JP2018018601A - Surface light source device and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make moire inconspicuous when using by combining a surface light source device and a liquid crystal panel and the like.SOLUTION: A surface light source device 20 includes a light guide plate 30 and an optical sheet 60. A rear surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 37. In each unit prism 70 of the optical sheet 60, an angle θformed by a first element surface with respect to a first direction, an angle θformed by a second element surface with respect to the first direction, and an angle θformed by a first prism surface 71 with respect to the first direction satisfy the following formula, with respect to a pitch p of an inclined surface, a depth d of the light guide plate, a refractive index nof the light guide plate, and a refractive index nof the unit prism, when K is 0 or a natural number. (k+0.25)×p<d×|tanφ(θ)-tanφ(θ)|<(k+0.75)×p, with θbeing θor θ, φ(θ)=sin((sin(θ+ψ(θ)))/n), ψ(θ)=sin(n×sin(180°-2×θ-θ))SELECTED DRAWING: Figure 1

Description

  The present invention relates to an edge light type surface light source device and a display device including the surface light source device.

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

  In an edge light type surface light source device as disclosed in Patent Document 1, a light guide plate, a light deflection element arranged to face the light exit surface of the light guide plate, and a face to one side of the light guide plate are arranged. A light source. The light guide plate distributes light from the light source so that the amount of light along the light guide direction is uniform. The incident side surface facing the light guide plate side of the light deflection element has a plurality of inclined surfaces arranged in a direction parallel to the light guide direction of the light guide plate, and is opposite to the light guide plate side of the light deflection element; The outgoing side surface 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 refraction at the incident side and refraction at the emission side.

JP-A-10-160939

  By the way, when a surface light source device is used in combination with a member having a periodic structure, for example, a liquid crystal display panel having a periodic pixel arrangement, moire (striped pattern) is visually recognized, and the surface light source device is Visibility when observing may be deteriorated. Moire is caused by interference between a bright and dark pattern generated by members included in the surface light source device and a bright and dark pattern generated by pixels of the liquid crystal panel. For example, in Patent Document 1, the pitch of the light guide plate or the prism of the optical sheet is adjusted to a predetermined range, thereby making the moire that may be caused by the pitch between the light guide plate or the optical sheet and the pixels of the liquid crystal panel inconspicuous. As described above, it has been conventionally studied to make the moire inconspicuous by adjusting the pitch of the members included in the surface light source device and the pitch of the pixels of the liquid crystal panel in direct association.

  However, in recent years, it has been demanded that the pitch of the pixels of the liquid crystal panel be made finer by increasing the definition of the display. In order to make the moire inconspicuous by the conventional method, the pitch of the members included in the surface light source device must be made fine according to the pitch of the pixels of the liquid crystal panel. However, some of the members included in the surface light source device have difficulty in reducing the pitch in relation to the manufacturing method. Therefore, it is becoming impossible to make the moire inconspicuous enough by the conventional method.

  As another method of making the moiré inconspicuous, the pattern generated by the member is blurred by adding light diffusing particles to the member included in the surface light source device or by adding a light diffusion film in the surface light source device. There is a way to do this. However, these methods have a problem that light emitted from the light source is absorbed by the particles and the film, resulting in loss.

  The present invention has been made in consideration of the above points, and effectively makes moire inconspicuous when used in combination with a member having another periodicity, such as a liquid crystal panel. An object of the present invention is to provide a surface light source device capable of performing the above and a display device including the surface light source device.

A surface light source device according to the present invention comprises:
A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, and a portion located on one side in the first direction of the side surfaces. A light guide plate forming a light incident surface;
A light source disposed facing the light incident surface;
An optical sheet disposed to face the light exit surface of the light guide plate,
The back surface of the light guide plate includes a plurality of inclined surfaces arranged in the first direction,
Each inclined surface is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction,
The optical sheet includes a sheet-like main body, and a plurality of unit prisms arranged in the first direction on the light guide plate side of the main body and extending linearly in a direction intersecting the first direction. And including
Each unit prism includes a first prism surface facing one side of the first direction, and a second prism surface facing the other side of the first direction,
The second prism surface includes a first element surface and a second element having different inclination angles with respect to the first direction in the main cutting surface of the optical sheet parallel to both the first direction and the normal direction of the main body. Including the face,
An angle θ ₁ [°] of less than 180 ° formed by the first element surface at the main cutting surface of the optical sheet with respect to the first direction, and the second element surface at the main cutting surface of the optical sheet is the An angle θ ₂ [°] of less than 180 ° made with respect to the first direction, and an angle θ ₃ [° of less than 180 ° made by the first prism surface with respect to the first direction of the main cutting surface of the optical sheet. ] Is a pitch p [mm] along the first direction of the inclined surface on the back surface of the light guide plate, a thickness d [mm] of the light guide plate, a refractive index n _{1 of} the light guide plate, and the unit prism. For the refractive index n ₂ , k is 0 or a natural number, and the following equation is satisfied.
(K + 0.25) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.75) × p
θ _t is θ ₁ or θ ₂ and
φ (θ _t ) = sin ⁻¹ ((sin (θ ₃ + ψ (θ _t ))) / n ₁ )
ψ (θ _t ) = sin ⁻¹ (n ₂ × sin (180 ° −2 × θ _t −θ ₃ ))

In the surface light source device according to the present invention, the following expression may be satisfied.
(K + 0.324) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.676) × p

In the surface light source device of the present invention,
The angle θ ₁ is smaller than the angle θ ₂ ,
The second element surface may be located on a side of the first element surface that is close to the main body.

In the surface light source device of the present invention,
The second prism surface further includes a third element surface;
An angle θ ₃ [°] of less than 180 ° formed by the third element surface at the main cutting surface of the optical sheet with respect to the first direction is different from the angle θ ₁ [°] and the angle θ ₂ [ °] may be different.

  In the surface light source device according to the present invention, the third element surface may be located between the first element surface and the second element surface.

A display device according to the present invention comprises:
The surface light source device according to the present invention described above;
A display panel disposed to face the surface light source device.

  According to the present invention, when a surface light source device is used in combination with a liquid crystal panel or the like, moire can be effectively made inconspicuous.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device and a surface light source device for explaining an embodiment according to the present invention. FIG. 2 is a diagram for explaining the operation of the surface light source device of FIG. FIG. 3 is a perspective view showing an optical sheet incorporated in the surface light source device of FIG. FIG. 4 is a partial cross-sectional view showing the optical sheet of FIG. 3 at its main cutting plane (cross section taken along line IV-IV of FIG. 3). FIG. 5 is a diagram for explaining the operation of the surface light source device of the present invention. FIG. 6 is a diagram for explaining the operation of the surface light source device of the present invention. FIG. 7 is a diagram for explaining the operation of the surface light source device of the present invention. FIG. 8 is a diagram for explaining the operation of the surface light source device of the present invention. FIG. 9 is a perspective view showing a modification of the light guide plate incorporated in the surface light source device of FIG. FIG. 10 is a sectional view showing a modification of the light guide plate incorporated in the surface light source device of FIG.

  Hereinafter, an embodiment and a modification of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product. In addition, as used in this specification, the shape and geometric conditions and the degree thereof are specified, for example, terms such as “parallel”, “orthogonal”, “identical”, length and angle values, etc. are strictly Without being bound by meaning, it should be interpreted including the extent to which similar functions can be expected.

  1 to 10 are diagrams for explaining an embodiment and a modification according to the present invention. Among these, FIG. 1 is a sectional view showing a schematic configuration of a liquid crystal display device and a surface light source device, and FIG. 2 is a sectional view for explaining the operation of the surface light source device. FIG. 3 is a perspective view showing an optical sheet included in the surface light source device, and FIG. 4 is a cross-sectional view showing the optical sheet on the main cutting surface of the optical sheet.

  As shown in FIG. 1, the display device 10 includes a liquid crystal display panel 15 and a surface light source device 20 that is disposed on the back side of the liquid crystal display panel 15 and illuminates the liquid crystal display panel 15 in a planar shape from the back side. . The display device 10 has a display surface 11 for displaying an image. The liquid crystal display panel 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel, and is configured to display an image on the display surface 11.

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

  An electric field can be applied to the liquid crystal layer 12 for each region where one pixel is formed. Then, the alignment direction of the liquid crystal molecules in the liquid crystal layer 12 changes depending on whether or not an electric field is applied. As an example, the polarization component in a specific direction transmitted through the lower polarizing plate 14 disposed on the light incident side rotates the polarization direction by 90 ° when passing through the liquid crystal layer 12 to which no electric field is applied, The polarization direction is maintained when passing through the liquid crystal layer 12 to which an electric field is applied. In this case, depending on whether or not an electric field is applied to the liquid crystal layer 12, does the polarized light component that vibrates in a specific direction transmitted through the lower polarizing plate 14 further pass through the upper polarizing plate 13 disposed on the light output side of the lower polarizing plate 14? Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 13.

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

  Next, the surface light source device 20 will be described. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and is used as a device that illuminates the liquid crystal display panel 15 from the back side in the present embodiment.

  As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device, and is disposed on the side of the light guide plate 30 and one side (left side in FIG. 1) of the light guide plate 30. And the optical sheet (prism sheet) 60 and the reflection sheet 28 disposed so as to face the light guide plate 30, respectively. In the illustrated example, the optical sheet 60 is disposed facing the liquid crystal display panel 15. The light emitting surface 21 of the surface light source device 20 is defined by the light exit surface 61 of the optical sheet 60.

  In the illustrated example, the light exit surface 31 of the light guide plate 30 is formed in a square shape in plan view, like the display surface 11 of the liquid crystal display device 10 and the light emitting surface 21 of the surface light source device 20. As a result, the light guide plate 30 is generally configured as a rectangular parallelepiped member having a pair of main surfaces (the light exit surface 31 and the back surface 32) in which the sides in the thickness direction are smaller than the other sides. A side surface defined between the pair of main surfaces includes four surfaces. Similarly, the optical sheet 60 and the reflection sheet 28 are generally configured as rectangular parallelepiped members having relatively thin sides in the thickness direction than other sides.

The light guide plate 30 includes a light output surface 31 constituted by one main surface on the liquid crystal display panel 15 side, a back surface 32 formed of the other main surface facing the light output surface 31, and a space between the light output surface 31 and the back surface 32. And a side surface extending. One of the two surfaces facing the first direction d ₁ of the side surfaces forms the light incident surface 33. As shown in FIG. 1, a light source 24 is provided facing the light incident surface 33. As shown in FIG. 2, the light that has entered the light guide plate 30 from the light incident surface 33 is directed substantially toward the opposite surface 34 that faces the light incident surface 33 along the first direction (light guide direction) d ₁ . comes to be guided in one direction (light guide direction) light guide plate 30 along the d _1. As shown in FIGS. 1 and 2, the optical sheet 60 is disposed so as to face the light exit surface 31 of the light guide plate 30, and the reflection sheet 28 is disposed so as to face the back surface 32 of the light guide plate 30. ing.

  The light source may be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), an incandescent lamp, and the like. The light source 24 in the present embodiment is configured by a large number of point-like light emitters 25, specifically, a large number of light emitting diodes (LEDs) arranged side by side along the longitudinal direction of the light incident surface 33. .

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

  By the way, in this specification, the “light-emitting side” means that the light source 24, the light guide plate 30, the optical sheet 60, the liquid crystal display panel 15, and the components of the display device 10 are advanced without going back to each other. It is the downstream side (observer side, for example, the upper side of the paper surface in FIG. 1) in the traveling direction of the light emitted and directed to the observer, and the “light incident side” is the light source 24, the light guide plate 30, and the optical sheet 60. It is the upstream side in the traveling direction of the light that proceeds from the liquid crystal display panel 15 and the components of the display device 10 without reversing and exits from the display device 10 toward the observer.

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

  Further, in this specification, the “sheet surface (plate surface, film surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed as a whole and globally. Refers to the surface. In the present embodiment, the plate surface of the light guide plate 30, the sheet surface (plate surface) of the base 40 described later of the light guide plate 30, the sheet surface of the optical sheet 60, and the sheet surface of the main body 65 described later of the optical sheet 60. The sheet surface of the reflective sheet 28, the panel surface of the liquid crystal display panel, the display surface 11 of the display device 10, and the light emitting surface 21 of the surface light source device 20 are parallel to each other. Furthermore, in this specification, the normal line direction of a sheet-like member refers to the normal line direction to the sheet | seat surface of the sheet-like member used as object. Further, in the present specification, the “front direction” is a normal direction to the light emitting surface 21 of the surface light source device 20, and in this embodiment, the normal to the light emitting surface 21 of the surface light source device 20. Direction, normal direction to the plate surface of the light guide plate 30, normal direction to the sheet surface of the optical sheet 60, normal direction to the sheet surface of the main body 65 of the optical sheet 60, to the display surface 11 of the display device 10. (For example, see FIG. 2).

  Next, the light guide plate 30 will be described in detail with reference to FIG. As well shown in FIG. 2, the light guide plate 30 has a base 40 formed in a plate shape. The base 40 is configured as a flat member having a pair of parallel main surfaces. The back surface 32 of the light guide plate 30 is configured by the surface 42 on the other side of the base 40 located on the side facing the reflection sheet 28.

The other side surface 42 of the base 40 that forms the back surface 32 of the light guide plate 30 is formed as an uneven surface. As a specific configuration, the back surface 32 has an inclined surface 37, a step surface 38 extending in the normal direction nd of the light guide plate 30, and a connection extending in the plate surface direction of the light guide plate 30 due to the unevenness of the other side surface 42 of the base 40. And a surface 39. The inclined surface 37, the stepped surface 38 and connecting surface 39 are a plurality repeatedly arranged in this order along the first direction d _1. The inclined surfaces 37, each stepped surface 38 and the connecting surface 39, the first direction d ₁ and the non-parallel directions, in especially the illustrated example extends in a direction perpendicular to the first direction d _1. The light guide in the light guide plate 30 is based on the total reflection action on the pair of main surfaces 31 and 32 of the light guide plate 30. On the other hand, the inclined surface 37 is inclined with respect to the plate surface of the light guide plate 30 so as to approach the light exit surface 31 from the light incident surface 33 side toward the opposite surface 34 side. Therefore, the incident angle when the light reflected by the inclined surface 37 enters the pair of main surfaces 31 and 32 becomes small. When the incident angle on the pair of main surfaces 31 and 32 is less than the total reflection critical angle by reflecting on the inclined surface 37, the light is emitted from the light guide plate 30. That is, the inclined surface 37 functions as an element for extracting light from the light guide plate 30.

The distribution of the inclined surface 37 along the first direction d ₁ is a light guiding direction by adjusting in the back surface 32, to adjust the first distribution along the direction d ₁ of the amount of light emitted from the light guide plate 30 it can. In the example shown in FIG. 2, as the light incident surface 33 approaches the opposite surface 34 along the light guide direction, the proportion of the inclined surface 37 in the back surface 32 increases. According to such a configuration, the emission of light from the light guide plate 30 in the region separated from the light incident surface 33 along the light guide direction is promoted, and the amount of emitted light decreases as the distance from the light incident surface 33 increases. Can be effectively prevented.

Note that in one example shown, the array pitch p of the inclined surface 37 in the first direction d ₁ is constant. In addition, the inclination angles of the inclined surfaces 37 are the same among the plurality of connection surfaces 39. On the other hand, the length of one connection surface 39 in the first direction d ₁ is different among the plurality of connection surfaces 39. Length in the first direction d ₁ of the connection surface 39, as position of the connecting surface 39 toward the other side from one side in the first direction d _1, gradually becomes shorter. As the length of the connecting surface 39 varies, the length of one inclined surface 37 in the first direction d ₁ differs among the plurality of inclined surfaces 37. Length in the first direction d ₁ of the inclined surface 37, as position of the inclined surface 37 toward the other side from one side in the first direction d _1, gradually becomes longer. Note that "gradually shorter (or longer)", always shorter (or longer) so as to need not continue to change, therefore, and two connecting surfaces 39 adjacent in the first direction d ₁ first direction d length in the first direction d ₁ of the two inclined surfaces 37 adjacent to _1, it may be made identical to each other. In other words, “slowly shorter” means that the lengths of the plurality of connection surfaces 39 in the first direction d ₁ are not constant, and the length of one connection surface 39 in the first direction d ₁ It means that it is not longer than the length in the first direction d ₁ of the other connection surface 39 located on one side in the first direction d ₁ than the connection surface 39. Similarly, “slowly longer” means that the lengths of the plurality of inclined surfaces 37 in the first direction d ₁ are not constant, and the length of one inclined surface 37 in the first direction d ₁ is equal to the _one in the first direction d ₁ . This means that it is not shorter than the length in the first direction d ₁ of the other inclined surface 37 located on one side in the first direction d ₁ than the one inclined surface 37.

  Here, the thickness of the light guide plate 30, that is, the distance between the outgoing surface 31 and the rear surface 32 is defined as d. As described above, the back surface 32 has the inclined surface 37, the step surface 38, and the connection surface 39. Since the change in the thickness due to these is sufficiently smaller than d, the thickness of the light guide plate 30 is d. It can be considered constant. When unevenness is formed on the surface of the light guide plate 30, the thickness between the tops of the unevenness is defined as the thickness d of the light guide plate 30. In the illustrated example, the separation distance along the normal direction nd of the light guide plate 30 between the light exit surface 31 and the connection surface 39 of the light guide plate 30 is considered as the thickness d of the light guide plate 30. Further, in the example shown in FIG. 9 to be described later, the separation distance along the normal direction nd of the light guide plate 30 between the front end portion 52a of the unit optical element 50 of the light guide plate 30 and the connection surface 39 is set to be equal to that of the light guide plate 30. Consider thickness d.

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

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

  As shown in FIG. 3, the optical sheet 60 includes a main body portion 65 formed in a plate shape and a plurality of unit prisms (unit shape elements, unit units) formed on the light incident side surface 67 of the main body portion 65. Optical element, unit lens) 70. The main body portion 65 is configured as a flat plate-like member having a pair of parallel main surfaces. The light exit surface 61 of the optical sheet 60 is configured by the light exit side surface 66 of the main body 65 located on the side not facing the light guide plate 30.

  Next, the unit prism 70 provided on the light incident side surface of the main body 65 will be described. As well shown in FIGS. 2 and 3, the plurality of unit prisms 70 are arranged side by side on the light incident side surface 67 of the main body 65. Each unit prism 70 is formed in a columnar shape and extends in a direction intersecting with the arrangement direction.

  In the present embodiment, each unit prism 70 extends linearly. Each unit prism 70 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction. Further, the plurality of unit prisms 70 are arranged on the light incident side surface 67 of the main body 65 with no gap along the direction orthogonal to the longitudinal direction. Therefore, the light incident surface 62 of the optical sheet 60 is formed by the surfaces (prism surfaces) 71 and 72 of the unit prisms 70 arranged on the main body portion 65 without a gap.

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

As shown well in FIG. 2, each unit prism 70 includes a first prism surface 71 and a second prism that are arranged to face each other along the arrangement direction of the unit prisms 70, that is, the first direction d _1. A surface 72 is provided. The first prism surface 71 of each unit prism 70 is located on one side in the first direction (left side of the paper surface of FIGS. 1 and 2), and the second prism surface 72 is on the other side in the first direction (FIGS. 1 and 2). It is located on the right side in FIG. More specifically, the first prism surface 71 of each unit prism 70 faces the one side in the first direction d ₁ positioned on the side of the light source 24 in the first direction d _1. The second prism surface 72 of each unit prism 70 is located on the side away from the light source 24 in the first direction d _1, it faces the other side in the first direction d _1. As will be described later, the first prism surface 71 mainly travels from the light source 24 arranged on one side in the first direction d ₁ into the light guide plate 30, and then the light emitted from the light guide plate 30 is converted into the optical sheet 60. It functions as an incident surface when entering the lens. On the other hand, the second prism surface 72 has a function of reflecting light incident on the optical sheet 60 and correcting the optical path of the light.

  As shown well in FIG. 4, the first prism surface 71 and the second prism surface 72 extend from the main body portion 65 and are connected to each other. A base end portion 75b of the unit prism 70 is defined at a position where the first prism surface 71 and the second prism surface 72 are connected to the main body portion 65, respectively. In addition, at a position where the first prism surface 71 and the second prism surface 72 are connected to each other, a tip portion (a top portion) 75a of the unit prism 70 that protrudes most from the main body portion 65 to the light incident side is defined.

As described above and as shown in FIG. 4, in the normal direction nd to the sheet surface of the main body 65 (the light incident side surface 67 of the main body 65, the sheet surface of the optical sheet 60) and the arrangement direction of the unit prisms 70. The cross-sectional shape of each unit prism 70 in a cross section parallel to both of the first directions d ₁ (hereinafter, also simply referred to as the main cutting surface of the optical sheet) is the longitudinal direction (straightly extending) of the unit prism 70. It is constant along the direction).

  Hereinafter, the cross-sectional shape of the unit prism 70 on the main cutting surface of the optical sheet will be described in more detail. FIG. 4 shows a cross section of the optical sheet taken along line IV-IV in FIG. 3 corresponding to the main cut surface of the optical sheet. As shown in FIG. 4, in the present embodiment, the cross-sectional shape of each unit prism 70 on the main cut surface of the optical sheet is a shape that tapers toward the light incident side (light guide plate side). Yes. In other words, the width of the unit prism 70 parallel to the sheet surface of the main body 65 on the main cut surface decreases as the distance from the main body 65 increases along the normal direction nd of the main body 65.

In the present embodiment, the second prism surface 72 that forms part of the outer contour of the unit prism 70 on the main cutting surface of the optical sheet 60 (the second prism surface 72 that forms part of the light incident side surface) is in the first direction. When the angle formed with respect to d ₁ and the inclination angle theta _t, the inclination angle theta _t of at least one of the unit prisms 70 is not in the constant in the second prism surface 72. As shown in FIG. 4, the inclination angle θ _t is the base end of the unit prism 60 closest to the main body 65 from the front end 75 a of the unit prism farthest from the main body 65 in the second prism surface 72. It changes so that it may become large toward the part 75b. According to such a unit prism 60, the base end portion 75b in which the relatively rising light traveling in the direction in which the inclination angle with respect to the front direction nd of the second prism surface 72 becomes relatively small is mainly incident. In both the area on the side and the area on the side of the tip 75a where the relatively sleeping light that travels in the direction in which the tilt angle with respect to the front direction nd becomes very large is mainly incident. can do.

As a specific configuration, the inclination angle θ _t with respect to the first direction d ₁ gradually increases from the distal end portion 75a side to the proximal end portion 75b side of the unit prism 70 on the main cut surface of the optical sheet. In this way, n element surfaces 73 (n is a natural number of 2 or more), that is, a plurality of element surfaces are included. In the illustrated embodiment, the contour of the second prism surface 72 of the unit prism 70 is formed by joining the straight portions on the main cut surface of the optical sheet, or joining the straight portions and chamfering the joint. The shape is In other words, the outer contour of the second prism surface 72 of the unit prism 70 is formed in a polygonal line shape or a shape formed by chamfering the corners of the polygonal line. In particular, in the illustrated example, the second prism surface 72 includes a first element surface 73a that defines the distal end portion 75a, and a second element surface 73b that is adjacent to the first element surface 73a from the main body 65 side. Have. As shown in FIG. 7, the inclination angle θ ₁ of the first element surface 73a is smaller than the inclination angle θ ₂ of the second element surface 73b.

As described above, the inclination angles θ _t , θ ₁ , and θ ₂ are such that the light incident side surface (second prism surface 72) of the unit prism 60 is in the first direction d ₁ on the main cut surface of the optical sheet 60. It is the angle to make. The angle formed between each element surface 73 constituting the broken line and the first direction d ₁ (strictly speaking, the smaller one of the two formed angles (subordinate angle)) is the inclination angle. θ _t, θ _1, the θ _2.

In addition, a first prism surface 71 (a first prism surface 71 forming a part of a light incident side surface) that forms a part of the outer contour of the unit prism 70 on the main cutting surface of the optical sheet 60 with respect to the first direction d _1. The angle formed by the robot (strictly speaking, the smaller one of the two formed angles (the minor angle)) is defined as the inclination angle θ ₃ .

As a result of intensive studies, the inventors of the present application have determined that in the optical sheet 60 having the above-described configuration, the inclination angles θ ₁ , θ ₂ , and θ _{3 on} the main cutting surface of the optical sheet are equal to the thickness d of the light guide plate 30. The surface light source device 20 of the present invention has other periodicity by satisfying the following relationship with the pitch p along the first direction d ₁ of the inclined surface 37 on the back surface 32 of the light guide plate 30. It has been found that moire generated when used in combination with a member having a configuration (for example, the liquid crystal panel 15) can be made inconspicuous. Here, k is 0 or a natural number.
(K + 0.25) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.75) × p
θ _t is θ ₁ or θ ₂ and
φ (θ _t ) = sin ⁻¹ ((sin (θ ₃ + ψ (θ _t ))) / n ₁ )
ψ (θ _t ) = sin ⁻¹ (n ₂ × sin (180 ° −2 × θ _t −θ ₃ ))

As shown in FIG. 4, “θ _t ” in the above condition is t (t is 1 ≦ 1) from the front end 75a side to the base end 75b side of the unit prism 70 on the main cutting surface of the optical sheet. The natural angle satisfying t ≦ n) is the magnitude of the inclination angle described above with respect to the element surface 73 located in the position. In the present embodiment, θ _t represents θ ₁ or θ ₂ .

Moreover, the other dimension of the optical sheet 60 can be set as follows as an example. First, as a specific example of the unit prism 70 configured as described above, the arrangement pitch of the unit prisms 70 can be set to 10 μm or more and 200 μm or less. However, in recent years, the arrangement of the unit prisms 70 has been highly refined, and the arrangement pitch of the unit prisms 70 is preferably set to 10 μm or more and 40 μm or less. Similarly, the width of the second prism surface 72 of the unit prism 70 can be set to 5 μm or more and 100 μm or less, and can be set to 5 μm or more and 20 μm or less considering recent trends. Further, the projection height of the unit prism 70 from the main body 65 along the normal direction nd to the sheet surface of the optical sheet 60 can be set to 5.5 μm or more and 180 μm or less. Further, the inclination angle theta ₁ of the first element surface 73a of the second prism surface 72 can be a 45 ° to 60 °, the inclination angle theta ₂ of the second element surface 73b of the second prism surface 72 It can be set to 50 ° or more and 70 ° or less.

The optical sheet 60 having the above-described configuration can be produced by molding the optical sheet 60 on a base material or by extrusion molding. Various materials can be used as the material forming the main body 65 and the unit prism 70 of the optical sheet 60.
However, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, etc., and can be obtained at low cost, such as acrylic resin, polystyrene, polycarbonate, etc. Transparent resins mainly composed of one or more of polyethylene terephthalate, polyacrylonitrile, etc., and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins, etc.) can be suitably used.

  When the optical sheet 60 is produced by curing the ionizing radiation curable resin on the base material, the sheet-like land portion that is positioned between the unit prism 70 and the base material is used together with the unit prism 70. You may make it form on a material. In this case, the main body portion 65 is composed of a base material and a land portion formed of an ionizing radiation curable resin. On the other hand, in the optical sheet 60 produced by extrusion molding, the main body portion 65 and the plurality of unit prisms 70 on the light incident side surface 67 of the main body portion 65 can be integrally formed.

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

First, as shown in FIGS. 1 and 2, the light emitted from the light emitter 25 constituting the light source 24 enters the light guide plate 30 via the light incident surface 33. As shown in FIG. 2, the light L <b> 2 incident on the light guide plate 30 is totally reflected on the light exit surface 31 and the back surface 32 of the light guide plate 30 due to the difference in refractive index between the material forming the light guide plate 30 and air. The reflection is repeated and the light guide plate 30 proceeds in the first direction (light guide direction) d ₁ connecting the light incident surface 33 and the opposite surface 34.

  The back surface 32 of the light guide plate 30 has an inclined surface 37 that is inclined so as to approach the light exit surface 31 from the light incident surface 33 toward the opposite surface 34. The inclined surface 37 is connected via a step surface 38 and a connection surface 39. Among these, the step surface 38 extends in the normal direction nd of the plate surface of the light guide plate 30. Therefore, most of the light traveling in the light guide plate 30 from the light incident surface 33 side to the opposite surface 34 side does not enter the step surface 38 of the back surface 32, and is incident on the inclined surface 37 or the connection surface 39. Reflected. Then, when reflected by the inclined surface 37 of the back surface 32, the traveling direction of the light in the cross section shown in FIG. 2 increases the inclination angle with respect to the plate surface of the light guide plate 30. That is, when the light is reflected by the inclined surface 37 of the back surface 32, the incident angle of the light on the light output surface 31 and the back surface 32 in the following becomes small. Therefore, the incident angle of the light traveling in the light guide plate 30 to the light exit surface 31 and the back surface 32 is gradually reduced by one or more reflections on the inclined surface 37 of the back surface 32, and is less than the total reflection critical angle. Become. In this case, the light can be emitted from the light exit surface 31 and the back surface 32 of the light guide plate 30. The light L <b> 2 emitted from the light exit surface 31 travels to the optical sheet 60 disposed on the light exit side of the light guide plate 30. On the other hand, the light emitted from the back surface 32 is reflected by the reflection sheet 28 disposed on the back surface of the light guide plate 30, enters the light guide plate 30 again, and travels through the light guide plate 30.

In particular, in the illustrated example, as the light incident surface 33 approaches the opposite surface 34 along the first direction d ₁ that is the light guide direction, the proportion of the inclined surface 37 in the back surface 32 increases. Yes. More specifically, the inclined surface 37 has been arranged at a predetermined pitch p in the first direction d _1, the length along the first direction d ₁ of the inclined surfaces 37, in the first direction d ₁ The length gradually increases from one side to the other. This ensures a sufficient amount of light emitted from the light exit surface 31 of the light guide plate 30 in a region separated from the light incident surface 33 where the amount of emitted light tends to decrease, and the amount of emitted light uniform along the light guide direction. Can be achieved.

The incident angle of the light emitted from the light guide plate 30 to the light exit surface 31 is a surface parallel to the first direction (light guide direction) d ₁ as shown in FIG. 2 due to total reflection at the inclined surface 37. , The incident angle φ is slightly lower than the total reflection critical angle. That is, the emission angle of the first direction component d ₁ to the light exit 31 side of the light emitted from the light guide plate 30 is a relatively large angle slightly below 90 °. 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 d ₁ so as to approach the light exit surface 31 as it goes to the other side. As a result, as shown in FIG. 2, the emission direction of the light emitted from the light guide plate 30 on the surface parallel to the first direction (light guide direction) d ₁ is relatively inclined with a relatively large inclination from the front direction nd. There is a tendency to be biased within a narrow angle range where the emission angle is large.

The light emitted from the light guide plate 30 then enters the optical sheet 60 at an incident angle ψ, as indicated by the lights L7 and L8 in FIGS. As described above, the optical sheet 60 includes the unit prism 70 with the tip end portion 75a protruding toward the light guide plate 30 side. The unit prism 70 extends in the second direction d ₂ in the direction orthogonal to the light guide direction (first direction) d ₁ by the light guide plate 30.

As a result, first prism light L2 toward the optical sheet 60 through the light guide plate 30 is emitted by a light source 24 disposed (the left side in the plane of FIG. 2) the first one side in the direction d ₁ is connected to each other The light enters the unit prism 70 via the first prism surface 71 located on one side of the surface 71 and the second prism surface 72 which is the light source 24 side in the first direction d ₁ . As shown in light L7 of the light L2 and 7 of Figure 2, this light is then the second prism and the first light source in the direction d ₁ positioned on the other side of the opposite side (right side in the plane of FIG. 2) The surface 72 is totally reflected to change its traveling direction.

Then, by total reflection at the second prism surface 72 of the unit prisms 70, parallel to both the main cross (first direction (light guide direction) d ₁ and the front direction nd of the indicated light guide plate in FIG. 7 The light traveling in the direction inclined from the front direction nd in the cross section) is bent so that the angle formed by the traveling direction with respect to the front direction nd is small. That is, the optical sheet 60, the component of light along the first direction d _1, it will exert a light condensing effect toward the front direction nd.

  The light of one polarization component emitted from the optical sheet 60 forming the light emitting surface 21 of the surface light source device 20 is then incident on the liquid crystal display panel 15 and is transmitted through the lower polarizing plate 14. The light transmitted through the lower polarizing plate 14 selectively passes through the upper polarizing plate 13 according to the state of electric field application to each pixel. In this manner, the liquid crystal display panel 15 selectively transmits light from the surface light source device 20 for each pixel, so that an observer of the liquid crystal display device 10 can observe an image.

By the way, as described above, when the surface light source device 20 is used in combination with a member having a periodic structure, for example, the liquid crystal panel 15, moire can occur. The cause of the moiré is due to the light / dark pattern generated due to the periodicity of the structure of the light guide plate 30 and the optical sheet 60 included in the surface light source device 20 and the structure having the periodicity of the pixels of the liquid crystal panel 15 and the like. This is a phenomenon in which bright and dark patterns that are caused overlap each other and light and dark unevenness is emphasized and visually recognized. As a result of earnest research, the present inventor has improved the structures of the light guide plate 30 and the optical sheet 60 to blur (weaken) the light and dark pattern generated by the light guide plate 30 and the optical sheet 60, thereby generating the surface light source. It has been found that moire that can occur when the apparatus is combined with a member having another periodic configuration can be effectively inconspicuous. Specifically, the inclination angles θ ₁ , θ ₂ , and θ _{3 on} the main cut surface of the optical sheet are in the thickness d of the light guide plate 30 and the first direction d ₁ of the inclined surface 37 on the back surface 32 of the light guide plate 30. By satisfying the following relationship with the pitch p along, the moire when using the surface light source device 10 can be effectively made inconspicuous. Under the following conditions, k is 0 or a natural number.
(k + 0.25) × p <d × | tanφ (θ ₁ ) -tanφ (θ ₂ ) | <(k + 0.75) × p
θ _t is θ ₁ or θ ₂ and
φ (θ _t ) = sin ^-1 ((sin (θ ₃ + ψ (θ _t ))) / n ₁ )
ψ (θ _t ) = sin ^-1 (n ₂ × sin (180 ° -2 × θ _t -θ ₃ ))
In particular, according to this method, it is beneficial in that a countermeasure against moire can be realized by adjusting only the configuration of the surface light source device without adjusting the periodic pitch between the surface light source device and other members. It is. The principle will be described below.

  First, as described above, when the light guided through the light guide plate 30 is reflected by the inclined surface 37 of the back surface 32, the incident angle to the light exit surface 31 that is incident thereafter is reduced. On the other hand, when the light guided through the light guide plate 30 is reflected by the connection surface 39 of the back surface 32, the incident angle to the light exit surface 31 is maintained. Therefore, as shown in FIG. 5, most of the light emitted from the light exit surface 31 of the light guide plate 30 is light reflected by the inclined surface 37 immediately before entering the light exit surface 31. Here, FIG. 5 is a longitudinal sectional view along the light guide direction (first direction) showing the surface light source device 20.

The light emitted from the outgoing surface 31 of the light guide plate 30 enters the optical sheet 60. The optical sheet 60 has a condensing function in a specific direction due to the condensing function of the unit prism 70. Condensing function in the unit prisms 70 is due to reflection at the second prism surface 72, is inclined with respect to a predetermined angle by the normal direction nd corresponding to the inclination angle theta _t of the second prism surface 72 It is strong against light. Therefore, if the inclination angle theta _t of the second prism surface 72 is constant, light and dark pattern corresponding to the arrangement of the inclined surface 37 of the light guide plate 30 is observed from the front direction of the light collection direction of the brightest increases Become so. This bright and dark pattern can cause moiré in combination with other members having a periodic structure.

Meanwhile, as shown in FIG. 5, the light L5 to be deflected in the front direction by reflection at the second prism surface 72 inclined angle is theta _t inside the light guide plate 30, the inclination angle of the second prism surface 72 The light travels in the direction inclined with respect to the normal direction nd of the light guide plate 30 by an angle φ (θ _t ) corresponding to θ _t and travels toward the light exit surface 31. That is, as shown in FIG. 5, the light L5 reflected by the inclined surface 37 of the light guide plate 30 from the light guide plate 30 to be emitted, the light guiding direction by a distance D _t advances. This distance D _t is expressed as follows using the thickness d of the light guide plate 30 and the angle φ (θ _t ).
D _t = d × tan φ (θ _t )
The gap between the optical sheet 60 and the light guide plate 30 and the height of the unit prism 70 are negligibly small with respect to the thickness d of the light guide plate 30. Therefore, the bright portion Ax which can be observed from the front direction on the light exit surface of the optical sheet 60, at the same pitch of the inclined surface 37 of the light guide plate 30, deviates only from the inclined surface 37 a distance D _t in the light guiding direction other side position Become visible.

On the other hand, in the present embodiment, the second prism surface 72 includes a plurality of element surfaces 73 having different inclination angles θ _t , more specifically, a first element surface 73a having an inclination angle θ ₁ and an inclination angle of θ _{1. 2} and the second element surface 73b. As shown in FIG. 6, the traveling direction angle φ (θ ₁ ) in the light guide plate 30 for the light L 61 reflected by the first element surface 73 a of the second prism surface 72 and directed in the condensing direction (ie, the front direction). ) Is different from the traveling direction angle φ (θ ₂ ) in the light guide plate 30 for the light L62 reflected by the second element surface 73b and directed in the condensing direction. That is, L61 which is reflected by a certain inclined surface 37 and then directed in the condensing direction (front direction) by reflection on the first element surface 73a, and second element surface 73b after being reflected by the same inclined surface 37. light L62 directed to the condensing direction (front direction) by reflection, the distance in the light output Menjo optical sheet 60 | emitted from the area which is deviated by the light guide direction _| D 1 _-D 2. Then, by adjusting the distance | D ₁ -D ₂ |, the light and dark pattern along the light guide direction on the light exit surface of the optical sheet 60 can be blurred. Specifically, as shown in FIG. 6, the bright portion Aa caused by the light L61 reflected by the first element surface 73a of the second prism surface 72 and directed in the condensing direction (that is, the front direction), and the second Bright portions Ab caused by light L62 reflected by the second element surface 73b of the prism surface 72 and directed in the condensing direction (that is, the front direction) are alternately arranged in the light guide direction on the light exit surface of the optical sheet 60. As a result, the dark area on the light exit surface of the optical sheet 60 can be reduced, and further, the dark area can be eliminated. As a result, moire when the surface light source device 20 is combined with other members can be effectively made inconspicuous.

As a specific method, the distance | D ₁ -D ₂ | is about a half cycle of the arrangement pitch p of the inclined surfaces 37, specifically, from 0.25 cycle to 0.75 cycle, more preferably from 0.324 cycle. If it is shifted by 0.676 cycles, it is possible to effectively blur the light / dark pattern along the light guide direction on the light exit surface of the optical sheet 60. That is, when expressed by the formula, it is preferable to satisfy the following condition (a1), and more preferably to satisfy the following condition (a2). Condition (a1): (k + 0.25) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.75) × p
Condition (a2): (k + 0.324) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.676) × p
Under these conditions, k is 0 or a natural number. Further, “d × | tan φ (θ ₁ ) −tan φ (θ ₂ ) |” corresponds to the distance | D ₁ -D ₂ |.

Here, φ (θ ₁ ) and φ (θ ₂ ) can be specified by setting θ _t to θ ₁ or θ _{2 in} the following equations (b1) and (b2), respectively.
φ (θ _t ) = sin ⁻¹ ((sin (θ ₃ + ψ (θ _t ))) / n ₁ ) Equation (b1)
ψ (θ _t ) = sin ⁻¹ (n ₂ × sin (180 ° −2 × θ _t −θ ₃ )) Equation (b2)
Note that φ (θ _t ) is an angle representing the traveling direction in the light guide plate 30 of the light that is reflected in the front direction by the second prism surface 72 whose inclination angle is θ _t. Specifically, the traveling direction of these lights in the light guide plate 30 corresponds to an angle formed with respect to the normal direction of the light guide plate 30.

Here, the derivation of φ (θ _t ) expressed by the equations (b1) and (b2) will be described with reference to FIGS. As shown in FIG. 7, the following description is an example in which the second prism surface 72 is focused in the front direction by reflection on the second element surface, that is, “θ _t = θ ₂ ” is satisfied. The same applies to the case of “θ _t = θ ₁ ”.

First, the incident angle ψ (θ _t ) of the light incident on the first prism surface 71 of the optical sheet 60 expressed by the formula (b2) is derived. As shown in FIG. 7, the incident angle to the unit prism 70 is 180 ° − when geometrically considered as shown in FIG. 7 because the light L <b> 7 is totally reflected by the second prism surface 72. 2 × θ _t −θ ₃ When the refractive index of the unit prism 70 is n ₂ and the refractive index of air is 1, from Snell's law on the first prism surface 71,
sinψ (θ _t ) = n ₂ × sin (180 ° −2 × θ _t −θ ₃ )
It becomes. Therefore,
ψ (θ _t ) = sin ⁻¹ (n ₂ × sin (180 ° −2 × θ _t −θ ₃ ))
Thus, equation (b2) is derived.

Next, the incident angle φ (θ _t ) of the light emitted from the light exit surface 31 of the light guide plate 30 to the output surface 31 is derived using ψ (θ _t ) represented by the equation (b2). As shown in FIG. 8, the light L8 traveling inside the light guide plate 30 enters the light exit surface 31 at an incident angle φ (θ _t ). The light exit angle from the light exit surface 31 at this time is that the light L8 after exiting from the exit surface 31 enters the unit prism 70 of the optical sheet 60 at an incident angle ψ (θ _t ). It becomes “θ ₃ + ψ (θ _t )”. When the refractive index of the light guide plate 30 is n ₁ and the refractive index of air is ₁ , from Snell's law on the light exit surface 31,
n ₁ × sinφ (θ _t ) = sin (θ ₃ + ψ (θ _t ))
It becomes. Therefore,
φ (θ _t ) = sin ⁻¹ ((sin (θ ₃ + ψ (θ _t ))) / n ₁ )
Thus, the formula (b1) is derived.

As described above, the surface light source device 20 according to the present embodiment includes the light exit surface 31, the back surface 32 disposed to face the light exit surface 31, and the side surface located between the light exit surface 31 and the back surface 32. The light guide plate 30, the light source plate 30 facing the light incident surface 33, and the light exit surface of the light guide plate 30. an optical sheet 60 disposed to face the 31, includes a rear surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 37 arranged in the first direction d _1, the inclined surface is a first direction d ₁ , the optical sheet 60 is inclined with respect to the normal direction of the light guide plate 30 and the first direction d ₁ so as to approach the light exit surface 31 from one side to the other side. It is arranged in the first direction d ₁ to the light guide plate 30 side of the main body portion 65 and each of the Wherein the first direction d ₁ and a plurality of unit prisms 70 extending linearly in a direction intersecting, and each unit prism has a first prism surface 71 facing the first one side of the direction d _1, the first direction a second prism surface 72 facing the other side of d ₁ , and the second prism surface 72 is a main cut surface of the optical sheet 60 parallel to both the first direction d ₁ and the normal direction of the main body 65. comprises a first elementary surface 73a and the second element surface 73b inclined angle with respect to the first direction d ₁ are different from each other in, forms with respect to the first element face 73a is a first direction d ₁ of the main cutting surface of the optical sheet 60 An angle θ ₁ [°] less than 180 °, an angle θ ₂ [°] less than 180 ° formed by the second element surface 73b on the main cutting surface of the optical sheet 60 with respect to the first direction d ₁ , main cross the first prism surface 71 at forms 180 with respect to the first direction _{d 1} Less than the angle θ ₃ [°], the pitch p (mm) along the first direction d ₁ of the inclined surface 37 on the back surface 32 of the light guide plate 30, the light guide plate 30 thickness d [mm], of the light guide plate 30 With respect to the refractive index n ₁ and the refractive index n ₂ of the unit prism 70, the following formula is satisfied, where k is 0 or a natural number.
(k + 0.25) × p <d × | tanφ (θ ₁ ) -tanφ (θ ₂ ) | <(k + 0.75) × p
θ _t is θ ₁ or θ ₂ and
φ (θ _t ) = sin ^-1 ((sin (θ ₃ + ψ (θ _t ))) / n ₁ )
ψ (θ _t ) = sin ^-1 (n ₂ × sin (180 ° -2 × θ _t -θ ₃ ))
According to such a surface light source device 20, it is possible to blur a bright and dark pattern that can occur on the light emitting surface 21 of the surface light source device 20 due to the configuration of the light guide plate 30 and the optical sheet 60. Therefore, when this surface light source device 20 is combined with another member having a periodic structure, for example, the liquid crystal display panel 15 having a regular pixel arrangement, the moire is effectively inconspicuous. Can do.

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

  First, in the above-described embodiment, an example of the unit prism 70 of the optical sheet 60 has been described. However, the present invention is not limited to this example, and various modifications can be made. For example, the plurality of unit prisms 70 may have different configurations. Moreover, although the 2nd prism surface 72 showed the example containing two element surfaces 73, it is not restricted to this, The 2nd prism surface 72 may contain the 3 or more element surfaces 73. Furthermore, the cross-sectional shape of the main cutting surface of the unit prism 70 is not limited to the specific example shown in FIG. 4 and the like, and may be, for example, a pentagonal shape or a hexagonal shape.

Further, as shown in FIG. 9, the unit optical element 50 may be provided on the light exit surface 32 side of the light guide plate 30. As is well shown in FIG. 9, the plurality of unit optical elements 50 are arranged in an arrangement direction that intersects the first direction d ₁ and is parallel to the surface 41 on one side of the base 40. Arranged on the side surface 41. Each unit optical element 50 extends linearly on the surface 41 on one side of the base 40 in a direction intersecting with the arrangement direction.

In particular, in the present modification, as shown in FIG. 9, the plurality of unit optical elements 50 are arranged on a surface 41 on one side of the base 40 in a second direction (array direction) d ₂ orthogonal to the first direction d _1. They are arranged side by side without any gaps. Therefore, the light exit surface 31 of the light guide plate 30 is configured as inclined surfaces 35 and 36 formed by the surface of the unit optical element 50. Each unit optical element 50 extends linearly along a first direction d ₁ orthogonal to the arrangement direction. Further, each unit optical element 50 is formed in a column shape and has the same cross-sectional shape along the longitudinal direction thereof. In the present embodiment, the plurality of unit optical elements 50 are configured identically. As a result, the light guide plate 30 in the present embodiment, at each position along the first direction d _1, which is to have a constant cross-sectional shape.

The unit in the optical arrangement direction (second direction) of the element d ₂ and a cross section parallel to both the normal direction nd of the one side 41 of the base portion 40 (a plate surface of the light guide plate 30) (below 10, The cross-sectional shape of each unit optical element 50 at (simply referred to as the main cut surface of the light guide plate) is shown. As shown in FIG. 10, in the illustrated example, the cross-sectional shape of each unit optical element 50 on the main cut surface of the light guide plate is a shape that tapers toward the light output side. That is, in the main cut surface of the light guide plate, the width of the unit optical element 50 parallel to the plate surface of the light guide plate 30 decreases as the distance from the base 40 increases along the normal direction nd of the light guide plate 30.

In the example shown in FIG. 10, the outer contour (corresponding to the light emitting side surface 31) 51 on the main cutting surface of the unit optical element 50 is the light emitting surface whose angle is the angle formed by the outer contour with respect to the one side surface 41 of the base 40. angle theta _a is greater toward the base portion 40 to the farthest unit optical from the tip portion 52a of the outer contour 51 of the element 50 on the outer contour 51 of the unit optical elements 50 closest to the base portion 40 of the base end portion 52b It has changed.

Here, the light exit surface angle θ _a is an angle formed by the light exit side surface (outer contour) 51 of the unit optical element 50 with respect to the one side surface 41 of the base 40 in the main cut surface of the light guide plate as described above. It is. As in the example shown in FIG. 10, when the outer contour (light-emitting side surface) 51 in the main cut surface of the unit optical element 50 is formed in a polygonal line, each linear part constituting the polygonal line and one side of the base 40 (strictly, the smaller the angle of the ones of the two angles formed (angle of minor angle)) the angle formed between the 41 becomes the light exit surface an angle theta _a. On the other hand, when the outer contour (light-emitting side surface) 51 on the main cutting surface of the unit optical element 50 is configured by a curved surface, an angle formed between the tangent to the outer contour and one side surface 41 of the base 40 ( strictly speaking, the smaller the angle of the ones of the two angles formed (angle of minor angle)), and be identified as the light exit surface an angle theta _a.

  The unit optical element 50 as one specific example shown in FIG. 10 has one side located on one side surface 41 of the base 40 on the main cut surface of the light guide plate 30 and the tip 52a on the outer contour 51 and each base. It is a pentagonal shape in which two sides are located between the end 52b or a shape formed by chamfering one or more corners of this pentagonal shape. In the example shown in the drawing, the cross-sectional shape of the main cutting surface of the unit optical element 50 is symmetric with respect to the front direction nd. That is, as well shown in FIG. 6, the light exit side surface 51 of each unit optical element 50 is configured by a pair of bent surfaces 35 and 36 that are configured symmetrically about the front direction. The pair of bent surfaces 35 and 36 are connected to each other to define a tip portion 52a. Each folding surface 35, 36 has a first surface 35a, 36a that defines a tip 52a, and a second surface 35b, 36b that connects to the first surface 35a, 36a from the base 40 side. . The pair of first inclined surfaces 35a and 36a have a symmetric configuration with respect to the front direction nd, and the pair of second inclined surfaces 35b and 36b also have a symmetric configuration with the front direction nd as the center.

  As a general configuration of the unit optical element 50, the front surface from the base 40 of the unit optical element 50 on the main cutting surface of the light guide plate 30 with respect to the width Wa in the arrangement direction of the unit optical elements 50 on the main cutting surface of the light guide plate 30. It is preferable that the ratio (Ha / Wa) of the protrusion height Ha along the direction is 0.3 or more and 0.45 or less. According to such a unit optical element 50, an excellent light condensing function is exhibited with respect to light components along the arrangement direction (second direction) of the unit optical elements 50 due to refraction and reflection at the light exit side surface 51. And generation of side lobes can be effectively suppressed.

  In addition, the dimension of the light-guide plate 30 shown by FIG.9 and FIG.10 can be set as follows as an example. First, as a specific example of the unit optical element 50, the width Wa (see FIG. 10) can be set to 10 μm or more and 500 μm or less. On the other hand, the thickness of the base 40 can be 0.2 mm to 6 mm.

  Further, in the example shown in FIGS. 9 and 10, the example in which the unit optical element 50 is formed as a convex portion protruding from the base 40 is not limited to this example, and is formed as a concave concave portion. It may be.

  Although several modifications to the above-described embodiment have been described above, it is needless to say that a plurality of modifications can be combined as appropriate.

Industrial application fields

The surface light source device 20 or the display device 10 described above can be applied to the following uses as an example.
-Application of automatic teller machine (ATM) to display device and surface light source device of display device During operation of ATM, peeping from the side can be prevented.
・ Application to in-vehicle display device By controlling the direction of image light emission, it is possible to brighten the image for viewers such as drivers while preventing the image from being reflected on the windshield etc. .
・ Application to digital signage Optics suitable for the location of digital signage (also called electronic signage, electronic billboards, electronic bulletin boards, etc.) and the position of viewers by changing the direction of the unit prism of the optical sheet Characteristics can be obtained. Such suitable optical characteristics include, for example, the distribution of the estimated viewers by matching the luminance peak direction of the emitted light with the direction toward the viewer assumed from the display surface of the digital signage, and assuming the angular distribution of luminance. For example, the range may be included.
-Application to a display device in a train car Since the viewer observes the display device from below, it is preferable to display an image toward the viewer (downward from the installation position). In addition, when applied to the position of a hanging advertisement, the train is long and narrow, and it is not necessary to widen the viewing angle in the horizontal direction. Therefore, an image can be efficiently displayed for the viewer.
-Application to a display device such as a security room Each of a large number of display devices can have a light emission characteristic that matches the viewer (guard) located in the center.
-Application to table display The viewer is always located at the same relative position to the desk with built-in display. Therefore, it is possible to set the light output characteristics according to the position of the viewer.
-Application to amusement facilities For example, display devices of game machines installed at game centers, etc. When the positional relationship between the installation position and the user is usually constant, a specific user (observer) from the display surface It is possible to achieve an optical characteristic that matches the direction of the luminance peak of the emitted light in the direction toward.
-Application to lighting Light emission characteristics can be set as appropriate according to the usage of lighting, the installation position of lighting, such as indirect lighting and desk light.
・ Automatic ticket gate display device and application of the display device to a surface light source device Since the position of the line of sight of the ticket gate passer is limited, the light emission that matches the luminance peak direction of the emitted light to that position (or the direction of the line of sight) It is desirable to have characteristics.
-Application to a display device for a wristwatch It is necessary to twist an arm in order to view it from the front, and it is often observed from an oblique downward direction of the wristwatch. Therefore, the luminance peak direction of the emitted light and the luminance angle distribution are set so as to include a range in a direction connecting the position of the wristwatch and the position of the eyes of the observer that are normally used. Moreover, since it is often observed under sunlight, it is desirable to have high luminance.
Other examples include display devices behind the seats of airplanes, display devices used to explain safety equipment such as airplanes, display devices near the ceiling such as sightseeing buses, display devices for operation guidance such as airports and stations, The present invention can also be applied to at least one display device of a game machine having a plurality of screens (for example, a screen in a horizontal plane and a screen in a vertical plane), a liquid crystal operation panel (such as a keyboard), and the like.

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Display surface 12 Liquid crystal layer 13 Upper polarizing plate 14 Lower polarizing plate 15 Liquid crystal display panel 20 Surface light source device 21 Light emission surface 24 Light source 25 Light emitter 28 Reflective sheet 30 Light guide plate 31 Light emission surface 32 Back surface 33 Light incident 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 connecting surface 40 base 41 one side 42 other side 50 unit optical element 51 outer contour 52a tip 52b Base end portion 60 Optical sheet 61 Light exit surface 65 Main body portion 70 Unit prism 71 First prism surface 72 Second prism surface 73 Element surface 73a First element surface 73b Second element surface 75a Tip portion 75b Base end portion

Claims (6)

A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, and a portion located on one side in the first direction of the side surfaces. A light guide plate forming a light incident surface;
A light source disposed facing the light incident surface;
An optical sheet disposed to face the light exit surface of the light guide plate,
The back surface of the light guide plate includes a plurality of inclined surfaces arranged in the first direction,
Each inclined surface is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction,
The optical sheet includes a sheet-like main body, and a plurality of unit prisms arranged in the first direction on the light guide plate side of the main body and extending linearly in a direction intersecting the first direction. And including
Each unit prism includes a first prism surface facing one side of the first direction, and a second prism surface facing the other side of the first direction,
The second prism surface includes a first element surface and a second element having different inclination angles with respect to the first direction in the main cutting surface of the optical sheet parallel to both the first direction and the normal direction of the main body. Including the face,
An angle θ ₁ [°] of less than 180 ° formed by the first element surface at the main cutting surface of the optical sheet with respect to the first direction, and the second element surface at the main cutting surface of the optical sheet is the An angle θ ₂ [°] of less than 180 ° made with respect to the first direction, and an angle θ ₃ [° of less than 180 ° made by the first prism surface with respect to the first direction of the main cutting surface of the optical sheet. ] Is a pitch p [mm] along the first direction of the inclined surface on the back surface of the light guide plate, a thickness d [mm] of the light guide plate, a refractive index n _{1 of} the light guide plate, and the unit prism. A surface light source device that satisfies the following expression with respect to the refractive index n ₂ of k, where k is 0 or a natural number.
(K + 0.25) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.75) × p
θ _t is θ ₁ or θ ₂ and
φ (θ _t ) = sin ⁻¹ ((sin (θ ₃ + ψ (θ _t ))) / n ₁ )
ψ (θ _t ) = sin ⁻¹ (n ₂ × sin (180 ° −2 × θ _t −θ ₃ )) The surface light source device according to claim 1, wherein the following expression is satisfied.
(K + 0.324) × p <d × | tanφ (θ ₁ ) −tanφ (θ ₂ ) | <(k + 0.676) × p The angle θ ₁ is smaller than the angle θ ₂ ,
The surface light source device according to claim 1, wherein the second element surface is located on a side of the first element surface that is close to the main body. The second prism surface further includes a third element surface;
An angle θ ₃ [°] of less than 180 ° formed by the third element surface at the main cutting surface of the optical sheet with respect to the first direction is different from the angle θ ₁ [°] and the angle θ ₂ [ The surface light source device according to any one of claims 1 to 3, which is different from [°].   The surface light source device according to claim 4, wherein the third element surface is located between the first element surface and the second element surface. A surface light source device according to any one of claims 1 to 5,
A display panel disposed to face the surface light source device.

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