Optical sheet laminate, backlight unit, liquid crystal display device and information device

Abstract

To provide an optical sheet laminate that is easy to manufacture and can improve luminance uniformity.SOLUTION: An optical sheet laminate 10 comprises a color conversion sheet 44 that converts a wavelength of light, and a plurality of light diffusion sheets 43 on which a plurality of recess parts 105 having a substantially inverted polygonal pyramid shape is provided. The color conversion sheet 44 is arranged below or above the plurality of light diffusion sheets 43, and the arrangement surface and arrangement direction of the plurality of recess parts 105 in the plurality of light diffusion sheets 43 are the same.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an optical sheet laminate, 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 adopted, a light diffusion sheet having, for example, an approximately inverted pyramidal recess is used in order to eliminate the image of a light source such as an LED (Light Emitting Diode) on the display screen and increase brightness uniformity (see Patent Document 1).

[0004] When a light source other than a white light source (eg, a blue light source) is used as the light source for the direct backlight, it is necessary to place a color conversion sheet that converts the wavelength of light between the light source and the display screen. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-117707 A Summary of the Invention [Problem to be solved by the invention]

[0006] Thin displays for laptops, tablet devices, and the like require a sheet stacking structure that is thin and has high brightness uniformity. However, because the arrangement of the light source and the relative positions of the various optical sheets vary from product to product, sufficient brightness uniformity cannot always be obtained with conventional sheet stacking structures for some products.

[0007] An object of the present disclosure is to provide an optical sheet laminate that is easy to fabricate and can improve brightness uniformity, as well as a backlight unit, a liquid crystal display device, and an information device that use the optical sheet laminate. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the optical sheet laminate according to the first aspect of the present disclosure is an optical sheet laminate incorporated in a backlight unit that guides light emitted from a plurality of point light sources to a display screen of a liquid crystal display device, and comprises a color conversion sheet that converts the wavelength of the light, and a plurality of light diffusion sheets that are laminated between the color conversion sheet and the display screen and have a plurality of recesses each having an approximately inverted polygonal pyramid shape, and the arrangement surfaces and arrangement directions of the recesses in the plurality of light diffusion sheets are the same.

[0009] According to the optical sheet laminate according to the first aspect of the present disclosure, since a plurality of light diffusion sheets each having a plurality of recesses each having a substantially inverted polygonal pyramid shape are laminated between a color conversion sheet and a display screen, it is possible to improve the luminance uniformity. In addition, since the arrangement surface and arrangement direction of the recesses in the plurality of light diffusion sheets are the same, it is easy to manufacture.

[0010] In the optical sheet laminate according to the first aspect of the present disclosure, the plurality of point light sources and the plurality of recesses may be arranged in a two-dimensional matrix, the plurality of recesses may be provided on the light output surfaces of the plurality of light diffusion sheets, and the arrangement direction of the plurality of point light sources and the arrangement direction of the plurality of recesses may intersect. In this manner, in a configuration in which a plurality of light diffusion sheets, each having a plurality of recesses of a substantially inverted polygonal pyramid shape arranged in a two-dimensional matrix, are stacked between a color conversion sheet and a display screen, the brightness uniformity can be further improved by providing recesses on the light output surface of each light diffusion sheet and intersecting the arrangement direction of the point light sources and the arrangement direction of the recesses.

[0011] In the optical sheet laminate according to the first aspect of the present disclosure, the plurality of point light sources and the plurality of recesses may be arranged in a two-dimensional matrix, the plurality of recesses may be provided on the light entrance surfaces of the plurality of light diffusion sheets, and the arrangement direction of the plurality of point light sources and the arrangement direction of the plurality of recesses may intersect. In this manner, in a configuration in which a plurality of light diffusion sheets, each having a plurality of recesses of a substantially inverted polygonal pyramid shape arranged in a two-dimensional matrix, are stacked between a color conversion sheet and a display screen, by providing recesses on the light entrance surface of each light diffusion sheet and intersecting the arrangement direction of the point light sources and the arrangement direction of the recesses, it is possible to improve brightness while improving brightness uniformity.

[0012] In order to achieve the above-mentioned object, an optical sheet laminate according to a second aspect of the present disclosure is an optical sheet laminate incorporated in a backlight unit that guides light emitted from a plurality of point light sources to the display screen side of a liquid crystal display device, and comprises a color conversion sheet that converts the wavelength of the light, and a plurality of light diffusion sheets that are laminated between the color conversion sheet and the plurality of point light sources and have a plurality of recesses each having an approximately inverted polygonal pyramid shape, and the arrangement surfaces and arrangement directions of the recesses in the plurality of light diffusion sheets are the same.

[0013] According to the optical sheet laminate according to the second aspect of the present disclosure, since a plurality of light diffusion sheets each having a plurality of recesses each having a substantially inverted polygonal pyramid shape are laminated between the color conversion sheet and a plurality of point light sources, it is possible to improve the luminance uniformity. In addition, since the arrangement surface and arrangement direction of the recesses in the plurality of light diffusion sheets are the same, it is easy to manufacture. In addition, compared to a configuration in which a plurality of light diffusion sheets are laminated between the color conversion sheet and the display screen, it is possible to separate the color conversion sheet from the plurality of point light sources, and therefore it is possible to suppress deterioration of the color conversion sheet caused by heat.

[0014] In the optical sheet laminate according to the second aspect of the present disclosure, the plurality of point light sources and the plurality of recesses may be arranged in a two-dimensional matrix, the plurality of recesses may be provided on the light entrance surfaces of the plurality of light diffusion sheets, and the arrangement direction of the plurality of point light sources and the arrangement direction of the plurality of recesses may intersect. In this manner, in a configuration in which a plurality of light diffusion sheets, each having a plurality of recesses of a substantially inverted polygonal pyramid shape arranged in a two-dimensional matrix, are stacked between a color conversion sheet and a plurality of point light sources, the luminance uniformity can be further improved by providing a recess on the light entrance surface of each light diffusion sheet and intersecting the arrangement direction of the point light sources and the arrangement direction of the recesses.

[0015] In the optical sheet laminate according to the second aspect of the present disclosure, the plurality of point light sources and the plurality of recesses may be arranged in a two-dimensional matrix, and the plurality of recesses may be provided on the light output surfaces of the plurality of light diffusion sheets. In this manner, in a configuration in which a plurality of light diffusion sheets, each having a plurality of recesses of a substantially inverted polygonal pyramid shape provided in a two-dimensional matrix, are stacked between a color conversion sheet and a plurality of point light sources, by providing recesses on the light output surface of each light diffusion sheet, it is possible to improve the luminance while improving the luminance uniformity.

[0016] In the optical sheet laminate according to the first or second aspect of the present disclosure, when a brightness enhancing sheet, for example a prism sheet, is provided closer to the display screen than the color conversion sheet and the plurality of light diffusion sheets, the brightness can be improved while improving the brightness uniformity. In this case, when another light diffusion sheet, for example an upper light diffusion sheet, is provided closer to the display screen than the brightness enhancing sheet, the brightness unevenness caused by the arrangement of the brightness enhancing sheet can be suppressed.

[0017] The backlight unit according to the present disclosure is a backlight unit for directing light emitted from a plurality of point light sources to a display screen of a liquid crystal display device, and includes the light diffusion sheet according to the first or second aspect of the present disclosure between the display screen and the plurality of point light sources. The plurality of point light sources may be, for example, blue light sources.

[0018] The backlight unit according to the present disclosure includes the light diffusion sheet according to the first or second aspect of the present disclosure described above, and therefore can improve luminance uniformity and is easy to manufacture.

[0019] 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.

[0020] 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 and the display device is easy to manufacture.

[0021] An information device according to the present disclosure includes the liquid crystal display device according to the present disclosure described above.

[0022] According to the information device according to the present disclosure, since it includes the liquid crystal display device according to the present disclosure described above, it is possible to improve the luminance uniformity and the device is easy to manufacture. Effect of the Invention

[0023] According to the present disclosure, it is possible to provide an optical sheet laminate that is easy to fabricate and can improve brightness uniformity, as well as a backlight unit, a liquid crystal display device, and an information device that use the optical sheet laminate. [Brief description of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view of a liquid crystal display device according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a cross-sectional configuration of a backlight unit according to the embodiment. [Diagram 3] FIG. 13 is a diagram showing a cross-sectional configuration of a backlight unit according to a modified example. [Figure 4] FIG. 2 is a diagram showing a cross-sectional configuration of a light diffusion sheet included in the optical sheet laminate according to the embodiment. [Diagram 5] FIG. 2 is a diagram showing a cross-sectional configuration of a light diffusion sheet included in the optical sheet laminate according to the embodiment. [Figure 6]FIG. 2 is a perspective view of a light diffusing sheet included in the optical sheet laminate according to the embodiment, as viewed from a surface on which recesses are provided. [Figure 7] 4A and 4B are diagrams showing a planar configuration and a cross-sectional configuration of a recess provided in a light diffusing sheet included in the optical sheet laminate according to the embodiment. [Figure 8] 1A and 1B are diagrams showing the relationship between the arrangement direction of light sources and the arrangement direction of recesses of a light diffusion sheet in a backlight unit according to an embodiment, where (a) shows the arrangement of the light sources and (b) shows the arrangement of the recesses. [Figure 9] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness for an optical sheet laminate in which a color conversion sheet is placed on top of a light diffusion sheet and an inverted pyramid-shaped recess is placed on the light exit surface of the light diffusion sheet. [Figure 10] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness for an optical sheet laminate in which a color conversion sheet is placed on top of a light diffusion sheet and an inverted pyramid-shaped recess is placed on the light entrance surface of the light diffusion sheet. [Figure 11] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness uniformity for an optical sheet laminate in which a color conversion sheet is arranged on the upper side of a light diffusion sheet and an inverted pyramid-shaped recess is arranged on the light exit surface of the light diffusion sheet. [Figure 12] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness uniformity for an optical sheet laminate in which a color conversion sheet is placed on top of a light diffusion sheet and an inverted pyramid-shaped recess is placed on the light entrance surface of the light diffusion sheet. [Figure 13] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness for an optical sheet laminate in which a color conversion sheet is arranged below the light diffusion sheet and an inverted pyramid-shaped recess is arranged on the light exit surface of the light diffusion sheet. [Figure 14] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness for an optical sheet laminate in which a color conversion sheet is arranged below the light diffusion sheet and an inverted pyramid-shaped recess is arranged on the light entrance surface of the light diffusion sheet. [Figure 15] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness uniformity for an optical sheet laminate in which a color conversion sheet is arranged below the light diffusion sheet and an inverted pyramid-shaped recess is arranged on the light exit surface of the light diffusion sheet. [Figure 16] This figure shows the results of an investigation into the relationship between the angle of the recess array relative to the light source array and the brightness uniformity for an optical sheet laminate in which a color conversion sheet is arranged below the light diffusion sheet and an inverted pyramid-shaped recess is arranged on the light entrance surface of the light diffusion sheet. [Figure 17] 13 is a diagram showing a cross-sectional configuration of a light diffusion sheet included in an optical sheet laminate according to a modified example. FIG. [Figure 18] 13 is a diagram showing a cross-sectional configuration of a light diffusion sheet included in an optical sheet laminate according to a modified example. FIG. [Figure 19] 19A and 19B show the relationship between the arrangement direction of the recesses and the extension direction of the linear structures in the light diffusion sheet shown in FIG. 17 or FIG. 18, where (a) shows the case where the directions are aligned, and (b) shows the case where the directions intersect at 45°. [Figure 20] 19A and 19B are cross-sectional views showing variations of the linear structure provided on the light diffusion sheet shown in FIG. 17 or FIG. 18, where (a) shows the case where the linear structure forms a hairline, (b) shows the case where the linear structure forms a lenticular, and (c) shows the case where the linear structure forms a diffraction grating.

[0025] (Embodiment) Hereinafter, the optical sheet laminate, the backlight unit, the liquid crystal display device, and the information device according to the embodiment will be described with reference to the drawings. The scope of the present disclosure is not limited to the following embodiments, and can be changed as desired within the scope of the technical idea of ​​the present disclosure. In addition, since each drawing is intended to conceptually explain the present disclosure, dimensions, ratios, or numbers may be exaggerated or simplified as necessary for easy understanding.

[0026] <Liquid crystal display device> FIG. 1 is an example of a cross-sectional view of a liquid crystal display device according to this embodiment.

[0027] 1, a liquid crystal display device 50 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.

[0028] 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.

[0029] 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.

[0030] 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, personal digital assistants, portable game machines, copy machines, ticket vending machines, automated teller machines, etc.).

[0031] 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.

[0032] <Backlight unit> FIG. 2 shows a first example of the cross-sectional configuration of a backlight unit 40 according to this embodiment.

[0033] 2, the backlight unit 40 includes a reflection sheet 41, a plurality of point light sources 42 arranged two-dimensionally on the reflection sheet 41, and an optical sheet laminate 10 provided above the plurality of point light sources 42. The optical sheet laminate 10 includes a color conversion sheet 44 provided above the plurality of point light sources 42, a plurality of light diffusion sheets 43 provided above the color conversion sheet 44, a first prism sheet 45 and a second prism sheet 46 provided in this order above the plurality of light diffusion sheets 43, and an upper light diffusion sheet 47 provided above the second prism sheet 46.

[0034] In the example shown in FIG. 2, the light diffusion sheet 43 is provided in the backlight unit 40 by stacking three layers, but the light diffusion sheet 43 may be used in a single layer, or may be used by stacking two layers or four or more layers.

[0035] The reflective sheet 41 is made of, for example, a white polyethylene terephthalate resin film, a silver vapor deposition film, or the like.

[0036] The type of the point light source 42 is not particularly limited, but 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. In the example shown in FIG. 2, a blue LED element is used as the point light source 42. The blue LED element emits light with, for example, x<0.24 and y<0.18 in the chromaticity coordinates of CIE1931. The point light source 42 may have a rectangular shape when viewed in a plan view, and in this 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). When an LED element is used as the point light source 42, a plurality of LED elements may be arranged on the reflecting sheet 41 at regular intervals. In order to adjust the light output angle characteristic of the LED element that becomes the point light source 42, a lens may be attached to the LED element. The number of point light sources 42 to be arranged is not particularly limited, but when a plurality of point light sources 42 are arranged in a distributed manner, it is preferable to arrange them regularly on the reflecting sheet 41. Arranging them regularly means arranging them with a certain rule, and corresponds to, for example, the case where the point light sources 42 are arranged at equal intervals. When the point light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent point light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0037] The color conversion sheet 44 is a wavelength conversion sheet that converts light from the point light source 42 (blue light in the example shown in FIG. 2) into light having a peak wavelength of any color (e.g., green or red). For example, the color conversion sheet 44 converts blue light of a wavelength of 450 nm into green light of a wavelength of 540 nm and red light of a wavelength of 650 nm. In this case, if a point light source 42 that emits blue light of a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet 44, and the light transmitted through the color conversion sheet 44 becomes white light. For example, a QD (quantum dot) sheet, a fluorescent sheet, or the like may be used as the color conversion sheet 44.

[0038] The light diffusion sheet 43 diffuses the light incident from the point light source 42 and emits it. The matrix resin constituting the light diffusion sheet 43 is not particularly limited as long as it is made of a material that transmits light, and may be, for example, polycarbonate, acrylic, polystyrene, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. The thickness of the light diffusion sheet 43 is also not particularly limited, and may be, for example, 50 μm or more and 3 mm or less. If the thickness of the light diffusion sheet 43 exceeds 3 mm, it becomes difficult to achieve a thin liquid crystal display, while if the thickness of the light diffusion sheet 43 is less than 50 μm, it becomes difficult to obtain a sufficient light diffusion effect. As shown in FIG. 2, when a plurality of light diffusion sheets 43 are laminated, the total thickness of the laminated sheets may be about several hundred μm to several mm. The light diffusion sheet 43 may be in the form of a film or a plate (plate). The detailed configuration and manufacturing method of the light diffusion sheet 43 will be described later.

[0039] The first prism sheet 45 and the second prism sheet 46 are brightness improving sheets that refract the light beam incident from the light diffusion sheet 43 toward the normal direction. For example, a plurality of grooves having an isosceles triangular cross section are provided adjacent to each other on the light exit surface side of each of the prism sheets 45 and 46, and a prism is formed by a triangular prism portion sandwiched between a pair of adjacent grooves. The apex angle of the prism is, for example, about 90°. The grooves formed in the first prism sheet 45 and the grooves formed in the second prism sheet 46 may be arranged so as to be perpendicular to each other. In this way, the light beam incident from the light diffusion sheet 43 can be refracted toward the normal direction by the first prism sheet 45, and the light beam emitted from the first prism sheet 45 can be refracted by the second prism sheet 45 so as to proceed approximately perpendicular to the light entrance surface of the upper light diffusion sheet 47. The prism sheets 45 and 46 may be laminated separately, or may be formed integrally. The total thickness of the prism sheets 45 and 46 may be, for example, about 100 to 400 μm. The prism sheets 45 and 46 may be, for example, a PET (polyethylene terephthalate) film having a prism shape formed thereon by using a UV-curable acrylic resin.

[0040] In addition, instead of the prism sheets 45 and 46, a single-layer prism sheet may be used as the brightness enhancing sheet, or another type of optical sheet capable of increasing the brightness of the light emitted from the point light source 42 may be used.

[0041] The upper light diffusion sheet 47 diffuses the light rays incident from the second prism sheet 46 side to some extent, suppressing the luminance unevenness caused by the shape of the prism parts of the prism sheets 45 and 46. The upper light diffusion sheet 47 may be directly laminated on the surface of the second prism sheet 46. The thickness of the light diffusion sheet 47 is not particularly limited, but for example, it may be 50 μm or more and 3 mm or less. When the thickness of the upper light diffusion sheet 47 exceeds 3 mm, it becomes difficult to achieve the thinning of the liquid crystal display. On the other hand, when the thickness of the upper light diffusion sheet 47 is less than 50 μm, it becomes difficult to obtain a sufficient light diffusion effect. The upper light diffusion sheet 47 may be in the form of a film or a plate (sheet). The upper light diffusion sheet 47 may have a configuration including a base material layer and a light diffusion layer laminated on the light emitting surface of the base material layer and having a resin matrix and resin beads. Alternatively, as the upper light diffusion sheet 47, for example, a PET film with an uneven shape formed by using a UV-curable acrylic resin on at least one surface may be used.

[0042] <Modification example of the backlight unit> In the optical sheet laminate 10 of the backlight unit 40 shown in FIG. 2, a color conversion sheet 44 is provided below the light diffusion sheet 43, specifically, between the lowermost light diffusion sheet 43 and the plurality of point light sources 42. Instead of this, as in the optical sheet laminate 10 of the backlight unit 40 shown in FIG. 3, a color conversion sheet 44 may be provided above the light diffusion sheet 43, specifically, between the uppermost light diffusion sheet 43 and the first prism sheet 45.

[0043] In addition, in the configuration example of the backlight unit 40 shown in FIGS. 2 and 3, a blue light source is used as the point light source 42 and the color conversion sheet 44 is used. Instead of this, a configuration may be adopted in which a white light source is used as the point light source 42 and the color conversion sheet 44 is not arranged. In this case, the upper light diffusion sheet 47 may not be arranged either. The white light source is composed of an LED element with a peak wavelength in the blue region, an LED element with a peak wavelength in the green region, and an LED element with a peak wavelength in the red region, and may emit light with, for example, 0.24 < x < 0.42 and 0.18 < y < 0.48 in the chromaticity coordinates of CIE1931.

[0044] <Light diffusion sheet> As shown in FIG. 4 or FIG. 5, the light diffusion sheet 43 mainly includes a base layer 101 and a light diffusion layer 102 provided on the base layer 101. The light diffusion sheet 43 has a first surface (surface of the base layer 101) 101a which is one of the light entrance surface and the light exit surface, and a second surface (surface of the light diffusion layer 102) 102a which is the other of the light entrance surface and the light exit surface. The light diffusion layer 102 is provided with a plurality of recesses 105 having an uneven shape that diffuses light, for example, a substantially inverted pyramid shape (a substantially inverted quadrangular pyramid shape (inverted pyramid shape)). The first surface 101a of the light diffusion sheet 43 may be, for example, a matte surface or a flat surface.

[0045] Incidentally, FIG. 4 shows a case where the light diffusion sheet 43 is arranged so that the first surface 101a is the light entrance surface and the second surface 102a is the light exit surface, and FIG. 5 shows a case where the light diffusion sheet 43 is arranged so that the first surface 101a is the light exit surface and the second surface 102a is the light entrance surface.

[0046] The base layer 101 is formed mainly from a transparent (e.g., colorless and transparent) synthetic resin, since it is necessary to transmit light. The main component of the base layer 101 is not particularly limited, and may be, for example, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polystyrene, polyolefin, cellulose acetate, weather-resistant vinyl chloride, or the like. The term "main component" refers to the component with the highest content, for example, a component with a content of 50 mass % or more. The base layer 101 may contain a diffusing agent or other additives, or may substantially not contain additives. The additives that can be contained are not particularly limited, and may be, for example, inorganic particles such as silica, titanium oxide, aluminum hydroxide, barium sulfate, or organic particles such as acrylic, acrylonitrile, silicone, polystyrene, polyamide, or the like.

[0047] The lower limit of the average thickness of the base layer 101 is preferably about 10 μm, more preferably about 35 μm, and even more preferably about 50 μm. The upper limit of the average thickness of the base layer 101 is preferably about 500 μm, more preferably about 250 μm, and even more preferably about 180 μm. If the average thickness of the base layer 101 is less than the lower limit, curling may occur when the diffusion layer 102 is formed. Conversely, if the average thickness of the base layer 101 exceeds the upper limit, the brightness of the liquid crystal display device 50 may decrease, and the liquid crystal display device 50 may not meet the demand for a thinner thickness. The "average thickness" refers to the average value of thicknesses at any 10 points.

[0048] Since the light diffusion layer 102 needs to transmit light rays, it may be formed mainly from a transparent (e.g., colorless and transparent) synthetic resin. The light diffusion layer 102 may be molded integrally with the base material layer 101 during extrusion molding of the base material resin that becomes the base material layer 101, or may be molded separately using an ultraviolet curing resin after molding of the base material layer 101.

[0049] The plurality of recesses 105, each having a substantially inverted quadrangular pyramid shape (inverted pyramid shape) provided on the light diffusion layer 102 (the second surface 102a of the light diffusion sheet 43), may be arranged in a two-dimensional matrix, for example, as shown in FIG. 6. In other words, the plurality of recesses 105 may be arranged along two directions perpendicular to each other. Adjacent recesses 105 are partitioned by ridge lines 111. The ridge lines 111 extend along the two directions in which the recesses 105 are arranged. The arrangement pitch of the recesses 105 may be, for example, not less than about 50 μm and not more than about 500 μm. The center 112 (the apex of the inverted pyramid) of the recess 105 is the deepest part of the recess 105. The center (deepest part) 112 of the recess 105 may reach the surface (light output surface) of the base layer 101. In other words, the depth of the recess 105 may be equal to the thickness of the light diffusion layer 102. For simplicity, FIG. 6 illustrates an example in which the recesses 105 are arranged in a 5×5 matrix, but the actual number of recesses 105 arranged is much greater.

[0050] The apex angle θ of the recess 105 is set to, for example, about 90°. The apex angle θ of the recess 105 is an angle formed by the inclined surfaces of the recess 105 in a cross section (lower view of FIG. 7) that appears when the recess 105 is cut in a plane (longitudinal cross section) perpendicular to the placement surface (horizontal plane) of the light diffusion sheet 43, passing through the apex 112 of the inverted pyramid and vertically crossing a pair of ridge lines 111 that face each other across the apex 112, as shown in FIG. 7. The upper view of FIG. 7 shows the planar configuration of the recess 105. In FIG. 7, "H" indicates the depth of the recess 105 (height of the pyramid shape), and "P" indicates the horizontal width of the recess 105 (i.e., the arrangement pitch of the recess 105). The depth H of the recess 105 is determined by the arrangement pitch P of the recess 105 and the apex angle θ of the recess 105.

[0051] When a plurality of point light sources 42 are arranged in a square as shown in Fig. 8(a), the arrangement direction of the recesses 105 may be tilted by, for example, about 45° with respect to the arrangement direction of the point light sources 42 as a reference as shown in Fig. 8(b). When the recesses 105 are formed in an inverted pyramid shape, by intersecting the arrangement direction of the point light sources 42 and the arrangement direction of the recesses 105, it is possible to improve the luminance uniformity more than by aligning both arrangement directions.

[0052] In this embodiment, the concave and convex shapes are provided by arranging the concaves 105 in an inverted pyramid shape (approximately inverted square pyramid shape) in a two-dimensional matrix, but the concaves 105 may be arranged randomly to the extent that the effect of the present invention is not lost. When the concaves 105 are arranged regularly in two dimensions, gaps may be provided between the concaves 105, or may not be provided. The concaves 105 may have another approximately inverted polygonal pyramid shape different from the approximately inverted square pyramid shape. For example, the "inverted polygonal pyramid" shape of the concaves 105 may be an inverted triangular pyramid or an inverted hexagonal pyramid that can be arranged two-dimensionally without gaps like an inverted square pyramid. When the "inverted polygonal pyramid" shape of the concaves 105 is an inverted square pyramid, it is easy to improve the accuracy of the surface cutting work of the mold (metal roll) used in the manufacturing process such as extrusion molding or injection molding when providing the concaves 105.

[0053] In addition, in this disclosure, in consideration of the difficulty of forming a geometrically strict inverted polygonal pyramid recess by a normal shape transfer technology, the term "approximately inverted polygonal pyramid" is used, but the term "approximately inverted polygonal pyramid" includes shapes that can be regarded as genuine or substantially inverted polygonal pyramids. Furthermore, "approximately" means that it can be approximated, and for example, "approximately inverted square pyramid" refers to a shape that can be approximated to an inverted square pyramid. For example, "inverted polygonal pyramid truncated" with a flat apex is also included in the "approximately inverted polygonal pyramid" if the apex area is small enough that the effect of the present invention is not lost. Furthermore, shapes that are deformed from the "inverted polygonal pyramid" within the range of unavoidable shape variations due to the processing accuracy of industrial production are also included in the "approximately inverted polygonal pyramid".

[0054] <Manufacturing method of light diffusion sheet> The method for producing the light diffusion sheet 43 is not particularly limited, but for example, the light diffusion sheet 43 can be produced using any of the following production methods.

[0055] In the first manufacturing method, first, a pellet-shaped base resin (plastic resin) is made into a resin film by an extrusion molding machine. Then, one of two metal rolls is used, one of which has a convex pyramid shape on its surface, and the other roll is used, one of which has a flat shape or an inverted shape of a matte surface on its surface, and both rolls are pressed against the resin film to produce a light diffusion sheet 43 having an inverted pyramid shape (concave 105) on one side and a flat or matte surface on the other side. In this manufacturing method, the base layer 101 and the light diffusion layer 102 are integrally formed.

[0056] In the second manufacturing method, first, a base layer 101 mainly composed of, for example, polyethylene terephthalate is prepared. While sending this base layer 101 between a pair of pressing rolls, an ultraviolet curable resin (a resin composition for forming protrusions) is supplied to one surface of the base layer 101 immediately before the pair of pressing rolls. A pressing roll having a plurality of substantially square pyramid-shaped convex portions on its outer circumferential surface is used as the pressing roll that contacts the ultraviolet curable resin. After pressing the base layer 101 to which the ultraviolet curable resin has been supplied with the ultraviolet curable resin between the pair of pressing rolls, the ultraviolet curable resin is cured by irradiating it with ultraviolet light, and a plurality of inverted pyramid shapes (concave portions 105), which are the inverted shapes of the plurality of substantially square pyramid-shaped convex portions, are transferred to produce a light diffusion sheet 43 in which a light diffusion layer 102 is provided on one surface of the base layer 101. In this manufacturing method, the base layer 101 and the light diffusion layer 102 are formed separately.

[0057] <Features of the embodiment (including modified examples)> 2, the optical sheet laminate 10 of the backlight unit 40 of the embodiment shown in FIG. 2 has a plurality of light diffusion sheets 43, each having a plurality of recesses 105 each having a substantially inverted polygonal pyramid shape, laminated on the upper side of the color conversion sheet 44 (specifically, between the color conversion sheet 44 and the first prism sheet 45), thereby improving the luminance uniformity. By making the arrangement surface and arrangement direction of the recesses 105 of the plurality of light diffusion sheets 43 the same, the optical sheet laminate 10 can be easily produced.

[0058] In the optical sheet laminate 10 of the backlight unit 40 of the embodiment shown in Fig. 2, the plurality of point light sources 42 and the plurality of recesses 105 are arranged in a two-dimensional matrix, the plurality of recesses 105 are provided on the light output surfaces of the plurality of light diffusion sheets 43, and the arrangement direction of the plurality of point light sources 42 and the arrangement direction of the plurality of recesses 105 may cross. In this manner, in a configuration in which a plurality of light diffusion sheets 43, each having a plurality of recesses 105 of a substantially inverted polygonal pyramid shape arranged in a two-dimensional matrix, are laminated on the upper side of the color conversion sheet 44, the recesses 105 are provided on the light output surface of each light diffusion sheet 43, and the arrangement direction of the point light sources 42 and the arrangement direction of the recesses 105 cross each other, the luminance uniformity can be further improved.

[0059] In the optical sheet laminate 10 of the backlight unit 40 of the embodiment shown in Fig. 2, the plurality of point light sources 42 and the plurality of recesses 105 are arranged in a two-dimensional matrix, the plurality of recesses 105 are provided on the light entrance surfaces of the plurality of light diffusion sheets 43, and the arrangement direction of the plurality of point light sources 42 and the arrangement direction of the plurality of recesses 105 may cross. In this manner, in a configuration in which a plurality of light diffusion sheets 43, each having a plurality of recesses 105 of a substantially inverted polygonal pyramid shape arranged in a two-dimensional matrix, are laminated on the upper side of the color conversion sheet 44, the recesses 105 are provided on the light entrance surface of each light diffusion sheet 43, and the arrangement direction of the point light sources 42 and the arrangement direction of the recesses 105 cross each other, it is possible to improve the brightness while improving the brightness uniformity.

[0060] 3, the optical sheet laminate 10 of the backlight unit 40 of the modified example shown in FIG. 3 has a plurality of light diffusion sheets 43, each having a plurality of recesses 105 each having a substantially inverted polygonal pyramid shape, laminated between the color conversion sheet 44 and the plurality of point light sources 42, thereby improving the luminance uniformity. Here, by making the arrangement surface and arrangement direction of the recesses 105 of the plurality of light diffusion sheets 43 the same, the optical sheet laminate 10 can be easily produced.

[0061] In the optical sheet laminate 10 of the backlight unit 40 of the modified example shown in Fig. 3, the multiple point light sources 42 and the multiple recesses 105 are arranged in a two-dimensional matrix, the multiple recesses 105 are provided on the light entrance surfaces of the multiple light diffusion sheets 43, and the arrangement direction of the multiple point light sources 42 and the arrangement direction of the multiple recesses 105 may cross. In this manner, in a configuration in which multiple light diffusion sheets 43, each having a multiple recesses 105 of a substantially inverted polygonal pyramid shape arranged in a two-dimensional matrix, are laminated between the color conversion sheet 44 and the multiple point light sources 42, the luminance uniformity can be further improved by providing the recesses 105 on the light entrance surface of each light diffusion sheet 43 and crossing the arrangement direction of the point light sources 42 and the arrangement direction of the recesses 105.

[0062] 3, the optical sheet laminate 10 of the backlight unit 40 of the modified example shown in FIG. 3 may have the multiple point light sources 42 and the multiple recesses 105 arranged in a two-dimensional matrix, and the multiple recesses 105 may be provided on the light output surfaces of the multiple light diffusion sheets 43. In this manner, in a configuration in which multiple light diffusion sheets 43, each having a multiple number of recesses 105 of a substantially inverted polygonal pyramid shape provided in a two-dimensional matrix, are stacked between the color conversion sheet 44 and the multiple point light sources 42, by providing the recesses 105 on the light output surface of each light diffusion sheet 43, it is possible to improve the luminance while improving the luminance uniformity.

[0063] In the optical sheet laminate 10 of the backlight unit 40 of the embodiment shown in Fig. 2 or the optical sheet laminate 10 of the backlight unit 40 of the modified example shown in Fig. 3, the brightness can be improved while improving the brightness uniformity by providing a brightness improving sheet, for example, prism sheets 45, 46, above (close to the display screen 50a) the color conversion sheet 44 and the plurality of light diffusion sheets 43. In this case, by providing another light diffusion sheet, for example, upper light diffusion sheet 47, above (close to the display screen 50a) the brightness improving sheet, the brightness unevenness caused by the arrangement of the brightness improving sheet can be suppressed.

[0064] The backlight unit 40 of the embodiment or the modified example guides light emitted from a plurality of point light sources 42 to a display screen 50a of a liquid crystal display device. The backlight unit 40 includes the optical sheet laminate 10 described above between the display screen 50a and the point light sources 42. This makes it possible to improve the luminance uniformity and facilitates fabrication. The plurality of point light sources 42 may be, for example, blue light sources.

[0065] In the backlight unit 40 of the embodiment or the modified example, the multiple point light sources 42 may be disposed on the reflecting sheet 41 provided on the opposite side of the display screen 50a as viewed from the light diffusion sheet 43. In this way, the light is further diffused by multiple reflections between the light diffusion sheet 43 and the reflecting sheet 41, so that the luminance uniformity is further improved.

[0066] The liquid crystal display device 50 of the embodiment includes the backlight unit 40 of the embodiment or the modified example, and the liquid crystal display panel 5. Therefore, it is possible to improve the luminance uniformity and to easily manufacture the liquid crystal display device 50. The same effect can be obtained in information devices (personal computers, mobile phones, etc.) incorporating the liquid crystal display device 50 of the embodiment.

[0067] (Example) The results of evaluation of the luminance and luminance uniformity for examples of the optical sheet laminate 10 will be described below.

[0068] The evaluation of luminance and luminance uniformity was carried out using the backlight configuration shown in FIG. 2 or FIG.

[0069] Specifically, as the plurality of light sources 42, an LED array in which blue LED elements are arranged in a square (pitch: approximately 2.8 mm×approximately 2.8 mm) is used.

[0070] As the light diffusion sheet 43, two types of sample A were used: sample A in which the first surface 101a of a 95 μm thick polycarbonate sheet was a matte surface and the second surface 102a had inverted pyramidal recesses 105 with a depth of 50 μm and an apex angle of 90° arranged in a two-dimensional matrix with a pitch of 100 μm; and sample B in which the first surface 101a of a 112 μm thick polycarbonate sheet was a matte surface and the second surface 102a had inverted pyramidal recesses 105 with a depth of 50 μm and an apex angle of 90° arranged in a two-dimensional matrix with a pitch of 100 μm.

[0071] The color conversion sheet 44 is a QD (Quantum Dot) sheet.

[0072] The first prism sheet 45 was a 91 μm thick PET film with prisms of 12 μm height and 90° apex angle transferred using UV curable resin. The second prism sheet 46 was a 153 μm thick PET film with prisms of 25 μm height and 90° apex angle transferred using UV curable resin. The first prism sheet 45 and the second prism sheet 46 were arranged so that their prisms were perpendicular to each other and the prisms of the second prism sheet 46 formed an angle of 40° with the arrangement direction of the light sources 42.

[0073] The upper light diffusion sheet 47 was a PET film having a thickness of 138 μm and having been subjected to bead coating.

[0074] In the configuration described above, a transparent glass plate was placed on the upper light diffusion sheet 47 to prevent the sheets from floating, and the luminance and luminance uniformity were evaluated as follows. First, the luminance (cd m 2 ) was measured. Next, the obtained two-dimensional luminance distribution image was corrected for variations in the emission intensity of each LED, and a filtering process was performed to suppress bright and dark spot noise caused by foreign matter, after which the average value and standard deviation of the luminance of all pixels were calculated. Finally, the luminance and luminance uniformity were calculated by defining "luminance" as the "average value of luminance" and "luminance uniformity" as the "average value of luminance / standard deviation of luminance."

[0075] 9 shows the results of investigating the relationship between the intersection angle of the arrangement direction of the recesses 105 with the arrangement direction of the point light sources 42 (hereinafter referred to as the arrangement angle of the recesses 105) and the brightness when the recesses 105 are arranged on the light output surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 3 (configuration in which the color conversion sheet 44 is arranged above the light diffusion sheet 43). The arrangement angle of the recesses 105 is the angle obtained by rotating the light diffusion sheet 43 counterclockwise from a state in which the arrangement directions of the point light sources 42 and the recesses 105 are aligned.

[0076] FIG. 10 shows the results of an investigation into the relationship between the angle of the recesses 105 and the brightness when the recesses 105 are arranged on the light entrance surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 3 (a configuration in which the color conversion sheet 44 is arranged above the light diffusion sheet 43).

[0077] 9 and 10, the dashed line indicates the results when sample A of light diffusion sheet 43 is used, and the solid line indicates the results when sample B of light diffusion sheet 43 is used. The luminance is shown as a relative luminance with the luminance when the recesses 105 are arranged on the light output surface of sample A of light diffusion sheet 43 at an arrangement angle of 0° being taken as 100%.

[0078] 9 and 10, in a configuration in which the color conversion sheet 44 is disposed above the light diffusion sheet 43, the luminance was higher when the recesses 105 were provided on the light exit surface of each light diffusion sheet 43 than when the recesses 105 were provided on the light entrance surface of each light diffusion sheet 43. Moreover, the arrangement angle of the recesses 105 had almost no effect on the luminance.

[0079] FIG. 11 shows the results of an investigation into the relationship between the angle at which recesses 105 are arranged and brightness uniformity when recesses 105 are arranged on the light-emitting surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 3 (a configuration in which a color conversion sheet 44 is arranged above the light diffusion sheet 43).

[0080] FIG. 12 shows the results of an investigation into the relationship between the angle at which recesses 105 are arranged and brightness uniformity when recesses 105 are arranged on the light entrance surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 3 (a configuration in which a color conversion sheet 44 is arranged above the light diffusion sheet 43).

[0081] 11 and 12, the results when sample A of the light diffusion sheet 43 is used are shown by dashed lines, and the results when sample B of the light diffusion sheet 43 is used are shown by solid lines.

[0082] 11 and 12, in a configuration in which the color conversion sheet 44 is disposed above the light diffusion sheet 43, the luminance uniformity is higher when the recesses 105 are provided on the light entrance surface of each light diffusion sheet 43 than when the recesses 105 are provided on the light exit surface of each light diffusion sheet 43. In addition, the luminance uniformity is dependent on the arrangement angle of the recesses 105, and the luminance uniformity tends to increase when the arrangement angle of the recesses 105 is from 0° to 45°, and tends to decrease when the arrangement angle of the recesses 105 is from 45° to 90°. In other words, it was found that the luminance uniformity is further improved by intersecting the arrangement direction of the point light sources 42 and the arrangement direction of the recesses 105.

[0083] FIG. 13 shows the results of an investigation into the relationship between the angle at which recesses 105 are arranged and brightness when recesses 105 are arranged on the light output surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 2 (a configuration in which a color conversion sheet 44 is arranged below the light diffusion sheet 43).

[0084] FIG. 14 shows the results of an investigation into the relationship between the angle of the recesses 105 and the brightness when the recesses 105 are arranged on the light entrance surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 2 (a configuration in which the color conversion sheet 44 is arranged below the light diffusion sheet 43).

[0085] 13 and 14, the results when sample A of light diffusion sheet 43 was used are shown by dashed lines, and the results when sample B of light diffusion sheet 43 was used are shown by solid lines. The luminance is shown as a relative luminance when the recesses 105 are arranged at an arrangement angle of 0° on the light output surface of sample A of light diffusion sheet 43 in the backlight configuration shown in FIG. 3 (configuration in which color conversion sheet 44 is arranged above light diffusion sheet 43) is set to 100%.

[0086] As shown in Fig. 13 and Fig. 14, in the configuration in which the color conversion sheet 44 is disposed under the light diffusion sheet 43, the luminance is higher when the recesses 105 are provided on the light entrance surface of each light diffusion sheet 43 than when the recesses 105 are provided on the light exit surface of each light diffusion sheet 43. In addition, the luminance is dependent on the arrangement angle of the recesses 105, and when the recesses 105 are provided on the light entrance surface of each light diffusion sheet 43, the luminance tends to increase when the arrangement angle of the recesses 105 is 0° to 30°, the luminance is approximately constant when the arrangement angle is 30° to 60°, and the luminance tends to decrease when the arrangement angle is 60° to 90°. In other words, it was found that when the recesses 105 are provided on the light entrance surface of each light diffusion sheet 43, the luminance is further improved by intersecting the arrangement direction of the point light sources 42 and the arrangement direction of the recesses 105.

[0087] FIG. 15 shows the results of an investigation into the relationship between the angle at which recesses 105 are arranged and brightness uniformity when recesses 105 are arranged on the light-emitting surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 2 (a configuration in which a color conversion sheet 44 is arranged below the light diffusion sheet 43).

[0088] FIG. 16 shows the results of an investigation into the relationship between the angle at which the recesses 105 are arranged and the brightness uniformity when the recesses 105 are arranged on the light entrance surface of each light diffusion sheet 43 in the backlight configuration shown in FIG. 2 (a configuration in which the color conversion sheet 44 is arranged below the light diffusion sheet 43).

[0089] 15 and 16, the results when sample A of the light diffusion sheet 43 is used are shown by dashed lines, and the results when sample B of the light diffusion sheet 43 is used are shown by solid lines.

[0090] As shown in Fig. 15 and Fig. 16, in the configuration in which the color conversion sheet 44 is disposed under the light diffusion sheet 43, the luminance uniformity is higher when the recesses 105 are provided on the light exit surface of each light diffusion sheet 43 than when the recesses 105 are provided on the light entrance surface of each light diffusion sheet 43. In addition, when the recesses 105 are provided on the light exit surface of the light diffusion sheet 43, the luminance uniformity depends on the arrangement angle of the recesses 105. When the recesses 105 are provided on the light exit surface of the sample B of the light diffusion sheet 43, the luminance uniformity tends to increase when the arrangement angle of the recesses 105 is from 0° to 45°, and tends to decrease when the arrangement angle is from 45° to 90°. In other words, it was found that when the recesses 105 are provided on the light exit surface of the sample B of the light diffusion sheet 43, the luminance uniformity is further improved by intersecting the arrangement direction of the point light source 42 and the arrangement direction of the recesses 105.

[0091] (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.

[0092] In the above-described embodiment, the first surface 101a of the light diffusion sheet 43 included in the optical sheet laminate 10 is a matte surface or a flat surface. Alternatively, a functional layer 103 consisting of a plurality of linear structures 106 extending in a predetermined direction may be provided on the first surface 101a of the light diffusion sheet 43, as in the modified example shown in FIG. 17 or FIG. 18.

[0093] In Fig. 17 or 18, the same elements as those in the light diffusion sheet 43 of the embodiment described above and shown in Fig. 4 or 5 are denoted by the same reference numerals. Fig. 17 shows a case where the light diffusion sheet 43 of the modified example is arranged so that the first surface 101a is the light entrance surface and the second surface 102a is the light exit surface, and Fig. 18 shows a case where the light diffusion sheet 43 of the modified example is arranged so that the first surface 101a is the light exit surface and the second surface 102a is the light entrance surface.

[0094] Since the functional layer 103 needs to transmit light, it may be formed mainly from a transparent (e.g., colorless and transparent) synthetic resin. The functional layer 103 may be molded integrally with the base material layer 101 during extrusion molding of the base material resin that will become the base material layer 101, or may be molded separately using an ultraviolet curing resin after molding of the base material layer 101.

[0095] The linear structure 106 provided on the functional layer 103 (the first surface 101a of the light diffusion sheet 43) so as to extend in a predetermined direction may be, for example, a striped prism (triangular columnar body). The lower limit of the thickness of the functional layer 103 (the height from the surface (first surface 101a) of the base layer 101 to the apex of the prism that becomes the linear structure 106) may be, for example, about 5 μm, more preferably about 10 μm. The upper limit of the thickness of the functional layer 103 may be, for example, about 200 μm, more preferably about 100 μm. The lower limit of the pitch of the linear structure 106 may be, for example, about 10 μm, more preferably about 20 μm. The upper limit of the pitch of the linear structure 106 may be, for example, about 200 μm, more preferably about 100 μm. The lower limit of the refractive index of the prism that becomes the linear structure 106 may be, for example, 1.5, more preferably 1.55, and the upper limit of the refractive index may be, for example, 1.7.

[0096] As shown in FIG. 19, when a plurality of recesses 105 are arranged in a two-dimensional matrix, the linear structures 106 may be extended along one of the arrangement directions (i.e., the extension direction of the ridge line 111 (see FIG. 6)) (see FIG. 19(a)), or the arrangement direction may cross the extension direction of the linear structures 106 (see FIG. 19(b)). When the arrangement direction of the recesses 105 crosses the extension direction of the linear structures 106, the crossing angle may be, for example, 30° or more and 60° or less, preferably 40° or more and 50° or less. FIG. 19 is a plan view of a part of the light diffusion sheet 43 viewed from the recesses 105 (light diffusion layer 102) side.

[0097] When multiple light diffusion sheets 43 are stacked and used in the backlight unit 40, the extension direction of the linear structure 106 in one light diffusion sheet 43 may be the same as or may intersect with the extension direction of the linear structure 106 in another light diffusion sheet 43.

[0098] In the light diffusion sheet 43 shown in FIG. 17 or FIG. 18, stripe-shaped prisms are provided as the plurality of linear structures 106. However, the linear structures 106 are not particularly limited as long as they include convex bodies extending in a predetermined direction on the functional layer 103 (the first surface 101a of the light diffusion sheet 43). For example, as shown in FIG. 20, the plurality of linear structures 106 may be configured as hairlines (FIG. 20(a)), lenticulars (FIG. 20(b)), diffraction gratings (FIG. 20(c)), or the like. FIG. 20 shows a variation of the cross-sectional configuration of the functional layer 103 among the cross-sectional configurations of the light diffusion sheet 43 shown in FIG. 17 or FIG. 18. The hairlines that become the linear structures 106 may be, for example, elongated stripes generated by polishing the surface of the base layer 101 in a single direction. The lenticulars that become the linear structures 106 may be, for example, fine, elongated, semi-cylindrical convex lenses provided on the surface of the base layer 101. The diffraction grating that constitutes the linear structure 106 may be, for example, a grating pattern consisting of linear projections and recesses that are periodically arranged on the surface of the base layer 101. Depending on the type of the linear structure 106, the functional layer 103 exhibits various optical functions such as diffusion, light collection, and diffraction.

[0099] In addition, when a prism is provided as the linear structure 106, the height of the prism may be periodically changed along the vertical direction. That is, the top (ridge) of the prism that becomes the linear structure 106 may be moved up and down in the vertical direction to form a wave. The width of the prism may be changed along with the height of the prism. Specifically, the width of the prism may be wider where the height of the prism is high, and narrower where the height of the prism is low. The height and repetition period of the mountains that repeatedly appear on the prism ridge may be the same. By changing the height of the prism as described above, the contact area between the prism and another light diffusion sheet 43 to be superimposed can be reduced, thereby reducing the inclusion of foreign matter, scratches due to contact, and poor visibility for the user.

[0100] Furthermore, when prisms are provided as the linear structures 106, the prisms may be extended in a predetermined direction while periodically meandering in the horizontal direction. Specifically, the arrangement of the prism ridges may be periodically meandered without changing the shape (height, pitch, apex angle) of the prisms. That is, when the first surface 101a of the light diffusion sheet 43 is viewed from the front, the prisms that form the linear structures 106 may extend while waving. This makes it possible to suppress the occurrence of interference patterns caused by the combination of the inverted pyramid-shaped recesses 105 and the prisms that form the linear structures 106.

[0101] Hereinafter, a description will be given of the results of evaluating the luminance and luminance uniformity of the optical sheet laminate 10 using the light diffusion sheet 43 shown in Fig. 17 or 18. The evaluation of the luminance and luminance uniformity was carried out using the backlight configuration shown in Fig. 2 or 3.

[0102] Specifically, as the plurality of light sources 42, an LED array in which blue LED elements are arranged in a square (pitch of 2 mm×2 mm) is used.

[0103] As the light diffusion sheet 43 according to the above-mentioned embodiment, two types of samples were used: the above-mentioned sample B (a 112 μm-thick polycarbonate sheet having a matte first surface 101a and inverted pyramidal recesses 105 with a depth of 50 μm and an apex angle of 90° arranged on the second surface 102a at a pitch of 100 μm in a two-dimensional matrix), and sample B', a sheet having the same shape as sample B and manufactured by heat pressing with a transfer rate of 100%, and as the light diffusion sheet 43 according to this modified example, three types of samples C, D, and E described below were used.

[0104] Sample C is a 77 μm thick base layer 101 mainly composed of PET (polyethylene terephthalate), and is provided with a light diffusion layer 102 (inverted pyramid-shaped recesses 105) and a functional layer 103 (linear structures 106 consisting of striped prisms) using an ultraviolet curing resin. In Sample C, recesses 105 with a depth of 20 μm and a apex angle of 90° are arranged in a two-dimensional matrix on the second surface 102a at a pitch of 40 μm, and linear structures (prisms) 106 with a height of 12 μm and a apex angle of 90° are arranged on the first surface 101a at a pitch of 24 μm. The intersection angle between the arrangement direction of the recesses 105 and the extension direction of the linear structures 106 is set to 45°.

[0105] Sample D is a substrate layer 101 having a thickness of 110 μm and mainly composed of PC (polycarbonate), on which a light diffusion layer 102 (inverted pyramid-shaped recesses 105) and a functional layer 103 (linear structures 106 consisting of striped prisms) are provided by heat pressing with a transfer rate of 100%. In Sample D, recesses 105 having a depth of 50 μm and an apex angle of 90° are arranged in a two-dimensional matrix shape on the second surface 102a at a pitch of 100 μm, and linear structures (prisms) 106 having a height of 25 μm and an apex angle of 90° are arranged on the first surface 101a at a pitch of 50 μm. The intersection angle between the arrangement direction of the recesses 105 and the extension direction of the linear structures 106 was set to 0°.

[0106] Sample E is similar to sample D, except that the thickness of the base layer 101 is 160 μm.

[0107] The color conversion sheet 44 was a QD sheet.

[0108] The first prism sheet 45 was made by transferring prisms with a height of 12 μm and an apex angle of 90° onto an 87 μm thick PET film using UV curable resin. The second prism sheet 46 was made by transferring prisms with the same shape as the first prism sheet 45 onto a 150 μm thick PET film using UV curable resin. The first prism sheet 45 and the second prism sheet 46 were arranged so that their prisms were perpendicular to each other and the prisms of the second prism sheet 46 formed an angle of 0° with the arrangement direction of the light sources 42.

[0109] The upper light diffusion sheet 47 was a PET film having a thickness of 136 μm and having been subjected to bead coating.

[0110] In the configuration described above, a transparent glass plate was placed on the upper light diffusion sheet 47 to prevent the sheets from floating, and the luminance and luminance uniformity were evaluated as follows. First, the luminance (cd m 2 ) was measured. Next, the obtained two-dimensional luminance distribution image was corrected for variations in the emission intensity of each LED, and a filtering process was performed to suppress bright and dark spot noise caused by foreign matter, after which the average value and standard deviation of the luminance of all pixels were calculated. Finally, the luminance and luminance uniformity were calculated by defining "luminance" as the "average value of luminance" and "luminance uniformity" as the "average value of luminance / standard deviation of luminance."

[0111] Table 1 shows the evaluation results of the luminance and luminance uniformity for each sample of light diffusion sheet 43 in the backlight configuration shown in Figure 2 (configuration in which color conversion sheet 44 is arranged below light diffusion sheet 43 (QD under)) when "when recesses 105 are arranged on the light exit surface (arrangement orientation: pyramid above)" or "when recesses 105 are arranged on the light entrance surface (arrangement orientation: pyramid below)", and when "when the arrangement direction of recesses 105 is aligned with the arrangement direction of point light sources 42 (arrangement angle: 0°)" or "when the arrangement direction of recesses 105 intersects with the arrangement direction of point light sources 42 at 45° (arrangement angle: 45°)".

[0112] [Table 1]

[0113] Table 2 shows the evaluation results of the luminance and luminance uniformity for each sample of light diffusion sheet 43 in the backlight configuration shown in Figure 3 (configuration in which color conversion sheet 44 is arranged above light diffusion sheet 43 (QD above)) when "when recesses 105 are arranged on the light exit surface (arrangement orientation: pyramid above)" or "when recesses 105 are arranged on the light entrance surface (arrangement orientation: pyramid below)", and when "when the arrangement direction of recesses 105 is aligned with the arrangement direction of point light sources 42 (arrangement angle: 0°)" or "when the arrangement direction of recesses 105 is intersected at 45° (arrangement angle: 45°)".

[0114] [Table 2]

[0115] The luminance and luminance uniformity (uniformity) shown in Tables 1 and 2 are relative luminance and relative uniformity, respectively, with the luminance and uniformity when sample B shown in Table 1 (below QD) is placed on a pyramid at an angle of 0° as the reference (100%).

[0116] From the results shown in Tables 1 and 2, it was found that in the light diffusion sheet 43 according to this modification (samples C, D, and E), the configuration in which the color conversion sheet 44 is arranged on the upper side of the light diffusion sheet 43 (above QD) generally tends to have slightly lower luminance and higher uniformity. On the other hand, the configuration in which the color conversion sheet 44 is arranged on the lower side of the light diffusion sheet 43 (below QD) tends to have good luminance but lower uniformity. Also, for samples C and D, the configuration under the pyramid with an arrangement angle of 45° provided relatively higher uniformity.

[0117] In detail, from the results shown in Table 1 (under QD), in terms of luminance, samples B and B' were slightly better when placed under the pyramid at an angle of 0°, while samples C, D and E were almost unaffected by the orientation and angle of placement. In terms of uniformity, samples B and B' were better when placed on the pyramid at an angle of 45°, sample C was better when placed under the pyramid at an angle of 45°, sample D was slightly better when placed under the pyramid at an angle of 45°, and sample E was better when placed under the pyramid at an angle of 0°.

[0118] On the other hand, from the results shown in Table 2 (above QD), in terms of brightness, sample B performed better on the pyramid but the effect of the arrangement angle was almost nonexistent, sample B' performed better when arranged on the pyramid at a 45° angle, sample C performed better under the pyramid but the effect of the arrangement angle was almost nonexistent, and samples D and E were almost nonexistent in terms of arrangement direction and angle. In terms of uniformity, samples B and B' performed better when arranged under the pyramid at a 45° angle, sample C performed better under the pyramid at a 0° angle, and samples D and E performed better when arranged under the pyramid at a 45° angle. [Explanation of symbols]

[0119] 1 TFT substrate 2 CF board 3 Liquid crystal layer 5 Liquid crystal display panel 6 First polarizing plate 7 Second polarizing plate 10 Optical sheet laminate 40 Backlight unit 41 Reflective Sheet 42 point light source 43 Light diffusion sheet 44 Color conversion sheet 45 First prism sheet 46 Second prism sheet 47 Upper light diffusion sheet 50 LCD display device 50a display screen 101 Base material layer 102 Light diffusion layer 103 Functional Layer 105 Recess 106 Linear Structure

Claims

1. An optical sheet laminate to be incorporated in a backlight unit that guides light emitted from a plurality of point light sources to a display screen of a liquid crystal display device, a color conversion sheet that converts the wavelength of the light; a plurality of light diffusion sheets, each having a plurality of recesses of a substantially inverted polygonal pyramid shape, laminated between the color conversion sheet and the display screen; Equipped with The arrangement surfaces and arrangement directions of the recesses in the plurality of light diffusion sheets are the same. Optical sheet laminate.

2. the plurality of point light sources and the plurality of recesses are arranged in a two-dimensional matrix; The plurality of recesses are provided on the light output surfaces of the plurality of light diffusion sheets, an arrangement direction of the plurality of point light sources intersects with an arrangement direction of the plurality of recesses; The optical sheet laminate according to claim 1 .

3. the plurality of point light sources and the plurality of recesses are arranged in a two-dimensional matrix; The plurality of recesses are provided on the light incident surfaces of the plurality of light diffusion sheets, an arrangement direction of the plurality of point light sources intersects with an arrangement direction of the plurality of recesses; The optical sheet laminate according to claim 1 .

4. An optical sheet laminate to be incorporated in a backlight unit that guides light emitted from a plurality of point light sources to a display screen side of a liquid crystal display device, a color conversion sheet that converts the wavelength of the light; a plurality of light diffusion sheets, each having a plurality of recesses of a substantially inverted polygonal pyramid shape, stacked between the color conversion sheet and the plurality of point light sources; Equipped with The arrangement surfaces and arrangement directions of the recesses in the plurality of light diffusion sheets are the same. Optical sheet laminate.

5. the plurality of point light sources and the plurality of recesses are arranged in a two-dimensional matrix; The plurality of recesses are provided on the light incident surfaces of the plurality of light diffusion sheets, an arrangement direction of the plurality of point light sources intersects with an arrangement direction of the plurality of recesses; The optical sheet laminate according to claim 4 .

6. the plurality of point light sources and the plurality of recesses are arranged in a two-dimensional matrix; The plurality of recesses are provided on the light output surfaces of the plurality of light diffusion sheets. The optical sheet laminate according to claim 1 .

7. a brightness enhancement sheet is provided closer to the display screen than the color conversion sheet and the plurality of light diffusion sheets; The optical sheet laminate according to any one of claims 1 to 6.

8. Another light diffusing sheet is provided closer to the display screen than the brightness enhancing sheet. The optical sheet laminate according to claim 7 .

9. A backlight unit that guides light emitted from a plurality of point light sources to a display screen of a liquid crystal display device, The optical sheet laminate according to any one of claims 1 to 6 is provided between the display screen and the plurality of point light sources. Backlight unit.

10. The plurality of point light sources are blue light sources. The backlight unit according to claim 9 .

11. A backlight unit according to claim 9 ; A liquid crystal display panel. LCD display device.

12. An information device comprising the liquid crystal display device according to claim 11.

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