Manufacturing methods of light diffuser sheets, backlight units, liquid crystal display devices, information machines, and backlight units

Abstract

The present invention aims to provide a light diffuser sheet capable of improving brightness uniformity. The light diffuser sheet (43) is assembled in a backlight unit (40) that uses a plurality of light sources (42) arranged in a two-dimensional matrix. On at least one side of the light diffuser sheet (43), a plurality of slightly inverted quadrangular pyramidal recesses (22) are arranged in a two-dimensional matrix. The angle between the arrangement direction of the plurality of recesses (22) and the arrangement direction of the plurality of light sources (42) is 30° or more and 60° or less.

Description

Technical Field

[0001] The present invention relates to a light diffusion sheet, a backlight unit, a liquid crystal display device, an information device and a method for manufacturing the backlight unit. Prior Art

[0002] Liquid crystal display devices (hereinafter referred to as LCDs) are widely used as display devices in various information devices such as smartphones and tablet computers. As the backlight source of LCDs, the mainstream is the edge-lit type, in which the light source is placed near the side of the LCD panel.

[0003] When a direct backlight is used, a light diffusion sheet is used to diffuse light from a light source such as an LED (Light Emitting Diode) and improve the uniformity of brightness and color across the entire screen (see, for example, Patent Document 1).

[0004] In direct-lit backlight units for thin displays such as notebook computers and tablet computers, a light diffusion sheet having, for example, inverted pyramid-shaped recesses arranged two-dimensionally is used. [Prior Art Literature] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-129277. Summary of the Invention

[0006] [Problems to be solved by the invention] However, conventional light diffusers cannot achieve sufficient brightness uniformity.

[0007] An object of the present invention is to provide a light diffuser capable of improving brightness uniformity. [Methods used to solve the problem]

[0008] To achieve the aforementioned objectives, the light diffuser of the present invention is assembled into a backlight unit, which utilizes a plurality of light sources arranged in a two-dimensional matrix. On at least one side of the light diffuser, a plurality of slightly inverted quadrangular pyramidal recesses are arranged in a two-dimensional matrix, and the intersection angle between the arrangement direction of the plurality of recesses and the arrangement direction of the plurality of light sources is greater than 30° and less than 60°.

[0009] According to the light diffuser of the present invention, since the intersection angle between the arrangement direction of the recesses and the arrangement direction of the light sources is set to be greater than 30° and less than 60°, the intensity of light emitted from the light diffuser can be increased in the diagonal direction of the light source arrangement (a direction inclined 45° relative to the arrangement direction of the light sources), where the distance between the light sources is large and the brightness is easily reduced, thereby improving brightness uniformity.

[0010] It should be noted that, in the present invention, the description of "a plurality of light sources arranged in a two-dimensional matrix" includes "a situation in which a light source group consisting of a plurality of small light sources is arranged in a two-dimensional matrix." In this situation, the small light sources constituting each light source group may not themselves be arranged in a two-dimensional matrix.

[0011] In the light diffuser of the present invention, if the cross angle is greater than 35° and less than 55°, and more preferably greater than 40° and less than 50°, the brightness uniformity can be further improved.

[0012] In the light diffuser of the present invention, if the plurality of recesses are provided on the light emitting surface, the intensity of light emitted from the light diffuser can be easily increased in the diagonal direction of the light source arrangement.

[0013] The backlight unit of the present invention is assembled in a liquid crystal display device, and guides light emitted by a plurality of light sources arranged in a two-dimensional matrix toward the display screen. The light diffusion sheet of the present invention is included between the display screen and the plurality of light sources.

[0014] According to the backlight unit involved in the present invention, since it includes the aforementioned light diffusion sheet involved in the present invention, it is possible to improve brightness uniformity.

[0015] In the backlight unit of the present invention, if a plurality of the aforementioned light diffusion sheets are arranged, light will be repeatedly diffused by the plurality of light diffusion sheets, thereby further improving brightness uniformity.

[0016] The backlight unit according to the present invention may further include a color conversion sheet between the display screen and the plurality of light sources for converting the wavelength of light emitted by the plurality of light sources. In this manner, a backlight unit can be constructed using light sources other than white light sources.

[0017] In the backlight unit of the present invention, a brightness enhancement sheet is included between the light diffusion sheet and the display screen to enhance the brightness of the light emitted by the plurality of light sources. This improves brightness uniformity while also increasing brightness.

[0018] In the backlight unit of the present invention, the plurality of light sources can be arranged on a reflective sheet located on the opposite side of the display screen when viewed from the light diffuser. This allows light to be diffused by multiple reflections between the light diffuser and reflective sheet, further improving brightness uniformity.

[0019] The liquid crystal display device of the present invention includes the backlight unit of the present invention and a liquid crystal display panel.

[0020] According to the liquid crystal display device involved in the present invention, since it includes the backlight unit involved in the present invention, it can improve the brightness uniformity. The information device involved in the present invention includes the liquid crystal display device involved in the present invention.

[0021] According to the information device involved in the present invention, since it includes the liquid crystal display device involved in the present invention, it is possible to improve the brightness uniformity.

[0022] The present invention relates to a method for manufacturing a backlight unit, which is assembled into a liquid crystal display device and guides light emitted by a plurality of light sources arranged in a two-dimensional matrix to a display screen. The method comprises the following steps: arranging the plurality of light sources; arranging a light diffuser having a plurality of slightly inverted quadrangular pyramidal recesses arranged in a two-dimensional matrix on at least one side; and arranging the plurality of light sources and the light diffuser such that the intersection angle between the arrangement direction of the plurality of recesses and the arrangement direction of the plurality of light sources is greater than 30° and less than 60°.

[0023] According to the backlight unit manufacturing method of the present invention, the intersection angle between the arrangement direction of the recessed portions of the light diffuser sheet and the arrangement direction of the light sources is set to be between 30° and 60°. Consequently, the intensity of light emitted from the light diffuser sheet can be increased in the diagonal direction of the light source arrangement (a direction inclined 45° relative to the light source arrangement direction), where the distance between light sources is large and brightness tends to decrease, thereby improving brightness uniformity. [Effects of the invention]

[0024] According to the present invention, a light diffusion sheet capable of improving brightness uniformity can be provided. Simple diagram description

[0025] FIG1 is a cross-sectional view of a liquid crystal display device including a backlight unit according to an embodiment. FIG. 2 is a cross-sectional view of a backlight unit incorporating a light diffusion sheet according to an embodiment. FIG3 is a plan view showing an example of arrangement of light sources in the backlight unit shown in FIG2 . FIG4 is a cross-sectional view of a light diffusion sheet according to an embodiment. FIG5 is a perspective view of a light diffusion sheet according to an embodiment. FIG6 is a plan view showing an example of arrangement of recessed portions in a light diffusion sheet according to an embodiment. FIG. 7 is a diagram showing the relationship between the arrangement angle of the light diffuser sheet and the arrangement angle of the prism sheet according to the embodiment. FIG. 8 is a diagram showing changes in brightness uniformity when the arrangement angle of the light diffusion sheet according to the embodiment is changed. FIG. 9 is a graph showing changes in brightness uniformity when the arrangement angle of the light diffusion sheet according to the embodiment is fixed at 45° and 0° and the arrangement angle of the prism sheet is changed. FIG. 10 is a graph showing changes in brightness uniformity when the arrangement angle of the light diffusion sheet and the arrangement angle of the prism sheet according to the embodiment are changed together. FIG. 11 is a diagram showing the brightness uniformity when a light diffusion sheet according to an embodiment of the present invention is laminated with three layers and the arrangement angles of the sheets are varied. Implementation Method

[0026] The following describes, with reference to the accompanying drawings, a light diffuser, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing the backlight unit according to the embodiments. It should be noted that the scope of the present invention is not limited to the following embodiments and that any modifications can be made within the technical scope of the present invention. [Liquid Crystal Display Device]

[0027] As shown in FIG1 , the liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizer 6 adhered to the lower surface of the liquid crystal display panel 5, a second polarizer 7 adhered to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 arranged on the back side of the liquid crystal display panel 5 via the first polarizer 6.

[0028] The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 arranged opposite to each other, a liquid crystal layer 3 arranged between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) arranged in a frame shape to seal the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0029] The shape of the display screen 50a of the liquid crystal display device 50 viewed from the surface (top of FIG. 1 ) is in principle a rectangle or a square, but is not limited thereto and may be any shape such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or a car dashboard.

[0030] In each subpixel corresponding to each pixel electrode in the liquid crystal display device 50, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3. This adjusts the transmittance of light entering from the backlight unit 40 via the first polarizer 6. The light with adjusted transmittance is emitted through the second polarizer 7 to display an image.

[0031] The liquid crystal display device 50 of this embodiment can be used as a display device assembled in various information machines (such as vehicle-mounted devices such as car navigation, portable information terminal devices such as personal computers, mobile phones, notebook computers or tablets, portable game consoles, copiers, ticket machines, ATMs, etc.).

[0032] The TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film provided to cover each TFT, a plurality of pixel electrodes provided in a matrix on the interlayer insulating film and connected to corresponding TFTs in the plurality of TFTs, and an alignment film provided to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix provided in a grid pattern on a glass substrate, a color filter including a red layer, a green layer, and a blue layer provided between each grid of the black matrix, a common electrode provided to cover the black matrix and the color filter, and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is formed of, for example, a nematic liquid crystal material containing liquid crystal molecules having electro-optical properties. The first polarizer 6 and the second polarizer 7 each include, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers provided to sandwich the polarizer layer. [Backlight unit]

[0033] As shown in FIG. 2, the backlight unit 40 has: a reflector 41, a plurality of light sources 42 two-dimensionally arranged on the reflector 41, a light diffusion sheet 43 provided on the upper side of the plurality of light sources 42, and a brightness enhancement sheet 48 provided on the upper side of the light diffusion sheet 43 (on the display screen 50a side). In the backlight unit 40 shown in FIG. 2, a color conversion sheet 46 is disposed between the light source 42 and the light diffusion sheet 43, and an upper light diffusion sheet 47 is disposed on the upper side of the brightness enhancement sheet 48 (on the display screen 50a side). Details of the light diffusion sheet 43 will be described later. [Reflector]

[0034] The reflector 41 is formed, for example, of a white polyethylene terephthalate resin film, a silver vapor deposition film, or the like. [Light source]

[0035] The type of the light source 42 is not particularly limited. For example, it may be an LED element or a laser element, etc. From the viewpoints of cost, productivity, etc., an LED element can be used. In order to adjust the light emission angle characteristics of the LED element serving as the light source 42, a lens can be installed on the LED element. When viewed from above, the light source 42 may be rectangular. 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). The number of arranged light sources 42 is not particularly limited. When a plurality of light sources 42 are arranged in a dispersed manner, it is preferable to regularly arrange the plurality of light sources 42 on the reflector 41. Regular arrangement means arranging in a certain rule. For example, when the light sources 42 are arranged at equal intervals, it belongs to regular arrangement. In the case where the light sources 42 are arranged at equal intervals, the distance between the centers of two adjacent small light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0036] In the present embodiment, for example, as shown in FIG. 3, a plurality of light sources 42 formed of LED elements are arranged in a two-dimensional array in the X direction and the Y direction at a certain interval. In other words, the plurality of light sources 42 are arranged along two mutually orthogonal directions (the X direction and the Y direction). In the present embodiment, a blue light source is used as the light source 42. The blue light source can emit light with x < 0.24 and y < 0.18 in the chromaticity coordinates of CIE1931, for example. It should be noted that a white light source can also be used as the light source 42. The white light source can be 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. For example, it can emit light with 0.24 < x < 0.42 and 0.18 < y < 0.48 in the chromaticity coordinates of CIE1931. [Color conversion sheet]

[0037] The color conversion sheet 46 is a wavelength conversion sheet that converts light from the light source 42, which is a blue light source, into light with a peak wavelength of a desired color (e.g., green or red). For example, the color conversion sheet 46 converts 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, if the light source 42 emits blue light with a wavelength of 450 nm, the color conversion sheet 46 partially converts the blue light into green and red light, resulting in light that passes through the color conversion sheet 46 becoming white light. For example, a QD (quantum dot) sheet or a fluorescent sheet can be used as the color conversion sheet 46.

[0038] It should be noted that when a white light source is used as the light source 42, the color conversion sheet 46 may not be provided. The color conversion sheet 46 is not particularly limited as long as it is placed between the light source 42 and the brightness enhancement sheet 48 (described later). For example, the color conversion sheet 46 may be placed between the light diffusion sheet 43 and the brightness enhancement sheet 48. [Brightness Enhancement Sheet]

[0039] The brightness enhancement sheet 47 has a structure in which a lower prism sheet 44 and an upper prism sheet 45 are layered in layers, starting from the side closest to the light source 42. Because they need to allow light to pass through, the lower prism sheet 44 and the upper prism sheet 45 are primarily formed of a transparent (e.g., colorless and transparent) synthetic resin. The prism sheets 44 and 45 can be formed integrally. The lower prism sheet 44 includes a base layer 44a and a protrusion array formed by a plurality of protruding prism portions 44b laminated on the surface of the base layer 44a. Similarly, the upper prism sheet 45 includes a base layer 45a and a protrusion array formed by a plurality of protruding prism portions 45b laminated on the surface of the base layer 45a. The protruding prisms 44b and 45b are layered in stripes on the surfaces of the base layers 44a and 45a, respectively. The protruding prisms 44b and 45b are triangular prisms, with their back surfaces in contact with the surfaces of the base layers 44a and 45a, respectively. The extending directions of the protruding prisms 44b and 45b are perpendicular to each other. This allows the lower prism sheet 44 to refract light incident from the light diffuser 43 toward the normal direction, while the upper prism sheet 45 refracts light emitted from the lower prism sheet 44 so that it travels approximately perpendicularly to the display screen 50a.

[0040] The lower limit of the thickness of the prism sheets 44 and 45 (the height from the back surface of the base material layers 44a and 45a to the apex of the protruding prism portions 44b and 45b) is, for example, approximately 50 μm, more preferably approximately 100 μm. The upper limit of the thickness of the prism sheets 44 and 45 is approximately 200 μm, more preferably approximately 180 μm. The lower limit of the pitch between the protruding prism portions 44b and 45b in the prism sheets 44 and 45 is, for example, approximately 20 μm, more preferably approximately 25 μm. The upper limit of the pitch between the protruding prism portions 44b and 45b in the prism sheets 44 and 45 is, for example, approximately 100 μm, more preferably approximately 60 μm. The apex angle of the protruding prism portions 44b and 45b can be, for example, from 85° to 95°. The lower limit of the refractive index of the protruding prism portions 44b and 45b is, for example, 1.5, more preferably 1.55, and the upper limit of the refractive index of the protruding prism portions 44b and 45b is, for example, 1.7.

[0041] The prism sheets 44 and 45 can be formed, for example, by providing protruding prism portions 44b and 45b having a shape transferred using a UV-curable acrylic resin on base layers 44a and 45a formed of PET (polyethylene terephthalate) film, or the protruding prism portions 44b and 45b can be integrally formed with the base layers 44a and 45a.

[0042] It should be noted that, in this embodiment, the prism sheets 44 and 45 are used as the brightness enhancement sheet 48, but other optical sheets capable of increasing the brightness of the light emitted from the light source 42 may be used instead. [Upper side light diffuser]

[0043] The upper light diffuser sheet 47 is disposed on the upper side (display screen 50a side) of the upper prism sheet 45. The upper light diffuser sheet 47 can be constructed as a two-layer structure comprising a base layer and a light diffuser layer. Since the base layer needs to allow light to pass through, it can be primarily composed of a transparent (e.g., colorless and transparent) synthetic resin. The light diffuser layer can include a resin matrix and resin beads dispersed within the resin matrix. [Other optical sheets]

[0044] Although not shown, a polarizer may be provided on the upper side (display screen 50a side) of the upper light diffuser 47. The polarizer prevents light emitted from the backlight unit 40 from being absorbed by the first polarizer 6 of the liquid crystal display device 50, thereby improving the brightness of the display screen 50a. [Light Diffuser]

[0045] In the backlight unit 40 shown in FIG. 2 , a diffuser sheet 43 having the same structure is provided in the backlight unit 40, for example, by stacking three sheets. The diffuser sheet 43 can be stacked in one or two sheets, or in four or more sheets. As shown in FIG. 4 , the diffuser sheet 43 includes a base layer 21 . The diffuser sheet 43 (base layer 21 ) has a first surface 21 a , which serves as a light-emitting surface, and a second surface 21 b , which serves as a light-incident surface. Specifically, the second surface 21 b of the diffuser sheet 43 faces the light source 42 . The resin forming the matrix of the base layer 21 is not particularly limited, as long as it is a material that allows light to pass through. Examples of such materials include acrylate, polystyrene, polycarbonate, MS (methyl methacrylate / styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, and polyimide. The base layer 21 may contain a diffusing agent and other additives, or may be substantially additive-free. The additives that the substrate layer 21 may contain are not particularly limited, and may be, for example, inorganic particles such as silicon dioxide, titanium oxide, aluminum hydroxide, and barium sulfate, or organic particles such as acrylate, acrylonitrile, polysilicone, polystyrene, and polyamide.

[0046] The thickness of the light diffuser 43 is not particularly limited; for example, it can be 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 50 μm or more. If the thickness of the light diffuser 43 exceeds 3 mm, it will be difficult to achieve a thinner LCD display. If the thickness of the light diffuser 43 is less than 50 μm, it will be difficult to achieve uniform brightness. The light diffuser 43 can be in the form of a film or a sheet (plate).

[0047] As shown in Figure 5, on the first surface 21a (light-emitting surface) of the light diffuser 43, a plurality of recesses 22 in the shape of slightly inverted quadrangular pyramids (inverted pyramids) are arranged in a two-dimensional matrix. In other words, the recesses 22 are arranged in two mutually orthogonal directions (the X1 and Y1 directions shown in Figure 6). Adjacent recesses 22 are divided by ridge lines 111. Ridge lines 111 extend along the two directions in which the recesses 22 are arranged. The center 112 of a recess 22 (the apex of the inverted pyramid) is the deepest part of the recess 22. For simplicity of illustration, Figure 5 illustrates the recesses 22 arranged in a 5×5 matrix. However, the actual number of recesses 22 is much larger than shown. In this two-dimensional arrangement of the recesses 22, the recesses 22 can be arranged without gaps on the first surface 21a or at predetermined intervals. Alternatively, some recesses 22 can be randomly arranged to a degree that does not impair the light diffusion effect.

[0048] The vertex angle θ of the recesses 22 can be, for example, 90°, the arrangement pitch p of the recesses 22 can be, for example, 100 μm, and the depth of the recesses 22 can be, for example, 50 μm. Here, the vertex angle θ of the recesses 22 refers to the angle formed between the section lines of the inclined surfaces, when a pair of inclined surfaces, facing each other and passing through the center of the recess 22 (the vertex 112 of the inverted pyramid) is cut perpendicularly on a plane (longitudinal section) perpendicular to the arrangement surface of the light diffuser 43. The arrangement pitch p of the recesses 22 refers to the distance between the centers (the vertex 112 of the inverted pyramid) of adjacent recesses 22 (the distance along a direction parallel to the arrangement surface of the light diffuser 43).

[0049] The second surface 21 b of the light diffusion sheet 43 may be, for example, a flat surface (mirror surface) or an embossed surface.

[0050] The light diffuser 43 can be composed of a single-layer structure comprising a base layer 21 having a concavo-convex shape (concave portion 22) on the first surface 21a. Alternatively, the light diffuser 43 can be composed of a two-layer structure comprising a base layer having two flat surfaces and a layer having a concavo-convex shape on one surface. Alternatively, the light diffuser 43 can be composed of a structure comprising three or more layers, including a layer having a concavo-convex shape on one surface. The method for manufacturing the light diffuser 43 is not particularly limited, and methods such as extrusion molding and injection molding can be used.

[0051] The steps for producing a single-layer light diffuser sheet with a contoured surface using extrusion molding are as follows. First, granular plastic particles (optionally containing a diffusing agent) are fed into a single-screw extruder, where they are melted and kneaded while being heated. The molten resin extruded through a T-die is then clamped between two metal rollers. After cooling, it is conveyed by guide rollers and cut into single flat sheets using a slicer to produce the light diffuser sheet. By clamping the molten resin between metal rollers with a surface shape opposite to the desired contoured surface, the inverse of the roller surface shape is transferred to the resin, imparting the desired contoured surface to the diffuser sheet. Since the roller surface shape may not be 100% transferred to the resin, the roller surface shape can be designed by inversely calculating the degree of transfer.

[0052] When using extrusion molding to manufacture a double-layer light diffuser with a concave-convex surface, for example, granular plastic particles required to form each layer are fed into two single-screw extruders, and the same steps as above are performed on each layer to stack the sheets.

[0053] Alternatively, a two-layer light diffuser with an uneven surface can be produced as follows. First, granular plastic particles required for each layer are fed into two single-screw extruders, where they are melted and kneaded while being heated. The molten resin for each layer is then fed into a T-die, where it is laminated. The laminated molten resin extruded from the T-die is then clamped between two metal rollers and cooled. The laminated molten resin is then conveyed using guide rollers and cut into individual flat sheets using a slicer, thereby producing a two-layer light diffuser with an uneven surface.

[0054] A light-diffusing sheet can also be manufactured using UV (ultraviolet) shape transfer, as follows. First, uncured UV-curable resin is filled onto a roller with a shape that mirrors the desired concave-convex pattern. A substrate is then pressed against the resin. Next, while the roller and substrate are integrated, the resin is irradiated with UV light to cure the resin. The sheet, to which the concave-convex pattern has been transferred through the resin shape transfer, is then peeled from the roller. Finally, the sheet is irradiated with UV light again to completely cure the resin, producing a light-diffusing sheet with a concave-convex surface.

[0055] It should be noted that, in the present invention, the term "substantially inverted square pyramid" is used, considering the difficulty of forming a geometrically strictly defined inverted square pyramid concave portion using conventional shape transfer techniques. However, this term also encompasses shapes that are truly or substantially similar to an inverted square pyramid. "Substantially" means being able to approximate, and "substantially inverted square pyramid" refers to shapes that can approximate an inverted square pyramid. For example, a "substantially inverted square pyramid trapezoid" with a flat top is also included within the scope of a "substantially inverted square pyramid" as long as the functions and effects of the present invention are not compromised. Shapes that are deformed from an "inverted square pyramid" within the inevitable range of shape variations caused by processing accuracy in industrial production are also included within the scope of a "substantially inverted square pyramid." [Characteristics of the embodiment]

[0056] The light diffuser 43 of this embodiment is incorporated into a backlight unit 40, which utilizes a plurality of light sources 42 arranged in a two-dimensional matrix. On at least one surface of the light diffuser 43, a plurality of recesses 22 having a substantially inverted quadrangular pyramidal shape are arranged in a two-dimensional matrix. The angle of intersection between the arrangement direction of the plurality of recesses 22 (the X1 and Y1 directions in FIG. 6 ) and the arrangement direction of the plurality of light sources 42 (the X and Y directions in FIG. 3 ) is 30° to 60°.

[0057] According to the light diffuser 43 of this embodiment, the intersection angle between the arrangement direction of the recesses 22 and the arrangement direction of the light sources 42 is set to be between 30° and 60°. This increases the intensity of light emitted from the light diffuser 43 in the diagonal direction of the light source arrangement (a direction inclined 45° relative to the arrangement direction of the light sources 42), where the distance between light sources is large and brightness tends to decrease, thereby improving brightness uniformity. It should be noted that in this embodiment, the description of "a plurality of light sources 42 arranged in a two-dimensional matrix" includes "a light source group consisting of a plurality of small light sources arranged in a two-dimensional matrix." In this case, the small light sources constituting each light source group do not necessarily need to be arranged in a two-dimensional matrix.

[0058] In the light diffuser 43 of this embodiment, if the intersection angle between the arrangement direction of the recesses 22 and the arrangement direction of the light sources 42 is greater than 35° and less than 55°, and more preferably greater than 40° and less than 50°, the brightness uniformity can be further improved.

[0059] In the light diffuser 43 of this embodiment, if the recessed portion 22 is provided on the light emitting surface, the intensity of light emitted from the light diffuser 43 can be easily increased in the diagonal direction of the light source arrangement.

[0060] The backlight unit 40 of this embodiment is incorporated into a liquid crystal display device 50 and guides light emitted from a plurality of light sources 42 arranged in a two-dimensional matrix toward a display screen 50a. The backlight unit 40 includes the light diffusion sheet 43 of this embodiment described above between the display screen 50a and the plurality of light sources 42.

[0061] According to the backlight unit 40 of this embodiment, since it includes the light diffusion sheet 43 of this embodiment, it is possible to improve brightness uniformity.

[0062] In the backlight unit 40 of this embodiment, if multiple light diffusers 43 are provided, light is repeatedly diffused by the multiple light diffusers 43, further improving brightness uniformity. In this case, the intersection angle between the arrangement direction of the recesses 22 of at least one of the multiple light diffusers 43 and the arrangement direction of the light sources 42 is 30° or greater and 60° or less.

[0063] The backlight unit 40 of this embodiment may further include a color conversion sheet 46 between the display screen 50a and the plurality of light sources 42 for converting the wavelength of light emitted from the light sources 42. In this manner, the backlight unit 40 can be configured even when light sources other than white light sources are used as the light sources 42.

[0064] In the backlight unit 40 of this embodiment, a brightness enhancement sheet 48 for enhancing the brightness of light emitted from the light source 42 may be included between the light diffusion sheet 43 and the display screen 50a. In this way, the brightness can be increased while improving the brightness uniformity.

[0065] In the backlight unit 40 of this embodiment, the plurality of light sources 42 can be arranged on the reflective sheet 41, which is located on the opposite side of the display screen 50a when viewed from the light diffusion sheet 43. In this way, light is diffused by multiple reflections between the diffusion sheet 43 and the reflective sheet 41, thereby further improving brightness uniformity.

[0066] In the backlight unit 40 of this embodiment, if the distance between the light source 42 and the light diffuser 43 is 5 mm or less, the backlight unit 40 can be miniaturized. Considering the future trend toward thinner small and medium-sized liquid crystal displays, the distance between the light source 42 and the light diffuser 43 is preferably 2.5 mm or less, even more preferably 1 mm or less, and ultimately 0 mm.

[0067] The liquid crystal display device 50 of this embodiment includes the backlight unit 40 and the liquid crystal display panel 5 described above. Therefore, the backlight unit 40 can improve brightness uniformity. Similar effects can also be achieved in information devices (e.g., portable information terminals such as laptops and tablets) incorporating the liquid crystal display device 50.

[0068] The manufacturing method of the backlight unit 40 of this embodiment includes: a step of configuring a plurality of light sources 42; and a step of configuring a light diffuser 43, wherein the light diffuser 43 has a plurality of slightly inverted quadrangular pyramid-shaped recesses 22 arranged in a two-dimensional matrix on at least one side, and the plurality of light sources 42 and the light diffuser 43 are configured in such a manner that the intersection angle between the arrangement direction of the plurality of recesses 22 and the arrangement direction of the plurality of light sources 42 is greater than 30° and less than 60°.

[0069] According to the manufacturing method of the backlight unit 40 of this embodiment, the intersection angle between the arrangement direction of the recesses 22 of the light diffuser 43 and the arrangement direction of the light sources 42 is set to be greater than 30° and less than 60°. Therefore, the intensity of light emitted from the light diffuser 43 can be increased in the diagonal direction of the light source arrangement, where the distance between light sources is large and the brightness tends to decrease, thereby improving brightness uniformity. (Example) Hereinafter, embodiments will be described.

[0070] In the embodiment, as shown in FIG2 , three light diffusers 43 with a thickness of 110 μm and identical structure are stacked in the direction in which the recess 22 is positioned on the light-emitting surface (first surface 21 a). A lower prism sheet 44, an upper prism sheet 45, and an upper light diffuser sheet 47 are sequentially arranged on the light diffuser 43, with prism extension directions perpendicular to each other. A color conversion sheet 46 composed of a QD sheet is arranged below the light diffuser 43.

[0071] Inverted pyramid-shaped recesses 22 with a vertex angle of 90° are two-dimensionally arranged at a pitch of 100 μm on the light diffusion sheet 43. The light incident surface (second surface 21 b ) of the light diffusion sheet 43 is a flat surface.

[0072] Prism sheets 44 and 45 are formed by providing protruding prism sections 44b and 45b using a UV-curable acrylic resin formed from acrylate on base layers 44a and 45a formed of PET film. The protruding prism sections 44b of the lower prism sheet 44 have a total thickness of 90 μm, a height of 12 μm, and a 90° apex angle, arranged at a pitch of 24 μm. The protruding prism sections 45b of the upper prism sheet 45 have a total thickness of 155 μm, a height of 25 μm, and a 90° apex angle, arranged at a pitch of 50 μm.

[0073] Note that, as the plurality of light sources 42 , an LED array was used in which a plurality of blue LEDs having a peak wavelength of 450 nm (full width at half maximum of 16 nm) were two-dimensionally arranged at a pitch of 2.8 mm.

[0074] As described below, the brightness uniformity was analyzed and summarized while changing the intersection angle between the arrangement direction of the recesses 22 and the arrangement direction of the plurality of light sources 42 in the light diffusion sheet 43 of the embodiment.

[0075] As the initial state for brightness measurement, as shown in FIG7 , the light diffuser 43 is arranged so that one of the arrangement directions of the recesses 22 coincides with the reference direction (the arrangement direction of the light source 42 (X direction)) (the arrangement angle is 0°), the lower prism 44 is arranged so that the extension direction of the protruding prism portion 44b is rotated 130° counterclockwise relative to the X direction (the arrangement angle is 130°), and the upper prism 45 is arranged so that the extension direction of the protruding prism portion 45b is rotated 40° counterclockwise relative to the X direction (the arrangement angle is 40°).

[0076] As the first measurement, starting from the initial state, the arrangement direction (arrangement angle) of the three light diffusers 43 was rotated counterclockwise by 10° until it reached 90°, and changes in brightness uniformity were analyzed and summarized. Brightness uniformity evaluation was performed as follows. First, the color conversion sheet 46, three light diffusers 43, prism sheets 44 and 45, and upper light diffuser 47 were sequentially arranged on the plurality of light sources 42 (LED array) as described above. Furthermore, a transparent glass plate was placed on the upper light diffuser 47 to prevent the sheets from floating. The brightness in the vertically upward direction (from the LED array toward the glass plate) was measured using a 2D colorimeter UA-200 manufactured by TOPCON TECHNOHOUSE. The resulting 2D brightness distribution image was then corrected for variations in the luminous intensity of each LED and filtered to suppress bright / dark spot noise caused by foreign matter. The average and standard deviation of the brightness across all pixels were then calculated. Finally, we calculated brightness uniformity by defining it as "average brightness / standard deviation of brightness."

[0077] Figure 8 shows the change in brightness uniformity obtained in the first measurement (solid line). It should be noted that in Figure 8, the "arrangement angle" increases from 0° to 90° in 10° increments as the light diffuser 43 rotates. However, since the light diffuser 43 has equivalent arrangements at arrangement angles of 0° (180°) and 90° (270°), "arrangement angles" other than 0° to 90° can be converted to "arrangement angles" of 0° to 90° by adding or subtracting multiples of 90°. The resulting "arrangement angle" is equal to the intersection angle (hereinafter sometimes referred to as the "intersection angle") between the arrangement direction of the recesses 22 of the light diffuser 43 and the arrangement direction of the light sources 42.

[0078] As shown in Figure 8 , it can be seen that to improve brightness uniformity, the arrangement angle of the light diffuser 43, that is, the intersection angle between the arrangement direction of the recesses 22 and the arrangement direction of the light sources 42, can be set to between 30° and 60°, preferably between 35° and 55°, and more preferably between 40° and 50°. It should be noted that to analyze the influence of the arrangement angles of the prism sheets 44 and 45 in the first measurement, the same measurement as in the first measurement was performed, with the arrangement angle of the lower prism sheet 44 set at 90° and the arrangement angle of the upper prism sheet 45 set at 0°. The results confirmed the same correlation between brightness uniformity and the intersection angle (see the dotted line in Figure 8 ).

[0079] Next, as a second measurement, the three diffuser sheets 43 were fixed at their respective orientations (or angles) of 45° and 0°, while prism sheets 44 and 45 were rotated. Changes in brightness uniformity were analyzed and summarized. The brightness uniformity evaluation method was the same as for the first measurement.

[0080] Figure 9 shows the change in brightness uniformity obtained from the second measurement. Note that in Figure 9, the solid line represents the result when the light diffuser 43 is positioned at a 45° angle, while the dashed line represents the result when the light diffuser 43 is positioned at a 0° angle. The horizontal axis of Figure 9 represents the upper prism 45 positioning angle (the rotation angle of the direction in which the protruding prism portion 45b (ridgeline) extends relative to the direction in which the light sources 42 are arranged (the X direction)). The lower prism 44 positioning angle (the rotation angle of the direction in which the protruding prism portion 44b (ridgeline) extends relative to the direction in which the light sources 42 are arranged (the X direction)) is the upper prism 45 positioning angle + 90°.

[0081] As shown in Figure 9, when the arrangement angle (i.e., the cross angle) of light diffuser 43 is set to 45°, brightness uniformity is improved at various arrangement angles of prism sheets 44 and 45, compared to when it is set to 0°. Specifically, when the cross angle is set to 45°, brightness uniformity improves by approximately three times the range of variation depending on the arrangement angle of prism sheets 44 and 45.

[0082] Next, as a third measurement, the arrangement direction (arrangement angle) of the three light diffuser sheets 43, along with the prism sheets 44 and 45, was rotated counterclockwise by 10° increments until a full 180° rotation was achieved. Changes in brightness uniformity were analyzed and summarized. The brightness uniformity evaluation method was the same as for the first measurement.

[0083] Figure 10 shows the change in brightness uniformity obtained from the third measurement. As shown in Figure 10, even when light diffuser 43 and prism sheets 44 and 45 are rotated together relative to the arrangement direction of light source 42, similar to the results of the first measurement, brightness uniformity improves when the arrangement angle, i.e., the crossing angle, of light diffuser 43 is between 30° and 60°, preferably between 35° and 55°, and more preferably between 40° and 50°.

[0084] Next, as the fourth measurement, the arrangement direction (arrangement angle) of each of the three light diffusion sheets 43 was set to 0° or 45°, and the changes in brightness uniformity were analyzed and summarized. The evaluation method for brightness uniformity was the same as the first measurement.

[0085] Figure 11 shows the brightness uniformity obtained from the fourth measurement. It should be noted that in Figure 11, the "top," "middle," and "bottom" on the horizontal axis represent the top, second, and bottom layers of the three diffuser sheets 43, respectively. As shown in Figure 11, the more diffuser sheets 43 arranged at a 45° angle, the higher the brightness uniformity. When there are one or two layers of diffuser sheets 43 arranged at a 45° angle, the higher the brightness uniformity, the higher the placement of the diffuser sheet 43 in the top layer. (Other embodiments)

[0086] In the aforementioned embodiments (including examples, the same applies hereinafter), the backlight unit 40 is formed using the color conversion sheet 46, the light diffusion sheet 43, the brightness enhancement sheet 48, and the upper light diffusion sheet 47. However, the sheet composition (sheet type, arrangement, etc.) that constitutes the backlight unit 40 is not particularly limited.

[0087] In the above-mentioned embodiment, the second surface 21b of the light diffuser 43 is a plane (mirror surface) or an embossed surface, but a column of protrusions such as inverted polygonal cone-shaped recesses or protruding prisms that can be arranged in two dimensions can also be provided on the second surface 21b of the light diffuser 43.

[0088] While the embodiments of the present invention have been described above, the present invention is not limited to the aforementioned embodiments and various modifications are possible within the scope of the present invention. In other words, the description of the aforementioned embodiments is merely illustrative in nature and is not intended to limit the present invention, its applicable objects, or its use.

[0089] 1:TFT substrate 2:CF substrate 3: Liquid crystal layer 5: LCD panel 6: First polarizer 7: Second polarizer 21: base material layer 21a: Side 1 21b: Side 2 22: concave part 40: Backlight unit 41: Reflective sheet 42: Light Source 43: Light diffuser 44: Lower prism 44a: base material layer 44b: Protruding prism 45: Upper prism 45a: base material layer 45b: prism part 46: Color conversion film 47: Upper side light diffuser 48: Brightness enhancement film 50: Liquid crystal display device 50a: Display screen 111: Ridge 112: Center of concave part (apex of inverted pyramid)

Claims

1. A light diffuser sheet assembled in a backlight unit, wherein the backlight unit uses a plurality of light sources arranged in a two-dimensional matrix; on at least one side of the light diffuser sheet, a plurality of slightly inverted quadrangular pyramidal recesses are arranged in a two-dimensional matrix; the angle between the arrangement direction of the plurality of recesses and the arrangement direction of the plurality of light sources is 30° or more and 60° or less; and the brightness uniformity, defined as the average brightness / standard deviation of brightness, is 150 or more.

2. The light diffuser as described in claim 1, wherein the aforementioned cross angle is between 35° and 55°.

3. The light diffuser as described in claim 1 or 2, wherein the aforementioned plurality of recesses are disposed on the light-emitting surface.

4. A backlight unit, assembled in a liquid crystal display device, guides light emitted from a plurality of light sources arranged in a two-dimensional matrix to a display screen; a light diffuser sheet as described in any one of claims 1 to 3 is provided between the display screen and the plurality of light sources.

5. The backlight unit as described in claim 4, wherein a plurality of the aforementioned light diffuser sheets are disposed.

6. The backlight unit as described in claim 4 or 5, wherein a color conversion sheet is provided between the aforementioned display screen and the aforementioned plurality of light sources to convert the wavelength of light emitted from the aforementioned plurality of light sources.

7. The backlight unit as described in claim 4 or 5, wherein a brightness enhancement sheet is provided between the aforementioned light diffuser and the aforementioned display screen to enhance the brightness of light emitted from the aforementioned plurality of light sources.

8. The backlight unit as described in claim 4 or 5, wherein the aforementioned plurality of light sources are disposed on a reflective sheet on the opposite side of the aforementioned display screen when viewed from the aforementioned light diffuser sheet.

9. A liquid crystal display device comprising: a backlight unit as described in any one of claims 4 to 8; and a liquid crystal display panel.

10. An information machine comprising a liquid crystal display device as described in claim 9.

11. A method for manufacturing a backlight unit, used to manufacture a backlight unit assembled in a liquid crystal display device, wherein the backlight unit guides light emitted from a plurality of light sources arranged in a two-dimensional matrix to a display screen; the method for manufacturing the backlight unit includes the following steps: a step of arranging the plurality of light sources; and a step of arranging a light diffuser, wherein the light diffuser has a plurality of slightly inverted quadrangular pyramidal recesses arranged in a two-dimensional matrix on at least one side; the plurality of light sources and the light diffuser are arranged such that the angle between the arrangement direction of the plurality of recesses and the arrangement direction of the plurality of light sources is 30° or more and 60° or less, and the brightness uniformity defined as the average value of brightness / standard deviation of brightness is 150 or more.

Images