Optical sheet laminate

Abstract

An optical sheet laminate (100) assembled in a backlight unit (40) is provided with: a plurality of diffusion sheets (43) in which a plurality of substantially inverted rectangular pyramid-shaped recesses (22) are arranged in a two-dimensional matrix on a first surface (21a); the backlight unit (40) includes a pair of prism sheets (44, 45) in which prism extension directions are orthogonal to each other. The arrangement direction of the plurality of recesses (22) on the diffusion sheet (43) closest to the pair of prism sheets (44) and (45) among the plurality of diffusion sheets (43) intersects the prism extension direction at an angle of 5-15 DEG or 75-85 DEG.

Description

[0001] This application is a divisional application of an invention patent application with an application date of June 29, 2022, an application number of 202280047966.3 (international application number of PCT / JP2022 / 025924), and an invention name of "Optical sheet stack, backlight unit, liquid crystal display device, information equipment and method for manufacturing a backlight unit". Technical Field

[0002] The present disclosure relates to an optical sheet stack, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing the backlight unit. Background Art

[0003] In recent years, liquid crystal display devices (hereinafter also referred to as liquid crystal displays) have been widely used as display devices in various information devices such as smartphones and tablet terminals. As for the backlight of liquid crystal displays, since it is required to have high brightness and high contrast, the direct type in which the light source is arranged on the back of the liquid crystal panel has become the mainstream.

[0004] When a direct backlight is used, an optical sheet such as a diffusion sheet or a prism sheet is used to diffuse light from a light source such as an LED (Light Emitting Diode) to improve the brightness and color uniformity of the entire screen (see, for example, Patent Document 1).

[0005] In the direct-type backlight unit of a liquid crystal display of a notebook computer or tablet computer, a diffusion sheet having two-dimensionally arranged recesses such as inverted pyramids is used, and two prism sheets whose prism ridges are orthogonal to each other are usually arranged on the upper side of the diffusion sheet (display screen side).

[0006] Patent Document 1: Japanese Patent Publication No. 2011-129277 Summary of the invention

[0007] -Technical problem to be solved by the invention-

[0008] For portable information terminals such as notebook computers and tablet computers, the sheet stacking structure is required to be thin and have high brightness uniformity. However, since the arrangement of point light sources or the positional relationship of each optical sheet varies for each product, it is sometimes impossible to obtain sufficient brightness uniformity with the existing sheet stacking structure depending on the product.

[0009] An object of the present disclosure is to provide an optical sheet stack that can improve the brightness uniformity of a backlight unit.

[0010] -Technical solutions for solving technical problems-

[0011] In order to achieve the aforementioned objectives, the optical sheet stack involved in the present invention is assembled in a backlight unit, and the optical sheet stack includes a plurality of diffuser sheets and a pair of prism sheets, wherein the plurality of diffuser sheets have a plurality of recessed portions in the shape of approximately inverted quadrangular pyramids arranged in a two-dimensional matrix on at least one side, and the prism extension directions of the pair of prism sheets are orthogonal to each other, and a first arrangement direction of the plurality of recessed portions on a first diffuser sheet closest to the pair of prism sheets among the plurality of diffuser sheets intersects with the prism extension direction at an angle of greater than 0° and less than 20°, or greater than 70° and less than 90°.

[0012] According to the optical sheet stack involved in the present disclosure, by overlapping and using a plurality of diffusion sheets (hereinafter, sometimes also referred to as pyramid sheets) having a plurality of recesses in the shape of inverted quadrangular pyramids on one surface, the brightness uniformity of the backlight unit can be improved. Since the arrangement direction of the recesses on the first diffusion sheet closest to the prism sheet crosses the prism extension direction at an angle of 0° to 20° or 70° to 90°, the brightness uniformity of the backlight unit is further improved compared with the case where the same light source, the same power, and the same optical sheet stack structure cross at other angles.

[0013] In the optical sheet stack involved in the present disclosure, there is a second diffuser, which is at least one of the plurality of diffusers except the first diffuser, and the second arrangement direction of the plurality of recesses on the second diffuser can be substantially the same as the first arrangement direction. In this way, the brightness uniformity of the backlight unit can be further improved according to the arrangement of the point light sources, the positional relationship of the optical sheets, and other conditions. It should be noted that in the present disclosure, substantially the same direction means that the angle difference between the two directions is less than 5°, preferably less than 3°, and more preferably less than 1°.

[0014] In the optical sheet stack involved in the present disclosure, there is a second diffuser sheet, which is at least one of the plurality of diffusers except the first diffuser sheet, and the second arrangement direction of the plurality of recesses on the second diffuser sheet may be different from the first arrangement direction. In this way, the brightness uniformity of the backlight unit can be further improved according to the arrangement of the point light sources, the positional relationship of the optical sheets, and other conditions. It should be noted that in the present disclosure, the direction does not agree to mean that the angle difference between the two directions is greater than 5°, preferably greater than 10°.

[0015] The backlight unit involved in the present disclosure is assembled in a liquid crystal display device, and guides light emitted from a light source toward a display screen side. The optical sheet stack involved in the present disclosure is included between the display screen and the light source, and the diffusion sheet is arranged between the light source and the pair of prism sheets.

[0016] According to the backlight unit according to the present disclosure, since it includes the optical sheet stack according to the present disclosure, it is possible to improve brightness uniformity.

[0017] In the backlight unit of the present disclosure, the light source may be arranged on a reflective sheet arranged on the opposite side of the display screen when viewed from the plurality of diffusion sheets. In this way, light is further diffused by multiple reflections between the diffusion sheet and the reflective sheet, thereby further improving brightness uniformity.

[0018] In the backlight unit of the present disclosure, the distance between the light source and the diffusion sheet may be less than 5 mm, preferably less than 2.5 mm, and more preferably less than 1 mm. In this way, the backlight unit can be miniaturized.

[0019] The liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure and a liquid crystal display panel.

[0020] According to the liquid crystal display device involved in the present disclosure, including the backlight unit involved in the present disclosure, it is possible to improve the brightness uniformity.

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

[0022] According to the information equipment involved in the present disclosure, including the liquid crystal display device involved in the present disclosure, it is possible to improve the uniformity of brightness.

[0023] The manufacturing method of the backlight unit involved in the present disclosure is a manufacturing method of the backlight unit that assembles the backlight unit into a liquid crystal display device and guides the light emitted from a light source toward the display screen side. The manufacturing method of the backlight unit includes the following steps: a step of arranging a plurality of diffusion sheets on the side of the display screen observed from the light source, wherein the plurality of diffusion sheets have a plurality of substantially inverted quadrangular pyramid-shaped recesses arranged in a two-dimensional matrix on at least one side, and a step of arranging a pair of prism sheets whose prism extension directions are orthogonal to each other on the side of the display screen observed from the plurality of diffusion sheets. In the step of arranging the plurality of diffusion sheets, the brightness uniformity is evaluated while changing the intersection angle between the arrangement direction of the plurality of recesses on each of the plurality of diffusion sheets and the prism extension direction, and the arrangement direction of the plurality of recesses on each of the plurality of diffusion sheets is determined based on the evaluation result.

[0024] According to the manufacturing method of the backlight unit involved in the present disclosure, in the process of arranging multiple diffusion sheets, the intersection angle between the arrangement direction of the concave portions on each diffusion sheet and the extension direction of the prism is changed while evaluating the brightness uniformity, and the arrangement direction of the concave portions on each diffusion sheet is determined based on the evaluation result. Therefore, the arrangement direction of the concave portions on each diffusion sheet can be set to achieve the purpose of improving the brightness uniformity.

[0025] - Effects of the Invention -

[0026] According to the present disclosure, it is possible to provide an optical sheet stack capable of improving the brightness uniformity of a backlight unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a cross-sectional view of a liquid crystal display device including a backlight unit according to an embodiment;

[0028] Figure 2 is a cross-sectional view of a backlight unit in which an optical sheet stack according to an embodiment is assembled;

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

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

[0031] Figure 5 1 is a diagram showing an example of the relationship between the arrangement direction of the recesses on the diffusion sheet and the extending direction of the prisms of the prism sheet in the optical sheet stack according to the embodiment;

[0032] Figure 6 1 is a diagram showing the relationship between the arrangement angles of the diffusion sheet (pyramid sheet) and the prism sheet in the optical sheet stack according to Example 1;

[0033] Figure 7 1 is a diagram showing changes in brightness uniformity when the arrangement angle difference between the diffusion sheet (pyramid sheet) and the upper prism sheet is changed in the optical sheet stack according to Example 1;

[0034] Figure 8 1 is a diagram showing changes in brightness when the arrangement angle difference between the diffusion sheet (pyramid sheet) and the upper prism sheet is changed in the optical sheet stack according to the reference example;

[0035] Fig. 9 1 is a diagram showing changes in brightness uniformity when the arrangement angle of the upper prism sheet is changed in the optical sheet stack according to Example 4;

[0036] Fig.10This is a diagram showing changes in brightness when the arrangement angle of the upper prism sheet is changed in the optical sheet stack according to Example 4. DETAILED DESCRIPTION

[0037] (Implementation Method)

[0038] The optical sheet stack, backlight unit, liquid crystal display device, information device and method for manufacturing the backlight unit according to the embodiments are described below with reference to the accompanying drawings. It should be noted that the scope of the present disclosure is not limited to the following embodiments, and any changes can be made within the technical concept of the present disclosure. Each of the drawings is used to conceptually illustrate the present disclosure, so in order to facilitate understanding, the size, ratio or number is sometimes exaggerated or simplified as needed.

[0039] <Structure of Liquid Crystal Display Device>

[0040] like Figure 1 As shown, the liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizing plate 6 adhered to the lower surface of the liquid crystal display panel 5, a second polarizing plate 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 polarizing plate 6.

[0041] 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.

[0042] From the front ( Figure 1 The shape of the display screen 50a of the liquid crystal display device 50 as viewed from above is in principle a rectangle or a square. However, the shape is not limited thereto and may be any shape such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or an instrument panel.

[0043] In each sub-pixel corresponding to each pixel electrode of 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. In this way, the transmittance of light incident from the backlight unit 40 via the first polarizer 6 is adjusted. The light with the adjusted transmittance is emitted via the second polarizer 7 to display an image.

[0044] The liquid crystal display device 50 of this embodiment can be used as a display device assembled in various information devices (for example, vehicle-mounted devices such as car navigation, portable information terminals such as personal computers, mobile phones, notebook computers or tablet computers, portable game consoles, copiers, ticket machines, automatic teller machines, etc.).

[0045] The TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film arranged in a manner covering each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and respectively connected to the corresponding TFTs among the plurality of TFTs, and an orientation film arranged in a manner covering each pixel electrode. The CF substrate 2 includes, for example, a black matrix arranged in a grid on a glass substrate, a color filter including a red layer, a green layer, and a blue layer respectively arranged between each grid of the black matrix, a common electrode arranged in a manner covering the black matrix and the color filter, and an orientation film arranged in a manner covering the common electrode. The liquid crystal layer 3 is formed of a nematic liquid crystal material, etc., and the nematic liquid crystal material contains liquid crystal molecules having electro-optical properties. The first polarizer 6 and the second polarizer 7 both include, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers arranged in a manner sandwiching the polarizer layer.

[0046] <Structure of backlight unit and optical sheet laminate>

[0047] like Figure 2 As shown, the backlight unit 40 includes a reflective sheet 41, a plurality of light sources 42 arranged two-dimensionally on the reflective sheet 41, and an optical sheet stack 100 disposed on the upper side of the plurality of light sources 42. The optical sheet stack 100 includes a diffusion sheet 43 disposed on the side of the light source 42 and a pair of prism sheets 44 and 45 disposed on the upper side (display screen 50a side) of the diffusion sheet 43. The optical sheet stack 100 has a color conversion sheet 46 between the light source 42 and the diffusion sheet 43. It should be noted that each sheet constituting the optical sheet stack 100 may be in the form of a film or a plate.

[0048] In the present embodiment, for example, two diffusion sheets 43 having the same structure are stacked in the backlight unit 40. The diffusion sheet 43 may be used in one piece, or three or more pieces may be stacked. In particular, in the backlight unit 40, when the brightness uniformity can be sufficiently increased by the precise arrangement of the light source 42, etc., a single diffusion sheet 43 may be used. The pair of prism sheets 44 and 45 may be a lower prism sheet 44 and an upper prism sheet 45 whose prism extension directions (extension directions of prism ridges) are orthogonal to each other. The color conversion sheet 46 may also be arranged between the diffusion sheet 43 and the pair of prism sheets 44 and 45.

[0049] [Reflective sheet]

[0050] The reflection sheet 41 is formed of, for example, a white polyethylene terephthalate resin film, a silver vapor-deposited film, or the like.

[0051] [light source]

[0052] The light source 42 may be, for example, a blue light source, emitting light with x < 0.24, y < 0.18 in the chromaticity coordinates of CIE1931. The type of light source 42 is not particularly limited, and may be, for example, an LED element or a laser element, etc. From the viewpoint of cost, productivity, etc., it is preferred to use an LED element. Moreover, in order to adjust the light emission angle characteristics of the LED, a lens may be mounted on the LED element. In the case where the light source 42 is composed of an LED element, the LED element (chip) may be rectangular in a plan view, in which case the length of one side may be greater than 50 μm (preferably greater than 100 μm) and less than 1 mm. The LED chips may be arranged two-dimensionally on the reflective sheet 41 at certain intervals. In the case where a plurality of LED chips are arranged at equal intervals, the distance between the centers of two adjacent chips may be greater than 0.5 mm (preferably greater than 2 mm) and less than 20 mm.

[0053] It should be noted that a white light source may be used instead of a blue light source as the light source 42. The white light source may be composed of, for example, an LED element with a peak wavelength in the blue region, an LED element with a peak wavelength in the green region, and an LED element with a peak wavelength in the red region, and emits light with a chromaticity coordinate of 0.24<x<0.42 and 0.18<y<0.48 in CIE1931. When a white light source is used, the color conversion sheet 46 may not be provided.

[0054] [Diffuser]

[0055] like Figure 2 and Figure 3 As shown, the diffuser 43 has a substrate layer 21. The diffuser 43 (substrate layer 21) has a first surface 21a that becomes a light emitting surface and a second surface 21b that becomes a light incident surface. That is, the diffuser 43 is arranged so that its second surface 21b faces the light source 42. The resin that becomes the base material of the substrate layer 21 is not particularly limited as long as it is composed of a material that allows light to pass through. For example, it can be 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 may be substantially free of additives. The additives that the substrate layer 21 may contain are not particularly limited, for example, it may be inorganic particles such as silicon dioxide, titanium oxide, aluminum hydroxide, and barium sulfate, or it may be organic particles such as acrylate, acrylonitrile, polysilicone, polystyrene, and polyamide.

[0056] The thickness of the diffusion sheet 43 is not particularly limited, and can be, for example, less than 3 mm (preferably less than 2 mm, more preferably less than 1.5 mm, and further preferably less than 1 mm) and more than 0.1 mm. If the thickness of the diffusion sheet 43 exceeds 3 mm, it is difficult to achieve a thin liquid crystal display. If the thickness of the diffusion sheet 43 is less than 0.1 mm, it is difficult to make the brightness uniform. The diffusion sheet 43 can be in the form of a film or a plate.

[0057] like Figure 4 As shown, on the first surface 21a of the diffuser 43, a plurality of recesses 22 in the shape of an inverted quadrangular pyramid (inverted pyramid) are arranged in a two-dimensional matrix. In other words, the plurality of recesses 22 can also be arranged in two directions orthogonal to each other. Adjacent recesses 22 are divided by ridges 111. The ridges 111 extend in the two directions in which the recesses 22 are arranged. The center (apex of the inverted pyramid) 112 of the recess 22 is the deepest part of the recess 22. Figure 4 In the example, for simplicity, the recesses 22 are arranged in a 5×5 matrix, but the actual number of recesses 22 is very large. When a plurality of recesses 22 are arranged two-dimensionally, the recesses 22 may be arranged on the first surface 21a without gaps or with predetermined intervals. Some of the recesses 22 may be arranged randomly without damaging the light diffusion effect.

[0058] The vertex angle θ of the recess 22 may be, for example, 90°, the arrangement pitch p of the recess 22 may be, for example, 100 μm, and the depth of the recess 22 may be, for example, 50 μm. The vertex angle θ of the recess 22 refers to the angle between the section lines of the inclined surfaces in the cross section presented when the cross section is cut in a manner that passes through the center of the recess 22 (the vertex 112 of the inverted pyramid) and perpendicularly crosses a pair of inclined surfaces opposite to each other across the center on a plane (longitudinal section) perpendicular to the arrangement surface of the diffusion sheet 43. The arrangement pitch p of the recess 22 refers to the distance between the centers (the vertex 112 of the inverted pyramid) of adjacent recesses 22 (the distance along the direction parallel to the arrangement surface of the diffusion sheet 43).

[0059] The second surface 21b of the diffusion sheet 43 may be, for example, a flat surface (mirror surface) or an embossed surface. The diffusion sheet 43 may be formed by a single-layer structure of a substrate layer 21 having a concavo-convex shape (concave portion 22) on the first surface 21a. The diffusion sheet 43 may be formed by a double-layer structure of a substrate layer having flat surfaces on both sides and a layer having a concavo-convex shape on one side. The diffusion sheet 43 may be formed by a structure of three or more layers including a layer having a concavo-convex shape on one side.

[0060] [Method for manufacturing a diffusion sheet]

[0061] The method for manufacturing the diffusion sheet 43 is not particularly limited, and for example, an extrusion molding method, an injection molding method, or the like can be used.

[0062] The sequence of manufacturing a single-layer diffuser sheet having a concave-convex shape on the surface by using an extrusion molding method is as follows. First, granular plastic particles with a diffuser added (granular plastic particles without a diffuser added may also be added together) are put into a single-screw extruder, and melted and kneaded while heating. After that, the molten resin extruded from the T-die is clamped between two metal rollers and cooled, then transported by guide rollers and cut into single flat plates by a slicer to make a diffuser. Here, the opposite shape of the roller surface is transferred to the resin by clamping the molten resin with a metal roller whose surface shape is opposite to the desired concave-convex shape, so that the desired concave-convex shape can be given to the surface of the diffuser. Because the shape of the roller surface may not be 100% transferred to the resin, the shape of the roller surface can be designed by reverse calculation based on the degree of transfer.

[0063] When using extrusion molding to manufacture a double-layer diffuser with a concave-convex surface, for example, after respectively feeding the granular plastic particles required to form each layer into two single-screw extruders, the same sequence as described above is applied to each layer, and the sheets that have been produced can be stacked.

[0064] Alternatively, a diffuser sheet having a double-layer structure with a concavo-convex shape on the surface can also be produced as described below. First, granular plastic particles required to form each layer are respectively put into two single-screw extruders, and melted and kneaded while heating. Thereafter, the molten resin forming each layer is put into a T-die and stacked in the T-die, and the stacked molten resin extruded from the T-die is clamped by two metal rollers for cooling. Thereafter, the stacked molten resin can be transported by a guide roller and cut into a single flat plate by a slicer, thereby producing a diffuser sheet having a double-layer structure with a concavo-convex shape on the surface.

[0065] A diffusion sheet can also be manufactured by UV (ultraviolet) shape transfer as follows. First, uncured ultraviolet curing resin is filled into a roller having a shape opposite to the concave-convex shape to be transferred, and then a substrate is pressed onto the resin. Next, the roller filled with ultraviolet curing resin and the substrate are integrated, and ultraviolet rays are irradiated to cure the resin. Next, the sheet with the concave-convex shape transferred by the resin is peeled off from the roller. Finally, the sheet is irradiated with ultraviolet rays again to completely cure the resin, thereby manufacturing a diffusion sheet with a concave-convex shape on the surface.

[0066] It should be noted that in the present disclosure, the expression "roughly inverted quadrangular pyramid" is used in consideration of the difficulty in forming a geometrically strictly defined inverted quadrangular pyramid concave portion using ordinary shape transfer technology, but "roughly inverted quadrangular pyramid" certainly also includes shapes that are real or substantially can be regarded as inverted quadrangular pyramids. "Roughly" means being able to be approximated, and "roughly inverted quadrangular pyramid" refers to a shape that can be approximated to an inverted quadrangular pyramid. For example, with respect to an "inverted quadrangular pyramid" with a flat top, a shape with a small top area is also included in a "roughly inverted quadrangular pyramid" without losing the function and effect of the present invention. Within the inevitable range of shape deviation caused by processing accuracy in industrial production, shapes deformed from an "inverted quadrangular pyramid" are also included in a "roughly inverted quadrangular pyramid".

[0067] [Prism Sheet]

[0068] Since the prism sheets 44 and 45 need to allow light to pass through, they are mainly formed of a transparent (eg, colorless and transparent) synthetic resin. The prism sheets 44 and 45 may be formed as one piece. Figure 2 As shown, the lower prism sheet 44 has a substrate layer 44a and a protrusion column composed of a plurality of protrusion 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 protrusion column composed of a plurality of protrusion prism portions 45b stacked on the surface of the substrate layer 45a. The protrusion prism portions 44b and 45b are stacked in strips on the surfaces of the substrate layers 44a and 45a, respectively. The protrusion prism portions 44b and 45b are triangular prism-shaped bodies whose back surfaces are connected to the surfaces of the substrate layers 44a and 45a, respectively. The extension direction of the protrusion prism portion 44b and the extension direction of the protrusion prism portion 45b are orthogonal to each other. In this way, the light incident from the diffusion sheet 43 can be refracted toward the normal direction side through the lower prism sheet 44, and the light emitted from the lower prism sheet 44 can be refracted through the upper prism sheet 45 in a manner that advances approximately perpendicularly relative to the display screen 50a.

[0069] The lower limit of the thickness of the prism sheets 44 and 45 (the height from the back surface of the substrate layers 44a and 45a to the apex of the protruding prism portions 44b and 45b) is, for example, about 50 μm, and more preferably, it can be about 100 μm. The upper limit of the thickness of the prism sheets 44 and 45 is, for example, about 200 μm, and more preferably, it can be about 180 μm. The lower limit of the spacing of the protruding prism portions 44b and 45b of the prism sheets 44 and 45 is, for example, about 20 μm, and more preferably, it can be about 25 μm. The upper limit of the spacing of the protruding prism portions 44b and 45b of the prism sheets 44 and 45 is, for example, about 100 μm, and more preferably, it can be about 60 μm. The vertex angle of the protruding prism portions 44b and 45b can be, for example, not less than 85° and not more than 95°. The lower limit of the refractive index of the protruding prism portions 44b and 45b is, for example, 1.5, and more preferably, it can be 1.55. The upper limit of the refractive index of the protruding prism parts 44b and 45b may be 1.7, for example.

[0070] The prism sheets 44 and 45 are formed by placing protruding prism portions 44b and 45b obtained by shape transfer using UV-curable acrylic resin on base layers 44a and 45a formed of PET (polyethylene terephthalate) films; or they can also be formed by forming the protruding prism portions 44b and 45b and the base layers 44a and 45a into one piece.

[0071] [Color conversion sheet]

[0072] The color conversion sheet 46 is a wavelength conversion sheet that converts the light from the light source 42 into light having a wavelength of an arbitrary color (for example, green or red) as a peak wavelength. For example, if the light source 42 is a blue light source, the color conversion sheet 46 converts, for example, blue light having a wavelength of 450 nm into green light having a wavelength of 540 nm and red light having a wavelength of 650 nm. In this case, if a light source 42 that emits blue light having a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet 46, so that the light that passes through the color conversion sheet 46 becomes white light. As the color conversion sheet 46, for example, a QD (quantum dot) sheet, a fluorescent sheet, or the like can be used. In the case of using a white light source as the light source 42, the color conversion sheet 46 may not be provided.

[0073] [Other optical sheets]

[0074] Although not shown in the figure, a polarizing film may be provided on the upper side (display screen 50a side) of the prism sheets 44 and 45. The polarizing film prevents light emitted from the backlight unit 40 from being absorbed by the first polarizing plate 6 of the liquid crystal display device 50, thereby improving the brightness of the display screen 50a.

[0075] <Features of the embodiment>

[0076] The optical sheet stack 100 of this embodiment is assembled in the backlight unit 40. The optical sheet stack 100 includes: a plurality of diffusion sheets 43, on which a plurality of substantially inverted quadrangular pyramid-shaped recesses 22 are arranged in a two-dimensional matrix on the first surface 21a; and a pair of prism sheets 44 and 45, whose protruding prism portions 44b and 45b extend in directions (hereinafter sometimes referred to as prism extension directions) that are orthogonal to each other. For example, Figure 5 As shown, in the optical sheet stack 100, the arrangement direction of the plurality of recesses 22 on the diffusion sheet 43 closest to the pair of prism sheets 44 and 45 among the plurality of diffusion sheets 43 intersects the prism extension direction at an angle of 0° to 20° or 70° to 90°. Figure 5 In the figure, for simplicity, the illustration of the protruding prism portion 44b is omitted, but since the extension direction of the protruding prism portion 44b and the extension direction of the protruding prism portion 45b are orthogonal to each other, when the extension direction of the protruding prism portion 45b satisfies the above-mentioned intersection angle range, the extension direction of the protruding prism portion 44b also satisfies the above-mentioned intersection angle range.

[0077] According to the optical sheet stack 100 of the present embodiment, by overlapping a plurality of diffusion sheets (hereinafter, sometimes referred to as pyramid sheets) 43 each having a plurality of recesses 22 in the shape of an inverted quadrangular pyramid on one surface, the brightness uniformity of the backlight unit 40 can be improved. Since the recess arrangement direction of the diffusion sheet 43 closest to the prism sheets 44 and 45 intersects with the prism extension direction at an angle of 0° to 20° or 70° to 90°, the brightness uniformity of the backlight unit 40 is further improved compared with the case where the same light source, the same power, and the same optical sheet stack structure intersect at other angles.

[0078] In the optical sheet stack 100 of the present embodiment, the arrangement direction of the recesses 22 on the diffusion sheet 43 closest to the prism sheets 44 and 45 and the arrangement direction of the recesses 22 on other diffusion sheets 43 may be substantially the same or different depending on the arrangement of the light source 42, the positional relationship of the optical sheets in the optical sheet stack 100, and other conditions. In this way, the brightness uniformity of the backlight unit 40 can be further improved according to the arrangement of the light source 42, the positional relationship of the optical sheets in the optical sheet stack 100, and other conditions. It should be noted that the substantially same direction means that the angle difference between the two directions is less than 5°, preferably less than 3°, and more preferably less than 1°, and the different directions mean that the angle difference between the two directions exceeds 5°, preferably more than 10°.

[0079] The backlight unit 40 of this embodiment is assembled in the liquid crystal display device 50, and guides the light emitted from the light source 42 toward the display screen 50a. The backlight unit 40 includes the optical sheet stack 100 of this embodiment between the display screen 50a and the light source 42, and the plurality of diffusion sheets 43 are arranged between the light source 42 and the prism sheets 44 and 45.

[0080] According to the backlight unit 40 of the present embodiment, since it includes the optical sheet stack 100 of the present embodiment, it is possible to improve brightness uniformity.

[0081] In the backlight unit 40 of this embodiment, the light source 42 may be disposed on the reflective sheet 41 on the opposite side of the display screen 50a from the plurality of diffusion sheets 43. In this way, light is further diffused by multiple reflections between the diffusion sheet 43 and the reflective sheet 41, thereby improving brightness uniformity.

[0082] In the backlight unit 40 of the present embodiment, if the distance between the light source 42 and the plurality of diffusion sheets 43 (more precisely, the distance between the light source 42 and the diffusion sheet 43 closest to the light source 42) is 5 mm or less, the backlight unit 40 can be miniaturized. Considering the future thinning of small and medium-sized liquid crystal displays, the distance between the light source 42 and the diffusion sheet 43 is more preferably 2.5 mm or less, further preferably 1 mm or less, and finally may be 0 mm.

[0083] The liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and the liquid crystal display panel 5. Therefore, the brightness uniformity can be improved by the optical sheet laminate 100 assembled in the backlight unit 40. Information equipment (such as a portable information terminal such as a notebook computer and a tablet computer) assembled with the liquid crystal display device 50 can also receive the same effect.

[0084] The manufacturing method of the backlight unit 40 of the present embodiment is a method for manufacturing the backlight unit 40 in which the backlight unit 40 is assembled into a liquid crystal display device 50 and the light emitted from the light source 42 is guided toward the display screen 50a side. The manufacturing method of the backlight unit 40 of the present embodiment includes the following steps: a step of arranging a plurality of diffusion sheets 43 on the side where the display screen 50a is viewed from the light source 42, wherein the plurality of diffusion sheets 43 have a plurality of substantially inverted quadrangular pyramid-shaped recesses 22 arranged in a two-dimensional matrix on the first surface 21a; and a step of arranging a pair of prism sheets 44 and 45 whose prism extension directions are orthogonal to each other on the side where the display screen 50a is viewed from the plurality of diffusion sheets 43. In the step of arranging the plurality of diffusion sheets 43, the brightness uniformity is evaluated while changing the intersection angle between the arrangement direction of the recesses 22 on each diffusion sheet 43 and the prism extension direction, and the arrangement direction of the recesses 22 on each diffusion sheet 43 is determined based on the evaluation result.

[0085] According to the manufacturing method of the backlight unit 40 of the present embodiment, in the process of arranging a plurality of diffusion sheets 43, the intersection angle between the arrangement direction of the concave portions 22 on each diffusion sheet 43 and the prism extension direction is changed while evaluating the brightness uniformity, and based on the evaluation result, the arrangement direction of the concave portions 22 on each diffusion sheet 43 is determined. Therefore, the arrangement direction of the concave portions 22 on each diffusion sheet 43 can be set to achieve the purpose of improving the brightness uniformity.

[0086] (Example)

[0087] <Example 1>

[0088] Hereinafter, Example 1 (actual measurement of brightness uniformity) will be described.

[0089] Two diffusion sheets 43 with a thickness of 130 μm and the same structure are overlapped in the same direction, and a lower prism sheet 44 and an upper prism sheet 45 whose prism extending directions are orthogonal to each other are arranged thereon. The optical sheet stack obtained in this way is used as the optical sheet stack 100 of Example 1.

[0090] The diffusion sheet 43 is formed by two-dimensionally arranging the inverted pyramid-shaped recesses 22 with a vertex angle of 90° and a depth of 50 μm on a transparent polycarbonate sheet with a thickness of 80 μm at a pitch of 100 μm using a UV curable resin with a refractive index of 1.587. The diffusion sheet 43 is arranged so that the surface (first surface 21a) where the recesses 22 are formed becomes the light emitting surface. The second surface 21b of the diffusion sheet 43 is a flat surface (mirror surface).

[0091] The prism sheets 44 and 45 are formed by using UV curable acrylic resin formed by acrylate, and providing protruding prism parts 44b and 45b on base layers 44a and 45a formed by PET film. The total thickness of the lower prism sheet 44 is 145μm, and the protruding prism parts 44b with a height of 12μm and a vertex angle of 94° are arranged at a pitch of 25μm. The total thickness of the upper prism sheet 45 is 128μm, and the protruding prism parts 45b with a height of 24μm and a vertex angle of 93° are arranged at a pitch of 51μm.

[0092] As the light source 42, an LED array consisting of a plurality of blue LEDs with a peak wavelength of 450 nm (full width at half maximum of 16 nm) arranged two-dimensionally at a pitch of 2.8 mm was used, and the light source 42 was arranged on the lower side (the diffuser 43 side) of the optical sheet laminate 100 of this embodiment, and the brightness uniformity of the light passing through the optical sheet laminate 100 was analyzed while changing the arrangement relationship between the diffuser 43 and the prism sheets 44 and 45. It should be noted that the brightness uniformity was analyzed directly using the blue light from the light source 42 without providing the color conversion sheet 46.

[0093] like Figure 6As shown, as the initial state of the brightness uniformity evaluation, the diffusion sheet 43 is arranged so that one of the arrangement directions of the recesses 22 is consistent with the reference direction (X-axis direction) (arrangement angle 0°), the lower prism sheet 44 is arranged so that the extension direction of the protruding prism part 44b is rotated 102° counterclockwise relative to the X-axis (arrangement angle 102°), and the upper prism sheet 45 is arranged so that the extension direction of the protruding prism part 45b is rotated 12° counterclockwise relative to the X-axis (arrangement angle 12°). It should be noted that the LED array that becomes the light source 42 is arranged so that each LED is arranged two-dimensionally along the x-axis direction and the direction perpendicular to the x-axis direction.

[0094] As a first evaluation, the arrangement direction (arrangement angle) of the two diffusion sheets (pyramid sheets) 43 was rotated 180° counterclockwise in increments of 10° from the initial state, and the change in brightness uniformity was evaluated. As a second evaluation, the arrangement direction (arrangement angle) of the two prism sheets 44 and 45 was rotated 180° counterclockwise in increments of 10° from the initial state, and the change in brightness uniformity was evaluated.

[0095] The brightness uniformity evaluation is implemented in the following order. First, the optical sheet stack 100 of this embodiment is arranged on the light source 42 (LED array), and then a transparent glass plate is placed on it to suppress the floating of the sheet. The brightness of the vertically upward direction (from the LED array to the glass plate) of the 33mm square range is measured using a two-dimensional color brightness meter UA-200 manufactured by TOPCONTECHNOHOUSE. Next, for the obtained two-dimensional brightness distribution image, the luminous intensity deviation of each LED is corrected, and after filtering to suppress the bright spot / dark spot noise caused by foreign matter, the average value and standard deviation of the brightness of all pixels are calculated. Finally, the brightness uniformity is evaluated by defining "brightness uniformity = average value / standard deviation".

[0096] Figure 7 The figure shows the change in brightness uniformity obtained in the first evaluation (black dots in the figure) and the change in brightness uniformity obtained in the second evaluation (white dots in the figure). Figure 7 In the figure, the horizontal axis represents the "layout angle of the upper prism sheet 45" - "layout angle of the diffusion sheet (pyramid sheet) 43" (hereinafter, sometimes referred to as "layout angle difference"), and the layout angle difference in the initial state is 12° (refer to Figure 6 ).

[0097] It should be noted that in the first evaluation, the "layout angle difference" decreases by 10° each time as the diffusion sheet 43 rotates, and in the second evaluation, the "layout angle difference" increases by 10° each time as the upper prism sheet 45 rotates. However, since the diffusion sheet 43 has equivalent shapes at the layout angles of 0° (180°) and 90° (270°), the "layout angle difference" is converted as described below. That is, when the "layout angle difference" is a negative value, a multiple of 90° is added to the "layout angle difference" to convert it to a value of 0° to 90°. When the "layout angle difference" exceeds 90°, a multiple of 90° is subtracted from the "layout angle difference" to convert it to a value of 0° to 90°. In this way, there are multiple values ​​of brightness uniformity on the vertical axis for the same "layout angle difference" on the horizontal axis. The "arrangement angle difference" obtained after conversion as described above is equal to the intersection angle (hereinafter sometimes referred to as "intersection angle") between the arrangement direction of the recesses 22 of the diffusion sheet 43 and the prism extension direction (extension direction of the protruding prism portions 44b and 45b).

[0098] like Figure 7 As shown in FIG. 1 , compared with the case where the “layout angle difference” is in the range of 20° to 70° (i.e., the “crossing angle” is in the range of 20° to 70°), the brightness uniformity is significantly increased in the range of 0° to 20° and 70° to 90° (i.e., the “crossing angle” is in the range of 0° to 20° and 70° to 90°). In particular, when the “layout angle difference” is around 10° and around 80° (i.e., the “crossing angle” is around 10° and around 80°), the brightness uniformity reaches a maximum value, and a greater brightness uniformity is obtained in the range of ±5° of the “layout angle difference” that reaches the maximum value.

[0099] As described above, the optical sheet stack 100 of the present embodiment has increased brightness uniformity when the "crossing angle" is in the range of 0° to 20° and in the range of 70° to 90°, regardless of whether the arrangement angle of the diffusion sheet 43 is changed or the arrangement angle of the prism sheets 44 and 45 is changed. In particular, the brightness uniformity is significantly increased when the "crossing angle" is in the range of about 5° to 15° or in the range of about 75° to 85°.

[0100] <Reference example>

[0101] Figure 8 The change in brightness (average value) obtained in the first evaluation (black dots in the figure) and the change in brightness (average value) obtained in the second evaluation (white dots in the figure) are shown. Figure 8 In the figure, the horizontal axis represents the "layout angle of the upper prism sheet 45" - "layout angle of the diffusion sheet (pyramid sheet) 43", and the layout angle difference in the initial state is 12° (refer to Figure 6). It should be noted that the conversion method of the "layout angle difference" is the same as that of the aforementioned embodiment 1. Figure 8 In the graph, the brightness on the vertical axis is expressed as a relative brightness with one of the brightness measurement values ​​in the initial state of the optical sheet stack 100 (when the "arrangement angle difference" is 12°) being set to 100%.

[0102] like Figure 8 As shown, the brightness increases significantly when the "arrangement angle difference" is in the range of 20° to 70° (that is, the "crossing angle" is in the range of 20° to 70°), compared to when the "arrangement angle difference" is around 0° or around 90° (that is, the "crossing angle" is around 0° or around 90°).

[0103] That is, according to Figure 7 and Figure 8 The results shown show that the brightness and brightness uniformity are in a trade-off relationship with respect to the "layout angle difference". Therefore, in the case of a product that wants to balance the brightness and brightness uniformity, the "layout angle difference" can also be set in a range of about 10° to 30° (preferably about 15° to 25°) or about 60° to 80° (preferably about 65° to 75°).

[0104] <Example 2>

[0105] Next, Example 2 (Simulation of brightness uniformity) will be described.

[0106] Three diffusion sheets 43 of the same structure and thickness of 110 μm were stacked, and a lower prism sheet 44 and an upper prism sheet 45 whose prism extending directions were orthogonal to each other were arranged thereon. The optical sheet stack obtained in this way was used as the optical sheet stack 100 of Example 2.

[0107] Inverted pyramid-shaped recesses 22 with a vertex angle of 90° and a depth of 50 μm are two-dimensionally arranged at a pitch of 100 μm on the first surface 21a (light emitting surface) of the diffusion sheet 43. The second surface 21b of the diffusion sheet 43 is a flat surface (mirror surface).

[0108] On the lower prism sheet 44 and the upper prism sheet 45, protruding prism portions 44b and 45b with a height of 50μm and a vertex angle of 90° are arranged at a pitch of 100μm, and the thickness of the prism sheets 44 and 45 is set to 130μm. It should be noted that in the prism sheets 44 and 45, the base material layers 44a, 45a and the protruding prism portions 44b, 45b are configured as a single layer product having the same optical properties, and the refractive index and absorption properties are the same as the optical properties of polycarbonate.

[0109] As the light source 42, an LED array consisting of a plurality of blue LEDs with a peak wavelength of 450 nm (full width at half maximum of 16 nm) arranged two-dimensionally at a pitch of 2.8 mm (specifically, 3×3 in length and width) was used. The light source 42 was arranged on the lower side (the diffuser 43 side) of the optical sheet stack 100 of this embodiment, and the brightness uniformity of the light passing through the optical sheet stack 100 was evaluated by simulation while changing the arrangement relationship between the diffuser 43 and the prism sheets 44 and 45. It should be noted that the brightness uniformity was evaluated directly using the blue light from the light source 42 without providing the color conversion sheet 46.

[0110] In the brightness uniformity evaluation, the lower prism sheet 44 is arranged so that the extension direction of the protruding prism portion 44b is rotated 102° counterclockwise relative to the X-axis (at an arrangement angle of 102°), and the upper prism sheet 45 is arranged so that the extension direction of the protruding prism portion 45b is rotated 12° counterclockwise relative to the X-axis (at an arrangement angle of 12°) (refer to Figure 6 ). It should be noted that the LED array serving as the light source 42 is arranged so that each LED is arranged two-dimensionally along the x-axis direction and the direction perpendicular to the x-axis direction. The three diffusion sheets 43 are arranged so that the arrangement direction of the recesses 22 is at an angle of 0°, 12°, 30°, 45°, and 60° (hereinafter referred to as the arrangement angle) relative to the arrangement direction of the LED serving as a reference.

[0111] The brightness uniformity evaluation was carried out in the following order. First, a total of 10 7 Light rays. A virtual sensor of 8.4mm×8.4mm in size is set directly above the upper prism sheet 45 with 0.2mm square grids (42×42), and the surface brightness distribution is derived based on the intensity, number of rays, and light output angle of the light passing through each grid. Since the surface brightness distribution contains noise, in order to suppress the noise, the obtained surface brightness distribution is divided into 3×3 equal parts, and an average distribution is made from the nine divided distributions. The average value and standard deviation of the brightness of the average distribution are calculated, and the brightness uniformity is evaluated as "brightness uniformity = average value / standard deviation".

[0112] Table 1 shows the results of brightness uniformity evaluation when the arrangement angle of the diffusion sheet 43 (third sheet) closest to the upper prism sheet 45 is set to 0° (the arrangement angle difference relative to the upper prism sheet 45 is 12° (=12°-0°) and the arrangement angles of other diffusion sheets 43 (first sheet, second sheet) are set to 0°, 12°, 30°, 45°, and 60°, respectively.

[0113] (Table 1)

[0114]

[0115] Table 2 shows the results of brightness uniformity evaluation when the arrangement angle of the diffusion sheet 43 (the third sheet) closest to the upper prism sheet 45 is set to 30° (the arrangement angle difference relative to the upper prism sheet 45 is 72° (= (12°-30°)+90°)) and the arrangement angles of other diffusion sheets 43 (the first sheet, the second sheet) are set to 0°, 12°, 30°, 45°, and 60°, respectively.

[0116] (Table 2)

[0117]

[0118] As shown in Table 1, when the arrangement angle of the diffusion sheet 43 (the third sheet) is set to 0° (the difference in arrangement angle relative to the upper prism sheet 45 is 12°), when the arrangement angle of the diffusion sheet 43 (the first sheet) is 30° and the arrangement angle of the diffusion sheet 43 (the second sheet) is 45°, and when the arrangement angle of the diffusion sheet 43 (the first sheet) is 45° and the arrangement angle of the diffusion sheet 43 (the second sheet) is 45°, the brightness uniformity is significantly increased.

[0119] As shown in Table 2, when the arrangement angle of the diffusion sheet 43 (the third sheet) is set to 30° (the difference in arrangement angle relative to the upper prism sheet 45 is 72°), when the arrangement angle of the diffusion sheet 43 (the first sheet) is 12° to 60° and the arrangement angle of the diffusion sheet 43 (the second sheet) is 45°, when the arrangement angle of the diffusion sheet 43 (the first sheet) is 30° and the arrangement angle of the diffusion sheet 43 (the second sheet) is 30°, and when the arrangement angle of the diffusion sheet 43 (the first sheet) is 60° and the arrangement angle of the diffusion sheet 43 (the second sheet) is 60°, the brightness uniformity is significantly increased.

[0120] As described above, it can be known that: in the optical sheet stack 100 of the present embodiment, when the arrangement angle difference (cross angle) of the diffusion sheet 43 (the third sheet) relative to the upper prism sheet 45 falls within the range of 0° to 20° or the range of 70° to 90°, the brightness uniformity can be further improved by adjusting the arrangement angle of each diffusion sheet 43 (that is, the arrangement direction of the recessed portion 22).

[0121] <Example 3>

[0122] Next, Example 3 (actual measurement of brightness uniformity) will be described.

[0123] Three diffusion sheets 43 of the same structure and thickness of 110 μm were stacked, and a lower prism sheet 44 and an upper prism sheet 45 whose prism extending directions were orthogonal to each other were arranged thereon. The optical sheet stacked body thus obtained was used as the optical sheet stacked body 100 of Example 3.

[0124] The diffusion sheet 43 is formed by two-dimensionally arranging the inverted pyramid-shaped recesses 22 with a vertex angle of 90° and a depth of 50 μm at a pitch of 100 μm on a transparent polycarbonate sheet with a thickness of 60 μm using a UV curable resin with a refractive index of 1.587. The diffusion sheet 43 is arranged so that the surface (first surface 21a) where the recesses 22 are formed becomes the light emitting surface. The second surface 21b of the diffusion sheet 43 is set to a matte surface.

[0125] The prism sheets 44 and 45 are formed by using UV curable acrylic resin formed by acrylate, and providing protruding prism parts 44b and 45b on base layers 44a and 45a formed by PET film. The total thickness of the lower prism sheet 44 is 145μm, and the protruding prism parts 44b with a height of 12μm and a vertex angle of 94° are arranged at a pitch of 25μm. The total thickness of the upper prism sheet 45 is 128μm, and the protruding prism parts 45b with a height of 24μm and a vertex angle of 93° are arranged at a pitch of 51μm.

[0126] As the light source 42, an LED array consisting of a plurality of blue LEDs with a peak wavelength of 450 nm (full width at half maximum of 16 nm) arranged two-dimensionally at a pitch of 2.8 mm was used, and the light source 42 was arranged on the lower side (the diffuser 43 side) of the optical sheet laminate 100 of this embodiment, and the brightness uniformity of the light passing through the optical sheet laminate 100 was analyzed while changing the arrangement relationship between the diffuser 43 and the prism sheets 44 and 45. It should be noted that the brightness uniformity was analyzed directly using the blue light from the light source 42 without providing the color conversion sheet 46.

[0127] In the brightness uniformity evaluation, the lower prism sheet 44 is arranged so that the extension direction of the protruding prism portion 44b is rotated 102° counterclockwise relative to the X-axis (at an arrangement angle of 102°), and the upper prism sheet 45 is arranged so that the extension direction of the protruding prism portion 45b is rotated 12° counterclockwise relative to the X-axis (at an arrangement angle of 12°) (refer to Figure 6 ). It should be noted that the LED array serving as the light source 42 is arranged so that each LED is arranged two-dimensionally along the x-axis direction and the direction perpendicular to the x-axis direction. The three diffusion sheets 43 are arranged so that the arrangement direction of the recesses 22 forms angles of 0°, 30°, 45°, and 60° (hereinafter referred to as arrangement angles) with respect to the arrangement direction of the LEDs serving as a reference.

[0128] The brightness uniformity evaluation was performed in the same manner as in Example 1.

[0129] Table 3 shows the results of brightness uniformity evaluation when the arrangement angle of the diffusion sheet 43 (third sheet) closest to the upper prism sheet 45 is set to 30° (the arrangement angle difference relative to the upper prism sheet 45 is 72° (= (12°-30°)+90°)) and the arrangement angles of other diffusion sheets 43 (first sheet, second sheet) are set to 0°, 30°, 45°, and 60°, respectively.

[0130] (Table 3)

[0131]

[0132] As shown in Table 3, when the arrangement angle of the diffusion sheet 43 (third sheet) is set to 30° (the difference in arrangement angle relative to the upper prism sheet 45 is 72°), when the arrangement angle of the diffusion sheet 43 (first sheet) is 30° to 60° and the arrangement angle of the diffusion sheet 43 (second sheet) is 30° to 45°, and when the arrangement angle of the diffusion sheet 43 (first sheet) is 60° and the arrangement angle of the diffusion sheet 43 (second sheet) is 60°, the brightness uniformity is significantly increased. This shows a tendency that is substantially the same as the brightness uniformity of the aforementioned Example 2 shown in Table 2.

[0133] As described above, it can be known that: in the optical sheet stack 100 of the present embodiment, when the arrangement angle difference (cross angle) of the diffusion sheet 43 (the third sheet) relative to the upper prism sheet 45 is in the range of 70° to 90°, the brightness uniformity can be further improved by adjusting the arrangement angle of each diffusion sheet 43 (that is, the arrangement direction of the recessed portion 22).

[0134] <Example 4>

[0135] Hereinafter, Example 4 (actual measurement of brightness uniformity and brightness) will be described.

[0136] Three diffusion sheets 43 of the same structure with a thickness of 110 μm are stacked, and a lower prism sheet 44 and an upper prism sheet 45 whose prism extending directions are orthogonal to each other are arranged thereon. The optical sheet stack obtained in this way is used as the optical sheet stack 100 of Example 4.

[0137] As the light source 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.

[0138] The diffusion sheet 43 is formed by two-dimensionally arranging the inverted pyramid-shaped recesses 22 with a vertex angle of 90 degrees at a pitch of 100 μm. The diffusion sheet 43 is arranged so that the surface (first surface 21 a ) where the recesses 22 are formed becomes the light emission surface. The second surface 21 b of the diffusion sheet 43 is set as a flat surface.

[0139] The prism sheets 44 and 45 are formed by providing the protruding prism parts 44b and 45b on the base layers 44a and 45a formed of PET films using UV curing acrylic resin formed of acrylate. The lower prism sheet 44 has a total thickness of 90 μm, and the protruding prism parts 44b with a height of 12 μm and a vertex angle of 90° are arranged at a pitch of 24 μm. The upper prism sheet 45 has a total thickness of 155 μm, and the protruding prism parts 45b with a height of 25 μm and a vertex angle of 90° are arranged at a pitch of 50 μm.

[0140] It should be noted that, in this embodiment, a color conversion sheet 46 composed of a QD sheet is arranged on the lower side of the diffusion sheet 43, and an upper light diffusion sheet is arranged on the upper side of the upper prism sheet 45. The upper light diffusion sheet is composed of a double-layer structure of a base material layer and a light diffusion layer. The base material layer is mainly composed of a transparent resin in order to allow light to pass through, and the light diffusion layer is formed by dispersing resin beads in a resin matrix.

[0141] In this embodiment, the arrangement angles of the three diffusion sheets 43 (the intersection angles of the arrangement directions of the recesses 22 and the arrangement directions of the light sources 42) were fixed at 45° and 0°, respectively, and the brightness uniformity and brightness changes were analyzed while rotating the prism sheets 44 and 45. It should be noted that the brightness uniformity evaluation was carried out in the same order as in the above-mentioned embodiment 1, and the average value of the brightness obtained in the same order as in the above-mentioned embodiment 1 was used as the brightness.

[0142] Fig. 9 and Fig.10 They respectively represent the brightness uniformity and brightness change obtained in this embodiment. Fig. 9 and Fig.10 In FIG. 1 , the solid line indicates the result when the arrangement angle of the diffusion sheet 43 is set to 45°, and the dotted line indicates the result when the arrangement angle of the diffusion sheet 43 is set to 0°. Fig. 9 and Fig.10 The horizontal axis represents the arrangement angle of the upper prism sheet 45 (the rotation angle of the extension direction of the protruding prism portion 45b (edge ​​line) relative to the arrangement direction (X direction) of the light source 42), but the arrangement angle of the lower prism sheet 44 (the rotation angle of the extension direction of the protruding prism portion 44b (edge ​​line) relative to the arrangement direction (X direction) of the light source 42) is "the arrangement angle of the upper prism sheet 45" + 90°.

[0143] like Fig. 9As shown, when the arrangement angle of the diffusion sheet 43 is 0°, the brightness uniformity is improved when the arrangement angle of the upper prism sheet 45 is in the range of about 0° to about 20°, the range of about 70° to about 110°, and the range of about 160° to about 180°. When the arrangement angle of the diffusion sheet 43 is 45°, the brightness uniformity is improved when the arrangement angle of the upper prism sheet 45 is in the range of about 25° to about 65°, and the range of about 115° to about 155°.

[0144] As described above, in this embodiment, in any case where the arrangement angle of the diffusion sheet 43 is 45° and 0°, when the arrangement angle difference (= "arrangement angle of the upper prism sheet 45" - "arrangement angle of the diffusion sheet 43") is in the range of 0° to 20° and in the range of 70° to 90° (that is, the crossing angle is in the range of 0° to 20° and in the range of 70° to 90°), the brightness uniformity is improved.

[0145] In this embodiment, if Fig. 9 As shown in the figure, when the arrangement angle of the diffusion sheet 43 is set to 45°, the brightness uniformity is improved at all the arrangement angles of the prism sheets 44 and 45, compared with the case where the arrangement angle of the diffusion sheet 43 is set to 0°. Specifically, the average value of the brightness uniformity when the arrangement angle of the diffusion sheet 43 is set to 45° is about 180, while the average value of the brightness uniformity when the arrangement angle of the diffusion sheet 43 is set to 0° is about 150. Compared with the case where the arrangement angle of the diffusion sheet 43 is set to 0°, when the arrangement angle of the diffusion sheet 43 is set to 45°, the brightness uniformity is improved by about three times the variation range depending on the arrangement angle of the prism sheets 44 and 45.

[0146] In this embodiment, if Fig.10 As shown in FIG. 1 , when the diffusion sheet 43 is arranged at an angle of 45° or 0°, no significant brightness reduction due to the arrangement angle of the prism sheets 44 and 45 is found. Fig.10 In the figure, the brightness on the vertical axis is expressed as a relative brightness with a brightness measurement value when the arrangement angle of the diffusion sheet 43 is 0° being set as 100%, and "significant brightness reduction" means "brightness reduction exceeding 2%".

[0147] (Other embodiments)

[0148] In the above embodiments (including examples, the same below), the optical sheet stack 100 is composed of the diffusion sheet 43, the prism sheets 44 and 45, and the color conversion sheet 46. However, the optical sheet stack 100 may further include other optical sheets in addition to the diffusion sheet 43, the prism sheets 44 and 45, and the color conversion sheet 46.

[0149] In the aforementioned embodiment, the recessed portion 22 provided on the first surface 21a of the diffuser 43 included in the optical sheet stack 100 is configured such that the inverted polygonal pyramid shape of the recessed portion 22 is an inverted quadrangular pyramid, but it may be replaced by other shapes that can be arranged in two dimensions, such as an inverted triangular pyramid or an inverted hexagonal pyramid. Alternatively, a protrusion column such as a convex prism portion may be provided instead of the recessed portion 22 that can be arranged in two dimensions. The second surface 21b of the diffuser 43 is a flat surface (mirror surface) or an embossed surface, but a protrusion column such as a recessed portion or a convex prism portion that can be arranged in two dimensions may also be provided on the second surface 21b of the diffuser 43.

[0150] The embodiments of the present disclosure are described above, but the present disclosure is not limited to the aforementioned embodiments, and various modifications can be made within the scope of the present disclosure. That is, the description of the aforementioned embodiments is only an example in nature and is not intended to limit the present disclosure, its applicable objects or its uses.

[0151] - Explanation of symbols -

[0152] 1TFT substrate

[0153] 2CF substrate

[0154] 3 Liquid crystal layer

[0155] 5 LCD panel

[0156] 6First polarizing plate

[0157] 7. Second polarizing plate

[0158] 21 base material layer

[0159] 21a Page 1

[0160] 21b Side 2

[0161] 22 concavities

[0162] 40 Backlight Unit

[0163] 41 reflective sheet

[0164] 42 Light Source

[0165] 43 Diffuser

[0166] 44 lower prism lens

[0167] 44a Base material layer

[0168] 44b prism part

[0169] 45 upper prism lens

[0170] 45a Base material layer

[0171] 45b prism part

[0172] 46 Color conversion film

[0173] 50 Liquid crystal display device

[0174] 50a Display screen

[0175] 100 optical sheet laminate

[0176] 111 Edge

[0177] 112 The center of the concave portion (apex of the inverted pyramid).

Claims

1. An optical sheet stack, assembled in a backlight unit, the backlight unit comprising a pair of prism sheets whose prism extension directions are orthogonal to each other, characterized in that: The optical sheet stack includes a plurality of diffusion sheets. The plurality of diffusion sheets have a plurality of substantially inverted quadrangular pyramid-shaped recesses arranged in a two-dimensional matrix on at least one side. A first arrangement direction of the plurality of recesses on a first diffusion sheet among the plurality of diffusion sheets that is closest to the pair of prism sheets intersects the prism extending direction at an angle of 5° to 15°, or 75° to 85°.

2. The optical sheet laminate according to claim 1, wherein: It has a second diffusion sheet, which is at least one of the plurality of diffusion sheets except the first diffusion sheet, and the second arrangement direction of the plurality of recesses on the second diffusion sheet is substantially the same as the first arrangement direction.

3. The optical sheet stack according to claim 1, wherein: It has a second diffusion sheet, which is at least one of the plurality of diffusion sheets except the first diffusion sheet, and the second arrangement direction of the plurality of recesses on the second diffusion sheet is different from the first arrangement direction.

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