JP5293177B2 - Optical sheet, surface light source device and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which effectively improves the front direction luminance by improving efficiency of using optical source light. <P>SOLUTION: The optical sheet 40 includes a body part 42 and a plurality of unit shape elements 45 which are arranged side by side on the outgoing side of the body part and are respectively linearly extended in the directions crossing the arrangement direction. Each unit shape element includes a pair of side surfaces 47 which are extended from the body part and approach each other as being separated from the body part. Each unit shape element has a plurality of unit lenses 55 which are arranged side by side in the longitudinal direction of the unit shape element and are respectively extended in the directions of combining the pair of side surfaces to each other. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an optical sheet, a surface light source device, and a display device that can effectively improve the luminance in the front direction by improving the utilization efficiency of light source light.

  A surface light source device used for a transmissive display device includes a light source and a large number of optical sheets (optical films) for changing the traveling direction of light from the light source. Among the optical sheets, a light diffusing sheet that diffuses light from the light source and hides the image of the light source (makes it inconspicuous), and a light collection that narrows the light traveling direction to the front direction and improves the brightness in the front direction Sheet. Then, a surface light source device is configured by appropriately combining a light diffusing sheet whose degree of light diffusing performance is adjusted and a light collecting sheet whose degree of light condensing performance is adjusted, thereby having a desired front direction luminance. At the same time, a transmissive display device having a desired viewing angle and an inconspicuous light source image can be obtained.

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, a unit prism having a triangular cross section (main cut surface) perpendicular to the longitudinal direction, typically an apex angle of 90 ° and an isosceles triangle shape is known. It has been.
Japanese National Patent Publication No. 10-506500

  By the way, in the display device, the value of the luminance in the front direction is one of the most important evaluation items. The condensing sheet disclosed in Patent Document 1 can exhibit a condensing function due to the cross-sectional shape of the unit shape element. However, in the present situation, there is a demand for further improvement in front direction luminance. Further, not only the design of the light condensing sheet but also improvement of the luminance in the front direction has been studied not only by the combination of other members, for example, the specification of the light diffusing sheet and the configuration of the light source.

  In recent years, along with the social trend in which environmental issues are regarded as important, improving the utilization efficiency of light source light has been taken up as an important issue for transmissive display devices (typically liquid crystal display devices). ing. And it is very preferable if the luminance in the front direction of the display device can be improved with the improvement of the utilization efficiency of the light source light.

  The present invention has been made in consideration of such points, and an object thereof is to provide an optical sheet that can effectively improve the luminance in the front direction by improving the utilization efficiency of the light source light. It is another object of the present invention to provide a surface light source device and a display device that can effectively improve the luminance in the front direction by improving the utilization efficiency of the light source light.

  As a result of repeating various experiments, the present inventors can impart a sufficient polarization separation function to an optical sheet in which a plurality of unit shape elements (unit lenses, unit prisms) are arranged in a linear array, And it discovered that the utilization efficiency of light source light was improved by using this polarization | polarized-light separation function effectively, and, thereby, front direction brightness | luminance can be improved effectively. Specifically, a specific polarization component (for example, P wave) out of light incident on the light exit surface of the unit shape element at an incident angle that is emitted in the front direction due to refraction at the light exit surface of the unit shape element The transmittance of other polarization components (for example, S wave) other than the specific polarization component can be decreased (the reflectance can be increased), thereby improving the transmittance of the transmissive display unit. It has been found that it is possible to increase the utilization efficiency of the light source light and effectively improve the brightness in the front direction in combination with the above. The present invention is based on such knowledge of the present inventors.

  An optical sheet according to the present invention includes: a sheet-like main body portion; and a plurality of unit-shaped elements that are arranged side by side on the light output side of the main body portion and each extend linearly in a direction intersecting the arrangement direction. The unit shape element includes a pair of side surfaces extending from the main body portion, and includes a pair of side surfaces that approach each other as the unit shape element is separated from the main body portion, and each unit shape element includes a longitudinal direction of the unit shape element. A plurality of unit lenses arranged side by side, each having a plurality of unit lenses extending in a direction connecting the pair of side surfaces.

  In the optical sheet according to the present invention, in a cross section parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, to the end on the side surface of the unit shape element closest to the main body portion The angle formed by the tangent to the sheet surface of the main body may be 55 ° or more and 75 ° or less.

  Further, in the optical sheet according to the present invention, in the cross section parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, the side surface is at least the unit shape element closest to the main body portion. Extending from the end on the side surface to a position deviated by 15% of the width of the unit-shaped element in a direction parallel to the sheet surface of the main body, and the normal direction of the main body In the cross section parallel to both the arrangement direction of the unit shape elements, the unit shape in a direction parallel to the sheet surface of the main body portion from the end on the side surface of the unit shape element closest to the main body portion. An angle formed by a tangent line contacting the side surface of the unit-shaped element at a position shifted by a length of 15% of the element width with respect to the sheet surface of the main body may be 40 ° or more. .

  Furthermore, in the optical sheet according to the present invention, in a cross section parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, a tangent to the side surface of the unit shape elements is a sheet surface of the main body portion. The contact angle of the tangent to the unit-shaped element is from one end on the side surface closest to the main body, and the other end on the side surface farthest from the main body. You may make it become small as it goes to a part.

  A surface light source device according to the present invention includes a light source and any one of the optical sheets according to the present invention that receives light from the light source.

  The surface light source device according to the present invention further includes a light collecting sheet arranged on the light incident side of the optical sheet, and the light collecting sheet is arranged side by side on the light emitting side of the main body and the sheet-like main body. A plurality of unit shape elements each extending linearly in a direction intersecting the arrangement direction, and the light source has a linear light emitting portion, and the unit shape elements of the light collecting sheet The arrangement direction may be orthogonal to the longitudinal direction of the light emitting portion of the light source and may intersect the arrangement direction of the unit shape elements of the optical sheet. In such a surface light source device, in the main cutting surface of the light collecting sheet parallel to both the normal direction of the main body portion of the light collecting sheet and the arrangement direction of the unit shape elements of the light collecting sheet, the main body 1. The width of the unit shape element of the light collecting sheet parallel to the sheet surface of the portion is 1.8 times or more the height of the unit shape element of the light collecting sheet along the normal direction of the main body portion. It may be 3 times or less.

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

  In the surface light source device according to the present invention, the transmissive display unit includes a lower polarizing plate and an upper polarizing plate disposed on the light output side of the lower polarizing plate, and the transmission axis of the lower polarizing plate is the optical axis. The sheet may be parallel to the arrangement direction of the unit shape elements of the sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

  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 8 are views for explaining an embodiment according to the present invention. Among these, FIG. 1 is a perspective view showing a schematic configuration of a transmissive display device and a surface light source device. FIG. 2 is a perspective view showing the optical sheet. 3, 4, 5 and 7 are cross-sectional views showing the optical sheet. FIG. 6 is a graph showing the transmittance at each light exit surface angle for light incident on the light exit surface of the unit shape element at an angle that can be emitted in the front direction by refraction at the light exit surface. FIG. 8 is a cross-sectional view of the main cutting surface showing the condensing sheet.

  The transmissive display device 10 shown in FIG. 1 includes a transmissive display unit 15, 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, It has. 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 panel (liquid crystal cell). That is, the transmissive display device 10 functions as a liquid crystal display device. The liquid crystal 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 decompose the incident light into two orthogonal polarization components (P wave and S wave) and transmit the polarization component (for example, P wave) in one direction (direction parallel to the transmission axis). And has a function of absorbing a polarization component (for example, S wave) in the other direction (direction parallel to the absorption axis) perpendicular to the one direction.

  An electric field can be applied to the liquid crystal layer 18 for each region where one pixel is formed. Then, the orientation of the liquid crystal layer 18 applied with an electric field changes. Polarized light in a specific direction (in this embodiment, P wave) transmitted through the lower polarizing plate 16 disposed on the light incident side is rotated by 90 ° when passing through the liquid crystal layer 18 to which an electric field is applied. The polarization direction is maintained when passing through the liquid crystal layer 18 to which no electric field is applied. For this reason, depending on whether or not an electric field is applied to the liquid crystal layer 18, the polarized light (P wave) in a specific direction transmitted through the lower polarizing plate 16 further transmits through the upper polarizing plate 17 disposed on the light output side of the lower polarizing plate 16. Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 17.

  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 optical sheet 40 and the like without folding the traveling direction. 5 and FIG. 7, the “light incident side” is the upstream side in the traveling direction of light from the light source 25 to the observer through the optical sheet 40 and the like without folding the traveling direction. (The lower side in FIG. 2 to FIG. 5 and FIG. 7).

  Next, the surface light source device 20 will be described. As shown in FIG. 1, the surface light source device 20 includes a light source 25 and an optical sheet 40 that transmits light from the light source 25. In this Embodiment, the optical sheet 40 is arrange | positioned at the most light emission side of the surface light source device 20, and comprises a light emission surface (light emission surface). The optical sheet 40 is adjacent to the lower polarizing plate 16 of the transmissive display unit 15. In the example illustrated in FIG. 1, a light collecting sheet (also referred to as a light incident side optical sheet) 30 that is disposed on the light incident side of the optical sheet 40 and collects light, and a light incident side of the light collecting sheet 30. And a light diffusion sheet 28 that diffuses light is further provided.

  The surface light source device 20 may be configured in various forms such as an edge light (side light) type, but is configured as a direct type backlight unit in the present embodiment. Therefore, the light source 25 is disposed so as to face the optical sheet 40 on the light incident side of the optical sheet 40. The light source 25 is 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 optical sheet 40 side.

  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.

  In the present embodiment, the light source 25 has a plurality of light emitting portions 25a extending linearly. The linear light emitting portions 25a are arranged side by side so that their longitudinal directions are parallel to each other. The light emitting unit 25a can be configured by a fluorescent lamp such as a linear cold cathode tube, for example. However, the light source 25 is not limited to this example, and the light source 25 may include various types of light emitting units such as a point LED (light emitting diode), an incandescent light bulb, and a planar EL (electroluminescent).

  As shown in FIG. 1, the reflecting plate 22 is a member for directing light from the light source 25 toward the optical sheet 40. At least the inner surface of the reflecting plate 22 is made of a material having a high reflectance such as metal.

  Next, the light diffusion sheet 28 will be described. The light diffusion sheet 28 diffuses incident light, preferably isotropically diffuses incident light, alleviates luminance unevenness (also referred to as tube unevenness) according to the configuration of the light source 25, and makes the in-plane distribution of luminance uniform. This is a sheet-like member for making the image of the light source 25 inconspicuous. As such a light diffusion sheet 28, a sheet including a base portion and light diffusing particles dispersed in the base portion and having a light diffusion function may be used. As an example, by configuring the light diffusing particles from a material having a high reflectance, or by configuring the light diffusing particles from a material having a refractive index different from the material forming the base, A light diffusion function can be imparted.

  Next, the light collecting sheet 30 will be described. As shown in FIGS. 1 and 8, the light collecting sheet 30 includes a sheet-like main body portion 32 and a lens portion 34 positioned on the light output side of the main body portion 32. The lens unit 34 includes a large number of unit-shaped elements (unit optical elements) 35 arranged side by side on the light exit side surface 32 a of the sheet-like main body 32. This condensing sheet 30 has a function (condensing function) for intensively improving the brightness in the front direction (normal direction) nd by changing the traveling direction of the light incident from the light incident side to be emitted from the light exit side. Have.

  The unit shape elements 35 are arranged side by side on the light output side surface 32 a of the main body portion 32. As shown in FIG. 1, the unit shape elements 35 extend linearly in a direction intersecting with the arrangement direction of the unit shape elements 35. In the present embodiment, the unit shape element 35 extends linearly. The longitudinal direction of the unit shape elements 35 is orthogonal to the arrangement direction of the unit shape elements 35 on a plane parallel to the sheet surface of the main body portion 32. As shown in FIG. 1, in the present embodiment, the arrangement direction of the unit shape elements 35 is orthogonal to the longitudinal direction of the light emitting section 25a of the light source 25, and the longitudinal direction of each unit shape element 35 is the longitudinal direction of each light emitting section 25a. It is parallel to.

  As shown in FIG. 8, in the present embodiment, a cut surface parallel to both the normal direction nd of the main body 32 and the arrangement direction of the unit shape elements 35 (also referred to as “main cutting surface of the light collecting sheet”). The cross-sectional shape of each unit shape element 35 is constant along the longitudinal direction of the unit shape element 35 (direction extending linearly). Further, the plurality of unit shape elements 35 forming the lens portion 34 are all configured similarly. In the illustrated example, the unit shape element 35 has a shape corresponding to a part of an ellipse or a part of a circle on the main cutting surface of the light collecting sheet. However, the configuration is not limited to the illustrated example, and the configuration of the unit shape element 35 may be appropriately changed according to the configuration of the surface light source device 20 other than the light collecting sheet 30, for example, the configuration of the light source 25.

  As a specific example of the unit shape element 35 having the above-described configuration, the width W (see FIG. 8) of the unit shape element 35 can be set to 1 μm to 200 μm. Further, the projection height H (see FIG. 8) of the unit shape element 35 from the light exit side surface 32a of the main body 32 along the normal direction nd to the sheet surface of the light collecting sheet 30 is set to 0.25 μm to 50 μm. Can do. In addition, when the present inventors repeated experiments, the width W of the unit shape element 35 of the light collecting sheet 30 along the direction parallel to the sheet surface of the main body portion 32 on the main cutting surface of the light collecting sheet It is preferable that the height H is 1.8 times or more and 2.3 times or less of the height H of the unit shape element from the main body part 32 along the normal direction nd of the part 32 in the combination with the optical sheet 40 described later. It was discovered. This is because when the width W of the unit shape element 35 and the height H of the unit shape element 35 are set outside this range, the luminance in the front direction is significantly reduced.

  In the present 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 as a whole and globally. Refers to the surface. And in this Embodiment, the sheet surface of the main-body part 32 of the condensing sheet 30, the sheet surface of the main-body part 42 of the optical sheet 40 mentioned later, the sheet surface of the light-diffusion sheet 28, the light emission surface of the surface light source device 20, The display surface of the transmissive display device 10 is parallel to each other. Further, in the present application, the “front direction” is the normal direction nd (see, for example, FIG. 3) with respect to the sheet surface of the optical sheet 40, and the normal direction of the sheet surface of the light collecting sheet 30 and the surface light source device 20. This also coincides with the normal direction of the light emitting surface.

  Next, the optical sheet 40 will be described. As shown in FIGS. 1 and 2, the optical sheet 40 has substantially the same configuration as the light collecting sheet 30 described above except that a unit lens 55 described later is provided. The optical sheet 40 includes a sheet-like main body portion 42 and a lens portion 44 located on the light output side of the main body portion 42. The lens unit 44 has a large number of unit shape elements (unit optical elements, unit lenses) 45 arranged side by side on the light exit side surface 42 a of the sheet-like main body unit 42. In the present embodiment, the unit shape elements 45 are arranged on the light exit side surface 42 a of the main body 42 without 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.

  As will be described later, the optical sheet 40 selectively transmits a specific polarization component (in this embodiment, a P wave) out of transmitted light that is refracted and emitted in the front direction. It has a polarization separation function of selectively reflecting a polarization component other than a specific polarization component (S wave in this embodiment). Further, in the present embodiment, the optical sheet 40 changes the traveling direction of the light incident from the light incident side and emits the light from the light output side in the same manner as the light collecting sheet 30, and the front direction (normal direction) nd It also has a function for concentrating the brightness of light (condensing function).

  3 and 4 are cross sections parallel to both the normal direction nd of the sheet surface of the main body 42 of the optical sheet 40 and the arrangement direction of the unit shape elements 45 (hereinafter referred to as “first main cutting surface of the optical sheet”). The optical sheet 40 is shown in FIG. The cross section shown in FIGS. 3 and 4 also corresponds to the cross section taken along the line III-III in FIG.

  As shown in FIGS. 2 to 4, the main body 42 functions as a sheet-like member that supports the unit shape element 45. As shown in FIGS. 3 and 4, in the present embodiment, unit-shaped elements 45 are arranged side by side on the light output side surface 42 a of the main body 42 without a gap, and a lens portion 44 is formed on the main body 42. doing. On the other hand, as shown in FIGS. 3 and 4, in the present embodiment, the main body 42 is a flat (flat) that forms the light incident surface 40b of the optical sheet 40 as the light incident side surface 42b that faces the light output side surface 42a. ) Has a smooth surface.

  As used herein, “smoothing” means smoothing in an optical sense. That is, here, it means the degree that a certain percentage of visible light is refracted while satisfying Snell's law on the light incident surface 40b of the optical sheet 40 (light incident side surface 42b of the main body 42). Yes. Therefore, for example, if the ten-point average roughness Rz (JISB0601) of the light incident side surface 42b of the main body 42 (light incident surface 40b of the optical sheet 40) is equal to or shorter than the shortest visible light wavelength (0.38 μm), It is sufficiently smooth.

  Next, the unit shape element 45 will be described in detail. As shown in FIG. 2, the unit shape elements 45 extend linearly in a direction intersecting with the arrangement direction of the unit shape elements 45. 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 main body 42. As shown in FIG. 1, in the present embodiment, the arrangement direction of the unit shape elements 45 is parallel to the longitudinal direction of the light emitting portion 25a of the light source 25, and the longitudinal direction of each unit shape element 45 is the longitudinal direction of each light emitting portion 25a. It is orthogonal to the direction. As shown in FIG. 1, in the present embodiment, the arrangement direction of the unit shape elements 45 of the optical sheet 40 is orthogonal to the arrangement direction of the unit shape elements 35 of the light collecting sheet 30. Further, in the present embodiment, the arrangement direction of the unit shape elements 45 of the optical sheet 40 is parallel to the transmission axis of the lower polarizing plate 16 of the transmissive display unit 15.

  As shown in FIG. 1, in the present embodiment, the plurality of unit shape elements 45 forming the lens portion 44 of the optical sheet 40 are all configured similarly. As shown in FIG. 2, each unit shape element 45 has a pair of side surfaces 47 and 47 extending from the main body portion 42. The pair of side surfaces 47 and 47 approach each other as they are separated from the main body portion 42. The inclination angle of the main body portion 42 of each side surface 47 with respect to the sheet surface is constant without changing in the longitudinal direction of the unit shape element 45.

  Further, as shown in FIG. 2, each unit shape element 45 includes a large number of unit lenses (unit prisms) 55 arranged in a longitudinal direction of the unit shape element 45 and disposed between a pair of side surfaces 47, 47. Have. FIG. 5 is a cross section taken along the line V-V in FIG. 2, and is a cross section parallel to both the normal direction nd of the sheet surface of the main body 42 of the optical sheet 40 and the arrangement direction of the unit lenses 55 (hereinafter referred to as “cross section”). , Also referred to as “second main cut surface of the optical sheet”), the optical sheet 40 is shown. 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. 5, each unit lens 55 extends in a direction connecting the pair of side surfaces 47 and 47. In particular, in the present embodiment, each unit lens 55 extends in a direction orthogonal to the arrangement direction of the unit shape elements 45 of the optical sheet 40. That is, each unit lens 55 extends in a direction parallel to the arrangement direction of the unit shape elements 35 of the light collecting sheet 30 and the arrangement direction of the light emitting portions 25 a of the light source 25.

  As shown in FIG. 2, the unit lens 55 forms the top portion on the most light-emitting side, which is the farthest from the main body portion 42 among the unit shape elements 45. The plurality of unit lenses 45 are arranged side by side with no gap.

  Each unit lens 45 is connected to each of a pair of side surfaces 47 at both ends thereof. As a result, in the present embodiment, the light exit surface 45 a of the unit shape element 45, that is, the light exit surface 40 a of the optical sheet 40 is a pair of side surfaces 47, 47 and a light exit surface (prism surface, Lens surface) 57.

  In the present embodiment, the outer contour of each unit shape element 45 is symmetric about a plane parallel to both the normal direction nd of the main body 42 and the longitudinal direction of the unit shape element 45. Thereby, the luminance on the light exit surface 40a of the optical sheet 40 has a symmetrical angular distribution of luminance about the front direction on the surface parallel to the arrangement direction of the unit shape elements 45.

  Below, the cross-sectional shape in the 1st main cutting surface and the 2nd main cutting surface of the unit shape element 45 contained in the optical sheet 40 is demonstrated in detail.

  As shown in FIGS. 3 and 4, in the present embodiment, the cross-sectional shape of each unit-shaped element 45 on the first main cut surface of the optical sheet is a shape that tapers toward the light output side. Therefore, in the first main cut surface of the optical sheet, the width of the unit-shaped element 45 parallel to the sheet surface of the main body portion 42 becomes narrower as it is separated from the main body portion 42 along the normal direction nd of the main body portion 42. Go. As described above, the top portion of the unit shape element 45 located closest to the light output side is formed by the unit lens 55. A pair of side surfaces 47 and 47 extend from the main body 42 to the unit lens 55. For this reason, the pair of side surfaces 47 and 47 come closer to each other as they are separated from the main body portion 42.

  As shown in FIGS. 3 and 4, in the first main cut surface of the optical sheet, each side surface 47 of the unit shape element 45 is configured by an arc (arc or elliptical arc) or a combination of a plurality of arcs. ing. When this combination defines the contour of each side surface 47 of the unit-shaped element 45 in the first main cut surface of the optical sheet, two adjacent arcs joined together are tangents common to the joined portions. It is preferable to have. In this case, the angular distribution of luminance on the light exit surface 40a of the optical sheet 40 can be changed gently, and the brightness can be prevented from changing abruptly (cutoff occurs) when the observation direction is changed. This is because it can be done.

  On the other hand, as shown in FIG. 5, the cross-sectional shape of the unit lens 55 is a triangular shape on the second main cut surface of the optical sheet. The triangle forming the cross-sectional shape of the unit lens 55 on the second main cut surface of the optical sheet is preferably an isosceles triangle. This is because the luminance angle distribution has symmetry with respect to the front direction on a plane parallel to the arrangement direction of the unit lenses 55.

  Next, an angle formed by the tangent TL to the light exit surface 45a of the unit shape element 45 with respect to the sheet surface of the main body portion 42 (in the present embodiment, the light exit side surface 42a of the main body portion 42) in the main cut surface (“light exit”). Θa) (also referred to as “surface angle”) will be described. First, the light exit surface angle θa of the side surface 47 of the unit shape element 45 will be described.

  As shown in FIG. 3, in the present embodiment, the contact TP on the side surface 47 of the unit shape element 45 of the tangent line TL is on the side surface 47 adjacent to the main body 42 in the first main cut surface of the optical sheet. The light exit surface angle θa of the side surface 47 becomes smaller from one end portion (first end portion) 47a1 toward the other end portion (second end portion) 47a2 on the side surface farthest from the main body portion 42. . Here, the light exit surface angle θa is “becomes smaller” only when the light exit surface angle θa is constantly changing (an aspect in the present embodiment shown in FIGS. 3 and 4). In other words, the concept includes a case where the light exit surface angle θa does not change in at least a part of the region. That is, here, the light exit surface angle θa is “decreasing” when the contact point TP is directed from the first end portion 47a1 on the side surface 47 to the end portion 47a2 on the side surface 47. It means "do not grow".

  The light exit surface angle θa on the side surface 47 of the unit shape element 45 is preferably set as follows based on the research results of the present inventors. First, on the first main cut surface of the optical sheet, the light exit surface angle (“light exit surface bottom”) formed by the tangent TL to the first end 47a1 on the side surface 47 of the unit-shaped element 45 with respect to the sheet surface of the main body 42. Θaa) is also preferably 55 ° or more, and more preferably 65 ° or more. When this inventor confirmed, when the light emission surface bottom angle | corner (theta) aa was 55 degrees or more, the front direction brightness | luminance was able to be raised to such an extent that it can confirm visually. In addition, when the light exit surface bottom angle θaa of the unit shape element 45 is 65 ° or more, the front direction luminance can be increased more remarkably. On the other hand, as an upper limit, the light exit surface bottom angle θaa on the side surface 47 of the unit shape element 45 is preferably 75 ° or less. The front luminance can be increased by increasing the light exit surface bottom angle θaa, but if the light output surface bottom angle θaa is excessively increased, the front luminance increases and further the front luminance decreases. I will do it. Further, if the light exit surface bottom angle θaa is excessively increased, the spectral distribution of transmitted light becomes non-uniform, and the color reproducibility of the display device 10 is degraded.

  Further, in the first main cut surface of the optical sheet, the side surface 47 is at least from the end portion (first end portion 47a1 of the side surface 47) of the light exit surface 45a of the unit-shaped element 45 closest to the main body portion 42. It is preferable to extend to a position shifted by 15% of the width of the unit shape element 45 in a direction parallel to the sheet surface. In addition to this configuration, in the first main cut surface of the optical sheet, the width of the unit shape element 45 from the first end 47a1 on the side surface 47 of the unit shape element 45 in the direction parallel to the sheet surface of the main body 42. It is preferable that a tangent line TL that contacts the side surface 47 of the unit shape element 45 at a position shifted by a length of 15% of the angle forms an angle θa of 40 ° or more with respect to the sheet surface of the main body portion 42. That is, the side surface 47 of the unit shape element 45 at a position shifted from the first end 47a1 of the unit shape element 45 by a length of 15% of the width of the unit shape element 45 in the direction parallel to the sheet surface of the main body 42. The light exit surface angle θa is preferably 40 ° or more.

  As a result of extensive research conducted by the inventors of the present invention, as will be described in detail later, the polarization separation function capable of ensuring an increase in luminance in the front direction that can be visually determined is when the light exit surface angle θa is 40 ° or more. there were. Further, when the light exit surface angle θa is 40 ° or more in an area of 30% or more of the display area, the display device 10 can visually recognize the increase in front luminance.

  As a specific example of the unit shape element 45 configured as described above, the width of the unit shape element 45 on the first main cut surface of the optical sheet can be 1 μm to 200 μm. Moreover, the protrusion height of the unit shape element 35 from the light emission side surface 42a of the main-body part 42 along the normal line direction nd to the sheet | seat surface of the optical sheet 40 can be 0.25 micrometer-50 micrometers. The width of the unit lens 55 on the first main cutting surface of the optical sheet can be set to 30% to 70% of the width of the unit shape element 45 on the first main cutting surface of the optical sheet.

  The condensing sheet 30 and the optical sheet 40 having the above-described configuration can be manufactured by shaping the unit shape elements 35 and 45 on the base material. Moreover, the condensing sheet 30 and the optical sheet 40 can be produced by performing molding again using a molded product molded using a mold as a mold.

  Various materials can be used as the material forming the light collecting sheet 30 and the optical sheet 40. 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. In the case where a material widely used as a material for an optical sheet (light collecting sheet) incorporated in such a display device is used, refraction of the unit shape elements 45 and 35 of the produced optical sheet 40 and the light collecting sheet 30 is performed. The rate is in the range of 1.45 to 1.60.

  Next, operations of the optical sheet 40, the surface light source device 20, and the transmissive display device 10 as described above will be described.

  First, the overall operation of the transmissive 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 viewer side is isotropically diffused by the light diffusion sheet 28 and then enters the light collecting sheet 30.

  As shown in FIG. 8, the lights L <b> 81 and L <b> 82 emitted from the unit shape element 35 of the light collecting sheet 30 are refracted on the light exit surface (lens surface) of the unit shape element (unit lens) 35. Due to this refraction, the traveling direction (outgoing direction) of the light L81 and L82 traveling in the direction inclined from the front direction nd is mainly compared with the traveling direction of the light just before entering the condensing sheet 30. Is bent so that the angle with respect to the normal direction nd to the sheet surface becomes small. By such an action of the light collecting sheet, the unit shape element 35 can narrow the traveling direction of the transmitted light to the front direction nd side. That is, the unit shape element 35 has a condensing effect on the transmitted light.

  Note that such a light collecting action of the unit shape element 35 is effectively exerted on light that is greatly inclined from the front direction nd. Therefore, although depending on the degree of diffusion by the light diffusion sheet 28 disposed on the light source side with respect to the light collecting sheet 30, a large amount of light tends to enter from the light emitting portion 25 a of the light source 25 at a large incident angle. The brightness in the front direction can be effectively increased in a region away from the light emitting part 25a of a certain light source 25 (see light L82 in FIG. 8).

  On the other hand, as shown in FIG. 8, the light L83 having a small inclination angle in the traveling direction with respect to the front direction nd repeats total reflection on the light exit surface (lens surface) of the unit-shaped element 35, and the traveling direction is changed to the light incident side. It may change to (light source side). For this reason, depending on the degree of diffusion by the light diffusion sheet 28 disposed on the light source side of the light collecting sheet 30, a large amount of light tends to enter from the light source 25 at a small incident angle. It is possible to prevent the luminance from becoming too high at the position immediately above.

  As described above, the optical action mainly exerted from the unit shape element 35 on the transmitted light is different depending on the separation distance of the light source 25 from the light emitting portion 25a. Thereby, the luminance unevenness (tube unevenness) generated according to the arrangement of the light emitting portions 25a of the light source 25 can be effectively reduced, and the light source image (light image) can be made inconspicuous. That is, the light collecting sheet 30 also has a light diffusing function for making the in-plane variation in luminance uniform. In such a light diffusion function, the condensing sheet 30 is arranged with respect to the light source 25 so that the arrangement direction of the unit-shaped elements 35 of the condensing sheet 30 and the longitudinal direction of the light emitting portion 25a of the light source 25 intersect. It comes to be demonstrated by this. Further, as shown in FIG. 1, such a light diffusing function is performed so that the arrangement direction of the unit shape elements 35 of the light collecting sheet 30 and the longitudinal direction of the light emitting portion 25a of the light source 25 are orthogonal to each other, that is, the light collecting function. By arranging the condensing sheet 30 with respect to the light source 25 so that the arrangement direction of the unit-shaped elements 35 of the light sheet 30 and the arrangement direction of the arc tube 25a of the light source 25 are parallel to each other, it is effectively exhibited. Become so.

  As described above, the emission angle of the light emitted from the light collecting sheet 30 is narrowed down to a narrow angle range centering on the front direction on a plane parallel to the arrangement direction of the unit shape elements 35 of the light collecting sheet 30. .

  The light emitted from the light collecting sheet 30 then enters the optical sheet 40. In the optical sheet 40, one polarization component of the light emitted from the optical sheet 40 in the normal direction nd and incident on the transmissive display unit 15 at an incident angle of 0 °, in this embodiment, the transmittance of the P wave On the other hand, the transmittance of the other polarization component, that is, the S wave in the present embodiment, is lowered. That is, in the optical sheet 40, the polarization separation effect is exerted on the light collected by the light collecting sheet 30. This polarization separation action will be described in detail later. Note that light that does not pass through the optical sheet 40 is reflected by the optical sheet 40, and most of the reflected light has its traveling direction directed to the light incident side. The light returned to the incident light side is further reflected to change its polarization state (for example, the S wave becomes a P wave), and enters the optical sheet 40 again to be used. obtain.

  Note that the light transmitted through the optical sheet 40 is refracted at the light exit surface 40a of the optical sheet 40 (in this embodiment, the light exit surface 45a of the unit shape element 45), similarly to the light transmitted through the light collecting sheet 30. It mainly comes to have a light collecting effect. Thereby, as will be described below, it is possible to further increase the luminance in the front direction.

  First, the light exit surface (prism surface, lens surface) 57 of the unit lens 55 in the light exit surface 45a of the unit shape element 45 proceeds mainly in parallel with the second main cut surface of the optical sheet, as shown in FIG. The light condensing action is exerted on the light components L51 and L52. In addition, by appropriately setting the light exit surface angle θa of the light exit surface 57 of the unit lens 55, not only the light collecting action but also the above-described light component that travels in parallel with the second main cut surface of the optical sheet. In the same manner as the light collecting sheet 30, an action (light diffusing action) for making the in-plane distribution of luminance due to the configuration of the light source 25 uniform can also be exerted.

  However, in the present embodiment, the component of light mainly exerting an optical action from the unit lens 55 of the optical sheet 40 is the same as the component condensed by the condensing sheet 30. That is, most of the light incident on the light exit surface 57 of the unit lens 55 of the optical sheet 40 is light that has a traveling direction within a narrow angle range centered on the front direction. As a result, in the present embodiment, it is not necessary to give the unit lens 55 of the optical sheet 40 a strong condensing function or a strong light diffusion function, and as shown in FIG. Setting a small angle is sufficient.

  The arrangement direction of the unit lenses 55 (the arrangement direction of the unit shape elements 35 of the light collection sheet 30) by the light collection action by the unit lenses 55 of the unit shape elements 45 combined with the light collection action by the light collection sheet 30 as described above. The luminance in the front direction of the angular distribution of luminance in a plane parallel to the surface can be increased very effectively.

  On the other hand, the side surface 47 of the light exit surface 45a of the unit shape element 45 mainly exerts a condensing action on the light component (light L32 in FIG. 3) traveling in parallel with the first main cut surface of the optical sheet. That is, the side surface 47 of the unit shape element 45 exerts a light condensing effect on the light that cannot be exerted by the light condensing sheet 30. As a result, the luminance in the front direction of the angular distribution of luminance in a plane parallel to the arrangement direction of the unit shape elements 45 (longitudinal direction of the unit shape elements 35 of the light collecting sheet 30) can be effectively increased.

  The light emitted from the optical sheet 40 enters the lower polarizing plate 16 of the transmissive display unit 15. The lower polarizing plate 16 transmits one polarization component (P wave in this embodiment) of incident light and absorbs the other polarization component (S wave in this embodiment). 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.

  As described above, the luminance in the front direction on the light exit surface of the surface light source device 20 is enhanced by the light collecting action by the light collecting sheet 30 and the light collecting action by the optical sheet 40. Furthermore, due to the polarization separation function of the optical sheet 40, the polarization component (P wave) that can enter the lower polarizing plate 16 of the transmissive display unit 15 is incident on the light incident on the transmissive display unit 15 while traveling in the front direction. ) Is included at a high ratio, while the polarization component (S wave) absorbed by the lower polarizing plate 16 of the transmissive display unit 15 is included only at a low ratio. That is, in the light emitted in the normal direction nd of the main body 42 in a plane parallel to the arrangement direction of the unit shape elements 45 of the optical sheet 40, a component that can be used for forming an image on the transmissive display unit 15 is included. High percentage is included. That is, in the display device 10 according to the present embodiment, the unit shape elements 35 and 45 not only have a function of changing the traveling direction of light within a narrow angle range centered on the front direction (light collecting function), but also the front direction. By improving the use efficiency of the light source light by the polarization separation function of the optical sheet 40 with respect to the light to be emitted to the light, the front direction luminance can be increased extremely effectively.

  Here, the action exerted by the optical sheet 40 will be described in more detail.

  It is widely known that the reflectance at the interface and the transmittance at the interface change depending on the incident angle to the interface (the angle formed by the normal of the interface and the incident light) (for example, "Refractive index (by Shigeo Yamaguchi)", published by Kyoritsu Shuppansha) At this time, the P wave and the S wave, which are polarization components, exhibit different transmittances (reflectances). The behavior of the transmittance (reflectance) variation according to the incident angle also depends on the refractive index on both sides of the interface.

  On the other hand, the present inventors have studied to improve the utilization efficiency of the display device 10 using such characteristics. First, attention was focused on the light (see the light L31 in FIG. 3 and the light L41 in FIG. 4) refracted on the light exit surface of the optical sheet and emitted in the front direction. This is because the luminance in the front direction of the display device 10 can be directly improved if the utilization efficiency of the light emitted in the front direction in the transmissive display unit 15 can be improved.

  Specifically, the inventors of the present invention make the light L31, L41, L51 incident on the transmittance of the light L31, L41, L51 that is refracted at the light exit surface of the optical sheet and exits from the optical sheet in the front direction. Investigation was performed while changing the angle (light exit surface angle) θa formed by the light exit surface and the sheet surface of the optical sheet. As a result, if the refractive index is within the range of 1.45 or more and 1.60 or less of an inexpensive material that is widely used, the difference in refractive index is the exit surface angle of the transmittance of outgoing light in the front direction. The change behavior according to the light exit surface angle of the outgoing light transmittance in the front direction is almost the same even if the refractive index of the material forming the optical sheet changes. That was confirmed. As an example of the change behavior of the transmittance of outgoing light in the front direction according to the light exit surface angle, the results of an investigation conducted using the above-described optical sheet 40 made of a material having a refractive index of 1.49 are shown in FIG. .

  In addition, about the light which refracts by the unit shape element 45 and radiate | emits a front direction after injecting into the optical sheet 40, the following formula | equation (1)-Formula (3) are formed. Here, the angles θa, θ1, θ2, θ3, and θ4 in the equations (1) to (3) are as shown in FIG. That is, θ4 is an incident angle to the optical sheet 40 (the inclination angle of light with respect to the normal direction of the incident surface to the optical sheet 40 (in the present embodiment, the normal direction of the sheet surface of the main body portion 42)). is there. θ3 is an inclination angle when passing through the main body 42. θ2 is the incident angle of the unit shape element 45 with respect to the light exit surface 45a (the inclination angle of the light incident direction with respect to the normal direction of the light exit surface 45a of the unit shape element 45). θ1 is an emission angle of the unit shape element 45 with respect to the light output surface 45a (an inclination angle of the light emission direction with respect to the normal direction of the light output surface 45a of the unit shape element 45). Further, n in the formula is the value of the refractive index of the material forming the optical sheet (unit shape element and main body).

θa = θ1 = θ2 + θ3 (1)
sin (θ4) = n × sin (θ3) (2)
n × sin (θ2) = sin (θ1) (3)

  Then, by modifying the expressions (1) to (3), the incident angle θ4 to the optical sheet 40, the inclination angle θ3 when passing through the main body 42, and the incident angle of the unit shape element 45 with respect to the light exit surface 45a θ2 and the exit angle θ1 of the unit shape element 45 with respect to the light exit surface 45a can be specified using the light exit surface angle θa as shown in the following equations (4) to (7).

θ1 = θa (4)
θ2 = Arcsin (sin (θ1) / n) (5)
θ3 = θ1−Arcsin (sin (θ1) / n) (6)
θ4 = Arcsin (n × (θ1−Arcsin (sin (θ1) / n)))
... Formula (7)

  As shown also in FIG. 6, the light exit surface angle θa for light emitted in the front direction from the optical sheet 40 made of an inexpensive material (refractive index: 1.45 to 1.60) that is widely used. Was 62 ° to 65 °, the transmittance of one polarization component (P wave) was the highest. As the light exit surface angle θa decreases or increases from the peak region of 62 ° to 65 °, the transmittance of one polarization component (P wave) decreases. On the other hand, the transmittance of the other polarization component (S wave) gradually decreased as the light exit surface angle θa increased. That is, the transmittance of the other polarization component (S wave) was higher as the light exit surface angle θa was smaller.

  On the other hand, as described above, the lower polarizing plate 16 of the transmissive display unit 15 selectively transmits only the P wave that is one polarization component and absorbs the S wave that is the other polarization component. Therefore, it is preferable that the arrangement direction of the unit-shaped elements 45 of the optical sheet 40 is parallel to the transmission axis of the lower polarizing plate 16 as in the embodiment described above. According to such a configuration, as described below, by adjusting the light exit surface angle θa on the side surface 47 of the unit-shaped element 45 of the optical sheet 40, the light source light utilization efficiency in the transmissive display unit 15 can be improved. This is because it can be raised.

  According to the result of FIG. 6, it can be said that it is preferable to set the light exit surface angle θa as large as possible in order to increase the proportion of the P wave in the transmitted light. By setting the light exit surface angle θa as large as possible, the transmittance of the P wave can be increased. Further, by setting the light exit surface angle θa as large as possible, the reflectance of the S wave can be increased, thereby preventing the S wave from being absorbed by the lower polarizing plate 16 of the transmissive display unit 15. Conversely, the S wave can be directed to be reused.

  In the present embodiment, the light exit surface angle θa of the side surface 47 of the unit-shaped element 45 constituting the light exit surface 40a of the optical sheet 40 is separated from one end (first end) 47a1 adjacent to the main body 42. The other end (second end) 47a2 becomes smaller. Therefore, in order to set the light exit surface angle θa as large as possible for the entire side surface 47 of the unit shape element 45, it is preferable to set the light exit surface bottom angle (light exit surface angle at the first end portion 47a1) θaa to be larger. In particular, when the present inventor repeated various experiments while changing various conditions, in the optical sheet 40 made of a widely used inexpensive material (refractive index: 1.45 to 1.60), the bottom angle of the light exit surface. If θaa is 55 ° or more, the optical sheet 40 is disposed between the condensing sheet 30 and the lower polarizing plate 16 of the transmissive display unit 15, so that the optical sheet 40 is not incorporated into the display device 10. It was confirmed visually that the luminance in the front direction could be increased. From this point, it is preferable to set the light exit surface bottom angle θaa to 55 ° or more.

  Further, as shown in FIG. 6, in the optical sheet 40 made of a widely used inexpensive material (refractive index: 1.45 to 1.60), the light exit surface angle θa is 62 ° to 65 °. Thus, the transmittance of the P wave becomes the highest. Therefore, it is preferable that the light exit surface bottom angle θaa having the largest light exit surface angle θa is 65 ° or more. When the light exit surface bottom angle θaa is 65 ° or more, the P wave has the highest transmittance between the first end portion 47a1 and the second end portion 47a2 of the side surface 47 of the unit shape element 45. This is because an area to be transmitted is included. From this point, it is very preferable to set the light exit surface bottom angle θaa to 65 ° or more.

  On the other hand, when the inventors of the present invention changed the various conditions and repeated the experiment, when the light exit surface angle θa was excessively increased, the spectrum distribution of the transmitted light became non-uniform. In an optical sheet made of an inexpensive material (refractive index: 1.45 to 1.60) that is widely used, when the light exit surface angle θa exceeds 75 °, the color reproducibility of the display device 10 is visually deteriorated. I can feel it. Further, when the light exit surface angle θa exceeds 75 °, the P-wave transmittance starts to rapidly decrease as shown in FIG. Regarding the optical sheet 40 described above, when the light exit surface bottom angle θaa of the side surface 47 exceeds 75 °, the optical sheet 40 is disposed between the condensing sheet 30 and the lower polarizing plate 16 of the transmissive display unit 15. In the case where the optical sheet 40 is not incorporated in the display device 10, the magnitude of the luminance in the front direction cannot be visually determined. That is, when the light exit surface bottom angle θaa exceeds 75 °, it is no longer possible to increase the front luminance to an extent that can be visually determined by providing the optical sheet 40. From these points, it is preferable to set the light exit surface bottom angle θaa to 75 ° or less.

  In addition, when the inventors conducted experiments under various conditions, when the light exit surface bottom angle θaa exceeds 75 °, the slope is steep as described later with reference to FIG. There is a lot of light that is refracted and emitted from the other side surface 47 of the unit shape element 45 after being reflected by the end portion 47 a 1 of the one side surface 47 of the unit shape element 45. Such light leaks without being blocked by the transmissive display unit 15, and the contrast of the image displayed on the display device 10 is significantly reduced. In order to prevent such a decrease in contrast, it is preferable to set the light exit surface bottom angle θaa to 75 ° or less.

  Further, as described above, the unit shape element 45 at a position shifted from the end 45b2 of the unit shape element 45 by a length corresponding to 15% of the width of the unit shape element 45 in the direction parallel to the sheet surface of the main body 42. The light exit surface angle θa of the side surface 47 is preferably 40 ° or more. As a result of extensive research conducted by the present inventors, an optical sheet made of an inexpensive material (refractive index: 1.45 to 1.60) that is widely used ensures an increase in luminance in the front direction that can be visually judged. The polarization separation function that can be performed was expressed by setting the light exit surface angle θa to 40 ° or more. Further, it was confirmed that the increase in front direction luminance can be visually recognized in the display device 10 when the light exit surface angle θa is 40 ° or more in the region of 30% or more of the display region.

  By the way, when a conventional optical sheet including a unit shape element having a part of an elliptical cross section or a triangular shape is used, the luminance in the front direction can be improved, but a relatively large emission angle region different from the front direction. A small luminance peak may occur at (for example, 60 ° to 75 °). The luminance peak formed at such a large emission angle is also called a side lobe and cannot be effectively used in a display device. That is, when such light is generated, the energy efficiency of the light source (utilization efficiency of the light source light) is reduced. Furthermore, in a liquid crystal display panel (LCD panel) which is a typical transmissive display unit, such light cannot be completely blocked. Therefore, even when it is desired to display black, the light passes through the liquid crystal display panel, resulting in a decrease in contrast of the displayed image and a deterioration in image quality.

  The following are considered to be causes of the occurrence of a luminance peak other than in the front direction. As shown in FIG. 7, the light incident on the unit shape element includes light L <b> 71 that is reflected from the light exit surface of the unit shape element without being transmitted from the light exit surface of the unit shape element. A part L71 of such light repeats reflection on the light exit surface of the unit shape element and directs its traveling direction to the light incident side. On the other hand, part of such light also includes light L72 that is refracted and emitted from other regions of the light exit surface of the unit shape element after being reflected by the light exit surface of the unit shape element. . And it is thought that such light L72 forms the side lobe. This has been confirmed by simulation. Further, in the prism sheet having two flat surfaces as light output surfaces, the side lobe is conspicuous.

  And in this Embodiment mentioned above, the S wave which is one polarization component will be reflected with a higher reflectance than usual in the 1st main cut surface of an optical sheet. As shown in FIG. 6, the reflectance of the S wave increases as the light exit surface angle θa increases. Therefore, in particular, the S wave incident on the vicinity of the first end 47a1 of the side surface 47 of the unit-shaped element 45 having the largest light exit surface angle θa is reflected with the highest reflectance.

  On the other hand, in the present embodiment, as shown in FIG. 7, the light exit surface 45 a of the unit shape element 45 on the first main cut surface of the optical sheet is between the pair of side surfaces 47 and 47, and the light exit surface of the unit lens 55. 57 is formed in a straight line parallel to the sheet surface of the main body 42. That is, a light exit surface 45a having a light exit surface angle θa of 0 ° at the first main cut surface of the optical sheet is ensured between the side surfaces 47 and 47 formed to have a desired light collecting function and polarization separation function. Become so. As a result, even if the light (for example, the light L71a and the light L72a in FIG. 7) reflected by the unit shape element 45 increases due to the reflection of the S wave by the polarization separation function, the occurrence of side lobes is effectively suppressed. Will be able to.

  Specifically, the light L73 incident on the first end 47a1 of the side surface 47 of the unit shape element 45 that is reflected at the highest reflectance is once reflected by the light exit surface 45a of the unit shape element 45 and is then reflected by the unit lens 55. Is incident on the light exit surface 45a having a light exit surface angle θa of 0 °. Similarly, the light L74 incident on the side surface of the unit shape element 45 other than the first end 47a1 is once reflected on the side surface 47 of the unit shape element 45 and then incident on the light output surface 45a having the light output surface angle θa of 0 °. To do. Then, as shown in FIG. 7, these lights L73 and L74 are totally reflected by the light exit surface 45a having a light exit surface angle θa of 0 ° and easily return to the light incident side, or the light exit surface angle θa is 0 °. The light is refracted by the light exit surface 45a and is easily emitted at a very large emission angle.

  As a result, according to the present embodiment, even if the light reflected by the unit shape element 45 increases, the generation of side lobes can be effectively suppressed. In addition, about this point, the effect (suppression of a side lobe) is confirmed also by experiment of these inventors.

  According to the present embodiment as described above, the light incident on the light exit surface 45a of the unit-shaped element 45 of the optical sheet 40, particularly the side region of the light exit surface 45a, at an angle that can be refracted generally in the front direction. Among them, a specific polarization component (for example, P wave) can be emitted in the front direction with high transmittance, and the other polarization component (for example, S wave) can be reflected with high reflectance. As a result, the luminance in the front direction on the light exit surface 40a of the optical sheet 40 depending on other polarization components (for example, S wave) is reduced, but the light output of the optical sheet 40 depending on a specific polarization component (for example, P wave). The front direction luminance on the surface 40a can be significantly increased. Such a tendency becomes more prominent by providing a plurality of unit lenses 55 arranged in a linear array between a pair of side surfaces 47 and 47 that approach each other as they are separated from the main body 42.

  In the surface light source device 20, much of the light reflected by the light exit surface 45 a of the unit shape element 45 can be reused by being incident on the optical sheet 40 again by repeated reflection. And the polarization state of such light changes by reflection. That is, the other polarization component (for example, S wave) reflected on the light exit surface 45a of the unit shape element 45 can be incident on the optical sheet 40 again as a specific polarization component (for example, P wave). From this point, for example, the brightness in the front direction on the light exit surface 40a of the optical sheet 40 depending on the specific polarization component can be increased more effectively than expected from the data itself of FIG.

  That is, the optical sheet 40 has a polarization separation function that selects and extracts a specific polarization component (for example, P wave) from other polarization components (for example, S wave). And the optical sheet 40 is formed so that this polarization separation function can be exhibited very effectively with respect to the light emitted from the optical sheet 40 in the front direction. Therefore, when used in combination with a transmissive display unit 15 that uses only a specific polarization component of natural light, typically a liquid crystal panel, the utilization efficiency of light source light in the display device 10 is improved. The front luminance can be improved extremely effectively.

  In the optical sheet 40, the pair of side surfaces 47, 47 approach each other as they are separated from the main body portion 42 on the first main cut surface of the optical sheet, and the unit lens 55 is connected between the pair of side surfaces. Yes. Therefore, even if a part of the outer shape (side surface 47) of the unit shape element 45 is designed by paying attention to the improvement of the polarization separation function, the unit shape element as a whole is excellent in collection due to the outer shape of the unit shape element 45. Not only can the optical function be maintained, but it is also possible to prevent the occurrence of side lobes and the like.

  Various modifications can be made to the above embodiment. Hereinafter, an example of modification will be described.

  For example, in the above-described embodiment, the example in which the unit shape elements 45 of the optical sheet 40 are disposed adjacent to each other has been described, but the present invention is not limited thereto. For example, as shown in FIG. 9, a flat portion 48 may be formed between two adjacent unit shape elements 45, or as shown in FIG. May be formed.

  In FIGS. 9 and 10 for explaining the modification, the same reference numerals are given to the parts that can be configured in the same manner as the above-described embodiment shown in FIGS.

  In the above-described embodiment, an example has been shown in which the outer contour of the side surface 47 of the unit-shaped element 45 in the first main cut surface of the optical sheet is an arc (arc or elliptical arc) or a combination of arcs. Not limited. The outer contour of the side surface 47 of the unit-shaped element 45 on the first main cut surface of the optical sheet may be a straight line or a combination of a straight line and an arc. In the above-described embodiment, the example in which the outer contour of the unit lens 55 on the second main cut surface of the optical sheet is a triangular shape has been described. However, the present invention is not limited to this. For example, the outer contour of the unit lens 55 on the second main cut surface of the optical sheet may be an arc (arc or elliptical arc), a combination of arcs, a straight line, or a combination of a straight line and an arc. In this case, as described above, the transmittance of the S wave (P wave incident on the lower polarizing plate 16 of the transmissive display unit 15) emitted from the optical sheet 40 via the unit lens 55 is increased, and the unit lens 55 is also increased. Unit lens 55 on the second main cut surface of the optical sheet in order to reduce the transmittance of the P wave (S wave incident on the lower polarizing plate 16 of the transmissive display unit 15) emitted from the optical sheet 40 via Has an angle formed by the tangent to the end on the light exit surface of the unit lens 55 closest to the main body 42 and the sheet surface of the main body 52 is 0 ° or more. The angle is preferably less than 40 °. In addition, the angle formed by the tangent to the light exit surface 57 of the unit lens 55 and the sheet surface of the main body 42 on the second main cut surface of the optical sheet is 0 ° or more and 40 ° regardless of the position of the contact point of the tangent. It is preferable that it is less than °.

  Here, FIG. 11 shows a modification of the unit shape element 45. In the example shown in FIG. 11, the pair of side surfaces 47 of the unit shape element 45 are configured as flat surfaces. That is, in the first main cut surface of the optical sheet, the pair of side surfaces 47 has a linear outline. In the example shown in FIG. 11, the unit lens 55 of the unit shape element 45 has a shape corresponding to a part of an elliptic cylinder or a part of a cylinder. That is, the unit lens 55 has an outer contour corresponding to an elliptical arc or an arc on the second main cut surface of the optical sheet.

  In addition, in FIG. 11 for demonstrating a modification, the same code | symbol is attached | subjected to the part which can be comprised similarly to the above-mentioned embodiment shown in FIGS.

  Furthermore, in the above-described embodiment, the example in which the unit shape elements 45 of the optical sheet 40 all have the same configuration has been described, but the present invention is not limited thereto. As an example, unit-shaped elements having different configurations may be included in one optical sheet 40.

  Furthermore, although an example of the light collecting sheet 30 has been described in the above-described embodiment, the light collecting sheet 30 described above is merely an example, and various changes can be made. For example, although the cross-sectional shape of the unit shape element 35 of the light collecting sheet 30 is an example in which the main cutting surface of the light collecting sheet is a circular part or an elliptical part, the present invention is not limited thereto. The cross-sectional shape of the unit shape element 35 may be a polygonal shape such as a triangle, for example.

  In addition, the light collecting sheet 30 can be omitted from the display device 10. As described above, the optical sheet 40 can condense the transmitted light on the surface parallel to the arrangement direction of the unit shape elements 45 by refraction at the side surface 47 of the unit shape elements 45. That is, the refraction at the side surface 47 of the unit shape elements 45 can increase the brightness in the front direction in a plane parallel to the arrangement direction of the unit shape elements 45. In particular, in the above-described embodiment, the polarization separation function of the optical sheet 40 greatly improves the utilization efficiency in the transmissive display unit 15 for light emitted in the front direction due to refraction at the side surface 47. become. Therefore, when the light collecting sheet 30 is not included in the display device 10, as shown in FIG. 12, the region facing the light emitting unit 25a of the light source 25, depending on the degree of diffusion in the light diffusion sheet 28. And the front direction brightness | luminance (front direction brightness | luminance of the area | region Za shown with a satin in FIG. 12) on the side surface 47 in this surrounding area | region becomes high easily.

  Further, the optical sheet 40 can condense the transmitted light on the surface orthogonal to the arrangement direction of the unit shape elements 45 by refraction of the unit shape elements 45 in the unit lenses 55. At this time, the light exit surface angle θa of the light exit surface 57 of the unit lens 55 is set even in a situation where light is incident on the optical sheet 40 at various incident angles due to the absence of the light collecting sheet 30. By appropriately designing, the unit lens 55 can exhibit an excellent light collecting function. As a result, the refraction at the light exit surface 57 of the unit lens 55 can increase the luminance in the front direction in the plane orthogonal to the arrangement direction of the unit shape elements 45. In particular, as in the above-described embodiment, when the cross-sectional shape of the unit lenses 55 is a triangular shape in the cross-section along the arrangement direction (second main cut surface of the optical sheet), the light source 25 Thus, the traveling direction of light incident at a large incident angle can be changed to the front direction very effectively. For this reason, depending on the degree of diffusion in the light diffusion sheet 28, as shown in FIG. 12, the luminance in the front direction on the light exit surface 57 of the unit lens 55 in the region not facing the light emitting portion 25a of the light source 25 (see FIG. 12, the luminance in the front direction of the region Zb indicated by diagonal lines is likely to increase.

  As a result, the luminance in the front direction can be effectively improved over the entire display surface of the display device 10. In addition, by appropriately designing the size of the unit shape element 45, it is visually observed over the entire area of the display device 10 so that the in-plane distribution of luminance is extremely effectively uniformed.

  Note that the optical sheet 40 shown in FIG. 12 for explaining the in-plane distribution of luminance has the same configuration as the optical sheet 40 described above.

  Further, in the above-described embodiment, the light emitting unit 25a of the light source 25 of the surface light source device 20 is formed of a cold cathode tube extending linearly, but is not limited thereto. As the light source 25, a light emitting unit composed of a dot-like LED (light emitting diode), a planar EL (electroluminescent body), or the like may be provided. In the above-described embodiment, an example in which the optical sheet 40 is applied to the direct-type surface light source device 20 has been described, but the present invention is not limited thereto. It is also possible to apply the optical sheet 40 described above to, for example, an edge light type (also referred to as a side light type) surface light source device. In such a case as well, the optical sheet 40 is a direct type surface light source device 20. The effect similar to the case where it is applied to can be produced.

  Furthermore, in the above-described embodiment, an example of the overall configuration of the surface light source device 20 and the transmissive display device 10 in which the optical sheet 40 is incorporated has been described, but the present invention is not limited to this and can be changed as appropriate. For example, an optical sheet or the like having various functions may be further incorporated in the surface light source device 20 and the transmissive display device 10.

  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.

FIG. 1 is a diagram for explaining an embodiment according to the present invention, and is a perspective view showing a schematic configuration of a transmissive display device and a surface light source device. FIG. 2 is a perspective view showing an optical sheet incorporated in the surface light source device of FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2 and shows the optical sheet in FIG. FIG. 4 is an enlarged view showing the optical sheet of FIG. 3 in the same cross section as FIG. 5 is a cross-sectional view taken along line VV in FIG. 2 and shows the optical sheet in FIG. FIG. 6 is a graph showing a change in transmittance according to the light exit surface angle. FIG. 7 is an enlarged view showing the optical sheet of FIG. 3 in the same cross section as FIG. FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 1 and shows the light collecting sheet incorporated in the surface light source device in FIG. 1. FIG. 9 is a view for explaining a modification of the optical sheet in the same cross section as FIG. FIG. 10 is a diagram for explaining another modification of the optical sheet in the same cross section as FIG. 3. FIG. 11 is a perspective view corresponding to FIG. 2, and is a view showing a modification of the unit shape element of the optical sheet. FIG. 12 is a top view showing the optical sheet from the light exit side, and is a view for explaining the distribution of luminance in the front direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission type display apparatus 15 Transmission type display part 16 Lower polarizing plate 17 Upper polarizing plate 18 Liquid crystal layer 20 Surface light source device 25 Light source 28 Light diffusion sheet 30 Condensing sheet 32 Main body part 32a Light emission side surface 34 Lens part 35 Unit shape element 40 Optical Sheet 40a Light exit surface 40b Light entrance surface 42 Main body portion 42a Light exit side surface 44 Lens portion 45 Unit shape element 45a Light exit surface 47 Side surface 47a1 End (one end, first end)
47a2 end (the other end, the second end)
55 Unit lens 57 Light exit surface

Claims (8)

A sheet-like body,
A plurality of unit shape elements arranged side by side on the light exit side of the main body, each extending linearly in a direction intersecting the arrangement direction,
Each unit shape element includes a pair of side surfaces extending from the main body portion, and includes a pair of side surfaces approaching each other as the distance from the main body portion increases.
In a cross section parallel to both the normal direction of the main body and the arrangement direction of the unit shape elements, the side surface is formed in a curved shape,
The side surface has an angle formed by a tangent to the side surface of the unit shape element with respect to a sheet surface of the main body portion in a cross section parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements. Including at least a portion of 62 ° to 65 °,
Each unit shape element is a plurality of unit lenses arranged side by side in the longitudinal direction of the unit shape element, each extending in a direction connecting between edges of the pair of side surfaces that are separated from the main body portion. An optical sheet comprising a plurality of unit lenses. In a cross section parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, a tangent to the end on the side surface of the unit shape element closest to the main body portion is the main body portion. The optical sheet according to claim 1, wherein an angle formed with respect to the sheet surface is 55 ° or more and 75 ° or less. In a cross section parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, the side surface is at least from the end portion on the side surface of the unit shape element closest to the main body portion. Extending to a position shifted by 15% of the width of the unit-shaped element in a direction parallel to the sheet surface of the main body,
In a cross section parallel to both the normal direction of the main body part and the arrangement direction of the unit shape elements, the sheet surface of the main body part from the end on the side surface of the unit shape element closest to the main body part The angle formed by the tangent line that contacts the side surface of the unit shape element at a position shifted by a length of 15% of the width of the unit shape element in a direction parallel to the sheet shape element is 40 °. It is the above, The optical sheet of Claim 1 or 2 characterized by the above-mentioned. In a cross section parallel to both the normal direction of the main body part and the arrangement direction of the unit shape elements, the angle formed by the tangent to the side surface of the unit shape element with respect to the sheet surface of the main body part is the tangent line. The point of contact with the unit-shaped element becomes smaller from one end on the side surface closest to the main body to the other end on the side surface farthest from the main body. The optical sheet according to any one of claims 1 to 3, wherein: A light source;
A surface light source device comprising: the optical sheet according to claim 1 that receives light from the light source. A light collecting sheet disposed on the light incident side of the optical sheet;
The condensing sheet has a sheet-like main body, and a plurality of unit-shaped elements that are arranged side by side on the light output side of the main body, each extending linearly in a direction intersecting the arrangement direction,
The light source has a linear light emitting part,
The arrangement direction of the unit shape elements of the light collecting sheet intersects with the longitudinal direction of the light emitting portion of the light source, and intersects with the arrangement direction of the unit shape elements of the optical sheet,
In the main cutting surface of the light collecting sheet parallel to both the normal direction of the main body portion of the light collecting sheet and the arrangement direction of the unit shape elements of the light collecting sheet, the parallel to the sheet surface of the main body portion The width of the unit shape element of the light collecting sheet is 1.8 to 2.3 times the height of the unit shape element of the light collecting sheet along the normal direction of the main body. The surface light source device according to claim 5. A surface light source device according to claim 5 or 6,
And a transmissive display unit disposed on the light output side of the surface light source device. The transmissive display unit has a lower polarizing plate and an upper polarizing plate disposed on the light output side of the lower polarizing plate,
The display device according to claim 7, wherein a transmission axis of the lower polarizing plate is parallel to an arrangement direction of the unit shape elements of the optical sheet.

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