JP2010210904A - Optical diffusion sheet, and backlight device and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical diffusion sheet that extends the viewing angle and provides high front plane luminance. <P>SOLUTION: The optical diffusion sheet 16 is used for an edge light type backlight device. The optical diffusion sheet 16 includes a first refraction layer 17 having a front surface 171 having a plurality of linear prisms LP formed thereon. The optical diffusion sheet includes a second refraction layer 18 that is formed on the front surface 171 and has a refractive index different from that of the linear prisms LP. Light entering in the normal direction of the light diffusion sheet 16 from the rear surface 172 of the first refraction layer 17 is refracted on the front surface 171 as a boundary surface between the first and second refraction layers. At this time, the light is hardly totally-reflected, and retroreflection hardly occurs. The light having transmitted through the front surface 171 is further refracted on the front surface 181 of the second refraction layer 18, and goes to the outside. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light diffusing sheet, and more particularly to a light diffusing sheet used in an illumination device such as a backlight device mounted on a liquid crystal display device.

  A liquid crystal display device represented by a liquid crystal display is required to improve front luminance. In order to improve the front luminance, a lens sheet is used in the liquid crystal display device. Examples of the lens sheet include a prism sheet, a lenticular lens sheet, and a microlens array sheet.

  In the edge light type backlight device, the lens sheet is laid on the light guide plate. The light emitted from the light guide plate has directivity in a direction inclined by a predetermined angle from the normal direction of the light guide plate to the side opposite to the light source. The lens sheet receives light from the light guide plate and deflects the received light in the normal direction of the lens sheet, that is, in the front direction of the backlight device. Therefore, the front luminance of the backlight device is improved.

  As described above, in the edge light type backlight device, light having directivity in a predetermined direction is deflected to the front of the backlight device by the lens sheet. Therefore, the light emitted from the lens sheet also has directivity, and the light is excessively concentrated in the front direction. That is, the viewing angle is narrow. In addition to viewing the display screen from the front, the user may view the display screen from an oblique direction slightly shifted from the front. When the display screen is viewed from an oblique direction, the brightness is rapidly reduced as compared to the case of viewing from the front, and thus the user feels uncomfortable.

  In order to suppress such a sense of incongruity, generally, a viewing angle of the liquid crystal display device is expanded by laying a diffusion sheet on the lens sheet. The diffusion sheet includes a binder resin and a plurality of particles (beads) having a refractive index different from that of the binder resin. The diffusion sheet diffuses light by reflecting and refracting light at the boundary surface between the binder resin and the granular material.

  Certainly, if the above-described diffusion sheet is used, the light from the lens sheet is diffused, so that the viewing angle is widened. However, so-called retroreflection occurs in which part of incident light that has repeatedly reflected inside the diffusion sheet returns to the lens sheet direction. Retroreflective reduces the light utilization efficiency and thus reduces the front brightness.

  The optical sheet disclosed in Japanese Patent Application Laid-Open No. 2003-21706 includes a plurality of triangular portions arranged in parallel and a diffusing portion fitted between adjacent triangular portions. The diffusion portion is formed of a binder and beads having a refractive index different from that of the binder. The optical sheet disclosed in this document deviates a light beam incident in an oblique direction from the back surface of the optical sheet in the front direction of the display screen. Furthermore, it is said that the brightness can be made uniform by diffusing light rays in the diffusing section (see paragraphs [0014] and [0015]). However, the binder and beads of the diffusion part disclosed in this document have different refractive indexes. Therefore, a part of the light incident on the diffusing part is retroreflected, and the light use efficiency is considered to be reduced.

JP 2003-21706 A JP 2005-156923 A

  The objective of this invention is providing the light-diffusion sheet which can expand a viewing angle and can obtain high front luminance.

Means for Solving the Problems and Effects of the Invention

  The light diffusing sheet according to the present invention includes first and second refractive layers. The first refractive layer has a main surface on which a plurality of first protrusions are formed. The second refractive layer is formed on the main surface of the first refractive layer. The second refractive layer has a refractive index different from that of the first convex portion.

  In the light diffusing sheet according to the present invention, first and second refractive layers having different refractive indexes are laminated. Since the first and second refractive layers have different refractive indexes, they are refracted on the principal surface that is the boundary surface between the first and second refractive layers. Furthermore, since the refractive index of the second refractive layer is larger than the refractive index of air, light is difficult to totally reflect on the main surface. Therefore, in the light diffusing sheet in the present invention, retroreflection hardly occurs and the light use efficiency can be improved, so that high front luminance can be obtained. Further, the light refracted on the main surface of the first refractive layer is further refracted on the surface of the second refractive layer and emitted to the outside. That is, the light diffusion sheet refracts light twice and emits it to the outside. Therefore, the light diffusion sheet can diffuse light and can widen the viewing angle.

  Preferably, the second refractive layer further has a surface on which a plurality of second convex portions are formed.

  In this case, light can be further diffused on the surface of the second refractive layer.

  Preferably, the plurality of first convex portions are a plurality of columnar lenses arranged side by side, and a cross section in the width direction of the columnar lens has a shape in which the width becomes narrower from the bottom to the top of the columnar lens. .

  In this case, when light enters in the normal direction of the light diffusion sheet from the first refractive layer side, the light can be further diffused on the main surface of the first refractive layer.

  Preferably, the second convex portion has a cross-sectional shape whose width becomes narrower from the bottom to the top of the second convex portion.

  In this case, light can be further diffused on the surface of the second refractive layer.

  Preferably, the plurality of second convex portions are arranged in a matrix.

  In this case, light is easily diffused uniformly.

  Preferably, the second refractive layer contains a binder resin and a plurality of granular materials. The plurality of granular materials have the same refractive index as the binder resin. A 2nd convex part is formed when a part of granular material protrudes from the surface. Here, the same refractive index includes those whose difference in refractive index is within 0.05.

  In this case, light can be prevented from being refracted at the boundary surface between the binder resin and the granular material in the second refractive layer, and retroreflection can be suppressed.

  Preferably, the refractive index of the second refractive layer is larger than the refractive index of the first convex portion.

  In this case, since total reflection does not occur at the boundary surface between the first and second refractive layers, retroreflection can be suppressed.

  The backlight device according to the present invention includes a light guide plate, a light source disposed on a side surface of the light guide plate, a lens sheet, and the diffusion sheet. The lens sheet receives light emitted from the light guide plate and emits the received light in the normal direction of the light guide plate. A liquid crystal display device according to the present invention includes the above-described backlight device and a liquid crystal panel laid on the backlight device.

It is sectional drawing which shows the structure of the liquid crystal display device by embodiment of this invention. It is a figure which shows the brightness | luminance angle characteristic of the light-guide plate shown in FIG. It is sectional drawing of the light-guide plate and total reflection type prism sheet which were shown in FIG. It is sectional drawing of the light-diffusion sheet shown in FIG. It is a top view of the light-diffusion sheet shown in FIG. It is a figure which shows the locus | trajectory of the light which injected into the conventional prism sheet. It is a figure which shows the locus | trajectory of the light which injected into the conventional lenticular lens sheet. It is a figure which shows the locus | trajectory of the light which injected into the conventional light-diffusion sheet. It is a figure which shows an example of the locus | trajectory of the light which injected into the light-diffusion sheet | seat shown in FIG. It is a figure which shows examples other than FIG. 9 of the locus | trajectory of the light which injected into the light-diffusion sheet | seat shown in FIG. It is a figure which shows the other example of the light-diffusion sheet different from FIG. It is a figure which shows the other example of the light-diffusion sheet different from FIG.4 and FIG.11. It is a figure which shows the other example of the light-diffusion sheet different from FIG.4, FIG11 and FIG.12. It is a figure which shows the structure of the lenticular lens sheet | seat used in the Example. It is a figure which shows the luminance angle characteristic of the backlight apparatus measured in the Example. It is a figure which shows the other brightness angle characteristic different from FIG. It is a figure which shows the other brightness | luminance angle characteristic different from FIG.15 and FIG.16.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Configuration of liquid crystal display device]
Referring to FIG. 1, liquid crystal display device 1 according to the present embodiment includes a backlight device 10 and a liquid crystal panel 20. The liquid crystal panel 20 is laid on the backlight device 10. The liquid crystal panel 20 has a known structure.

  The backlight device 10 is an edge light type. The backlight device 10 includes a light source 11, a resin mold 12, a reflection sheet 13, a light guide plate 14, a prism sheet 15, and a light diffusion sheet 16.

  The light source 11 is a plurality of point light sources arranged in the normal direction of the paper surface of FIG. The point light source is, for example, an LED (Light Emitting Device). The light source 11 may be a line light source extending in the normal direction of the sheet of FIG. The line light source is, for example, an EEFL (External Electrode Fluorescent Lamp). The light source 11 may be composed of only one LED. The light source 11 is disposed adjacent to the side surface 141 of the light guide plate 14.

  The resin mold 12 is an opaque frame. A light source 11 and a light guide plate 14 are accommodated inside the resin mold 12. Reflective sheets 13 are laid on the top and bottom of the light source 11 and on the back surface 143 of the light guide plate 14. A reflective layer is formed on the main surface of the reflective sheet 13. The reflective layer may be a metal thin film such as silver or aluminum, or a white reflective film coated with a white powder such as titanium oxide or zirconium oxide. Moreover, the multilayer film which laminated | stacked the transparent thin film from which refractive index differs may be sufficient. The reflective layer faces the light source 11 and the light guide plate 14. The reflection sheet 13 guides the light emitted from the light source 11 to the light guide plate 14. Further, the light emitted from the back surface 143 of the light guide plate 14 is reflected and returned to the light guide plate 14. Thereby, the reflection sheet 13 suppresses light from leaking from a surface other than the main surface 142 of the light guide plate 14.

  The light guide plate 14 includes a sheet-like main body having a side surface 141, a main surface 142, and a back surface 143. The main surface 142 is orthogonal to the side surface 141. A back surface 143 is disposed on the opposite side of the main surface 142. The light guide plate 14 is made of, for example, a resin such as polycarbonate resin, cyclic olefin resin, acrylic resin, epoxy resin, or urethane resin. A dot pattern is formed on the back surface 143. Light from the light source 11 is incident on the side surface 141 and travels while being totally reflected in the light guide plate 14. When the light enters the dot pattern, the light is deviated in the direction of the main surface 142 and is emitted from the main surface 142 to the outside. The dot pattern may be formed by printing or may be formed by injection molding.

  An example of the luminance angle characteristic of the light emitted from the main surface 142 of the light guide plate 14 is shown in FIG. The horizontal axis in FIG. 2 indicates the inclination angle (deg) of the main surface 142 from the normal N14, as shown in FIG. The luminance at an angle of 0 (deg) indicates the luminance in the normal N14 direction. The plus (+) direction on the horizontal axis indicates an angle inclined from the normal line N14 to the opposite side to the light source 11 (+ X direction in the figure), and the minus (−) direction indicates the light source 11 side (in the figure from the normal line N14). The angle inclined in the direction opposite to the + X direction) is shown. The vertical axis in FIG.

  Referring to FIG. 2, the luminance angle characteristic of the light emitted from light guide plate 14 has a luminance peak in a direction inclined by angle A0 (deg) from normal line N14 to the side opposite to light source 11 (+ X direction). And the full width at half maximum is very narrow. That is, the light R0 emitted from the light guide plate 14 has directivity having a luminance peak in the direction of the angle A0. The inclination angle A0 (deg) is generally 65 ° to 80 °.

  With reference to FIGS. 1 and 3, the prism sheet 15 is a so-called lens sheet, and is laid on the light guide plate 14. The prism sheet 15 is a total reflection type prism sheet, and has a sheet-like or film-like main body. The prism sheet 15 has an entrance surface 151 and an exit surface 150 on the opposite side of the entrance surface 151. The incident surface 151 faces the main surface 142 of the light guide plate 14. Then, the light emitted from the light guide plate 14 is received. The incident surface 151 has a plurality of linear prisms 152 arranged in parallel with each other. The transverse shape of each linear prism 152 is triangular, and extends in the arrangement direction of the light sources 11 (in the case where the light source 11 is a linear light source, the extending direction of the light source 11). Each linear prism 152 includes two inclined surfaces 153 and 154 and a top 155 formed by the inclined surfaces 153 and 154. The inclined surface 153 is disposed on the light source 11 side, and the inclined surface 154 is disposed farther from the light source 11 than the inclined surface 153. Light emitted from the light guide plate 14 enters the inclined surface 153. The inclined surface 154 totally reflects the light incident from the inclined surface 153. At this time, the light R0 is deflected in the direction of the normal line N15 of the prism sheet 15 and is emitted from the emission surface 150 to the outside. That is, the light from the light source 11 is emitted in the front direction of the backlight device 10.

[Configuration of light diffusion sheet]
With reference to FIGS. 1 and 4, the light diffusion sheet 16 includes a first refractive layer 17 and a second refractive layer 18.

  The first refractive layer 17 has a sheet shape or a film shape, and has a structured front surface 171 and a back surface 172 opposite to the front surface 171. The back surface 172 faces the emission surface 150 of the prism sheet 15. The first refractive layer 17 receives light from the prism sheet 15, refracts the received light at the surface 171, and emits the light to the second refractive layer 18.

  The first refractive layer 17 includes a base material portion 173 and a plurality of linear prisms (Linear Prism) LP. The material of the base material part 173 is a resin having translucency, for example, a polyester resin, a polycarbonate resin, a polyacrylate resin, an alicyclic polyolefin resin, a polystyrene resin, a polyvinyl chloride resin, Examples thereof include polyvinyl acetate resin, polyether sulfonic acid resin, and triacetyl cellulose resin.

  Each linear prism LP extends in the arrangement direction of the point light sources when the light source 11 is a plurality of point light sources, and extends in the extending direction of the light sources 11 when the light source 11 is a linear light source. The plurality of linear prisms LP are arranged side by side in the width direction of the linear prism LP. The cross-sectional shape in the width direction of each linear prism LP is triangular. That is, the cross section of the linear prism LP has a shape in which the width gradually narrows from the bottom surface toward the top TP.

  The material of the plurality of linear prisms LP is made of translucent ionizing radiation curable resin. The ionizing radiation curable resin is cured by ionizing radiation such as ultraviolet rays and electron beams. Examples of ionizing radiation curable resins include polyester acrylate resins, urethane acrylate resins, polyether acrylate resins, epoxy acrylate resins, polyester methacrylate resins, urethane methacrylate resins, polyether methacrylate resins, and epoxy methacrylate resins. is there. The linear prism LP may be formed of a light-transmitting thermoplastic resin such as a polycarbonate resin, a polyacrylate ester resin, or an alicyclic polyolefin resin instead of the ionizing radiation curable resin. In short, the linear prism LP is made of resin.

  Moreover, the base material portion 173 of the first refractive layer 17 and the plurality of linear prisms LP may be made of the same material and integrally formed. In this case, the first refractive layer 17 is formed of the same material as the above-described base material portion 173, that is, any one of the above-described resins.

  The second refractive layer 18 is formed on the surface 171 of the first refractive layer 17. The material of the second refractive layer 18 is the same resin as the material of the base material portion 173 and the lens portion 174 described above. However, the refractive index of the second refractive layer 18 is different from the refractive index of the linear prism LP. Therefore, the light incident on the light diffusion sheet 16 is refracted at the boundary surface between the first refractive layer 17 and the second refractive layer 18, that is, the surface 171.

  The second refractive layer 18 refracts the light received from the first refractive layer 17 on the surface 181 and emits the light to the outside. A plurality of convex portions are formed on the surface 181. Specifically, as shown in FIGS. 4 and 5, a microlens array including a plurality of microlenses ML is formed on the surface 181. The microlens ML has an arcuate, arcuate or elliptical arcuate cross-sectional shape. In other words, it has a cross-sectional shape in which the width gradually decreases from the bottom toward the top. 4 and 5, the adjacent microlenses ML are in contact with each other, but the adjacent microlenses ML are separated from each other, and there may be a gap between them.

  The light refracted on the surface 171 of the first refractive layer 17 is further refracted on the surface 181 of the second refractive layer 18 and is emitted to the outside. That is, the light diffusion sheet 16 refracts light at the surfaces 171 and 181. The light emitted from the prism sheet 15 is diffused by the two refractions. Hereinafter, the operation of the light diffusion sheet will be described in detail.

[Operation of light diffusion sheet]
The light R15 emitted from the emission surface 150 of the prism sheet 15 travels in the normal N15 direction of the prism sheet 15, in other words, in the front direction of the backlight device 10, as shown in FIG. Here, as shown in FIG. 6, a case is assumed where a refractive prism sheet (a type in which linear prisms are arranged on the upper side) is laid on the prism sheet 15 instead of the light diffusion sheet 16. In this case, the light R15 is totally reflected by the two inclined surfaces of each linear prism of the refractive prism sheet, and returns to the prism sheet 15. That is, the light R15 is retroreflected.

  Further, as shown in FIG. 7, the same applies when a lenticular lens sheet is laid instead of the light diffusion sheet 16. The light R15 is totally reflected a plurality of times by the convex surface of each cylindrical lens on the lenticular lens sheet, and returns to the prism sheet 15. That is, retroreflection occurs.

  As shown in FIG. 8, when the diffusion sheet 300 is laid on the prism sheet 15 instead of the light diffusion sheet 16, retroreflection occurs as in FIGS. 6 and 7. The diffusion sheet 300 includes a binder resin 301 and a plurality of beads 302. The beads 302 have a refractive index different from that of the binder resin 301. When the light R15 enters the diffusion sheet 300, refraction or reflection at the boundary surface between the binder resin 301 and the beads 302 is repeated. As a result, retroreflection occurs, and a part of the light R15 returns to the prism sheet 15.

  On the other hand, the light diffusion sheet 16 according to the present embodiment suppresses retroreflection of the light R15 and improves the light utilization efficiency. The refractive index nLP of the plurality of linear prisms LP forming the surface 171 of the first refractive layer 17 is different from the refractive index n18 of the second refractive layer 18. Further, since the second refractive layer 18 is made of resin, its refractive index n18 is larger than the refractive index n0 of air. Therefore, the relative refractive index (n18 / nLP) when the light R15 travels from the first refractive layer 17 to the second refractive layer 18 is shown in FIG. The relative refractive index (n0 / nLP) when going from the same prism LP to the atmosphere. As a result, the critical angle at the boundary surface (surface 171) between the first refracting layer 17 and the second refracting layer 18 is increased, and the light R15 is less likely to be totally reflected by the surface 171.

  As described above, the light R15 is refracted without being totally reflected by the surface 171 and proceeds to the second refractive layer 18. At this time, the light R15 is diffused on the surface 171 of the first refractive layer. The light R15 is further diffused by the microlens ML on the surface 181 of the second refractive layer 18, and is emitted to the outside. Therefore, the light R15 is diffused by the two surfaces 171 and 181 respectively.

  As described above, the light diffusion sheet 16 improves the light use efficiency by suppressing the retroreflection and improves the front luminance. The light diffusion sheet 16 can further widen the viewing angle by diffusing light twice. Hereinafter, the case where the refractive index nLP is larger than the refractive index n18 and the case where the refractive index nLP is smaller will be described in detail.

[When refractive index nLP is smaller than refractive index n18]
When the refractive index nLP is smaller than the refractive index n18, the light R15 is not totally reflected by the surface 171. Therefore, as shown in FIG. 9, the light is refracted in opposite directions on the slope S1 and the slope S2 of the linear prism LP. As a result of the refraction, the light R15 travels in the second refracting layer 18 with a deviation from the direction of the normal line N16 (parallel to the normal line N15 and corresponding to the front direction of the backlight device 10). Thus, the light R15 is diffused on the surface 171.

  Subsequently, the light R15 traveling in the second refractive layer 18 reaches the convex surface of the microlens ML on the surface 181. If the light R15 travels in parallel with the normal line N15, it is easy to retroreflect the convex surface of the microlens ML. However, as described above, the light R15 enters the microlens ML from a direction deviated from the normal line N15. Therefore, the light R15 is difficult to retroreflect, and is refracted by the microlens ML and emitted to the outside. As a result, the light R15 is difficult to retroreflect and is diffused by the surface 171 and the surface 181.

[When refractive index nLP is larger than refractive index n18]
In general, total reflection can occur when light travels from a medium having a large refractive index to a medium having a small refractive index. However, the relative refractive index n18 / nLP is larger than the relative refractive index n0 / nLP. Therefore, the critical angle at the surface 171 which is the boundary surface is larger than that in the case of FIG. Therefore, even when the refractive index nLP is larger than the refractive index n18, the light R15 is difficult to totally reflect on the surface 171 and the light R15 is refracted on the surface 171 as shown in FIG. At this time, the light R15 is refracted in the direction opposite to that in FIG. The light R15 traveling in the second refraction layer is further refracted by the microlens ML on the surface 181 and emitted to the outside as in FIG. As a result, the light R15 is difficult to retroreflect and is diffused by the surface 171 and the surface 181.

  As described above, in the light diffusion sheet 16, the refractive index nLP of the linear prism LP of the first refractive layer is different from the refractive index n18 of the second refractive layer 18. Therefore, the light diffusion sheet 16 diffuses light on the surface 171 of the first refractive layer. Further, light is diffused also on the surface 181 of the second refractive layer 18. Further, retroreflection of light at the surfaces 171 and 181 can be suppressed. Therefore, the viewing angle can be widened, the light use efficiency can be improved, and the front luminance can be increased.

  The light diffusing sheet 16 can achieve the above-described effects if the refractive indexes nLP and n18 are different, but it is preferable that the refractive index n18 is larger than the refractive index nLP. This is because total reflection cannot occur on the surface 171.

When the refractive index n18 is smaller than the refractive index nLP, and referring to FIG. 10, if the base angle of the linear prism LP of the first refractive layer 17 is ALP (deg), the base angle ALP is expressed by the following formula ( It is preferable to satisfy 1).
ALP ≦ sin ⁻¹ (n18 / nLP) (1)
In this case, since total reflection does not occur on the slopes S1 and S2 of the linear prism LP, retroreflection can be further suppressed.

[Production method]
A method for manufacturing the light diffusion sheet 16 will be described. First, the first refractive layer 17 is manufactured. The manufacturing method of the 1st refractive layer 17 is as follows. Prepare a roll mold. Pattern grooves corresponding to the plurality of linear prisms LP are formed on the surface of the roll-shaped mold by cutting. Subsequently, a base film corresponding to the base portion 173 is prepared. An ionizing radiation curable resin is filled between the prepared base film and the mold surface, and cured by irradiating with ionizing radiation. The ionizing radiation curable resin is filled with, for example, a die coater. Subsequently, the base film on which the cured ionizing radiation curable resin is formed is peeled from the roll mold. The first refractive layer 17 is obtained by the above method.

  When the base material portion 173 and the lens portion 174 of the first refractive layer 17 are integrally formed of the same material, the first refractive layer 17 is manufactured by the following method. A base material is produced with a thermoplastic resin. Then, the uneven | corrugated pattern corresponding to the linear prism LP is heat-pressed to the base material by the metal mold | die formed in the surface by cutting, and an uneven | corrugated pattern is transcribe | transferred to the base material surface. The first refractive layer 17 is manufactured by the above process. The first refractive layer 17 may be manufactured by a known extrusion molding method, press molding method, or an injection molding method in which a molten resin is injected into a mold.

  Subsequently, the second refractive layer 18 is formed on the surface 171 of the first refractive layer 17. First, a roll mold is prepared. Holes corresponding to the plurality of microlenses ML on the surface 181 are formed on the surface of the roll-shaped mold. Next, an ionizing radiation curable resin for the second refractive layer 18 is prepared. At this time, the ionizing radiation curable resin is selected so that the refractive index of the second refractive layer 18 is different from the refractive index of the linear prism LP of the first refractive layer 17. The prepared ionizing radiation curable resin is filled between the surface 171 of the first refractive layer 17 and the mold surface, and cured by irradiation with ionizing radiation. Then, the first refractive layer 17 on which the cured second refractive layer 18 is formed is peeled off from the roll mold. The light diffusion sheet 16 is manufactured by the above method.

[Other forms of light diffusion sheet]
In the light diffusion sheet 16 shown in FIG. 4, a plurality of microlenses ML are formed on the surface 181 of the second refractive layer 18. However, the surface 181 is not limited to the microlens ML, and convex portions having other shapes are formed. May be. For example, instead of the microlens ML, a lens array such as a cone, a pyramid, a truncated cone, and a truncated pyramid may be formed. Further, instead of the microlens ML, a plurality of linear lenses such as a linear prism and a cylindrical lens may be arranged side by side in the width direction of each lens. At this time, the extending direction of the columnar lens on the surface 181 is preferably parallel to the extending direction of the linear prism LP on the surface 171. Further, as shown in FIG. 11, a convex portion having a trapezoidal cross-sectional shape in the same direction as the width direction of the linear prism LP may be formed.

  In short, the convex portion formed on the surface 181 may have a cross-sectional shape whose width becomes narrower from the bottom to the top of the convex portion. Preferably, the cross-sectional shape in the same direction as the width direction of the linear prism LP becomes narrower from the bottom toward the top. More preferably, the transverse shape of the protrusion on the surface 181 is arcuate. In this case, the contact angle A18 (see FIG. 4) formed by the bottom and the surface of the convex portion is preferably 30 deg or less. In this case, the light incident on the surface 181 is less likely to be retroreflected.

  In the light diffusion sheet 16 shown in FIG. 4, the first refractive layer 17 includes a plurality of linear prisms LP, but a plurality of cylindrical lenses may be provided in parallel instead of the plurality of linear prisms LP. . Further, it may be a columnar lens arranged side by side like the linear prism LP, and the cross-sectional shape in the width direction may be trapezoidal. The cross-section in the width direction of the columnar lens only needs to have a shape in which the width becomes narrower from the bottom to the top of the columnar lens. In place of the linear prism LP, a plurality of microlenses arranged in a matrix on the surface of the base material portion 173, or a lens array such as a cone, a pyramid, a truncated cone, and a truncated pyramid may be formed.

  In short, the surface 171 of the first refracting layer 17 and the surface 181 of the second refracting layer 18 have a plurality of protrusions, and each protrusion narrows from the bottom toward the top. It is only necessary to have a cross-sectional shape. The plurality of convex portions may be columnar lenses or lenses constituting a lens array. However, when the convex portion is a columnar lens, the cross-sectional shape in the width direction is a shape in which the width becomes narrower from the bottom to the top. Further, in the case where the convex portion is a lens constituting a lens array, the longitudinal cross-sectional shape is a shape whose width becomes narrower from the bottom to the top.

  However, the surface 171 preferably has a plurality of columnar lenses extending in the arrangement direction of the light sources 11 (in the case of a point light source) or in the extending direction (in the case of a line light source), and more preferably the columnar lenses are shown in FIG. Thus, the linear prism LP is preferable. This is because the linear prism LP can refract the light R15 more than a cylindrical lens or a lens array.

[Second Embodiment]
Referring to FIG. 12, the light diffusion sheet 26 according to the second embodiment includes a first refractive layer 17 and a second refractive layer 28.

  The second refractive layer 28 contains a binder resin 282 and a plurality of granular materials 283. The material of the binder resin 282 is the same as the material of the second refractive layer 18 in the first embodiment. The granular material 283 is a substantially spherical organic or inorganic material having translucency. The granular material 283 is, for example, a light-transmitting inorganic material such as an oxide or nitride such as silica, titania, alumina, or zirconia, an acrylic resin, or a styrene resin. A plurality of convex portions are formed on the surface 281 of the second refractive layer 28 by partially protruding the granular material 283.

  The granular material 283 has the same refractive index as the binder resin 282. Here, the same refractive index means that the difference in refractive index between each other is within 0.05. Further, as in the first embodiment, the second refractive layer 28 has a refractive index different from that of the first refractive layer 17.

  A plurality of convex portions are formed on the surface 281 of the second refractive layer 28 by the granular material 283. Therefore, the second refractive layer 28 has the same function as the second refractive layer 18 in the first embodiment. Further, the granular material 283 has the same refractive index as that of the binder resin 282. Therefore, it is possible to suppress the occurrence of reflection and refraction at the boundary surface between the granular material 283 and the binder resin 282, and it is possible to suppress the occurrence of retroreflection.

[Third Embodiment]
Referring to FIG. 13, the light diffusion sheet 36 according to the third embodiment includes a first refractive layer 17 and a second refractive layer 38. The configuration of the first refractive layer 17 is the same as that of the first embodiment.

  The material of the second refraction layer 38 is the same as that of the second refraction layer 18 of the first embodiment. The second refractive layer 38 has a refractive index different from that of the first refractive layer 17.

  Unlike the surface 181 of the second refractive layer 18 of the first embodiment, the surface 381 of the second refractive layer 38 is flat. That is, the surface 381 has no unevenness. Even if the surface 381 is flat, the light R15 is refracted by the surface 381. When the light R15 is refracted on the surface 171, it deviates from the normal direction of the light diffusion sheet 36. Therefore, the incident angle when the light R15 emitted from the surface 171 enters the surface 181 is larger than 0 deg. As a result, the light R15 is refracted and diffused to some extent on the surface 381.

The light diffusion sheets of the inventive examples and comparative examples shown in Table 1 were prepared, and a backlight device was manufactured. And the brightness angle characteristic of each backlight apparatus was investigated.

[Invention Example 1]
The light diffusion sheet of Example 1 of the present invention was configured as shown in FIG. As shown in Table 1, the refractive index of the first refractive layer (base material portion and linear prism) was 1.56. The refractive index of the second refractive layer was 1.49. The cross-sectional shape in the width direction of the linear prism was an isosceles triangle, the width WLP of the linear prism was 16 μm, and the base angle ALP was 45 deg. Further, the width WML of the microlens ML was 3.5 μm, the height HML was 0.56 μm, and the curvature radius RML of the convex surface was 3 μm.
[Invention Example 2]
The light diffusion sheet of Example 2 of the present invention was configured as shown in FIG. The refractive index of the first refractive layer was 1.60. Further, in the second refractive layer, the refractive index of the binder resin and the granular material (bead) is substantially the same, the refractive index of the binder resin is 1.49, and the refractive index of the granular material (bead) is 1.51. It was. The granular material was spherical and had a diameter of 2 μm. Further, the maximum value of the height H283 (see FIG. 12) of the granular material protruding from the surface of the second refractive layer was 0.37 μm.
[Invention Example 3]
The light diffusion sheet of Example 3 of the present invention was configured as shown in FIG. The refractive index of the first refractive layer was 1.6, and the refractive index of the second refractive layer was 1.4. Other configurations were the same as those of Example 1 of the present invention.
[Comparative Example 1]
In Comparative Example 1, a light diffusion sheet having a trade name of D122S manufactured by Tsujiden Corporation was used. The haze value of this light diffusion sheet was 75%.
[Comparative Example 2]
In Comparative Example 2, a light diffusion sheet having a trade name of BS-510 manufactured by Ewasha Co., Ltd. was used. The haze value of this light diffusion sheet was 85%.
[Comparative Example 3]
In Comparative Example 3, a light diffusion sheet having a trade name of BS-910 manufactured by Ewasha Co., Ltd. was used. The haze value of this light diffusion sheet was 89.5%.
[Comparative Example 4]
In Comparative Example 4, a microlens array sheet shown in FIG. 14 was used as the light diffusion sheet.

[Brightness angle characteristics survey]
A backlight device having the same configuration as the backlight device 10 of FIG. 1 was manufactured for each of the present invention examples and comparative examples (hereinafter referred to as each example) using the above-described light diffusion sheet. Specifically, the backlight device 30 including a configuration other than the light diffusion sheet 16 in FIG. 1 was manufactured. And the light-diffusion sheet | seat for every example was laid on the backlight apparatus 30, and the backlight apparatus for every example was manufactured.

  With respect to each manufactured backlight device, the luminance angle characteristic in the X-axis direction in FIG. 1 was investigated. Referring to FIG. 1, the normal direction of the display screen (corresponding to the normal N14 direction) is the 0 degree axis, the inclination angle from the 0 degree axis to the + X direction in FIG. 1 is plus (+), and the + X direction The angle of inclination in the opposite direction was minus (−). The luminance at each angle was measured with a luminance meter, and the luminance was measured at the front center of the backlight device.

  FIG. 15 shows the luminance angle characteristics of Example 1 and Comparative Example 1. FIG. 16 shows luminance angle characteristics of Example 2 of the present invention and Comparative Examples 2 and 4, and FIG. 17 shows luminance angle characteristics of Example 3 of the present invention and Comparative Example 3. The horizontal axis in the figure is the angle from the 0 degree axis. The vertical axis represents the ratio of the luminance at each angle with respect to the front luminance (brightness on the 0-degree axis) of the backlight device 30, that is, the backlight device excluding the light diffusion sheet.

[Full width at half maximum]
The full width at half maximum of the luminance angle characteristic of the backlight device of each example was obtained. Here, the half-value width refers to an angle range indicating a luminance that is 1/2 or more of the luminance peak in the luminance angle characteristic. Further, the luminance angle characteristic of the backlight device 30 was measured, and the half width was obtained.

As an index indicating the degree of expansion of the viewing angle of the backlight device of each example, the half-width expansion degree shown in Expression (2) was defined, and the half-width expansion degree of each example was obtained.
Half-width expansion factor = half-width of each example / half-width of backlight device 30 (2)

[Investigation result]
Table 1 shows the full width at half maximum. In each example (invention example and comparative example), the viewing angle was larger than that of the backlight device 30 having no light diffusing sheet.

  Furthermore, among the backlight devices of each example, the luminance angle dependency of the backlight devices having the same degree of half-width expansion was compared. Referring to FIG. 15, the first half of the present invention example 1 (solid line in the figure) and the comparative example 1 (broken line in the figure) had the same half-value width expansion degree, but the front luminance ratio of the first example of the invention was higher. High, above 1.2. Since the light diffusion sheet of Invention Example 1 suppressed the retroreflection of light, the light utilization efficiency was improved, and as a result, it was estimated that the front luminance was high.

  Similarly, with reference to FIG. 16, Example 2 (solid line in the figure) and Comparative Examples 2 (dashed line in the figure) and 4 (dashed line in the figure) showed the same degree of half-width expansion, The front luminance ratio of Invention Example 2 was the highest, exceeding 1.2. Referring to FIG. 17, the present invention example 3 (solid line in the figure) and comparative example 3 (broken line in the figure) showed the same degree of half-width expansion, but the front luminance ratio is the same as that of the example 3 of the present invention. It was higher and exceeded 1.0.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 10/30 Backlight apparatus 11 Light source 14 Light guide plate 15 Total reflection type prism sheet 16, 26, 36 Light diffusion sheet 17 1st refractive layer 18, 28, 38 2nd refractive layer 20 Liquid crystal panel 173 Base material part 174 Lens part 282 Binder resin 283 Granular matter

Claims (10)

A first refractive layer having a main surface on which a plurality of first convex portions are formed;
A light diffusion sheet, comprising: a second refractive layer formed on the main surface and having a refractive index different from that of the first convex portion. The light diffusing sheet according to claim 1,
The light diffusion sheet, wherein the second refractive layer further has a surface on which a plurality of second convex portions are formed. The light diffusing sheet according to claim 2,
The plurality of first convex portions are a plurality of columnar lenses arranged side by side, and a cross section in the width direction of the columnar lens has a shape in which a width becomes narrower from the bottom to the top of the columnar lens. A light diffusion sheet characterized by that. The light diffusing sheet according to claim 3,
The light diffusing sheet according to claim 2, wherein the second convex portion has a cross-sectional shape whose width becomes narrower from the bottom to the top of the second convex portion. The light diffusing sheet according to claim 4,
The light diffusion sheet, wherein the plurality of second convex portions are arranged in a matrix. The light diffusing sheet according to claim 2 or 3,
The second refractive layer is
A binder resin,
Containing a plurality of particulates having the same refractive index as the binder resin,
The second convex portion is formed by projecting a part of the granular material from the surface. The light diffusing sheet according to any one of claims 1 to 6,
The light diffusion sheet, wherein a refractive index of the second refractive layer is larger than a refractive index of the first convex portion. The light diffusion sheet according to any one of claims 1 to 7,
The first refractive layer has a back surface opposite to the main surface,
The light diffusion sheet, wherein the first refractive layer receives light in a normal direction of the light diffusion sheet from the back surface. A light guide plate;
A light source disposed on a side surface of the light guide plate;
A lens sheet that receives light emitted from the light guide plate and emits the received light in a normal direction of the light guide plate;
A backlight device comprising: the light diffusion sheet according to claim 1 laid on the lens sheet. The backlight device according to claim 9;
A liquid crystal display device comprising: a liquid crystal panel laid on the backlight device.

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