, and the second structured surface 72 may have three or more element surfaces, may be a curved surface, or may be a single element surface. ..

As described above, the inclination angles θ _{t , θ 1} and θ ₂ are the angles formed by the second structured surface of the structural row with respect to the surface parallel to the sheet surface of the optical sheet in the main cut surface of the optical sheet 60. Is. More specifically, the angle formed between each element surface 73 forming a polygonal line on the main cut surface of the optical sheet 60 and a surface parallel to the sheet surface of the optical sheet (strictly speaking, two formed). The smaller of the two angles (the inferior angle)) is the tilt angle θ _t , θ ₁ , and θ ₂ .
_{When the first structured surface and the second structured surface have a curved surface, the inclination angles θ t} , θ ₁ , and θ ₂ are set depending on the angle formed by the tangent line of the curved surface with respect to the surface parallel to the sheet surface of the optical sheet. It may be calculated.

On the main cut surface of the optical sheet, the width of the structural row along the arrangement direction of the structural row 70 is defined as "W _b ", and the height of the structural row along the normal direction nd of the main body 65 is _{defined as "H b} ". At that time, the aspect ratio (W _b / H _b ) of the second structured surface and the inclination angle θ _t of each element surface forming the second structured surface 72 are the light-collecting property and the light-collecting direction of the optical sheet 60. , Affects the direction of maximum brightness.

In FIG. 9, the positions showing the maximum brightness are determined by preventing the lights L91 and L92 emitted from the light emitting surface 31 of the light guide plate from intersecting with the normal nd passing through the tip portion 75a after being reflected by the element surface 73. It is caused in a direction inclined to the first direction d _1.
In order to obtain light emission as shown in FIG. 9, the aspect ratio (W _b / H _{b ) of the structural row, the inclination angle θ 1} of the first element surface 73a, and the inclination angle θ ₂ of the second element surface 73b are within the following ranges. Is preferable.
The aspect ratio (W _b / H _b ) of the structural row is preferably 1.15 or more and 1.50 or less. _{It is preferable that the inclination angle θ 1} of the first element surface 73a is 38 ° or more and 53 ° or less, and the inclination angle θ ₂ of the second element surface 73b is 43 ° or more and 57 ° or less.
Further, when the second structured surface 72 has three element surfaces and the third element surface is 73c and the inclination angle is θ ₃ , the aspect ratio (W _b / H _b ) of the structural row is 1.15 or more. It is preferably 1.50 or less, the inclination angle θ ₁ of the first element surface 73a is 38 ° or more and 53 ° or less, the inclination angle θ ₂ of the second element surface 73b is 42 ° or more and 56 ° or less, and the third element surface. The inclination angle θ _{3 of} 73c is preferably 53 ° or more and 64 ° or less.
By setting W _b / H _b , θ ₁ , θ ₂ , or W _b / H _b , θ ₁ , θ ₂ and θ ₃ in the above range, the above conditions 1-1, 1-2, 1-3, 2 -1 can be easily satisfied.

In FIG. 10, the positions showing the maximum brightness are determined by allowing the lights L101 and L102 emitted from the light emitting surface 31 of the light guide plate to intersect the normal nd passing through the tip portion 75a after being reflected by the element surface 73. and causing the direction inclined with respect to one direction d _1.
In order to obtain light emission as shown in FIG. 10, the aspect ratio (W _b / H _{b ) of the structural row, the inclination angle θ 1} of the first element surface 73a, and the inclination angle θ ₂ of the second element surface 73b are within the following ranges. Is preferable.
The aspect ratio (W _b / H _b ) of the structural row is preferably 1.15 or more and 1.50 or less. _{It is preferable that the inclination angle θ 1} of the first element surface 73a is 53 ° or more and 68 ° or less, and the inclination angle θ ₂ of the second element surface 73b is 59 ° or more and 72 ° or less.
Further, when the second structured surface 72 has three element surfaces and the third element surface is 73c and the inclination angle is θ ₃ , the aspect ratio (W _b / H _b ) of the structural row is 1.15 or more. It is preferably 1.50 or less, the inclination angle θ ₁ of the first element surface 73a is 52 ° or more and 68 ° or less, the inclination angle θ ₂ of the second element surface 73b is 56 ° or more and 68 ° or less, and the third element surface. The inclination angle θ _{3 of} 73c is preferably 63 ° or more and 76 ° or less.
In the embodiment of FIGS. 9 and 10, the angle formed between the first structured surface and the surface parallel to the sheet surface of the optical sheet (strictly speaking, of the two angles formed). The smaller angle (inferior angle)) is not particularly limited, but is usually 50 to 80 °.

Other dimensions of the optical sheet 60 can be set as follows, as an example.
For example, (corresponding to the width W _b of the structure column in the illustrated example) arrangement pitch of the structures column may be a 10μm or 200μm or less. However, in recent years, the arrangement of each structural row 70 has been rapidly improved in definition, and it is preferable that the arrangement pitch of the structural row 70 is 10 μm or more and 35 μm or less.
_{Further, the width W b2} of the second structured surface of the structural row 70 can be 5 μm or more and 100 μm or less, and in consideration of recent trends, it is preferably 5 μm or more and 20 μm or less.
_{Further, the height H b} of the structural row from the main body 65 along the normal direction nd of the sheet surface of the optical sheet can be 5.5 μm or more and 180 μm or less, and considering the recent tendency, 5.5 μm. It is preferably 30 μm or more.

The optical sheet 60 having the above structure can be manufactured by imposing a structural row 70 on a light transmissive base material, extruding, or the like.
Various materials can be used as the material of the main body portion 65 and the structural row 70 of the optical sheet, but a material having excellent mechanical properties, optical properties, stability, and workability is preferable. Examples of such a material include thermoplastic resins such as acrylic resin, polystyrene resin, polycarbonate resin, polyester resin and polyacrylonitrile, and transparent resins such as ionizing radiation curable resins such as epoxy acrylate resin and urethane acrylate resin.

When forming a structural row on a light-transmitting base material, a sheet-shaped land portion may be formed between the base material and the structural row. In this case, the main body portion 65 is composed of a light-transmitting base material and a land portion. On the other hand, in the optical sheet manufactured by extrusion molding, the outer side 65 and a plurality of structural rows 70 on the surface of the main body on the light receiving side are integrally formed.

<Action of surface light source device>
Next, the operation of the surface light source device 20 will be described.

As shown in FIGS. 1 and 2, the light emitted by the light emitting body 25 forming the light source 24 is incident on the light guide plate 30 via the light incoming surface 33. Then, as shown in FIG. 2, the lights L21 and L22 incident on the light guide plate 30 repeat total reflection on the light emitting surface 31 and the back surface 32 of the light guide plate 30, and are opposite to the light input surface 33 of the light guide plate 30. Proceed in the direction connecting with (first direction d ₁ , light guide direction).

The back surface 32 of the light guide plate 30 has an inclined surface 37 that is inclined so as to approach the light emitting surface 31 as it goes from the incoming surface 33 to the opposite surface 34. Each inclined surface 37 is connected via a stepped surface 38 and a connecting surface 39. The step surface 38 extends in the normal direction nd of the light guide plate 30.
Therefore, most of the light that travels in the light guide plate 30 from the side of the incoming light surface 33 to the side of the opposite surface 34 does not enter the stepped surface 38 of the back surface 32 and is applied to the inclined surface 37 or the connecting surface 39. It will be incident and reflected. Then, when the light is reflected by the inclined surface 37 of the back surface 32, the angle of incidence of the light on the light emitting surface 31 and the back surface 32 after that is reduced. Therefore, the angle of incidence of the light traveling in the light guide plate 30 on the light emitting surface 31 and the back surface 32 gradually becomes smaller due to the reflection on the inclined surface 37 of the back surface 32, and when the light emission becomes less than the total reflection critical angle, the light is emitted. It comes out from the front surface 31 or the back surface 32.
The lights L21 and L22 emitted from the light emitting surface 31 head toward the optical sheet 60 arranged on the light emitting side of the light guide plate 30. On the other hand, the light emitted from the back surface 32 is reflected by the reflective sheet 28 arranged on the back surface of the light guide plate 30, enters the light guide plate again, and travels in the light guide plate.

In the illustrated example, the proportion of the inclined surface 37 out of the back surface 32 increases as the surface 34 on the side opposite to the light entering surface 33 approaches. Specifically, the inclined surface 37 has been arranged at a predetermined pitch Ps in the first direction d _1, the length along the first direction d ₁ of the inclined surface 37 is one in the first direction d ₁ It gradually becomes longer from one side to the other. Therefore, even in a region away from the light entering surface 33, it is possible to sufficiently secure the amount of emitted light from the light emitting surface 31 of the light guide plate 30 and to make the amount of emitted light along the light guide direction uniform.

The light emitting surface 31 of the light guide plate 30 shown in the drawing is composed of a plurality of optical elements 50, and the cross-sectional shape of each optical element 50 on the main cutting surface is a pentagonal shape symmetrical about the normal direction or the pentagonal shape. It has a shape with one or more corners chamfered. More specifically, as described above, the light emitting surface 31 of the light guide plate 30 is configured as a bent surface inclined with respect to a surface parallel to the plate surface of the light guide plate (see FIG. 6).
This bent surface is formed of inclined surfaces 35a, 36a, 35b, 36b that are inclined to the opposite sides of the base 40 with the nd in the normal direction to the surface 41 on the light emitting side.
The light that is totally reflected by the inclined surfaces 35 and 36 and travels in the light guide plate 30 and the light that passes through these inclined surfaces and is emitted from the light guide plate have the actions described below by the inclined surfaces. Will be.

First, the action of total internal reflection on the inclined surfaces 35 and 36 and affecting the light traveling in the light guide plate 30 will be described.
FIG. 6 shows the optical paths of the lights L61 and L62 traveling in the light guide plate 30 while repeating total reflection on the light emitting surface 31 and the back surface 32.
As described above, the inclined surfaces 35 and 36 forming the light emitting surface 31 of the light guide plate 30 are two types of surfaces inclined opposite to each other with the normal direction nd to the light emitting side surface 41 of the base 40 being interposed. Includes. Also, two inclined surfaces 35 and 36 inclined in opposite side each other, are arranged alternately along the second direction d _2.
Then, as shown in FIG. 6, the lights L61 and L62 incident on the light emitting surface 31 are often in the normal direction to the surface 41 on the light emitting side of the base 40 of the two types of inclined surfaces 35 and 36. With reference to nd, the light is incident on an inclined surface inclined in the direction opposite to the traveling direction of the light.

As a result, as shown in FIG. 6, the light L61, L62 traveling in the light guide plate 30 are often totally reflected by the inclined surfaces 35 and 36, as component along the second direction d ₂ is reduced Become. Further, on the main cut surface, the traveling direction of the totally reflected light is directed to the opposite side with respect to the normal direction nd.
Thus, the inclined surfaces 35, 36 forming the exit surface 31 of the light guide plate 30, light emitted radially emitting point there is, it is restricted to continue spreading it in the second direction d _2. In other words, the light from the light emitter 25 is incident largely inclined emitted toward the light guide plate 30 with respect to the first direction d ₁ of the light source 24 also while being restricted from moving in the second direction d _2, primarily the first It will proceed in the direction _{d 1.}

Next, the action affecting the light emitted from the light guide plate 30 through the light emitting surface 31 will be described.
As shown in FIG. 6, the lights L61 and L62 emitted from the light guide plate 30 via the light emitting surface 31 are refracted on the surface of the optical element 50 on the light emitting side when emitted from the light guide plate 30.
Due to this refraction, the traveling direction (emission direction) of the lights L61 and L62 traveling in the direction inclined from the normal direction nd on the main cutting surface is in the normal direction nd as compared with the traveling direction of the light in the light guide plate 30. Bend to get closer. By such an action, the optical element 50 can narrow down the traveling direction of the transmitted light to the nd side in the normal direction with respect to the light component along _{the second direction d 2 orthogonal to the light guide direction.}
That is, the optical element 50, the component of light along the second direction d ₂ perpendicular to the light guiding direction, so exert a light condensing effect. In this way, the emission angle of the light emitted from the light guide plate 30 is narrowed down within a narrow angle range centered on the normal direction in a plane parallel to the arrangement direction of the optical elements 50 of the light guide plate 30.

As described above, the emission angle of the light emitted from the light guide plate 30 is narrowed down within a narrow angle range centered on the normal direction nd in the arrangement direction of the optical elements of the light guide plate 30. On the other hand, the emission angle of the light emitted from the light guide plate 30 is due to the fact that the light emitted from the light guide plate 30 has traveled mainly in the light guide plate 30 in the first direction d1, as shown in FIG. In the optical direction) d _{1 , the emission angle θ k} is relatively large and inclined from the normal direction nd. _{That is, the emission angle θ k} of the component in the first direction of the light emitted from the light guide plate 30 is a relatively large angle.
In particular, in the present embodiment, the back surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 37 arranged in _{the first direction d 1} , and each inclined surface 37 is from one side in _{the first direction d 1.} The light guide plate 30 is inclined with respect to the normal direction nd and the first direction d1 so as to approach the light emitting surface 31 toward the other side.
As a result, as shown in FIG. 2, in the first direction (light guide direction) d ₁ , the luminance distribution emitted from the light guide plate 30 tends to be biased toward a narrow angle range that is relatively large and inclined from the normal direction nd. Occurs.
By the above action, the light emitted from the light emitting surface 31 of the light guide plate 30 satisfies the above-mentioned conditions 3-1 and 3-2.

11 and 12 show an example of actually measuring the angular distribution of the brightness emitted from the light emitting surface 31 of the light guide plate 30 having the configuration shown in FIGS. 4 to 6.
Indicated luminance distribution in FIG. 11 is an example of a first direction d ₁ and the normal direction nd actually measured results the luminance distribution of each direction within a plane parallel to both directions. In the graph shown in FIG. 11, the normal direction is 0 °, and the angle inclined from the normal direction to the side opposite to the light entry surface of the light guide plate is the positive angle. Here, Iamax1 is a luminance peak, θaImax1 is an angle at which a luminance peak is obtained, (1/2) Iamax1 is a luminance peak (1/2), and θaIα1 is a luminance peak (1/2). ) Means the change in angle from θaImax1.
The luminance distribution shown in FIG. 12 is an example of the result of actually measuring the luminance distribution in each direction in the plane parallel to both _{the second direction d 2 and the normal direction nd.} In the graph shown in FIG. 12, the angle inclined to the left in the normal direction when viewed from the light receiving surface side of the light guide plate is the angle in the minus direction (y), and the normal direction when viewed from the light receiving surface side of the light guide plate. The angle inclined to the right side of is defined as the angle (x) in the plus direction (x). Here, Iamax2 is the luminance peak, θaImax2 is the angle at which the luminance peak is obtained, (1/2) Iamax2 is (1/2) of the luminance peak, and θaIα2x and θaIα2y have the luminance peak (1 / 2). It is the change in the angle from θaImax2 until 2), and θaIα2 represents the average value thereof (θaIα2 = (θaIα2x + θaIα2y) × (1/2)).

The brightness of the light emitted from the light emitting surface 31 of the light guide plate 30 and the brightness distribution of the light emitted from the light emitting surface of the optical sheet can be measured by scanning the receiver arranged on the light emitting surface side at 0.5 ° intervals. When measuring the brightness (luminous intensity), the aperture angle of the receiver detected by the aperture of the receiver is set to 0.5 °. Therefore, for example, the range of ± 0.25 ° is measured in the measurement of 0 °, the range of 0.25 to 0.75 ° is measured in the measurement of 0.5 °, and −0 is measured in the measurement of -1 °. The range of .25 to −0.75 ° will be measured.
The device for measuring the luminance is not particularly limited, and for example, a general-purpose luminance meter or the like can be used for the measurement. In the present invention, a viewing angle measuring device (EZCONTLAST 160R manufactured by ELDIM) capable of measuring the brightness of the elevation angle and the azimuth angle was used.

The light emitted from the light guide plate 30 is then incident on the optical sheet 60. As described above, the optical sheet 60 has a structural row 70 in which the tip portion 75a projects toward the light guide plate 30 side.
As shown in FIG. 3, the structural rows 70 are arranged in the third direction d ₃ and extend in the direction intersecting the light guide direction (first direction d ₁ ) (fourth direction d _4).

As a result, the light L21 toward the optical sheet 60 through the light guide plate 30, L22 is one of the first structured surface 71 and a second structured surface 72 connected to each other, the light source 24 side in the first direction _{d 1} It is incident on the structural row 70 through the first structured surface 71 located at.
Then, as shown in FIG. 2, the light L21, L22 is then totally reflected by the second structured surface 72 located on the opposite side (right side in the plane of FIG. 2) and the light source in the first direction d ₁ Will change the direction of travel.

Then, due to total reflection on the second structured surface 72 of the structural row 70, in _{a cross section parallel to both the first direction d 1} (light guide direction) and the normal direction nd, the direction inclined from the normal direction nd. The traveling light L91, L92, L101, and L102 are bent so that the angle formed by the traveling direction with respect to the normal direction nd is small (see FIGS. 9 and 10).
However, in the present embodiment, _{by adjusting the inclination angle θ t of} the second structured surface 72, the structural row 70 has a light component along the light _{guide direction (first direction d 1).} The traveling direction of the transmitted light can be narrowed down from the front direction nd to the inclined direction. That is, the optical sheet 60, the component of light along the first direction d _1, it will exert a focusing effect in a direction inclined from the normal direction nd.

In this embodiment, structure column 70 has a first structured surface 71 forming the entrance surface of the third one oriented side (light source side) of the direction d _3, and light emitted from the light exit surface 31 of the light guide plate 30 When, a second structured surface 72 for totally reflecting the light incident on the third faces (opposite side to the light source) other side of the direction d _3, and the structure in the column through the first structured surface 71 have. The light collecting function of the structural row 70 is due to the total reflection function of the second structured surface 72.
Therefore, the optical sheet 60 can greatly change the traveling direction of light, and can adjust the focusing direction with a high degree of freedom. In the example shown in Figure 9, the traveling direction of the light L91, L92 which come forward from the light exit surface 31 of the light guide plate 30, so as not completely returned to normal direction nd, with respect to the first direction d ₁ of the peak of the luminance It is generated in the direction of inclination. On the other hand, in the example shown in FIG. 10, the traveling direction of the lights L101 and L102 advancing from the light emitting surface 31 of the light guide plate 30 is changed beyond the normal direction nd, and the peak brightness is set in the first direction d. It is generated in a direction inclined with respect to _1.
That is, according to the surface light source device 20 having the optical sheet 60 of the present embodiment, a peak of brightness on the light emitting surface 21 can be generated in a direction other than the normal direction by a simple configuration.

13 to 17 show the brightness of the light emitted from the center on the light emitting surface of the optical sheet (the surface opposite to the light guide plate of the optical sheet) 61 at an elevation angle of 0.5 ° and an azimuth angle of 0.5 °. This is an example of the results of measurement in a matrix for each.
The surface light source device 20 used for the luminance distribution measurement of FIGS. 13 to 17 has a light guide plate 30 having the light emission characteristics of FIGS. 11 and 12 and an optical sheet A having the following dimensions.
<Dimensions of optical sheet A (see FIG. 8 for reference numerals)>
Width W _{b along the third direction d 3} of the structural row 70: 18 μm
_{Height H b} along the normal direction nd of the structural row 70: 14 μm
Width W _b 2: 7.5 μm _{along the third direction d 3} of the second structured surface 72
_{The inclination angle θ 1} : 63.0 ° of the first element surface 73a of the second structured surface 72.
_{The inclination angle θ 2} : 63.5 ° of the second element surface 73b of the second structured surface 72.
-Inclination angle of the first structured surface: 53.13 °

Further, in the surface light source device 20 used for the luminance distribution measurement of FIGS. 13 to 17, the bias angles θ _d1d3 of the optical sheet are changed to 0 °, 10 °, 20 °, 30 °, and 40 °. In this measurement, the third direction d ₃ is the direction shown in FIG. 3 with respect to the first direction d ₁ (the direction in which the structured surface of the arbitrary structure row 70 approaches the light source side with reference to the arbitrary structure row 70). The bias angle of the optical sheet is changed as described above.

Direction connecting the 0 and 180 in the circular graph shown in FIGS. 13 to 17 show a first direction _{d 1.} Meanwhile, the direction connecting the 90 and 270 in the circular graph shown in FIGS. 13 to 17 show a second direction _{d 2.}
Further, the center of the circular graph shows the brightness measured in the normal direction (elevation angle 0 °), and the brightness measured at a larger elevation angle is shown as the distance from the center of the circular graph increases. The minimum value of the elevation angle is 0 ° in the normal direction (the center of the circular graph is in the normal direction), and the maximum value of the elevation angle is 90 ° in the horizontal direction.
Further, in the direction connecting 90 and 270 in the circular graph, the side of 270 has _{the normal direction nd in the cross section parallel to both the second direction d 2} and the normal direction nd to the sheet surface of the optical sheet. The left side as a reference is shown, and the 90 side shows the right side with respect to the nd in the normal direction in the cross section.
Further, in the direction connecting the 0 and 180 in the circular graph, side 0, in a cross section parallel to both the normal direction nd of the first direction d ₁ and the seat surface of the optical sheet, the normal direction nd The reference light source side is shown, and the 180 side shows the side opposite to the light source with respect to the normal direction nd in the cross section.

The brightness distribution of FIGS. 13 to 17 divides the relative ratio of the brightness of each angle to the maximum brightness shown in FIG. 13 into five (Z1: 90% or more, Z2: 80% or more and less than 90%, Z3: 70. % Or more and less than 80%, Z4: 50% or more and less than 70%, Z5: less than 50%,).
From 13 to 17, the simple configuration of tilting the third direction d ₃ to the first direction d _1, the direction in which the maximum brightness of on the light emitting surface 21 appears (the direction in which the region Z1 appears) It can be confirmed that not only the normal direction can be shifted to the first direction d ₁ , but also the second direction d _{2 can be shifted.}
The deviation of the direction in which the maximum brightness appears in the first direction d ₁ or the second direction d ₂ means that the above condition 1-1 is satisfied. Further, the fact that the direction in which the maximum brightness appears _{deviates to the second direction d 2} means that the above conditions 1-2 are satisfied.

In the example shown in FIG. 13 (the bias angle of the optical sheet is 0 °), the elevation angle indicating the maximum brightness is 22.0 ° and the azimuth angle indicating the maximum brightness is 359.0 °.
That is, in the example shown in FIG. 13, the condition 1-1 is satisfied, but the condition 1-2 is not satisfied.
On the other hand, in the example shown in FIG. 14 (the bias angle of the optical sheet is 10 °), the elevation angle indicating the maximum brightness is 25.5 ° and the azimuth angle indicating the maximum brightness is 320.0 °. In the example shown in FIG. 15 (the bias angle of the optical sheet is 20 °), the elevation angle indicating the maximum brightness is 33.0 ° and the azimuth angle indicating the maximum brightness is 285.0 °. In the example shown in FIG. 16 (the bias angle of the optical sheet is 30 °), the elevation angle indicating the maximum brightness is 35.0 °, and the azimuth angle indicating the maximum brightness is 270.0 °. In the example shown in FIG. 17 (the bias angle of the optical sheet is 40 °), the elevation angle indicating the maximum brightness is 41.5 ° and the azimuth angle indicating the maximum brightness is 253.3 °.
That is, in the examples shown in FIGS. 14 to 17, conditions 1-1 and conditions 1-2 are satisfied.
As described above, according to the surface light source device of the present embodiment, the peak brightness is generated in a direction other than the normal direction by a simple configuration in _{which the third direction d 3} is inclined with respect to the first direction d _1. Can be done.

Further, when the maximum brightness of the example shown in FIG. 13 is Re and the maximum brightness of the example shown in FIGS. 14, 15, 16 and 17 is P _max , P of FIGS. 14 to 17 is taken. _max / Re indicates the following values.
14: 1.01, FIG. 15: 1.02, FIG. 16: 1.01, FIG. 17: 0.96.
That is, in the examples shown in FIGS. 14 to 16, 1.0 ≦ P _max / Ref, and the conditions 1-3 are satisfied. This indicates that the surface light source device of the present embodiment can generate a luminance peak other than the normal direction while maintaining a constant luminance peak.

18 to 22 are luminance distribution diagrams A relating to the above condition 2-1 created based on the luminance measured in creating FIGS. 13 to 17.
The horizontal axis of the luminance distribution chart A, as shown in the azimuth in elevation EA _max, the reference azimuth azimuth DA _max giving the luminance of P _max (0 ° denoted; in brackets the actual indicates the value) and , The relative angles on the minus direction side and the plus direction side from the reference azimuth are shown.
After calculating the _{DA -20 / + 20 / DA -45} / + 45 conditions 2-1 from 18 to 22, FIG. _{18 DA -20 / + 20 / DA} -45 / + 45 of the (bias angle 0 °) is 0.49 _{, DA -20 / + 20 / DA} -45 / + 45 of the _{DA -20 / + 20 / DA -45} / + 45 0.51 FIG. 19 (bias angle 10 °), FIG. 20 (bias angle 20 °) is 0.59 , 21 (bias angle 30 °) is _{DA -20 / + 20 / DA -45} / + 45 of _{0.62, DA -20 / + 20 /} DA -45 / + 45 in FIG. 22 (bias angle 40 °) is 0.66 Is.
That is, in the examples shown in FIGS. 20 to 22, 0.55 ≦ DA _{-20 / + 20} / DA _{−45 / + 45} is satisfied.

Satisfying 0.55 ≤ DA- _{20 / + 20} / DA- _{45 / + 45} indicates that the brightness distribution in the azimuthal direction centered on the peak direction is sharp in a specific range and the degree of light collection is high. ing.

Further, FIGS. 23 to 27 are luminance distribution diagrams B relating to the above condition 2-1 created based on the luminance measured in creating FIGS. 13 to 17.
The horizontal axis of the brightness distribution diagram B indicates the elevation _{angle at the azimuth angle DA max, and the elevation angle EA max} that gives the brightness of _{P max} is used as the reference elevation angle (expressed as 0 °; the actual value is shown in parentheses) as a reference. The relative angles from the elevation angle to the minus direction side and the plus direction side are shown.
After calculating the _{EA -20 / + 20 / EA -45} / + 45 conditions 2-1 from 23 to _{27, EA -20 / + 20 /} EA -45 / + 45 in FIG. 23 (bias angle 0 °) is 0.76 , 24 (bias angle 10 °) is _{EA -20 / + 20 / EA -45} / + 45 of 0.76, _{EA -20 / + 20 / EA -45} / + 45 in FIG. 25 (bias angle 20 °) is 0.76 _{, EA -20 / + 20 / EA} -45 / + 45 are _{0.76, EA -20 / + 20 /} EA -45 / + 45 in FIG. 27 (bias angle 40 °) in FIG. 26 (bias angle 30 °) is 0.69 Is.
That is, in the examples shown in FIGS. 23 to 26, EA- _{20 / + 20} / EA- _{45 / + 45} ≥ 0.70 is satisfied.
In addition, in FIGS. 23 to 27, the plus direction of the elevation angle is, for example, the maximum brightness when the position of the elevation angle giving the maximum brightness and the center position are connected by a straight line in the circular graphs of FIGS. 13 to 17. The direction from the position of the given elevation angle toward the outer circumference of the circular graph, and the minus direction of the elevation angle indicate the direction toward the center.

Satisfying EA- _{20 / + 20} / EA- _{45 / + 45} ≥ 0.70 indicates that the brightness distribution in the elevation angle direction centered on the peak direction is sharp in a specific range and the degree of light collection is high. There is.

From the above, when (DA- _{20 / + 20} / DA- _{45 / + 45} ) / (EA- _{20 / + 20} / EA- _{45 / + 45} ) is calculated from FIGS. 18 to 22 and 23 to 27, the bias angle is 0 °. (DA _{-20 / + 20} / DA- _{45 / + 45} ) / (EA- _{20 / + 20} / EA- _{45 / + 45} ) is 1.54, and the bias angle is 10 ° (DA _{-20 / + 20} / DA- _{45 / + 45).} ) / (EA- _{20 / + 20} / EA- _{45 / + 45} ) is 1.47, with a bias angle of 20 (DA- _{20 / + 20} / DA- _{45 / + 45} ) / (EA- _{20 / + 20} / EA- _{45 / + 45)} ) Is 1.29, the bias angle is 30 °, (DA- _{20 / + 20} / DA- _{45 / + 45} ) / (EA- _{20 / + 20} / EA- _{45 / + 45} ) is 1.22, and the bias angle is 40 ° (DA). _{-20 / + 20} / DA- _{45 / + 45} ) / (EA _{-20 / + 20} / EA _{-45 / + 45} ) is 1.05.
That is, in the examples shown in FIGS. 20 to 22 and 25 to 27, 0.77 ≦ (DA _{-20 / + 20} / DA _{−45 / + 45} ) / (EA- _{20 / + 20} / EA _{−45 / + 45).} ) ≤ 1.30, which satisfies the condition 2-1.

Satisfying condition 2-1 indicates that the symmetry of the luminance distribution between the azimuth and elevation directions centered on the direction showing the peak luminance is high.
When the conditions 2-1 and 0.55 ≤ DA- _{20 / + 20} / DA- _{45 / + 45} and EA- _{20 / + 20} / EA- _{45 / + 45} ≥0.70 are satisfied at the same time, the direction showing the peak is the center. It shows that the degree of light collection in the azimuth and elevation directions is high and the symmetry is high.

After calculating the above conditions 2-3 _{(β D1 + β D2) /} 2 from 18 to _{22, (β D1 + β D2} ) of FIG. 18 (bias angle 0 °) / 2 is 72.0 °, 19 ( bias angle 10 °) of _{(β D1 + β D2) /} 2 is 63.0 °, 20 (bias angle 20 °) of _{(β D1 + β D2) /} 2 is 45.0 °, 21 (bias angle 30 ° ) of _{(β D1 + β D2) /} 2 is _{37.3 °, (β D1 + β} D2) / 2 in FIG. 22 (bias angle 40 °) is 33.0 °.
That is, in the examples shown in FIGS. 20 to 22, 20 ° ≦ (β _D1 + β _D2 ) / 2 ≦ 60 °, which satisfies the conditions 2-3.

Satisfying conditions 2-3 means that the brightness distribution of the azimuth angle centered on the direction indicating the peak brightness is within the above specific range ((β _D1 + β _D2 ) / 2: the angle indicating 1/3 of the peak brightness. ) Shows that it can be controlled.

After calculating the above conditions 2-4 _{(β E1 + β E2) /} 2 from 23 to 27, FIG. 23 (bias angle _{0 °) (β E1 + β} E2) / 2 is 18.8 °, FIG. 24 ( bias angle 10 °) of _{(β E1 + β E2) /} 2 is 18.3 °, 25 (bias angle 20 °) of _{(β E1 + β E2) /} 2 is 20.8 °, 26 (bias angle 30 ° ) of _{(β E1 + β E2) /} 2 is 20.8 °, FIG. 27 (bias angle _{40 °) (β E1 + β} E2) / 2 is 21.0 °.
That is, in the examples shown in FIGS. 25 to 27, 20 ° ≦ (β _E1 + β _E2 ) / 2 ≦ 30 °, which satisfies the conditions 2-4.

Satisfying conditions 2-4 means that the brightness distribution of the elevation angle centered on the direction indicating the peak brightness is within the above specific range ((β _E1 + β _E2 ) / 2: the angle indicating 1/3 of the peak brightness). It shows that it can be controlled over.

Applications for which display in a specific direction is important include display devices for automobile center consoles, display devices for automobile rear-view mirrors, display devices for automobile side mirrors, and the like.

The surface light source device of the present embodiment can make various changes to the above-described embodiment as described below.

For example, with respect to the optical sheet 60, the plurality of structural rows 70 may have different structural rows.
Further, as the second structured surface 72 of the optical sheet 60, an example having two element surfaces 73 has been shown, but the present invention is not limited to this, and the second structured surface 72 has three or more element surfaces 73. You may. Further, the cross-sectional shape of the main cut surface of the structural row 70 is not limited to a quadrangular shape, and may be a pentagonal shape or a hexagonal shape, and further, at least a part of the cross-sectional shape may include a curved surface.

Further, the light diffusing layer may be provided on the light emitting surface 61 opposite to the surface formed by the structural rows 70 of the optical sheet 60. Examples of the light diffusing layer include a structure containing a transparent resin and light diffusing particles. Such a light diffusing layer causes internal diffusion due to the difference in refractive index between the transparent resin and the light diffusing particles and / or external diffusion due to surface irregularities, and makes defects generated in the optical sheet 60 and the light guide plate 30 less noticeable. At the same time, the brightness distribution emitted from the light emitting surface of the surface light source device can be smoothed.
Examples of the transparent resin include acrylic resin, polyester resin, urethane resin, epoxy resin and the like. Further, as the curing form, a thermosetting type, an ionization radiation curing type (these cured forms of resin are also referred to as a thermosetting resin or an ionization radiation curing type resin), or a solvent drying curing type made of a thermoplastic resin, Examples thereof include a curing form such as a heating, melting, cooling, and solidifying type. Among these, an ionizing radiation curable acrylic resin having excellent processability and high transmittance is preferably used.

Further, with respect to the light guide plate 30, the plurality of optical elements 50 may have different optical elements. Further, the cross-sectional shape of the optical element 50 on the main cut surface is not limited to a pentagonal shape, and may be a triangular shape or a semicircular shape.

Further, the light emitting surface angle θa, which is the angle formed by the outer contour 51 on the main cut surface of the optical element 50 and the surface 41 on one side of the base 40, is from the tip 52a on the outer contour 51, contrary to FIG. It may be changed so as to become smaller toward the base end portion 52b. Further, in FIG. 6, the optical element 50 is formed as a convex portion protruding from the base portion 40, but may be formed as a concave concave portion.

Further, in the surface light source device 20, a reflective polarizing element and light are formed between the light emitting surface of the optical sheet 60 (light emitting surface 21 in FIG. 1) and the lower polarizing element 14 of the display panel 15 (liquid crystal display panel 15A). It may have a diffusion sheet or the like.

Further, the light source 24 may be installed not only on one side of the light guide plate 30 but also on the opposite surface side of the one side. In this case, the azimuth angle of 0 ° may be set with reference to one of the light sources. Specifically, when the surface light source device is viewed from the normal direction, the direction from the center of the light emitting surface of the surface light source device toward the side opposite to the reference light source may be set as "azimuth angle 0 °".

[Display device]
The display device of the present invention includes a surface light source device of the present invention, which will be described later, and a display panel arranged to face the surface light source device.

FIG. 1 is a cross-sectional view showing an embodiment of the display device of the present invention.
In FIG. 1, the display device 10 includes a display panel 15 and a surface light source device 20 arranged on the back side of the display panel and illuminating the display panel in a plane shape from the back side. The display device 10 has a display surface 11 for displaying an image.

In FIG. 1, the display panel 15 is a liquid crystal display panel 15A. The liquid crystal display panel 15A functions as a shutter that controls the transmission or blocking of light from the surface light source device 20 for each pixel, and is configured to display an image on the display surface 11.
Further, the liquid crystal display panel 15A of FIG. 1 is arranged between the upper polarizing element 13 arranged on the light emitting side, the lower polarizing element 14 arranged on the incoming light side, and the polarizing element 14 as the upper polarizing element 13. It has a polarized liquid crystal cell 12. The polarizers 13 and 14 decompose the incident light into two linearly polarized light components (P wave and S wave), and generate a linearly polarized light component (for example, P wave) that oscillates in one direction (direction parallel to the transmission axis). It has a function of transmitting and absorbing a linearly polarized light component (for example, S wave) that vibrates in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.
It is preferable that both sides of the upper polarizing element 13 and the lower polarizing element 14 are covered with a transparent plate such as a plastic film.

An electric field can be applied to the liquid crystal layer 12 for each region forming one pixel. Then, the orientation direction of the liquid crystal molecules in the liquid crystal layer 12 changes depending on the presence or absence of the electric field application. As an example, the polarization component in a specific direction transmitted through the lower polarizing element 14 arranged on the light entry side rotates its polarization direction by 90 ° when passing through the liquid crystal layer 12 to which no electric field is applied, while rotating the polarization direction by 90 °. The polarization direction is maintained as it passes through the liquid crystal layer 12 to which an electric field is applied. In this case, depending on the presence or absence of an electric field applied to the liquid crystal layer 12, whether the polarizing component vibrating in a specific direction transmitted through the lower polarizing element 14 further transmits the upper polarizing element 13 arranged on the light emitting side of the lower polarizing element 14. Alternatively, it is possible to control whether or not it is absorbed by the upper polarizing element 13 and blocked.
In this way, the liquid crystal display panel 15A can control the transmission or blocking of light from the surface light source device 20 for each pixel.

10 Display device 11 Display surface 12 Liquid crystal layer 13 Upper polarizing element 14 Lower polarizing element 15 Display panel 15A Liquid crystal display panel 20 Surface light source device 21 Light emitting surface 24 Light source 25 Light emitter 28 Reflective sheet 30 Light guide plate 31 Light emitting surface 32 Back surface 33 Back surface 33 Incoming light Surface 34 Opposite surface 35 Inclined surface 35a First surface 35b Second surface 36 Inclined surface 36a First surface 36b Second surface 37 Inclined surface 38 Step surface 39 Connection surface 40 Base 41 One side surface 42 Other side surface 50 Optical element 51 Outer contour 52a Tip 52b Base end 60 Optical sheet 61 Emitting surface 65 Main body 66 Emitting side surface 67 Incoming light side surface 70 Structural row 71 First structured surface 72 Second structured surface 73 Element surface 73a 1 element surface 73b 2nd element surface 75a Tip 75b Base end

Claims (10)

A light guide plate having a light emitting surface, a back surface facing the light emitting surface, and a side surface located between the light emitting surface and the back surface, and any side surface of the side surface is an incoming light surface.
A light source arranged facing the incoming light surface and
A surface light source device including an optical sheet arranged to face the light emitting surface of the light guide plate.
The optical sheet has a sheet-shaped main body portion and a plurality of structural rows provided on the surface of the main body portion on the light guide plate side.
When the direction perpendicular to the light entering surface of the light guide plate is the first direction d ₁ and the arrangement direction of the structural rows is the third direction d ₃ , the first direction d ₁ and the third direction d ₃ are non-parallel. And
A surface light source device that satisfies the following conditions 1-1 and 2-1 when the brightness of light emitted from the center of the surface of the optical sheet opposite to the light guide plate is measured.
<Condition 1-1>
The maximum brightness when the brightness distribution of the light emitted from the center of the surface of the optical sheet opposite to the light guide plate is measured in a matrix at every 0.5 ° elevation and 0.5 ° azimuth is P _max. And. Here, when the surface light source device is viewed from the normal direction, the direction of the perpendicular line drawn from the center to the light entry surface side is "azimuth angle 0 °", and the surface of the optical sheet opposite to the light guide plate. The direction from to the normal direction is defined as "elevation angle 0 °".
When the elevation angle indicating _{P max is EA max} and the azimuth indicating _{P max is DA max} , the EA _max indicates a value other than 0 °.
<Condition 2-1>
Based on the brightness of each angle measured under the condition 1-1, a brightness distribution map A for each azimuth angle at the _{elevation angle EA max is created.} In the luminance distribution diagram A, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The integral value of the brightness in the range of the azimuth angle "(DA _max −45 °) to (DA _{max + 45 °)" of the luminance distribution map A is DA −45 / + 45} , and the azimuth angle “(DA _{max + 45 °) of the luminance distribution map A”.} The integrated value of the brightness in the range of -20 °) to DA _max to (DA _{max + 20 °) is set to DA -20 / + 20} .
Based on the brightness of each angle measured under condition 1-1, a brightness distribution map B for each elevation _{angle at the azimuth angle DA max is created.} In the luminance distribution diagram B, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The integrated value of the luminance in the range of the elevation angle "(EA _max −45 °) to (EA _{max + 45 °)” of the luminance distribution diagram B is EA −45 / + 45} , and the azimuth angle “(EA _max −” of the luminance distribution diagram A is The integrated value of the luminance in the range of "20 °) to (EA _{max + 20 °)" is defined as EA-20 / + 20} .
In the above, 0.77 ≦ (DA _{-20 / + 20} / DA _{−45 / + 45} ) / (EA _{-20 / + 20} / EA _{−45 / + 45} ) ≦ 1.30 is satisfied. The surface light source device according to claim 1, wherein the condition 1-1 further _{satisfies the condition of 27 ° ≤ EA max ≤ 60 °.} The surface light source device according to claim 1 or 2, which further satisfies the following conditions 1-2.
<Condition 1-2>
DA _max indicates a value other than 0 ° or 180 °. The surface light source device according to claim 3, wherein the condition 1-2 _{satisfies the condition of 240 ° ≤ DA max ≤ 310 °.} The surface light source device according to any one of claims 1 to 4, which satisfies the following conditions 2-3.
<Condition 2-3>
Based on the brightness of each angle measured under the condition 1-1, a brightness distribution map A for each azimuth angle at the _{elevation angle EA max is created.} In the luminance distribution diagram A, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
With the azimuth DA _max as the reference azimuth, the angle of the azimuth that first shows the brightness that is 1/3 or less _{of P max} in the azimuth on the minus direction side from the reference azimuth of the _{brightness distribution map A is −βDA max} . _{Let + βDA max be} the angle of the azimuth that first shows the brightness that is 1/3 or less _{of P max} in the azimuth on the plus direction side from the reference azimuth.
_{Let β D1} be the angle interval between the reference azimuth and −βDA _{max, and β D2} be the angle interval between the reference elevation angle and + βDA _max.
In the above, the condition of 20 ° ≦ (β _D1 + β _D2 ) / 2 ≦ 60 ° is satisfied. The surface light source device according to any one of claims 1 to 5, which satisfies the following conditions 2-4.
<Condition 2-4>
Based on the brightness of each angle measured under condition 1-1, a brightness distribution map B for each elevation _{angle at the azimuth angle DA max is created.} In the luminance distribution diagram B, it is assumed that _{the luminance of P max} is 1.0 and all the luminances are standardized.
The elevation angle EA _max is used as a reference elevation angle, and the elevation angle inclined toward the normal direction is defined as the "minus direction elevation angle", and the elevation angle inclined toward the side away from the normal direction is defined as the "plus direction side elevation angle".
The elevation angle showing brightness that is 1/3 or less _{of P max} first at the elevation angle on the minus direction side from the reference elevation angle of the _{brightness distribution diagram B is −βEA max , and P max} is first at the elevation angle on the plus direction side from the reference elevation angle. _{Let + βEA max be} the angle of elevation that indicates the brightness that is 1/3 or less of.
The spacing angle between the reference elevation angle and the -βEA _max β _E1, the spacing angle between the reference elevation angle and the + βEA _max and beta _E2.
In the above, the condition of 20 ° ≦ (β _E1 + β _E2 ) / 2 ≦ 30 ° is satisfied. The surface light source device according to any one of claims 1 to 6, wherein the angle θ _{d1 d3} formed by the first direction d ₁ and the third direction d ₃ satisfies 15 ° ≤ θ _{d1 d3 ≤ 50 °.} The surface light source device according to any one of claims 1 to 7, further satisfying the following conditions 1-3.
<Condition 1-3>
In the surface light source device, the surface light source device in which the first direction d ₁ and the third direction d ₃ are parallel is referred to as a comparative surface light source device. When the brightness of the light emitted in the normal direction from the center of the surface of the optical sheet of the comparative surface light source device opposite to the light guide plate is measured and the brightness is set to Ref, 1.0 ≦ P _max / Ref. Meet. Claims 1 to 8 in which the _{DA-20 / + 20} / DA- _{45 / + 45} is 0.55 or more and the EA- _{20 / + 20} / EA- _{45 / + 45} is 0.70 or more in the condition 2-1. The surface light source device according to any one of the above items. A display device including the surface light source device according to any one of claims 1 to 9 and a display panel arranged to face the surface light source device.

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