JP2011215548A - Lens sheet, surface light source unit and display device - Google Patents

Abstract

A lens sheet capable of making an image of a light emitting portion inconspicuous is provided.
A lens sheet includes a main body portion and a plurality of unit lenses on the main body portion. In the main cut surface, the lens surface angle θa1 formed by the outer contour 35a of the unit lens with respect to the sheet surface increases from the top 35b1 toward the end 35b2. The lens surface angle α (°) at the reference point SP on the outer contour intersecting with the straight line SL that contacts the adjacent unit lens that forms an angle of 80 ° with respect to the normal direction, and the reference point SP and the end are connected. The angle β (°) formed by the reference line segment with respect to the reference tangent at the reference point and the lens surface angle γ (°) at the end have a predetermined relationship.
[Selection] Figure 3

Description

  The present invention relates to a lens sheet, a surface light source device, and a display device that can make in-plane variations in luminance uniform and make an image of a light emitting unit that forms a light source inconspicuous.

  A direct type surface light source device used in a transmissive display device includes a light source and a plurality of light control sheets for changing the traveling direction of light from the light source. As a light source, a light source formed by arranging a plurality of light emitting units in parallel is widely used. Among the plurality of light control sheets, generally, a light diffusion sheet that diffuses light from a light source and hides the image of the light emitting part (makes it inconspicuous), and narrows the light traveling direction to the front direction, and the front direction And a light collecting sheet for improving luminance.

  As the condensing sheet, an optical sheet formed by arranging unit-shaped elements (unit optical elements) extending linearly in a direction orthogonal to the longitudinal direction (so-called linear array) is widely used (for example, Patent Document 1). ). In particular, as a unit shape element that is generally used, there is known a unit lens whose shape in a cross section perpendicular to the longitudinal direction thereof is a circular part or an elliptic part.

  On the other hand, a diffuser plate (milky white plate) in which a light diffusing agent is dispersed has been frequently used as a light diffusion sheet for uniformizing luminance unevenness due to the configuration of the light source. However, if an image of the light emitting part that forms the light source is erased using a diffusion plate containing a light diffusing agent, it is necessary to disperse the light diffusing agent in a large amount, and in this case, the utilization efficiency of the light source light is reduced. Another problem will occur.

  For this reason, for example, as disclosed in Patent Document 2, a diffusion sheet having a main body portion and a plurality of convex lenses having the same shape arranged on the main body portion has also been proposed. In the diffusion sheet disclosed in Patent Document 2, the convex lens has a shape formed of a part of an elliptic cylinder. This convex lens totally reflects the direct incident light from the light emitting part a plurality of times in the region immediately above the light emitting part of the light source and returns it to the light source side. Thereby, it is prevented that the brightness | luminance in the front direction in the area | region right above a light emission part becomes high too much. On the other hand, in a region facing an intermediate point between two adjacent light emitting units, the traveling direction of the directly incident light from the inclined light source is changed so that the angle with respect to the front direction becomes small, and the light is changed. Make it transparent.

WO2007 / 094426A1 JP2006-65277A

  However, in the surface light source device using the diffusion sheet disclosed in Patent Document 2, the in-plane luminance distribution from the front direction can be made uniform to some extent, but the in-plane luminance measured from the oblique direction can be obtained. The distribution may not be sufficiently uniform. That is, in the observation from the front direction, the image of the light emitting unit that makes up the light source can be made somewhat inconspicuous, but when observed from an oblique direction, unevenness of light and darkness corresponding to the configuration of the light emitting unit occurs. May be observed.

  The present invention has been made in consideration of such points, and the in-plane variation of the luminance is sufficiently uniformed so that the image of the light emitting portion is conspicuous not only in the front direction but also in the inclined direction. It is an object of the present invention to provide a lens sheet, a surface light source device, and a display device that can be eliminated.

The lens sheet according to the present invention is:
A lens sheet used in a surface light source device having a plurality of light sources and arranged facing the light source,
A sheet-like body,
A plurality of unit lenses provided on the light exit side of the main body,
In the main cutting plane that passes through the normal direction of the main body part and each apex most distant from the main body part of two adjacent unit lenses, the tangent to the outer contour of the unit lens is the sheet surface of the main body part The contact angle of the tangent line to the unit lens is on the outer contour of the unit lens closest to the main body from the top side on the outer contour of the unit lens. Towards the end side,
In the main cut surface, a straight line that forms an angle of 80 ° with respect to the normal direction of the main body portion and touches the outer contour of one of the two unit lenses is one of the two unit lenses. Two points on the outer contour of the other unit lens, with a point first intersecting with the other unit lens as a reference point, a tangent to the outer contour of the other unit lens at the reference point as a reference tangent When the line segment connecting the end portion on the side away from the one unit lens and the reference point is a reference line segment, the lens surface angle α (°) of the reference tangent line and the reference line An angle β (°) formed by the minute with respect to the reference tangent, and a lens surface angle γ (°) of a tangent that is in contact with an outer contour of the other unit lens at an end portion on a side away from the one unit lens, Refractive index of the material forming the unit lens DOO satisfies the following two formulas (A) and (B).
Arccos (n × cosβ) ≦ α + 10 Formula (A)
sinγ ≤ 1 / n ... Formula (B)

The lens sheet according to the present invention comprises a base material and a diffusion component dispersed in the base material,
In the main cut surface, the maximum length of a perpendicular line drawn from the portion delimited by the reference line segment in the outer contour of the other unit lens is defined as d, and is defined by the unit lens. A portion obtained by dividing a volume ratio of the diffusing component in the lens surface layer portion by an average radius of the diffusing component contained in the lens surface layer portion is a lens surface layer portion where the distance from the lens surface is d or less. Less than the value obtained by dividing the volume ratio of the diffusing component in the portion other than the lens surface layer portion of the lens sheet by the average radius of the diffusing component included in the portion other than the lens surface layer portion of the lens sheet. Alternatively, a diffusion component may not be included in the lens surface layer portion.

Alternatively, the lens sheet according to the present invention includes a base material and a diffusion component dispersed in the base material,
In the main cut surface, the maximum length of a perpendicular line drawn from the portion delimited by the reference line segment in the outer contour of the other unit lens is defined as d, and is defined by the unit lens. A portion obtained by dividing a volume ratio of the diffusing component in the lens surface layer portion by an average radius of the diffusing component contained in the lens surface layer portion is a lens surface layer portion where the distance from the lens surface is d or less. The volume ratio of the diffusion component in the portion other than the lens surface layer portion of the lens sheet is equal to or less than the value obtained by dividing the volume ratio of the diffusion component contained in the portion other than the lens surface layer portion of the lens sheet. May be.

  In the lens sheet according to the present invention, the plurality of unit lenses may be arranged in a certain arrangement direction on the main body, and each unit lens may extend in a direction intersecting the arrangement direction.

  Furthermore, in the lens sheet according to the present invention, in the main cut surface, the outer contour of the unit lens may be configured as a line that can be approximated by one or a combination of an arc, an elliptic arc, and a straight line. Good.

  A surface light source device according to the present invention includes a light source and a lens sheet that is one of the lens sheets according to the present invention described above and is disposed to face the light source.

The surface light source device according to the present invention further comprises an optical sheet disposed on the light output side of the lens sheet,
The plurality of unit lenses of the lens sheet are arranged in a certain arrangement direction on the main body, and each unit lens extends in a direction intersecting the arrangement direction,
The optical sheet has a sheet-like base, and a plurality of unit-shaped elements arranged on the light exit side surface of the base, each extending linearly in a direction intersecting the arrangement direction,
The lens sheet and the optical sheet may be arranged so that the arrangement direction of the unit lenses of the lens sheet is parallel to the arrangement direction of the unit shape elements of the optical sheet.

  Further, in the lens sheet according to the present invention, the normal of the base of the optical sheet is within the main cutting plane of the optical sheet parallel to both the normal direction of the base of the optical sheet and the arrangement direction of the unit shape elements. When a parallel light beam traveling in a direction inclined by 80 ° with respect to the direction is incident on the light incident surface of the optical sheet, the luminance of the light exit surface of the optical sheet measured at the main cut surface of the optical sheet is measured. In the angular distribution, the peak luminance may appear in a range of 45 ° or less from the front direction, and the width of the angular region in which half the peak luminance is ensured may be 15 ° or less.

Furthermore, in the lens sheet according to the present invention,
In the main cutting surface of the optical sheet parallel to both the normal direction of the base portion of the optical sheet and the arrangement direction of the unit shape elements, the light exit surface of the unit shape element is the normal line of the base portion of the optical sheet. Symmetric about the direction,
In the main cut surface of the optical sheet, the light exit surface angle formed by the outer contour of the unit shape element with respect to the sheet surface of the base, or the tangent to the outer contour of the unit shape element with respect to the sheet surface of the base The angle of the light exit surface formed from the top of the unit shape element that is the farthest from the base on the light exit surface is increased or constant from the side of the end of the unit shape element on the light exit surface. Yes,
A distance h along the normal direction of the main body portion of the lens sheet from the lens sheet to the light emitting portion of the light source at the main cutting surface of the lens sheet;
In the main cut surface of the lens sheet, a distance k along the arrangement direction of the unit lenses between two adjacent light emitting portions, and
The refractive index n of the material forming the lens sheet;
The lens surface angle γ at the end of the unit lens;
A refractive index n2 of the material forming the optical sheet;
The light exit surface angle θe at the end of the unit shape element may satisfy the following expressions (C) to (F).
-10 ° ≦ (θe)-Arcsin ((n2) × sin ((θe)-(θia2))) ≦ 10 ° ・ ・ ・ Formula (C)
(θia2) = Arcsin ((1 / (n2)) × (sin (θi2))) (Equation (D)
(θi2) = γ- Arcsin (n × sin (γ- (θia1))) ・ ・ ・ Equation (E)
(θia1) = Arcsin ((1 / n) × (sin (Arctan (k / 2 / h)))) ・ ・ ・ Formula (F)

  Furthermore, the surface light source device according to the present invention further includes a second optical sheet disposed on the light output side of the optical sheet, and the haze value of the second optical sheet is 10 or more and 90 or less. Also good.

  Furthermore, the surface light source device according to the present invention may further include a polarization separation sheet disposed on the light output side of the optical sheet.

  Furthermore, in the surface light source device according to the present invention, the light source has a plurality of light emitting units arranged in a direction parallel to the arrangement direction of the unit lenses of the lens sheet, and each light emitting unit intersects the arrangement direction. You may extend in the direction to do.

  A display device according to the present invention includes any one of the above-described surface light source devices according to the present invention and a transmissive display unit disposed to face the surface light source device.

  According to the present invention, the in-plane variation in luminance can be sufficiently uniformed so that the image of the light emitting portion that makes up the light source is inconspicuous not only from the front direction but also from an inclined direction.

FIG. 1 is a perspective view showing 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 perspective view showing a lens sheet incorporated in the surface light source device of FIG. FIG. 3 is a cross-sectional view showing the lens sheet in a cross section taken along line III-III in FIG. 2. FIG. 4 is a cross-sectional view showing the surface light source device in a cross section taken along the line IV-IV in FIG. 1, and is a view for explaining the operation of the surface light source device. FIG. 5 is a diagram for explaining the operation of the surface light source device in the same cross section as FIG. 4. FIG. 6 is a view for explaining a modification of the lens sheet in the same cross section as FIG. FIG. 7 is a view for explaining another modified example of the lens sheet in the same cross section as FIG. 3. FIG. 8 is a diagram corresponding to FIG. 5 for explaining a modification of the optical sheet. FIG. 9 is a diagram corresponding to FIG. 1 and is a diagram for explaining a modification of the surface light source device and the display device. FIG. 10 is a diagram corresponding to FIG. 1 and is a diagram for explaining another modification of the surface light source device and the display device. FIG. 11 is a graph showing the angular distribution of luminance measured on the exit surface of the optical sheet when a parallel light beam with an incident angle of 80 ° is incident on the entrance surface of a commercially available optical sheet.

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

  1 to 5 are diagrams for explaining an embodiment according to the present invention. Among these, FIG. 1 is a perspective view showing a schematic configuration of the display device and the surface light source device. FIG. 2 is a perspective view of the lens sheet, and FIG. 3 is a cross-sectional view of the main cut surface of the lens sheet. 4 and 5 are diagrams showing the surface light source device in a cross section passing through the main cutting surface of the lens sheet, and are diagrams for explaining the operation of the surface light source device.

  The display device 10 illustrated in FIG. 1 includes a transmissive display unit 15 and a surface light source device 20 that is disposed on the back side of the transmissive display unit 15 and illuminates the transmissive display unit 15 in a planar shape from the back side. ing. The transmissive display unit 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel and forms an image.

  In the present embodiment, the transmissive display unit 15 includes a liquid crystal display panel. That is, the transmissive display device 10 functions as a liquid crystal display device. The liquid crystal display panel (transmissive display unit) 15 has a pair of polarizing plates 16 and 17 and a liquid crystal layer 18 disposed between the pair of polarizing plates. The polarizing plates 16 and 17 have a function of decomposing incident light into two orthogonal polarization components, transmitting the polarization component in one direction, and absorbing the polarization component in the other direction orthogonal to the one direction. is doing.

  An electric field can be applied to the liquid crystal layer 18 for each region where one pixel is formed. Then, the orientation of the liquid crystal layer 18 applied with an electric field changes. The polarized light in a specific direction transmitted through the lower polarizing plate 16 disposed on the light incident side rotates the polarization direction by 90 ° when passing through the liquid crystal layer 18 to which an electric field is applied. Maintains its polarization direction as it passes. For this reason, depending on whether or not an electric field is applied to the liquid crystal layer 18, polarized light in a specific direction transmitted through the lower polarizing plate 16 is further transmitted through the upper polarizing plate 17 disposed on the light output side of the lower polarizing plate 16, or Whether the light is absorbed and blocked by the upper polarizing plate 17 can be controlled.

  In this way, the liquid crystal panel (transmission type display unit) 15 can control transmission or blocking of light from the surface light source device 20 for each pixel. The configuration of the liquid crystal panel (liquid crystal cell) can be configured in the same manner as a device (member) incorporated in a conventional liquid crystal display device, and detailed description thereof is omitted here.

  By the way, in this specification, the “light exit side” means the downstream side (observer side, FIG. 2 to FIG. 2) in the traveling direction of light from the light source 25 to the observer through the transmissive display unit 15 without turning back the traveling direction. In FIG. 5, the upper side of the paper surface is the “incident side”, and the upstream side in the traveling direction of light traveling from the light source 25 to the observer through the transmissive display unit 15 without being folded back. That is.

  In addition, terms used in this specification for specifying shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, and “symmetric” are not limited to strict meanings, Interpretation will be made including errors to the extent that an expected function can be expected.

  Next, the surface light source device 20 will be described. The surface light source device 20 is configured as a direct type backlight unit. For this reason, as shown in FIG. 1, the surface light source device 20 includes a light source 25 and a plurality of light control sheets arranged to face the light source 25. The light control sheet includes a lens sheet 30 disposed at a position facing the light source 25, an optical sheet 40 disposed on the light output side of the lens sheet 30, and a second optical sheet disposed on the light output side of the optical sheet 40. And a polarized light separating sheet 50 as the above. Here, “facing” means that the lens sheet 30 is disposed closest to the light source among the plurality of light control sheets.

  The light source 25 has a plurality of linear light emitting portions 25a. The plurality of light emitting units 25a are regularly arranged on a certain virtual plane. Specifically, the plurality of light emitting units 25a are arranged in one arrangement direction on the virtual plane, and each light emitting unit 25a extends in a direction on the virtual plane intersecting the arrangement direction. In the illustrated example, the plurality of light emitting units 25a are configured by cold cathode tubes arranged in parallel, and are arranged so as to extend in the horizontal direction, for example.

  A plurality of light emitting portions 25 a constituting the light source 25 are covered from the back side by the reflection plate 22. The reflection plate 22 is formed in a box shape having an opening (window) on the lens sheet 30 side. As shown in FIG. 1, the reflection plate 22 is a member for directing light from the light source 25 toward the transmissive display unit 15. At least the inner surface of the reflecting plate 22 is made of a material having a high reflectance such as metal.

  Next, the lens sheet 30 will be described. As shown in FIG. 1, the lens sheet 30 is arranged to face the light emitting unit 25a of the light source 25 so that the sheet surface thereof is parallel to a virtual plane on which the light emitting units 25a forming the light source 25 are arranged. ing. As will be described in detail later, the lens sheet 30 exerts a different optical action on the linearly incident light from the light emitting unit 25a of the light source 25 depending on the distance from each light emitting unit 25a. It mainly has the function of making the image inconspicuous (light diffusion function).

  In the present specification, the terms “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 (film surface, plate surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed globally and globally. Refers to the surface. In the present embodiment, the sheet surface of the lens sheet 30, the sheet surface of the main body 32 described later of the lens sheet 30, the sheet surface of the optical sheet 40, the sheet surface of the polarization separation sheet (second optical sheet) 50, The light emitting surface 20a of the surface light source device 20 and the display surface 10a of the transmissive display device 10 are parallel to each other.

  Further, in this specification, the “front direction” is a normal direction nd (see, for example, FIG. 3) with respect to the light emitting surface 20a of the surface light source device 20, and the normal direction nd to the sheet surface of the lens sheet 30 is optical. It also coincides with the normal direction nd to the sheet surface of the sheet 40, the normal direction nd of the display surface 10a of the display device 10, and the like.

  Further, in this specification, the term “lens” refers to a so-called narrow-sense lens composed of a curved surface such as a spherical surface, a so-called narrow-sense prism composed of a plane, and an optical element composed of a curved surface and a plane. It is used in a broad sense that includes

  As shown in FIG. 2, the lens sheet 30 includes a main body portion 32 and a plurality of unit lenses (unit optical elements, unit shape elements) 35 provided on the main body portion 32. As shown in FIGS. 2 and 3, the main body 32 is formed as a sheet-like member having a light exiting side surface 32 a and a light incident side surface 32 b facing each other. The main body 32 functions as a sheet-like member that supports the unit lens 35.

  As shown in FIGS. 2 and 3, in the present embodiment, unit lenses 35 are arranged side by side on the light output side surface 32 a of the main body portion 32 without leaving a gap. As a result, the light exit surface 30 a of the lens sheet 30 is constituted only by the light exit surface (lens surface) 35 a of the unit lens 35. On the other hand, as shown in FIG. 3, in the present embodiment, the light incident side surface 32b of the main body 32 constitutes a light incident surface 30b of the lens sheet 30 as a flat (flat) surface.

  Next, the unit lens 35 will be described in detail. As shown in FIG. 1, a large number of unit lenses 35 are arranged in a certain arrangement direction on the light output side surface 32 a of the main body 32. Each unit lens 35 extends linearly in a direction intersecting with the arrangement direction. In particular, in the present embodiment, the unit lens 35 extends linearly. The longitudinal direction of the unit lenses 35 is orthogonal to the arrangement direction of the unit lenses 35 on a plane parallel to the sheet surface of the main body 32. Further, as shown in FIG. 1, the arrangement direction of the unit lenses 35 is parallel to the arrangement direction of the light emitting portions 25 a of the light source 25.

  3 to 5, in a cross section parallel to both the normal direction nd of the sheet surface of the main body portion 32 of the lens sheet 30 and the arrangement direction of the unit lenses 35 (also referred to as “the main cutting surface of the lens sheet”), the lens A sheet 30 is shown. As shown in FIG. 2, in the present embodiment, the cross-sectional shape of each unit lens 35 on the main cutting surface of the lens sheet is constant along the longitudinal direction of the unit lens 35 (direction extending linearly). ing. The plurality of unit lenses 35 included in the lens sheet 30 are all configured similarly. Hereinafter, the cross-sectional shape of the main cutting surface of the unit lens 35 included in the lens sheet 30 will be described in more detail.

  As shown in FIGS. 3 to 5, in the present embodiment, the cross-sectional shape of each unit lens 35 on the main cut surface of the lens sheet is a shape that tapers toward the light output side. That is, on the main cutting surface of the lens sheet, the width of the unit lens 35 parallel to the sheet surface of the main body portion 32 decreases as the distance from the main body portion 32 increases along the normal direction nd of the main body portion 32.

  On the main cut surface of the lens sheet, the outer contour of the unit lens 35 is configured as a line that can be approximated by one of an arc, an elliptical arc, and a straight line, or a combination of two or more thereof. In particular, in the present embodiment, the cross-sectional shape of the unit lens 35 on the main cutting surface of the lens sheet has a shape corresponding to a part of an ellipse or a part of a circle. In the present embodiment, the outer contour of the unit lens 35 on the main cut surface of the lens sheet is axisymmetric with respect to an axis parallel to the normal direction nd of the main body 32. Thereby, the angular distribution of the luminance on the light exit surface 30a of the lens sheet 30 is substantially symmetric with respect to the front direction on the surface parallel to the arrangement direction of the unit lenses 35.

  Further, as shown in FIG. 3, the tangent TL to the outer contour (lens surface) 35a of the unit lens 35 is the sheet surface of the lens sheet 30 in the main cut surface (in this embodiment, the light exit side surface 32a of the main body 32). ) (Also referred to as “lens surface angle”) θa1 of the unit lens 35 where the contact point TP of the tangent TL to the unit lens 35 is farthest from the main body 32 in the normal direction nd of the main body 32. It increases from the top 35b1 on the outer contour (lens surface) 35a toward both ends 35b2 on the outer contour (lens surface) 35a of the unit lens 35 closest to the main body 32 in the normal direction nd of the main body 32. To go. Here, the light exit surface angle θa1 “becomes larger” is not limited to the fact that the light exit surface angle θa1 constantly changes greatly (the mode in the present embodiment shown in FIG. 3). This is a concept including a case where the light exit surface angle θa1 does not change in at least a part of the region. That is, here, the light exit surface angle θa1 is “increased” when the contact point TP goes from the top 35b1 on the outer contour (light exit surface) 35a to the end portion 35b2 on the outer contour (light exit surface) 35a. Further, it means that the light exit surface angle θa1 is “not reduced”.

In the present embodiment, as shown in FIG. 3, two unit lenses 35-adjacent to each other at an angle of 80 ° with respect to the normal direction nd of the main body 32 on the main cut surface of the lens sheet. 1, 35-2, a point where a straight line SL in contact with the outer contour 35 a of one unit lens 35-1 first intersects with the other unit lens 35-2 as a reference point SP,
A tangent to the outer contour 35a of the other unit lens 35-2 at the reference point SP is defined as a reference tangent STL,
Of the two end portions 35b2 on the outer contour 35a of the other unit lens 35-2, a line segment connecting the end portion 35b2-2 on the side away from the one unit lens 35-1 and the reference point SP is obtained. When the reference line segment SS is used,
The lens surface angle α (°) of the reference tangent STL,
An angle β (°) of 90 ° or less of angles formed by the reference line segment SS with respect to the reference tangent line STL, and
The lens surface angle γ (°) of the tangent TL that contacts the outer contour (lens surface) 35a of the other unit lens 35-2 at the end 35b2-2 on the side away from the one unit lens 35-1.
The refractive index n1 of the material forming the lens sheet 30 satisfies the following expressions (1) and (2).
Arccos ((n1) x cosβ) ≤ α + 10 ... Formula (1)
cosγ ≤ 1 / (n1) ... Formula (2)
According to such a lens sheet 50, as will be described in detail later, it is possible to effectively prevent generation of light emitted from the light exit surface 30a of the lens sheet 30 at an exit angle of approximately 80 °.

  As a specific example of the unit lens 35 configured as described above, the arrangement pitch P1 of the unit lenses 35 along the arrangement direction of the unit lenses 35 (see FIG. 5, corresponding to the width of the unit lens 35 in the present embodiment). To 1 μm to 500 μm. Moreover, the protrusion height H1 (see FIG. 5) of the unit lens 35 from the light exit side surface 32a of the main body 32 along the normal direction nd to the sheet surface of the lens sheet 30 can be set to 0.25 μm to 250 μm. .

  Such a lens sheet 30 can be manufactured very easily by extrusion processing or by molding the unit lens 35 on a substrate. Various materials can be used as the material forming the lens sheet 30. However, it is widely used as a material for an optical sheet (condensing sheet) incorporated in a display device, and has excellent mechanical characteristics, optical characteristics, stability, workability and the like, and can be obtained at a low price, for example, Transparent resins mainly composed of one or more of acrylic, styrene, polycarbonate, polyethylene terephthalate, acrylonitrile and the like, and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins and the like) can be suitably used. When a material widely used as a material for an optical sheet (light condensing sheet) incorporated in such a display device is used, the refractive index of the unit lens 35 of the produced lens sheet 30 is 1.45-1. Within the range of 65.

  Moreover, the diffusion component may be dispersed in the base material made of the exemplified transparent resin. Here, the diffusion component is a particulate matter having a refractive index different from that of the base material. The particulate matter constituting the diffusion component may be a metal compound, a porous material containing a gas, or a simple bubble.

  In addition, when the lens sheet 30 has a base material and a diffusion component, the optical function of the lens surface 35a expressed by satisfying the above-described formulas (1) and (2) may be impaired. It is preferable that the lens surface layer portion 39 (see FIG. 3) is configured as follows so as not to be present. Here, as shown in FIG. 3, on the main cut surface of the lens sheet, the portion of the outer contour 35 a of the other unit lens 35-2 that is divided by the reference line segment SS is taken down to the reference line segment SS. The maximum length of the vertical line PL is d, and the lens surface layer portion 39 is a portion whose distance from the lens surface 35a defined by the unit lens 35 is d or less.

  First, it is preferable that a diffusion component is not locally given to the lens surface layer portion 39 in the lens sheet 30 so that the optical function of the lens surface 35a of the unit lens 35 is not impaired. That is, the value (= (ν1) / (r1)) obtained by dividing the volume ratio (ν1) of the diffusing component in the lens surface layer portion 39 by the average radius (r1) of the diffusing component contained in the lens surface layer portion 39. The volume ratio (ν2) of the diffusion component in the portion other than the lens surface layer portion 39 of the lens sheet 30 is divided by the average radius (r2) of the diffusion component contained in the portion other than the lens surface layer portion 39 of the lens sheet 30. It is preferably less than the value (= (ν2) / (r2)). A large value obtained by dividing the volume ratio of the diffusing component by the average radius of the diffusing component means that light traveling in the lens sheet 30 easily collides with the diffusing component. Therefore, when the diffusion component is made of a substance containing gas, the volume ratio here means the ratio of the volume occupied by the diffusion component including the gas portion to the reference volume.

  Further, the lens surface layer portion 39 is dispersed with a diffusion component at a lower rate than the portion other than the lens surface layer portion 39, and the diffusion function of the lens surface layer portion 39 is more than the diffusion function of the portion other than the lens surface layer portion 39 of the lens sheet 30. Is preferably weak. That is, the value (= (ν1) / (r1)) obtained by dividing the volume ratio (ν1) of the diffusing component in the lens surface layer portion 39 by the average radius (r1) of the diffusing component contained in the lens surface layer portion 39. The volume ratio (ν2) of the diffusion component in the portion other than the lens surface layer portion 39 of the lens sheet 30 is divided by the average radius (r2) of the diffusion component contained in the portion other than the lens surface layer portion 39 of the lens sheet 30. It is preferable that it is below the value (= (ν2) / (r2)).

More preferably, the lens surface layer part 39 does not contain a diffusion component. In addition, the term “does not contain a diffusing component” as used herein means that the optical function expressed by satisfying the above-described formulas (1) and (2) is harmed without being judged in a strict sense. It is judged by whether or not it contains a diffusion component. Specifically, the volume ratio of the diffusion component in the lens surface layer portion 39 (numerical value of 0 or more and 1 or less: ν1), the length L (μm) of the reference line segment SS at the main cutting surface of the lens sheet, the lens surface layer When the average radius r1 (μm) of the diffusion component contained in the portion 39 satisfies the following equation (i), it is determined that no diffusion component is contained in the lens surface layer portion 39.
L × (ν1) / (r1) ≦ 0.07 Formula (i)

  By the way, in this specification, the radius of the diffusion component dispersed in the lens sheet 30 is specified by the radius of a sphere having the same volume as the diffusion component. Similarly to the volume ratio (volume ratio) described above, when the diffusion component is made of a substance containing a gas, the volume of the diffusion component is measured including the portion of the contained air, and from the substance containing the gas. The radius of the diffusion component is calculated.

  Next, the optical sheet 40 will be described. The optical sheet 40 mainly has a function (condensing function) that changes the traveling direction of light incident from the light incident side and emits the light from the light output side, and intensively improves the luminance in the front direction nd and the vicinity thereof. Have.

  The optical sheet 40 includes a base 42 and a plurality of unit shape elements (unit optical elements, unit prisms) 45 provided on the base 42. As shown in FIGS. 4 and 5, the base portion 42 is formed as a sheet-like member having a light exiting side surface 42 a and a light incident side surface 42 b facing each other. The base 42 functions as a sheet-like member that supports the unit shape element 45.

  As shown in FIGS. 4 and 5, in the present embodiment, unit shape elements 45 are arranged side by side on the light output side surface 42 a of the base portion 42 without leaving a gap. As a result, the light exit surface 40 a of the optical sheet 40 is constituted only by the light exit surface 45 a of the unit shape element 45. On the other hand, as shown in FIG. 3, in the present embodiment, the light incident side surface 42 b of the base 42 constitutes a light incident surface 40 b of the optical sheet 40 as a flat (flat) surface.

  As shown in FIG. 1, a large number of unit shape elements 45 are arranged in a certain arrangement direction on the light output side surface 42 a of the base portion 42. Each unit shape element 45 extends linearly in a direction intersecting with the arrangement direction. In particular, in the present embodiment, the unit shape element 45 extends linearly. Further, the longitudinal direction of the unit shape elements 45 is orthogonal to the arrangement direction of the unit shape elements 45 on a plane parallel to the sheet surface of the base portion 42.

  As shown in FIG. 1, in the observation from the front direction, the arrangement direction of the unit shape elements 45 of the optical sheet 40 is parallel to the arrangement direction of the unit lenses 35 of the lens sheet 30. Therefore, the arrangement direction of the unit shape elements 45 is parallel to the arrangement direction of the light emitting portions 25 a of the light source 25.

  4 and 5, in a cross section parallel to both the normal direction nd of the sheet surface of the base portion 42 of the optical sheet 40 and the arrangement direction of the unit shape elements 45 (also referred to as “main cutting surface of the optical sheet”), A sheet 40 is shown. In the present embodiment, as shown in FIGS. 4 and 5, each unit shape element 45 has a triangular shape protruding toward the light exit side on the main cut surface of the optical sheet. From the viewpoint of intensively improving the luminance in the front direction, the cross-sectional shape is particularly an isosceles triangle shape, and the apex angle located between the equilateral sides protrudes from the light emitting side surface 42a of the base portion 42 to the light emitting side. In addition, each unit shape element 45 is configured.

  Further, in the present embodiment, the cross-sectional shape of each unit shape element 45 on the main cutting surface of the optical sheet is a right-angled isosceles triangle shape, and the longitudinal direction of the unit shape element 45 (direction extending linearly) ) Is constant along. The plurality of unit shape elements 45 included in the optical sheet 40 are all configured in the same manner.

  As a specific example of the unit shape elements 45 having the above-described configuration, the arrangement pitch P2 of the unit shape elements 45 along the arrangement direction of the unit shape elements 45 (see FIG. 5: in the present embodiment, the second unit shape). (Corresponding to the width of the element 45) can be 1 μm to 200 μm. Further, the protrusion height H2 (see FIG. 5) of the second unit shape element 45 from the light exit side surface 42a of the base portion 42 along the normal direction nd to the sheet surface of the optical sheet 40 is set to 0.25 μm to 150 μm. Can do. Such an optical sheet 40 can be formed by the same method as the lens sheet 30 described above and using the same material as the lens sheet 30 described above. Further, when the cross-sectional shape of the unit shape element 55 is an isosceles triangle, from the viewpoint of intensively improving the luminance in the front direction, the apex angle θd (which is located between the equilateral sides and protrudes toward the light output side). 5) is preferably 80 ° to 120 °, more preferably 90 °.

As described above, in the present embodiment, the lens sheet 30 and the optical sheet 40 are positioned with respect to each other so that the arrangement direction of the unit shape elements 45 and the arrangement direction of the unit lenses 35 are parallel to each other. . In such an embodiment, moire may occur due to the arrangement of the unit shape elements 45 and the arrangement of the unit lenses 35. In order to make such moire inconspicuous, the pitch P1 of the unit lens 35 in the lens sheet 30 and the pitch P2 of the unit shape element 45 in the optical sheet 40 are set so that both of the following two expressions are satisfied. It is effective. In the following equation, Pb is the larger value of pitch P1 and pitch P2, Ps is the smaller value of pitch P1 and pitch P2, and n is 0 or an integer.
(Pb) / (Ps) ≧ 2.3
(Pb) / (Ps) ≠ n to n ± 0.2

  Further, as described above, the optical sheet 40 is expected to exhibit an excellent light collecting function. For example, when a parallel light flux traveling in a direction inclined by 80 ° with respect to the normal direction nd of the base portion 42 of the optical sheet 40 in the main cut surface of the optical sheet is incident on the light incident surface 40b of the optical sheet 40, In the angular distribution of luminance at the light exit surface 40a of the optical sheet 40 measured at the main cutting surface of the optical sheet, the peak luminance appears in a range of 45 ° or less from the front direction, and half the peak luminance is secured. It is preferable that the width of the angle range (hereinafter, also simply referred to as half width) is 15 ° or less. According to such an optical sheet 40, an excellent light collecting function can be exerted on the transmitted light.

  The half width of an optical sheet (light collecting sheet) incorporated in a surface light source device of a liquid crystal television that is actually marketed is usually 15 ° or less. Here, FIG. 11 shows three types of optical sheets that are widely used as a condensing sheet for a surface light source device, each having a sheet-like base and a plurality of unit shapes arranged in parallel on the base. The graph which investigated the angular distribution of the brightness | luminance about the optical sheet which has an element is shown. In this graph, the vertical axis represents the luminance ratio, and the horizontal axis represents the angle at which each luminance was measured. The luminance angular distribution shown on the graph is measured on the light exit surface of the optical sheet, and is a luminance distribution for each direction in the main cutting plane of the optical sheet. The incident light on the optical sheet was a parallel light beam that was inclined by 80 ° with respect to the front direction and traveled along the main cut surface of the optical sheet. The peak luminance for sample A was measured in a direction inclined approximately 38 ° from the front direction, and the peak luminance for sample B and sample C was measured in a direction inclined approximately 37 ° from the front direction. The full width at half maximum for sample A was approximately 3 °, the full width at half maximum for sample B was approximately 4 °, and the full width at half maximum for sample C was approximately 14 °.

  On the other hand, when the same measurement as the samples A to C is performed, the optical component according to the comparative sample A in which the peak luminance appears in a direction inclined by 60 ° from the front direction and the half-value width becomes 30 °. A sheet was produced. When the optical sheet according to this comparative sample A was incorporated as a condensing sheet in a general surface light source device, the image of the arc tube forming the light source was not visually recognized from the oblique direction, but the light source was formed from the front direction. An image of the arc tube was seen.

In addition, in the present embodiment, the distance h along the normal direction nd of the main body portion 32 of the lens sheet 30 from the lens sheet 30 to the light emitting portion 25a of the light source 25 on the main cut surface of the lens sheet (the light emitting portion). When the size cannot be ignored, the distance between the lens sheet 30 and the center of the light emitting portion 25a) and the arrangement direction of the unit lenses 35 between the two adjacent light emitting portions 25a on the main cut surface of the lens sheet. The distance k (the distance between the centers of the two light emitting portions 25a when the size of the light emitting portion cannot be ignored), the refractive index n1 of the material forming the lens sheet 30, and the end 35b2 of the unit lens 35. The lens surface angle γ, the refractive index n2 of the material forming the optical sheet 40, and the light exit surface angle θe at the end 45b2 of the unit shape element 45 satisfy the following expressions (3) to (6). Has become The According to such a combination of the lens sheet 30 and the optical sheet 40, as will be described in detail later, even in a region facing an intermediate point between two adjacent light emitting units 25a that tend to decrease the luminance in the front direction. It is possible to ensure high front direction luminance.
-10 ° ≦ (θe)-Arcsin ((n2) × sin ((θe)-(θia2))) ≦ 10 ° ・ ・ ・ Equation (3)
(θia2) = Arcsin ((1 / (n2)) × (sin (θi2))) (4)
(θi2) = γ- Arcsin ((n1) × sin (γ- (θia1))) (5)
(θia1) = Arcsin ((1 / (n1)) × (sin (Arctan (k / 2 / h)))) (6)

  Next, the polarization separation sheet 50 will be described. The polarization separation sheet 50 is a so-called reflection-type polarization sheet that transmits light of a specific polarization component that can pass through the lower polarizing plate 16 of the liquid crystal display panel 15 and reflects light of a polarization component other than the specific polarization component. It is the member comprised. The light of the polarization component other than the specific polarization component reflected by the polarization separation sheet 50 returns to the optical sheet 40 and the lens sheet 30 side. Such return light can change its polarization state by reflection or refraction at the optical sheet 40 or the lens sheet 30. When the return light is incident on the polarization separation sheet 50 again after changing the polarization state, the return light can be effectively used as light for transmitting the polarization separation sheet 50 and displaying an image.

  As such a polarization separation sheet 50, “DBEF” (registered trademark) available from 3M Corporation of the United States can be used. In addition to “DBEF”, a high-intensity polarizing sheet “WRPS” (registered trademark) available from Shinwha Intertek, Korea, a wire grid polarizer, or the like can also be used. Further, for example, an optical rotation selection layer composed of a cholesteric liquid crystal layer having cholesteric regularity, and a quarter wavelength layer (λ / 4 retardation layer) laminated on the liquid crystal display panel 15 side of the optical rotation selection layer, The film member that is provided can be used as the polarization separation sheet 50.

  Next, the operation of the surface light source device 20 and the display device 10 as described above will be described. First, the overall operation of the display device 10 and the surface light source device 20 will be described.

  The light emitted from the light emitting unit 25a of the light source 25 travels to the viewer side directly or after being reflected by the reflecting plate 22. The light traveling toward the observer side enters the lens sheet 30.

  As shown in FIG. 4, the light L41 and L43 having a small inclination angle in the traveling direction with respect to the front direction nd, that is, the lights L41 and L43 having a small incident angle are totally reflected on the light exit surface (lens surface) 35a of the unit lens 35. It tends to be easy to do. Typically, when light L41 and L43 having a small incident angle is incident on a region having a large lens surface angle θa1 among the lens surfaces 35a of the unit lens 35, total reflection is likely to occur.

  Here, as shown in FIG. 4, when light reflected by the reflector 22 and incident on the lens sheet 30 is excluded, that is, light directly incident on the lens sheet 30 from the light emitting portion 25a of the light source 25. Regarding L41 to L48, as the incident position of the light on the lens sheet 30 moves away from the light emitting unit 25a of the light source 25 in the direction parallel to the sheet surface of the lens sheet 30, the incident angle on the lens sheet 30 increases. That is, for light source light that travels in a straight line and is directly incident on the lens sheet 30 (hereinafter also referred to as “direct incident light”), as the incident position moves away from the light emitting unit 25a, the normal direction nd of the lens sheet 30 is increased. The inclination angle increases.

  That is, such total reflection is likely to occur at a position directly above the light emitting portion 25a of the light source 25 where light from the light source 25 is directly incident at a small incident angle. The light totally reflected on the light exit surface (lens surface) 35a of the unit shape element 35 includes a lot of lights L41 and L43 that subsequently repeat total reflection and change the traveling direction to the light incident side (light source side). . Thereby, it is possible to prevent the luminance from becoming excessively high in a region located immediately above the light emitting unit 25a of the light source 25, where the luminance in the front direction tends to be excessively high as compared with other regions.

  Even if the light L42 has a small incident angle, when the light enters the region of the lens surface 35a of the unit lens 35 where the lens surface angle θa1 is small, the lens L is not totally reflected and passes through the lens surface 35a. The light is emitted from the sheet 30. For this reason, it is prevented that the brightness in the area | region which faces the light emission part 25a of the light source 25 becomes too dark.

  On the other hand, light having a relatively large inclination angle in the traveling direction with respect to the front direction nd, that is, light having a relatively large incident angle is hardly totally reflected on the light exit surface (lens surface) 35a of the unit shape element 35. There is a tendency to exit from the lens sheet 30 via the lens surface 35a. As described above, for the directly incident light that greatly affects the luminance distribution, the inclination angle of the lens sheet 30 with respect to the normal direction nd increases as the incident position moves away from the light emitting portion 25a. Thereby, sufficient brightness can be ensured in a region facing the midpoint CP between two adjacent light emitting units 25a, which tends to be darker than other regions.

  As shown in FIG. 4, the light L <b> 42 and L <b> 44 to L <b> 47 emitted from the unit lens 35 of the lens sheet 30 is refracted on the light exit surface (lens surface) 35 a of the unit lens (unit lens) 35. Due to this refraction, the traveling direction (outgoing direction) of the light L42, L44 to L47 traveling in the direction inclined from the front direction nd is mainly compared with the traveling direction of the light just before entering the lens sheet 30. Is bent so that the angle with respect to the normal direction nd to the sheet surface becomes small. That is, the unit lens 35 also has a condensing effect on the transmitted light.

  Note that the amount of change in the angle of the traveling direction of light before entering the lens sheet 30 and after exiting from the lens sheet 30 tends to increase with respect to the light incident on the lens sheet 30 with a large inclination from the front direction nd. There is. That is, the light condensing action of the unit lens 35 is more effectively exerted on the light traveling greatly inclined from the front direction nd. Thereby, the front direction luminance can be effectively increased in a region facing the midpoint CP of the two adjacent light emitting units 25a, where the front direction luminance tends to be darker than other regions.

  As described above, the optical action mainly exerted from the unit lens 35 on the incident light is different depending on the separation distance of the light source 25 from the light emitting portion 25a. Thereby, the distribution of brightness along the arrangement direction of the light emitting units 25a constituting the light source 25, in particular, the distribution of luminance in the front direction can be made uniform.

  The light emitted from the lens sheet 30 then enters the optical sheet 40 disposed on the light output side of the lens sheet 30. The optical sheet 40 emits light by changing the traveling direction of light by refraction at the light exit surface (prism surface) 45 a of the unit shape element 45. In refraction at the light exit surface (prism surface) 45a of the unit shape element 45, the traveling directions (outgoing directions) of the light L42, L44, L45, and L47 traveling in the direction inclined from the front direction nd are mainly incident on the lens sheet 30. The lens sheet 30 is bent so that an angle with respect to the normal direction nd to the sheet surface of the lens sheet 30 is smaller than the light traveling direction just before. On the other hand, the light L48 that has entered the light exit surface 45a of the unit shape element 45 from a direction that is not significantly inclined with respect to the front direction nd is totally reflected by the light exit surface 45a and changes its traveling direction to the light source 25 side. .

  In this way, the optical sheet 40 deflects the traveling direction of light in the front direction nd and emits it. On the other hand, light whose traveling direction cannot be deflected in the front direction, typically light that has already traveled in the front direction or in the vicinity of the front direction, is returned to the light source side by total reflection with no reflection loss. ing. In this way, the optical sheet 40 intensively improves the luminance in the front direction nd and the vicinity thereof without losing the light source light.

  In the surface light source device 20 in the present embodiment, as described above, the lens sheet 30 and the optical sheet 40 are designed so that the expressions (3) to (6) are satisfied. According to such a combination of the lens sheet 30 and the optical sheet 40, the front direction is high even at a position facing the intermediate point CP between two adjacent light emitting units 25a where the luminance in the front direction tends to decrease. It becomes possible to ensure luminance. More specifically, the direct incident light L51 (see FIG. 5) incident on the lens sheet 30 at the largest incident angle, that is, one of the two light emitting portions 25a adjacent to each other along the arrangement direction of the unit lenses 35. The direct incident light L51 that is emitted at the position facing the intermediate point CP between the two adjacent light emitting portions 25a and enters the lens sheet 30 passes through the end portion 35b2 of the lens surface 35a of the unit lens 35. The light is emitted from the sheet 30 and then travels in a direction within an angle range of ± 10 ° with respect to the front direction nd by the light collecting function in the optical sheet 40. This point will be discussed in detail with reference to FIG.

  First, referring mainly to FIG. 5, light is emitted from one of the two light emitting portions 25a adjacent to each other along the arrangement direction of the unit lenses 35, and an intermediate point CP between the two adjacent light emitting portions 25a. The emission angle θi2 of the light emitted from the lens sheet 30 through the unit lens 35 facing the lens (the angle formed by the traveling direction of the emitted light from the lens sheet 30 with respect to the normal direction nd of the lens sheet 30) is examined. . Specifically, the entrance angle of the directly incident light L51 incident on the lens sheet 30 at a position facing the intermediate point CP between the two adjacent light emitting portions 25a (the traveling direction of the light in the lens sheet 30 is that of the lens sheet 30). First, the angle θia1 formed with respect to the normal direction nd is specified. Next, the emission angle θi2 of the light emitted from the lens sheet 30 is specified using the approach angle θia1.

As shown in FIG. 5, light is emitted from one of the two light emitting portions 25a adjacent to each other along the arrangement direction of the unit lenses 35, and faces the intermediate point CP of the two adjacent light emitting portions 25a. The incident angle θi1 of the directly incident light incident on the lens sheet 30 through the light incident surface 30b at the position is expressed by the following equation (7). And about the refraction | bending in the light-incidence surface 30b to the lens sheet 30 of the said light, Formula (8) is formed according to Snell's law. And above-mentioned formula (6) is derived from formula (7) and formula (8).
(θi1) = Arctan (k / 2 / h) (7)
sin (θi1) = (n1) × sin (θia1) (8)
(θia1) = Arcsin ((1 / (n1)) × (sin (Arctan (k / 2 / h)))) (6)

Next, with respect to refraction of the light L51 on the lens surface (outer contour) 35a of the unit lens 35, Equation (9) is established according to Snell's law. In Expression (9), as shown in FIG. 5, the angle θx1 is an incident angle to the lens surface (outer contour) 35a of the unit lens 35, and the angle θy1 is from the lens surface (outer contour) 35a of the unit lens 35. Is an emission angle. For the incident angle θx1, as can be understood from FIG.
(n1) x sin (θx1) = sin (θy1) (9)
(θx1) = γ-(θia1) (10)

Then, light is emitted from one of the two light emitting units 25a adjacent to each other along the arrangement direction of the unit lenses 35a, and passes through the unit lens 35 facing the intermediate point CP of the two adjacent light emitting units 25a. The emission angle θi2 of the light emitted from the lens sheet 30 (the angle formed by the emission direction with respect to the normal direction nd of the lens sheet 30) is expressed by Expression (11).
(θi2) = γ-(θy1) (11)

The calculated emission angle θi2 of the light emitted from the lens sheet 30 corresponds to the incident angle to the optical sheet 40. The emission angle θz of the light emitted from the optical sheet 40 is calculated as follows in the same manner as the emission angle θi2 of the light emitted from the lens sheet 30. First, as shown in FIG. 5, the optical sheet is formed with an entrance angle of light incident on the optical sheet 40 (an angle formed by the light traveling direction in the optical sheet 40 with respect to the normal direction nd of the optical sheet 40). Between the refractive index n2 of the material, the incident angle θx2 to the light exit surface (outer contour) 45a of the unit shape element 45, and the exit angle θy2 from the lens surface (outer contour) 35a of the unit lens 35, 12) to (14) hold. As a result, the light emission angle θz (angle formed with respect to the normal direction of the optical sheet) is the angle θe formed by the light output surface 45a of the unit shape element 45 of the optical sheet 40 with respect to the sheet surface of the optical sheet 40. And is represented by equation (15). Then, Expression (16) is derived from Expression (12) to Expression (15).
sin (θi2) = (n2) × sin (θia2) (12)
(θx2) = θe-(θia2) (13)
(n2) x sin (θx2) = sin (θy2) (14)
(θz) = θe-(θy2) (15)
(θz) = θe-Arcsin ((n2) x sin ((θe)-(θia2))) (16)

  Therefore, when the above-described formula (3) is satisfied, light is emitted from one of the two light emitting portions 25a adjacent to each other along the arrangement direction of the unit lenses 35, and the two adjacent light emitting portions 25a. The direct incident light L51 incident on the lens sheet 30 at a position facing the intermediate point CP is emitted from the optical sheet 40 in the direction of an angle range of ± 10 ° with respect to the front direction nd.

  As described above, the emission angle of the light emitted from the optical sheet 40 is narrowed down to a narrow angle range centering on the front direction on a plane parallel to the arrangement direction of the unit shape elements 45 of the optical sheet 40.

  The light emitted from the optical sheet 40 then enters the polarization separation sheet 50. In the polarization separation sheet 50, only a polarization component that can be transmitted through the lower polarizing plate 16 of the transmission type display unit 15 disposed on the light output side of the polarization separation sheet 50 is transmitted, and the other polarization components can be reused. Reflects to the side.

  The light emitted from the surface light source device 20 through the polarization separation sheet 50 enters the lower polarizing plate 16 of the transmissive display unit 15. The light transmitted through the lower polarizing plate 16 selectively passes through the upper polarizing plate 17 according to the state of electric field application to each pixel. In this manner, the light from the surface light source device 20 is selectively transmitted for each pixel by the transmissive display unit 15 so that the observer of the transmissive display device 10 can observe the image. Become.

  The above is the overall operation of the surface light source device 20 and the display device 10.

  Incidentally, as described above, in a surface light source device (for example, Patent Document 2: JP20006-65277A described above) using a diffusion sheet having a conventional linearly arranged convex lens, the in-plane distribution of luminance in the front direction is obtained. Even if it can be made uniform, there is a problem that an image of the arc tube that forms a light source that is not observed from the front direction nd is visually recognized when the surface light source device or the display device is observed from an oblique direction. It was.

  The inventors of the present invention have intensively studied the cause of the fact that the image of the light emitting part is easily observed from an oblique direction, and as a result, have found the following. As a result of investigating the angular distribution of luminance on the light exit side of the diffusion sheet disclosed in Patent Document 2, a peak is observed in an area of 70 ° or more, particularly around 80 °, separately from the main lobe centered on the front direction. Having side lobes had appeared. That is, in the angular distribution of luminance at the light exit surface of the diffusion sheet incorporated in the surface light source device, side lobes are formed in a direction greatly inclined from the front direction.

  When the side lobe was further investigated, it was incident on the lens surface of the convex lens and once totally reflected by the lens surface, and then the side surface was reflected by light emitted from the diffusion sheet through the other lens surface of the convex lens. It was confirmed that the lobe was constructed. The light that enters the lens surface of the convex lens and is totally reflected by the lens surface is light that travels in a direction that does not significantly incline with respect to the front direction, as already described in the present embodiment. is there. That is, incident light that enters the region of the diffusion sheet that faces the light emitting portion from the light emitting portion without largely tilting from the front direction mainly forms side lobes.

  The light emitted from the diffusion sheet to the light exit side can be changed in its traveling direction by a light control sheet such as a light condensing sheet, but the light that forms this side lobe is not diffused but rather condensed. It is condensed in the direction of a narrow angle range by the sheet. In particular, the light having a large emission angle from the diffusion sheet among the light forming the side lobes is narrowed down in a narrow angle range so that it is difficult to distinguish visually.

  As described above, the light that forms the side lobe is mainly light that is incident on the diffusion sheet facing the light emitting unit from each light emitting unit, and is incident on the diffusion sheet with a distribution corresponding to the configuration of the light source. Therefore, in the observation from the direction of the narrow angle region where the sidelobe light is collected, there is a region that is brightly observed with a distribution corresponding to the configuration of the light source. This brightly observed area is the image of the light emitting part that forms the light source.

  Further, in this investigation, the inventors of the present invention are the main factors that make visible the image of the arc tube from the oblique direction, among the light forming the side lobes, the light traveling at an angle of about 80 ° with respect to the front direction. It was confirmed that

  The condensing sheet (optical sheet) having the excellent condensing function as described in the present embodiment described above is in the direction within the angle range where the light that forms the main lobe on the light exit side of the diffusion sheet exits. The light that formed the side lobe is also deflected. Of the light forming the side lobes, the light that has formed a relatively large amount of the main lobe is deflected in the direction in which the light having a relatively small inclination angle with respect to the front direction is deflected. Therefore, light having a small inclination angle with respect to the front direction among the light forming the side lobes becomes relatively inconspicuous light. On the other hand, only a small amount of light forming the main lobe is deflected in the direction in which light having a relatively large inclination angle with respect to the front direction is deflected. For this reason, light having a relatively large inclination angle with respect to the front direction among the light forming the side lobes is distinguished from the light forming the main lobe and is viewed from an oblique direction.

  On the other hand, the reflectance of the light which is emitted from the diffusion sheet at an emission angle exceeding 80 ° and enters the light collecting sheet at an incident angle exceeding 80 ° is extremely high, and the diffusion sheet is emitted at an emission angle exceeding 80 °. Most of the light emitted from the light does not enter the optical sheet. That is, it cannot be light that forms an image of the arc tube observed from an oblique direction.

  In the first place, a side lobe having a high peak around 70 ° is generally difficult to form, and a side lobe having a high peak is formed so that the peak appears around 80 °.

  In consideration of the above, the lens sheet 30 according to the present embodiment mainly forms an image of the light emitting portion 25a that can be observed from an oblique direction by satisfying the above-described expressions (1) and (2). The lens surface 35a has a feature in the region 35ab where the light to be emitted, that is, the light constituting the side lobe, in particular, the light inclined by 80 ° with respect to the front direction, can be emitted. By suppressing the emission of the light to be formed from the lens surface 35a of the lens sheet 30, the image of the light emitting portion 25a that forms the light source 25 is made inconspicuous even when the surface light source device 20 is observed from an oblique direction. . This will be further described with reference mainly to FIG.

  First, as a precondition, the lens sheet 30 must have a function of equalizing the in-plane distribution of luminance in the front direction by suppressing the brightness of the area facing directly above the light emitting unit 25a. For this reason, at least the light traveling in the front direction must be totally reflected by the lens surface 35a of the unit lens 35 of the lens sheet 30. In particular, in the present embodiment, the lens surface angle θa1 of the unit lens 35, that is, the angle θa1 formed by the tangent TL to the lens surface 35a with respect to the sheet surface of the main body portion 32, the contact of the tangent TL is on the lens surface. It becomes smaller from the top 35b1 toward the end 35b2. Therefore, the light traveling in the front direction must be totally reflected at the end 35b2 of the lens surface 35a where the total reflection is most likely to occur. The above-described equation (2) is a condition for the light traveling in the front direction to be totally reflected by the end portion 35b2 of the lens surface 35a of the unit lens 35.

  Next, as shown in FIG. 3, the main cut surface of the lens sheet 30 is adjacent to the straight line SL that is inclined by 80 ° with respect to the front direction nd of the lens surface 35 a of the unit lens 35. A side lobe is mainly configured by emitting light from a region 35ab from the reference point SP to the top portion 35b1, which is an intersection with the straight line SL in contact with the other unit lens 35, in a direction inclined by 80 ° to one side with respect to the front direction. The light that comes into play can be emitted. The lens surface angle θa1 of the unit lens 35 increases from the top 35b1 toward the end 35b2.

  Therefore, after the total reflection once by the lens surface 35a of the unit lens 35, the incident angle (the incident direction of the light is incident on the lens surface 35a) of the light incident on the region from the top 35b2 on the lens surface 35a to the reference point SP. The angle formed with respect to the tangent to the lens surface 35a is the smallest at the position of the reference point SP. That is, the light that has been totally reflected once by the lens surface 35a that can mainly constitute the side lobe is most totally reflected when it enters the reference point SP in the region from the top 35b2 on the lens surface 35a to the reference point SP. It becomes easy to pass through the lens surface 35a without being emitted from the lens sheet 30. In addition, when the position where the light is totally reflected by the lens surface 35a is the end portion 35b2 on the lens surface 35a, the incident angle with respect to the lens surface 35a when entering the lens surface 35a next becomes the smallest.

  From the above, the light passing through the optical path along the reference line segment SS connecting the end 35b2 on the lens surface 35a and the reference point SP is totally reflected once on the lens surface 35a constituting the side lobe. Of the light, it is the light that is most likely to be emitted from the lens sheet via the region 35ab on the lens surface 35a from which light inclined by 80 ° with respect to the front direction can be emitted. From Snell's law, the angle formed by the emission direction of light incident on the lens surface 35a on the reference point SP along the reference line segment SS with respect to the reference tangent line STL is expressed by the left side “Arccos ((n1 ) × cosβ) ”. Therefore, when Expression (1) is satisfied, the light that travels along the optical path along the reference line segment, passes through the reference point SP, and exits the lens sheet 30 once has the same height as the adjacent unit lens 35-1. To enter. The light is changed in the direction of travel by the unit lens 35-1, and can no longer form a side lobe that causes an image of the light emitting portion 25a that is visually recognized in an oblique observation.

  That is, when the above-described equations (1) and (2) are satisfied, light that is inclined by 80 ° with respect to the front direction nd, which is considered to be a main cause of generating an image of the light emitting unit 25a in an oblique direction, is emitted. Even if light once totally reflected by the lens surface 35a is emitted from the area 35ab to be obtained, there is a tendency to enter the adjacent unit lens 35. As a result, when the expressions (1) and (2) are satisfied, it is possible to prevent a conspicuous side lobe from being formed, and to observe the surface light source device 20 or the display device 10 from an oblique direction. In addition, similarly to the front direction nd, it is possible to effectively prevent the image of the light emitting unit 25a forming the light source 25 from being visually recognized.

  As described above, according to the present embodiment, the in-plane variation of the luminance in the front direction can be effectively uniformed so that the image of the light emitting unit 25a forming the light source 25 is not noticeable in the observation from the front direction nd. it can. Furthermore, according to the present embodiment, the light once totally reflected on the lens surface 35a of the unit lens 35 can be observed from an oblique direction by the lens sheet 30 satisfying the expressions (1) and (2). The light that mainly forms the image of the light emitting portion 25a, that is, the light constituting the side lobe, particularly the light inclined by 80 ° with respect to the front direction nd, passes through the region 35ab on the lens surface 35a. The direction of emission is limited. Thereby, the in-plane distribution of the luminance measured in the oblique direction on the light emitting surface 20a of the surface light source device 20 is made uniform, and the light emitted from the light source 25 even when observed from the oblique direction as well as from the front direction nd. The image of the portion 25a (tube unevenness) can be effectively made inconspicuous.

From the viewpoint of making the image of the light emitting portion 25a inconspicuous, as described above, when the lens sheet 30 contains a diffusing component,
Condition (a): Value obtained by dividing the volume ratio (ν1) of the diffusion component in the lens surface layer portion 39 by the average radius (r1) of the diffusion component contained in the lens surface layer portion 39 (= (ν1) / (r1) ) Is the volume ratio (ν2) of the diffusion component in the portion other than the lens surface layer portion 39 of the lens sheet 30 by the average radius (r2) of the diffusion component contained in the portion other than the lens surface layer portion 39 of the lens sheet 30. It is preferably less than or equal to the divided value (= (ν2) / (r2))
Condition (b): A value obtained by dividing the volume ratio (ν1) of the diffusing component in the lens surface layer portion 39 by the average radius (r1) of the diffusing component contained in the lens surface layer portion 39 (= (ν1) / (r1) ) Is the volume ratio (volume ratio (ν2)) of the diffusion component in the portion other than the lens surface layer portion 39 of the lens sheet 30, and the average radius of the diffusion component contained in the portion other than the lens surface layer portion 39 of the lens sheet 30 ( More preferably, it is less than the value divided by (r2) (= (ν2) / (r2)),
Condition (c): It is more preferable that no diffusion component is contained in the lens surface layer portion 39.

  As described above, in the lens sheet 30 according to the present embodiment, the light passing through the lens surface layer portion 39 does not form side lobes. In order to prevent light passing through the lens surface layer portion 39 from colliding with the diffusion component and changing the traveling direction irregularly, thereby forming side lobes, the above conditions (a) to ( c) becomes effective.

  Actually, a plurality of lens sheets containing diffusing components at different volume ratios were prepared and tested. The radii of the diffusion components included in the plurality of lens sheets are all the same. The plurality of lens sheets have the same cross-sectional shape at the main cut surface and differ from each other only in the volume ratio of the diffusion component. Further, the plurality of lens sheets satisfied the above-described expressions (1) and (2).

  Each lens sheet was disposed at a position facing the light source, and a reflector was provided on the back surface of the light source. As the light source and the reflection plate, a light source and a reflection plate incorporated in a commercially available liquid crystal television, which are a cold cathode tube arranged in parallel and a diffuse reflection plate arranged on the back of the cold cathode tube. We used each.

  Furthermore, an optical sheet was disposed on the light output side of the lens sheet, and a surface light source device including a reflector, a light source, a lens sheet, and an optical sheet was produced. As optical sheets for each lens sheet, three kinds of light collecting sheets that are widely used in practice (optical sheet 1: “BEF” available from 3M, optical sheet 2: “RBEF” available from 3M, “H2K” available from Dai Nippon Printing Co., Ltd. was used. In any combination of the lens sheet and the optical sheet, the above-described formulas (3) to (6) were satisfied.

  When the surface light source device was observed from an oblique direction, it was investigated whether or not an image of the cold cathode tube forming the light source was visually recognized. From the investigation results, it was confirmed that the above conditions (a) to (c) were effective in order to make the arc tube image inconspicuous. Table 1 shows a part of the experimental results. In Table 1, “◎” is attached to a sample in which unevenness in brightness corresponding to the configuration of the light source could not be confirmed even by careful observation. “◯” is attached to a sample that is not so conspicuous that the unevenness of brightness corresponding to the configuration of the light source cannot be visually recognized with normal observation power. “Δ” is attached to a sample in which uneven brightness is slightly generated corresponding to the configuration of the light source. Furthermore, the left side of the above-described formula (i) was obtained for each sample. The calculated value is attached to the column of “Expression (i)” in Table 1. The optical sheet according to Sample 3 did not satisfy any of the conditions (a) to (c) described above.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to FIGS. 6 to 10 as appropriate. In FIGS. 6 to 10 referred to below, the reference numerals used in the above-described embodiment are used for portions corresponding to the portions described in the above-described embodiment.

  For example, in the above-described embodiment, the example in which the unit lenses 35 of the lens sheet 30 are disposed adjacent to each other has been described. However, the present invention is not limited to this. For example, as shown in FIG. 6, a flat portion 37 may be formed between two adjacent unit lenses 35, or a recess 38 is formed between two adjacent unit lenses 35 as shown in FIG. May be.

  In the above-described embodiment, an example in which only the unit lens 35 having a single shape is provided on the light output side of the main body portion 32 of the lens sheet 30 is not limited thereto. The sheet 30 may include a plurality of first unit lenses that are configured identically and a plurality of second unit lenses that are configured identically. In this modification, it is preferable that the unit lens having a higher height satisfies the above-described formulas (1) and (2) at the position facing the light emitting unit 25a of the light source 25.

  Furthermore, although the example which has the linear unit lens with which the lens sheet 30 was arrange | positioned in parallel was shown in embodiment mentioned above, it is not restricted to this. The lens sheet 30 may have unit lenses that are two-dimensionally arranged, that is, distributed in two different directions on a plane. In this modification, the unit lens may have a shape corresponding to a part of a sphere (for example, a hemisphere) or a shape corresponding to a part of a spheroid.

  Furthermore, although the optical sheet 40 has been exemplified in the above-described embodiment, optical sheets having different configurations can be used. For example, the cross-sectional shape of the main cutting surface of the unit shape element 45 of the optical sheet 40 may be formed in a curved shape as shown in FIG. Moreover, although the optical sheet 40 showed the example which contains only the unit shape element 45 of a single structure, it is not restricted to this, Even if the optical sheet contains the unit shape element which has a mutually different structure. Good.

As shown in FIG. 8, when the unit shape element 45 has a curved outer contour on the main cut surface, the tangent TL to the outer contour 45 of the unit shape element 45 is on the main cut surface of the optical sheet. The light exit surface angle θa2 formed with respect to the sheet surface of the base portion 42 is such that the end portion 45b2 of the unit shape element 45 on the light exit surface 45a from the side of the top portion 45b1 that is farthest from the base portion 42 on the light exit surface 45a of the unit shape element 45. It is preferable that it is configured to satisfy the following formulas (17) to (20) in the combination with the lens sheet.
−10 ° ≦ (θe) −Arcsin ((n2) × sin ((θe) − (θia2))) ≦ 10 ° ・ ・ ・ Equation (17)
(θia2) = Arcsin ((1 / (n2)) × (sin (θi2))) (18)
(θi2) = γ-Arcsin (n × sin (γ- (θia1))) (19)
(θia1) = Arcsin ((1 / n) × (sin (Arctan (k / 2 / h)))) (20)
In these equations, θe is the light exit surface angle θa2 at the end 45b2 of the lens surface 45a, n2 is the refractive index of the material of the optical sheet 40, and the other symbols are the same as in the above embodiment. It is. In Expression (18) to Expression (20), the advance angle θia1 in the lens sheet 30, the exit angle from the lens sheet 30 (incident angle to the optical sheet 40) θi2, and the advance angle θia2 in the optical sheet 40 Is calculated in the same manner as in the above-described embodiment. In Expression (17), “(θe) −Arcsin ((n2) × sin ((θe) − (θia2)))” represents the emission angle θz from the optical sheet 40 (see FIG. 8). . The emission angle θz is calculated from the following equations (21) and (23).
(θx2) = θe-(θia2) (21)
(n2) x sin (θx2) = sin (θy2) Equation (22)
(θz) = θe-(θy2) (23)

  When Expressions (17) to (20) are satisfied, light is emitted from one of the two light emitting parts 25a adjacent to each other along the arrangement direction of the unit lenses 35, and the two adjacent light emitting parts 25a. The direct incident light L81 incident on the lens sheet 30 at a position facing the intermediate point CP of the light is emitted from the optical sheet 40 in a direction within an angle range of ± 10 ° with respect to the front direction nd. Thereby, high front direction luminance can be ensured even in a region facing the midpoint CP of the two adjacent light emitting units 25a that tend to decrease front direction luminance. Also in the example shown in FIG. 8, the light exit surface 45 a of the unit shape element 45 is symmetric about the normal direction nd of the base portion 42 of the optical sheet 45 in the main cut surface of the optical sheet.

  Furthermore, in the above-described embodiment, the example in which the light source 25 is configured by the linear cold cathode tubes arranged in parallel has been described, but the present invention is not limited thereto. For example, as shown in FIG. 9, the light source 25 is configured by point-like light emitters 25b (for example, light emitting diodes (LEDs)) arranged two-dimensionally on a virtual plane parallel to the sheet surface of the lens sheet. Also good. In the example shown in FIG. 9, the point light emitters are arranged at a constant pitch in each of two different directions.

  Furthermore, in the above-described embodiment, an example of the overall configuration of the surface light source device 20 and the display device 10 in which the lens sheet 30 is incorporated has been described. However, the configuration is not limited to this example, and can be changed as appropriate. For example, as shown in FIGS. 9 and 10, a further optical sheet 60 may be incorporated in the surface light source device 20. The further optical sheet 60 includes a main body portion 62 and a plurality of unit shape elements 65 provided on the light exit side surface of the main body portion, and can be configured in the same manner as the optical sheet 40 described above. However, in the example shown in FIGS. 9 and 10, the arrangement direction of the unit shape elements 45 of the optical sheet 40 and the arrangement direction of the unit shape elements 65 of the further optical sheet 60 intersect (orthogonal in the illustrated example). ing. According to the example shown in FIGS. 9 and 10, different two-way components can be condensed by the light collecting function of the optical sheet 40 and the light collecting function of the further optical sheet 60. In the example shown in FIG. 9, a further optical sheet 60 is disposed between the lens sheet 30 and the optical sheet 40. On the other hand, in the example shown in FIG. 10, a further optical sheet 40 is positioned between the lens sheet 30 and the further optical sheet 60.

  Further, as shown in FIGS. 9 and 10, the polarization separation sheet 50 may be deleted from the surface light source device 20. Alternatively, a light diffusion sheet having a haze value of 10 or more and 90 or less may be incorporated into the surface light source device 20.

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

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

(Surface light source device according to Example 1)
A light source, a reflector covering the light source from the back side, a lens sheet disposed at a position facing the light source, an optical sheet (condensing sheet) disposed on the light output side of the lens sheet, and a light output side of the optical sheet A surface light source device according to Example 1 having a light diffusing sheet disposed and forming a light emitting surface was produced. That is, the optical sheet according to Example 1 is different from the surface light source device described in the above-described embodiment in that the polarization separation sheet is replaced with a light diffusion sheet, and other configurations are the same as those in the above-described embodiment. The same as the surface light source device described.

  The light source and the reflector used what was mounted in the commercially available liquid crystal television. The light source is composed of cold cathode tubes arranged in parallel as in the above-described embodiment.

  As the optical sheet, RBEF (registered trademark) available from 3M USA was used. The arrangement pitch of the unit shape elements (unit prisms) was 50 μm. In addition, the light diffusing sheet was mounted on a commercially available liquid crystal television and had a haze value of 80.

  As the lens sheet, a lens sheet having the same configuration as that of the above-described embodiment is used. The arrangement pitch of the unit lenses was 225 μm. Further, the unit lens of this lens sheet satisfied the above-described formulas (1) and (2). Note that the value on the left side of Equation (1) was 5 (°) smaller than the value on the right side of Equation (1).

(Surface light source device according to Comparative Example 1)
A light source, a reflector covering the light source from the back side, a lens sheet disposed at a position facing the light source, an optical sheet (condensing sheet) disposed on the light output side of the lens sheet, and a light output side of the optical sheet A surface light source device according to Comparative Example 1 having a light diffusing sheet disposed and forming a light emitting surface was produced. The surface light source device according to Comparative Example 1 is different from the surface light source device according to Example 1 in that different lens sheets are used, and other components (that is, a light source, a reflector, an optical sheet, and a light diffusion sheet) are: The same surface light source device as in Example 1 was used.

  In the lens sheet of the surface light source device according to Comparative Example 1, the arrangement pitch of the unit lenses was 225 μm. Further, the unit lens of the lens sheet according to Comparative Example 1 satisfied the above-described formula (2), but did not satisfy the above-described formula (1). Note that the value on the left side of Equation (1) was 10 (°) larger than the value on the right side of Equation (1).

  With the surface light source device emitting light, the brightness unevenness corresponding to the configuration of the light source was evaluated. That is, it was evaluated whether or not bright regions corresponding to each arc tube were formed at intervals along the arrangement direction of the arc tubes forming the light source. The presence or absence of uneven brightness corresponding to the configuration of the light source can be determined by observing the surface light source device from the front direction and from the direction inclined from the front direction in the plane including the arrangement direction of the arc tube and the front direction. And if confirmed.

  The results are shown in Table 2. In Table 2, “front unevenness” indicates the result when the surface light source device is observed from the front direction, and “oblique unevenness” indicates the result when the surface light source device is observed from the oblique direction. . In Table 2, “◯” is attached to a sample in which unevenness of brightness corresponding to the configuration of the light source could not be confirmed even by careful observation. “Δ” is attached to a sample in which uneven brightness is slightly generated corresponding to the configuration of the light source. “X” is attached to a sample in which uneven brightness is clearly generated corresponding to the configuration of the light source.

DESCRIPTION OF SYMBOLS 10 Display apparatus 10a Display surface 15 Transmission type display part 20 Surface light source device 20a Light emission surface 25 Light source 25a Light emission part (arc tube)
30 Lens sheet 30a Light exit surface 30b Light entrance surface 32 Main body 32a Light exit side surface 32b Light entrance side surface 35 Unit lens 35a Lens surface (light exit surface, outer contour)
35b1 top 35b2 end (base end)
37 Flat part 38 Concave part 39 Lens surface layer part 40 Optical sheet (condensing sheet)
40a Light exit surface 40b Light entrance surface 42 Main body 42a Light exit side surface 42b Light entrance side surface 45 Unit shape element 45a Lens surface (light exit surface, outer contour)
45b1 Top 45b2 End (base end)
50 Polarized light separation sheet

Claims (13)

A lens sheet used in a surface light source device having a plurality of light sources and arranged facing the light source,
A sheet-like body,
A plurality of unit lenses provided on the light exit side of the main body,
In the main cutting plane that passes through the normal direction of the main body part and each apex most distant from the main body part of two adjacent unit lenses, the tangent to the outer contour of the unit lens is the sheet surface of the main body part The contact angle of the tangent line to the unit lens is on the outer contour of the unit lens closest to the main body from the top side on the outer contour of the unit lens. Towards the end side,
In the main cut surface, a straight line that forms an angle of 80 ° with respect to the normal direction of the main body portion and touches the outer contour of one of the two unit lenses is one of the two unit lenses. Two points on the outer contour of the other unit lens, with a point first intersecting with the other unit lens as a reference point, a tangent to the outer contour of the other unit lens at the reference point as a reference tangent When the line segment connecting the end portion on the side away from the one unit lens and the reference point is a reference line segment, the lens surface angle α (°) of the reference tangent line and the reference line An angle β (°) formed by the minute with respect to the reference tangent, and a lens surface angle γ (°) of a tangent that is in contact with an outer contour of the other unit lens at an end portion on a side away from the one unit lens, Refractive index of the material forming the unit lens DOO satisfies the following formula (A) and (B), the lens sheet.
Arccos (n × cosβ) ≦ α + 10 Formula (A)
sinγ ≤ 1 / n ... Formula (B) A base material, and a diffusion component dispersed in the base material,
In the main cut surface, the maximum length of a perpendicular line drawn from the portion delimited by the reference line segment in the outer contour of the other unit lens is defined as d, and is defined by the unit lens. A portion obtained by dividing a volume ratio of the diffusing component in the lens surface layer portion by an average radius of the diffusing component contained in the lens surface layer portion is a lens surface layer portion where the distance from the lens surface is d or less. Less than the value obtained by dividing the volume ratio of the diffusing component in the portion other than the lens surface layer portion of the lens sheet by the average radius of the diffusing component included in the portion other than the lens surface layer portion of the lens sheet. The lens sheet according to claim 1, wherein a diffusion component is not included in the lens surface layer portion. A base material, and a diffusion component dispersed in the base material,
In the main cut surface, the maximum length of a perpendicular line drawn from the portion delimited by the reference line segment in the outer contour of the other unit lens is defined as d, and is defined by the unit lens. A portion obtained by dividing a volume ratio of the diffusing component in the lens surface layer portion by an average radius of the diffusing component contained in the lens surface layer portion is a lens surface layer portion where the distance from the lens surface is d or less. Less than the value obtained by dividing the volume ratio of the diffusing component in the portion other than the lens surface layer portion of the lens sheet by the average radius of the diffusing component included in the portion other than the lens surface layer portion of the lens sheet. The lens sheet according to claim 1.   The lens sheet according to claim 1, wherein the plurality of unit lenses are arranged in a certain arrangement direction on the main body, and each unit lens extends in a direction intersecting the arrangement direction.   5. The outer contour of the unit lens in the main cutting plane is configured as a line that can be approximated by one of a circular arc, an elliptical arc, and a straight line, or a plurality of combinations. The lens sheet according to item. A light source;
A surface light source device comprising: the lens sheet according to claim 1, wherein the lens sheet is disposed facing the light source. An optical sheet disposed on the light output side of the lens sheet;
The plurality of unit lenses of the lens sheet are arranged in a certain arrangement direction on the main body, and each unit lens extends in a direction intersecting the arrangement direction,
The optical sheet has a sheet-like base, and a plurality of unit-shaped elements arranged on the light exit side surface of the base, each extending linearly in a direction intersecting the arrangement direction,
The lens sheet and the optical sheet are arranged so that an arrangement direction of the unit lenses of the lens sheet is parallel to an arrangement direction of the unit shape elements of the optical sheet. Surface light source device.   A direction inclined by 80 ° with respect to the normal direction of the base of the optical sheet within the main cutting plane of the optical sheet parallel to both the normal direction of the base of the optical sheet and the arrangement direction of the unit shape elements In the angular distribution of the luminance at the light exit surface of the optical sheet measured at the main cutting surface of the optical sheet, the peak luminance is in the front direction when the parallel light flux traveling to is incident on the light incident surface of the optical sheet The surface light source device according to claim 7, wherein the surface light source device appears in a range of 45 ° or less and a width of an angle region in which half the peak luminance is secured is 15 ° or less. In the main cutting surface of the optical sheet parallel to both the normal direction of the base portion of the optical sheet and the arrangement direction of the unit shape elements, the light exit surface of the unit shape element is the normal line of the base portion of the optical sheet. Symmetric about the direction,
In the main cut surface of the optical sheet, the light exit surface angle formed by the outer contour of the unit shape element with respect to the sheet surface of the base, or the tangent to the outer contour of the unit shape element with respect to the sheet surface of the base The angle of the light exit surface formed from the top of the unit shape element that is the farthest from the base on the light exit surface is increased or constant from the side of the end of the unit shape element on the light exit surface. Yes,
A distance h along the normal direction of the main body portion of the lens sheet from the lens sheet to the light emitting portion of the light source at the main cutting surface of the lens sheet;
In the main cut surface of the lens sheet, a distance k along the arrangement direction of the unit lenses between two adjacent light emitting portions, and
The refractive index n of the material forming the lens sheet;
The lens surface angle γ at the end of the unit lens;
A refractive index n2 of the material forming the optical sheet;
The surface light source device according to claim 7 or 8, wherein a light exit surface angle θe at an end of the unit shape element satisfies the following expressions (C) to (F).
-10 ° ≦ (θe)-Arcsin ((n2) × sin ((θe)-(θia2))) ≦ 10 ° ・ ・ ・ Formula (C)
(θia2) = Arcsin ((1 / (n2)) × (sin (θi2))) (Equation (D)
(θi2) = γ- Arcsin (n × sin (γ- (θia1))) ・ ・ ・ Equation (E)
(θia1) = Arcsin ((1 / n) × (sin (Arctan (k / 2 / h)))) ・ ・ ・ Formula (F) A second optical sheet disposed on the light exit side of the optical sheet,
The surface light source device according to claim 7, wherein the second optical sheet has a haze value of 10 or more and 90 or less.   The surface light source device according to claim 7, further comprising a polarization separation sheet disposed on the light output side of the optical sheet.   The light source includes a plurality of light emitting units arranged in a direction parallel to the arrangement direction of the unit lenses of the lens sheet, and each light emitting unit extends in a direction intersecting with the arrangement direction. The surface light source device as described in any one of -11. A surface light source device according to any one of claims 6 to 12,
A transmissive display unit disposed to face the surface light source device.

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