Light diffusion sheet, backlight unit, liquid crystal display device, information apparatus, and method of manufacturing light diffusion sheet

Abstract

The light diffusion sheet (43) includes a plurality of recessed portions (22) formed in an approximately inverted polygonal pyramid shape at least on the first surface (43a). The ridge lines (23) separating the plurality of recessed portions (22) have a recessed shape between intersection points (23a) of the ridge lines (23) with respect to a straight line connecting the intersection points (23a). When an arrangement pitch of the plurality of recessed portions 22 is represented by P, and a size occupied by a curved portion of a vertex of each of the ridge lines 23 in an arrangement direction of the plurality of recessed portions 22 is represented by Wr, a ratio Wr / P is 0.3 or less. The maximum height difference d between a straight line connecting the intersection points 23a of the ridge lines 23 and the ridge lines 23 is 1 [mu] m or more and 10 [mu] m or less. The plurality of recessed portions (22) include recessed portions (22) in which the apex of an approximately inverted polygonal pyramid is formed in a linear shape.

Description

Technical Field

[0001] The present disclosure relates to a light diffuser, a backlight unit, a liquid crystal display device, an information device, and a method of manufacturing the light diffuser. Background Art

[0002] In recent years, liquid crystal display devices (hereinafter also referred to as liquid crystal displays) have been widely used as display devices for various information devices including smartphones and tablet terminals. As a backlight device of the liquid crystal display, a direct-type system in which a light source is arranged on the rear surface of a liquid crystal panel or an edge-type light system in which a light source is arranged near a side surface of the liquid crystal panel is mainly used.

[0003] When a direct-type backlight device is employed, a light diffusion member (a light diffusion plate, a light diffusion sheet, or a light diffusion film) is used in order to erase the image of a light source such as an LED (Light Emitting Diode) and increase the uniformity of in-plane brightness on a light emitting surface.

[0004] In the direct-type backlight device disclosed in PTL 1, in order to improve brightness uniformity, a light diffuser plate provided with a plurality of recessed portions having an inverted polygonal cone shape (inverted pyramid shape) or an inverted truncated polygonal cone shape is used. PTL 1 discloses that in a stacked structure of the light diffuser plate and another optical film, the inner side surface of each recessed portion of the light diffuser plate is made a curved surface having a center of curvature located on one side in the depth direction of the recessed portion at an opening edge portion, so as to prevent the light diffuser plate and the other optical film from being worn and damaged due to vibration during transportation.

[0005] Reference List

[0006] Patent Literature

[0007] PTL 1 Japanese Patent Application Publication No. 2010-117707 Summary of the invention

[0008] Technical issues

[0009] However, with the direct type backlight device disclosed in PTL 1, damage to the light diffusion plate and other optical films cannot be sufficiently suppressed.

[0010] In view of this, an object of the present disclosure is to provide a light diffusion sheet that is not easily damaged even when stacked while improving brightness uniformity.

[0011] Solution to the problem

[0012] In order to achieve the above-mentioned purpose, the light diffuser according to the present disclosure includes a plurality of recessed portions formed into approximately inverted polygonal cones on at least the first surface. The ridge lines separating the plurality of recessed portions have a recessed shape between the intersection points of the ridge lines relative to the straight line connecting the intersection points. When the arrangement pitch of the plurality of recessed portions is represented by P, and the size occupied by the curved portion of the vertex of each ridge line in the arrangement direction of the plurality of recessed portions is represented by Wr, the ratio Wr / P is 0.3 or less. The maximum height difference d between the straight line and the ridge line is greater than or equal to 1 μm and less than or equal to 10 μm. The plurality of recessed portions include recessed portions whose vertices of approximately inverted polygonal cones are formed into linear shapes.

[0013] According to the light diffuser sheet disclosed herein, since the light diffuser sheet includes a plurality of recessed portions formed into approximately inverted polygonal cones at least on the first surface, the brightness uniformity can be improved. In addition, although the ridge lines (opening edges of the recessed portions) separating the recessed portions cause wear and damage, the ridge lines have a recessed shape between the intersections of the ridge lines. Therefore, even when the light diffuser sheet is used by stacking with other optical sheets or other light diffusers, wear and damage are unlikely to occur. In addition, the size Wr occupied by the curved portion of the vertex of each of these ridge lines in the arrangement direction of the recessed portions is maintained at 30% or less of the arrangement pitch P of the recessed portions. Therefore, since the vertex of the ridge line can maintain a steep shape, even if the ridge line is recessed between the intersections of the ridge lines, the brightness uniformity is not easily reduced. In addition, since the maximum height difference d between the straight line connecting the intersections of the ridge lines and the ridge line is set to 1 μm or more, the scratch resistance is improved, and at the same time, since the maximum height difference d is set to 10 μm or less, the brightness uniformity can be suppressed from decreasing. Furthermore, since the apex of the approximately inverted polygonal pyramid (in other words, the bottom of the concave portion) is formed in a linear shape, mass production of the light diffusion sheet that prevents a decrease in brightness uniformity can be easily performed.

[0014] Although the expression "approximately an inverted polygonal cone" is used in consideration of the difficulty in forming a geometrically strict inverted polygonal cone recessed portion using ordinary shape transfer technology in the light diffuser according to the present disclosure, it goes without saying that the expression includes a true inverted polygonal cone and a shape that is basically an inverted polygonal cone.

[0015] Furthermore, although the ridge lines preferably have a concave shape between all intersections of the ridge lines in the light diffusion sheet according to the present disclosure, it is not essential that the ridge lines have a concave shape between all intersections. In other words, the ridge lines do not need to have a concave shape between the intersections.

[0016] In addition, in the present disclosure, a “light diffusion sheet” includes a “light diffusion plate” in a plate shape and a “light diffusion film” in a film shape.

[0017] Also, in the present disclosure, an “optical sheet” refers to a sheet having various optical functions such as diffusion, light condensing, refraction, and reflection, and a “light diffusion sheet” is one of such “optical sheets”.

[0018] In the light diffuser according to the present disclosure, when the maximum height difference d is greater than or equal to 1.5 μm and less than or equal to 7 μm, both the scratch resistance and the brightness uniformity can be further improved. In this case, when the maximum height difference d is greater than or equal to 2.5 μm and less than or equal to 5 μm, both the scratch resistance and the brightness uniformity can be even further improved.

[0019] In the light diffuser according to the present disclosure, when the ratio Wr / P is 0.2 or less, the brightness uniformity may be further improved. In this case, when the ratio Wr / P is 0.1 or less, the brightness uniformity may be even further improved.

[0020] In the light diffuser according to the present disclosure, when the arrangement pitch P is greater than or equal to 50 μm and less than or equal to 500 μm, and when the angle formed between the wall surface of the plurality of recessed portions (in other words, the inclined surface of the approximately inverted polygonal cone) and the sheet surface of the light diffuser is greater than or equal to 40 degrees and less than or equal to 65 degrees, the brightness uniformity can be improved.

[0021] In the light diffusion sheet according to the present disclosure, when the ridge line is recessed in an approximately parabola shape, an approximately circular arc shape, an approximately triangular shape, or an approximately trapezoidal shape between intersections, scratch resistance may be improved.

[0022] In the light diffuser according to the present disclosure, a plurality of recessed portions may be formed to approximate inverted quadrangular pyramids. In this case, the ridge line may extend in the first direction and the second direction. In addition, the maximum height difference d may be the average of the maximum height difference dx between the straight line and the ridge line in the first direction and the maximum height difference dy between the straight line and the ridge line in the second direction. In addition, the arrangement spacing P may be the average of the arrangement spacing Px of the plurality of recessed portions in the first direction and the arrangement spacing Py of the plurality of recessed portions in the second direction. Moreover, the dimension Wr is the average of the dimension Wrx occupied by the curved portion of the vertex of each ridge line in the first direction and the dimension Wry occupied by the curved portion of the vertex of each ridge line in the second direction. Accordingly, a light diffuser having excellent scratch resistance and brightness uniformity may be easily manufactured.

[0023] In the light diffusion sheet according to the present disclosure, when the plurality of recessed portions are provided only on the first surface and the second surface is a matte surface, the brightness uniformity can be further improved while suppressing abrasion and damage on the second surface.

[0024] In the light diffuser according to the present disclosure, the ratio of the concave portion whose apex is formed into a linear shape among the plurality of concave portions may be 10% or more. Alternatively, the ratio may be 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100%.

[0025] The backlight unit according to the present disclosure is a backlight unit built into a liquid crystal display device, which guides light emitted by a light source toward a display screen, and includes the aforementioned light diffusion sheet according to the present disclosure between the display screen and the light source.

[0026] Since the backlight unit according to the present disclosure includes the aforementioned light diffusion sheet according to the present disclosure, even when the light diffusion sheet and other optical sheets are stacked, brightness uniformity may be improved while damage may be suppressed.

[0027] In the backlight unit according to the present disclosure, when the light source is arranged on a reflection sheet disposed on a side opposite to the display screen when viewed from the light diffusion sheet, the brightness uniformity is even further improved.

[0028] In the backlight unit according to the present disclosure, a plurality of light diffusers (e.g., three or more) may be stacked together and arranged between the display screen and the light source. Accordingly, the brightness uniformity is further improved. In the case of stacking three or more light diffusers, when the light diffuser closest to the display screen contains a diffuser and the other light diffusers substantially do not contain a diffuser, the brightness uniformity is even further improved.

[0029] The liquid crystal display device according to the present disclosure includes a liquid crystal display panel and the aforementioned backlight unit according to the present disclosure.

[0030] Since the liquid crystal display device according to the present disclosure includes the aforementioned backlight unit according to the present disclosure, even when a light diffusion sheet and other optical sheets are stacked, brightness uniformity can be improved while damage can be suppressed.

[0031] The information equipment according to the present disclosure includes the aforementioned liquid crystal display device according to the present disclosure.

[0032] Since the information equipment according to the present disclosure includes the aforementioned liquid crystal display device according to the present disclosure, even when a light diffusion sheet and other optical sheets are stacked, brightness uniformity can be improved while damage can be suppressed.

[0033] The method for manufacturing a light diffuser according to the present disclosure is a method for manufacturing the aforementioned light diffuser according to the present disclosure, wherein the light diffuser is extruded at a line speed greater than or equal to 10 m / min and less than or equal to 30 m / min and a compressible linear pressure greater than or equal to 100 kgf / cm and less than or equal to 500 kgf / cm.

[0034] By using the method for manufacturing a light diffuser according to the present disclosure, since the dimension Wr occupied by the curved portion of the vertex of the ridge line in the arrangement direction of the recessed portions can be maintained at 30% or less of the arrangement pitch P of the recessed portions, a light diffuser can be manufactured in which the shape of the vertex of the ridge line is steep and has excellent brightness uniformity.

[0035] In addition, by the method of manufacturing a light diffuser according to the present disclosure, the maximum height difference d between the straight line connecting the intersection points of the ridge lines and the ridge lines can be set to be greater than or equal to 1 μm and less than or equal to 10 μm. In other words, a light diffuser is obtained in which the ridge lines are concave between the intersection points of the ridge lines and convex at the portions of the intersection points of the ridge lines. Therefore, even when the light diffuser and other optical sheets are stacked, since the ridge lines are less likely to contact with the other optical sheets between the intersection points of the ridge lines, wear and damage are less likely to occur, and since the ridge lines are in point contact with the other optical sheets at the intersection points of the ridge lines, slippage is generated and the slippage reduces wear and damage. As a result, a light diffuser with excellent scratch resistance can be manufactured.

[0036] In addition, through the method of manufacturing a light diffuser sheet according to the present disclosure, since extrusion molding is used, the aforementioned light diffuser sheet according to the present disclosure can be manufactured at a low cost.

[0037] In order to achieve the above-mentioned purpose, according to another aspect of the present disclosure, a light diffuser includes a plurality of recessed portions formed into approximately inverted polygonal cones on at least the first surface. The ridge lines separating the plurality of recessed portions have a recessed shape between the intersection points of the ridge lines relative to the straight line connecting the intersection points. When the arrangement pitch of the plurality of recessed portions is represented by P, and the size occupied by the curved portion of the vertex of each ridge line in the arrangement direction of the plurality of recessed portions is represented by Wr, the ratio Wr / P is 0.3 or less. The maximum height difference d between the straight line and the ridge line is greater than or equal to 1 μm and less than or equal to 10 μm. The plurality of recessed portions include a recessed portion whose vertex is approximately an inverted polygonal cone and is formed into a rectangular shape.

[0038] According to another aspect of the light diffuser of the present disclosure, since the light diffuser includes a plurality of recessed portions formed into approximately inverted polygonal cones at least on the first surface, the brightness uniformity can be improved. In addition, although the ridge lines (opening edges of the recessed portions) separating the recessed portions cause wear and damage, the ridge lines have a recessed shape between the intersections of the ridge lines. Therefore, even when the light diffuser is used by stacking with other optical sheets or other light diffusers, wear and damage are unlikely to occur. In addition, the size Wr occupied by the curved portion of the vertex of each of these ridge lines in the arrangement direction of the recessed portions is maintained at 30% or less of the arrangement pitch P of the recessed portions. Therefore, since the vertex of the ridge line can maintain a steep shape, even if the ridge line is recessed between the intersections of the ridge lines, the brightness uniformity is not easily reduced. In addition, since the maximum height difference d between the straight line connecting the intersections of the ridge lines and the ridge line is set to 1 μm or more, the scratch resistance is improved, and at the same time, since the maximum height difference d is set to 10 μm or less, the brightness uniformity can be suppressed from decreasing. Furthermore, since the apex of the approximately inverted polygonal pyramid (in other words, the bottom of the concave portion) is formed in a rectangular shape, mass production of a light diffusion sheet that prevents a decrease in brightness uniformity can be easily performed.

[0039] Advantageous Effects of the Invention

[0040] According to the present disclosure, it is possible to provide a light diffusion sheet which is not easily damaged even when stacked with other optical sheets while improving brightness uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a cross-sectional view of a liquid crystal display device according to an embodiment.

[0042] Figure 2 is a cross-sectional view of a backlight unit according to an embodiment.

[0043] Figure 3 It shows Figure 2 2 is a plan view of an arrangement example of light sources in a backlight unit shown in FIG.

[0044] Figure 4 is a perspective view of a light diffusion sheet according to an embodiment.

[0045] Figure 5 is an enlarged perspective view showing a concave portion formed on a light diffusion sheet according to an embodiment.

[0046] Figure 6 : is a schematic diagram showing an example of the shape of the X-direction ridge line that partitions the concave portions in the light diffusion sheet according to the embodiment.

[0047] Figure 7: is a schematic diagram showing an example of the shape of the Y-direction ridge line that partitions the concave portions in the light diffusion sheet according to the embodiment.

[0048] Figure 8 1 is a schematic diagram showing changes in the shape of a ridge line that separates the concave portions in the light diffusion sheet according to the embodiment.

[0049] Fig. 9 : is a schematic diagram showing an example of a cross-sectional structure of a light diffusion sheet according to an embodiment when it is cut along a plane passing through respective centers of recessed portions adjacent to each other in the X direction and a midpoint of a ridge line between the recessed portions and perpendicular to the sheet surface.

[0050] Fig.10 : is a schematic diagram showing an example of a cross-sectional structure of a light diffuser according to an embodiment when cut along a plane passing through corresponding centers of recessed portions adjacent to each other in the Y direction and a midpoint of a ridge line between the recessed portions and perpendicular to the sheet surface.

[0051] Fig.11 The laser microscope shows Figure 6 An example of the results of measuring the shape and size of the X-direction ridge line is shown in FIG.

[0052] Fig.12 The laser microscope shows Figure 7 An example of the results of measuring the shape and size of the Y-direction ridge line is shown in FIG.

[0053] Fig.13 The laser microscope is used to Fig. 9 An illustration of an example of the results of measuring the shape, size, etc. of the cross-sectional structure shown in FIG.

[0054] Fig.14 The laser microscope is used to Fig.10 An illustration of an example of the results of measuring the shape, size, etc. of the cross-sectional structure shown in FIG.

[0055] Fig.15 : is a schematic diagram showing the shape of the vertex of each concave portion (inverted quadrangular pyramid) formed on the light diffusion sheet according to the embodiment.

[0056] Fig.16 is a diagram illustrating the configuration of an apparatus used for measuring the scratch resistance of a light diffusion sheet in each example.

[0057] Fig.17 : are diagrams showing the shape of a regular quadrangular pyramid on a roll used for manufacturing a light diffusion sheet in each example.

[0058] Fig.18: is a diagram showing the shape of a regular quadrangular pyramid on a flat plate used for manufacturing a light diffusion sheet in each comparative example.

[0059] Fig.19 is a graph showing the results of a scratch resistance test conducted on each sample of each example and each comparative example.

[0060] Fig. 20 is a cross-sectional view of a backlight unit according to a modification.

[0061] Fig.21 is a diagram for explaining a method of checking the occurrence rate of linear vertices in a concave portion formed on a light diffusion sheet in each example. DETAILED DESCRIPTION

[0062] (Example)

[0063] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the scope of the present disclosure is not limited to the embodiments described below, and any modifications may be made without departing from the scope of the technical idea of ​​the present disclosure.

[0064] <Liquid Crystal Display Device>

[0065] like Figure 1 As shown in , the liquid crystal display device 50 according to the present embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the bottom surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the top surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the rear surface side of the liquid crystal display panel 5 via the first polarizing plate 6. The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 provided facing each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) provided in a frame shape between the TFT substrate 1 and the CF substrate 2 so as to seal the liquid crystal layer 3.

[0066] Although from the front ( Figure 1 The display screen 50a of the liquid crystal display device 50 is generally rectangular or square in shape when viewed from above in the figure, but the shape is not limited thereto and may be any shape, such as a rectangular shape with rounded corners, an elliptical shape, a circular shape, a trapezoidal shape, or the shape of a car dashboard.

[0067] In the liquid crystal display device 50, an image is displayed by applying a voltage of a predetermined magnitude to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3, adjusting the transmittance of light incident from the backlight unit 40 via the first polarizing plate 6, and emitting light via the second polarizing plate 7 in each sub-pixel corresponding to each pixel electrode.

[0068] According to this embodiment, the liquid crystal display device 50 is used as a display device to be built into various information devices (for example, vehicle-mounted devices for car navigation, etc., personal computers, mobile phones, portable information terminals, portable game consoles, copiers, ticket vending machines, and automatic teller machines).

[0069] For example, the TFT substrate 1 includes: a plurality of TFTs arranged on a glass substrate in a matrix pattern; an interlayer insulating film arranged to cover each TFT; a plurality of pixel electrodes arranged on the interlayer insulating film in a matrix pattern and respectively connected to the plurality of TFTs; and an alignment film arranged to cover each pixel electrode. For example, the CF substrate 2 includes: a black matrix arranged on a glass substrate in a grid pattern; a color filter including a red layer, a green layer, and a blue layer respectively arranged between corresponding grids of the black matrix; a common electrode arranged to cover the black matrix and the color filter; and an alignment film arranged to cover the common electrode. The liquid crystal layer 3 is composed of a nematic liquid crystal material containing liquid crystal molecules having electro-optical properties, etc. For example, the first polarizing plate 6 and the second polarizing plate 7 include a polarizer layer with a polarization axis in one direction and a pair of protective layers arranged to sandwich the polarizer layer.

[0070] <Backlight Unit>

[0071] like Figure 2 As shown in , the backlight unit 40 according to the present embodiment includes a reflective sheet 41, a plurality of small light sources 42 arranged in a two-dimensional shape on the reflective sheet 41, a stack of first light diffusers 43 disposed above the plurality of small light sources 42, a second light diffuser 44 disposed above the stack of first light diffusers 43, and a first prism sheet 45 and a second prism sheet 46 sequentially disposed above the second light diffuser 44. In this example, the stack of first light diffusers 43 is constructed by stacking two layers of first light diffusers 43 having the same structure. Although not shown, a polarizing sheet may be disposed above the second prism sheet 46.

[0072] For example, the reflection sheet 41 is composed of a film made of white polyethylene terephthalate resin, a silver deposition film, or the like.

[0073] Although the type of the small light source 42 is not particularly limited, for example, the small light source 42 may be an LED element, a laser element, etc., and an LED element may be used from the perspective of cost, productivity, etc. A lens may be attached to the LED element to be used as the small light source 42 in order to adjust the emission angle characteristics of the LED element. Figure 3As shown in , a plurality of small light sources 42 made of LED elements of several square millimeters are arranged in a two-dimensional array shape at constant intervals. The small light source 42 may have a rectangular shape in a plan view, and in this case, the length of one side may be greater than or equal to 10 μm (preferably, 50 μm or more) and less than or equal to 20 mm (preferably 10 mm or less, more preferably 5 mm or less).

[0074] In addition, although the number of arranged small light sources 42 is not particularly limited, when a plurality of small light sources 42 are arranged in a distributed manner, the small light sources 42 are preferably regularly arranged on the reflective sheet 41. Regular arrangement means arranging in a certain regularity, for example, arranging the small light sources 42 at equal intervals constitutes a regular arrangement. When the small light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent small light sources 42 may be greater than or equal to 0.5 mm (preferably 2 mm or more) and less than or equal to 20 mm.

[0075] Each first light diffuser 43 includes a substrate layer 21. A plurality of recessed portions 22 are provided on a first surface (surface opposite to the small light source 42) 43a of the first light diffuser 43. A plurality of recessed portions 22 are formed to approximate inverted polygonal pyramids. In this example, a plurality of recessed portions 22 are formed to approximate inverted quadrangular pyramids. The recessed portions 22 adjacent to each other are separated by ridge lines 23. The arrangement pitch of the plurality of recessed portions 22 is, for example, greater than or equal to about 50 μm and less than or equal to about 500 μm. The angle formed between the wall surface of the recessed portion 22 (the inclined surface of the approximate inverted polygonal pyramid) and the sheet surface of the first light diffuser 43 (the virtual mirror surface without the recessed portion 22) is set to, for example, greater than or equal to 40 degrees and less than or equal to 65 degrees. In other words, the vertex angle of the recessed portion 22 is set to, for example, greater than or equal to 50 degrees and less than or equal to 100 degrees. Although the second surface 43b of the first light diffusion sheet 43 may be a mirror surface, the second surface 43b is preferably a matte surface to improve diffusibility. Figure 4 The case where the recessed portions 22 formed into approximately inverted quadrangular pyramids are arranged in a 5×5 matrix pattern on the first surface 43 a of the first light diffusion sheet 43 is illustrated.

[0076] Although the substrate layer 21 is constructed using, for example, polycarbonate as a substrate (base resin) and preferably does not contain a diffusing agent, the substrate layer 21 may contain up to, for example, about 0.1 to 4% by mass of a diffusing agent per 100% by mass of the substrate. Known materials may be appropriately used as diffusing agents. Although the first light diffuser 43 has a one-layer structure of the substrate layer 21 in this example, alternatively, the first light diffuser 43 may have a two-layer or more-layer structure including a layer on which the recessed portion 22 is formed.

[0077] The second light diffuser 44 may include a matte surface on the first surface (the surface opposite to the first prism sheet 45) 44a and a mirror surface or a concave portion formed as an approximately inverted quadrangular pyramid on the second surface 44b. The second light diffuser 44 is constructed using, for example, polycarbonate as a substrate (base resin), and preferably contains a diffusing agent, and for example, the second light diffuser 44 may contain about 0.5 to 4% by mass of the diffusing agent per 100% by mass of the substrate. The second light diffuser 44 is constructed by, for example, mixing 1 part by mass of a siloxane composite powder (average particle size of 2.0 μm) as a diffusing agent per 99 parts by mass of an aromatic polycarbonate resin.

[0078] The first prism sheet 45 and the second prism sheet 46 are, for example, films formed so that a plurality of groove lines having isosceles triangle cross-sections are adjacent to each other, and the vertex angle of the prism sandwiched between a pair of adjacent groove lines is about 90 degrees. In this case, each groove line formed on the first prism sheet 45 and each groove line formed on the second prism sheet 46 are arranged to be orthogonal to each other. The first prism sheet 45 and the second prism sheet 46 may be formed integrally. For example, a PET (polyethylene terephthalate) film in which a prism shape is presented using a UV-curing acrylic resin may be used as the first prism sheet 45 and the second prism sheet 46.

[0079] Although not shown, when a polarizing plate is disposed above the second prism sheet 46, for example, DBEF series manufactured by 3M Company can be used as the polarizing plate. The polarizing plate improves the brightness of the display screen 50a by preventing light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50.

[0080] <Detailed Configuration of Light Diffuser>

[0081] Although in Figure 2 In the example shown in , a plurality of recessed portions 22 are formed on a first surface (a surface opposite to the small light source 42) 43a of a first light diffuser 43, but in addition to or instead of the recessed portions 22, a plurality of other recessed portions similar to the recessed portions 22 may also be formed on a second surface 43b of the first light diffuser 43.

[0082] A plurality of recessed portions 22 may be formed to approximate inverted polygonal pyramids. A plurality of recessed portions 22 may be regularly arranged in two dimensions. As the "inverted polygonal pyramid", a triangular pyramid, a quadrangular pyramid or a hexagonal pyramid that can be arranged in two dimensions in a seamless manner is preferred. Although a mold (metal roller) is used in a manufacturing step such as extrusion molding and injection molding when the recessed portions 22 are provided, an inverted quadrangular pyramid may be selected as the "inverted polygonal pyramid" in consideration of the accuracy of the cutting operation on the surface of the mold (metal roller).

[0083] Although the expression "approximately an inverted polygonal pyramid" is used in consideration of the difficulty in forming a geometrically strict inverted polygonal pyramid concave portion using a common shape transfer technique, it is needless to say that the expression includes a true inverted polygonal pyramid and a shape that is substantially an inverted polygonal pyramid. In addition, "approximately" means "can be approximated", for example, "approximately a quadrangular pyramid" means a shape that can be approximated to a quadrangular pyramid. In addition, within the range of inevitable shape variability caused by machining accuracy in industrial production, a shape deformed from an "inverted polygonal pyramid" is also included in "approximately an inverted polygonal pyramid".

[0084] When the plurality of recessed portions 22 are regularly arranged two-dimensionally, the plurality of recessed portions 22 may be seamlessly disposed on the entire surface of the first light diffusion sheet 43 or may be disposed at constant intervals (pitch).

[0085] The first light diffuser 43 may be composed of a substrate layer 21 (such as a substrate layer 21 made of transparent polycarbonate) that does not contain a diffuser. When the substrate layer 21 contains a diffuser, although the material of the diffuser is not particularly limited, inorganic particles of silicon dioxide, titanium oxide, aluminum hydroxide, barium sulfate, etc., or organic particles of acrylic acid, acrylonitrile, siloxane, polystyrene, polyamide, etc. can be used. From the perspective of the light diffusion effect, the particle size of the diffuser can be set to, for example, greater than or equal to 0.1 μm (preferably, 1 μm or more) and less than or equal to 10 μm (preferably, 8 μm or less). Although the first light diffuser 43 preferably does not include a diffuser from the perspective of the reflection and refraction effect of the approximately inverted polygonal pyramid shape and the light diffusion effect of the diffuser, the content of the diffuser can be set to, for example, greater than or equal to 0.1 mass % (preferably, 0.3 mass % or more) and less than or equal to 10 mass % (preferably, 8 mass % or less), wherein the material (matrix) constituting the substrate layer 21 is 100 mass %. The difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base material layer 21 may be 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and most preferably 0.15 or more. When the difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base material layer 21 is less than 0.01, the diffusion effect of the diffusing agent becomes insufficient.

[0086] Although the resin constituting the matrix of the substrate layer 21 is not particularly limited as long as a light-transmitting material is used, for example, acrylic, polystyrene, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate or polyimide can be used.

[0087] Although the thickness of the first light diffuser 43 is not particularly limited, for example, the thickness may be less than or equal to 3 mm (preferably 2 mm or less, more preferably 1.5 mm or less, and even more preferably 1 mm or less) and greater than or equal to 0.1 mm. When the thickness of the first light diffuser 43 exceeds 3 mm, it becomes difficult to realize a thinner liquid crystal display. On the other hand, when the thickness of the first light diffuser 43 drops below 0.1 mm, it becomes difficult to produce an effect of improving brightness uniformity.

[0088] When the first light diffuser 43 has a multilayer structure (for example, a substrate layer constituting a first layer and a recessed portion forming layer constituting a second layer), the thickness of the recessed portion forming layer is greater than the maximum depth of the recessed portion 22. For example, in the case where a layer is provided with a recessed portion having a depth of 20 μm, the thickness of the layer is set to be greater than 20 μm. The first light diffuser 43 may be configured to have a structure of three or more layers including a substrate layer and a recessed portion forming layer. Alternatively, the substrate layer and the recessed portion forming layer may be configured as separate sheets, respectively, and the sheets may be stacked or arranged separately.

[0089] <Method for Manufacturing Light Diffusing Sheet>

[0090] Hereinafter, a method for manufacturing the first light diffuser 43 will be described. Although the method for manufacturing the first light diffuser 43 is not particularly limited, for example, an extrusion molding method or an injection molding method may be used. When the first light diffuser 43 is extruded, for example, a line speed may be set to be greater than or equal to 10 m / min and less than or equal to 30 m / min, and a compressible linear pressure may be set to be greater than or equal to 100 kgf / cm and less than or equal to 500 kgf / cm.

[0091] The procedure for manufacturing a single-layer light diffuser having an uneven shape on its surface using an extrusion molding method is as follows. First, pellet-shaped plastic particles to which a diffusing agent has been added (pellet-shaped plastic particles to which no diffusing agent has been added may be mixed therewith) are fed into a single screw extruder and melted and kneaded while applying heat. Subsequently, after clamping the melted resin extruded by a T-die with two metal rollers and cooling the melted resin, the diffuser is manufactured by conveying the resin using a guide roller and cutting the resin into flat sheets using a slicer. In this case, since the melted resin is clamped using a metal roller having a surface having a shape inverted from the desired uneven shape, the inverted shape on the roller surface is transferred to the resin, and thus the desired uneven shape can be formed on the surface of the diffuser. In addition, since the shape transferred to the resin does not necessarily represent a 100% transfer of the roller surface shape, the shape of the roller surface can be reversely designed according to the degree of transfer.

[0092] When a light diffuser having a two-layer structure having an uneven shape on the surface is manufactured using an extrusion molding method, for example, after plastic particles in the shape of pellets required to form each layer are fed into each of two single-screw extruders, a procedure similar to that described previously can be performed for each layer, and the corresponding manufactured sheets can be stacked.

[0093] Alternatively, a light diffuser having a two-layer structure with an uneven shape on the surface can be manufactured as described below. First, plastic particles in a pellet shape required to form each layer are fed into each of two single-screw extruders, and melted and kneaded when heat is applied. Subsequently, the molten resin that will become each layer is fed into a T-die, and the stacked molten resin that has been stacked in the T-die and extruded from the T-die is sandwiched between two metal rollers and cooled. Subsequently, a diffuser having a two-layer structure with an uneven shape on the surface can be manufactured by conveying the stacked molten resin using a guide roller and cutting the resin into flat sheets using a slicer.

[0094] In addition, a light diffusion sheet can be manufactured by shape transfer using UV (ultraviolet light) as described below. First, a roller with an inverted shape having an uneven shape to be transferred is filled with uncured ultraviolet curing resin, and a substrate is pressed against the resin. Next, ultraviolet light is irradiated to cure the ultraviolet curing resin to a state where the roller filled with the resin and the substrate become one. Next, the sheet to which the uneven shape has been shape-transferred by the resin is separated from the roller. Finally, the sheet is irradiated with ultraviolet light again to completely cure the resin, and a diffusion sheet having an uneven shape on the surface is manufactured.

[0095] <Characteristics of Light Diffuser>

[0096] In the following, reference will be made to Figures 5 to 10 Features of the first light diffusion sheet 43 according to the present embodiment are described in detail.

[0097] like Figure 5 As shown in the figure, a plurality of recessed portions 22 are provided on the first surface 43a of the first light diffuser 43, and the plurality of recessed portions are formed into, for example, approximately inverted quadrangular pyramids. The center 22a of each recessed portion 22 is the deepest part of the recessed portion 22. The plurality of recessed portions 22 are arranged in the X direction (first direction) and the Y direction (second direction) orthogonal to each other. The recessed portions 22 adjacent to each other are separated by ridge lines 23. The ridge lines 23 extend in the X direction and the Y direction.

[0098] As a feature of the first light diffuser 43, the ridge line 23 has a concave shape between the intersections 23a relative to the straight lines Lx and Ly connecting the intersections 23a of the ridge line 23. In this case, the maximum height difference d between the straight lines Lx and Ly connecting the intersections 23a and the ridge line 23 should be greater than or equal to 1 μm and less than or equal to 10 μm, and may preferably be greater than or equal to 1.5 μm and less than or equal to 7 μm, and more preferably may be greater than or equal to 2.5 μm and less than or equal to 5 μm.

[0099] Although the ridge line preferably has a concave shape between all intersections 23a of the ridge line in the first light diffusion sheet 43, it is not essential that the ridge line 23 has a concave shape between all intersections 23a. In other words, the ridge line 23 does not need to have a concave shape between parts of the intersections 23a.

[0100] Figure 6 It shows that when viewed from a direction parallel to the sheet surface and perpendicular to the X direction, the Figure 5 An example of the shape of the ridge line 23 extending in the X direction along the line Ax-Bx shown in FIG. Figure 7 It shows that when viewed from a direction parallel to the sheet surface and perpendicular to the Y direction, Figure 5 An example of the shape of the ridge line 23 where the line Ay-By shown in FIG. extends in the Y direction. Figure 6 As shown in FIG. 1 , the ridge line 23 has a concave shape between the intersection points 23a relative to the straight line Lx connecting the intersection points 23a of the ridge line 23 in the X direction. For example, when the arrangement pitch of the concave portions 22 in the X direction is represented by Px, the ridge line 23 extending in the X direction has the lowest point 23b at a position Px / 2 (half the pitch) away from the intersection points 23a, and the distance (maximum height difference) from the straight line Lx to the lowest point 23b is dx. In addition, as Figure 7 As shown in FIG. 1 , the ridge line 23 has a concave shape between the intersection points 23a relative to the straight line Ly connecting the intersection points 23a of the ridge line 23 in the Y direction. For example, when the arrangement pitch of the concave portions 22 in the Y direction is represented by Py, the ridge line 23 extending in the Y direction has the lowest point 23b at a position Py / 2 (half the pitch) away from the intersection points 23a, and the distance (maximum height difference) from the straight line Ly to the lowest point 23b is dy.

[0101] When the recessed portions 22 are formed into an inverted quadrangular pyramid, the arrangement pitch Px of the recessed portions 22 in the X direction is equal to the spacing (horizontal distance) between the intersection points 23a in the X direction, and the arrangement pitch Py of the recessed portions 22 in the Y direction is equal to the spacing (horizontal distance) between the intersection points 23a in the Y direction.

[0102] In addition, when the maximum height difference d represents the average value of the maximum height difference dx in the X direction and the maximum height difference dy in the Y direction, the maximum height difference d should be set to be greater than or equal to 1 μm and less than or equal to 10 μm, preferably can be set to be greater than or equal to 1.5 μm and less than or equal to 7 μm, and more preferably can be set to be greater than or equal to 2.5 μm and less than or equal to 5 μm.

[0103] In addition, although the concave shape of the ridge line 23 between the intersection points 23a is not particularly limited, for example, Figure 8 As shown in FIG. 2 , the ridge line 23 may be recessed into an approximately circular arc shape relative to the straight line L connecting the intersection points 23a ( Figure 8 (A) in the figure), the approximate parabolic shape ( Figure 8 (B) in the figure), approximately triangular shape ( Figure 8 (C)) or a trapezoidal shape ( Figure 8 (D) in the.

[0104] As another feature of the first light diffuser 43, when the arrangement pitch of the recessed portions 22 is represented by P, and the size occupied by the curved portion of the vertex of each of these ridge lines 23 in the arrangement direction of the recessed portions 22 is represented by Wr, the ratio Wr / P should be 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less.

[0105] Fig. 9 The first light diffuser 43 is shown along Figure 5 An example of a cross-sectional structure of the line Cx-Dx in FIG. Fig.10 The first light diffuser 43 is shown along Figure 5 An example of a cross-sectional structure of the line Cy-Dy in FIG. Specifically, Fig. 9 The cross-sectional structure is shown when the first light diffuser 43 is cut along a plane that passes through a midpoint between respective centers 22a of the recessed portions 22 adjacent to each other in the X direction and an intersection 23a of the ridge lines 23 between the recessed portions 22 and is perpendicular to the sheet surface. Fig.10 The cross-sectional structure is shown when the first light diffuser 43 is cut along a plane that passes through a midpoint between respective centers 22a of the recessed portions 22 adjacent to each other in the Y direction and an intersection 23a of the ridge lines 23 between the recessed portions 22 and is perpendicular to the sheet surface.

[0106] exist Fig. 9In the cross-sectional structure shown, the interval (horizontal distance) between the corresponding centers 22a of the concave portions 22 adjacent to each other in the X direction is equal to the arrangement pitch Px of the concave portions 22 in the X direction. The size occupied by the curved portion of the vertex of the ridge line 23 in the X direction is represented by Wrx. The size occupied by the straight portion of the corresponding wall surface (inclined surface of the inverted quadrangular pyramid) of the concave portions 22 adjacent to each other across the ridge line 23 in the X direction is represented by Wsx1 and Wsx2. The angle formed between the wall surface (inclined surface of the inverted quadrangular pyramid) of the concave portion 22 in the X direction and the sheet surface is represented by θx. The height from the center 22a of each concave portion 22 to the vertex (midpoint between the intersection points 23a) of each ridge line 23 (ridge line 23 extending in the Y direction) is represented by Hx.

[0107] exist Fig.10 In the cross-sectional structure shown, the interval (horizontal distance) between the corresponding centers 22a of the recessed portions 22 adjacent to each other in the Y direction is equal to the arrangement pitch Py of the recessed portions 22 in the Y direction. The size occupied in the Y direction by the curved portion of the vertex of the ridge line 23 is represented by Wry. The size occupied in the Y direction by the straight portion of the corresponding wall surface (inclined surface of the inverted quadrangular pyramid) of the recessed portions 22 adjacent to each other across the ridge line 23 is represented by Wsy1 and Wsy2. The angle formed between the wall surface (inclined surface of the inverted quadrangular pyramid) of the recessed portion 22 in the Y direction and the sheet surface is represented by θy. The height from the center 22a of each recessed portion 22 to the vertex (midpoint between the intersection points 23a) of each ridge line 23 (ridge line 23 extending in the X direction) is represented by Hy.

[0108] When the recessed portion 22 is formed into an inverted quadrangular pyramid, and the average value of the arrangement pitch Px and the arrangement pitch Py is represented by P, and the average value of the size Wrx and the size Wry is represented by Wr, the ratio Wr / P should be set to 0.3 or less, preferably can be set to 0.2 or less, and more preferably can be set to 0.1 or less.

[0109] Fig.11 The laser microscope shows Figure 6 An example of the results of measuring the shape and size of the X-direction ridgeline is shown in Fig.12 The laser microscope shows Figure 7 An example of the results of measuring the shape and size of the Y-direction ridgeline is shown in Fig.13 The laser microscope shows Fig. 9 Examples of the results of measuring the shape, size and angle of the cross-sectional structure shown in FIG. Fig.14 The laser microscope shows Fig.10 Examples of the results of measuring the shape, size, and angles of the cross-sectional structure shown in FIG.

[0110] exist Fig.11 and Fig.12 In the measurement of the maximum value (maximum height difference) dx and dy of the distance between the straight lines Lx and Ly connecting the intersection point 23a of the ridge line 23 and the ridge line 23, the maximum value of the length of a perpendicular line drawn at right angles from a point on the ridge line 23 to the straight lines Lx and Ly is represented by dx and dy.

[0111] In addition, in the measurement of the arrangement pitches Px and Py, the "horizontal distance between the intersections 23a" in each direction of the X direction and the Y direction is obtained as Px and Py. In this way, even in the method of measuring the "horizontal distance between the intersections 23a", the arrangement pitches Px and Py can be easily and accurately obtained.

[0112] Another feature of the first light diffuser 43 is that, for example, Fig.15 As shown in , the plurality of recessed portions 22 include a recessed portion 22 in which the vertex 22b of an approximately inverted polygonal pyramid (in this example, an approximately inverted quadrangular pyramid) is formed into a linear shape. In other words, the plurality of recessed portions 22 include a recessed portion 22 in which the vertex 22b of an approximately inverted quadrangular pyramid is formed into a point shape and a recessed portion 22 in which the vertex 22b of an approximately inverted quadrangular pyramid is formed into a linear shape. When the vertex 22b of the approximately inverted quadrangular pyramid forms a point shape in the recessed portion 22, the vertex 22b becomes the center 22a of the recessed portion 22. In the first light diffuser 43, the vertices 22b of all the recessed portions 22 may be formed into a linear shape. Note that in Fig.15 In FIG. 1 , the vertex 22 b having a linear shape is shown to be enlarged compared to the actual shape. In addition, Fig.15 (a) shows a vertex 22b extending in a linear shape in the X direction, and Fig.15 (b) in FIG. 1 shows the vertex 22 b extending in a linear shape in the Y direction.

[0113] <Advantageous Effects of Embodiment>

[0114] As described above, the first light diffuser 43 according to the present embodiment includes a plurality of recessed portions 22 formed into approximately inverted polygonal pyramids at least on the first surface 43a. The ridge lines 23 separating the plurality of recessed portions 22 have a recessed shape between the intersection points 23a of the ridge lines 23 relative to the straight line connecting the intersection points 23a. When the arrangement pitch of the plurality of recessed portions 22 is represented by P and the size occupied by the curved portion of the vertex of each of the ridge lines 23 in the arrangement direction of the plurality of recessed portions 22 is represented by Wr, the ratio Wr / P is 0.3 or less. The maximum height difference d between the intersection point 23a connecting the ridge lines 23 and the ridge line 23 is greater than or equal to 1μm and less than or equal to 10μm. The plurality of recessed portions 22 include a recessed portion 22 formed into an approximately inverted polygonal pyramid and having a vertex 22b with a linear shape.

[0115] By the first light diffuser 43 according to the present embodiment, since the first light diffuser 43 includes a plurality of recessed portions 22 formed into approximately inverted polygonal cones at least on the first surface 43a, the brightness uniformity can be improved. In addition, although the ridge line 23 (the opening edge of the recessed portion 22) separating the recessed portions 22 causes wear and damage, the ridge line 23 has a recessed shape between the intersections 23a of the ridge line 23. Therefore, even when the light diffuser is used by stacking with other optical sheets or other light diffusers, wear and damage are unlikely to occur. In addition, the size Wr occupied by the curved portion of the vertex of each of these ridge lines 23 in the arrangement direction of the recessed portions 22 is maintained at 30% or less of the arrangement pitch P of the recessed portions. Therefore, since the vertex of the ridge line 23 can maintain a steep shape, even if the ridge line 23 is recessed between the intersections 23a, the brightness uniformity is not easily reduced. In addition, since the maximum height difference d between the straight line connecting the intersection 23a and the ridge line 23 is set to 1 μm or more, the scratch resistance is improved, and since the maximum height difference d is set to 10 μm or less, the brightness uniformity can be suppressed from decreasing. Moreover, since the vertex 22b of the concave portion 22 (approximately an inverted polygonal cone) is formed in a linear shape, the mass production of the first light diffusion sheet 43 that prevents the brightness uniformity from decreasing can be easily performed.

[0116] In the first light diffuser 43 according to the present embodiment, when the maximum height difference d between the straight line connecting the intersection 23a and the ridge line 23 is greater than or equal to 1.5 μm and less than or equal to 7 μm, the scratch resistance and the brightness uniformity can be further improved. In this case, when the maximum height difference d is greater than or equal to 2.5 μm and less than or equal to 5 μm, the scratch resistance and the brightness uniformity can be even further improved.

[0117] In the first light diffusion sheet 43 according to the present embodiment, when the arrangement pitch of the plurality of recessed portions 22 is represented by P and the size occupied by the curved portion of the vertex of each of the ridge lines 23 in the arrangement direction of the plurality of recessed portions 22 is represented by Wr, the brightness uniformity can be further improved when the ratio Wr / P is 0.2 or less. In this case, the brightness uniformity can be even further improved when the ratio Wr / P is 0.1 or less.

[0118] In the first light diffuser 43 according to the present embodiment, when the arrangement pitch P of the plurality of recessed portions 22 is greater than or equal to 50 μm and less than or equal to 500 μm and the angle formed between the wall surface of the plurality of recessed portions 22 (in other words, the inclined surface of an approximately inverted polygonal cone) and the sheet surface is greater than or equal to 40 degrees and less than or equal to 65 degrees, the brightness uniformity can be improved.

[0119] In the first light diffusion sheet 43 according to the present embodiment, when the ridge line 23 is recessed in an approximately parabola shape, an approximately circular arc shape, an approximately triangular shape, or an approximately trapezoidal shape between the intersections 23 a , scratch resistance may be improved.

[0120] In the first light diffuser 43 according to the present embodiment, a plurality of recessed portions 22 may be formed to approximate inverted quadrangular pyramids. In this case, the ridge line 23 may extend in the X direction (first direction) and the Y direction (second direction). In addition, the maximum height difference d between the straight line connecting the intersection 23a and the ridge line 23 may be the average of the maximum height difference dx between the straight line and the ridge line 23 in the X direction and the maximum height difference dy between the straight line and the ridge line 23 in the Y direction. In addition, the arrangement pitch P of the plurality of recessed portions 22 may be the average of the arrangement pitch Px of the recessed portions 22 in the X direction and the arrangement pitch Py of the recessed portions 22 in the Y direction. Moreover, the dimension Wr occupied by the curved portion of the vertex of each of the ridge lines 23 in the arrangement direction of the recessed portions 22 may be the average of the dimension Wrx occupied by the curved portion of the vertex of each of the ridge lines 23 in the X direction and the dimension Wry occupied by the curved portion of the vertex of each of the ridge lines 23 in the Y direction. Accordingly, a light diffuser having excellent scratch resistance and brightness uniformity may be easily manufactured.

[0121] In the first light diffusion sheet 43 according to the present embodiment, when the plurality of recessed portions 22 are provided only on the first surface 43a and the second surface 43b is a matte surface, luminance uniformity can be further improved while suppressing wear and damage on the second surface 43b.

[0122] In the first light diffusion sheet 43 according to the present embodiment, the ratio of the recessed portion 22 whose vertex 22b is formed in a linear shape may be 10% or more among the plurality of recessed portions 22. Alternatively, the ratio may be 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 100%.

[0123] The backlight unit 40 according to the present embodiment is built in the liquid crystal display device 50 and guides light emitted by the light source 42 toward the display screen 50 a , and includes a first light diffusion sheet 43 according to the present embodiment between the display screen 50 a and the light source 42 .

[0124] Since the backlight unit 40 according to the present embodiment includes the first light diffusion sheet 43 according to the present embodiment, even when a plurality of first light diffusion sheets 43 are stacked or the first light diffusion sheet 43 and other optical sheets are stacked, brightness uniformity can be improved while damage can be suppressed.

[0125] In the backlight unit 40 according to the present embodiment, when the light source 42 is arranged on the reflective sheet 41 which is disposed on the side opposite to the display screen 50a when viewed from the first light diffusion sheet 43, the brightness uniformity is further improved.

[0126] The liquid crystal display device 50 according to the present embodiment includes a liquid crystal display panel 5 and a backlight unit 40 according to the present embodiment.

[0127] Since the liquid crystal display device 50 according to the present embodiment and the information equipment including the liquid crystal display device 50 include the backlight unit 40 according to the present embodiment, the brightness uniformity can be improved and damage can be suppressed even when multiple first light diffusers 43 are stacked or the first light diffuser 43 and other optical sheets are stacked.

[0128] The method for manufacturing a light diffuser according to the present embodiment is a method for manufacturing a first light diffuser 43 according to the present embodiment, wherein the first light diffuser 43 is extruded at a line speed greater than or equal to 10 m / min and less than or equal to 30 m / min and a compressible linear pressure greater than or equal to 100 kgf / cm and less than or equal to 500 kgf / cm.

[0129] By using the method for manufacturing a light diffuser according to the present embodiment, since the dimension Wr occupied by the curved portion of the vertex of the ridge line 23 in the arrangement direction of the recessed portions 22 can be maintained at 30% or less of the arrangement pitch P of the recessed portions 22, a first light diffuser 43 can be manufactured in which the shape of the vertex of the ridge line 23 is steep and has excellent brightness uniformity.

[0130] In addition, by the method for manufacturing a light diffuser according to the present embodiment, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 can be set to be greater than or equal to 1μm and less than or equal to 10μm. In other words, a first light diffuser 43 is obtained in which the ridge line 23 is concave between the intersections 23a and convex at the portion of the intersections 23a. Therefore, even when a plurality of first light diffusers 43 are stacked or the first light diffuser 43 and other optical sheets are stacked, since the ridge line 23 is unlikely to contact with other optical sheets between the intersections 23a, wear and damage are unlikely to occur, and since the ridge line 23 is in point contact with, for example, other optical sheets at the intersections 23a, slippage is generated and the slippage reduces wear and damage. As a result, a first light diffuser 43 having excellent scratch resistance can be manufactured.

[0131] In addition, with the method of manufacturing a light diffusion sheet according to the present embodiment, since extrusion molding is used, the first light diffusion sheet 43 according to the present embodiment can be manufactured at low cost.

[0132] Although in the first light diffuser 43 according to the present embodiment, the vertex 22b of the recessed portion 22 (approximately an inverted polygonal cone) is formed into a linear shape, even when the planar shape of the vertex 22b is formed into a rectangular shape instead of a linear shape, similar advantageous effects as those of the present embodiment can be produced.

[0133] (Example)

[0134] Hereinafter, the first light diffusion sheet 43 according to each example will be described by comparing the example with a comparative example.

[0135] <Measurement of the shape, size and angle of the recessed portion>

[0136] The shape of the recessed portion 22 formed on the first light diffusion sheet 43 according to each example described below was observed using a laser microscope VK-100 manufactured by KEYENCE CORPORATION. Specifically, the following items were measured: the cross-sectional shape ( Figure 6 , Figure 7 , Fig. 9 and Fig.10 The cross-sectional shape shown in ); Figure 6 and Figure 7 The maximum height differences dx and dy (the maximum values ​​of the distances between the straight line connecting the intersection point 23a and the ridge line 23) and their average values ​​d shown in FIG. Fig. 9 and Fig.10 The heights Hx and Hy (the height from the center 22a of the recessed portion 22 to the ridge line 23) and their average value H shown in FIG. Fig. 9 and Fig.10 The dimensions Wrx and Wry (dimensions occupied by the curved portion of the vertex of each of these ridge lines 23 in the X direction and the Y direction) shown in FIG. 2 and their average value Wr; Figure 6 and Figure 7 The arrangement pitches Px and Py (horizontal distances between the intersections 23a in the X and Y directions) of the recessed portions 22 shown in FIG. 1 and their average value P; the ratio Wr / P (unit: %) of the size Wr to the arrangement pitch P; and Fig. 9 and Fig.10 The angles θx and θy shown in FIG. 4 (angles formed in the X direction and the Y direction between the wall surface (the inclined surface of the inverted quadrangular pyramid) of the recessed portion 22 and the sheet surface of the first light diffusion sheet 43 ).

[0137] <Measurement of optical properties>

[0138] As the optical characteristics of the first light diffuser 43 according to each example described below, the haze and the transmittance of the wavelength of 450nm were measured. The haze was measured by making light incident on the surface (first surface 43a) having the recessed portion 22 formed as an inverted quadrangular pyramid using HZ-2 manufactured by Suga Test Instruments Co., Ltd. of Japan. In addition, the transmittance of the wavelength of 450nm was measured by making light incident on the surface (first surface 43a) having the recessed portion 22 formed as an inverted quadrangular pyramid using V-670 manufactured by JASCO Corporation.

[0139] <Evaluation of Scratch Resistance>

[0140] Fig.16 The equipment shown is used for the scratch resistance test of the first light diffusion sheet 43 of each example described later. Fig.16 As shown in, by using the lower surface of the first light diffuser 43 as a fixed sample as the first surface 43a (the surface on which the concave portion 22 having an inverted quadrangular pyramid shape is formed) and using the upper surface of the first light diffuser 43 as a moving sample as the second surface 43b (matte surface), the moving sample and the fixed sample are stacked on a glass plate in sequence, a weight with a load of 516 gf is placed from above on a circular area with a diameter of 20 mm, the moving sample is taken out at a take-out speed of 10 mm / sec, the moving sample is moved 100 mm, and the degree of scratches on the friction surfaces of the moving sample and the fixed sample are visually inspected and determined. The inspection and determination are performed on the lower surface of the fixed sample (the formation surface of the concave portion 22 of the inverted quadrangular pyramid) and the upper surface of the moving sample (matte surface).

[0141] The evaluation in the inspection and determination is based on the following criteria.

[0142] AA: The light diffuser is extremely scratch resistant, with absolutely no visible scratches.

[0143] A: The light diffuser has high scratch resistance and there are almost no noticeable scratches.

[0144] B: The scratch resistance of the light diffuser is slightly high, and the number of noticeable scratches is extremely small.

[0145] C: The scratch resistance of the light diffuser is close to the acceptable lower limit, with some noticeable scratches.

[0146] X: The light diffuser has poor scratch resistance and has a large number of obvious scratches.

[0147] <Measurement of brightness and brightness uniformity>

[0148] use Figure 2 and Figure 3 The configuration of the backlight unit 40 shown in , the brightness and brightness uniformity of the first light diffuser 43 according to each example described below were measured. In other words, two sheets of the first light diffuser 43 having the recessed portion 22 in the shape of an inverted quadrangular pyramid obtained in the example to be described below were stacked and arranged on the small light sources 42 (LED array) arranged in an array so that the first surface 43a on which the recessed portion 22 was formed faced the light source 42 side. A sheet of the second light diffuser 44 with a thickness of 120 μm was stacked and arranged on the stack of the first light diffuser 43 so that the second surface 44b as a mirror surface faced the light source 42 side. The same diffusing agent of the same composition as in Example 18 to be described later was used and mixed with the same aromatic polycarbonate resin. When manufacturing the second light diffuser 44, a mirror surface roller was used as one roller and a roller having the same random matte shape (surface roughness Ra=2.5 μm) on its surface as in Example 1 was used as another roller, and the second light diffuser 44 was produced by the same method as in Example 1 to be described later. In the second light diffuser 44, the surface roughness Ra of the matte surface (first surface 44a) side is 1.6μm, and the surface roughness Ra of the mirror surface (second surface 44b) side is 0.4μm. Two prism sheets 45 and 46 are stacked and arranged on the second light diffuser 44. The brightness and brightness uniformity are measured using the above configuration. An array with an LED pitch of 3mm is used as the LED array, and a blue LED (part number XPGDRY-L1-0000-00501) manufactured by CreeLED is used as the LED (small light source 42).

[0149] In the measurement of brightness uniformity, first, Figure 3 In the LED array (6×6) shown in FIG, the cross-sectional brightness is obtained along the diagonal line L passing directly above the LED (small light source 42), and secondly, the average value and standard deviation of the cross-sectional brightness are calculated, and thirdly, the brightness uniformity is obtained according to the calculation formula expressed as brightness uniformity = (average value of cross-sectional brightness) / (standard deviation of cross-sectional brightness). The brightness uniformity obtained in this way shows that the higher the value of the brightness uniformity, the more uniform the brightness.

[0150] The evaluation criteria for brightness uniformity are as follows.

[0151] AA: The luminance uniformity of the light diffusion sheet is 210 or more, and exhibits the highest uniformity at a level with absolutely no noticeable luminance unevenness.

[0152] A: The luminance uniformity of the light diffusion sheet is 200 or more and less than 210, and exhibits high uniformity at a level at which bright spots are hardly seen.

[0153] B: The luminance uniformity of the light diffusion sheet was 190 or more and less than 200, and exhibited an acceptable level of uniformity with an extremely small amount of noticeable bright spots.

[0154] C: The luminance uniformity of the light diffuser is 180 or more and less than 190, and exhibits the minimum acceptable level of uniformity with noticeable bright spots.

[0155] X: The brightness uniformity of the light diffuser is less than 180, and exhibits poor uniformity with clear and obvious bright spots.

[0156] In addition, the evaluation criteria of brightness are as follows.

[0157] A: The average cross-sectional brightness of the light diffuser is 3150cd / m 2 or above.

[0158] B: The average cross-sectional brightness of the light diffuser is 3100 cd / m 2 or above and below 3150cd / m 2 .

[0159] C: The average cross-sectional brightness of the light diffuser is 3050 cd / m 2 Or above and below 3100cd / m 2 .

[0160] <Overall Assessment>

[0161] Based on the results of the scratch resistance test and the evaluation results of the luminance uniformity, the first light diffusion sheet 43 according to each example to be described later was generally evaluated according to the following criteria.

[0162] AA: The light diffuser is the best overall, scoring A or more in all the evaluation results of the scratch resistance test and the evaluation results of the brightness uniformity test for both the inverted quadrangular pyramid surface and the matte surface, and scoring two or more AA.

[0163] A: The light diffuser is the best overall (excluding items evaluated as AA), scoring A or above in all the evaluation results of the scratch resistance test of both the inverted quadrangular pyramid surface and the matte surface and the evaluation results of the brightness uniformity.

[0164] B: The overall light diffusion sheet is high (excluding items evaluated as AA and evaluated as A), scoring B or above in all the evaluation results of the scratch resistance test of both the inverted quadrangular pyramid surface and the matte surface and the evaluation results of the brightness uniformity.

[0165] C: The light diffuser is usable (excluding items evaluated as AA, evaluated as A, and evaluated as B), has the lowest overall acceptable performance level, and scores C or above in all the evaluation results of the scratch resistance test of both the inverted quadrangular pyramid surface and the matte surface and the evaluation results of brightness uniformity.

[0166] X: The overall light diffusion sheet is poor, and is evaluated as X in any one of the evaluation results of the scratch resistance test and the evaluation results of the brightness uniformity of both the inverted quadrangular pyramid surface and the matte surface.

[0167] <Example 1>

[0168] The method of manufacturing the first light diffusion sheet 43 according to Example 1 is as follows. First, an aromatic polycarbonate resin having a melt mass flow rate of 15 g / 10 min measured according to ISO 1133 is fed into an extruder, melted and kneaded, and extruded through a T-die. Fig.17 A roller having the shape shown in (A) and (B) ((B) is a shape diagram showing a view from the direction of a cross section taken along line XY in (A)) (a shape of a regular tetrahedron with a height of 50 μm, a pitch of 100 μm, and a vertex angle of 90 degrees) is used as one of the two metal rollers, and a roller having a random matte shape on the surface (surface roughness Ra=2.5 μm) is used as the other roller, and the molten resin extruded by a T-die is sandwiched between the two rollers and cooled while the shape transfer is being performed. Accordingly, as shown in Table 1, a 180 μm thick single-layer light diffuser is produced by extrusion molding, the light diffuser having a recessed (inverted) pyramid shape on one surface whose depth depends on the height of the regular tetrahedron on the roller and a matte surface with a surface roughness Ra=1.67 μm on the other surface. As shown in Table 1, a light diffuser sheet was obtained under molding conditions including applying pressure until the line speed was set to 17 m / min, the compressive force between the two rollers (compressible linear pressure) was set to 280 kgf / cm, and under resin temperature conditions (230°C to 310°C) that enable the shape to be favorably transferred to the polycarbonate resin and the sheet to be favorably separated from the rollers.

[0169] [Table 1]

[0170]

[0171]

[0172] The shape of the recessed portion (inverted quadrangular pyramid) 22 formed on the first light diffusion sheet 43 according to Example 1 manufactured as described above was observed using a laser microscope VK-100 manufactured by KEYENCE Corporation of Japan. Specifically, the following items were measured: the cross-sectional shape ( Figure 6 , Figure 7 , Fig. 9 and Fig.10 The cross-sectional shape shown in ); Figure 6 and Figure 7 The maximum height differences dx and dy (the maximum values ​​of the distances between the straight line connecting the intersection point 23a and the ridge line 23) and their average values ​​d shown in FIG. Fig. 9 and Fig.10 The heights Hx and Hy (the height from the center 22a of the recessed portion 22 to the ridge line 23) and their average value H shown in FIG. Fig. 9 and Fig.10 The dimensions Wrx and Wry (dimensions occupied by the curved portion of the vertex of each of these ridge lines 23 in the X direction and the Y direction) shown in FIG. 2 and their average value Wr; Figure 6 and Figure 7 The arrangement pitches Px and Py (horizontal distances between the intersections 23a in the X and Y directions) of the recessed portions 22 shown in FIG. 1 and their average value P; the ratio Wr / P (unit: %) of the size Wr to the arrangement pitch P; and Fig. 9 and Fig.10 The angles θx and θy shown in FIG. 4 (angles formed in the X direction and the Y direction between the wall surface (the inclined surface of the inverted quadrangular pyramid) of the recessed portion 22 and the sheet surface of the first light diffusion sheet 43 ).

[0173] <Examples 2 and 3>

[0174] In the method of manufacturing the first light diffuser 43 according to Example 2, as shown in Table 1, the same conditions as in Example 1 are used, except that a roller having a regular tetrahedral pyramid shape with a height of 54.6 μm, a pitch of 100 μm and a vertex angle of 85 degrees on the surface is used as the roller having a regular tetrahedral pyramid shape among the two metal rollers.

[0175] In the method of manufacturing the first light diffuser 43 according to Example 3, as shown in Table 1, the same conditions as in Example 1 are used, except that a roller having a regular tetrahedral pyramid shape with a height of 59.6 μm, a pitch of 100 μm and a vertex angle of 80 degrees on the surface is used as the roller having a regular tetrahedral pyramid shape among the two metal rollers.

[0176] <Comparative Examples 1 to 3>

[0177] In Comparative Example 1, first, a pressed original plate having a thickness of 1 mm was produced using the same aromatic polycarbonate resin as in Example 1. Next, a pressed original plate having a thickness of 1 mm was produced using Fig.18 A flat metal mold having the shape shown in (A) and (B) ((B) is a shape diagram showing a view from the cross-sectional direction taken along the line XY in (A)) (a shape produced by rounding the valley portion of a pyramid having the same regular quadrangular pyramid shape as in Example 1 into a curved surface shape having a curvature radius of 4.2 μm), and a flat metal mold having the same random matte shape (surface roughness Ra=2.5 μm) as in Example 1 on the surface, a pressed original plate is sandwiched between these two metal molds, placed in a press having a heating and cooling device, and subjected to a pressure including a press plate temperature of 250°C and a pressure of 200 kg / cm 2 The platen was then pressed for 20 minutes under a surface pressure of . Subsequently, the platen temperature was cooled to 20° C. while maintaining the pressure, and the resin plate was kept under pressure until sufficiently cooled, thereby producing a 180 μm thick light diffuser sheet as shown in Table 1 by compression molding.

[0178] In Comparative Example 2, after producing a pressed original plate in a manner similar to Comparative Example 1, a 180 μm thick light diffuser shown in Table 1 was produced by a compression molding method by heating, pressing and cooling under the same conditions as in Comparative Example 1, except that a flat metal mold having a shape on the surface produced by rounding the valley portion of a pyramid in the same regular tetrahedral shape as Example 2 into a curved surface shape with a curvature radius of 4.2 μm was used (in a manner similar to Comparative Example 1).

[0179] In Comparative Example 3, after producing a pressed original plate in a manner similar to Comparative Examples 1 and 2, a 180 μm thick light diffuser shown in Table 1 was produced by a compression molding method by heating, pressing and cooling under the same conditions as in Comparative Example 1, except that a flat metal mold having a shape on the surface produced by rounding the valley portion of a pyramid in the same regular tetrahedral shape as Example 3 into a curved surface shape with a curvature radius of 4.2 μm (in a manner similar to Comparative Examples 1 and 2) was used.

[0180] <Evaluation of Examples 1 to 3 and Comparative Examples 1 to 3>

[0181] Regarding the first light diffuser 43 obtained by Examples 1 to 3, the shape, size, angle, etc. of each element obtained by measurement are shown in Table 2 together with Comparative Examples 1 to 3, and the measurement results of optical properties, the results of scratch resistance tests, the evaluation results of brightness and brightness uniformity, and the overall evaluation results are shown in Table 3 together with Comparative Examples 1 to 3.

[0182] [Table 2]

[0183]

[0184]

[0185] [Table 3]

[0186]

[0187] According to the results shown in Tables 2 and 3, in the first light diffusion sheet 43 on which the concave portion 22 having an inverted quadrangular pyramid shape was formed obtained in Examples 1 to 3, the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 was 1.0 μm or more, and the ridge line 23 had a shape that was concave in a substantially parabolic shape between the intersection points 23a. Therefore, since abrasion and damage caused by the ridge line 23 are unlikely to occur even when used in a stacked manner, the scratch resistance test produced a good result.

[0188] On the other hand, in Comparative Examples 1 to 3, although a curved surface shape with a curvature radius of about 4.2 μm was imparted near the apex of the ridge line 23, the maximum height difference d was 0 μm, the ridge line 23 did not have any depression, and the ridge line 23 between the intersections 23a had a horizontal shape. Therefore, the result in terms of scratch resistance was poor due to damage caused by the ridge line 23 that occurred during the scratch resistance test.

[0189] Furthermore, in all of Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, the ratio Wr / P was 10% or less, and since the steep shape of the vertex of the ridge line 23 was maintained, good evaluation results comparable to each other were produced in terms of brightness uniformity.

[0190] As can be seen from the above, the overall evaluation of Examples 1 to 3 is "C", while the overall evaluation of Comparative Examples 1 to 3 is "X".

[0191] <Examples 4 to 10 and Comparative Example 4>

[0192] In Examples 4 to 7, as shown in Table 4, light diffusion sheets were manufactured by the same method as in Example 1, except that the line speed in the molding conditions was changed to 15 m / min to 4 m / min.

[0193] In Examples 8 to 10 and Comparative Example 4, as shown in Table 4, light diffusion sheets were manufactured by the same method as Example 1, except that the compressible linear pressure between two rollers in the molding conditions was changed to range from 180 kgf / cm to 40 kgf / cm.

[0194] [Table 4]

[0195] <Evaluation of Examples 4 to 10 and Comparative Example 4>

[0196] Regarding the first light diffuser 43 obtained by Examples 4 to 10, the shape, size, angle, etc. of each element obtained by measurement are shown in Table 5 together with Comparative Example 4, and the measurement results of optical properties, the results of the scratch resistance test, the evaluation results of brightness and brightness uniformity, and the overall evaluation results are shown in Table 6 together with Comparative Example 4.

[0197] [Table 5]

[0198]

[0199]

[0200] [Table 6]

[0201]

[0202] According to the results shown in Tables 5 and 6, in the first light diffusion sheet 43 on which the concave portion 22 having an inverted quadrangular pyramid shape was formed, obtained in Examples 4 to 10 and Comparative Example 4, the maximum height difference d between the straight line connecting the intersections 23a and the ridge line 23 was 1.0 μm or more, and the ridge line 23 had a shape that was concave in a substantially parabolic shape between the intersections 23a. Therefore, since abrasion and damage caused by the ridge line 23 are unlikely to occur even when used in a stacked manner, the scratch resistance test produced a good result.

[0203] Furthermore, in Examples 4 to 10, the ratio Wr / P was 30% or less in all the examples, and since the steep shape of the apex of the ridge line 23 was maintained, good evaluation results comparable to each other were produced in terms of luminance uniformity.

[0204] However, in Comparative Example 4, since the ratio Wr / P exceeded 30%, the steep shape of the vertex of the ridge line 23 was not maintained, and poor results were produced in terms of luminance uniformity.

[0205] As can be seen from the above, the overall evaluation of Examples 4 to 10 is "C", while the overall evaluation of Comparative Example 4 is "X".

[0206] <Examples 11 to 14>

[0207] In the method of manufacturing the first light diffuser 43 according to Example 11, the 200 μm thick light diffuser shown in Table 7 is manufactured using conditions almost the same as those in Example 1, except that a roller having a regular tetrahedral pyramid shape with a height of 90.0 μm, a pitch of 180 μm and a vertex angle of 90 degrees on the surface is used as the roller having a regular tetrahedral pyramid shape among the two metal rollers.

[0208] [Table 7]

[0209]

[0210] In the method of manufacturing the first light diffuser 43 according to Example 12, the 200 μm thick light diffuser shown in Table 7 is manufactured using conditions almost the same as those in Example 1, except that a roller having a regular tetrahedral pyramid shape with a height of 98.2 μm, a pitch of 180 μm and a vertex angle of 85 degrees on the surface is used as the roller having a regular tetrahedral pyramid shape among the two metal rollers.

[0211] In the method of manufacturing the first light diffuser 43 according to Example 13, the 200 μm thick light diffuser shown in Table 7 is manufactured using conditions almost the same as those in Example 1, except that a roller having a regular tetrahedral pyramid shape with a height of 107.3 μm, a pitch of 180 μm and a vertex angle of 80 degrees on the surface is used as the roller having a regular tetrahedral pyramid shape among the two metal rollers.

[0212] In the method of manufacturing the first light diffuser 43 according to Example 14, the 200 μm thick light diffuser shown in Table 7 is manufactured using conditions almost the same as those in Example 1, except that a roller having a regular tetrahedral pyramid shape with a height of 117.3 μm, a pitch of 180 μm and a vertex angle of 75 degrees on the surface is used as the roller having a regular tetrahedral pyramid shape among the two metal rollers.

[0213] <Examples 15 to 17 and Comparative Example 5>

[0214] In Examples 15 to 17, a 200 μm thick light diffusion sheet was manufactured using the same roller as in Example 13 but by changing the line speed in the molding conditions to 15 m / min to 11 m / min as shown in Table 7.

[0215] In Comparative Example 5, after producing a pressed original plate in a manner similar to Comparative Example 1, a 200 μm thick light diffuser shown in Table 7 is produced by a compression molding method by heating, pressing and cooling under the same conditions as in Comparative Example 1, except that a flat metal mold is used having a shape on its surface produced by rounding the valley portion of the pyramid into a curved surface shape with a curvature radius of 4.2 μm in a regular tetrahedron having the same shape as Example 11 (in a manner similar to Comparative Example 1).

[0216] <Evaluation of Examples 11 to 17 and Comparative Example 5>

[0217] Regarding the first light diffuser 43 obtained by Examples 11 to 17, the shape, size, angle, etc. of each element obtained by measurement are shown in Table 8 together with Comparative Example 5, and the measurement results of optical properties, the results of the scratch resistance test, the evaluation results of brightness and brightness uniformity, and the overall evaluation results are shown in Table 9 together with Comparative Example 5.

[0218] [Table 8]

[0219]

[0220] [Table 9]

[0221]

[0222] According to the results shown in Tables 8 and 9, in the first light diffusion sheet 43 on which the concave portion 22 having an inverted quadrangular pyramid shape was formed obtained in Examples 11 to 17, the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 was 2.5 μm or more, and the ridge line 23 had a shape that was concave in a substantially parabolic shape between the intersection points 23a. Therefore, since wear and damage caused by the ridge line 23 are less likely to occur even when used in a stacked manner, the scratch resistance test produced the most favorable results in each example.

[0223] On the other hand, in Comparative Example 5, although a curved surface shape is imparted near the apex of the ridge line 23, the maximum height difference d is 0 μm, the ridge line 23 does not have any depression, and the ridge line 23 between the intersections 23a has a horizontal shape. Therefore, due to damage caused by the ridge line 23 that occurred during the scratch resistance test, the result in terms of scratch resistance was poor.

[0224] Furthermore, in Examples 11 to 17 and Comparative Example 5, in all the Examples and Comparative Example, the ratio Wr / P was 10% or less, and since the steeper shape of the apex of the ridge line 23 was maintained, particularly good evaluation results were produced in terms of luminance uniformity. In particular, in Examples 11 to 17, since the maximum height difference d was 5.0 μm or less, a decrease in luminance uniformity due to the ridge line 23 having a concave shape between the intersections 23 a was not observed.

[0225] As can be seen from the above, the overall evaluation of Example 11 is "A", the overall evaluations of Examples 12 to 17 are "AA" indicating the highest score, and the overall evaluation of Comparative Example 5 is "X".

[0226] <Examples 18 to 23>

[0227] In Example 18, the 180 μm thick light diffuser shown in Table 10 is manufactured using the same conditions as in Example 1, except that a pre-prepared mixture (1 part by mass of a silicone composite powder (average particle size of 2.0 μm) as a diffuser for every 99 parts by mass of aromatic polycarbonate resin used in Example 1) is fed into an extruder and melted and kneaded.

[0228] [Table 10]

[0229] In Examples 19 to 23, a 180 μm thick light diffusion sheet was manufactured using the same method as in Example 18 except that the line speed in the molding conditions was changed to 15 m / min to 9 m / min (as shown in Table 10).

[0230] <Evaluation of Examples 18 to 23>

[0231] Regarding the first light diffuser 43 obtained by Examples 18 to 23, the shape, size, angle, etc. of each element obtained by measurement are shown in Table 11, and the measurement results of optical properties, the results of scratch resistance test, the evaluation results of brightness and brightness uniformity, and the overall evaluation results are shown in Table 12.

[0232] [Table 11]

[0233]

[0234] [Table 12]

[0235]

[0236] According to the results shown in Tables 11 and 12, in the first light diffusion sheet 43 on which the concave portion 22 having an inverted quadrangular pyramid shape was formed obtained in Examples 18 to 23, the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 was 1.6 μm or more, and the ridge line 23 had a shape that was concave in a substantially parabolic shape between the intersection points 23a. Therefore, since abrasion and damage caused by the ridge line 23 are unlikely to occur even when used in a stacked manner, the scratch resistance test produced a good result.

[0237] Furthermore, in Examples 18 to 23, the ratio Wr / P was within the range of 6% to 13%, and since the steep shape of the apex of the ridge line 23 was maintained, good evaluation results were produced in terms of luminance uniformity.

[0238] From the above, it can be seen that the overall evaluation of Examples 18 to 23 is "C".

[0239] <Examples 24 to 27>

[0240] In Example 24, using the aromatic polycarbonate resin used in Example 1 and the molding conditions shown in Table 13, a Fig.17 A roller having the shape shown in (A) and (B) (a regular tetrahedral pyramid shape with a height of 50 μm, a pitch of 100 μm and a vertex angle of 90 degrees) is used as one of the two metal rollers, and a roller having a random matte shape on the surface (surface roughness Ra = 1.6 μm) is used as the other roller to manufacture the 120 μm thick light diffuser shown in Table 13.

[0241] [Table 13]

[0242] In Example 25, the same diffusing agent-containing aromatic polycarbonate resin as in Example 18, the molding conditions shown in Table 13, and the same two metal rolls as in Example 24 were used to manufacture a 120 μm-thick light diffusing sheet shown in Table 13.

[0243] In Example 26, the same aromatic polycarbonate resin as in Example 24 and the molding conditions shown in Table 13 are used, and the roller having a regular tetrahedral pyramid shape with a height of 107.3 μm, a pitch of 180 μm and a vertex angle of 80 degrees on the surface used in Example 13 is used as one of the two metal rollers, and a roller having a random matte shape (surface roughness Ra = 2.0 μm) on the surface is used as the other roller to manufacture a 200 μm thick light diffuser shown in Table 13.

[0244] In Example 27, the same aromatic polycarbonate resin containing a diffusant as in Example 25, the molding conditions shown in Table 13, the same roller having a regular tetrahedral pyramid shape on the surface as in Examples 24 and 25 is used as one of the two metal rollers, and a roller having a random matte shape (surface roughness Ra = 2.0 μm) on the surface is used as the other roller to manufacture a 200 μm thick light diffuser shown in Table 13.

[0245] <Evaluation of Examples 24 to 27>

[0246] Regarding the first light diffusion sheet 43 obtained from Examples 24 to 27, the shape, size, angle, etc. of each element obtained by measurement are shown in Table 14, and the measurement results of optical characteristics, the results of the scratch resistance test, the evaluation results of brightness and brightness uniformity, and the overall evaluation results are shown in Table 15. In addition, Fig.19 Surface photographs of the samples after the scratch resistance test in each of Examples 24 to 27 and Comparative Example 1, or more specifically, surface photographs of the lower surface (inverted quadrangular pyramid surface) of the fixed sample and the upper surface (matte surface) of the moving sample are shown in FIG.

[0247] [Table 14]

[0248]

[0249] [Table 15]

[0250]

[0251] According to the results shown in Table 14 and Table 15, in the first light diffusion sheet 43 on which the concave portion 22 having an inverted quadrangular pyramid shape was formed obtained in Examples 24 to 27, the maximum height difference d between the straight line connecting the intersection points 23a and the ridge line 23 was 2.7 μm or more, and the ridge line 23 had a shape that was concave in a substantially parabolic shape between the intersection points 23a. Therefore, since even if Fig.19 When the stack shown is used, wear and damage due to the ridges 23 are also unlikely to occur, so the scratch resistance test produces good results not only for the matte surface (upper surface of the moving sample) but also for the inverted quadrangular pyramid surface (lower surface of the fixed sample). Fig.19 As shown in, in Comparative Example 1, as described above (see Table 2, etc.), since the maximum height difference d is 0 μm, the ridge line 23 has absolutely no depression, and the ridge line 23 has a horizontal shape between the intersection points 23a, during the scratch resistance test on the inverted quadrangular pyramid surface (the lower surface of the fixed sample), damage due to the ridge line 23 obviously occurred, resulting in poor scratch resistance.

[0252] Note that in Examples 24 and 25, a relatively large depression appears in the ridge line 23 due to the relatively thin thickness of the first light diffuser 43, while in Example 26, a relatively large depression appears in the ridge line 23 due to the relatively large inverted quadrangular pyramid of the recessed portion 22.

[0253] Furthermore, in Examples 24 to 27, the ratio Wr / P was in the range of about 5% to 11%, and since the steep shape of the apex of the ridge line 23 was maintained, good evaluation results were produced in terms of luminance uniformity.

[0254] As can be seen from the above, the overall evaluation of Example 24 is "A", the overall evaluations of Examples 25 and 27 are "C", and the overall evaluation of Example 26 is "AA", indicating the highest score.

[0255] <Shape evaluation of the apex of an inverted quadrangular pyramid (concave portion)>

[0256] Table 16 shows the results of examining the shape of the apex of each inverted quadrangular pyramid with respect to five samples S1 to S5 different in the inverted quadrangular pyramid shape of the recessed portion 22 in the first light diffusion sheet 43 according to the above-described example.

[0257] [Table 16]

[0258]

[0259] As shown in Table 16, in each of the samples S1 to S5, it was found that 50% or more of the vertices of the inverted quadrangular pyramids were formed into linear shapes in both the X direction and the Y direction (see Fig.15 In other words, it was found that in the first light diffusion sheet 43 according to each example, the plurality of recessed portions 22 included recessed portions 22 whose apexes of inverted quadrangular pyramids were formed in dot shapes and recessed portions 22 whose apexes of inverted quadrangular pyramids were formed in linear shapes.

[0260] <Occurrence rate of linear vertices of inverted quadrangular pyramids (concave parts)>

[0261] Using three pyramidal rollers (rollers having a regular quadrangular pyramid shape on the surface) having the same design dimensions, Fig.21 The method shown in checks the ratio of the vertices of the inverted quadrangular pyramids formed in a linear shape in the plurality of recessed portions 22 provided on the first light diffuser 43 (the occurrence rate of the linear vertices). Specifically, a pyramid roller is used in which regular quadrangular pyramids (pyramid shapes) with a height of 50 μm and a vertex angle of 90 degrees are two-dimensionally arranged at a pitch of 100 μm on its surface. A roller having a random matte shape (surface roughness Ra = 2.5 μm) on the surface is used as another roller. In addition, as Fig.21 As shown in, 15 (5 (MD direction or roller rotation direction) × 3 (TD direction or width direction)) flat plate size (length in MD direction: 267 mm, length in TD direction: 200 mm) samples of the first light diffuser 43 are taken out from the base sheet corresponding to one cycle of the pyramid roller, and numbers (1A to 5A, 1B to 5B, and 1C to 5C) are assigned to the respective samples. In addition, each sample is divided into 20 (5 (MD direction) × 4 (TD direction)) areas of approximately 50 mm × 50 mm in size, and with respect to each area, the shapes of the vertices of any six adjacent recessed portions 22 are checked.

[0262] Tables 17 to 19 show the results of examining the occurrence rate of linear vertices with respect to 15 samples respectively manufactured using three pyramidal rollers (hereinafter also referred to as the first roller to the third roller). In addition, Tables 20 to 21 show the results of examining the occurrence rate with respect to samples manufactured using the first roller and the third roller by classifying the linear vertices into linear vertices having a size of 1.0 μm or less and linear vertices having a size greater than 1.0 μm.

[0263] The size of the vertex (bottom portion of the recessed portion 22) of the inverted quadrangular pyramid was measured using a shape measuring laser microscope VK-X110 in the 3D laser scanning confocal microscope VK-X series manufactured by KEYENCE Corporation of Japan (and an analysis application version 3.6.1.0 manufactured by the same manufacturer as the analysis software). Specifically, the size of the vertex (bottom portion of the recessed portion 22) of the inverted quadrangular pyramid was measured with respect to each of the X direction and the Y direction (see Fig.15 ), the shape profile of the cross section passing through the vertex of the inverted quadrangular pyramid (the bottom part of the concave portion 22) and being orthogonal to the ridge line 23 of the concave portion 22 is measured, and the size of the vertex is determined from the obtained shape profile. In addition, when one of the X-direction dimension and the Y-direction dimension of the vertex of the inverted quadrangular pyramid is 0.1 μm or more and the other is less than 0.1 μm, the vertex is determined to be a linear vertex, and the longer dimension is adopted as the size of the linear vertex. On the other hand, when both the X-direction dimension and the Y-direction dimension are less than 0.1 μm, the vertex is determined to be a point-like vertex even if the X-direction dimension and the Y-direction dimension are different from each other.

[0264] [Table 17]

[0265] [Table 18]

[0266] [Table 19]

[0267] [Table 20]

[0268] Point shape 1.0μm or less More than 1.0μm 1-A 0.0％ 0.0％ 100.0％ 2-A 0.0％ 4.2％ 95.8％ 3-A 7.5％ 27.5％ 65.0％ 4-A 33.3％ 42.5％ 24.2％ 5-A 25.8％ 24.2％ 50.0％ 1-B 0.0％ 3.3％ 96.7％ 2-B 41.7％ 30.8％ 27.5％ 3-B 70.8％ 22.5％ 6.7％ 4-B 35.0％ 44.2％ 20.8％ 5-B 39.2％ 40.0％ 20.8％ 1-C 5.0％ 10.0％ 85.0％ 2-C 87.5％ 11.7％ 0.8％ 3-C 57.5％ 35.0％ 7.5％ 4-C 11.7％ 38.3％ 50.0％ 5-C 47.5％ 33.3％ 19.2％

[0269] [Table 21]

[0270] Point shape 1.0μm or less More than 1.0μm 1-A 5.0％ 52.5％ 42.5％ 2-A 80.8％ 19.2％ 0.0％ 3-A 45.0％ 45.8％ 9.2％ 4-A 40.8％ 44.2％ 15.0％ 5-A 5.0％ 36.7％ 58.3％ 1-B 33.3％ 55.0％ 11.7％ 2-B 65.0％ 32.5％ 2.5％ 3-B 76.7％ 19.2％ 4.2％ 4-B 80.0％ 18.3％ 1.7％ 5-B 40.0％ 38.3％ 21.7％ 1-C 65.8％ 29.2％ 5.0％ 2-C 6.7％ 64.2％ 29.2％ 3-C 27.5％ 55.8％ 16.7％ 4-C 26.7％ 46.7％ 26.7％ 5-C 69.2％ 30.0％ 0.8％

[0271] As shown in Tables 17 to 19, no matter which pyramidal roller was used, the ratio of the recessed portions 22 in which the apex 22b was formed in a linear shape among the plurality of recessed portions 22, or in other words, the occurrence rate of the linear apex was 10% or more.

[0272] Specifically, when the first roller was used, as shown in Table 17, the occurrence rate of linear vertices was 20% or more in all samples except one, the occurrence rate of linear vertices was 40% or more in many samples, the occurrence rate of linear vertices was 60% or more in most samples, and the occurrence rate of linear vertices was 80% or more in almost half of the samples. In addition, when the first roller was used, as shown in Table 20, the occurrence rate of linear vertices having a size greater than 1.0 μm was 50% or more in almost half of the samples.

[0273] When the second roller was used, as shown in Table 18, the occurrence rate of linear apexes was 70% or more in all samples, 90% or more in all samples except one sample, and 100% in most samples.

[0274] When the third roller was used, the occurrence rate of linear vertices was 30% or more in many samples, and the occurrence rate of linear vertices was 50% or more in most samples, as shown in Table 19. In addition, when the third roller was used, as shown in Table 21, in one sample, the occurrence rate of linear vertices having a size greater than 1.0 μm was 50% or more.

[0275] According to the above results, it was found that when the apex 22 b of the concave portion 22 was formed in a linear shape, mass production of the first light diffusion sheet 43 that prevents a decrease in luminance uniformity can be easily performed.

[0276] Note that the vertex 22b of the recessed portion 22 may be formed in a rectangular shape instead of a linear shape. Specifically, "the vertex 22b of the recessed portion 22 is a rectangular shape" means that the X-direction dimension and the Y-direction dimension of the vertex of the inverted quadrangular pyramid are different from each other, and both dimensions are 0.1 μm or more. In this case, the size difference between the X-direction dimension and the Y-direction dimension may be 10% or more of the longer dimension. Alternatively, the size difference may be 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more of the longer dimension. In addition, from the perspective of suppressing the decrease in uniformity, the longer dimension of the X-direction dimension and the Y-direction dimension is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less.

[0277] (Other embodiments)

[0278] Although the embodiments of the present disclosure have been described above (including examples: the same applies below), the present disclosure is not limited to the above-described embodiments, and various modifications can be made within the scope of the present disclosure. In other words, the foregoing description of the embodiments is illustrative in nature and is not intended to limit the present disclosure, its application or its use. For example, it goes without saying that the configuration (layer structure, material, etc.) of the light diffuser is not limited to the configuration of the first light diffuser 43 according to the above-described embodiment. In addition, it goes without saying that the configuration of the backlight device to which the light diffuser is applied and the configuration of the liquid crystal display device including the backlight device are also not limited to the configuration of the backlight unit 40 and the liquid crystal display device 50 according to the above-described embodiment.

[0279] For example, in the above-mentioned embodiments and Figure 2In the backlight unit 40 shown in FIG. 1 , instead of the stacked combination of two sheets of the first light diffusion sheet 43 and the second light diffusion sheet 44, a Fig. 20 In the modification shown in FIG. 4 , three first light diffusers 43 are used as a stack, or four or more first light diffusers 43 may be stacked. When three or more first light diffusers 43 are stacked, from the perspective of the trade-off between the reflection and refraction effect of the approximately inverted polygonal pyramid shape and the light diffusion effect of the diffuser, the light diffuser 43 (in other words, the first prism sheet 45) closest to the display screen 50a may contain a diffuser, while the other light diffusers 43 basically do not need to contain a diffuser. Accordingly, the brightness uniformity can be even further improved.

[0280] List of Reference Numerals

[0281] 1 TFT substrate

[0282] 2 CF substrate

[0283] 3 Liquid crystal layer

[0284] 5 LCD panel

[0285] 6. First polarizing plate

[0286] 7 Second polarizing plate

[0287] 21. Base material layer

[0288] 22 Depression

[0289] 22a Center

[0290] 22b Vertex

[0291] 23 Ridgeline

[0292] 23a Intersection

[0293] 23b Lowest point

[0294] 40 Backlight unit

[0295] 41 Reflective sheet

[0296] 42 Small light source

[0297] 43 First light diffuser

[0298] 43a First surface

[0299] 43b Second surface

[0300] 44 Second light diffuser

[0301] 44a First surface

[0302] 44b Second surface

[0303] 45 First Prism

[0304] 46 Second prism

[0305] 50 Liquid crystal display device

[0306] 50a display.

Claims

1. A light diffuser, comprising a plurality of concave portions formed into approximately inverted polygonal cones at least on a first surface, in, The ridge lines separating the plurality of recessed portions each have a recessed shape between intersections of the ridge lines with respect to a straight line connecting the intersections, When the arrangement pitch of the plurality of recessed portions is represented by P, and the size occupied by the curved portion of the vertex of each of the ridge lines in the arrangement direction of the plurality of recessed portions is represented by Wr, a ratio Wr / P is 0.3 or less, The maximum height difference d between the straight line and the ridge line is greater than or equal to 1 μm and less than or equal to 10 μm, and The plurality of recessed portions include a recessed portion in which the apex of the approximately inverted polygonal pyramid is formed in a linear shape.

2. The light diffuser according to claim 1, in, The maximum height difference d is greater than or equal to 1.5 μm and less than or equal to 7 μm.

3. The light diffuser according to claim 2, in, The maximum height difference d is greater than or equal to 2.5 μm and less than or equal to 5 μm.

4. The light diffuser according to any one of claims 1 to 3, in, The ratio Wr / P is 0.2 or less.

5. The light diffuser according to claim 4, in, The ratio Wr / P is 0.1 or less.

6. The light diffuser according to any one of claims 1 to 3, in, The arrangement pitch P is greater than or equal to 50 μm and less than or equal to 500 μm, and An angle formed between wall surfaces of the plurality of recessed portions and a sheet surface of the light diffusion sheet is greater than or equal to 40 degrees and less than or equal to 65 degrees.

7. The light diffuser according to any one of claims 1 to 3, in, Each of the ridge lines is recessed into an approximately parabola shape, an approximately circular arc shape, an approximately triangular shape, or an approximately trapezoidal shape between the intersection points.

8. The light diffuser according to any one of claims 1 to 3, in, The plurality of recessed portions are formed into approximately inverted quadrangular pyramids, The ridge lines each extend in a first direction and a second direction, The maximum height difference d is an average of a maximum height difference dx between the straight line and the ridge line in the first direction and a maximum height difference dy between the straight line and the ridge line in the second direction, The arrangement pitch P is an average of an arrangement pitch Px of the plurality of recessed portions in the first direction and an arrangement pitch Py of the plurality of recessed portions in the second direction, and The size Wr is an average of a size Wrx occupied by a curved portion of the apex of each of the ridge lines in the first direction and a size Wry occupied by a curved portion of the apex of each of the ridge lines in the second direction.

9. The light diffuser according to any one of claims 1 to 3, in, The plurality of recessed portions are provided only on the first surface, and The second surface is a matte surface.

10. The light diffuser according to any one of claims 1 to 3, in, The ratio of the concave portion whose apex is formed in a linear shape among the plurality of concave portions is 10% or more.

11. A backlight unit, which is built into a liquid crystal display device and guides light emitted by a light source toward a display screen, wherein the backlight unit include: The light diffuser according to any one of claims 1 to 3, wherein the light diffuser is located between the display screen and the light source.

12. The backlight unit according to claim 11, in, The light source is disposed on a reflective sheet, and the reflective sheet is disposed on a side opposite to the display screen when viewed from the light diffusion sheet.

13. The backlight unit according to claim 11, in, A plurality of the light diffusion sheets are stacked together and arranged between the display screen and the light source.

14. The backlight unit according to claim 13, in, Three or more light diffusion sheets are stacked together and arranged between the display screen and the light source.

15. The backlight unit according to claim 14, in, Among the three or more stacked light diffuser sheets, the light diffuser sheet closest to the display screen contains a diffuser, and the other light diffuser sheets substantially do not contain the diffuser.

16. A liquid crystal display device, include: The backlight unit according to claim 11; as well as Liquid crystal display panel.

17. An information device, include: A liquid crystal display device according to claim 16.

18. A method for manufacturing a light diffuser according to any one of claims 1 to 3, in, The light diffusion sheet is extrusion-molded at a line speed of greater than or equal to 10 m / min and less than or equal to 30 m / min and a compressible linear pressure of greater than or equal to 100 kgf / cm and less than or equal to 500 kgf / cm.

19. A light diffusion sheet comprising a plurality of concave portions formed into approximately inverted polygonal pyramids at least on a first surface, in, A ridge line separating the plurality of recessed portions has a recessed shape between intersections of the ridge lines with respect to a straight line connecting the intersections, When the arrangement pitch of the plurality of recessed portions is represented by P, and the size occupied by the curved portion of the vertex of each of the ridge lines in the arrangement direction of the plurality of recessed portions is represented by Wr, a ratio Wr / P is 0.3 or less, The maximum height difference d between the straight line and each of the ridge lines is greater than or equal to 1 μm and less than or equal to 10 μm, and The plurality of recessed portions include a recessed portion in which a vertex of the approximately inverted polygonal pyramid is formed in a rectangular shape.

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