JP2005189303A - Optical sheet, surface light source device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a selective light scattering sheet functioning as an optical sheet capable of eliminating luminance irregularity when it is viewed from an oblique direction without lowering the front luminance of a backlight device. <P>SOLUTION: The selective light scattering sheet 6 has a lower surface on which light is made incident and an upper surface from which the light is emitted, and is composed of base material A and material B whose refractive indexes are different from each other. A refractive index boundary 8 between the base material A and the material B satisfies relation H≥3L when it is assumed that projection length in the thickness direction of the sheet 6 is H and a distance between the boundary 8 and the adjacent boundary 8 is L, and the material B has columnar shape or square pillar shape or truncated cone shape. The sheet 6 has structure obtained by embedding a plurality of members of material B in the base material A. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical sheet that scatters light emitted from a light guide plate, a planar light source device having the optical sheet, and a liquid crystal display device.

  A planar light source device that illuminates a liquid crystal display element or the like from the back, that is, a backlight device, is a corner incident type top view shown in FIG. 14, an edge incident type top view shown in FIG. 15, and FIG. The light guide plate 102 designed to emit light uniformly from the exit surface and the side or apex of the exit surface, as shown in the sectional view showing the section AA ′ of FIG. 15 or the section BB ′ of FIG. It includes a light source 101 disposed on the end face of the light guide plate.

  In the backlight device 100, the light that has entered the light guide plate 102 is totally reflected on the exit surface of the light guide plate 102 and the surface facing the exit surface, thereby spreading in the direction parallel to the exit surface and the light guide plate 102. Propagate through. A reflector 103 having a pyramid, hemisphere, or triangular groove shape is formed on the surface facing the exit surface, and the distribution and exit direction of the emitted light are determined by the density and shape of the reflector 103 (for example, Patent Documents). 1).

  In the current backlight device, high front luminance is realized by converging outgoing light in the front direction. However, on the other hand, since the directivity of light has been increased, there has been a drawback that a slight difference in the emission direction is easily visually recognized as a noticeable luminance unevenness. In particular, when viewed from an oblique direction, luminance unevenness is observed, which is called a bright line. The photograph in FIG. 17 shows that the camera 110 is placed on the diagonal line of the backlight device 100 as shown in FIG. 18 and is observed from a direction inclined by 20 ° from the vertical, and a linear bright line having a width from the light source 101 is observed. The resulting state is observed.

  FIG. 19 is a result of analyzing the backlight device having the same shape by using a light tool (manufactured by Optical Research Associates, version 3.3.0) of a three-dimensional optical simulator. Brightness distribution. As described above, the bright lines are not caused by processing defects or the like because they are also reproduced by optical simulation, and can be said to be an essential problem of the high-intensity light guide plate. As a solution to this, methods such as adding a light diffusion film to the backlight device, providing a diffusion shape on the surface of the light guide plate, and dispersing light scatterers in the light guide plate are used. In any case, since the luminance unevenness is eliminated by reducing the directivity of all the emitted light, a decrease in front luminance is inevitable.

  The cause of the bright line is that the emission position and the emission direction of the oblique light emitted from the backlight device have a strong correlation. This will be described below with reference to FIGS. 14 and 16.

  Light incident from the light source 101 located at the corner of the rectangular light guide plate 102 is guided through the light guide plate 102 as shown in the vertical sectional view of FIG. The light is reflected by the reflector 103 and is emitted in the vertical direction as in the path a. Further, depending on the route, the light may be emitted obliquely as in the route b.

  In the case of the high-brightness backlight device 100, the light guide plate is designed to minimize the scattering of light in the horizontal direction (lateral direction) in order to emit light with the light converged as much as possible. Therefore, as illustrated in FIG. 14, the obliquely emitted light at each point of P, P ′, Q, and Q ′ spreads almost only in the direction indicated by the white arrow, that is, the direction connecting the light source 101 and each point. Progress without. Therefore, when viewed from the observer located at the R point, only the obliquely emitted light from the point on the line connecting the light source 101 and the R point, represented by the P and P ′ points, reaches the observer, and the others , Q, and Q ′ light from points typified by the point does not reach the observer, so that a linear bright portion as shown in FIG. 17, that is, a bright line is generated. Such a theory can be similarly applied to the backlight device 100 in which the light source 101 is arranged on the side of the rectangular light guide plate 102 as shown in FIG.

As a method for solving the luminance unevenness represented by such bright lines, a light diffusing film is used or a light diffusing shape is provided on the surface of the light guide plate 102 to scatter light and weaken the emission position-emission direction correlation. Techniques for reducing luminance unevenness have been proposed previously (see, for example, Patent Documents 2 and 3). However, this method also scatters vertically emitted light in the same manner, which causes a disadvantage that the front luminance is lowered.
Japanese Patent No. 2739730 JP-A-10-153778 JP 2002-323607 A

  In view of such problems, the present invention provides an optical sheet, a planar light source device, and a liquid crystal display device that eliminate uneven luminance when viewed from an oblique direction without reducing the front luminance of the backlight device. With the goal.

  In order to eliminate the bright line while maintaining the front luminance, an optical sheet that selectively diffuses only oblique light is required. The inventors have conceived that if a bright line is generated by the mechanism already described, the bright line can be eliminated by weakening the correlation between the emission position and the emission direction of oblique light as shown in FIG. The present invention has been achieved.

  This invention solves said subject by providing the optical sheet of a specific structure on a light-guide plate in a backlight apparatus. More specifically, the optical sheet includes an interface of two types of media having different refractive indexes inside, and defines the angle of the interface within a certain range.

  That is, the optical sheet according to the present invention is an optical sheet composed of two media having a lower surface on which light is incident and an upper surface on which light is emitted and having different refractive indexes, and the first sheet between the media. The angle between the boundary surface and the lower surface is 80 ° or more and 90 ° or less.

  It is preferable that the upper surface and the lower surface are substantially parallel.

  For light incident perpendicularly to the lower surface, the intensity ratio of light emitted perpendicularly from the upper surface is 90% or more, and for light incident obliquely with respect to the lower surface, the emission angle from the upper surface is the lower surface It is preferable that the angle of incidence is smaller than that.

  When the projected length of the first boundary surface in the thickness direction of the optical sheet is H and the distance between the first boundary surface and the adjacent first boundary surface is L, the relationship of H ≧ 3L is established. It is preferable to satisfy.

  The two media are a base material A and a material B having a refractive index different from the base material A, and the material B has a cylindrical shape, a prismatic shape, or a truncated cone shape, and a plurality of materials B include a base material. It is preferable to have a structure embedded in the material A.

  The material B preferably has a higher refractive index than the base material A.

  The material B preferably has a refractive index smaller than that of the base material A.

  The first boundary surface is preferably lamellar.

  The sheet made of the base material A has a structure in which a through-hole is provided, and the through-hole is preferably a cylindrical, prismatic, truncated cone-shaped or truncated cone-shaped through-hole.

  It is preferable to have a structure in which a large number of cylindrical or prismatic members made of the base material A are bundled, and there are gaps between the members.

  It is preferable to have a second boundary surface having an angle of 0 ° to 10 ° with the lower surface.

  The surface of the optical sheet made of the base material A is preferably provided with a conical, truncated conical, conical or truncated conical protrusion or recess.

  A conical, truncated conical, conical or truncated conical recess is provided on the surface of the optical sheet made of the base material A, and the base material A and a material B having a different refractive index are filled in the concave portion. It preferably has a structure.

  The planar light source device according to the present invention includes a light source, a light guide that emits incident light from the light source from a surface different from the incident surface, and the optical sheet provided to face the emission surface of the light guide. It has.

  The liquid crystal display device according to the present invention has a structure in which the optical sheet is provided on the back surface of the liquid crystal display element.

  According to the present invention, it is possible to selectively diffuse the light emitted from the light guide plate in an oblique direction, and to minimize the influence on the light emitted vertically from the backlight device.

  Hereinafter, the present invention will be described with reference to an example in which an optical sheet as a selective light scattering sheet made of two kinds of materials having different refractive indexes is placed on the front surface of a light deflection sheet, as shown in FIG.

  FIGS. 1A and 1B are a top view showing an example of a backlight device and a cross-sectional view cut perpendicularly along a cross-section AA ′. The light incident on the light guide plate 2 from the light source 1 is guided through the light guide plate 2 while being reflected by the reflector 3 and the like, and is emitted from the emission surface. The emitted light passes through the light deflection film 4 and the selective light diffusion sheet 6 and is emitted from the backlight device 10.

  In order to simplify the explanation, only one refractive index boundary 8 serving as a first boundary surface between the first region 7 made of the material B and the second region 7 ′ made of the base material A is shown in FIG. However, as will be described later, the higher the density of the refractive index boundary 8, the higher the oblique light scattering effect, and a preferable result is obtained. Further, the installation position of the selective light scattering sheet 6 is not limited to the example of FIG. For example, it may be between the light guide plate 2 and the light deflection film 4. Further, the light deflection film 4 is not essential, and is appropriately selected and used depending on the application and required specifications. If the backlight device 10 does not use the light deflection film 4, the selective light scattering sheet 6 may be provided directly above the light guide plate 2.

  As shown in FIG. 1, the selective light diffusing sheet 6 includes refractive index boundaries 8 of two regions 7 and 7 ′ having different refractive indexes, and the refractive index boundary 8 is substantially on the upper and lower surfaces of the selective light scattering sheet 6. It is vertical. When oblique light from the light deflecting film 4 enters the selective light scattering sheet 6, the traveling direction is changed by being reflected at the refractive index boundary 8 as in the path c or being refracted as in the paths d and e. To do. When the refractive index of the first region 7 is higher than that of the second region 7 ', refraction occurs as in the path d, and when it is lower, it is refracted as in the path e.

  On the other hand, when the vertically emitted light from the light deflecting film 4 is incident on the selective light diffusion sheet 6, the light traveling direction and the refractive index boundary 8 are parallel, so that the refractive index as shown by the path f in FIG. The light is transmitted as it is without being scattered at the boundary 8. In order to obtain such an effect, the angle formed by the refractive index boundary 8 and the upper and lower surfaces of the selective light diffusion sheet 6 is preferably as close to 90 ° as possible.

  As described above, by using the selective light scattering sheet 6 including the refractive index boundary 8 between the regions 7 and 7 ′ having different refractive indexes, which forms approximately 90 ° with respect to the upper and lower surfaces of the selective light scattering sheet 6. The oblique outgoing light among the outgoing lights from the constituent members of the backlight device 10 such as the light guide plate 2 and the light deflecting film 4 can be selectively diffused and transmitted without affecting the vertical outgoing light. . In this way, bright lines can be eliminated without reducing the front luminance.

  If the distance L between the refractive index boundaries 8 is sufficiently narrow, in other words, if the density of the refractive index boundaries 8 is sufficiently high, oblique light can be effectively diffused as shown by paths g and h in FIG. On the other hand, when the distance L between the refractive index boundaries 8 is wide, a light beam that passes through the selective light scattering sheet 6 without being scattered is generated as in the path j.

  With respect to this point, as a result of investigating the bright line elimination effect on the selective light diffusion sheet 6 including the columnar refractive index boundary 8 by simulation, the vertical direction of the refractive index boundary 8 shown in FIG. The ratio of the height H in the thickness direction to 6 and the distance L between the refractive index boundaries 8 or the distance L between the cylinder and the adjacent cylinder is preferably H / L ≧ 1, and H / L ≧ 3 is more preferable. The front luminance drop at this time was within 2% as shown in FIG. In the case of H / L ≦ 1, there is a tendency that the bright line elimination effect cannot be obtained to a sufficient extent.

  Further, there may be a case where the refractive index boundary 8 that is completely perpendicular to the upper and lower surfaces of the selective light scattering sheet 6 cannot be formed due to the problem of processing accuracy or ease of processing. When the refractive index boundary 8 is inclined, even vertically emitted light is refracted or reflected at the refractive index boundary 8 as shown by the paths m and n in FIG. FIG. 5 shows that a refractive index boundary 8 having a frustoconical shape (see FIG. 6B) having a side surface inclined by 80 ° with respect to the horizontal plane of the selective light diffusion sheet 6 is formed in the selective light diffusion sheet 6. In the case of a large number, the luminance distribution is oblique 20 ° from the vertical direction. It can be seen that there is a bright line elimination effect equivalent to FIG. 12 described later. Further, the angular distribution of luminance at this time is as shown in FIG. In this case, the decrease in front luminance was about 10%.

  That is, in order to avoid a decrease in front luminance due to scattering of vertical light, as shown in FIGS. 6 (a) and 6 (c), FIGS. 7 (a) and (c), and FIGS. 8 (a) and 8 (c) Most preferably, columnar regions with perpendicular angles to the upper and lower surfaces are formed in the sheet or as protrusions from the sheet. As shown in FIGS. 6 (b) and (d), FIGS. 7 (b) and (d), and FIGS. 8 (b) and (d), the regions constituting the refractive index boundary are truncated cones. The inclination of the side surface with respect to the upper and lower surfaces of the sheet is preferably 80 ° or more.

  Similarly to these, it was found from the simulation that when the angle formed by the side surface of the refractive index boundary 8 is less than 80 ° with respect to the upper and lower surfaces of the selective light scattering sheet 6, the front luminance rapidly decreases. Therefore, the angle between the refractive index boundary 8 and the horizontal plane of the selective light scattering sheet 6 is preferably 80 ° or more, more preferably 83 ° or more, still more preferably 85 or more, extremely preferably 87 ° or more, 90 ° Most preferably.

  As a method of manufacturing the selective light scattering sheet 6 (optical sheet having the refractive index boundary surface 8 of 80 ° or more with respect to the horizontal plane) as described above, for example, a large number of optical fibers are bundled and bonded and thinly sliced. A method of applying a photocurable resin to a mold in which a large number of columnar protrusions are arranged, and curing and peeling by light irradiation, a method of applying a thermosetting resin to the mold and curing and heating and then peeling, A method in which a thermoplastic resin is applied to a mold in a molten state and then solidified by cooling, a method obtained by injection molding using a mold having cavities in which columnar protrusions are arranged, a protrusion or a void by etching after exposing the photosensitive resin to a mask , A method of forming a region with different refractive index by exposing a light-modulating resin film to a mask, and a mixture of resins having different refractive indexes to form a lamellar (chain polymer folded) And a method of forming a lamellar structure using a block copolymer resin in which two or more sites having different refractive indexes are combined.

  For the same reason as described above, the first region 7 made of the material B having a different refractive index from the second region 7 ′ made of the base material A as shown in FIG. 9 does not penetrate the selective light diffusion sheet 6. In this case, a refractive index boundary 8 ′ exists as a second boundary surface on the upper surface or the lower surface of the first region 7. Further, as shown in FIG. 8, the second refractive index boundary 8 'is similarly formed even when the protrusion is formed on the sheet. The refractive index boundary 8 ′ is preferably close to the horizontal only with respect to the upper surface or the lower surface of the selective light diffusion sheet 6. If the refractive index boundary 8 'is horizontal, the vertically emitted light passes through the selective light diffusion sheet 6 without being affected by the upper and lower refractive index boundaries 8' as shown in the path s of FIG. On the other hand, when the upper or lower refractive index boundary 8 ′ is inclined with respect to the horizontal direction, the vertically emitted light is scattered as shown by a path t in the figure, leading to a decrease in front luminance. From the simulation results, the angle formed by the upper or lower refractive index boundary 8 ′ and the horizontal plane is preferably within 10 °.

  On the other hand, the direction distribution in the horizontal plane of the refractive index boundary 8 as the first boundary surface is preferably as uniform and random as possible because it can diffuse oblique light evenly. As an extreme example, FIG. 10 shows a case where all the refractive index boundaries 8 are perpendicular to the upper surface or the lower surface of the selective light scattering sheet 6, that is, parallel to each other. Of the oblique light, light that is not parallel to the refractive index boundary 8 is refracted or reflected by the refractive index boundary as shown by paths q and r in the figure. As shown in the path p in the figure, the light is transmitted through the selective light scattering sheet 6 without being scattered by the refractive index boundary 8.

  Therefore, in order to obtain a homogeneous oblique light scattering effect in the horizontal direction on the upper and lower surfaces of the sheet, the refractive index boundaries are shown in FIGS. 6 (a) and 6 (b), FIGS. 7 (a) and 7 (b), FIG. Those having a circular cross-sectional shape as shown in a) and (b) are most preferable. Another preferred example is a lamellar structure obtained when incompatible resins having different refractive indexes as shown in FIG. 11 are mixed. As shown in FIGS. 6 (c) and (d), FIGS. 7 (c) and (d), and FIGS. 8 (c) and (d), each polygonal prism has a polygonal cross section. It is preferable to make the orientation in the horizontal plane random.

  As a method for producing such a sheet, for example, a method in which a large number of optical fibers are bundled and bonded and sliced thinly, a photocurable resin is applied to a mold in which a large number of columnar protrusions are arranged, and cured by light irradiation and peeled off. A method in which a thermosetting resin is applied to the mold and cured by heating and then peeled off, a method in which a thermoplastic resin is applied to the mold in a molten state and then cooled and solidified, a mold having cavities in which columnar protrusions are arranged A method of obtaining by injection molding using a mold, a method of forming protrusions or voids by etching after exposing a photosensitive resin to a mask, a method of forming a region having a different refractive index by exposing a light-modulating resin film to a mask, A method of forming a lamellar structure by mixing different resins, A method of forming a lamellar structure using a block copolymer resin in which two or more kinds of sites having different refractive indexes are combined Etc., and the like.

  The thickness of the selective light scattering sheet 6 of the present invention is not particularly limited, but is preferably 200 μm or less from the viewpoint of light transmittance, and is preferably 60 μm or more in order to suppress scattering of front emission light due to diffraction. Furthermore, in view of manufacturing and handling convenience, it is more preferably 100 μm or more and 150 μm or less.

  In summary, the most effective embodiment of the present invention is (1) a transparent sheet-like optical sheet having a columnar protrusion, a columnar through-hole, or a columnar region having a different refractive index. (2) The ratio of the height H of the refractive index boundary 8 formed by the cylinder in the sheet thickness direction and the distance L between adjacent refractive index boundaries is H / L ≧ 3. It is what has become. Further, (3) when the first and second regions 7 and 7 'having different refractive indexes in the selective light scattering sheet 6 have a refractive index boundary 8' as a second boundary surface at the upper part or the lower part, Most preferably, the refractive index boundary 8 ′ is parallel to the upper and lower surfaces of the selective light scattering sheet 6.

  As an example of the most effective embodiment of the present invention, there is a selective light scattering sheet 6 in which a columnar refractive index boundary 8 is arranged as shown in FIG. In this example, the refractive index of the first region 7 made of the material B that becomes the columnar region may be larger or smaller than the first region 7 ′ made of the surrounding base material A. As an example in the case where the refractive index is small, there is an example in which holes 9 such as columnar voids and dents of the selective light scattering sheet 6 are provided as shown in FIG. Alternatively, as shown in FIG. 8A, the selective light scattering sheet 6 having the above-described projections has the same effect.

  Further, the effective embodiment of the present invention is (1) a transparent sheet including a refractive index boundary surface 8 as a first boundary surface between the first and second media 7 and 7 ′ having different refractive indexes. (2) The ratio of the height H of the refractive index boundary 8 in the sheet thickness direction and the distance L between the adjacent refractive index boundaries 8 is H / L ≧ 3. (3) The angle between the refractive index boundary 8 and the upper and lower surfaces of the sheet is 80 ° or more. (4) The direction distribution of the refractive index boundary 8 in the horizontal plane of the sheet is uniform and random. (5) When the first and second regions 7 and 7 ′ having different refractive indexes in the selective light scattering sheet 6 have the refractive index boundary surface 8 ′ as the second boundary surface at the upper or lower portion, The angle between the refractive index boundary 8 ′ and the upper and lower surfaces of the selective light scattering sheet 6 is preferably 10 ° or less. As an example, a selective light scattering sheet 6 in which a refractive index boundary 8 having a cylindrical or frustoconical shape is arranged as shown in FIGS. 6 (a) and 6 (b), and a prism as shown in FIGS. 6 (c) and 6 (d). Or the selective light-scattering sheet | seat 6 etc. which have arrange | positioned the truncated pyramid-shaped refractive index boundary 8 so that the direction in a horizontal surface may become random. In these two examples, the refractive index of the first region 7 made of the material B that becomes the columnar or frustoconical region is smaller or larger than the refractive index of the first region 7 ′ made of the surrounding base material A. Also good. As an example in the case where the refractive index is small, a selective light scattering sheet 6 as shown in FIG. 7 may be provided with holes 9 such as columnar or frustoconical voids and dents. Alternatively, a selective light scattering sheet 6 having protrusions having the above shape as shown in FIG. 8 has the same effect. In this case, the protrusions may be provided on either the upper surface or the lower surface of the selective light scattering sheet 6. Moreover, as shown in FIG. 11, a sheet including a lamellar refractive index boundary 8 randomly formed in the horizontal plane of the selective light scattering sheet 6 can be used. However, the scope of the present invention is not limited to these examples.

  FIG. 12 is a photograph taken by placing the selective light scattering sheet 6 on which the optical fibers are vertically aligned and hardened on the same backlight device as FIG. The optical fiber has a structure in which a thin line with a high refractive index is covered with a low refractive index material, and can be said to be one form of the selective light diffusion sheet 6 assumed in the present invention. Compared with FIG. 17, it can be seen that the bright lines are eliminated. FIG. 13 shows simulation results assuming the same situation. Since FIG. 17 and FIG. 19 and FIG. 12 and FIG. 13 show good agreement, it can be seen that the characteristics of the selective light diffusion sheet 6 can be effectively predicted by using simulation. As a result of simulation, the decrease in front luminance due to the selective diffusion sheet 6 was within 2%.

It is a figure which shows a backlight apparatus, Comprising: (a) shows the principle of the oblique light scattering by the refractive index boundary seen from the output surface side, (b) shows the oblique light by the refractive index boundary seen in the cross section of the backlight apparatus. It is a figure which shows the principle of scattering. It is a figure explaining the change of diagonal light scattering ability when the refractive index boundary space | interval L of a selective light-diffusion sheet is changed. It is a graph which shows the influence on front luminance by a selective light diffusion sheet. It is a figure explaining scattering of the perpendicular | vertical outgoing light which arises when the 1st refractive index boundary of a selective light-diffusion sheet inclines from perpendicular | vertical. It is a figure which shows the bright line cancellation effect by the selective light-diffusion sheet | seat simulated for the case where the frustoconical type | mold refractive index boundary which has a side surface of 80 degrees with respect to a horizontal surface is included. It is a figure which shows the example of a selective light-diffusion sheet, Comprising: (a) contains the cylindrical area | region where a refractive index differs from a base material, (b) contains the frustoconical area | region where a refractive index differs from a base material, (C) includes a prismatic region whose refractive index faces a random direction different from that of the base material, and (d) includes a truncated pyramid region whose refractive index faces a random direction different from that of the base material. It is a figure which shows the example of a selective light-diffusion sheet | seat, Comprising: (a) contains a cylindrical space | gap, (b) contains a frustoconical space | gap, (c) is the prismatic shape which faced the random direction. (D) includes truncated pyramid-shaped voids oriented in random directions. It is a figure which shows the example of a selective light-diffusion sheet, (a) has a cylindrical protrusion, (b) has a frustoconical protrusion, (c) turned to the random direction. (D) has truncated pyramid-shaped protrusions oriented in a random direction. It is a figure explaining scattering of the perpendicular | vertical emitted light when the refractive index boundary as a 2nd boundary surface inclines from horizontal. It is a figure explaining the oblique light-scattering effect seen from the output surface side in case the refractive index boundary as a 1st interface is aligned. It is a front view of the example of the selective light-diffusion sheet | seat containing the lamellar-shaped refractive index boundary formed with two types of materials from which a refractive index differs. It is the photograph of the corner light incident type backlight apparatus image | photographed from the point which inclined 20 degrees from the perpendicular direction along the diagonal of a backlight apparatus at the time of using a selective light-diffusion sheet. This is a luminance distribution obtained from a simulation when a selective light diffusion sheet is used and viewed from a point inclined 20 ° from the vertical direction along the diagonal line of the backlight device. It is the schematic diagram which looked at the corner light-incident type backlight device from the exit surface side, and explains the bright line generation mechanism. It is the model which looked at the edge light-incident type backlight device from the exit surface side, and explains the bright line generation mechanism. FIG. 15 is a cross-sectional view taken along the line A-A ′ of FIG. 14 or the line B-B ′ of FIG. 15, showing how light propagates in the backlight device. It is the photograph of the corner light incident type backlight device taken from a point inclined 20 ° from the vertical direction along the diagonal line of the backlight device. It is a schematic diagram which shows the camera position when the photograph of FIG. 17 was image | photographed. It is a luminance distribution obtained from a simulation and viewed from a point inclined 20 ° from the vertical direction along the diagonal line of the backlight device. It is a figure explaining the principle of the bright line cancellation by the selective diffusion sheet seen from the output surface side of the backlight device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Light guide plate 3 Reflector 4 Light deflection film 5 Reflector plate 6 Selective light diffusion sheet 7, 7 'Selection of first and second regions 8, 8' having different refractive indexes in the selective light diffusion sheet Refractive Index Boundary 9 as First and Second Interface in Optical Light Diffusing Sheet 10 Holes in Selective Light Diffusing Sheet Backlight Device 100 Backlight Device 101 Light Source 102 Light Guide Plate 103 Reflector 104 Light Polarizing Film 105 Reflector 110 camera

Claims (15)

An optical sheet composed of two media having a lower surface on which light is incident and an upper surface from which light is emitted and having different refractive indexes,
The optical sheet, wherein an angle between the first boundary surface between the media and the lower surface is 80 ° or more and 90 ° or less.   The optical sheet according to claim 1, wherein the upper surface and the lower surface are substantially parallel.   For light incident perpendicularly to the lower surface, the intensity ratio of light emitted perpendicularly from the upper surface is 90% or more, and for light incident obliquely with respect to the lower surface, the emission angle from the upper surface is the lower surface The optical sheet according to claim 1, wherein the optical sheet is smaller than an incident angle on the optical sheet.   When the projected length of the first boundary surface in the thickness direction of the optical sheet is H and the distance between the first boundary surface and the adjacent first boundary surface is L, the relationship of H ≧ 3L is established. The optical sheet according to claim 1, wherein the optical sheet is satisfied.   The two media are a base material A and a material B having a refractive index different from the base material A, and the material B has a cylindrical shape, a prismatic shape, or a truncated cone shape, and a plurality of materials B include a base material. The optical sheet according to claim 1, wherein the optical sheet has a structure embedded in the material A.   The optical sheet according to claim 5, wherein the material B has a refractive index larger than that of the base material A.   The optical sheet according to claim 5, wherein the material B has a refractive index smaller than that of the base material A.   The optical sheet according to claim 1, wherein the first boundary surface has a lamellar shape.   The sheet made of the base material A has a structure in which a through hole is provided, and the through hole is a cylindrical, prismatic, truncated cone-shaped or truncated cone-shaped through-hole. An optical sheet according to any one of the above.   5. The optical sheet according to claim 1, wherein the optical sheet has a structure in which a large number of cylindrical or prismatic members made of the base material A are bundled, and each member has a gap.   The optical sheet according to claim 1, wherein the optical sheet has a second boundary surface having an angle of 0 ° or more and 10 ° or less with the lower surface.   The optical sheet according to claim 11, wherein conical, truncated conical, conical or truncated conical projections or depressions are provided on the surface of the optical sheet made of the base material A.   A conical, truncated conical, conical or truncated conical recess is provided on the surface of the optical sheet made of the base material A, and the base material A and a material B having a different refractive index are filled in the concave portion. The optical sheet according to claim 11, having the structure described above.   The optical sheet according to any one of claims 1 to 13, provided with a light source, a light guide that emits incident light from the light source from a surface different from the incident surface, and an output surface of the light guide. And a planar light source device. A liquid crystal display device having a structure in which the optical sheet according to claim 1 is provided on a back surface of a liquid crystal display element.

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