JP2009003183A - Optical sheet, manufacturing method of optical sheet and back light unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which can constitute a backlight having a sufficient viewing angle and sufficient luminance as a backlight used for an on-vehicle liquid crystal display device. <P>SOLUTION: The optical sheet 2 has the first surface 21, which has a shape where a lot of convex stripes 23 with a convex arc-shaped transverse cross section and a lot of concave stripes 24 with a concave arc-shaped transverse cross section are alternately arranged about in parallel with each other, and the second surface 22 which is a non-smooth surface. In the convex stripe 23, a radius of curvature of the convex arc-shaped transverse cross section is 10 μm to 30 μm. In the concave stripe 24, the radius of curvature of the concave arc-shaped transverse cross section is 10 μm to 30 μm. The non-smooth surface has surface roughness where an arithmetic mean roughness (Ra) is 0.5 μm to 2 μm and a maximum height roughness (Rz) is 5 μm to 30 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical sheet that can be used as a component of a backlight unit such as a liquid crystal display device, a manufacturing method thereof, and a backlight unit.

  Conventionally, as a backlight unit such as a liquid crystal display device, a cold cathode tube is used as a light source, the light source is placed on an end face (edge) of the light guide plate, an optical sheet or the like is placed on the light exit surface of the light guide plate, and the light guide plate An edge light system in which a reflective material is placed on the lower surface (opposite surface of the light emission surface) is generally used. In addition, by adjusting the shape of the light guide plate, the shape and type of the optical sheet, etc., the light utilization efficiency is improved and the brightness is improved, or light is emitted as uniformly as possible in all directions from the light emission surface. Ingenuity has been made.

The backlight unit described in Patent Document 1 is devised so that light is intensively emitted in the normal direction with respect to the light emission surface using a prism, and the luminance in the normal direction is improved. Further, in the backlight unit described in Patent Document 2, the surface shape that is the exit surface of the light control sheet and the back surface shape that is the contact surface with the light guide plate are devised to obtain high brightness in the front direction and the field of view. The corner is configured to be large.
JP 62-144102 A JP-A-5-313004

  For example, in a liquid crystal display device used for car navigation, it is desired to have a sufficient viewing angle and high luminance, and improvement in light utilization efficiency has been desired. In the backlight unit using a prism as in Patent Document 1, since the light incident direction and the light emitting direction are too strictly determined, the light emitting direction is deflected in the front direction in a narrow angle range, and the viewing angle of the screen is narrowed. There was a problem of passing. In Patent Document 2, there is a problem that the luminance of the viewing angle cannot be sufficiently secured.

  The present invention has been made in view of such circumstances, and an object thereof is an optical sheet that can constitute a backlight unit having a viewing angle and luminance sufficient as a backlight used in an in-vehicle liquid crystal display device, It is an object of the present invention to provide a method for manufacturing the optical sheet and a backlight unit using the optical sheet.

  In order to solve the above-mentioned problems, the optical sheet of the present invention has a shape in which a large number of ridges having a cross-sectional convex arc shape and a large number of ridges having a cross-sectional concave arc shape are arranged alternately and substantially in parallel. The convex surface has a curvature radius of 10 μm to 30 μm in a cross-section convex arc shape, and the concave stripe has a curvature in a cross-section concave arc shape. The radius is 10 μm to 30 μm. The non-smooth surface has a surface roughness of 0.5 μm to 2 μm in arithmetic average roughness (Ra) and 5 μm to 30 μm in maximum height roughness (Rz). In this specification, arithmetic mean roughness (Ra) and maximum height roughness (Rz) are as described in JIS B 0601-2001.

  The optical sheet is preferably made of polycarbonate. The thickness of the optical sheet is preferably 50 μm to 500 μm.

  Further, the present invention is a method for producing the optical sheet, comprising the step of passing the gap between the sheet-shaped resin material extruded from the extrusion die while being pressed by at least a pair of pressure rolls, The surface of at least one of the pair of pressure rolls is made of an elastic material. The second surface which is a non-smooth surface can be formed by a pressure roll whose surface is made of an elastic material. Further, by using a pair of pressure rolls in which the surface of one pressure roll is made of an elastic material and the surface of the other pressure roll is made of a metal material, the surface of the second pressure roll is made of an elastic material. The first surface can be formed by a pressure roll whose surface is made of a metal material.

  The backlight unit of the present invention includes a light source, a light guide plate, and the optical sheet, and the light from the light source is incident on the first surface of the optical sheet through the light guide plate. It is the structure radiate | emitted from two surfaces.

  According to the optical sheet of the present invention, it is possible to provide a backlight unit having a sufficient viewing angle and brightness suitable for an on-vehicle liquid crystal display device. Moreover, according to the production method of the present invention, an optical sheet having a sufficient viewing angle and brightness and free from uneven polarization can be provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Hereinafter, a case where the present invention is applied to a planar backlight unit will be described, but the optical sheet of the present invention is not limited to the planar backlight unit.

[Configuration of backlight unit]
FIG. 1 is a cross-sectional view schematically showing a configuration of a planar backlight unit including the optical sheet of the present invention. The planar backlight unit 1 includes an optical sheet 2 of the present invention, a light guide plate 3 provided behind the optical sheet 2, light sources 4 provided on both side surfaces of the light guide plate 3, and the rear of the light guide plate 3. And a reflection plate 5 provided on the surface.

  Next, each element constituting the backlight unit 1 will be described. FIG. 2 is a cross-sectional view schematically showing a partial configuration of the optical sheet 2 of the present invention. In the optical sheet 2, a large number of ridges 23 whose first surface 21 in contact with the light guide plate 3 has a cross-sectional convex arc shape and a large number of concave ridges 24 whose cross-section concave arc shape is arranged alternately and substantially in parallel. The second surface 22 that is a light emitting surface is a non-smooth surface. In the first surface 21, the ridges 23 have a radius of curvature r1 having a convex arc shape in the cross section of 10 μm to 30 μm, and the ridges 24 have a curvature radius r2 of a concave arc shape in the cross section of 10 μm to 30 μm. Preferably, the curvature radius r1 is 20 μm to 30 μm, and the curvature radius r2 is 18 μm to 28 μm. It should be noted that the ridges 23 and the ridges 24 described above include those that are slightly curved or bent within a range having the above-described curvature radius. Further, in the first surface 21, a large number of ridges 23 and a large number of ridges 24 are arranged alternately and substantially in parallel with each other. It means that each trough part 24a is substantially parallel to each other. The distance l1 between the top portions 23a of the adjacent ridges 23 is preferably 80 μm to 110 μm, and more preferably 93 μm to 100 μm.

  In the second surface 22, the non-smooth surface has a surface roughness of 0.5 μm to 2 μm in arithmetic average roughness (Ra) and 5 μm to 30 μm in maximum height roughness (Rz). Preferably, the surface roughness is 0.8 μm to 1.1 μm in arithmetic mean roughness (Ra) and 6 μm to 12 μm in maximum height roughness (Rz). In the backlight unit 1, the optical sheet 2 is disposed such that the first surface 21 is a light incident surface and the second surface 22 is a light exit surface, but the arrangement direction of the optical sheet may be reversed. That is, you may arrange | position so that the 2nd surface 22 may be a light-incident surface and the 1st surface 21 may become a light-emitting surface. However, it is more preferable that the first surface 21 be a light incident surface and the second surface 22 be a light output surface. Since the light exit surface of the optical sheet 2 is a non-smooth surface such as the second surface 22, high luminance can be obtained and high light utilization efficiency can be obtained.

  The thickness h1 of the optical sheet 2 is preferably 50 μm to 500 μm. If it is less than 50 μm, it may be difficult to mold the ridges 23 and the ridges 24.

  The material of the optical sheet 2 is not particularly limited as long as it is a transparent organic material or inorganic material. Examples of the transparent organic material include resins such as polycarbonate, polyester, polymethyl methacrylate, polyvinyl chloride, polyolefin, and cyclic polyolefin. An example of the transparent inorganic material is glass. Polycarbonate is preferably used because of its optically high transparency, heat resistance, and low cost.

  Other elements constituting the backlight unit 1 shown in FIG. 1 will be described. As the light source 4, a cathode tube is usually used. The cathode tube may be a cold cathode tube or a hot cathode tube. The light sources 4 are provided on the left and right side surfaces of the light guide plate 3. The light source 4 is provided on both upper and lower side surfaces of the light guide plate 3, provided on only one of the four side surfaces, provided on three side surfaces, or provided on all four side surfaces. It may be configured as described above.

  The light guide plate 3 is made of a highly transparent material such as glass, polycarbonate, polyester, polymethyl methacrylate, and the like. The light from the light source 4 is evenly distributed on the back surface, that is, the surface on the reflecting plate 5 side from any position on the light emitting surface. It is preferable to have a printed dot pattern that causes irregular reflection so as to emit light.

  The reflecting plate 5 is not limited as long as it has a plate-like shape that blocks light, and examples thereof include a resin plate mixed with a white pigment, a foamed resin plate, a metal resin plate, and a metal plate. The reflection plate 5 is disposed so as to contact the non-light-emitting surface side of the light guide plate 3.

  In addition, you may comprise other elements other than the above-mentioned element. For example, the light diffusing sheet may be further provided on the light exit surface side of the optical sheet 2 or the surface side facing the light guide plate 3. Since the light diffusing sheet diffuses light, for example, when a printed dot pattern is formed on the light guide plate, a sheet having a function of diffusing light rays so that the shape of the printed dot pattern is not visually recognized by the user is preferable. As the light diffusion sheet, a conventionally known light diffusing agent kneading type or random unevenness processing type can be used. Although the thickness of a light-diffusion sheet is not limited, Usually, 10 micrometers or more, Preferably it is 20 micrometers-300 micrometers. If the thickness is less than 10 μm, sufficient diffusibility may not be obtained. The resin constituting the light diffusion sheet is not particularly limited as long as it is a transparent resin, and examples thereof include polycarbonate, polyester, and polymethyl methacrylate. As the light diffusing agent, conventionally known ones can be applied, and examples thereof include glass fibers, glass beads, or fine particles composed of titanium oxide, silica, alumina, acrylic, urethane, polyester, and nylon.

  In the backlight unit 1, the light emitted from the light source 4 enters the light guide plate 3, is reflected by the reflection plate 5, enters the first surface 21 of the optical sheet 2, and then exits from the second surface 22. The

  The method for manufacturing the optical sheet 2 and the method for forming the ridges 23 and the ridges 24 on the first surface 21 may be selected as appropriate depending on the material used, for example, casting, solvent casting, profile extrusion molding, extrusion molding. Roll embossing, hot pressing on a flat plate, monomer casting, injection molding, and the like, but are not limited thereto. In addition, as a method for forming the non-smooth surface on the second surface 22, a method of transferring a pattern such as a roll and a mold simultaneously with the formation of the first surface 21, calendering on a molded sheet, sand blasting, chemical etching, A method of forming by a mat processing method, a press method or the like is applicable. A particularly suitable method for producing the optical sheet 2 is an extrusion method.

[Optical sheet manufacturing method]
Hereinafter, an embodiment of the method for producing the optical sheet 2 of the present invention will be described with reference to FIG.

  FIG. 3 is a schematic view showing a part of a sheet extrusion molding apparatus for producing an optical sheet. In FIG. 3, the die | dye 11, the elastic roll 12, the metal roll 13, and the guide roll 14 of the sheet | seat extrusion molding apparatus 10 are shown. The elastic roll 12 and the metal roll 13 constitute a pair of pressure rolls. The core of the elastic roll 12 is not particularly limited as long as at least the surface thereof is made of an elastic material. For example, the elastic roll 12 can be formed of an elastic material or a metal material. Further, the diameter of the elastic roll 12 is not limited as long as the mechanical strength can be maintained. Furthermore, in an elastic roll having a structure in which the surface of the core is covered with an elastic sheet made of an elastic material, the thickness of the elastic sheet is not limited as long as the mechanical strength can be maintained. The elastic material for forming the elastic roll 12 is not limited as long as it is a material that does not melt even when the sheet-like resin material 15 comes into contact with it, and does not exhibit adhesiveness. Silicon rubber, nitrile rubber (NBR) Examples thereof include rubber materials such as ethylene propylene rubber (EPT, EPDM), urethane rubber, chlorosulfonated polyethylene rubber (CSM), and fluorine rubber. The surface of the elastic roll 12 is a non-smooth surface. The non-smooth surface can be formed by providing fine irregularities by polishing.

  The metal roll 13 is made of a metal material, and a fine uneven pattern is formed on the surface thereof. The formation method of the fine uneven | corrugated pattern on the surface of the metal roll 13 is not specifically limited. For example, a glass master coated with a photosensitive resin is exposed and developed using a photomask or the like to produce a glass master with a concavo-convex pattern, and electroless nickel plating is applied to the master, followed by nickel in an electroforming tank By further increasing the thickness, a metal member having a concavo-convex pattern is obtained, and the concavo-convex pattern is directly cut using a method of using this as a surface member of the metal roll 13 or a metal plate such as a brass plate using a precision lathe. The method to take out is mentioned.

  The resin material melted and mixed in an unillustrated extrusion mixing section is supplied to the extrusion die 11. The molten or softened sheet-shaped resin material 15 processed into a sheet shape inside the extrusion die 11 is pressed in the gap between the elastic roll 12 and the metal roll 13, and the fine surface of the metal roll 13 is brought into contact with the metal roll 13. The surface on which the concavo-convex pattern is transferred and is in contact with the elastic roll 12 is a non-smooth surface. Then, the warp and the residual distortion are adjusted at the same time as passing through the guide roll 14 and being cooled, and the resin sheet 16 is wound up by a winding unit (not shown). And the optical sheet 2 provided with the 1st surface 21 cut by the desired magnitude | size, and the 2nd surface 22 which is a non-smooth surface and the 1st surface 21 in which many convex shapes and many concave shapes were formed in parallel alternately. Manufactured. In the optical sheet 2, the surface in contact with the metal roll 13 becomes the first surface 21, and the surface in contact with the elastic roll 12 becomes the second surface 22. This is because the metal roll 13 is easily subjected to desired uneven processing, and is easy to perform processing for imparting a regular repeated uneven shape as in the first surface 21.

  By the way, in the case where both of the pair of pressure rolls are made of metal rolls, if unevenness in thickness occurs in the resin, there is no escape space in the resin, so stress may concentrate and uneven polarization may occur. Moreover, in order to improve the transferability of the concave / convex pattern of the pressure roll, it is necessary to set the pressing pressure of the pressure roll high. This may cause uneven polarization. In the manufacturing method described above, since the surfaces of one of the rolls constituting the pair of pressure rolls are formed of an elastic material, an optical sheet that is less likely to cause uneven resin thickness and resin accumulation and hardly cause uneven polarization is produced. It becomes possible.

  The backlight unit of the above-described embodiment can be used for a liquid crystal display device. For example, it is suitable for use in an in-vehicle liquid crystal display device because of its luminance characteristics and viewing angle characteristics.

  The present invention will be specifically described with reference to examples.

  In the backlight unit of the above-described embodiment, the following optical sheets were used as the optical sheets of Example 1, Comparative Example 1, and Comparative Example 2, respectively.

  Example 1: The optical sheet 2 was formed by the manufacturing method of the above-described embodiment. A first surface having a shape in which a plurality of ridges having a cross-sectional convex arc shape and a plurality of concave ridges having a cross-sectional concave arc shape are alternately and substantially parallel to each other, and a second surface being a non-smooth surface An optical sheet having the following was obtained. Polycarbonate was used as the resin material. The thickness h1 of the optical sheet 2 of Example 1 is 150 μm, and on the first surface 21, the cross section radius r1 of the ridges 23 is 25.3 μm, the cross section radius r2 of the recesses 24 is 23.9 μm, and adjacent ridges. The distance l1 between the top portions 23a of 23 was 96.7 μm, and the height difference h2 between the valley portion 24a of the concave stripes 24 and the top portion 23a of the convex stripes 23 was 26.0 μm. On the second surface 22, the surface roughness was 1.09 μm in arithmetic mean roughness (Ra) and 9.36 μm in maximum height roughness (Rz).

  Comparative Example 1: The optical sheet manufacturing method of Example 1 is different from the method for manufacturing an optical sheet only in that a metal roll having a mirror surface is used instead of the elastic roll 12. A first surface having a shape in which a plurality of ridges having a cross-sectional convex arc shape and a plurality of concave ridges having a cross-sectional concave arc shape are alternately and substantially parallel to each other, and a second surface being a smooth surface An optical sheet having the following was obtained. The thickness h1 of the optical sheet of Comparative Example 1 is 150 μm, and on the first surface, the cross section radius r1 of the ridges is 16.3 μm, the cross section radius r2 of the ridges 24 is 25.3 μm, and between the tops of adjacent ridges The distance l1 was 96.7 μm, and the height difference h2 between the valley of the concave stripe and the top of the convex stripe was 35.8 μm.

  Comparative Example 2: A commercially available optical sheet (trade name: W818, manufactured by Sekisui Chemical Co., Ltd.) was used. Such an optical sheet includes a first surface having a shape in which a plurality of ridges having a cross-sectional convex arc shape and a plurality of concave ridges having a cross-sectional concave arc shape are alternately and substantially parallel, and a non-smooth surface And an optical sheet having a second surface. The thickness h1 of the optical sheet of Comparative Example 2 is 177 μm, and on the first surface, the cross section radius r1 of the ridges is 20.6 μm, the cross section radius r2 of the ridges 24 is 15.9 μm, and between the tops of adjacent ridges The distance l1 was 99 μm, and the height difference h2 between the valley of the concave stripe and the top of the convex stripe was 33.5 μm. On the second surface, the surface roughness was 0.27 μm in arithmetic mean roughness (Ra) and 2.36 μm in maximum height roughness (Rz).

  In Example 1 and Comparative Examples 1 and 2, the thickness h1, the cross-sectional radius r1, the cross-sectional radius r2, the distance l1, and the height difference h2 were cut out with a size of 30 mm × 30 mm, and an ultra-deep shape measurement was performed. It is a value measured based on an image obtained with a microscope (VK-8500, manufactured by Keyence Corporation). The arithmetic average roughness (Ra) and the maximum height roughness (Rz) are measured with a surface roughness measuring machine (surf Test SJ-201P, manufactured by Mitutoyo Corporation).

(Brightness evaluation test)
For the backlight unit in which the optical sheets of Example 1 and Comparative Examples 1 and 2 are arranged such that the first surface is the light incident surface and the second surface is the light output surface, the luminance in the direction parallel to the light source, and the light source The brightness in the vertical direction was measured.

  A method for measuring luminance in the direction parallel to the light source will be described with reference to FIG. FIG. 4 is a cross-sectional view in a direction (left-right direction) parallel to the light source of the planar light emitting device 1 in which light sources (not shown) are arranged on the upper and lower side surfaces. The normal direction of the light exit surface is 0 °, an arbitrary point A on the planar light emitting device 1 is a measurement target point, and a range from −80 ° to + 80 ° with a straight line passing through the point A and parallel to the light source as an axis. The luminance meter 7 was used to measure from a plurality of positions (positions 50 cm from the point A).

  In the luminance measurement, the planar light emitting device 1 was configured using the following as a cathode tube, a light guide plate, and a reflection plate. The following was used as the luminance meter 7.

Cathode tube: Cold cathode tube having a diameter of 3.0 mm and a length of 130 mm Light guide plate: 130 mm long, 260 mm wide, 3.0 mm thick, material acrylic resin, and the lower surface is subjected to irregular reflection printing Reflector plate: thickness 100 μm Polycarbonate kneaded with 20% by weight of white pigment (titanium oxide) Luminance meter: BM-7 (Topcon)
Table 1 shows luminance values at the respective measurement positions in the direction parallel to the light source. FIG. 5 is a plot of the values in Table 1 and shows the relationship between the measurement position and the luminance in the direction parallel to the light source.

  Luminance in the direction perpendicular to the light source was measured in a similar manner except that it only differed in direction from the luminance measurement in the direction parallel to the light source. Table 2 shows luminance values at respective measurement positions in the direction perpendicular to the light source. FIG. 6 is a plot of the values in Table 2, and is a diagram showing the relationship between the measurement position and the luminance in the direction perpendicular to the light source.

図５，図６からわかるように、実施例１の光学シートを用いた場合、比較例１の光学シートを用いた場合より法線方向近傍において優れた輝度を示し、また比較例２の光学シートを用いた場合より法線方向近傍を含む全領域において優れた輝度を示す。したがって、所定以上の輝度が得られる範囲が実施例１の光学シートを用いた場合の方が比較例２の光学シートを用いた場合より広く、広視野角のバックライトユニットの構成が容易である。例えば、上述の輝度評価試験において、平行方向において２７５０（ｃｄ／ｍ^２）以上の輝度が得られる範囲は、実施例１の光学シートを用いた場合−４０°〜＋３７．５であるのに対し、比較例２の光学シートを用いた場合−３５°〜＋３５°である。

As can be seen from FIGS. 5 and 6, when the optical sheet of Example 1 was used, the luminance was superior in the vicinity of the normal direction than when the optical sheet of Comparative Example 1 was used, and the optical sheet of Comparative Example 2 In the entire region including the vicinity in the normal direction, the luminance is superior to that in the case of using. Therefore, the range in which the luminance higher than the predetermined value is obtained is wider when the optical sheet of Example 1 is used than when the optical sheet of Comparative Example 2 is used, and the configuration of the backlight unit having a wide viewing angle is easy. . For example, in the above-described luminance evaluation test, the range in which the luminance of 2750 (cd / m ² ) or more is obtained in the parallel direction is −40 ° to +37.5 when the optical sheet of Example 1 is used. When the optical sheet of Comparative Example 2 is used, the angle is −35 ° to + 35 °.

(Polarization unevenness evaluation test)
About the backlight unit provided with the optical sheet of Example 1 and Comparative Examples 1 and 2, retardation values (birefringence) at arbitrary five points were measured. The retardation value was measured for a wavelength of 590 nm using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Instruments. The results are shown in Table 3.

表３に示す結果から、実施例１の光学シートを用いた場合、比較例１の光学シートを用いた場合より、リタデーション値のバラツキが小さいことがわかる。すなわち、実施例１の光学シートは、比較例１の光学シートと比較して偏光ムラが少ないことになる。

From the results shown in Table 3, it can be seen that when the optical sheet of Example 1 is used, the variation in retardation value is smaller than when the optical sheet of Comparative Example 1 is used. That is, the optical sheet of Example 1 has less polarization unevenness than the optical sheet of Comparative Example 1.

  The optical sheet of the present invention is useful as a component of a light source device of a liquid crystal display device, and is particularly useful as a component of a light source device of a vehicle-mounted liquid crystal display device.

It is sectional drawing which shows typically the structure of a planar light source device provided with the optical sheet of this invention. It is sectional drawing which shows typically a partial structure of the optical sheet 2 of this invention. It is the schematic which shows a part of sheet | seat extrusion molding apparatus for manufacturing an optical sheet. It is a figure which shows the measuring method of the brightness | luminance of a parallel direction with respect to a light source. It is a figure which shows the relationship between the measurement position of a parallel direction with respect to a light source, and a brightness | luminance. It is a figure which shows the relationship between the measurement position of a perpendicular direction with respect to a light source, and a brightness | luminance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight unit 2 Optical sheet 3 Light guide plate 4 Light source 5 Reflector 7 Luminance meter 10 Extrusion apparatus 11 Die 12 Elastic roll 13 Metal roll 14 Guide roll 15 Sheet-like resin material 16 Resin sheet 21 First surface 22 Second surface 23 Convex ridge 23a Convex ridge 24 Convex 24a Convex valley

Claims (6)

A first surface having a shape in which a plurality of ridges having a cross-sectional convex arc shape and a plurality of concave ridges having a cross-sectional concave arc shape are alternately and substantially parallel to each other, and a second surface being a non-smooth surface And
The protrusion has a curvature radius of 10 μm to 30 μm in a convex arc shape in cross section,
The concave streak has a concave cross-sectional arc-shaped radius of curvature of 10 μm to 30 μm,
2. The optical sheet according to claim 1, wherein the non-smooth surface has a surface roughness of 0.5 μm to 2 μm in arithmetic mean roughness (Ra) and 5 μm to 30 μm in maximum height roughness (Rz).   The optical sheet according to claim 1, comprising polycarbonate.   The optical sheet according to claim 1, wherein the thickness is 50 μm to 500 μm. A method for producing an optical sheet according to any one of claims 1 to 3,
The sheet-shaped resin material extruded from the extrusion die has a pressure step of passing through the gap while being pressed by at least a pair of pressure rolls,
The method for producing an optical sheet, wherein a surface of at least one of the pair of pressure rolls is made of an elastic material.   The manufacturing method according to claim 4, wherein the surface of one pressure roll of the pair of pressure rolls is made of an elastic material, and the surface of the other pressure roll is made of a metal material. A light source, a light guide plate, and the optical sheet according to any one of claims 1 to 3,
The backlight unit in which the light from the light source is incident on the first surface of the optical sheet via the light guide plate and is emitted from the second surface.

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