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

Abstract

An optical sheet laminate (100) is assembled in a backlight unit (40) using a blue light source (42). The optical sheet laminate (100) includes a diffusion sheet (43) provided with a plurality of recesses (22) in a substantially inverted quadrangular pyramid shape on a first surface (21a), and a pair of prismatic sheets (44) and (45) whose prismatic extension directions are orthogonal to each other. The diffusion sheet (43) is arranged in one sheet or a plurality of sheets laminated. The plurality of recesses (22) are arranged in a two-dimensional matrix, and the intersection angle of the arrangement direction of the arrangement and the prismatic extension direction is 20° or more and 70° or less.

Description

Technical Field

[0001] This disclosure relates to an optical sheet laminate, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing the backlight unit. Background Technology

[0002] In recent years, liquid crystal displays (hereinafter also referred to as LCD screens) have been widely used as display devices for various information devices such as smartphones or tablet computers. As for the backlight of LCDs, the mainstream types are direct-lit type, where the light source is arranged on the back of the LCD panel, or edge-lit type, where the light source is arranged near the side of the LCD panel.

[0003] In the case of direct backlighting, optical sheets such as diffusers and prism sheets are used to diffuse light from light sources such as LEDs (Light Emitting Diodes) in order to improve the brightness and color uniformity of the entire screen (see, for example, Patent Document 1).

[0004] In the direct-lit backlight unit of a thin display such as a laptop or tablet, a diffuser sheet with a two-dimensional arrangement of recesses, such as an inverted pyramid shape, is used, and two prism sheets with orthogonal prism edges are usually arranged on the upper side of the diffuser sheet (the display side).

[0005] Patent Document 1: Japanese Patent Publication No. 2011-129277 Summary of the Invention

[0006] -The technical problem the invention aims to solve-

[0007] For portable information terminals such as laptops or tablets, low power consumption is increasingly required. Consequently, the optical panels assembled in the backlight unit also need to achieve high brightness at low power.

[0008] The purpose of this disclosure is to achieve a high-brightness image even at low power in the backlight unit.

[0009] -Technical solutions for solving technical problems-

[0010] To achieve the above objectives, the optical sheet stack disclosed herein is an optical sheet stack assembled in a backlight unit using a blue light source. The optical sheet stack includes a diffuser and a pair of prism sheets. At least one surface of the diffuser has a plurality of recesses in the shape of a generally inverted quadrangular pyramid. The prism extension directions of the pair of prism sheets are orthogonal to each other. The diffuser is arranged in a single sheet or in multiple stacks. The plurality of recesses are arranged in a two-dimensional matrix. The angle between the arrangement direction and the prism extension direction is more than 20° and less than 70°.

[0011] According to the optical sheet stack of this disclosure, compared with the same light source, the same power, and the same optical sheet stack structure, the brightness of the optical sheet stack of this disclosure is increased compared to the case where the angle difference between the arrangement direction of the concave portion (inverted square pyramid) of the diffuser and the prism extension direction of the prism sheet is around 0° or around 90°. Therefore, in the backlight unit, a high-brightness image can be achieved even at low power.

[0012] In the optical sheet stacks disclosed herein, when the aforementioned cross angle is 25° or more and 35° or less, or 55° or more and 65° or less, the brightness can be further increased.

[0013] The backlight unit disclosed herein is assembled in a liquid crystal display device and guides light emitted from a blue light source to the display screen side via a color conversion sheet. An optical sheet stack as described above is included between the display screen and the blue light source, and the diffuser sheet is arranged between the blue light source and the pair of prism sheets.

[0014] According to the backlight unit disclosed herein, since it includes the optical sheet stack mentioned above, a high-brightness image can be achieved even at low power.

[0015] In the backlight unit disclosed herein, the blue light source can be arranged on a reflective sheet, which is positioned on the opposite side of the displayed image when viewed with reference to the diffuser sheet. In this way, the light is further diffused through multiple reflections between the diffuser and the reflective sheet, thus improving brightness uniformity.

[0016] In the backlight unit disclosed herein, the diffuser sheets can be arranged in multiple stacked layers between the pair of prism sheets and the blue light source. In this way, light directly incident from the blue light source is repeatedly diffused by the multiple diffuser sheets, thus improving brightness uniformity.

[0017] In the backlight unit disclosed herein, the distance between the blue light source and the diffuser can be less than 5 mm, preferably less than 2.5 mm, and more preferably less than 1 mm. This allows for the miniaturization of the backlight unit.

[0018] In the backlight unit disclosed herein, the color conversion sheet can be arranged between the blue light source and the diffuser, or between the diffuser and the pair of prism sheets. This allows the color conversion sheet to convert light emitted from the blue light source into white light.

[0019] The liquid crystal display device involved in this disclosure includes the backlight unit and liquid crystal display panel mentioned above.

[0020] According to the liquid crystal display device disclosed herein, since it includes the backlight unit disclosed herein, it is possible to achieve a high-brightness image even at low power.

[0021] The information equipment involved in this disclosure includes the liquid crystal display device mentioned above.

[0022] According to the information device disclosed herein, since it includes the liquid crystal display device disclosed herein, a high-brightness image can be achieved even at low power.

[0023] The method for manufacturing a backlight unit disclosed herein is a method for manufacturing a backlight unit assembled in a liquid crystal display device and guiding light emitted from a blue light source to the display screen side via a color conversion sheet. It includes a step of arranging a diffuser sheet, either as a single sheet or in multiple stacks, on the display screen side when viewed with the blue light source as a reference, wherein at least one side of the diffuser sheet has a plurality of recesses in a generally inverted quadrangular pyramid shape; and a step of arranging a pair of prism sheets with prism extension directions orthogonal to each other on the display screen side when viewed with the diffuser sheet as a reference. In the backlight unit, the plurality of recesses are arranged in a two-dimensional matrix, and the diffuser sheet and the pair of prism sheets are arranged such that the angle between the arrangement direction and the prism extension direction is 20° or more and 70° or less.

[0024] According to the manufacturing method of the backlight unit disclosed herein, comparing with the same light source, the same power, and the same optical sheet stacking structure, the manufacturing method of the backlight unit disclosed herein can increase brightness compared to cases where the angle difference between the arrangement direction of the concave portion (inverted square pyramid) of the diffuser and the prism extension direction of the prism sheet is around 0° or around 90°. Therefore, a backlight unit that can achieve high brightness even at low power can be obtained.

[0025] -The Effects of the Invention-

[0026] According to this disclosure, a high-brightness image can be achieved even at low power in the backlight unit. Attached Figure Description

[0027] Figure 1 It is a cross-sectional view of a liquid crystal display device including the backlight unit involved in the embodiment;

[0028] Figure 2 This is a cross-sectional view of a backlight unit assembled with the optical sheet stack according to the embodiment;

[0029] Figure 3 It is a cross-sectional view of the diffuser sheet included in the optical sheet stack according to the embodiment;

[0030] Figure 4 It is a perspective view of the diffuser sheet included in the optical sheet stack according to the embodiment;

[0031] Figure 5 This is a diagram illustrating an example of the relationship between the arrangement direction of the recesses of the diffuser sheet and the prism extension direction of the prism sheet in the optical sheet stack according to the embodiment.

[0032] Figure 6 This is a diagram illustrating the relationship between the arrangement angles of the diffuser (inverted pyramid) and prism sheets in the optical sheet stack involved in the embodiment;

[0033] Figure 7 This is a diagram showing the brightness variation when the arrangement angle of the diffuser (inverted pyramid plate) is changed in the optical sheet stack involved in the embodiment;

[0034] Figure 8 This is a diagram showing the brightness change when the arrangement angle of the upper prism is changed in the optical sheet stack involved in the embodiment. Detailed Implementation

[0035] (Implementation Method)

[0036] The optical laminate, backlight unit, liquid crystal display device, information device, and manufacturing method of the backlight unit according to the embodiments will now be described with reference to the accompanying drawings. It should be noted that the scope of this disclosure is not limited to the following embodiments, and modifications can be made freely within the scope of the technical concept of this disclosure.

[0037] <Structure of a Liquid Crystal Display Device>

[0038] like Figure 1 As shown, the 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 disposed on the back side of the liquid crystal display panel 5 through the first polarizing plate 6.

[0039] The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 disposed opposite to each other, a liquid crystal layer 3 disposed between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) disposed in a frame shape for sealing the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0040] From the front ( Figure 1 The shape of the display screen 50a of the liquid crystal display device 50 (viewed from above) is, in principle, rectangular or square. However, it is not limited to this and can be any shape such as a rectangle with rounded corners, oval, circular, trapezoidal, or an instrument panel.

[0041] In each sub-pixel corresponding to each pixel electrode in the liquid crystal display device 50, a predetermined voltage is applied to the liquid crystal layer 3 to change the orientation state of the liquid crystal layer 3. This adjusts the transmittance of light incident from the backlight unit 40 via the first polarizing plate 6. The light with adjusted transmittance is then emitted via the second polarizing plate 7 to display an image.

[0042] The liquid crystal display device 50 of this embodiment can be used as a display device assembled in various information devices (such as in-vehicle devices such as car navigation systems, personal computers, mobile phones, laptops or tablets, portable information terminals, portable game consoles, photocopiers, ticket vending machines, ATMs, etc.).

[0043] TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film disposed covering each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and respectively connected to the plurality of TFTs, and an alignment film disposed covering each pixel electrode. CF substrate 2 includes, for example, a black matrix arranged in a grid on a glass substrate, color filters containing red, green, and blue layers disposed between each grid of the black matrix, a common electrode disposed covering the black matrix and the color filters, and an alignment film disposed covering the common electrode. Liquid crystal layer 3 is formed of a nematic liquid crystal material, etc., which contains liquid crystal molecules with electro-optic properties. First polarizing plate 6 and second polarizing plate 7 include, for example, a polarizing layer having a unidirectional polarization axis and a pair of protective layers disposed to sandwich the polarizing layer.

[0044] <Structure of Backlight Unit and Optical Sheet Stack>

[0045] like Figure 2 As shown, the backlight unit 40 includes: a reflective sheet 41, a plurality of blue light sources 42 arranged two-dimensionally on the reflective sheet 41, and an optical sheet stack 100 disposed above the plurality of blue light sources 42. The optical sheet stack 100 has a diffuser 43 disposed on the side of the blue light sources 42, and a pair of prism sheets 44 and 45 disposed on the upper side of the diffuser 43 (on the side of the display screen 50a). In addition, the optical sheet stack 100 has a color conversion sheet 46 between the blue light sources 42 and the diffuser 43.

[0046] In this embodiment, diffuser sheets 43 of the same structure are stacked, for example, in two layers in the backlight unit 40. One diffuser sheet 43 can be used, or three or more can be stacked. In particular, if sufficient brightness uniformity can be achieved by precisely arranging the blue light source 42 of the backlight unit 40, a single diffuser sheet 43 can also be used. The pair of prism sheets 44 and 45 can also be a lower prism sheet 44 and an upper prism sheet 45 whose prism extension directions (the directions in which the prism edges extend) are orthogonal to each other. A color conversion sheet 46 is arranged between the diffuser sheet 43 and the pair of prism sheets 44 and 45.

[0047] The reflective sheet 41 is formed, for example, from a thin film of white polyethylene terephthalate resin, a silver vapor-deposited film, etc.

[0048] The type of blue light source 42 is not particularly limited; it can be, for example, an LED element or a laser element. From the perspective of cost and productivity, an LED element is preferred. To adjust the light emission angle characteristics of the LED, a lens can be mounted on the LED element. The blue light source 42 emits light, for example, light with x < 0.24 and y < 0.18 in the CIE 1931 chromaticity coordinates. When the blue light source 42 is composed of an LED element, the LED element (chip) can be rectangular when viewed from above. In this case, the length of one side of the LED element can be 10 μm or more (preferably 50 μm or more) and 20 mm or less (preferably 10 mm or less, more preferably 5 mm or less). LED chips with a side length of a few millimeters can also be arranged two-dimensionally on the reflector 41 at constant intervals. When multiple LED chips are arranged at equal intervals, the distance between the centers of two adjacent chips can be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0049] like Figure 3 As shown, the diffuser 43 has a substrate layer 21. The diffuser 43 (substrate layer 21) has a first surface 21a that serves as a light emitting surface and a second surface 21b that serves as a light incident surface. That is, the diffuser 43 is arranged such that the second surface 21b faces the blue light source 42. The resin that forms the base material of the substrate layer 21 is not particularly limited as long as it is composed of a light-transmitting material, such as acrylate, polystyrene, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. The substrate layer 21 may contain a diffuser or other additives, or it may not contain additives at all. The additives that may be contained in the substrate layer 21 are not particularly limited, and may be inorganic particles such as silica, titanium dioxide, aluminum hydroxide, barium sulfate, etc., or organic particles such as acrylate, acrylonitrile, polysilicon, polystyrene, polyamide, etc.

[0050] The thickness of the 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 0.1 mm or more. If the thickness of the diffuser 43 exceeds 3 mm, it is difficult to achieve a thinner liquid crystal display. If the thickness of the diffuser 43 is less than 0.1 mm, it is difficult to achieve uniform brightness. The diffuser 43 can be in the form of a thin film or a sheet (plate).

[0051] like Figure 4 As shown, a plurality of recesses 22, roughly inverted square pyramid shape (inverted pyramid shape), are arranged in a two-dimensional matrix on the first surface 21a of the diffuser 43. In other words, the recesses 22 are arranged along two mutually orthogonal directions. Adjacent recesses 22 are separated from each other by edges 111. Edges 111 extend along the two directions in which the recesses 22 are arranged. The center (apex of the inverted pyramid) 112 of the recesses 22 is the deepest part of the recesses 22. Figure 4 For simplicity, the illustration shows the recesses 22 arranged in a 5×5 matrix, but the actual number of recesses 22 is much greater. In a two-dimensional arrangement of multiple recesses 22, each recess 22 can be provided on the first surface 21a without gaps, or it can be provided at predetermined intervals. In addition, some recesses 22 can also be arranged randomly without compromising the light diffusion effect.

[0052] The apex angle θ of the recess 22 can be, for example, 90°, the spacing p of the recesses 22 can be, for example, 100 μm, and the depth of the recesses 22 can be, for example, 50 μm. The apex angle θ of the recess 22 refers to the angle formed by the section lines of the inclined planes in the cross-section obtained by cutting through the center (apex 112 of the inverted pyramid) of the recess 22 with a plane perpendicular to the arrangement surface of the diffuser 43 (longitudinal section) and perpendicularly cutting through a pair of opposing inclined planes sandwiching that center. Furthermore, the spacing p of the recesses 22 refers to the distance between the centers (apex 112 of the inverted pyramid) of adjacent recesses 22 (distance along a direction parallel to the arrangement surface of the diffuser 43).

[0053] The second surface 21b of the diffuser sheet 43 can be, for example, a flat surface (mirror surface) or an embossed surface. The diffuser sheet 43 can be composed of a single-layer structure, such as a substrate layer 21, which has an uneven shape (recess 22) on the first surface 21a. The diffuser sheet 43 can also be composed of a double-layer structure, wherein one layer is a substrate layer with flat surfaces on both sides, and the other layer has an uneven shape on one side. The diffuser sheet 43 can also be composed of a structure with three or more layers, including a layer with an uneven shape on one side. The manufacturing method of the diffuser sheet 43 is not particularly limited, and for example, extrusion molding, injection molding, etc. can be used.

[0054] The steps for manufacturing a single-layer diffused sheet with an uneven surface using extrusion molding are as follows. First, granular plastic granules with added diffusing agent (which may also be mixed with granular plastic granules without diffusing agent) are fed into a single-screw extruder and melted and mixed while heated. Then, the molten resin extruded from a T-die is clamped between two metal rollers and cooled, then transported by guide rollers and cut into single-sheet plates by a slicer, thereby producing the diffused sheet. Here, by using metal rollers with surface shapes opposite to the desired unevenness to clamp the molten resin, the opposite shape of the roller surface is transferred to the resin, thus imparting the desired unevenness to the surface of the diffused sheet. Because the shape of the roller surface is not necessarily 100% transferred to the resin, the shape of the roller surface can be designed by reverse calculation based on the degree of transfer.

[0055] When manufacturing diffuse sheets with a two-layer structure having an uneven surface using extrusion molding, for example, after feeding the granular plastic granules required to form each layer into two single-screw extruders, the same steps as described above are performed on each layer, and the resulting sheets are stacked together.

[0056] Alternatively, a diffuse sheet with a textured surface and a double-layer structure can be produced as follows: First, granular plastic granules required to form each layer are fed into two single-screw extruders, where they are heated, melted, and mixed. Then, the molten resin forming each layer is fed into a T-die, stacked within the die, and the stacked molten resin extruded from the die is cooled using two metal rollers. Subsequently, the stacked molten resin can be conveyed using guide rollers and cut into single-sheet plates using a slicer, thereby producing a diffuse sheet with a textured surface and a double-layer structure.

[0057] Alternatively, UV (ultraviolet) shaped transfer can be used to manufacture diffused sheets as described below. First, uncured UV-curable resin is filled onto a roller with a shape opposite to the desired raised or recessed shape. The substrate is then pressed onto the resin. Next, with the roller and substrate integrated, UV light is irradiated to cure the resin. The sheet with the raised or recessed shape transferred through the resin is then peeled off the roller. Finally, the sheet is irradiated with UV light again to fully cure the resin, thus creating a diffused sheet with a raised or recessed surface.

[0058] It should be noted that in this disclosure, considering the difficulty in forming geometrically strictly defined inverted square pyramid recesses using conventional shape transfer techniques, the term "approximately inverted square pyramid" is used. However, "approximately inverted square pyramid" naturally includes shapes that are truly or substantially inverted square pyramids. "Approximately" means approximating, and "approximately inverted square pyramid" means a shape that can approximate an inverted square pyramid. For example, for an inverted square frustum with a flat top, an inverted square frustum with a small top area is also included in "approximately inverted square pyramid" without losing the function and effect of the invention. Within the range of unavoidable shape deviations caused by the processing precision in industrial production, the shape after deformation of an inverted square pyramid is also included in "approximately inverted square pyramid".

[0059] Because light needs to pass through, prism sheets 44 and 45 are formed primarily of transparent (e.g., colorless and transparent) synthetic resin. Prism sheets 44 and 45 can also be formed as a single unit. The lower prism sheet 44 has a substrate layer 44a and a row of protrusions formed by a plurality of protruding prism portions 44b stacked on the surface of the substrate layer 44a. Similarly, the upper prism sheet 45 has a substrate layer 45a and a row of protrusions formed by a plurality of protruding prism portions 45b stacked on the surface of the substrate layer 45a. The protruding prism portions 44b and 45b are respectively stacked in strips on the surfaces of the substrate layers 44a and 45a. The protruding prism portions 44b and 45b are triangular prisms whose back surfaces are in contact with the surfaces of the substrate layers 44a and 45a. The extending directions of the protruding prism portions 44b and 45b are orthogonal to each other. In this way, the lower prism 44 can be used to refract the light rays incident from the diffuser 43 toward the normal direction, and the upper prism 45 can be used to refract the light rays emitted from the lower prism 44 in a manner that is approximately perpendicular to the display screen 50a.

[0060] The lower limit of the thickness of prism sheets 44 and 45 (the height from the back surface of substrate layers 44a and 45a to the apex of the ribbed prism portions 44b and 45b) can be, for example, about 50 μm, more preferably about 100 μm. The upper limit of the thickness of prism sheets 44 and 45 can be about 200 μm, more preferably about 180 μm. The lower limit of the spacing between the ribbed prism portions 44b and 45b on prism sheets 44 and 45 can be, for example, about 20 μm, more preferably about 25 μm. The upper limit of the spacing between the ribbed prism portions 44b and 45b on prism sheets 44 and 45 can be, for example, about 100 μm, more preferably about 60 μm. The apex angle of the ribbed prism portions 44b and 45b can be, for example, 85° or more and 95° or less. The lower limit of the refractive index of the ribbed prism portions 44b and 45b can be, for example, 1.5, more preferably 1.55. The upper limit of the refractive index of the raised prism portions 44b and 45b can be, for example, 1.7.

[0061] The prism sheets 44 and 45 can be prism sheets formed by providing raised prism portions 44b and 45b on substrate layers 44a and 45a formed of, for example, PET (polyethylene terephthalate) film, by shape transfer using UV-curable acrylic resin, or they can be prism sheets integrally formed with the raised prism portions 44b and 45b and the substrate layers 44a and 45a.

[0062] Color conversion sheet 46 is a wavelength conversion sheet that converts light from blue light source 42 into light with a peak wavelength of any color (e.g., green or red). For example, 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 blue light source 42 emits blue light with a wavelength of 450 nm, since a portion of the blue light is converted into green and red light by color conversion sheet 46, the light passing through color conversion sheet 46 becomes white light. For example, QD (quantum dot) sheets, fluorescent sheets, etc., can be used as color conversion sheet 46.

[0063] A polarizer may also be provided on the upper side of the prism sheets 44 and 45 (on the side of the display screen 50a), but the illustration is omitted. The polarizer increases the brightness of the display screen 50a by preventing the light emitted from the backlight unit 40 from being absorbed by the first polarizer 6 of the liquid crystal display device 50.

[0064] In the optical sheet laminate 100 of this embodiment described above, for example, as Figure 5 As shown, the arrangement direction (X and Y directions) of the recesses 22 of the diffuser 43 intersects the extending directions of the protruding prism portions 44b and 45b of the prism sheets 44 and 45 at an angle of 20° or more and 70° or less, more preferably at an angle of 25° or more and 35° or less, or at an angle of 55° or more and 65° or less. It should be noted that in Figure 5 For simplicity, the illustration of the protruding prism portion 44b is omitted. However, since the extension direction of the protruding prism portion 44b is orthogonal to the extension direction of the protruding prism portion 45b, the extension direction of the protruding prism portion 44b also satisfies the aforementioned cross angle range when the extension direction of the protruding prism portion 45b satisfies the aforementioned cross angle range.

[0065] <Features of the Implementation Method>

[0066] The optical sheet stack 100 of this embodiment is assembled in a backlight unit 40 using a blue light source 42. The optical sheet stack 100 includes: a diffuser sheet 43 having a plurality of recesses 22 in the shape of a generally inverted quadrangular pyramid on a first surface 21a; and a pair of prism sheets 44 and 45 whose extending directions (hereinafter sometimes referred to as prism extending directions) are orthogonal to each other. The diffuser sheet 43 is arranged in a single sheet or in multiple stacks. The plurality of recesses 22 are arranged in a two-dimensional matrix, and the angle between the arrangement direction and the prism extending direction is 20° or more and 70° or less.

[0067] According to the optical sheet stack 100 of this embodiment, compared with the same light source, the same power, and the same optical sheet stack structure, the brightness of the optical sheet stack 100 is increased compared to the case where the angle difference between the arrangement direction of the concave portion (inverted square pyramid) of the diffuser 43 and the prism extension direction of the prism sheets 44 and 45 is around 0° or around 90°. Therefore, in the backlight unit 40, a high-brightness image can be achieved even at low power.

[0068] In the optical sheet stack 100 of this embodiment, when the above-mentioned cross angle is 25° or more and 35° or less, or 55° or more and 65° or less, the brightness can be further increased.

[0069] In this embodiment, the backlight unit 40 is assembled in the liquid crystal display device 50, and guides the light emitted from the blue light source 42 to the display screen 50a side via the color conversion sheet 46. The backlight unit 40 includes the optical sheet laminate 100 of this embodiment between the display screen 50a and the blue light source 42, and the diffuser sheet 43 is arranged between the blue light source 42 and the prism sheets 44 and 45.

[0070] According to the backlight unit 40 of this embodiment, since it includes the optical sheet laminate 100 of this embodiment, a high-brightness image can be achieved even at low power.

[0071] In the backlight unit 40 of this embodiment, the blue light source 42 can be arranged on the reflective sheet 41, which is located on the opposite side of the displayed image 50a when viewed with reference to the diffuser sheet 43. In this way, the light is further diffused by multiple reflections between the diffuser sheet 43 and the reflective sheet 41, thus improving the brightness uniformity.

[0072] In the backlight unit 40 of this embodiment, multiple diffuser sheets 43 can be stacked and arranged between the prism sheets 44 and 45 and the blue light source 42. In this way, the light directly emitted from the blue light source 42 is repeatedly diffused by the multiple diffuser sheets 43, thus improving the brightness uniformity.

[0073] In the backlight unit 40 of this embodiment, when the distance between the blue light source 42 and the diffuser 43 is 5 mm or less, the backlight unit 40 can be miniaturized. In addition, considering the future trend of thinner small and medium-sized liquid crystal displays, the distance between the blue light source 42 and the diffuser 43 is more preferably 2.5 mm or less, further preferably 1 mm or less, and ultimately, extremely preferably 0 mm.

[0074] In the backlight unit 40 of this embodiment, the color conversion sheet 46 can also be arranged between the blue light source 42 and the diffuser 43, or between the diffuser 43 and the prism sheets 44 and 45. In this way, the light emitted from the blue light source 42 can be converted into white light using the color conversion sheet 46.

[0075] The manufacturing method of the backlight unit 40 in this embodiment includes: arranging a diffuser sheet 43, which has a plurality of recesses 22 in the shape of a generally inverted quadrangular pyramid, on the side of the display screen 50a relative to the blue light source 42, either as a single sheet or in multiple stacks; and arranging a pair of prism sheets 44 and 45, whose prism extension directions are orthogonal to each other, on the side of the display screen 50a when viewed with the diffuser sheet 43 as a reference. The plurality of recesses 22 are arranged in a two-dimensional matrix, and the diffuser sheet 43 and the pair of prism sheets 44 and 45 are arranged such that the angle between the arrangement direction of this arrangement and the prism extension direction is 20° or more and 70° or less.

[0076] According to the manufacturing method of the backlight unit 40 of this embodiment, comparing with the same light source, the same power, and the same optical sheet stacking structure, the manufacturing method of the backlight unit 40 of this embodiment can increase the brightness when the angle difference between the arrangement direction of the concave portion (inverted square pyramid) of the diffuser 43 and the prism extension direction of the prism sheets 44 and 45 is around 0° or around 90°. Therefore, a backlight unit 40 that can achieve a high brightness image even at low power can be obtained.

[0077] The liquid crystal display device 50 of this embodiment includes a liquid crystal display panel 5 and a backlight unit 40 of this embodiment. Therefore, by using the backlight unit 40, a high-brightness image can be achieved even at low power. The same effect can be obtained in information devices (such as laptops, tablets, and other portable information terminals) that are equipped with the liquid crystal display device 50.

[0078] (Example)

[0079] The following describes the embodiments.

[0080] As an example, the optical sheet stack 100 uses an optical sheet stack configured as follows: two diffuser sheets 43 of the same structure with a thickness of 130 μm are stacked in the same direction, and a lower prism sheet 44 and an upper prism sheet 45 with prism extension directions orthogonal to each other are arranged on top of them. It should be noted that, as an example, two types of optical sheet stack 100 are prepared, one of which has a color conversion sheet 46 composed of QD sheet arranged on the lower side of the diffuser sheet 43, and the other does not have a color conversion sheet 46 arranged.

[0081] Using a UV-curable resin with a refractive index of 1.587, inverted pyramid-shaped recesses 22 with a vertices of 90° and a depth of 50 μm are arranged two-dimensionally at 100 μm intervals on a transparent polycarbonate sheet with a thickness of 80 μm, thereby forming a diffuser sheet 43. The diffuser sheet 43 is arranged such that the forming surface of the recesses 22 (first surface 21a) becomes the light emitting surface. The second surface 21b of the diffuser sheet 43 is configured as a flat surface (mirror surface).

[0082] The raised prism portions 44b and 45b are formed on the substrate layers 44a and 45a made of PET film using a UV-curable acrylic resin composed of acrylate. The lower prism portion 44 is formed by arranging raised prism portions 44b with a total thickness of 145 μm, a height of 12 μm, and a apex angle of 94° at a spacing of 25 μm. The upper prism portion 45 is formed by arranging raised prism portions 45b with a total thickness of 128 μm, a height of 24 μm, and a apex angle of 93° at a spacing of 51 μm.

[0083] A blue light source 42 is arranged on the lower side (diffuser 43 side) of the optical sheet stack 100 in the embodiment. The brightness of the light passing through the optical sheet stack 100 is checked while changing the arrangement relationship between the diffuser 43 and the prism sheets 44 and 45. As the blue light source 42, an LED array is used, which consists of multiple blue LEDs with a peak wavelength of 450nm (half-width 16nm) arranged two-dimensionally at a spacing of 2.8mm.

[0084] As the initial state for brightness measurement, such as Figure 6 As shown, the diffuser sheet 43 is arranged such that one of the arrangement directions of the recess 22 is aligned with the reference direction (X-axis) (arrangement angle is 0°), the lower prism sheet 44 is arranged such that the extension direction of the protruding prism portion 44b is rotated 102° counterclockwise relative to the X-axis (arrangement angle is 102°), and the upper prism sheet 45 is arranged such that the extension direction of the protruding prism portion 45b is rotated 12° counterclockwise relative to the X-axis (arrangement angle is 12°).

[0085] As a first brightness measurement, starting from the initial state described above, the brightness change is measured while rotating the arrangement direction (arrangement angle) of the two diffuser sheets (inverted pyramid sheets) 43 180° counterclockwise at a rate of 10° each time. Furthermore, for comparison, as a second brightness measurement, the brightness change is measured while rotating the arrangement direction (arrangement angle) of the two prism sheets 44 and 45 180° counterclockwise at a rate of 10° each time, starting from the initial state described above.

[0086] In each brightness measurement, the optical sheet stack 100 of the embodiment is arranged above the blue light source 42 (LED array), and a transparent glass plate is further placed above the optical sheet stack 100 to suppress sheet lifting. A UA-200 two-dimensional color luminance meter manufactured by Topcon Techno House is used to measure the brightness in the vertical direction (from the LED array towards the glass plate) over a 33mm square area. Based on the obtained two-dimensional brightness distribution image, the luminous intensity deviation of each LED is corrected, and after filtering to suppress bright / dark spot noise caused by foreign objects, the average brightness of all pixels is calculated.

[0087] Figure 7 and Figure 8 The brightness changes obtained from the first and second brightness measurements described above are shown respectively. Figure 7 and Figure 8 In the diagram, the horizontal axis represents the difference between the arrangement angle of the upper prism sheet (45°) and the arrangement angle of the diffuse sheet (inverted pyramid sheet) (43°) (hereinafter sometimes simply referred to as the "arrangement angle difference"). The initial arrangement angle difference is 12° (refer to...). Figure 6 ).

[0088] It should be noted that, in Figure 7 During this process, as the diffuser plate 43 rotates, the "arrangement angle difference" decreases by 10° each time. Figure 8During the rotation of the upper prism sheet 45, the "arrangement angle difference" increases by 10° each time. However, since the diffuser sheet 43 has equivalent shapes at arrangement angles of 0° (180°) and 90° (270°), the "arrangement angle difference" is converted as follows. That is, when the "arrangement angle difference" is negative, it is converted to a value greater than or equal to 0° and less than or equal to 90° by adding a multiple of 90° to the "arrangement angle difference"; when the "arrangement angle difference" exceeds 90°, it is converted to a value greater than or equal to 0° and less than or equal to 90° by subtracting a multiple of 90° from the "arrangement angle difference". In this way, for the same "arrangement angle difference" on the horizontal axis, there will be multiple brightness measurement values ​​on the vertical axis. In addition, the "arrangement angle difference" calculated according to the above description is equal to the intersection angle (hereinafter sometimes simply referred to as the "intersection angle") between the arrangement direction of the recess 22 of the diffuser sheet 43 and the extension direction of the protruding prism portions 44b and 45b of the prism sheets 44 and 45.

[0089] In addition, Figure 7 and Figure 8 In this context, brightness is expressed as relative brightness, which is 100% of the brightness measurement of the optical sheet stack 100 with the color conversion sheet 46 set in its initial state (when the "arrangement angle difference" is 12°).

[0090] like Figure 7 and Figure 8 As shown, regardless of the presence of the color conversion chip 46, compared to when the "arrangement angle difference" is near 0° or 90° (i.e., the "cross angle" is near 0° or 90°), the brightness is significantly increased within the range of 20° to 70° (i.e., the "cross angle" is in the range of 20° to 70°). In particular, when the "arrangement angle difference" is near 30° and 60° (i.e., the "cross angle" is near 30° and 60°), the relative brightness reaches its maximum value, and relatively large brightness can be obtained within ±5° of the "arrangement angle difference" that reaches this maximum value.

[0091] As explained above, it can be seen that in the optical sheet stack 100 of the embodiment, whether the arrangement angle of the diffuser 43 is changed or the arrangement angle of the prism sheets 44 and 45 is changed, the brightness increases in the range of 20° to 70° of the "cross angle", and in particular, the brightness increases significantly in the range of 25° to 35° or 55° to 65° of the "cross angle".

[0092] (Other implementation methods)

[0093] In the above embodiments (including examples, the same below), the optical sheet laminate 100 is composed of diffuser sheet 43, prism sheets 44 and 45, and color conversion sheet 46. However, the optical sheet laminate 100 may also include other optical sheets in addition to diffuser sheet 43, prism sheets 44 and 45, and color conversion sheet 46.

[0094] Furthermore, in the above embodiment, regarding the recess 22 provided on the first surface 21a of the diffuser sheet 43 included in the optical sheet laminate 100, the inverted polygonal pyramid shape of the recess 22 is an inverted square pyramid, but it can also be replaced by other shapes that can be arranged in two dimensions, such as an inverted triangular pyramid or an inverted hexagonal pyramid. Alternatively, instead of the recess 22 that can be arranged in two dimensions, a row of protrusions such as prism sections can be provided. In addition, the second surface 21b of the diffuser sheet 43 is a flat surface (mirror surface) or an embossed surface, but a row of protrusions such as an inverted polygonal pyramid shape or prism sections that can be arranged in two dimensions can also be provided on the second surface 21b of the diffuser sheet 43.

[0095] The embodiments of this disclosure have been described above, but this disclosure is not limited to the above embodiments, and various modifications can be made within the scope of this disclosure. That is, the description of the above embodiments is merely an example in essence and is not intended to limit this disclosure, its application, or its uses.

[0096] -Symbol Explanation-

[0097] 1 TFT substrate

[0098] 2 CF substrate

[0099] 3. Liquid crystal layer

[0100] 5 LCD display panel

[0101] 6 First polarizing plate

[0102] 7 Second polarizing plate

[0103] 21 Substrate layer

[0104] 21a First page

[0105] 21b Second page

[0106] 22 recess

[0107] 40 backlight units

[0108] 41 Reflector

[0109] 42 Blue light source

[0110] 43 Diffuse Film

[0111] 44. Lower prism lens

[0112] 44a Substrate layer

[0113] 44b Protruding prism section

[0114] 45 Upper prism lens

[0115] 45a Substrate Layer

[0116] 45b Raised prism section

[0117] 46 Color Converter

[0118] 50 LCD display devices

[0119] 50a display screen

[0120] 100 optical sheet laminates

[0121] 111 Edge

[0122] 112 Center of the concave section (apex of the inverted pyramid).

Claims

1. An optical sheet laminate assembled in a backlight unit using a blue light source, characterized in that: The optical sheet stack includes a diffuser and a pair of prism sheets. At least one surface of the diffuser sheet has a plurality of recesses in the shape of approximately an inverted quadrangular pyramid. The prisms of the pair of prism sheets extend in directions that are orthogonal to each other. The diffuser sheets are arranged in one piece or in multiple stacked pieces. The plurality of recesses are arranged in a two-dimensional matrix, and the angle between the arrangement direction and the extension direction of the prism is greater than 20° and less than 70°.

2. The optical sheet laminate according to claim 1, characterized in that: The intersection angle is 25° or more and 35° or less, or 55° or more and 65° or less.

3. A backlight unit, assembled in a liquid crystal display device, guides light emitted from a blue light source to the display screen side via a color conversion sheet, characterized in that: The display screen and the blue light source include an optical sheet laminate as described in claim 1 or 2. The diffuser sheet is arranged between the blue light source and the pair of prism sheets.

4. The backlight unit according to claim 3, characterized in that: The blue light source is arranged on a reflective sheet, which is positioned on the opposite side of the displayed image when viewed with reference to the diffuser sheet.

5. The backlight unit according to claim 3, characterized in that: The diffuser sheet is arranged in multiple layers between the pair of prism sheets and the blue light source.

6. The backlight unit according to claim 3, characterized in that: The distance between the blue light source and the diffuser is less than 5 mm.

7. The backlight unit according to claim 3, characterized in that: The color conversion sheet is arranged between the blue light source and the diffuser, or between the diffuser and the pair of prism sheets.

8. A liquid crystal display device, characterized in that: The liquid crystal display device includes a backlight unit as described in any one of claims 3 to 7, and a liquid crystal display panel.

9. An information device, characterized in that: The information device includes the liquid crystal display device as described in claim 8.

10. A method for manufacturing a backlight unit, wherein the backlight unit is assembled in a liquid crystal display device, and guides light emitted from a blue light source to the display screen side via a color conversion sheet, characterized in that: The method for manufacturing the backlight unit includes: The process of arranging diffuser sheets, either as a single sheet or in multiple stacks, on the side of the display screen when viewed against the blue light source, wherein at least one side of the diffuser sheet has a plurality of recesses in the shape of a generally inverted quadrangular pyramid; and The process of arranging a pair of prism sheets with orthogonal extension directions on the side of the display screen when viewed with the diffuser as a reference. In the backlight unit, the plurality of recesses are arranged in a two-dimensional matrix, and the diffuser sheet and the pair of prism sheets are arranged such that the intersection angle between the arrangement direction and the extension direction of the prism is more than 20° and less than 70°.

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