JP5182128B2 - Optical sheet, surface light source device and display device - Google Patents

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.

  In addition, when the front direction luminance is improved, there is a possibility that an abrupt change (so-called cut-off) may occur in the luminance angle distribution as the front direction luminance increases. In the optical sheet, the surface light source device, and the display device according to the present invention, it is more convenient if the occurrence of such a problem can be prevented.

  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 comprises: 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, each extending linearly in a direction intersecting the arrangement direction. In the main cutting plane parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, the unit shape element has a tapered cross-sectional shape, and the main cutting surface is closest to the main body portion. The angle formed by the tangent to the end on the outer contour of the unit-shaped element with respect to the sheet surface of the main body is 55 ° or more and 75 ° or less, and the main body mainly transmits transmitted light. It has an anisotropic diffusion function of diffusing in the arrangement direction of the unit shape elements.

  In the optical sheet according to the present invention, the light incident side surface of the main body is formed by a large number of unit lenses arranged side by side, and each unit lens extends linearly in a direction that intersects the array direction of the large number of unit lenses. You may do it.

  Alternatively, in the optical sheet according to the present invention, irregularities may be formed on the light incident side surface of the main body, and the concave and convex portions forming the irregularities may extend linearly.

  Moreover, the optical sheet by this invention WHEREIN: The said unevenness | corrugation may be formed by the hairline process.

  Furthermore, in the optical sheet according to the present invention, an angle formed by a tangent to the end portion of the unit shape element on the outer contour with respect to the sheet surface of the main body portion is 65 ° or more and 75 in the main cut surface. You may make it be below.

  Furthermore, in the optical sheet according to the present invention, the main cutting plane is displaced from the end of the unit shape element by a length of 15% of the width of the unit shape element in a direction parallel to the sheet surface of the main body. The angle formed by the tangent line that touches the outer contour of the unit-shaped element at a certain position 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 the main cutting plane, the position of the contact point of the tangent to the outer contour of the unit shape element is the full width of the unit shape element in a direction parallel to the sheet surface of the main body portion. The tangent to the outer contour of the unit-shaped element may form an angle of 0 ° or more and 15 ° or less with respect to the sheet surface of the main body portion. .

  Furthermore, in the optical sheet according to the present invention, the optical sheet proceeds in a direction parallel to the main cutting surface and faces the end portion of the unit-shaped element, and a part thereof is refracted by the light-emitting surface of the unit-shaped element and is normal to the body portion Of the light that is emitted in the direction, the light reflected without being refracted by the light exit surface of the unit shape element is then emitted from the unit shape element at an emission angle of 80 ° or more, or the unit The unit shape element may be configured to enter the adjacent unit shape element after exiting from the shape element.

  Furthermore, in the optical sheet according to the present invention, the angle formed by the tangent to the outer contour of the unit shape element with respect to the sheet surface of the main body portion on the main cut surface is a contact point of the tangent to the unit shape element. However, you may make it become large as it goes to the said edge part on the said outer outline of the said unit shape element from the top part on the said outer outline of the said unit shape element most spaced apart from the said main-body part.

  Furthermore, in the optical sheet according to the present invention, in the main cutting plane, the outer contour of the unit-shaped element is composed of three or more arcs joined together, and the two arcs joined together are common in the joining portion. You may make it have a tangent.

  Furthermore, in the optical sheet according to the present invention, the outer contour of the unit-shaped element on the main cutting plane may be line symmetric with respect to an axis parallel to the normal direction of the main body.

  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 intersect with the longitudinal direction of the light emitting part of the light source, and may intersect with 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 The width of the unit-shaped element of the light-collecting sheet parallel to the sheet surface of the part is 1 .. the height of the unit-shaped element of the light-collecting sheet from the main body along the normal direction of the main body. It may be 8 times or more and 2.3 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.

  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 7 are diagrams 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. 2, 3 and 5 are cross-sectional views of the main cut surface showing the optical sheet. FIG. 5 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. 6 is a cross-sectional view of the main cutting surface showing the light collecting 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 in the traveling direction of light from the light source 25 to the observer through the optical sheet 40 or the like without turning back the traveling direction (observer side, FIG. 1, FIG. 2, the upper side of the drawing in FIG. 3 and FIG. 5, and “light incident side” refers to the traveling direction of light from the light source 25 toward the observer through the optical sheet 40 and the like without folding the traveling direction. Is the upstream side (the lower side of the paper in FIGS. 2, 3 and 5).

  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 6, 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. 6, in the present embodiment, a cut surface parallel to both the normal direction nd of the main body portion 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 configuration, the width W (see FIG. 6) of the unit shape element 35 can be set to 1 μm to 200 μm. Further, the projecting height H (see FIG. 6) of the unit shape element 35 from the light emitting 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 direction nd of the normal to the sheet surface of the optical sheet 40 (see, for example, FIG. 2), 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. In the present embodiment, as shown in FIG. 1, the optical sheet 40 has substantially the same configuration as the light collecting sheet 30 described above except that a unit lens 46 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).

  2 and 3 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 (also referred to as “main cutting surface of the optical sheet”). An optical sheet 40 is shown. 2 and 3 also correspond to the cross section taken along the line II-II in FIG.

  As shown in FIGS. 2 and 3, the main body 42 functions as a sheet-like member that supports the unit-shaped element 45. As shown in FIGS. 1 and 2, in the present embodiment, unit-shaped elements 45 are arranged side by side without a gap on the light exit side surface 42 a of the main body portion 42, and the lens portion 44 is formed on the main body portion 42. doing.

  The main body 42 has an anisotropic diffusion function for diffusing transmitted light mainly in the arrangement direction of the unit shape elements 45. In the present embodiment, as shown in FIG. 2, a unit lens 46 is formed on the light incident side surface 42 b of the main body 42. The unit lens 46 provides a light diffusion function to the main body 42. In the present embodiment, the unit lenses 46 are arranged side by side without a gap, and the light incident surface 40 b of the optical sheet 40 is formed by only a large number of unit lenses 46.

  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

  The unit lenses 46 extend linearly (in the present embodiment, linear) in a direction that intersects the arrangement direction of the unit lenses 46. In the present embodiment, the longitudinal direction of the unit lenses 46 is orthogonal to the arrangement direction of the unit lenses 46 on a plane parallel to the sheet surface of the main body 42. As shown in FIGS. 1 and 2, the arrangement direction of the unit lenses 46 is 45 on a plane parallel to the sheet surface of the main body portion 42 with respect to the longitudinal direction of the unit shape elements 45 of the optical sheet 40 to be described in detail later. Intersect at an angle greater than 135 ° and less than 135 °. In particular, in the present embodiment, the arrangement direction of the unit lenses 46 is parallel to the arrangement direction of the unit shape elements 45 of the optical sheet 40. Thereby, the diffusion function of the main body 42 expressed by the unit lenses 46 arranged in parallel has anisotropy that diffuses light mainly in the arrangement direction of the unit shape elements 45.

  In the present embodiment, as shown in FIG. 2, the unit lens 46 has a triangular shape (prism shape) in a cross section orthogonal to the longitudinal direction. The cross-sectional shape of the unit lens 46 is constant along the longitudinal direction (direction extending linearly) of the unit lens 46. The plurality of unit lenses 46 have the same shape.

  The configuration of the plurality of unit lenses 46 forming the light incident side surface 42b of the main body 42 is not particularly limited as long as a rough surface capable of diffusing light can be formed on the light incident side surface 42b of the main body 42. Here, the rough surface refers to a rough surface in an optical sense. Therefore, for example, if the ten-point average roughness Rz (JISB0601) of the light incident side surface 42b (light incident surface 40b of the optical sheet 40) of the main body 42 is equal to or longer than the shortest visible light wavelength (0.38 μm), It is sufficiently rough.

  Next, the unit shape element 45 will be described in detail. As shown in FIG. 1, 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. Furthermore, as described above, the arrangement direction of the unit shape elements 45 of the optical sheet 40 is parallel to the arrangement direction of the unit lenses 46 that form the light incident surface 42 b of the main body 42 of the optical sheet 40.

  As shown in FIG. 1, in the present embodiment, the cross-sectional shape of each unit shape element 45 on the main cutting surface of the optical sheet is along the longitudinal direction (direction extending linearly) of the unit shape element 45. It is constant. The plurality of unit shape elements 45 forming the lens portion 44 of the optical sheet 40 are all configured similarly. Below, the cross-sectional shape in the main cut surface of the unit shape element 45 contained in the optical sheet 40 is demonstrated in detail.

  As shown in FIGS. 2 and 3, in the present embodiment, the cross-sectional shape of each unit shape element 45 on the main cut surface of the optical sheet is a shape that tapers toward the light output side. In other words, the width of the unit-shaped element 45 parallel to the sheet surface of the main body 42 on the main cut surface decreases as the distance from the main body 42 increases along the normal direction nd of the main body 42.

  Further, as shown in FIG. 3, the outer contour of the unit-shaped element 45 on the main cut surface of the optical sheet is composed of three or more arcs (arcs or elliptical arcs) joined together, and in this embodiment, three elliptical arcs A1. , A2 and A3. Two adjacent arcs connected to each other (arc A1 and arc A2, and arc A2 and arc A3) have common tangent lines CTL1 and CTL2 at the connecting portion. That is, two adjacent arcs are connected continuously. As a result, the angular distribution of the 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 (cut-off occurs) when the observation direction is changed. can do.

  In the present embodiment, the outer contour of the unit shape element 45 on the main cut surface of the optical sheet is line symmetric with respect to an axis parallel to the normal direction nd of the main body 42. 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.

  Further, as shown in FIG. 2, the tangent TL to the outer contour of the unit shape element 45 is in the main cut surface with respect to the sheet surface of the main body 42 (in the present embodiment, the light exit side surface 42a of the main body 42). The angle θa (also referred to as “light exit surface angle”) θa is the outer contour of the unit shape element 45 where the contact point TP of the tangent TL to the unit shape element 45 is farthest from the main body portion 42 in the normal direction nd of the main body portion 42. (Light exit surface) increases from the top 45b1 on the light exit surface 45a toward both ends 45b2 on the outer contour (light exit surface) 45a of the unit shape element 45 adjacent to the body portion 42 in the normal direction nd of the body portion 42. Go. Here, the light exit surface angle θa “becomes larger” only means that the light exit surface angle θa constantly changes greatly (the mode in the present embodiment shown in FIGS. 2 and 3). 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 “increased” when the contact TP goes from the top 45b1 on the outer contour (light exit surface) 45a to the end 45b2 on the outer contour (light exit surface) 45a. Further, it means that the light exit surface angle θa is “not reduced”.

  The light exit surface angle θa of the unit shape element is preferably set as follows based on the research results of the present inventors. First, on the main cut surface of the optical sheet, the light exit surface angle (also referred to as “light exit surface bottom angle”) formed by the tangent line TL to the end portion 45b2 on the outer contour of the unit shape element 45 with respect to the sheet surface of the main body portion 42. ) Θaa is preferably 55 ° or more, and more preferably 65 ° or more. As a result of confirmation by the present inventor, when the light exit surface bottom angle θaa of the unit shape element 45 is 55 ° or more, the luminance in the front direction can be increased to such an extent that it can be visually confirmed. 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 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, on the main cutting surface of the optical sheet 40, the unit is 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. It is preferable that the tangent line TL contacting the outer contour of the shape element 45 forms an angle θa of 40 ° or more with respect to the sheet surface of the main body portion 42. That is, the light exit surface angle θa of the unit shape element 45 at a position displaced from the end 45b2 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 is obtained. 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.

  Further, at the main cutting surface of the optical sheet, the position of the contact TP of the tangent TL to the outer contour of the unit shape element 45 is at least of the full width of the unit shape element 45 in the direction parallel to the sheet surface of the main body 42. When it is in a region that occupies 15%, the tangent line TL to the outer contour of the unit shape element 45 forms an angle of 15 ° or less with respect to the sheet surface of the main body 42. That is, it is preferable that the light exit surface angle θa of the unit shape element 45 is 0 ° or more and 15 ° or less in a region of 15% or more of the unit shape elements 45 in the ratio in the direction parallel to the sheet surface of the main body portion 42. . In the present embodiment, as described above, the cross-sectional shape of the unit shape element 45 is axisymmetric on the main cut surface of the optical sheet, and the light exit surface angle θa increases from the top 45b1 toward the end 45b2. . Therefore, in other words, the unit shape element 45 is displaced from the top 45b1 of the unit shape element 45 by a length corresponding to 7.5% of the width of the unit shape element 45 in the direction parallel to the sheet surface of the main body 42. It is preferable that the tangent TL in contact with the outer contour forms an angle θa of 15 ° or less with respect to the sheet surface of the main body portion 42. As a result of extensive research conducted by the inventors of the present invention, according to such a setting, the process proceeds in a direction parallel to the main cutting surface of the optical sheet and proceeds toward the end 45b2 of the unit shape element 45, and a part thereof is the unit shape element 45. Of the light that is refracted by the light exit surface 45a and exits in the normal direction nd of the main body 42, the other light reflected without being refracted by the light exit surface 45a of the unit shape element 45 is The unit shape element 45 emits at an emission angle of 80 ° or more (an angle formed by the light emission direction with respect to the normal direction of the optical sheet), or enters the adjacent unit shape element after exiting from the unit shape element. Tend to exhibit.

  As a specific example of the unit shape element 45 configured as described above, the width of the unit shape element 45 can be set to 1 μm to 200 μm. Moreover, the protrusion height of the unit shape element 45 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 micrometers-50 micrometers.

  The condensing sheet 30 and the optical sheet 40 having the above-described configuration can be manufactured very easily by extrusion processing or by forming the unit shape elements 35 and 45 on a base material. 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. 6, the light L <b> 61 and L <b> 62 emitted from the unit shape element 35 of the light collecting sheet 30 is 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 L61 and L62 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 luminance in the front direction can be effectively increased in a region away from the light emitting unit 25a of a certain light source 25 (see the light L62 in FIG. 6).

  On the other hand, as shown in FIG. 6, the light L63 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-shaped 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, 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 through the light incident surface 40b of the optical sheet 40. As described above, on the light incident side surface 42b of the main body portion 42 forming the light incident surface 40b of the optical sheet 40, a large number of unit lenses 46 extending linearly are provided in a linear array. The large number of unit lenses 46 form a rough surface on the light incident surface 40 b of the optical sheet 40, and diffuses light incident on the optical sheet 40.

  However, the diffusion by the unit lenses 46 is diffusion in a direction parallel to the arrangement direction of the unit lenses 46 and has anisotropy. That is, the direction in which the light collecting action is exerted by the light collecting sheet 40 disposed on the light incident side of the optical sheet 30 is orthogonal to the direction in which the diffusion action is exerted by the unit lens 46 of the optical sheet 30. Accordingly, the traveling direction of the light whose traveling direction is narrowed down to a narrow range centered on the front direction by the light collecting sheet 30 is again diffused by the unit lens 46 of the optical sheet 30 and again narrowed about the front direction. Is prevented from being distracted. That is, the ideal angular distribution in the plane parallel to the arrangement direction of the unit shape elements 35 of the light collecting sheet 30 on the light exit surface of the light collecting sheet 30 is impaired by the diffusion action of the unit lenses 46 of the optical sheet 30. It will generally be maintained without being lost.

  In the optical sheet 40, one polarization component of 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, P wave in the present embodiment. 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.

  Similarly to the light collecting sheet 30, the optical sheet 40 also has a light collecting effect on the transmitted light due to refraction at the light exit surface 45 a of the unit shape element 45. However, the light whose direction of travel is changed by the optical sheet 40 is a component that travels parallel to the main cutting surface of the optical sheet 40, and is different from the component condensed by the light collecting sheet 30. That is, the condensing sheet 30 narrows the traveling direction of light within a narrow angle range centered on the front direction on a plane parallel to the arrangement direction of the unit shape elements 35 of the condensing sheet 30. The optical sheet 40 narrows the light traveling direction within 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. Therefore, the front direction luminance can be further increased by the optical action of the optical sheet 40 without harming the front direction luminance increased by the light collecting sheet 30.

  As described above, the main body portion 42 of the optical sheet 40 has a diffusion function of diffusing light mainly in the arrangement direction of the unit shape elements of the optical sheet 40. Therefore, the angular distribution in the plane parallel to the arrangement direction of the unit shape elements 45 of the optical sheet 40 having the luminance on the light exit surface 40b of the optical sheet 40 can be smoothly changed. In particular, since the main body portion 42 having a diffusing function is disposed immediately before the lens 44 having a condensing function, the angular distribution of luminance can be changed extremely smoothly and abrupt changes can be made in the angular distribution of luminance. It is possible to effectively prevent (cutoff) from occurring. As an example, FIG. 7 shows the angular distribution (solid line) of luminance when the anisotropic diffusion function is given to the main body portion 42 of the optical sheet 40, and the anisotropic diffusion function is given to the main body portion 42 of the optical sheet 40. The result of the investigation of the angular distribution (dashed line) of the luminance when there is no such error is shown. The investigation when the anisotropic diffusion function was added was performed using the display device having the above-described configuration. In addition, the display device used for the investigation when the anisotropic diffusion function was not given is the case where the anisotropic diffusion function was given, except that the light incident side surface of the main body part was a smooth surface. The display device was the same as that used for the survey.

  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 light that is emitted in the normal direction nd of the main body 42 in the plane parallel to the arrangement direction of the unit shape elements 45 of the optical sheet 40 is transmitted to the transmission type display unit. 15 includes a polarization component (P wave) that can be incident on the lower polarizing plate 16 at a high ratio. On the other hand, the polarization component (S wave) absorbed by the lower polarizing plate 16 of the transmissive display unit 15 is Contained only at a low rate. 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 (condensing function) for changing the traveling direction of light within a narrow angle range centered on the front direction, but also in 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, the luminance in the front direction can be extremely effectively increased.

  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 L21 in FIG. 2 and the light L31 in FIG. 3) 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 present inventors determine the transmittance of the light L21 and L31 refracted on the light exit surface of the optical sheet and emitted from the optical sheet in the front direction, and the light exit surface on which the light L21 and L31 are incident and the optical surface. The angle (light exit surface angle) θa formed by the sheet surface of the sheet was changed and investigated. 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, the following formula | equation (1) and Formula (2) hold | maintain about the light which refracts by the unit shape element 45 and radiate | emits a front direction after injecting into the optical sheet 40. Here, the angles θa, θ1, θ2, and θ3 in the equations (1) and (2) are as shown in FIG. That is, 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)
n × sin (θ2) = sin (θ1) (2)

  Then, by modifying Expression (1) and Expression (2), the inclination angle θ3 when passing through the main body 42, the incident angle θ2 of the unit shape element 45 with respect to the light exit surface 45a, and the unit shape element 45 The emission angle θ1 with respect to the light exit surface 45a can be specified using the light exit surface angle θa as shown in the following formulas (3) to (5).

θ1 = θa (3)
θ2 = Arcsin (sin (θ1) / n) (4)
θ3 = θ1−Arcsin (sin (θ1) / n) (5)

  As shown in FIG. 4, the light exit surface angle θa for the 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. This is because the use efficiency of the light source light in the transmissive display unit 15 can be increased by adjusting the light exit surface angle θa of the optical sheet 40 according to such a configuration.

  From the results shown in FIG. 4, 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 decreases from the end 45b2 toward the top 45b1. Therefore, in order to set the light output surface angle θa as large as possible for the entire light output surface of the unit shape element 45, it is preferable to set the light output surface bottom angle (light output surface angle at the end 45b2) 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.

  In addition, as shown in FIG. 4, 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 region where the P wave is transmitted with the highest transmittance between the end 45b2 and the top 45b1 of the light exit surface 45a of the unit shape element 45. It is because it comes to be 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 transmittance of the P wave starts to rapidly decrease as shown in FIG. As for the optical sheet 40 described above, when the light exit surface bottom angle θaa exceeds 75 °, the optical sheet 40 is disposed between the light collecting 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 into the display device 10, it is impossible to visually determine the magnitude of the luminance in the front direction. 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. After being reflected by the end portion 45b2 of the unit shape element 45, a large amount of light (for example, the light L52 in FIG. 5) that is refracted and emitted from another region of the light exit surface 45a of the unit shape element 45 exists. 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 main body 42 of the optical sheet 40 has a diffusion function of diffusing light mainly in the arrangement direction of the unit shape elements 45 of the optical sheet 40. And according to such an optical sheet 40, it becomes possible to raise the utilization efficiency of light source light very effectively.

  Usually, like the angular distribution of luminance indicated by the dotted line in FIG. 2, the light L22 incident on the optical sheet 40 contains the most light traveling in the front direction due to the action of the reflecting plate 22 and the like. Such light L22 is diffused in the main cutting plane of the optical sheet by the light diffusing action from the main body portion 42, and for example, as shown by the solid line in FIG. 2 from the angular distribution of luminance as shown by the dotted line in FIG. Changes to a simple angular distribution. That is, due to the diffusing action of the main body portion 42 of the optical sheet 40, the plane parallel to the arrangement direction of the unit-shaped elements 45 of the optical sheet 40 is within a certain angle range centering on the front direction with the front direction as a peak. The angular distribution of the brightness is flattened as a whole while lowering the peak brightness.

  On the other hand, as described above, in the optical sheet 40 manufactured using a material having a refractive index in the range of 1.45 to 1.60, which is widely used, it is refracted and emitted in the front direction. The light exit surface angle θa of the unit-shaped element 45 that can most effectively exert the polarization separation action on the light L21 to be set is 62 ° to 65 °. The light refracted in the front direction on the light exit surface having such a light exit surface angle θa (62 ° to 65 °) is inclined at an angle θ3 (about 25 ° to 30 ° with respect to the normal direction nd of the main body 45. Light (for example, light L22b and light L22c in FIG. 2) traveling in the main body 42 toward the light exit surface 45a of the unit shape element 45 in FIG.

  According to the present embodiment, as described above, the polarization separation function from the unit shape element 45 is effectively reduced by the diffusion action of the main body portion 42 immediately before entering the unit shape element 45 of the optical sheet 40. The direction of travel of the light can be changed in a direction that can be exerted. That is, the amount of light that effectively receives the polarization separation function from the unit shape element 45 of the optical sheet 40 can be increased by the diffusion function of the main body 42. Thereby, the light use efficiency can be effectively improved, and as a result, the front direction luminance can be further improved.

  Note that the light L22a traveling in the front direction (see FIG. 2) is diffused by the diffusion function of the main body 42, and the traveling direction of the light L22a changes in a direction other than the front direction. That is, there is a possibility that the front direction luminance after the incidence of the optical sheet 40 on the main body 42 is lower than the front direction luminance before the incidence. However, the unit-shaped element 45 is provided on the light output side of the main body 42, and the unit-shaped element 45 can exhibit a light collecting function by refraction at the light output surface 45a. In addition, as described above, the polarization separation function of the unit-shaped element 45 can be exhibited extremely effectively by the diffusion function of the main body 42, thereby effectively improving the light utilization efficiency. As a result, the front luminance can be further improved.

  In the investigation result shown in FIG. 7, the front luminance is slightly increased by providing the anisotropic diffusion function of the main body 42. On the other hand, from FIG. 7, by providing the anisotropic diffusion function of the main body portion 42, the utilization efficiency of the light source light is greatly increased, and the change in the angular distribution of luminance becomes gentle. Can be clearly understood.

  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 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. As a specific measurement result, a 5% increase in luminance in the front direction was obtained.

  By the way, when the optical sheet 40 including the unit shape element 45 is used, the luminance in the front direction can be improved, but it is small in a relatively large emission angle region (for example, 60 ° to 75 °) different from the front direction. It may cause a luminance peak. 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. 5, the light incident on the unit shape element 45 includes light L <b> 51 that is reflected by the light output surface 45 a of the unit shape element 45 without passing through the light output surface 45 a of the unit shape element 45. A part L51 of such light repeats reflection on the light exit surface 45a of the unit shape element 45 and directs its traveling direction toward the light incident side. On the other hand, part of such light also includes light L52 that is reflected by the light exit surface 45a of the unit shape element 45 and then refracted and emitted from another region of the light exit surface 45a of the unit shape element 45. include. And it is thought that such light L52 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 comes to be reflected with a higher reflectance than usual. As shown in FIG. 4, 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 end 45b2 of the unit shape 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 described above, the light exit surface angle θa is in the region of 15% or more centered on the top 45b1 in the ratio to the total width of the unit shape element 45 in the main cut surface of the optical sheet. It is 15 degrees or less. That is, the light exit surface 45a having an extremely small light exit surface angle θa is provided in a region centered on the top 45b1. As a result, even if the light reflected by the unit shape element 45 increases due to the reflection of the S wave by the polarization separation function, the generation of side lobes can be effectively suppressed.

  Specifically, the light L53 incident on the end portion 45b2 of the unit shape element 45 reflected at the highest reflectance is once reflected by the light exit surface 45a of the unit shape element 45, and the light exit surface angle θa is 15 ° or less. Is incident on the light exit surface 45a or the light exit surface 45a where the light exit surface angle θa is not so large. Similarly, the light L54 incident on the unit shape element 45 somewhat on the side of the top 45b1 from the end 45b2 is once reflected by the light output surface 45a of the unit shape element 45, and then the light output surface angle θa is 15 ° or less or so much. The light enters the light exit surface 45a in a region that is not a large angle. As shown in FIG. 5, these lights L53 and L54 are refracted and emitted at an extremely large emission angle, or totally reflected and returned to the light incident side.

  As a result of repeated experiments by the inventors, when the emission angle is 80 ° or more, the light is wasted, but the image quality is high enough to be incident on the transmissive display unit 15 and visually determined. There was no deterioration. And in the ratio with respect to the full width of the unit-shaped element 45 in the main cut surface of the optical sheet, when the light exit surface angle θa is 15 ° or less in the region of 15% or more including the top portion 45b1, it goes to the front direction. The light L53 reflected at the end 45b2 of the unit shape element 45 at the incident angle of refraction and reflected at the end 45b2 is then emitted from the unit shape element 45 at an output angle of 80 ° or more, or the unit After exiting from the shape element 45, the light enters the adjacent unit shape element.

  In the unit shape element 45 in which the light exit surface angle θa decreases from the end 45b2 toward the top 45b1, the light exit surface 45a in a region away from the end 45b2 of the unit shape element 45 at an incident angle refracting in the front direction. The light L55 incident on the surface tends not to cause side lobes. In the first place, the incident angle of such light L55 on the light exit surface 45a of the unit shape element 45 is relatively small. Therefore, as shown in FIG. 4, the amount of light reflected when entering the light exit surface 45a of the unit shape element 45 is small. Further, even if the light is reflected when it enters the light exit surface 45a of the unit shape element 45, in most cases, the course direction is directed to the light incident side and re-enters the main body 42 or to the adjacent unit shape element. Incident. From the above, the light L55 incident on the light exit surface 45a in the region away from the end 45b2 of the unit-shaped element 45 at an incident angle refracted in the front direction (for example, in the vicinity of the top 45b1) Less likely to cause side lobes.

  Further, a part of the light incident on the light exit surface 45a of the unit shape element 45 is light L51 (FIG. 5) that is totally reflected by the light exit surface 45a because the incident angle exceeds the total reflection critical angle. See also). And when the present inventors changed the various conditions and repeated the experiment, the unit-shaped element 45 whose light exit surface angle θa becomes smaller from the end 45b2 to the top 45b1, the main cutting surface of the optical sheet Is designed so that the light exit surface angle θa is 15 ° or less within a region of 15% or more including the top 45b1, so that the light L51 totally reflected by the light exit surface 45a is obtained. The resulting side lobe could also be effectively suppressed.

  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 the main body portion 42 of the optical sheet 40 with an anisotropic diffusion function that diffuses transmitted light mainly in the arrangement direction of the unit shape elements 45 of the optical sheet 40.

  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 a 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 cross-sectional shape of the main cutting surface of the unit shape element 45 is tapered toward the light output side. Therefore, even if a part of the outer shape of the unit shape element 45 (the region on the end 45b2 side) is designed by paying attention to the improvement of the polarization separation function, the unit shape element as a whole is attributed to the outer shape of the unit shape element 45. It is possible not only to maintain the excellent light collecting function, but also 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. 8, a flat portion 48 may be formed between two adjacent unit shape elements 45, or as shown in FIG. May be formed.

  In FIGS. 8 and 9 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, the example in which all the unit shape elements 45 of the optical sheet 40 have the same configuration has been described, but the present invention is not limited thereto. As an example, unit-shaped elements having different shapes may be included in one optical sheet 40.

  Furthermore, in the above-described embodiment, an example of the unit lens 46 that forms the light incident side surface 42b (the light incident surface 40b of the optical sheet 40) of the main body 42 of the optical sheet 40 has been described. It is only an example and various changes can be made. For example, the cross-sectional shape of the unit lens 46 may be a shape corresponding to a part of an ellipse or a shape corresponding to a part of a circle. The cross-sectional shape of the unit lens 46 may change along the longitudinal direction of the unit lens 46. Furthermore, a large number of unit lenses 46 arranged side by side may have different configurations.

  Further, in the above-described embodiment, the unit lens 46 that forms the light incident side surface 42b (the light incident surface 40b of the optical sheet 40) of the main body portion 42 of the optical sheet 40 is anisotropic to the main body portion 42 of the optical sheet 40. Although an example in which the light diffusion function is given has been shown, the present invention is not limited to this. For example, irregularities may be formed on the light incident side surface 42b of the main body 42, and the concave and convex portions forming the irregularities may extend linearly. When the longitudinal direction of the concave portion and the convex portion forms an angle of less than 45 ° with respect to the longitudinal direction of the unit optical element 45 of the optical sheet 40 on the sheet surface of the optical sheet, the main body portion 42 transmits the transmitted light due to the unevenness. Has an anisotropic diffusion function of diffusing mainly in the arrangement direction of the unit shape elements 45. Such irregularities can be formed by various known methods. As an example, by performing hairline processing on the light incident side surface 42 b of the main body portion 42, irregularities can be formed very easily on the light incident side surface 42 b of the main body portion 42.

  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-shaped element 35 of the light collecting sheet 30 is an example in which the main cutting plane 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.

  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 cross-sectional view taken along the line II-II in FIG. 1 and shows an optical sheet incorporated in the surface light source device of FIG. FIG. 3 is an enlarged view showing the optical sheet of FIG. 2 in the same cross section as FIG. FIG. 4 is a graph showing a change in transmittance according to the light exit surface angle. FIG. 5 is an enlarged view showing the optical sheet of FIG. 2 in the same cross section as FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 1 and is a view showing a condensing sheet incorporated in the surface light source device in FIG. 1. FIG. 7 is a graph showing the angular distribution of luminance when the main body portion has an anisotropic diffusion function and the angular distribution of luminance when the main body portion does not have an anisotropic diffusion function. FIG. 8 is a view for explaining a modification of the optical sheet in the same cross section as FIG. FIG. 9 is a diagram for explaining another modification of the optical sheet in the same cross section as FIG.

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 Body portion 42a Light exit side surface 44 Lens portion 45 Unit shape element 45a Light exit surface 45b1 Top portion 45b2 End portion 46 Unit lens

Claims (13)

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,
In the main cutting plane parallel to both the normal direction of the main body part and the arrangement direction of the unit shape elements , the unit shape element has a cross-sectional shape and a curved outer contour tapering to the light output side,
In the main cutting plane, the angle formed by the tangent to the outer contour of the unit shape element with respect to the sheet surface of the main body is such that the contact point of the tangent to the unit shape element is farthest from the main body. As it goes from the top on the outer contour of the unit shape element to the end on the outer contour of the unit shape element,
In the main cut surface, an angle formed by a tangent to an end portion of the outer contour of the unit-shaped element closest to the main body portion with respect to a sheet surface of the main body portion is 65 ° or more and 75 ° or less. Yes,
The optical sheet, wherein the main body has an anisotropic diffusion function of diffusing transmitted light mainly in the arrangement direction of the unit shape elements. The light incident side surface of the main body is formed by a large number of unit lenses arranged side by side,
2. The optical sheet according to claim 1, wherein each unit lens extends linearly in a direction intersecting with an arrangement direction of the plurality of unit lenses. Unevenness is formed on the light incident side surface of the main body,
The optical sheet according to claim 1, wherein the concave and convex portions forming the concave and convex portions extend linearly. The optical sheet according to claim 3, wherein the unevenness is formed by hairline processing. In the main cutting surface, the unit-shaped element has a position shifted from the end of the unit-shaped element by a length of 15% of the width of the unit-shaped element in a direction parallel to the sheet surface of the main body. The optical sheet according to any one of claims 1 to 4 , wherein an angle formed by a tangent to the outer contour with respect to a sheet surface of the main body is 40 ° or more. In the main cutting plane, a region in which the position of a tangent to the outer contour of the unit shape element occupies at least 15% of the total width of the unit shape element in a direction parallel to the sheet surface of the main body portion when in the tangential of claims 1-5, characterized in that so it forms a 15 ° angle of less than 0 ° or more with respect to the seat surface of the main body portion to the outer contour of the unit shaped elements The optical sheet according to any one of the above. A light beam that travels in a direction parallel to the main cutting surface and faces the end of the unit-shaped element, and a part thereof is refracted by the light-emitting surface of the unit-shaped element and is emitted in the normal direction of the main body. Of these, the light reflected without being refracted by the light exit surface of the unit shape element is then emitted from the unit shape element at an emission angle of 80 ° or more, or after being emitted from the unit shape element, the adjacent unit. to be incident on the shaped element, an optical sheet according to any one of claims 1 to 6, characterized in that the unit shaped element is configured. The outer contour of the unit-shaped element is composed of three or more arcs joined together in the main cutting plane, and the two arcs joined together have a common tangent at the joining portion. Item 8. The optical sheet according to any one of Items 1 to 7 . The outer contour of the unit shaped elements in said main cutting plane, the axis parallel to the normal direction of the main body portion as the symmetry axis, one of the claims 1-8, characterized in that the axisymmetric The optical sheet according to 1. A light source;
The surface light source device characterized in that it comprises an optical sheet, a according to any one of claims 1 to 9, receiving 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 10 . A surface light source device according to claim 10 or 11 ,
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 12 , 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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