JP2002333509A - Optical diffusion sheet and backlight unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical diffusion sheet with high light diffusibility, with wide angle of visibility and high total transmittance of light rays and further with high scratch resistance even when used in an overlapped state and with excellent easiness for handling and to provide a backlight unit using the same. SOLUTION: The optical diffusion sheet 1 is provided with an opening part 4 on which polygonal concave lens parts 3 having polygonal shapes and curved in recession are tightly formed with no space between themselves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusion sheet incorporated in a backlight unit of a liquid crystal display and a backlight unit using the same.

[0002]

2. Description of the Related Art In a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back surface to emit light has become widespread, and a backlight unit is provided on a lower surface side of the liquid crystal layer. As shown in FIG. 6 (a), the backlight unit 50 generally includes a rod-shaped lamp 51 as a light source and a rectangular plate-shaped light guide plate 52 arranged so that an end of the lamp 51 extends along the lamp 51. And a plurality of optical sheets 53 laminated on the front side of the light guide plate 52. This optical sheet 5
Reference numerals 3 denote specific optical properties such as refraction and diffusion, and more specifically, a light diffusion sheet 54 disposed on the surface side of the light guide plate 52 and a light diffusion sheet 54 disposed on the surface side of the light diffusion sheet 54. The prism sheet 55 to be provided corresponds to this.

The function of the backlight unit 50 will be described. First, a light beam incident on the light guide plate 52 from the lamp 51 is reflected by a reflection dot or a reflection sheet (not shown) on the back surface of the light guide plate 52 and each side surface. The light is emitted from the surface of the light guide plate 52. Light emitted from the light guide plate 52 enters the light diffusion sheet 54, is diffused, and is emitted from the surface of the light diffusion sheet 54. Thereafter, the light beam emitted from the light diffusion sheet 54 enters the prism sheet 55, and is emitted by the prism portion 55a formed on the surface of the prism sheet 55 as a light beam having a distribution showing a peak almost directly above. Thus, the light beam emitted from the lamp 51 is
The light is diffused by the light diffusion sheet 54, is refracted by the prism sheet 55 so as to show a peak almost directly above, and illuminates the entire liquid crystal layer (not shown) further above.

[0004] Although not shown, there is also a backlight unit in which a light diffusion sheet or a prism sheet is further disposed on the surface side of the prism sheet 55 in consideration of the light-collecting characteristics of the prism sheet 55 described above.

As the light diffusion sheet 54 of the backlight unit 50 having the above-mentioned structure, there are a so-called bead coating type and a light diffusion sheet having a large number of hemispherical convex lens portions formed on the surface. Specifically, the light diffusion sheet 54 of the bead coating type has a substrate layer 5 as shown in FIG.
6 and a light diffusion layer 57 are laminated, and the light diffusion layer 57 has a structure in which beads 59 made of a synthetic resin, glass, or the like are dispersed in a binder 58 made of a synthetic resin.

[0006]

The light diffusion sheet 54 of the bead coating type or the convex lens type shown in FIG.
Has the following disadvantages. That is, (1) The beads 5 are added to the resin composition constituting the binder 58.
9 is mixed to form a light diffusion layer coating solution, and this coating solution is applied to the base layer 56 to form the light diffusion layer 57. The beads 59 are uniformly dispersed in the binder 58. It is not easy to disperse and it is difficult to provide uniform diffusivity. Therefore, it is not easy to produce the light diffusion sheet 54 that is uniform and has a predetermined diffusion property.

(2) The light diffusion sheet 54 of the above-mentioned bead coating type or convex lens type has a bead 59 from the surface.
And the convex lens portion protrudes, the light beam which is inclined by a predetermined angle or more from the normal direction, and the light emitted from the periphery of the bead 59 or the convex lens portion hits the adjacent bead 59 or the convex lens portion and is emitted to the surface side. Can not. In this way, the viewing angle becomes narrower by the amount of light that cannot be emitted by hitting the adjacent beads 59 and the like, and the total light transmittance is reduced.

(3) In the conventional light diffusion sheet 54, since the beads 59 and the convex lens portions protrude from the surface as described above, the backlight unit 50 in which the light guide plate 52 and other optical sheets 53 are laminated is provided. Or, when storing or transporting a plurality of stacked sheets, stress is concentrated on the protruding beads 59 and the like, and the overlapped surface is likely to be scratched, which may cause a decrease in light transmittance. .

(4) Since the beads 59 and the convex lens portions contributing to the diffusion of light are spherical in principle, even if they are formed densely, a gap is formed, and an area of the light diffusion layer 57 which does not contribute to the diffusion is generated. Thus, there is a certain limit in improving the diffusion efficiency.

The present invention has been made in view of these inconveniences, and has a high light diffusion property, a large viewing angle and a high total light transmittance, and can prevent scratches even when used repeatedly.
It is an object of the present invention to provide a light diffusion sheet having excellent handleability and a backlight unit using the same.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a light diffusing sheet in which an opening is polygonal and a concavely curved polygonal lens is formed densely without any gap. is there. According to the light diffusion sheet, the following effects can be exerted.

(1) Since the polygonal concave lens portion is densely formed in the light diffusion sheet, there is no gap and the entire sheet surface is covered with the polygonal concave lens portion. Therefore, the light diffusion sheet has no portion that does not contribute to the diffusion of light, in other words, the area that contributes to the diffusion is maximized, so that the diffusion efficiency can be dramatically improved.

(2) Further, since the light diffusing sheet can uniformly form a polygonal concave lens portion exhibiting light diffusing property,
There is no difference in light diffusing ability, and there is little luminance unevenness due to the difference in light diffusing ability.

(3) Further, the light diffusing sheet has a light diffusing effect due to the polygonal concave lens portion, and has no protrusions such as beads and convex lens portions of the conventional light diffusing sheet. Also, there is no stress concentration, scratches are prevented, and as a result, handleability is dramatically improved.

(4) Since the light diffusion sheet has no protrusions such as beads and convex lens portions of the conventional light diffusion sheet on the surface as described above, the light emission is inclined at a predetermined angle or less from the normal direction. There is no inconvenience that a light beam hits an adjacent bead or the like and is not emitted, and the viewing angle and the total light transmittance can be remarkably increased as compared with a conventional light diffusion sheet of a bead coating type or a convex lens type.

(5) In the light diffusion sheet, the field angle can be adjusted by changing the curvature of the curved concave lens surface in the polygonal concave lens portion.

The polygonal shape of the opening of the polygonal concave lens portion is preferably a regular hexagon. The regular hexagon is a polygon of the maximum number of angles that can be densely formed without gaps in a certain size, and can exhibit light diffusing ability closest to a spherical lens part. The effect of improving and the effect of improving the uniformity of diffusion can be promoted.

The shape of the opening of the polygonal concave lens portion is preferably a flat hexagon extending in a certain direction. In this manner, by making the shape of the opening a flat hexagon elongated in a certain direction, the radius of curvature of the polygonal concave lens portion is based on the extension direction of the flat hexagon, and is perpendicular to the extension direction of the flat hexagon. In contrast to the case where the standard is used, the diffusion action is small in the extension direction of the flat hexagon, and the diffusion action is relatively large in the direction perpendicular to the extension direction of the flat hexagon. That is, this means enables anisotropic diffusion.

The aspect ratio of the flat hexagon is 1: 2 to
1: 5 is preferred. Thus, by adjusting the aspect ratio of the flat hexagon within the above range, while exhibiting the light diffusion function,
The anisotropy of the light emission characteristics of the backlight unit can be improved, the amount of light emitted in the normal direction can be increased compared to the case where an isotropic diffusion sheet is used, and the viewing angle of the backlight unit can be controlled. can do.

The minimum width of the opening of the polygonal concave lens portion is preferably 1 μm or more and 100 μm or less. Here, the “minimum width of the opening” means the diameter of a polygonal inscribed circle formed by the opening. By setting the minimum width of the opening of the polygonal concave lens portion in the above range, light diffusibility can be enhanced while ensuring the formability of the polygonal concave lens portion.

The ratio of the depth to the minimum width of the opening in the polygonal concave lens portion is preferably 5% or more and 50% or less. By setting the ratio of the depth of the polygonal concave lens portion to the minimum width of the opening portion in the above range, light diffusivity and total light transmittance can be balanced at a high level.

The light diffusion sheet may include a transparent synthetic resin base layer and a light diffusion layer, and the polygonal concave lens portion may be formed on the light diffusion layer. According to this means, the strength required for the light diffusion sheet can be secured by the base material layer, and a synthetic resin in which the polygonal concave lens portion can be easily formed can be selected for forming the light diffusion layer. The production of the diffusion sheet can be facilitated.

Accordingly, as a material for forming the light diffusion layer, an ultraviolet curable resin capable of forming a polygonal concave lens portion accurately and easily is preferable.

It is preferable that a synthetic resin layer having a refractive index different from that of the base of the polygonal concave lens portion is laminated on the polygonal concave lens portion side to form a smooth sheet surface on the polygonal concave lens portion side. According to this means, since the unevenness of the polygonal concave lens portion is completely covered with the synthetic resin layer and the light diffusion sheet is smoothed, the light diffusion sheet is overlapped with another sheet or the like at the time of assembling or transporting the backlight unit. Even if it is used, the completeness of scratch prevention is promoted, and a decrease in optical performance due to scratches can be prevented.

The refractive index difference between the base of the polygonal concave lens portion and the synthetic resin layer is preferably 0.01 or more and 0.5 or less. According to this means, it is possible to exhibit sufficient diffusing ability as a light diffusing sheet, and it is possible to reduce a decrease in light transmittance due to reflection at the interface between the polygonal concave lens portion and the synthetic resin layer.

In the light diffusion sheet, an anti-sticking layer can be laminated on the front surface and / or the back surface. By laminating the anti-sticking layer on the light diffusion sheet in this manner, sticking with a light guide plate, a prism sheet, or the like provided on the front side or the back side can be prevented. Such an anti-sticking layer may have a structure in which beads are dispersed in a binder, or may have a structure in which an uneven shape is formed on the surface.

Further, instead of the above-mentioned anti-sticking layer, a protective layer having a flat surface can be laminated on the front and / or back surface of the light diffusion sheet. By laminating the protective layer on the light diffusion sheet in this way, it is possible to physically protect the front surface and / or the back surface of the light diffusion sheet and to prevent the prism sheet or the like from being damaged. .

Therefore, in a backlight unit for a liquid crystal display device comprising a lamp and an optical sheet for dispersing light rays emitted from the lamp and guiding the light to the front side, the light diffusion sheet of the present invention is used as the optical sheet. Good to use. According to the backlight unit, since the diffusivity of the light diffusion sheet is high as described above, it is possible to prevent the occurrence of luminance unevenness, and to control the viewing angle to be wide and arbitrarily.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate. FIGS. 1A and 1B are a schematic plan view and a schematic cross-sectional view showing a light diffusion sheet according to an embodiment of the present invention, and FIGS. 2, 3, 4 and 5 show the light of FIG. It is a typical sectional view showing the light diffusion sheet concerning the form different from a diffusion sheet.

Light diffusion sheet 1 shown in FIGS. 1 (a) and 1 (b)
Has a single-layer structure composed of the base material layer 2, and a large number of polygonal concave lens portions 3 are densely formed on the surface of the base material layer 2 without gaps. The polygonal concave lens portion 3 has a regular hexagonal shape of the opening 4 and a concave lens surface 5 curved in a concave shape, and the concave lens surface 5 exerts light diffusing ability.

By forming the polygonal concave lens portion 3 into a regular hexagon as described above, the light-diffusing sheet 1 can form a portion having a light-diffusing property without any gaps. The uniformity of the properties and the diffusing ability can be improved. In addition, since the polygonal concave lens portion 4 that expresses light diffusivity is concave as described above, there is no protruding portion where stress concentration occurs on the surface, and scratches can be prevented even when used repeatedly.

The base material layer 2 is made of a transparent, particularly colorless and transparent synthetic resin because it is necessary to transmit light. Examples of the synthetic resin used for the base layer 2 include:
There is no particular limitation, and examples include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather-resistant vinyl chloride. Although the thickness of the base material layer 2 is not particularly limited, for example, 10 μm or more and 500 μm or less, preferably 75 μm
It is not less than 250 μm. This is because if the thickness of the base material layer 2 is less than the above range, inconveniences such as curling easily occurring when forming the light diffusing layer 3 and difficulty in handling occur. On the other hand, if the thickness of the base layer 2 exceeds the above range, the brightness of the liquid crystal display device may be reduced, and the thickness of the backlight unit may be increased to be against the demand for thinning the liquid crystal display device. This is because

The minimum width D (diameter of an inscribed circle of the opening 4) D of the opening 4 of the polygonal concave lens portion 3 is preferably 1 μm or more and 100 μm or less, particularly preferably 1 μm or more and 10 μm or less.
If the minimum width of the opening 4 of the polygonal concave lens portion 3 is smaller than the above range, it becomes difficult to form the polygonal concave lens portion 3, and conversely, if the minimum width exceeds the above range, the light diffusion sheet may be used. This is because the light diffusion property cannot be obtained.

The ratio (H / D) of the depth H to the minimum width D of the opening 4 in the polygonal concave lens portion 3 is preferably 5% or more and 50% or less, particularly preferably 20% or more and 45% or less. This is because if the depth ratio H / D of the polygonal concave lens portion 3 is smaller than the above range, the light diffusing property required as a light diffusing sheet cannot be exerted. Above the range, the total reflection increases on the concave lens surface 5,
This is because the total light transmittance is reduced.

As a method for forming the light diffusion sheet 1 having the above structure, specifically, (a) a synthetic resin is laminated on a sheet type having a shape obtained by inverting the surface shape of the light diffusion sheet 1, and the sheet is formed. A method of forming the polygonal concave lens portion 3 on the surface of the base material layer 2 by peeling off the mold, (b) the light diffusion sheet 1
Injection molding method of injecting molten resin into a mold having an inverted shape of the surface of (c), (c) reheating the sheeted resin, pressing between the same mold and metal plate as above, and pressing (D) an extruded sheet that transfers a molten sheet-like resin through a nip between a roll having an inverted shape of the surface of the light diffusion sheet 1 on the peripheral surface and another roll to transfer the shape. There are molding methods and the like.

Accordingly, a rod-shaped lamp 51 as a light source as shown in FIG. 6A, a rectangular light guide plate 52 arranged so that an end thereof is along the lamp 51, and a surface side of the light guide plate 52 Light diffusion sheet 54 and light diffusion sheet 5
And a prism sheet 55 disposed on the front surface side of the backlight unit 4.
When the light diffusing sheet 1 is used, the diffusivity of the light diffusing sheet 1 is high, and the occurrence of luminance unevenness can be prevented.
Further, since there is no protruding portion on the surface of the light diffusion sheet 1, scratches on the back surface of the stacked prism sheets 55 can be reduced, and luminance unevenness due to the scratches can be prevented.

The light diffusion sheet 11 of FIG. 2 includes a transparent film-like base layer 12 and a light diffusion layer 13 laminated on the surface of the base layer 12. Many polygonal concave lens portions 3 are densely formed on the surface without gaps. The polygonal concave lens portion 3 is similar to the light diffusion sheet 1 of FIG. 1 and has the same operation and effect as the light diffusion sheet 1 of FIG. The base layer 12 is the same as the base layer 2 of the light diffusion sheet 1 in FIG.

As a method for forming the light diffusion sheet 11 having the above structure, specifically, (a) U
A method in which a V-cured resin is applied and pressed onto a roll having an inverted shape similar to the above to transfer the shape to an uncured UV-cured resin, and thereafter, ultraviolet light is applied to cure the UV-cured resin. There is a method using an EB cured resin instead of the cured resin.

Since the light diffusing sheet 11 can be made of a UV curable resin or the like as described above as a base for forming the polygonal concave lens portion 3, the polygonal concave lens portion 3 can be easily formed, and the shape of the polygonal concave lens portion 3 can be easily adjusted. Can be made precise and delicate, and as a result, the light diffusion property and the uniformity of the light diffusion can be promoted.

The light diffusing sheet 21 of FIG. 3 is similar to the light diffusing sheet 1 of FIG. 1 in that the light diffusing sheet 21 is composed of a base material layer 2 having a polygonal concave lens portion 3 formed on its surface. To play. Since the light diffusion sheet 21 has the synthetic resin layer 22 laminated on the polygonal concave lens portion 3 side and the sheet surface 23 on the polygonal concave lens portion 3 side is formed smoothly, the integrity of the scratch prevention is promoted, Even when used repeatedly, it is possible to prevent a decrease in optical performance due to damage.

As the synthetic resin constituting the synthetic resin layer 22, a synthetic resin having a refractive index different from that of the base material layer 2 is used. For example, acrylic resin, polyurethane, polyester, fluorine resin, silicone resin , Polyamide imide, epoxy resin and the like. The difference in refractive index between the synthetic resin layer 22 and the base material layer 2 is preferably 0.01 or more and 0.5 or less. If the refractive index difference is smaller than the above range, the diffusing ability of the polygonal concave lens portion 3 becomes small and the optical performance as the light diffusion sheet cannot be exhibited. This is because a light beam transmitted at the interface between the second resin layer 2 and the synthetic resin layer 22 is reflected, which causes a decrease in light transmittance.

The light diffusing sheet 31 shown in FIG. 4 is the same as the light diffusing sheet 1 except that the base layer 2 on which the polygonal concave lens portion 3 is formed.
In addition, an anti-sticking layer 32 is laminated on the back surface side of the base material layer 2.

The anti-sticking layer 32 is composed of a binder 33 and beads 34 dispersed in the binder 33.
This prevents sticking with a prism sheet or the like disposed on the front side. Also, by forming such an anti-sticking layer 32, the surface of the light diffusion sheet 31 can be physically protected and the prism sheet can be prevented from being damaged.

Examples of the polymer used for the binder 33 include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamide imides, epoxy resins and the like. Further, in addition to the above-mentioned polymer, for example, a plasticizer, a stabilizer, a deterioration preventing agent, a dispersant, and the like may be blended in the binder 33. The binder 33 is transparent because it needs to transmit light, and is preferably colorless and transparent.

The beads 34 have a substantially spherical shape, and examples of the material include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and the like. The beads 34 are preferably transparent in order to increase the amount of light transmitted through the light diffusion sheet 5, and are particularly preferably colorless and transparent.

The average particle diameter of the beads 34 is preferably 1 μm or more and 30 μm or less, and particularly preferably 1 μm or more and 15 μm or less from the viewpoint of preventing sticking. The amount of the beads 34 is relatively small. The beads 34 are separated from each other and dispersed in the binder 33, and most of the beads 34 have lower ends protruding from the binder 33. The thickness of the sticking prevention layer 4 (the thickness of the portion of the binder 33 excluding the beads 34) is not particularly limited, but is, for example, about 1 μm or more and 10 μm or less.

In the above, the sticking prevention layer 3 in which the beads 34 are dispersed in the binder 33 is used.
2 has been described, but the structure of the anti-sticking layer is not limited to this. For example, a sticking prevention layer having an uneven surface formed by embossing or the like may be formed. Also in this case, similarly to the case where the anti-sticking layer 32 is formed, it is possible to prevent sticking with a prism sheet or the like disposed on the surface side by the convex portion formed on the surface of the anti-sticking layer. .

Further, instead of forming the sticking prevention layer as described above, a protective layer having a flat surface may be formed on the surface of the light diffusion layer 31. By forming such a protective layer, the surface of the light diffusion sheet 31 can be physically protected, and the effect of preventing the prism sheet from being damaged as compared with the case of forming the anti-sticking layer can be improved. Be larger.

The light diffusion sheet 41 shown in FIGS. 5A, 5B and 5C has a single-layer structure composed of the base material layer 2.
The light diffusing sheet 1 shown in FIG. 1 is different from the light diffusing sheet 1 shown in FIG.
Is the same as However, the polygonal concave lens portion 42 is a hexagon in which the shape of the opening 43 extends in a certain direction (the front-back direction in the drawing). Accordingly, when the concave lens surface 44 of the polygonal lens portion 42 is viewed perpendicularly to the extending direction, FIG.
As shown in FIG. 5, the radius of curvature becomes small, and when viewed parallel to the extension direction, the radius of curvature becomes large as shown in FIG. Therefore, the light diffusing sheet 41 can exhibit anisotropic diffusing ability in which the light diffusing ability in the extending direction of the polygonal lens portion 42 is small and the light diffusing ability in the direction perpendicular to the extending direction is large.

The light diffusing sheet of the present invention is not limited to the above embodiment. For example, the opening 4 of the polygonal concave lens portion 3 is not limited to a regular hexagon, but may be a quadrangle if it can be formed densely with no gap. May be. Further, a light diffusion sheet having both a synthetic resin layer and an anti-sticking layer is also possible.

[0051]

As described above, according to the light diffusing sheet of the present invention, the light diffusing property is high, the viewing angle and the total light transmittance are large, and it is possible to prevent scratches even when used repeatedly. Excellent handleability.

[Brief description of the drawings]

FIG. 1A is a schematic plan view showing a light diffusion sheet according to an embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of the light diffusion sheet of FIG.

FIG. 2 is a schematic sectional view showing a light diffusion sheet according to a mode different from the light diffusion sheet of FIG.

FIG. 3 is a schematic cross-sectional view showing a light diffusion sheet according to a form different from the light diffusion sheets of FIGS. 1 and 2.

FIG. 4 is a schematic sectional view showing a light diffusion sheet according to a different form from the light diffusion sheets of FIGS. 1, 2 and 3;

5A and 5B show a light diffusion sheet according to a different form from the light diffusion sheets of FIGS. 1 to 4, wherein FIG. 5A is a schematic plan view, and FIG.
FIG. 4 is a schematic cross-sectional view in a direction perpendicular to the direction of extension of the shape of the opening of the polygonal lens portion, and FIG.

6A is a schematic perspective view illustrating a general backlight unit, and FIG. 6B is a schematic cross-sectional view illustrating a general bead-coated light diffusion sheet.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light diffusion sheet 2 base layer 3 polygonal concave lens portion 4 opening 5 concave lens surface 11 light diffusion sheet 12 base layer 13 light diffusion layer 21 light diffusion sheet 22 synthetic resin layer 23 sheet surface 31 light diffusion sheet 32 sticking prevention layer 33 Binder 34 Bead 41 Light diffusion sheet 42 Polygon lens part 43 Opening 44 Concave lens surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G02F 1/13357 G02F 1/13357 // F21Y 103: 00 F21Y 103: 00

Claims (13)

[Claims] 1. A light diffusion sheet having an opening having a polygonal shape and a concavely curved polygonal lens portion formed densely without any gap. 2. The light diffusion sheet according to claim 1, wherein the opening of the polygonal concave lens portion is a regular hexagon. 3. The light diffusion sheet according to claim 1, wherein the opening of the polygonal concave lens portion is a flat hexagon extending in a certain direction. 4. The aspect ratio of the flat hexagon is 1: 2 to 1:
The light diffusion sheet according to claim 3, wherein the light diffusion sheet is 5. 5. The minimum width of the opening of the polygonal concave lens portion is 1 μm or more and 100 μm or less.
The light diffusion sheet according to any one of the above items. 6. The light diffusing sheet according to claim 1, wherein a ratio of a depth to a minimum width of the opening in the polygonal concave lens portion is 5% or more and 50% or less. 7. A light diffusion layer comprising a transparent synthetic resin base material layer and a light diffusion layer, wherein the polygonal concave lens portion is formed in the light diffusion layer. The light diffusion sheet according to 1. 8. The light diffusion sheet according to claim 7, wherein the light diffusion layer is formed from an ultraviolet curing resin. 9. The polygonal concave lens portion side further has a synthetic resin layer having a refractive index different from that of the base of the polygonal concave lens portion laminated thereon, and a sheet surface on the polygonal concave lens portion side is formed smoothly. 9. The light diffusion sheet according to any one of items 8 to 8. 10. The light diffusion sheet according to claim 9, wherein a difference in refractive index between the base of the polygonal concave lens portion and the synthetic resin layer is 0.01 or more and 0.5 or less. 11. The light diffusion sheet according to claim 1, wherein an anti-sticking layer is laminated on the front surface and / or the back surface. 12. The method according to claim 1, wherein the protective layer having a flat surface is laminated on the front surface and / or the rear surface.
0. The light diffusion sheet according to any one of 0. 13. A backlight unit for a liquid crystal display device comprising a lamp and an optical sheet for dispersing a light beam emitted from the lamp and guiding the dispersed light to the front side, wherein the optical sheet according to claim 1 is used as the optical sheet. A backlight unit for a liquid crystal display device, wherein the light diffusion sheet according to claim 1 is used.