Backlight unit, liquid crystal display device, and information device

Abstract

To provide a light diffusion sheet that can improve luminance uniformity while avoiding a reduction in luminance.SOLUTION: A light diffusion sheet 43 has a plurality of concave parts 22 formed in a substantially inverted polygonal pyramid shape or a substantially inverted polygonal frustum shape on at least a first surface 43a. The arrangement pitch of the plurality of concave parts 22 is 300 μm or more and 1500 μm or less. The width of a boundary part between the adjacent concave parts 22 of the plurality of convex parts 22 is 25% or less of the arrangement pitch.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a light diffusion sheet, a backlight unit, a liquid crystal display device, and an information device. [Background technology]

[0002] Liquid crystal display devices are widely used as display devices for various information devices such as smartphones, tablet terminals, etc. The mainstream backlight for liquid crystal display devices is the direct type, in which a light source is placed on the back of the liquid crystal panel.

[0003] When a direct type backlight is employed, a light diffusion sheet is used to eliminate the image of a light source such as an LED (Light Emitting Diode) on the light emitting surface and increase the uniformity of in-plane luminance (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-129277 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional direct-type backlights, a decrease in brightness can occur in areas between light sources (areas where no light sources are located) due to the reduction in thickness of the light diffusion sheet or the distance between the light source and the light diffusion sheet, or the reduction in the number of light sources to reduce costs.

[0006] In response to this, attempts have been made to eliminate the brightness unevenness that occurs between the area directly above the light source and the area between the light sources by printing a light-reflecting white ink in the area directly above the light source on the light diffusion sheet, thereby reducing the brightness of the area directly above the light source. However, in this case, a reduction in brightness across the entire screen is unavoidable.

[0007] An object of the present disclosure is to provide a light diffusion sheet capable of improving luminance uniformity while avoiding a decrease in luminance. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the light diffusion sheet of the present disclosure has a plurality of recesses formed in an approximately inverted polygonal pyramid or an approximately inverted polygonal truncated pyramid shape on at least a first surface, the arrangement pitch of the plurality of recesses is 300 μm or more and 1500 μm or less, and the width of the boundary between adjacent recesses in the plurality of recesses is 25% or less of the arrangement pitch.

[0009] According to the light diffusion sheet of the present disclosure, at least the first surface has a plurality of recesses formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal truncated pyramid shape, so that the luminance uniformity can be improved. In addition, since the boundaries between the recesses are flatter than the recess wall surfaces, the light from the light source is less likely to be diffused (reflected or refracted), by setting the arrangement pitch of the recesses to a large value of 300 μm or more, it is possible to reduce the area ratio of the boundaries on the first surface. This makes it possible to improve the luminance uniformity without performing any treatment on the light diffusion sheet that would reduce the luminance.

[0010] In the light diffusion sheet according to the present disclosure, in order to reduce the area ratio of the boundary portions, the width of the boundary portions is set to 25% or less, preferably 20% or less, more preferably 15% or less of the arrangement pitch of the recesses. However, in order to avoid a decrease in abrasion resistance, the width of the boundary portions is set to 0.5% or more, preferably 1.0% or more of the arrangement pitch of the recesses.

[0011] In the light diffusion sheet of the present disclosure, if the arrangement pitch of the recesses exceeds 1500 μm, for example in the case of an inverted pyramid with an apex angle of 80°, the thickness of the light diffusion sheet will be 1 mm or more, making it difficult to reduce the thickness of the backlight unit, especially when multiple light diffusion sheets are stacked. Therefore, the arrangement pitch of the recesses is set to 1500 μm or less.

[0012] In this disclosure, the "boundary between recesses" means "the width of a flat portion intentionally placed between the recesses" when the recesses are arranged with a gap therebetween, and means "the width of the curved portion of the top of the ridge that defines the recesses" when the recesses are arranged without any gaps.

[0013] In addition, in this disclosure, taking into consideration the difficulty of forming a recess having a geometrically strict inverted pyramid or inverted truncated pyramid shape using conventional shape transfer techniques, the terms "approximately inverted pyramid" or "approximately inverted truncated pyramid" are used, but it goes without saying that these terms include shapes that can be regarded as true or substantially inverted pyramids or inverted truncated pyramids.

[0014] In addition, in the present disclosure, the term "light diffusion sheet" encompasses a plate-shaped "light diffusion plate" and a film-shaped "light diffusion film."

[0015] In addition, in the present disclosure, an "optical sheet" refers to a sheet having various optical functions such as diffusion, light collection, refraction, and reflection, and a "light diffusion sheet" is one type of "optical sheet".

[0016] In the light diffusion sheet according to the present disclosure, when the arrangement pitch is 1000 μm or less, an increase in the thickness of the light diffusion sheet can be suppressed, enabling a thin backlight unit to be achieved.

[0017] In the light diffusion sheet according to the present disclosure, when the width of the boundary is the width of the curved portion of the apex of the ridge line dividing the plurality of recesses, in other words, when the recesses are arranged without gaps, the luminance uniformity can be improved compared to when the recesses are arranged at intervals. In this case, the plurality of recesses are formed in a substantially inverted quadrangular pyramid or a substantially inverted quadrangular pyramid truncated shape, the ridge line extends in a first direction and a second direction, the arrangement pitch is the average value of a first arrangement pitch of the plurality of recesses in the first direction and a second arrangement pitch of the plurality of recesses in the second direction, and the width of the boundary may be the average value of a width occupied by the curved portion of the apex of the ridge line in the first direction and a width occupied by the curved portion of the apex of the ridge line in the second direction. This makes it easy to form the recesses.

[0018] In the light diffusion sheet according to the present disclosure, when the angle between the wall surfaces of the plurality of recesses and the sheet surface of the light diffusion sheet is 40 degrees or more and 65 degrees or less, the recesses can provide a sufficient effect of improving brightness uniformity.

[0019] In the light diffusion sheet according to the present disclosure, when a plurality of recesses are provided only on the first surface and the second surface of the light diffusion sheet is a flat or matte surface, it is possible to obtain the effect of improving brightness uniformity while suppressing wear and damage on the second surface.

[0020] The backlight unit according to the present disclosure is a backlight unit that is incorporated into a liquid crystal display device and directs light emitted from a light source toward a display screen, and includes at least one light diffusion sheet according to the present disclosure described above between the display screen and the light source.

[0021] The backlight unit according to the present disclosure includes the light diffusion sheet according to the present disclosure, and therefore can improve the brightness uniformity while avoiding the brightness decrease over the entire screen. In particular, when a plurality of light diffusion sheets according to the present disclosure are used, it is possible to obtain an excellent effect of improving the brightness uniformity while suppressing the brightness decrease.

[0022] In the backlight unit according to the present disclosure, it is preferable that the backlight unit includes a plurality of the light diffusion sheets, and the first surface of the light diffusion sheet farthest from the light source among the plurality of light diffusion sheets is the light entrance surface. In this way, in a backlight unit including a plurality of light diffusion sheets, the luminance uniformity can be further improved compared to a case where the first surface (recess formation surface) of the light diffusion sheet farthest from the light source is the light exit surface.

[0023] In the backlight unit according to the present disclosure, at least one other light diffusion sheet that does not have a recess formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal truncated pyramid shape may be further provided between the display screen and the light source. In this way, by combining different types of light diffusion sheets, both the brightness and the brightness uniformity can be improved.

[0024] In the case where the backlight unit according to the present disclosure includes the other light diffusion sheet, the backlight unit may include a plurality of the light diffusion sheets, the other light diffusion sheets may be disposed between the display screen and the plurality of the light diffusion sheets, and both sides of the other light diffusion sheets may have a matte surface with a surface roughness Ra of 0.1 μm or more and 10 μm or less. In this way, both the brightness and the brightness uniformity can be further improved. In this case, it is more preferable that the difference in surface roughness Ra between both sides of the other light diffusion sheet is 0.5 μm or more, and the surface of the other light diffusion sheet with the smaller surface roughness Ra is the light entrance surface. It is also more preferable that the other light diffusion sheet contains a light diffusing agent in an amount of 0.5 parts by mass to 1.5 parts by mass relative to 100 parts by mass of the matrix resin.

[0025] In the case where the backlight unit according to the present disclosure includes the other light diffusion sheet, the other light diffusion sheet may contain a light diffusing agent and be disposed so as to face the light output surface of the other light diffusion sheet, and the backlight unit may further include a brightness enhancement sheet disposed so as to face the light output surface of the other light diffusion sheet. In this way, both the brightness and the brightness uniformity can be further improved.

[0026] When the backlight unit according to the present disclosure includes the other light diffusion sheet, the other light diffusion sheet may be disposed closer to the display screen than the light diffusion sheet. In this way, both the luminance and the luminance uniformity can be further improved. In this case, the light diffusion sheet may be disposed such that the second surface faces the light source. In this way, both the luminance and the luminance uniformity can be further improved.

[0027] A liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure described above and a liquid crystal display panel.

[0028] According to the liquid crystal display device according to the present disclosure, since the liquid crystal display device includes the backlight unit according to the present disclosure described above, it is possible to improve the luminance uniformity while avoiding a decrease in luminance across the entire screen.

[0029] An information device according to the present disclosure includes the liquid crystal display device according to the present disclosure described above.

[0030] According to an information device according to the present disclosure, since the information device includes the liquid crystal display device according to the present disclosure described above, it is possible to improve brightness uniformity while avoiding a decrease in brightness across the entire screen. Effect of the Invention

[0031] According to the present disclosure, it is possible to provide a light diffusion sheet capable of improving luminance uniformity while avoiding a decrease in luminance. [Brief description of the drawings]

[0032] [Figure 1] 1 is a cross-sectional view of a liquid crystal display device according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of an example of a backlight unit according to the embodiment. [Diagram 3] 3 is a plan view showing an example of the arrangement of light sources in the backlight unit shown in FIG. 2. [Figure 4] 1 is a perspective view of a light diffusion sheet according to an embodiment of the present invention; [Diagram 5] FIG. 11 is a cross-sectional view of another example of the backlight unit according to the embodiment. [Figure 6] FIG. 4 is an enlarged perspective view showing a recess formed in the light diffusion sheet according to the embodiment. [Figure 7] 5A and 5B are schematic diagrams showing examples of the shapes of X-direction ridgelines that define recesses in the light diffusion sheet according to the embodiment. [Figure 8] 5A to 5C are schematic diagrams showing examples of the shapes of ridgelines in the Y direction that define recesses in the light diffusion sheet according to the embodiment. [Figure 9] 5A to 5C are schematic diagrams showing variations in the shape of ridge lines that define recesses in the light diffusing sheet according to the embodiment. [Figure 10] FIG. 1 is a schematic diagram showing an example of a cross-sectional configuration of a light diffusion sheet according to an embodiment, taken along a plane that passes through the centers of adjacent recesses in the X direction and the midpoints of the ridges between the recesses and is perpendicular to the sheet surface. [Figure 11] FIG. 1 is a schematic diagram showing an example of a cross-sectional configuration of a light diffusion sheet according to an embodiment when cut along a plane that passes through the centers of adjacent recesses in the Y direction and the midpoint of the ridge line between the recesses and is perpendicular to the sheet surface. [Figure 12] 8 is a diagram showing an example of the results of measuring the shape and dimensions of the X-direction ridgeline shown in FIG. 7 by a laser microscope. FIG. [Figure 13] 9 is a diagram showing an example of the results of measuring the shape and dimensions of the Y-direction ridgeline shown in FIG. 8 using a laser microscope. [Figure 14] 11 is a diagram showing an example of the results of measuring the shape, dimensions, etc. of the cross-sectional configuration shown in FIG. 10 by a laser microscope. FIG. [Figure 15] 12 is a diagram showing an example of the results of measuring the shape, dimensions, etc. of the cross-sectional configuration shown in FIG. 11 by a laser microscope. FIG. [Figure 16] FIG. 2 is a diagram showing the shape of a regular square pyramid on a roll used in producing a light diffusion sheet in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] (Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments, and can be arbitrarily modified within the scope of the technical concept of the present disclosure.

[0034] <Liquid crystal display device> 1, a liquid crystal display device 50 of this embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the rear 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 to face each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a sealant (not shown) provided in a frame shape to enclose the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0035] The shape of the display screen 50a of the liquid crystal display device 50 when viewed from the front (top of Figure 1) is, in principle, a rectangle or a square, but is not limited to this and may be any shape, such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or an automobile instrument panel.

[0036] In the liquid crystal display device 50, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 in each sub-pixel corresponding to each pixel electrode to change the alignment state of the liquid crystal layer 3. This adjusts the transmittance of light incident from the backlight unit 40 through the first polarizing plate 6. The light with the adjusted transmittance is emitted through the second polarizing plate 7 to display an image.

[0037] The liquid crystal display device 50 of this embodiment is used as a display device incorporated into various information devices (e.g., in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as notebook computers and tablets, portable game machines, copy machines, ticket vending machines, automated teller machines, etc.).

[0038] The TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film arranged to cover each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and connected to each of the plurality of TFTs, and an alignment film arranged to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix arranged in a lattice on a glass substrate, color filters including a red layer, a green layer, and a blue layer arranged between each lattice 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 made of a nematic liquid crystal material containing liquid crystal molecules having electro-optical properties. The first polarizing plate 6 and the second polarizing plate 7 include, for example, a polarizer layer having a polarization axis in one direction and a pair of protective layers arranged to sandwich the polarizer layer.

[0039] <Backlight unit> In the example shown in FIG. 2, the backlight unit 40 of the present embodiment includes a reflecting sheet 41, a plurality of light sources 42 arranged two-dimensionally on the reflecting sheet 41, a first light diffusion sheet 43 provided on the upper side of the plurality of light sources 42, a second light diffusion sheet 44 provided on the upper side of the first light diffusion sheet 43, and a brightness improvement sheet 47 provided on the upper side of the second light diffusion sheet 44. At least one first light diffusion sheet 43 is used, but in this example, two first light diffusion sheets 43 are used by laminating them. The brightness improvement sheet 47 is not particularly limited as long as it can increase the brightness of the light emitted from the light source 42, but in this example, the brightness improvement sheet 47 is used by laminating a first prism sheet 45 in the lower layer and a second prism sheet 46 in the upper layer. Although not shown in the figure, a polarizing sheet may be provided on the upper side of the brightness improvement sheet 47.

[0040] In this disclosure, the term "light diffusion sheet" includes a plate-shaped "light diffusion plate" and a film-shaped "light diffusion film." Furthermore, the term "optical sheet" refers to a sheet having optical functions such as diffusion, light collection, refraction, and reflection, and includes "light diffusion sheet," "reflection sheet," "brightness improvement sheet," and the like.

[0041] [Reflective sheet] The reflective sheet 41 is made of, for example, a white polyethylene terephthalate resin film, a silver vapor deposition film, or the like.

[0042] [light source] The type of the light source 42 is not particularly limited, and may be, for example, an LED element or a laser element, and may be an LED element from the viewpoint of cost, productivity, and the like. A lens may be attached to the LED element to adjust the light emission angle characteristic of the LED element serving as the light source 42. The light source 42 may have a rectangular shape when viewed in a plane, and in that case, the length of one side may be 10 μm or more (preferably 50 μm or more) and 10 mm or less (preferably 5 mm or less). The number of the light sources 42 is not particularly limited, but when multiple light sources 42 are distributed and arranged, it is preferable to arrange them regularly on the reflection sheet 41. Arranging regularly means arranging according to a certain rule, and corresponds to, for example, the case where the light sources 42 are arranged at equal intervals. When the light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0043] In this embodiment, for example, as shown in FIG. 3, a plurality of light sources 42 each composed of an LED element are arranged in a two-dimensional array at regular intervals. In other words, the plurality of light sources 42 are arranged along two directions orthogonal to each other. As the light source 42, a white light source may be used. The white light source is composed of an LED element having a peak wavelength in the blue region, an LED element having a peak wavelength in the green region, and an LED element having a peak wavelength in the red region, and may emit light, for example, with 0.24 < x < 0.42 and 0.18 < y < 0.48 in the chromaticity coordinates of CIE1931. Alternatively, as the light source 42, a blue light source may be used. The blue light source may emit light, for example, with x < 0.24 and y < 0.18 in the chromaticity coordinates of CIE1931. When using a blue light source, a color conversion sheet is arranged between the light source 42 and the luminance improvement sheet 47. The color conversion sheet is, for example, a wavelength conversion sheet that converts light from the light source 42, which is a blue light source, into light having an arbitrary color (for example, green or red) as the peak wavelength. The color conversion sheet converts, for example, blue light with a wavelength of 450 nm into green light with a wavelength of 540 nm and red light with a wavelength of 650 nm. In this case, when using the light source 42 that emits blue light with a wavelength of 450 nm, the blue light is partially converted into green light and red light by the color conversion sheet, so the light transmitted through the color conversion sheet becomes white light. As the color conversion sheet, a QD (quantum dot) sheet, a fluorescent sheet, or the like may be used.

[0044] [First Light Diffusion Sheet] The first light diffusion sheet 43 has a base material layer 21. A plurality of recesses 22 are provided on the first surface 43a (the light incident surface in this example) of the first light diffusion sheet 43. The plurality of recesses 22 are formed in a substantially inverted pyramid or a substantially inverted truncated pyramid shape. In this example, the plurality of recesses 22 are formed in a substantially inverted regular quadrangular pyramid shape. Adjacent recesses 22 are partitioned by ridge lines 23.

[0045] The arrangement pitch of the recesses 22 is set to, for example, about 50 μm or more. As a feature of the present embodiment, in at least one of the first light diffusing sheets 43, the arrangement pitch of the recesses 22 is set to 300 μm or more and 1500 μm or less, preferably 300 μm or more and 1000 μm or less, more preferably 300 μm or more and 700 μm or less, and further preferably 400 μm or more and 550 μm or less.

[0046] The angle that the wall surface of the recesses 22 (the slope of the approximately inverted polygonal pyramid or the approximately inverted polygonal truncated pyramid) makes with the sheet surface of the first light diffusion sheet 43 (a virtual mirror surface without the recesses 22) is set to, for example, 40 degrees or more and 65 degrees or less, preferably 45 degrees or more and 60 degrees or less, and more preferably 47 degrees or more and 55 degrees or less. In other words, the apex angle of the recesses 22 is set to, for example, 50 degrees or more and 100 degrees or less, preferably 60 degrees or more and 90 degrees or less, and more preferably 70 degrees or more and 86 degrees or less.

[0047] The second surface 43b of the first light diffusing sheet 43 may be a flat surface (mirror surface), but may also be a matte surface in order to improve the diffusibility.

[0048] In this example, the first light diffusion sheet 43 is disposed so that the first surface 43a is the light entrance surface, but instead, the first light diffusion sheet 43 may be disposed so that the first surface 43a is the light exit surface. When a plurality of first light diffusion sheets 43 are used, the first light diffusion sheets 43 whose first surface 43a is the light entrance surface and the first light diffusion sheets 43 whose first surface 43a is the light exit surface may be mixed. When a plurality of first light diffusion sheets 43 are used, a plurality of types of first light diffusion sheets 43 whose dimensions, shapes, and arrangement pitches of the recesses 22 and the surface shapes of the second surfaces 43b are different may be used.

[0049] As shown in FIG. 4, a plurality of recesses 22 having a substantially inverted quadrangular pyramid shape (inverted pyramid shape) are arranged in a two-dimensional matrix on the first surface 21a of the first light diffusion sheet 43. In other words, the plurality of recesses 22 are arranged along two directions perpendicular to each other. Adjacent recesses 22 are partitioned by ridge lines 23. The ridge lines 23 extend along the two directions in which the recesses 22 are arranged. The center of the recesses 22 (the apex of the inverted pyramid) is the deepest part of the recesses 22. For simplicity, FIG. 4 illustrates an example in which the recesses 22 are arranged in a 5×5 matrix, but the actual number of recesses 22 arranged is much greater. In the two-dimensional arrangement of the plurality of recesses 22, each recess 22 may be provided on the first surface 21a without any gaps, or may be provided at a predetermined interval. In addition, some recesses 22 may be arranged randomly to the extent that the light diffusion effect is not impaired.

[0050] The base layer 21 is preferably made of, for example, polycarbonate as a base material (matrix resin) and does not contain a diffusing agent, but may contain, for example, about 10% by mass or less of a diffusing agent relative to 100% by mass of the base material. Any known material can be used as the diffusing agent. In this example, the first light diffusion sheet 43 has a single layer structure of the base layer 21, but instead of this, it may have a structure of two or more layers including a layer in which the recesses 22 are formed.

[0051] The first light diffusing sheet 43 will be described in detail later.

[0052] [Second light diffusion sheet] The second light diffusion sheet 44 does not have a recess formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal pyramid frustum. In this example, one second light diffusion sheet 44 is used, but two or more second light diffusion sheets 44 may be used. The second light diffusion sheet 44 may have, for example, a matte surface on the first surface (surface facing the first prism sheet 45) 44a and a flat surface (mirror surface) on the second surface 44b. The second light diffusion sheet 44 is preferably formed, for example, of polycarbonate as a base material (matrix resin) and contains a diffusing agent, and may contain, for example, about 0.5 to 4 parts by mass (preferably about 0.5 to 1.5 parts by mass) of the diffusing agent relative to 100 parts by mass of the base material. The second light diffusion sheet 44 is formed, for example, by mixing 1 part by mass of silicone composite powder (average particle size 2.0 μm) as a diffusing agent with 99 parts by mass of aromatic polycarbonate resin.

[0053] [Brightness enhancement sheet] In this embodiment, the first prism sheet 45 and the second prism sheet 46 constituting the brightness enhancing sheet 47 are, for example, a film in which a plurality of grooves having an isosceles triangular cross section are formed adjacent to each other, and the apex angle of the prism sandwiched between a pair of adjacent grooves is formed at about 90°. Here, each groove formed in the first prism sheet 45 and each groove formed in the second prism sheet 46 are arranged so as to be perpendicular to each other. The first prism sheet 45 and the second prism sheet 46 may be formed integrally. For example, the first prism sheet 45 and the second prism sheet 46 may be a PET (polyethylene terephthalate) film having a prism shape formed by using a UV-curable acrylic resin.

[0054] [Other optical sheets] Although not shown in the figure, a polarizing sheet may be provided above the second prism sheet 46. The polarizing sheet prevents the light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50, thereby improving the brightness of the display screen 50a.

[0055] <Modification of the backlight unit> In the configuration example of the backlight unit 40 shown in FIG. 2, a combination of two laminated first light diffusion sheets 43 and a second light diffusion sheet 44 is used. Instead of this, as in the modified example shown in FIG. 5, a laminated first light diffusion sheet 43 may be used with three laminated first light diffusion sheets 43 without using the second light diffusion sheet 44. Alternatively, although not shown, four or more first light diffusion sheets 43 may be laminated. In this modified example as well, in at least one of the first light diffusion sheets 43, the arrangement pitch of the recesses 22 is set to 300 μm or more and 1500 μm or less, preferably 300 μm or more and 1000 μm or less, more preferably 300 μm or more and 700 μm or less, and even more preferably 400 μm or more and 550 μm or less.

[0056] In this modification, the first light diffusion sheet 43 is disposed so that the first surface 43a is the light entrance surface, but instead, the first light diffusion sheet 43 may be disposed so that the first surface 43a is the light exit surface. Also, a first light diffusion sheet 43 whose first surface 43a is the light entrance surface and a first light diffusion sheet 43 whose first surface 43a is the light exit surface may be mixed.

[0057] <Details of the first light diffusion sheet> In the example shown in Figure 2 or Figure 5, multiple recesses 22 are formed on the first surface 43a of the first light diffusion sheet 43, but in addition to this, multiple other recesses similar to the recesses 22 may also be formed on the second surface 43b of the first light diffusion sheet 43.

[0058] The recesses 22 may be formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal pyramid trapezoid. The recesses 22 may be regularly arranged in two dimensions. As the "inverted polygonal pyramid (trapezoid)", a triangular pyramid (trapezoid), a square pyramid (trapezoid), or a hexagonal pyramid (trapezoid) that can be arranged two-dimensionally without gaps are preferable. A metal mold (metal roll) is used in a manufacturing process such as extrusion molding or injection molding when forming the recesses 22, and an inverted square pyramid (trapezoid) may be selected as the "inverted polygonal pyramid (trapezoid)" in consideration of the accuracy of the cutting work of the surface of the metal mold (metal roll).

[0059] In this disclosure, in consideration of the difficulty of forming a recess having a geometrically strict inverted polygonal pyramid or inverted polygonal truncated pyramid shape by a normal shape transfer technique, the terms "approximately inverted polygonal pyramid" or "approximately inverted polygonal truncated pyramid" are used, but it goes without saying that these terms include shapes that can be regarded as genuine or substantially inverted polygonal pyramids or inverted polygonal truncated pyramids. Furthermore, "approximately" means that it can be approximated, for example, "approximately square pyramid" refers to a shape that can be approximated to a square pyramid. Furthermore, shapes that are deformed from an "inverted polygonal pyramid" or "inverted polygonal truncated pyramid" within the range of unavoidable shape variations due to processing accuracy in industrial production are also included in "approximately inverted polygonal pyramid" or "approximately inverted polygonal pyramid truncated pyramid".

[0060] When multiple recesses 22 are regularly arranged in two dimensions, the multiple recesses 22 may be provided without gaps across the entire surface of the first light diffusion sheet 43, or flat portions of a predetermined width may be provided between the recesses 22.

[0061] The first light diffusion sheet 43 may be composed of a base material layer 21 that does not contain a diffusing agent, for example, a base material layer 21 made of clear polycarbonate. When the base material layer 21 contains a diffusing agent, the material of the diffusing agent is not particularly limited, but inorganic particles such as silica, titanium oxide, aluminum hydroxide, barium sulfate, etc., and organic particles such as acrylic, acrylonitrile, silicone, polystyrene, polyamide, etc. may be used. The particle size of the diffusing agent may be, for example, 0.1 μm or more (preferably 1 μm or more) and 10 μm or less (preferably 8 μm or less) from the viewpoint of the light diffusion effect. It is preferable that the first light diffusion sheet 43 does not contain a diffusing agent from the viewpoint of the reflection and refraction effects due to the approximately inverted polygonal pyramid shape and the light diffusion effect due to the diffusing agent, but the content of the diffusing agent may be, for example, 0.1 mass % or more (preferably 0.3 mass % or more) and 10 mass % or less (preferably 8 mass % or less) with the material (matrix) constituting the base material layer 21 being 100 mass %. The difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base 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. If the difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base layer 21 is less than 0.01, the diffusing effect of the diffusing agent will be insufficient.

[0062] The resin that forms the matrix of the base layer 21 is not particularly limited as long as it is a material that transmits light, but for example, acrylic, polystyrene, styrene acrylic, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. may be used.

[0063] The thickness of the first light diffusion sheet 43 is not particularly limited, and may be, for example, 3 mm or less (preferably 2 mm or less, more preferably 1.5 mm or less, and even more preferably 1 mm or less) and 0.1 mm or more (preferably 0.2 mm or more, and more preferably 0.3 mm or more). If the thickness of the first light diffusion sheet 43 exceeds 3 mm, it becomes difficult to achieve a thin liquid crystal display. On the other hand, if the thickness of the first light diffusion sheet 43 is less than 0.1 mm, it becomes difficult to achieve the effect of improving brightness uniformity.

[0064] When the first light diffusion sheet 43 has a multi-layer structure (e.g., a first base layer and a second recess-forming layer), the thickness of the recess-forming layer is greater than the maximum depth of the recesses 22. For example, in the case of a layer in which recesses having a depth of 20 μm are provided, the thickness is made greater than 20 μm. The first light diffusion sheet 43 may be configured with a three or more layer structure including the base layer and the recess-forming layer. Alternatively, the base layer and the recess-forming layer may each be configured as independent sheets, and the two may be laminated or disposed separately.

[0065] <Method of manufacturing the first light diffusion sheet> Hereinafter, a method for manufacturing the first light diffusion sheet 43 will be described. The method for manufacturing the first light diffusion sheet 43 is not particularly limited, and may be, for example, an extrusion molding method, a compression molding method, a transfer method using a UV-curable resin or a thermosetting resin, or an injection molding method. When the first light diffusion sheet 43 is extrusion molded, for example, the line speed may be set to preferably 2 m / min or more and 20 m / min or less (more preferably 3 m / min or more and 10 m / min or less), and the compression line pressure may be set to preferably 100 kgf / cm or more and 800 kgf / cm or less (more preferably 200 kgf / cm or more and 500 kgf / cm or less). If the line speed exceeds 50 m / min, the shape transfer rate is likely to decrease, while if the line speed is less than 1 m / min, the productivity is likely to decrease. If the compression line pressure exceeds 1000 kgf / cm, the mechanical strength of the manufacturing equipment may be exceeded, while if the compression line pressure is less than 50 kgf / cm, the shape transfer rate is likely to decrease.

[0066] The procedure for manufacturing a single-layer light diffusion sheet having a concave-convex shape on its surface using the extrusion molding method is as follows. First, pellet-shaped plastic particles (to which a diffusion agent may be added) are put into a single-screw extruder, and melted and kneaded while being heated. After that, the molten resin extruded by a T-die is sandwiched between two metal rolls and cooled, and then conveyed using a guide roll and cut into a single flat plate by a sheet cutter to produce a light diffusion sheet. Here, by sandwiching the molten resin using metal rolls having a shape on their surface that is an inversion of a desired concave-convex shape, the inverted shape of the roll surface is transferred to the resin, so that the desired concave-convex shape can be formed on the surface of the light diffusion sheet. In addition, the shape transferred to the resin is not necessarily 100% the shape of the roll surface, so the shape of the roll surface may be designed by calculating backwards from the degree of transfer.

[0067] When using an extrusion molding method to manufacture a two-layer light diffusion sheet having an uneven surface, for example, the pellet-shaped plastic particles required to form each layer are fed into each of two single-screw extruders, and then the same procedure as described above is carried out for each layer, and the sheets thus produced are laminated.

[0068] Alternatively, a two-layer light diffusion sheet having an uneven surface may be produced as follows. First, pellet-shaped plastic particles required for forming each layer are fed into each of two single-screw extruders, and melted and kneaded while being heated. Then, the molten resins for each layer are fed into one T-die, laminated in the T-die, and the laminated molten resin extruded by the T-die is sandwiched between two metal rolls and cooled. Then, the laminated molten resin is conveyed using a guide roll, and cut into a single flat plate by a sheet cutter, thereby producing a two-layer light diffusion sheet having an uneven surface.

[0069] Alternatively, a light diffusion sheet may be manufactured by shape transfer using UV (ultraviolet rays) as follows. First, a roll having an inverted shape of the concave-convex shape to be transferred is filled with uncured UV-curable resin, and a substrate is pressed against the resin. Next, while the roll filled with the UV-curable resin and the substrate are integrated, the resin is cured by irradiating with UV rays. Next, the sheet to which the concave-convex shape has been transferred by the resin is peeled off from the roll. Finally, the sheet is irradiated with UV rays again to completely cure the resin, and a light diffusion sheet having a concave-convex shape on its surface is manufactured.

[0070] <Features of the first light diffusion sheet> The features of the first light diffusing sheet 43 of this embodiment will be described in detail below with reference to FIGS.

[0071] As shown in FIG. 6, a first surface 43a of the first light diffusion sheet 43 is provided with a plurality of recesses 22 formed, for example, in a substantially inverted square pyramid shape. The plurality of recesses 22 may be formed in a substantially inverted square pyramid shape. The center 22a of the recess 22 is the deepest part of the recess 22. The plurality of recesses 22 are arranged along the X direction (first direction) and the Y direction (second direction) which are perpendicular to each other. Adjacent recesses 22 are partitioned by ridge lines 23. The ridge lines 23 extend along the X direction and the Y direction.

[0072] In the first light diffusion sheet 43, the ridge lines 23 may have a recessed shape between the intersection points 23a with respect to the straight lines Lx, Ly connecting the intersection points 23a of the ridge lines 23. The maximum height difference d between the straight lines Lx, Ly connecting the intersection points 23a and the ridge lines 23 may be 1 μm or more and 10 μm or less, preferably 1.5 μm or more and 7 μm or less, and more preferably 2.5 μm or more and 5 μm or less.

[0073] In the first light diffusing sheet 43, the ridges 23 may be recessed between all of the intersections 23a of the ridges, or the ridges 23 may not be recessed between some of the intersections 23a.

[0074] Fig. 7 shows an example of the shape of the ridge line 23 extending in the X direction along the line Ax-Bx in Fig. 6 when viewed from a direction parallel to the sheet surface and perpendicular to the X direction, and Fig. 8 shows an example of the shape of the ridge line 23 extending in the Y direction along the line Ay-By in Fig. 6 when viewed from a direction parallel to the sheet surface and perpendicular to the Y direction. As shown in Fig. 7, the ridge line 23 may have a recessed shape between the intersection points 23a with respect to the straight line Lx connecting the intersection points 23a of the ridge lines 23 in the X direction. In this case, the arrangement pitch of the recesses 22 in the X direction is Px, and the ridge line 23 extending in the X direction has the lowest point 23b at a position Px / 2 (half pitch) from the intersection point 23a, for example, and the distance (maximum height difference) from the straight line Lx to the lowest point 23b is dx. 8, the ridges 23 may have a recessed shape between the intersections 23a of the ridges 23 in the Y direction with respect to a straight line Ly connecting the intersections 23a of the ridges 23. In this case, the arrangement pitch of the recesses 22 in the Y direction is Py, and the ridges 23 extending in the Y direction have the lowest point 23b at a position Py / 2 (half pitch) from the intersection 23a, for example, and the distance (maximum height difference) from the straight line Ly to the lowest point 23b is dy.

[0075] When the recesses 22 are formed into an inverted square pyramid, the arrangement pitch Px of the recesses 22 in the X direction is equal to the distance (horizontal distance) between the intersections 23a in the X direction, and the arrangement pitch Py of the recesses 22 in the Y direction is equal to the distance (horizontal distance) between the intersections 23a in the Y direction.

[0076] The maximum height difference d may be set to an average value of the maximum height difference dx in the X direction and the maximum height difference dy in the Y direction, and may be set to 1 μm or more and 10 μm or less, preferably 1.5 μm or more and 7 μm or less, and more preferably 2.5 μm or more and 5 μm or less.

[0077] The concave shape of the ridge line 23 between the intersection points 23a is not particularly limited, but for example, as shown in Figure 9, the ridge line 23 may be concave between the intersection points 23a in an approximately arc shape (Figure 9(A)), an approximately parabolic shape (Figure 9(B)), an approximately triangular shape (Figure 9(C)), or an approximately trapezoidal shape (Figure 9(D)) with respect to the straight line L connecting the intersection points 23a.

[0078] As a feature of the first light diffusion sheet 43, if the arrangement pitch of the recesses 22 is P and the dimension occupied by the curved portions of the tops of the ridge lines 23 in the arrangement direction of the recesses 22 is Wr, the ratio Wr / P must be 0.25 (25%) or less, preferably 0.2 (20%) or less, and more preferably 0.15 (15%) or less. However, in order to avoid a decrease in abrasion resistance, the ratio Wr / P is set to 0.005 (0.5%) or more, preferably 0.01 (1.0%) or more.

[0079] In this disclosure, when the recesses 22 are arranged without gaps as shown in Fig. 6, the "curved portion of the top of the ridge line 23" is regarded as the "boundary portion between the recesses 22". When the recesses 22 are arranged with gaps between them, the "flat portion intentionally arranged between the recesses 22" is regarded as the "boundary portion between the recesses 22".

[0080] Fig. 10 shows an example of a cross-sectional configuration of the first light diffusion sheet 43 taken along the Cx-Dx line in Fig. 6, and Fig. 11 shows an example of a cross-sectional configuration of the first light diffusion sheet 43 taken along the Cy-Dy line in Fig. 6. In detail, Fig. 10 shows a cross-sectional configuration when the first light diffusion sheet 43 is cut along a plane that passes through the centers 22a of the recesses 22 adjacent to each other in the X direction and the midpoint between the intersections 23a of the ridges 23 located between the recesses 22, and is perpendicular to the sheet surface. Fig. 11 shows a cross-sectional configuration when the first light diffusion sheet 43 is cut along a plane that passes through the centers 22a of the recesses 22 adjacent to each other in the Y direction and the midpoint between the intersections 23a of the ridges 23 located between the recesses 22, and is perpendicular to the sheet surface.

[0081] In the cross-sectional configuration shown in FIG. 10, the interval (horizontal distance) between the centers 22a of the recesses 22 adjacent in the X direction is equal to the arrangement pitch Px of the recesses 22 in the X direction. The dimension occupied in the X direction by the curved portion (boundary portion) of the apex of the ridge line 23 is Wrx. The dimensions occupied in the X direction by the straight portions of the wall surfaces (slope of the inverted pyramid) of the recesses 22 adjacent to each other across the ridge line 23 are Wsx1 and Wsx2. The angle formed between the wall surface (slope of the inverted pyramid) of the recess 22 and the sheet surface in the X direction is θx. The height from the center 22a of the recess 22 to the apex (midpoint between the intersections 23a) of the ridge line 23 (ridge line 23 extending in the Y direction) is Hx.

[0082] In the cross-sectional configuration shown in FIG. 11, the interval (horizontal distance) between the centers 22a of the recesses 22 adjacent in the Y direction is equal to the arrangement pitch Py of the recesses 22 in the Y direction. The dimension occupied in the Y direction by the curved portion (boundary portion) of the apex of the ridge line 23 is Wry. The dimensions occupied in the Y direction by the straight portions of the wall surfaces (slope of the inverted pyramid) of the recesses 22 adjacent to each other across the ridge line 23 are Wsy1 and Wsy2. The angle formed between the wall surface (slope of the inverted pyramid) of the recess 22 and the sheet surface in the Y direction is θy. The height from the center 22a of the recess 22 to the apex (midpoint between the intersections 23a) of the ridge line 23 (ridge line 23 extending in the X direction) is Hy.

[0083] When the recess 22 is formed into an inverted pyramid, the average value of the arrangement pitch Px and the arrangement pitch Py is defined as P, and the average value of the dimension Wrx and the dimension Wry is defined as Wr, and it is necessary to set the ratio Wr / P to 0.25 (25%) or less, preferably to 0.2 (20%) or less, and more preferably to 0.15 (15%) or less.

[0084] FIG. 12 shows an example of the results of measuring the shape and dimensions of the X-direction ridgeline shown in FIG. 7 by a laser microscope, FIG. 13 shows an example of the results of measuring the shape and dimensions of the Y-direction ridgeline shown in FIG. 8 by a laser microscope, FIG. 14 shows an example of the results of measuring the shape, dimensions, and angles of the cross-sectional configuration shown in FIG. 10 by a laser microscope, and FIG. 15 shows an example of the results of measuring the shape, dimensions, and angles of the cross-sectional configuration shown in FIG. 11 by a laser microscope. In addition, in measuring the maximum distance (maximum height difference) dx and dy between the straight lines Lx and Ly connecting the intersections 23a of the ridgeline 23 and the ridgeline 23, the maximum values ​​of the lengths of perpendicular lines drawn perpendicularly to the straight lines Lx and Ly from points on the ridgeline 23 were taken as dx and dy. In measuring the arrangement pitches Px and Py, the "horizontal distance between the intersections 23a" in the X direction and the Y direction were obtained as Px and Py, respectively. In this way, the method of measuring the "horizontal distance between the intersections 23a" can also easily and accurately obtain the arrangement pitches Px and Py.

[0085] <Effects of the embodiment (including modifications)> As described above, the first light diffusion sheet 43 of this embodiment has a plurality of recesses 22 formed in the shape of an approximately inverted polygonal pyramid or an approximately inverted polygonal truncated pyramid on at least the first surface 43a, the arrangement pitch of the recesses 22 is 300 μm or more and 1500 μm or less, and the width of the boundary between adjacent recesses 22 is 25% or less of the arrangement pitch.

[0086] According to the first light diffusion sheet 43 of this embodiment, at least the first surface 43a has a plurality of recesses 22 formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal pyramid frustum, so that the luminance uniformity can be improved. In addition, since the boundary portions between the recesses 22 are flatter than the wall surfaces of the recesses 22, the light from the light source 42 is less likely to be diffused (reflected or refracted), by setting the arrangement pitch of the recesses 22 to a large value of 300 μm or more, it is possible to reduce the area ratio of the boundary portions to the first surface 43a. As a result, the luminance uniformity can be improved without performing a treatment on the first light diffusion sheet 43 that reduces the luminance.

[0087] In the first light diffusion sheet 43 of the present embodiment, in order to reduce the area ratio of the boundaries, the width of the boundaries is set to 25% or less, preferably 20% or less, and more preferably 15% or less of the arrangement pitch of the recesses 22. However, in order to avoid a decrease in abrasion resistance, the width of the boundaries is set to 0.5% or more, preferably 1.0% or more of the arrangement pitch of the recesses 22.

[0088] In the first light diffusion sheet 43 of this embodiment, if the arrangement pitch of the recesses 22 exceeds 1500 μm, for example in the case of an inverted pyramid with an apex angle of 80°, the sheet thickness will be 1 mm or more, making it difficult to reduce the thickness of the backlight unit 40, especially when multiple first light diffusion sheets 43 are stacked. Therefore, the arrangement pitch of the recesses 22 is set to 1500 μm or less.

[0089] In the first light diffusing sheet 43 of the present embodiment, when the arrangement pitch of the recesses 22 is 1000 μm or less, an increase in the sheet thickness can be suppressed, and the backlight unit 40 can be made thinner.

[0090] In the first light diffusing sheet 43 of the present embodiment, the width of the boundary between the recesses 22 may be the width of the curved portion at the apex of the ridge line 23 that separates the recesses 22. In this case, the recesses 22 are arranged without any gaps, so that the luminance uniformity can be improved compared to the case where the recesses 22 are arranged with intervals. Furthermore, when the recesses 22 are formed in a substantially inverted square pyramid or a substantially inverted square truncated pyramid shape, the recesses 22 can be easily formed.

[0091] In the first light diffusing sheet 43 of the present embodiment, when the angle between the wall surface of the recesses 22 and the sheet surface is 40 degrees or more and 65 degrees or less, the recesses 22 can provide a sufficient effect of improving luminance uniformity.

[0092] In the first light diffusion sheet 43 of this embodiment, the recesses 22 are provided only on the first surface 43a, and the second surface 43b is a flat or matte surface, so that the effect of improving brightness uniformity can be obtained while suppressing wear and damage on the second surface 43b.

[0093] In the first light diffusion sheet 43 of the present embodiment, the ridges 23 (opening edges of the recesses 22) that define the recesses 22 are a cause of wear and damage. However, when the ridges 23 have a recessed shape between the intersections 23a of the ridges 23, wear and damage are unlikely to occur even when the sheet is used in combination with other optical sheets or other light diffusion sheets. In addition, the dimension Wr of the curved portion of the top of the ridges 23 in the arrangement direction of the recesses 22 is suppressed to 25% or less of the arrangement pitch P of the recesses. Therefore, the top of the ridges 23 can be kept in a steep shape, so that the brightness uniformity is unlikely to decrease even if the ridges 23 are recessed between the intersections 23a. In addition, when the maximum height difference d between the straight line connecting the intersections 23a and the ridges 23 is 1 μm or more, the scratch resistance is improved, and when the maximum height difference d is 10 μm or less, the decrease in brightness uniformity can be suppressed. In particular, when the maximum height difference d is 1.5 μm or more and 7 μm or less, both the scratch resistance and the brightness uniformity can be further improved, and when the maximum height difference d is 2.5 μm or more and 5 μm or less, both the scratch resistance and the brightness uniformity can be further improved.

[0094] The backlight unit 40 of this embodiment is incorporated into a liquid crystal display device 50 and directs light emitted from a light source 42 toward a display screen 50a, and includes at least one first light diffusion sheet 43 of this embodiment between the display screen 50a and the light source 42.

[0095] The backlight unit 40 of the present embodiment includes the first light diffusion sheet 43, and therefore can improve the brightness uniformity while avoiding a decrease in brightness across the entire screen. In particular, when a plurality of first light diffusion sheets 43 are used, it is possible to obtain an excellent effect of improving the brightness uniformity while suppressing a decrease in brightness.

[0096] The backlight unit 40 of the present embodiment includes a plurality of first light diffusion sheets 43, and the first surface 43a of the first light diffusion sheet 43 that is farthest from the light source 42 among the plurality of first light diffusion sheets 43 may be the light entrance surface. In this way, it is possible to further improve the luminance uniformity compared to the case where the first surface 43a (the surface on which the recesses 22 are formed) of the first light diffusion sheet 43 that is farthest from the light source 42 is the light exit surface.

[0097] In the backlight unit 40 of the present embodiment, at least one second light diffusion sheet 44 (another light diffusion sheet) that does not have a recess formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal truncated pyramid shape may be further provided between the display screen 50a and the light source 42. In this way, by combining different types of light diffusion sheets, both the brightness and the brightness uniformity can be improved.

[0098] When the second light diffusion sheet 44 is provided, a plurality of first light diffusion sheets 43 may be provided, and both sides of the second light diffusion sheet 44 may have a matte surface with a surface roughness Ra of 0.1 μm or more and 10 μm or less. In this way, both the brightness and brightness uniformity can be further improved. In this case, the first surface 43a of the first light diffusion sheet 43 farthest from the light source 42 among the plurality of first light diffusion sheets 43 is the light output surface, and the second light diffusion sheet 44 is disposed so as to face the first surface 43a, and the difference in surface roughness Ra between both surfaces of the second light diffusion sheet 44 is preferably 0.5 μm or more, and the surface of the second light diffusion sheet 44 with the smaller surface roughness Ra is the light input surface. In addition, the second light diffusion sheet 44 preferably contains a light diffusing agent of 0.5 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the matrix resin.

[0099] When the second light diffusion sheet 44 is provided, the second light diffusion sheet 44 contains a light diffusing agent and is arranged to face the light output surface of the first light diffusion sheet 43 (in the case where a plurality of first light diffusion sheets 43 are provided, the first light diffusion sheet 43 that is farthest from the light source 42), and may further include a brightness enhancing sheet 47 arranged to face the light output surface of the second light diffusion sheet 44. In this way, both the brightness and the brightness uniformity can be further improved.

[0100] When the second light diffusion sheet 44 is provided, the second light diffusion sheet 44 may be disposed closer to the first prism sheet 45 (i.e., closer to the display screen 50a) than the first light diffusion sheet 43 (in the case where a plurality of first light diffusion sheets 43 are provided, the first light diffusion sheet 43 farthest from the light source 42). In this way, both the luminance and the luminance uniformity can be further improved. In this case, the first light diffusion sheet 43 (in the case where a plurality of first light diffusion sheets 43 are provided, the first light diffusion sheet 43 farthest from the light source 42) may be disposed so that the second surface 43b faces the light source 42. In this way, both the luminance and the luminance uniformity can be further improved.

[0101] In the backlight unit 40 of the present embodiment, if the light sources 42 are disposed on the reflective sheet 41 provided on the opposite side of the display screen 50a as viewed from the first light diffusing sheet 43, the luminance uniformity is further improved.

[0102] The liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and a liquid crystal display panel 5.

[0103] The liquid crystal display device 50 of this embodiment and an information device equipped with the liquid crystal display device 50 are equipped with the backlight unit 40 of this embodiment, and therefore it is possible to improve brightness uniformity while avoiding a decrease in brightness across the entire screen.

[0104] (Example) Examples will be described below together with comparative examples and reference examples.

[0105] <Light diffusion sheet used> The configurations and optical properties of various light diffusion sheets (Sheets #1 to #16) used in the Examples, Comparative Examples, and Reference Examples are shown in Table 1. In Table 1, "ridge width Wr" means "the width of the curved portion at the top of the ridge line," or in other words, "the width of the boundary between the recesses."

[0106] [Table 1]

[0107] Sheet #1 was produced as follows. First, aromatic polycarbonate resin with a melt mass flow rate of 15 g / 10 min measured in accordance with ISO1133 was put into an extruder, melted and kneaded, and then extruded from a T-die. Then, one of the two metal rolls was used as a cast roll, with a shape (a regular square pyramid shape with a height of 107 μm, a pitch of 180 μm, and an apex angle of 80 degrees) shown on the surface as shown in (A) and (B) of FIG. 16 ((B) is a shape diagram seen from the XY line cross section direction of (A)), and the other roll was used as a pressing roll, with a random matte shape (surface roughness Ra=2.6 μm) on the surface, and the molten resin extruded from the T-die was sandwiched between the two rolls and cooled while transferring the shape. In this way, a single-layer sheet #1 with a thickness of 650 μm was produced by extrusion molding. As shown in Table 1, sheet #1 does not contain a diffusion agent, has depressions (inverted pyramids) on one surface (first surface 43a) with a height (depth) H of 87 μm, which depends on the height of the regular pyramids on the roll, and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.47 μm. The arrangement pitch P of the inverted pyramids, the apex angle, the ridge width Wr, and Wr / P are 180 μm, 80 degrees, 36 μm, and 20%, respectively.

[0108] For sheet #2, 100 parts by mass of the same aromatic polycarbonate resin as sheet #1 and 0.8 parts by mass of silicone composite powder (average particle size 2.0 μm) as a diffusion agent were mixed in advance and fed into an extruder, and the same process as for sheet #1 was carried out to produce sheet #2 with a thickness of 650 μm. As shown in Table 1, sheet #2 contains 0.8 parts by mass of diffusion agent per 100 parts by mass of matrix resin, has a recess (inverted square pyramid) with a height (depth) H of 85 μm depending on the height of the regular square pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.39 μm. In addition, the arrangement pitch P of the inverted square pyramid, the apex angle, the width Wr of the ridge line, and Wr / P are 180 μm, 80 degrees, 41 μm, and 23%, respectively.

[0109] For sheets #3 to #5, the same resin as sheet #1 was used, and one roll was used as a cast roll having a surface shape shown in (A) and (B) of FIG. 16 (a regular square pyramid shape with a height of about 300 μm, a pitch of 500 μm, and an apex angle of 80 degrees), and the other roll was used as a pressing roll having a surface shape with a random matte shape similar to that of sheet #1. The thicknesses of sheets #3 to #5 were adjusted to 650 μm for sheet #3, 750 μm for sheet #4, and 850 μm for sheet #5. The surface roughness and manufacturing conditions of the pressing roll were selected so as to obtain sheets with the target surface roughness. As shown in Table 1, sheets #3 to #5 do not contain a diffusing agent. Sheet #3 has a recess (inverted pyramid) with a height (depth) H of 259 μm depending on the height of the regular pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.45 μm, and the arrangement pitch P of the inverted pyramids, the apex angle, the ridge width Wr, and Wr / P are 500 μm, 80 degrees, 40 μm, and 8%, respectively. Sheet #4 has a recess (inverted pyramid) with a height (depth) H of 249 μm depending on the height of the regular pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.41 μm, and the arrangement pitch P of the inverted pyramids, the apex angle, the ridge width Wr, and Wr / P are 500 μm, 80 degrees, 52 μm, and 10%, respectively. Sheet #5 has a recess (inverted pyramid) on one surface (first surface 43a) with a height (depth) H of 239 μm, which depends on the height of the regular pyramid on the roll, and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.38 μm, and the arrangement pitch P of the inverted pyramids, the apex angle, the ridge width Wr, and Wr / P are 500 μm, 80 degrees, 64 μm, and 13%, respectively.

[0110] For the light diffusion sheets with matte on both sides, sheets #6, #8 to #10, and #15, resin and diffusion agent of the composition shown in Table 1 were used, and a matte roll with a surface roughness Ra of 4.5 μm was used as a cast roll for the first side, and the roll for the second side was the same as that for sheet #1 (a roll with a random matte shape (surface roughness Ra = 2.6 μm) on the surface) as a pressing roll, to create sheets #6, #8 to #10, and #15 having a matte surface 1 (M1 surface) with a relatively large surface roughness Ra and a matte surface 2 (M2 surface) with a relatively small surface roughness Ra. As shown in Table 1, sheet #6 has a thickness of 1000 μm and does not contain a diffusion agent, and one surface (first surface 43a) is a matte surface with a surface roughness Ra = 2.3 μm, and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.91 μm. Sheet #8 has a thickness of 1000 μm, contains 0.8 parts by mass of diffusing agent relative to 100 parts by mass of matrix resin, has one surface (first surface 43a) which is a matte surface with a surface roughness of Ra = 2.2 μm, and the other surface (second surface 43b) which is a matte surface with a surface roughness of Ra = 0.92 μm, as shown in Table 1. Sheet #9 has a thickness of 1000 μm, contains 2.0 parts by mass of diffusing agent relative to 100 parts by mass of matrix resin, has one surface (first surface 43a) which is a matte surface with a surface roughness of Ra = 4.0 μm, and the other surface (second surface 43b) which is a matte surface with a surface roughness of Ra = 0.53 μm, as shown in Table 1. As shown in Table 1, sheet #10 has a thickness of 1200 μm, contains 0.8 parts by mass of diffusing agent relative to 100 parts by mass of matrix resin, has one surface (first surface 43a) which is a matte surface with a surface roughness of Ra = 1.9 μm, and the other surface (second surface 43b) which is a matte surface with a surface roughness of Ra = 0.90 μm. As shown in Table 1, sheet #15 has a thickness of 1200 μm, contains 2.0 parts by mass of diffusing agent relative to 100 parts by mass of matrix resin, has one surface (first surface 43a) which is a matte surface with a surface roughness of Ra = 2.1 μm, and the other surface (second surface 43b) which is a matte surface with a surface roughness of Ra = 0.68 μm.

[0111] For sheet #7, a resin and a diffusing agent with the composition shown in Table 1 were used, and the roll for the first surface was a matte roll with a surface roughness Ra of 4.5 μm as in sheet #6, which was used as a cast roll, and the roll for the second surface was a mirror roll, which was used as a pressing roll, to produce sheet #7 having a rough matte surface and a mirror surface. As shown in Table 1, sheet #7 is 1000 μm thick and contains 0.8 parts by mass of diffusing agent per 100 parts by mass of matrix resin, with one surface (first surface 43a) being a matte surface with a surface roughness Ra of 3.2 μm and the other surface (second surface 43b) being a mirror surface (flat surface) with a surface roughness Ra of 0.04 μm.

[0112] Sheet #11 was molded using the same resin composition and roll as sheet #3, but with a lower linear compression pressure, resulting in sheet #11 with a thickness of 650 μm and a low shape transfer rate. As shown in Table 1, sheet #11 does not contain a diffusion agent, has a recess (inverted pyramid) on one surface (first surface 43a) with a height (depth) H of 180 μm, which depends on the height of the regular pyramid on the roll, and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.47 μm. The arrangement pitch P of the inverted pyramids, the apex angle, the width Wr of the ridgeline, and Wr / P are 500 μm, 80 degrees, 175 μm, and 35%, respectively.

[0113] For sheet #12, the same resin as sheet #1 was used, and one roll was used as a cast roll having a shape similar to that of (A) and (B) of FIG. 16 (a regular pyramid shape with a height of about 149 μm, a pitch of 250 μm, and an apex angle of 80 degrees), and the other roll was used as a pressing roll having a random matte shape similar to that of sheet #1, and the thickness was adjusted to 650 μm to produce sheet #12. As shown in Table 1, sheet #12 does not contain a diffusion agent, and has a recess (inverted square pyramid) with a height (depth) H of 130 μm depending on the height of the regular square pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.47 μm. The arrangement pitch P of the inverted square pyramids, the apex angle, the width Wr of the ridge line, and Wr / P are 250 μm, 80 degrees, 38 μm, and 15%, respectively.

[0114] For sheet #13, the same resin as sheet #1 was used, and one roll was used as a cast roll having a shape similar to that of (A) and (B) of FIG. 16 (a regular pyramid shape with a height of about 191 μm, a pitch of 320 μm, and an apex angle of 80 degrees), and the other roll was used as a pressing roll having a random matte shape similar to that of sheet #1, and the thickness was adjusted to 650 μm to produce sheet #13. As shown in Table 1, sheet #13 does not contain a diffusion agent, and has a recess (inverted square pyramid) with a height (depth) H of 166 μm depending on the height of the regular square pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 0.47 μm. The arrangement pitch P of the inverted square pyramids, the apex angle, the width Wr of the ridge line, and Wr / P are 320 μm, 80 degrees, 40 μm, and 13%, respectively.

[0115] For sheets #14 and #16, the same resin as for sheet #1 was used, and one roll was used as a cast roll having a surface shape shown in (A) and (B) of FIG. 16 (a regular square pyramid shape with a height of about 300 μm, a pitch of 500 μm, and an apex angle of 80 degrees), and the other roll was used as a pressing roll having a surface shape with a random matte shape similar to that of sheet #1. The thickness of sheet #14 was adjusted to 450 μm, and that of sheet #16 was adjusted to 650 μm, to produce sheets #14 and #16. The surface roughness and manufacturing conditions of the pressing roll were selected so as to obtain sheets with the target surface roughness. As shown in Table 1, sheets #14 and #16 do not contain a diffusing agent. Sheet #14 has a recess (inverted pyramid) with a height (depth) H of 284 μm depending on the height of the regular pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 2.0 μm, and the arrangement pitch P of the inverted pyramids, the apex angle, the ridge width Wr, and Wr / P are 500 μm, 80 degrees, 24 μm, and 5%, respectively. Sheet #16 has a recess (inverted pyramid) with a height (depth) H of 263 μm depending on the height of the regular pyramid on the roll on one surface (first surface 43a), and the other surface (second surface 43b) is a matte surface with a surface roughness Ra = 8.0 μm, and the arrangement pitch P of the inverted pyramids, the apex angle, the ridge width Wr, and Wr / P are 500 μm, 80 degrees, 40 μm, and 8%, respectively.

[0116] <Measurement of the arrangement pitch of the recesses, the apex angle, the width of the ridge line, and the height of the inverted pyramid> The shape of the recesses (inverted square pyramids) formed in the sheets #1 to #5, #11 to #14, and #16 shown in Table 1 was measured using a laser microscope. Specifically, the arrangement pitches Px and Py (horizontal distances between intersections 23a in the X and Y directions) of the recesses 22 shown in Figs. 7 and 8 were measured, and the arrangement pitch P was calculated as the average value. In addition, the angles θx and θy (angles between the wall surface (slope of the inverted square pyramid) of the recesses 22 and the sheet surface in the X and Y directions) shown in Figs. 10 and 11 were measured, and the apex angle (apex angle = 180 degrees - (θx + θy)) was calculated based on the average value. In addition, the dimensions Wrx and Wry (dimensions occupied by the curved part of the apex of the ridge line 23 in the X and Y directions) shown in Figs. 10 and 11 were measured, and the width Wr of the ridge line was calculated as the average value. The unit of the ratio Wr / P of the width Wr to the arrangement pitch P is %. Further, the heights Hx and Hy (height from center 22a of recess 22 to the apex of edge 23) shown in Figs. 10 and 11 were measured, and the height H of the inverted pyramid was calculated as the average value.

[0117] <Measurement of surface roughness (Ra) of light diffusion sheet> The surface roughness (Ra) of the matte or mirror surface of sheets #1 to #16 shown in Table 1 was measured using SJ-210 manufactured by Mitutoyo Corporation in accordance with JIS B-601.

[0118] <Optical property measurement> The light transmittance and light reflectance at a wavelength of 450 nm of sheets #1 to #16 shown in Table 1 were measured using a V-670 manufactured by JASCO Corporation, and the haze was measured using an HZ-2 manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS-K7361:2000. The optical properties were measured as follows: (1) for sheets #1 to #5, #11 to #14, and #16 having inverted pyramids, the surface having the inverted pyramids was used as the light-entering surface, (2) for sheet #7 having a matte surface and a mirror surface, the matte surface was used as the light-entering surface, and (3) for sheets #6, #8 to #10, and #15, both of which were matte on both sides, the matte surface with the large surface roughness Ra (M1 surface) was used as the light-entering surface.

[0119] <Measurement of luminance and luminance uniformity> In the examples, reference examples, and comparative examples described later, the luminance and luminance uniformity were measured using, for example, three light diffusion sheets selected from sheets #1 to #16 shown in Table 1 in the same configuration as the backlight unit 40 shown in FIG. 2 or FIG. 5, and an LED array in which light sources 42 are arranged as shown in FIG. 3. That is, optical sheets such as a light diffusion sheet and a luminance improvement sheet were arranged on the light sources (LEDs) 42 arranged in an array, and the luminance and luminance uniformity were measured. Specifically, an LED array in which Cree's blue LEDs (product number XPGDRY-L1-0000-00501) serving as the light sources 42 are arranged at a pitch of 12.5 mm was used, three light diffusion sheets were arranged on the LED array, and a luminance improvement sheet 47 (prism sheets 45 and 46) was arranged on top of the light diffusion sheets via a color conversion sheet so that the ridges of the prism sheets 45 and 46 are mutually orthogonal, and the luminance and luminance uniformity were measured. The three light diffusion sheets used may include two or three sheets of the same type.

[0120] In measuring the luminance uniformity, first, an LED array (6 x 6) as shown in Figure 3 was used to measure the two-dimensional luminance distribution on the surface of the uppermost luminance enhancing sheet 47 in the sheet stacking configuration of the backlight unit described above. After that, the average value and standard deviation were calculated for the actual luminance measurements of all 22,500 pixels (150 x 150 pixels with a pixel pitch of 0.25 mm) within an area of ​​3 LEDs vertically x 3 LEDs horizontally. This average value was used to evaluate the luminance, and the luminance uniformity was evaluated using the average value and standard deviation of the luminance. Luminance uniformity = (average luminance (cd / m 2 ))÷(Standard deviation of luminance (cd / m 2 )) The brightness uniformity was calculated according to the formula: The higher the brightness uniformity value calculated in this way, the more uniform the brightness is.

[0121] <Evaluation of luminance uniformity> The luminance uniformity of the examples, comparative examples, and reference examples described later was evaluated according to the following criteria. AA: The luminance uniformity value is 55 or more, which means the luminance uniformity is very good. A: The luminance uniformity value is between 45 and 55, which means the luminance uniformity is excellent. B: The luminance uniformity value is 35 or more and less than 45, and the luminance uniformity is somewhat excellent. C: The luminance uniformity value is between 25 and 35, and the luminance uniformity meets the minimum required value. X: The luminance uniformity value is less than 25, and the luminance uniformity is insufficient.

[0122] In Tables 2 to 5 below showing the evaluation results of luminance uniformity, the overlapping directions of the light diffusion sheets are described as follows. i) For sheets #1 to #5, #11 to #14, and #16, which have an inverted square pyramid on the first side and a matte surface on the second side, if the first side is the light entering side it is described as "inverted square pyramid bottom," and if the first side is the light emitting side it is described as "inverted square pyramid top." ii) For sheet #7, which has a matte first surface and a mirror second surface, if the matte surface is the light entering surface and the mirror surface is the light emitting surface, it is written as "M surface below, mirror surface above." Conversely, if the mirror surface is the light entering surface and the matte surface is the light emitting surface, it is written as "mirror surface below, M surface above." iii) For sheets #6, #8 to #10, and #15, which are matte on both sides, the side with the greater matte surface roughness Ra is side M1, and the side with the smaller matte surface roughness Ra is side M2. If side M1 is the light entering surface and side M2 ​​is the light emitting surface, it is described as "side M1 down," and if side M2 ​​is the light entering surface and side M1 is the light emitting surface, it is described as "side M1 up."

[0123] <Examples 1 to 8, Comparative Examples 1 to 4, Reference Examples 1 to 2> In Examples 1 to 8, Comparative Examples 1 to 4, and Reference Examples 1 and 2, three light diffusion sheets selected from sheets #1 to #5 and #11 shown in Table 1 were stacked in the order and orientation shown in Table 2, and the luminance and luminance uniformity were measured. The total thickness, luminance and luminance uniformity measurements of the three light diffusion sheets, and the evaluation results of the luminance uniformity are shown in Table 2.

[0124] [Table 2]

[0125] As shown in Table 2, in Examples 1 to 8, by using two or more sheets #3 to #5 in which the inverted pyramidal recesses are arranged at a pitch of 500 μm, it was possible to improve the brightness uniformity while suppressing the brightness decrease, compared to Comparative Examples 1 to 4 in which the sheets #1 and #2 in which the inverted pyramidal recesses are arranged at a pitch of 180 μm were used. In addition, as can be seen from the comparison between Example 1 and Example 2, the comparison between Example 3 and Example 4, the comparison between Example 5 and Example 6, and the comparison between Example 7 and Example 8, when the same type of light diffusion sheets are stacked in the same order, the brightness uniformity of the light diffusion sheet farthest from the light source can be further improved by making the surface on which the inverted pyramidal recesses are provided as the light entrance surface. In addition, as can be seen from Reference Examples 1 and 2, when the sheet #11 in which Wr / P exceeds 25% because the width of the ridge line (the width of the boundary between the recesses) is large is used, the brightness uniformity is not sufficiently improved even if the inverted pyramidal recesses are arranged at a pitch of 500 μm.

[0126] <Examples 9 to 20, Reference Examples 3 to 4> In Examples 9 to 20 and Reference Examples 3 to 4, three light diffusion sheets selected from sheets #3 to #5, #6, and #8 to #10 shown in Table 1 were stacked in the order and orientation shown in Table 3, and the luminance and luminance uniformity were measured. The total thickness, luminance and luminance uniformity measurements, and luminance uniformity evaluation results of the three light diffusion sheets are shown in Table 3. In Examples 9 to 20 and Reference Examples 3 to 4, any of sheets #6 and #8 to #10, both of which are matte surfaces (having no inverted pyramidal recesses), was used as the light diffusion sheet furthest from the light source, and any of sheets #3 to #5, in which inverted pyramidal recesses are arranged at a pitch of 500 μm, was used as the other two light diffusion sheets.

[0127] [Table 3]

[0128] As shown in Table 3, in Examples 9 to 20, by disposing any one of sheets #8 to #10, both of which have matte surfaces, on two light diffusion sheets selected from sheets #3 to #5, in which inverted pyramidal recesses are arranged at a pitch of 500 μm, it was possible to improve the luminance uniformity while suppressing the decrease in luminance, as compared with Comparative Examples 1 to 4 (see Table 2). In addition, as can be seen from the comparison between Example 9 and Example 10, the comparison between Example 11 and Example 12, the comparison between Example 13 and Example 14, the comparison between Example 15 and Example 16, the comparison between Example 17 and Example 18, and the comparison between Example 19 and Example 20, when the same type of light diffusion sheets are stacked in the same order, in sheets #8 to #10 (light diffusion sheets farthest from the light source), both of which have matte surfaces, by using the M1 surface, which has a larger surface roughness Ra of the matte surface, as the light output surface, in other words, by using the M2 surface, which has a smaller surface roughness Ra of the matte surface, as the light input surface, it was possible to further improve the luminance uniformity. Furthermore, as can be seen from a comparison between Examples 17 to 20 and Reference Examples 3 to 4, in order to improve brightness uniformity, it is preferable to incorporate a diffusing agent into a light diffusion sheet having matte surfaces on both sides, and it is particularly preferable to incorporate 0.5 to 1.5 parts by mass of diffusing agent per 100 parts by mass of matrix resin.

[0129] <Examples 21 to 26> In Examples 21 to 26, three light diffusion sheets selected from sheets #1, #3, #5, and #7 shown in Table 1 were stacked in the order and orientation shown in Table 4, and the luminance and luminance uniformity were measured. The total thickness, luminance and luminance uniformity measurements, and luminance uniformity evaluation results of the three light diffusion sheets are shown in Table 4. In Examples 21 to 26, sheet #7 having a rough matte surface and a mirror surface (without inverted pyramidal recesses) was used as the light diffusion sheet furthest from the light source, and sheet #1 having inverted pyramidal recesses arranged at a pitch of 180 μm, and sheet #3 or #5 having inverted pyramidal recesses arranged at a pitch of 500 μm were used as the other two light diffusion sheets.

[0130] [Table 4]

[0131] As shown in Table 4, in Examples 21 to 26, by disposing sheet #7 having a matte surface and a mirror surface on two light diffusion sheets selected from sheets #1, #3, and #5 on which inverted pyramidal recesses are arranged, it was possible to improve the brightness uniformity while suppressing the decrease in brightness, compared to Comparative Examples 1 to 4 (see Table 2). In addition, in Examples 21 to 22, even when only one light diffusion sheet (sheet #3) on which inverted pyramidal recesses are arranged at a pitch of 500 μm is used, the effect of improving the brightness uniformity was obtained. Note that, as can be seen from the comparison between Example 25 and Example 15 (see Table 3) and the comparison between Example 26 and Example 16 (see Table 3), the use of sheet #8 (with the same diffusion agent concentration as sheet #7) with both matte surfaces as the light diffusion sheet farthest from the light source, compared to sheet #7 with a matte surface and a mirror surface, was able to further improve the brightness uniformity.

[0132] <Examples 27 to 28, Comparative Examples 5 to 6> In Examples 27 and 28, three sheets of sheet #13 shown in Table 1 were stacked in the direction shown in Table 5, and in Comparative Examples 5 and 6, three sheets of sheet #12 shown in Table 1 were stacked in the direction shown in Table 5, and the luminance and luminance uniformity were measured for each. The total thickness of the three light diffusion sheets, the measured values ​​of luminance and luminance uniformity, and the evaluation results of luminance uniformity are shown in Table 5.

[0133] [Table 5]

[0134] As shown in Table 5, in Examples 27 to 28, which used sheet #13 with an arrangement pitch P of inverted square pyramids of 320 μm, the luminance uniformity could be improved while suppressing the decrease in luminance compared to Comparative Examples 1 to 4 (see Table 2). However, in Comparative Examples 5 to 6, which used sheet #12 with an arrangement pitch P of inverted square pyramids of 250 μm, the luminance uniformity could not be improved.

[0135] <Examples 29 to 33> In Examples 29 to 33, three light diffusion sheets selected from sheets #3, #5, #10, #14, #15, and #16 shown in Table 1 were stacked in the order and orientation shown in Table 6, and the luminance and luminance uniformity were measured. Table 6 shows the total thickness, luminance and luminance uniformity measurements of the three light diffusion sheets, and the evaluation results of the luminance uniformity.

[0136] [Table 6]

[0137] As shown in Table 6, in Examples 31 to 33, sheets #3 and #16 with an inverted pyramid arrangement pitch P of 500 μm were used as the first and second sheets, with the surfaces with inverted pyramid-shaped recesses as the light-emitting surfaces, and sheets #10 and #15 with matte surfaces on both sides (without inverted pyramid-shaped recesses) were used as the third sheet, so that excellent luminance uniformity could be obtained. In particular, in Example 33, sheets #16 with inverted pyramid-shaped recesses on the first side and matte surfaces with a surface roughness (Ra) of 8.0 μm were used as the first and second sheets, and sheet #10 with matte surfaces on both sides (without inverted pyramid-shaped recesses) was used as the third sheet, so that very excellent luminance and luminance uniformity could be obtained.

[0138] (Other embodiments) Although the embodiments of the present disclosure (including examples; the same applies below) have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the disclosure. In other words, the description of the above-described embodiments is essentially merely illustrative, and is not intended to limit the present disclosure, its applications, or its uses.

[0139] For example, the configuration (layer structure, materials, etc.) of the light diffusion sheet is not limited to the configuration of the first light diffusion sheet 43 of the above-mentioned embodiment, so long as it is a light diffusion sheet having "a plurality of recesses formed into an approximately inverted polygonal pyramid or an approximately inverted polygonal pyramid trapezoid on at least a first surface, the arrangement pitch of the recesses being 300 μm or more and 1500 μm or less, and the width of the boundary between the recesses being 25% or less of the arrangement pitch."

[0140] Furthermore, the configuration of the backlight to which the light diffusion sheet is applied and the liquid crystal display device including the backlight are not limited to the configuration of the backlight unit 40 or the liquid crystal display device 50 of the above-mentioned embodiment, so long as the backlight includes at least one light diffusion sheet "having, on at least a first surface, a plurality of recesses formed in a substantially inverted polygonal pyramid or a substantially inverted polygonal truncated pyramid shape, the arrangement pitch of the recesses being 300 μm or more and 1500 μm or less, and the width of the boundary between the recesses being 25% or less of the arrangement pitch." In other words, as long as the effect of the present invention is not impaired, other optical sheets having different structures can be used in appropriate combination as long as the backlight includes at least one light diffusion sheet of the present invention. For example, one light diffusion sheet "having, on its first surface, a plurality of depressions formed into an approximately inverted quadrangular pyramid shape, the arrangement pitch of the depressions being 300 μm or more and 1500 μm or less, and the width of the boundary between the depressions being 25% or less of the arrangement pitch" may be used in combination with one other light diffusion sheet "having, on its first surface, a plurality of depressions similar in shape to the depressions of the light diffusion sheet, and the arrangement pitch of the depressions being 300 μm or less." [Explanation of symbols]

[0141] 1 TFT substrate 2 CF board 3 Liquid crystal layer 5 Liquid crystal display panel 6 First polarizing plate 7 Second polarizing plate 21 Base material layer 22 Recess 22a center 23 Ridgeline 23a intersection 23b lowest point 40 Backlight unit 41 Reflective sheet 42 Light source 43 First light diffusion sheet 43a 1st page 43b 2nd side 44 Second light diffusion sheet 44a 1st page 44b 2nd side 45 First prism sheet 46 Second prism sheet 47 Brightness enhancing sheet 50 LCD display device 50a display screen

Claims

1. A backlight unit incorporated in a liquid crystal display device that guides light emitted from a light source toward a display screen, at least one light diffusion sheet is provided between the display screen and the light source; the light diffusion sheet has a plurality of recesses formed in the shape of a substantially inverted polygonal pyramid or a substantially inverted polygonal truncated pyramid on at least a first surface; the plurality of recesses are provided only on the first surface, the second surface of the light diffusion sheet is a flat surface or a matte surface, and further comprising at least one other light diffusion sheet between the display screen and the light source, the other light diffusion sheet not having a recess formed in the shape of a substantially inverted polygonal pyramid or a substantially inverted polygonal pyramid truncated shape; the other light diffusion sheet is disposed closer to the display screen than the light diffusion sheet, the light diffusion sheet is disposed so that a second surface opposite to the first surface faces the light source; the arrangement pitch of the plurality of recesses is 300 μm or more and 1500 μm or less; The width of the boundary between adjacent recesses in the plurality of recesses is 25% or less of the arrangement pitch. Backlight unit.

2. The arrangement pitch is 1000 μm or less. The backlight unit according to claim 1 .

3. an apex of a ridge line that defines the plurality of recesses has a curved portion; The width of the boundary is the width of the curved portion. The backlight unit according to claim 1 .

4. The plurality of recesses are formed in a substantially inverted quadrangular pyramid shape or a substantially inverted truncated quadrangular pyramid shape, The ridge line extends in a first direction and a second direction, the arrangement pitch is an average value of a first arrangement pitch of the plurality of recesses in the first direction and a second arrangement pitch of the plurality of recesses in the second direction, the width of the boundary portion is an average value of the width of the curved portion of the apex of the ridge line in the first direction and the width of the curved portion of the apex of the ridge line in the second direction; The backlight unit according to claim 3 .

5. an angle formed by the wall surfaces of the plurality of recesses and the sheet surface of the light diffusion sheet is equal to or greater than 40 degrees and equal to or less than 65 degrees; The backlight unit according to claim 1 .

6. the second surface of the light diffusion sheet is a matte surface having a surface roughness Ra of 0.1 μm or more and 10 μm or less; The backlight unit according to claim 1 .

7. A plurality of the light diffusion sheets are provided, the other light diffusion sheet is disposed between the display screen and the plurality of light diffusion sheets; Both surfaces of the other light diffusing sheet have a matte surface with a surface roughness Ra of 0.1 μm or more and 10 μm or less. The backlight unit according to claim 1 .

8. the difference in surface roughness Ra between both surfaces of the other light diffusion sheet is 0.5 μm or more; The surface of the other light diffusing sheet with the smaller surface roughness Ra is the light incident surface. The backlight unit according to claim 7 .

9. The other light-diffusing sheet contains 0.5 parts by mass or more and 1.5 parts by mass or less of a light-diffusing agent relative to 100 parts by mass of a matrix resin. The backlight unit according to claim 7 .

10. the other light diffusion sheet contains a light diffusing agent and is disposed so as to face the light output surface of the light diffusion sheet, The light emitting device further includes a brightness enhancement sheet disposed to face the light output surface of the second light diffusion sheet. The backlight unit according to claim 1 .

11. the second surface of the light diffusion sheet is a matte surface having a surface roughness Ra of 0.1 μm or more and 10 μm or less; Both surfaces of the other light diffusion sheet have a matte surface having a surface roughness Ra of 0.1 μm or more and 10 μm or less. The backlight unit according to claim 1 .

12. The backlight unit according to any one of claims 1 to 11, A liquid crystal display panel. LCD display device.

13. A liquid crystal display device comprising: Information equipment.

Images