Optical sheet laminate, backlight unit, liquid crystal display device, information equipment, and production method for optical sheet laminate

Abstract

An optical sheet laminate (100) is embedded in a liquid crystal display device in which a plurality of point light sources (42) are dispersed on the back side of a display screen. The optical sheet laminate (100) has a first optical sheet (43) having a first printing pattern (101A) formed on a first surface (21b) that at least partially suppresses light transmission from the plurality of point light sources (42). A second optical sheet (43) different from the first optical sheet (43), or a second printing pattern (101B) that at least partially suppresses light transmission from the plurality of point light sources (42) is formed on a second surface (21a) of the first optical sheet (43). By the first printing pattern (101A) and the second printing pattern (101B), the luminance non-uniformity caused by the plurality of point light sources (42) is suppressed, and the luminance is made uniform.

Description

Technology Field

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

[0002] Liquid crystal displays (LCDs) are widely used as display devices for various information devices, such as smartphones and tablets. For the backlights of LCDs, the direct-type method, in which the light source is placed on the back of the liquid crystal panel, is becoming the mainstream.

[0003] When employing a direct-type backlight, light-diffusing materials (light-diffusing plates, light-diffusing sheets, light-diffusing films) are used to erase the image of light sources, such as LEDs (Light Emitting Diodes), from the light-emitting surface and to improve the uniformity of brightness within the surface.

[0004] In the optical sheet disclosed in Patent Document 1, to resolve the luminance non-uniformity in which the region directly above the light source becomes high luminance while the region between light sources becomes low luminance, white ink printing is performed on the region directly above the high luminance light source to suppress light transmission, thereby improving luminance uniformity. Prior art literature

[0005] Japanese Patent Publication No. 2012-163785 The problem to be solved

[0006] However, in conventional optical sheets, since luminance uniformity is improved by forming a printing pattern according to the luminance distribution (luminance non-uniformity), there is a problem in that luminance uniformity deteriorates when the position of the printing pattern is misaligned with respect to the position of the light source.

[0007] The present disclosure aims to improve the brightness uniformity of a direct-type backlight. means of solving the problem

[0008] An optical sheet laminate according to the present disclosure is an optical sheet laminate embedded in a liquid crystal display device having a plurality of point light sources dispersed on the back side of a display screen, and comprises a first optical sheet having a first printing pattern formed on a first surface that suppresses at least partially light transmission from the plurality of point light sources. A second optical sheet different from the first optical sheet, or a second printing pattern that suppresses at least partially light transmission from the plurality of point light sources, is formed on a second surface of the first optical sheet. By the first printing pattern and the second printing pattern, luminance non-uniformity caused by the plurality of point light sources is suppressed, and luminance is made uniform.

[0009] According to the optical sheet laminate of the present disclosure, a first printing pattern and a second printing pattern for suppressing luminance non-uniformity are disposed on both sides of a plurality of different optical sheets or the same optical sheet. Accordingly, compared to the case where luminance non-uniformity is suppressed by a single printing pattern, the amount of change in printing density (tone change) in the first printing pattern and the second printing pattern can be reduced. Accordingly, even if the first printing pattern and / or the second printing pattern are misaligned with respect to the position of the light source, the deterioration of luminance uniformity can be suppressed.

[0010] In the optical sheet laminate according to the present disclosure, the first printing pattern and the second printing pattern are a collection of unit patterns having a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the plurality of point light sources toward an intermediate region with the adjacent point light source, and the first printing pattern and the second printing pattern may be formed by arranging the unit patterns two-dimensionally without localization. Alternatively, at least one of the first printing pattern or the second printing pattern is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources when the first printing pattern and the second printing pattern are not formed, and the luminance and the printing density may have a positive correlation. Alternatively, the pattern formed by overlapping the first printing pattern and the second printing pattern is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources when the first printing pattern and the second printing pattern are not formed, and the luminance and the printing density may have a positive correlation. In this way, luminance non-uniformity caused by a plurality of point light sources is suppressed by the first printing pattern and the second printing pattern, thereby improving luminance uniformity. In this case, the region with high luminance in the luminance distribution may be the region directly above the plurality of point light sources, or the region between adjacent point light sources among the plurality of point light sources, depending on the configuration of the optical sheet laminate or the characteristics of the point light sources. By doing so, luminance in the region directly above the point light sources or the region between the point light sources can be suppressed, thereby improving luminance uniformity.

[0011] In the optical sheet laminate according to the present disclosure, the first optical sheet may be a first light-diffusing sheet. By doing so, the luminance non-uniformity can be further suppressed by the first light-diffusing sheet. In this case, the second printing pattern is formed on the second optical sheet, and in the first light-diffusing sheet, the first surface is a flat surface or a matte surface, and a plurality of concave portions arranged two-dimensionally are formed on the second surface, and the second optical sheet is a second light-diffusing sheet having a flat surface or a matte surface on which the second printing pattern is formed, then the first printing pattern and the second printing pattern can be easily formed on a flat surface or a matte surface with small undulations. Alternatively, the second printing pattern is formed on the first light-diffusing sheet, and in the first light-diffusing sheet, a plurality of concave portions arranged two-dimensionally are formed on one of the first surface and the second surface, and the other of the first surface and the second surface is a flat surface or a matte surface, so that the first printing pattern or the second printing pattern is formed thickly by filling the concave portions, thereby further suppressing light transmission. In addition, the plurality of concave portions may have an inverted polygonal pyramid shape, an inverted polygonal frustum shape, or a lower hemisphere shape. By doing so, the light-diffusing properties of the light-diffusing sheet can be improved.

[0012] A backlight unit according to the present disclosure is a backlight unit embedded in the liquid crystal display device and guiding light emitted from the plurality of point light sources toward the display screen side, and comprises an optical sheet laminate according to the present disclosure described above between the display screen and the plurality of point light sources.

[0013] According to the backlight unit of the present disclosure, brightness uniformity can be improved because it is equipped with an optical sheet laminate according to the above-described present disclosure.

[0014] In the backlight unit according to the present disclosure, the distance between the plurality of point light sources and the optical sheet laminate may be 2 mm or less. By doing so, brightness uniformity can be improved even in configurations where brightness non-uniformity is prone to occur in conventional configurations.

[0015] In the backlight unit according to the present disclosure, the plurality of point light sources may be LED elements. By doing so, sufficient brightness can be obtained across the entire screen even if the number of light sources is reduced.

[0016] In the backlight unit according to the present disclosure, the plurality of point light sources may be disposed on a reflective member positioned on the side opposite to the display screen when viewed from the optical sheet laminate. By doing so, luminance uniformity is further improved.

[0017] A liquid crystal display device according to the present disclosure comprises a backlight unit according to the above-described present disclosure and a liquid crystal display panel.

[0018] According to the liquid crystal display device of the present disclosure, brightness uniformity is improved because it is equipped with a backlight unit according to the above-described present disclosure.

[0019] The information device according to the present disclosure comprises a liquid crystal display device according to the above-described present disclosure.

[0020] According to the information device of the present disclosure, brightness uniformity is improved because it is equipped with a liquid crystal display device according to the present disclosure described above.

[0021] The method for manufacturing an optical sheet laminate according to the present disclosure is a method for manufacturing an optical sheet laminate embedded in a liquid crystal display device in which a plurality of point light sources are dispersed on the back side of a display screen. The method for manufacturing an optical sheet laminate according to the present disclosure comprises: a process A of forming a first printing pattern on a first surface of a first optical sheet that at least partially suppresses light transmission from the plurality of point light sources; and a process B of forming a second printing pattern on a second optical sheet different from the first optical sheet, or on a second surface of the first optical sheet that at least partially suppresses light transmission from the plurality of point light sources. The process A and the process B are performed such that the luminance non-uniformity caused by the plurality of point light sources is suppressed by the first printing pattern and the second printing pattern, thereby making the luminance uniform.

[0022] According to the method for manufacturing an optical sheet laminate according to the present disclosure, a first printing pattern and a second printing pattern for suppressing luminance non-uniformity are formed on both sides of a plurality of different optical sheets or the same optical sheet. Accordingly, compared to the case where luminance non-uniformity is suppressed by a single printing pattern, the tonal variation in the first printing pattern and the second printing pattern can be reduced. Accordingly, even if the first printing pattern and / or the second printing pattern are misaligned with respect to the position of the light source, the deterioration of luminance uniformity can be suppressed.

[0023] In the method for manufacturing an optical sheet laminate according to the present disclosure, the first printing pattern and the second printing pattern are a collection of unit patterns having a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the plurality of point light sources toward an intermediate region with the adjacent point light source, and the first printing pattern and the second printing pattern may be formed by arranging the unit patterns two-dimensionally without localization. Alternatively, at least one of the first printing pattern or the second printing pattern is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources when the first printing pattern and the second printing pattern are not formed, and the luminance and the printing density may have a positive correlation. Alternatively, the pattern formed by overlapping the first printing pattern and the second printing pattern is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources when the first printing pattern and the second printing pattern are not formed, and the luminance and the printing density may have a positive correlation. In this way, luminance non-uniformity caused by a plurality of point light sources is suppressed by the first printing pattern and the second printing pattern, thereby improving luminance uniformity. In this case, the region with high luminance in the luminance distribution may be the region directly above the plurality of point light sources, or the region between adjacent point light sources among the plurality of point light sources, depending on the configuration of the optical sheet laminate or the characteristics of the point light sources. By doing so, luminance in the region directly above the point light sources or the region between the point light sources can be suppressed, thereby improving luminance uniformity. Effects of the invention

[0024] According to the present disclosure, the brightness uniformity of a direct-type backlight can be improved. Brief explanation of the drawing

[0025] FIG. 1 is a cross-sectional view of a liquid crystal display device according to an embodiment. FIG. 2 is a cross-sectional view of a backlight unit according to an embodiment. FIG. 3 is a cross-sectional view of a light-diffusing sheet according to an embodiment. FIG. 4 is a perspective view of a light-diffusing sheet according to an embodiment. Figure 5 is a cross-sectional view showing a printed pattern formed on one side of a light-diffusing sheet in a comparative example. Figure 6 is a plan view of a printed pattern formed on a light-diffusing sheet in a comparative example. Figure 7 is a diagram showing the relationship between the printing pattern of a light-diffusing sheet and the placement of a point light source according to a comparative example. Figure 8 is a schematic diagram showing the positional misalignment of the printing pattern in the comparative example. FIG. 9 is a cross-sectional view showing the appearance of a printed pattern formed on each of two light-diffusing sheets in an embodiment. FIG. 10 is a plan view of a printing pattern formed on each of two light-diffusing sheets in an embodiment. FIG. 11 is a diagram showing the relationship between the printing pattern of a light-diffusing sheet and the arrangement of point light sources according to an embodiment. FIG. 12 is a cross-sectional view showing the appearance of printing patterns formed on both sides of a light-diffusing sheet in a modified example. FIG. 13 is a drawing showing that brightness non-uniformity is suppressed by the first printing pattern and the second printing pattern in an embodiment, and brightness is uniformized. FIG. 14 is a figure showing the results of investigating the effect of positional misalignment of printing patterns on luminance uniformity in the examples and comparative examples. Specific details for implementing the invention

[0026] (Embodiment)

[0027] Hereinafter, an optical sheet laminate, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing an optical sheet laminate according to an embodiment will be described with reference to the drawings. Furthermore, the scope of the present disclosure is not limited to the following embodiments and may be modified arbitrarily within the scope of the technical concept of the present disclosure.

[0028] <Composition of Liquid Crystal Display>

[0029] As shown in FIG. 1, the liquid crystal display device (50) comprises a liquid crystal display panel (5), a first polarizing plate (6) bonded to the lower surface of the liquid crystal display panel (5), a second polarizing plate (7) bonded 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) with the first polarizing plate (6) interposed therein.

[0030] The liquid crystal display panel (5) comprises a TFT substrate (1) and a CF substrate (2) arranged to face 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 enclose the liquid crystal layer (3) between the TFT substrate (1) and the CF substrate (2).

[0031] The shape of the display screen (50a) of the liquid crystal display device (50) viewed from the front (upper part of FIG. 1) is, in principle, a rectangle or a square, but is not limited thereto and may be any shape such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or a car instrument panel.

[0032] In the liquid crystal display device (50), a voltage of a predetermined magnitude is applied to the liquid crystal layer (3) at each subpixel corresponding to each pixel electrode to change the orientation state of the liquid crystal layer (3). As a result, the transmittance of light incident from the backlight unit (40) through the first polarizer (6) is adjusted. The light with adjusted transmittance is emitted through the second polarizer (7), and an image is displayed on the display screen (50a).

[0033] The liquid crystal display device (50) of the present embodiment is used as a display device embedded in various information devices (e.g., vehicle-mounted devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as laptop computers or tablet terminals, portable game consoles, photocopiers, ticket machines, automatic cash deposit and withdrawal machines, etc.).

[0034] The TFT substrate (1) comprises, for example, a plurality of TFTs arranged in a matrix shape on a glass substrate, an interlayer insulating film arranged to cover each TFT, a plurality of pixel electrodes arranged in a matrix shape on the interlayer insulating film and each connected to the plurality of TFTs, and an alignment film arranged to cover each pixel electrode. The CF substrate (2) comprises, for example, a black matrix arranged in a grid shape on a glass substrate, a color filter including a red layer, a green layer, and a blue layer arranged between each grid of the black matrix, a common electrode arranged to cover the black matrix and the color filter, and an alignment film formed to cover the common electrode. The liquid crystal layer (3) is composed of a nematic liquid crystal material, such as one containing liquid crystal molecules having electro-optical properties. The first polarizer (6) and the second polarizer (7) comprise, for example, a polarizer layer having a polarization axis in one direction and a pair of protective layers arranged to cover the polarizer layer.

[0035] <Backlight Unit Composition>

[0036] As shown in FIG. 2, the backlight unit (40) comprises a reflective member (41), a plurality of point light sources (42) arranged in a two-dimensional shape on the reflective member (41), and an optical sheet laminate (100) arranged above the plurality of point light sources (42). The optical sheet laminate (100) comprises a light diffusion sheet (43) arranged above the plurality of point light sources (42), a color conversion sheet (44) arranged above the light diffusion sheet (43), a pair of prism sheets (45, 46) arranged above the color conversion sheet (44), and another light diffusion sheet (47) arranged above the pair of prism sheets (45, 46).

[0037] In this embodiment, two light-diffusing sheets (43) are stacked, for example, and placed in the backlight unit (40). The light-diffusing sheets (43) may be used as a single sheet, or three or more sheets may be stacked and used. In particular, if the uniformity of brightness can be sufficiently increased by the precise placement of the point light source (42), the light-diffusing sheets (43) may be used as a single sheet. When multiple light-diffusing sheets (43) are used, the specifications (material, thickness, surface shape, etc.) of each light-diffusing sheet (43) may be the same or different. A pair of prism sheets (45, 46) may be a first prism sheet (45) and a second prism sheet (46) in which the prism extension direction (the direction in which the prism ridge is extended) is orthogonal to each other.

[0038] [Absence of reflection]

[0039] The reflective member (41) is composed of, for example, a white polyethylene terephthalate resin film, a silver deposition film, etc.

[0040] [Point source]

[0041] The type of point light source (42) is not particularly limited, but, for example, it may be an LED element or a laser element, and an LED element may be used for reasons such as cost and productivity. To control the light emission angle characteristics of the LED element, a lens may be mounted on the LED element. The LED element (chip) may have a rectangular shape when viewed from a flat surface, and in that case, the length of one side may 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). The LED chips may be arranged alternately at regular intervals in two dimensions on the reflective sheet (41). When multiple LED chips are arranged at equal intervals, the distance between the centers of two adjacent chips may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less. By regularly arranging point light sources (42), such as LED elements, the uniformity of brightness is improved.

[0042] The point light source (42) may be placed on a reflective member (41) formed in a sheet shape. Alternatively, the point light source (42) may be inserted into the reflective member (41) so that only the light-emitting part of the point light source (42) (e.g., a lens mounted on an LED element) is exposed.

[0043] The point light source (42) may be a blue light source. When using a blue light source, for example, a color conversion sheet (44) that converts blue light into light of any color (e.g., green or red) is placed between the light diffusion sheet (43) and the first prism sheet (45). For example, a QD (quantum dot) sheet or a fluorescent sheet may be used as the color conversion sheet. The point light source (42) may be a white light source. The white light source may be composed of an LED element with a peak wavelength in the blue region, an LED element with a peak wavelength in the green region, and an LED element with a peak wavelength in the red region. When the point light source (42) is a white light source, the color conversion sheet (44) does not need to be placed.

[0044] [Light Diffusion Sheet]

[0045] As shown in FIG. 3, the light-diffusing sheet (43) has a substrate layer (21). The light-diffusing sheet (43) (substrate layer (21)) has a light-receiving surface (21a) and a light-emitting surface (21b). That is, the light-diffusing sheet (43) is positioned so that the light-receiving surface (21a) faces toward a point light source (42). The resin that forms the matrix of the substrate layer (21) is not particularly limited as long as it is composed of a material that transmits light, but for example, it may be acrylic, polystyrene, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. The substrate layer (21) may contain additives such as a diffusing agent, or may not substantially contain any additives. The additives that can be contained in the substrate layer (21) are not particularly limited, but may be inorganic particles such as silica, titanium oxide, aluminum hydroxide, and barium sulfate, for example, or organic particles such as acrylic, acrylonitrile, silicone, polystyrene, and polyamide.

[0046] The thickness of the light diffusion sheet (43) is not particularly limited, but, for example, it may be 1.5 mm or less (preferably 1 mm or less) and 0.1 mm or more. If the thickness of the light diffusion sheet (43) exceeds 1.5 mm, it becomes difficult to thin the liquid crystal display device (50). If the thickness of the light diffusion sheet (43) is less than 0.1 mm, it becomes difficult to uniformize the brightness, and problems such as a decrease in the rigidity of the light diffusion sheet (43) are likely to occur. The light diffusion sheet (43) may be in the shape of a film or a plate.

[0047] On the light-receiving surface (21a) of the light-diffusing sheet (43), as shown in FIGS. 3 and 4, a plurality of concave portions (22), for example, in the shape of an inverted pyramid (inverted pyramid shape), are arranged in a two-dimensional matrix shape. The plurality of concave portions (22) may be arranged along two directions that are orthogonal to each other. Adjacent concave portions (22) are separated by a ridge (111). The ridge (111) extends along the two directions in which the concave portions (22) are arranged. The center (vertex of the inverted pyramid) (112) of the concave portion (22) is the deepest part of the concave portion (22). In FIG. 4, for simplification, the concave portions (22) in the light-diffusing sheet (43) are shown arranged in a 5x5 matrix shape. In the two-dimensional arrangement of the concave portions (22), each concave portion (22) may be formed without gaps or may be formed with a predetermined spacing. Additionally, some of the concave portions (22) may be randomly arranged to the extent that the light diffusion effect is not impaired.

[0048] The apex angle (θ) of the concave portion (22) may be, for example, 90°, the arrangement pitch (P) of the concave portion (22) may be, for example, 100 μm, and the depth of the concave portion (22) may be, for example, 50 μm. The apex angle (θ) of the concave portion (22) refers to the angle formed by the cross-section lines of the inclined planes in the cross-section (longitudinal cross-section) that appears when a plane perpendicular to the arrangement plane of the light-diffusing sheet (43) is cut through the center of the concave portion (22) (the vertex (112) of the inverted pyramid) and vertically crosses a pair of inclined planes facing each other with the center in between. In addition, the arrangement pitch (P) of the concave portion (22) refers to the distance between the centers of adjacent concave portions (22) (the vertex (112) of the inverted pyramid) (distance along the direction parallel to the arrangement plane of the light-diffusing sheet (43)).

[0049] In addition, in this disclosure, considering that it is difficult to form a geometrically strict inverted pyramidal concave portion by conventional shape transfer technology, "inverted pyramidal" includes not only a shape that can be considered a true or substantially inverted pyramidal, but also an "approximately inverted pyramidal." "Approximately" means that it is approximate, and "approximately inverted pyramidal" refers to a shape that is approximate to an inverted pyramidal. Shapes that are deformed from an "inverted pyramidal" within the range of inevitable shape deviations caused by processing precision in industrial production are also included in "approximately inverted pyramidal." In this embodiment, an inverted pyramidal concave portion (22) is formed, but the same applies when an inverted polygonal pyramidal other than an inverted pyramidal, an inverted polygonal truncated pyramidal including an inverted pyramidal truncated pyramidal, an inverted cone, an inverted cone, a truncated cone, a lower hemisphere, etc., are formed instead.

[0050] The light-emitting surface (21b) of the light-diffusing sheet (43) may be, for example, a flat surface (mirror surface), a matte surface, or an embossed surface. Alternatively, an uneven shape may be formed on the light-emitting surface (21b) of the light-diffusing sheet (43) in the same way as on the light-receiving surface (21a). The light-diffusing sheet (43) may be composed of a single-layer structure of a substrate layer (21) having an uneven shape (concave portion (22)) on the light-receiving surface (21a). The light-diffusing sheet (43) may be composed of a two-layer structure of a substrate layer that is flat on both sides and a layer having an uneven shape on one side. The light-diffusing sheet (43) may be composed of a structure of three or more layers including a layer having an uneven shape on one side. In this embodiment, a concave portion (22) is formed on the light-receiving surface (21a) of the light-diffusing sheet (43), but instead, a concave portion (22) may be formed on the light-emitting surface (21b).

[0051] [Color Conversion Sheet]

[0052] The color conversion sheet (44) is a wavelength conversion sheet that converts light (e.g., blue light) from a point light source (42) into light with a peak wavelength of any color (e.g., green or red). The color conversion sheet (44) converts, for example, blue light with a wavelength of 450 nm into green light with a wavelength of 540 nm and red light with a wavelength of 650 nm. In this case, if a point light source (42) emitting blue light with a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet (44), so the light transmitted through the color conversion sheet (44) becomes white light. For example, a QD (quantum dot) sheet or a fluorescent sheet may be used as the color conversion sheet (44).

[0053] [Prism Sheet]

[0054] The first prism sheet (45) and the second prism sheet (46) refract light rays incident from the color conversion sheet (44) toward the normal direction. On the light-emitting side of each prism sheet (45, 46), for example, a plurality of groove sets having an isosceles triangle cross section are formed adjacent to each other, and a prism is formed by a triangular prism portion sandwiched between a pair of adjacent groove sets. The apex angle of the prism is, for example, about 90°. Each groove set formed in the first prism sheet (45) and each groove set formed in the second prism sheet (46) may be arranged to be orthogonal to each other. In this way, light rays incident from the color conversion sheet (44) can be refracted toward the normal direction by the first prism sheet (45), and additionally, light rays emitted from the first prism sheet (45) can be refracted by the second prism sheet (46) so as to travel approximately perpendicularly to the light incident surface of another light diffusion sheet (47). The prism sheets (45, 46) may be laminated separately or formed integrally. The total thickness of the prism sheets (45, 46) may be, for example, about 100 to 400 μm. As for the prism sheets (45, 46), for example, a prism shape may be imparted to a PET (polyethylene terephthalate) film using a UV-curable acrylic resin.

[0055] The lower limit of the thickness of the prism sheets (45, 46) may be, for example, about 50 μm, more preferably about 100 μm. The upper limit of the thickness of the prism sheets (45, 46) may be, for example, about 200 μm, more preferably about 180 μm. The lower limit of the pitch of the prism structure in the prism sheets (45, 46) may be, for example, about 20 μm, more preferably about 25 μm. The upper limit of the pitch of the prism structure in the prism sheets (45, 46) may be, for example, about 100 μm, more preferably about 60 μm.

[0056] [Other light diffusion sheets]

[0057] The other light-diffusing sheet (47) slightly diffuses light rays incident from the side of the second prism sheet (46) to suppress brightness non-uniformity caused by the shape of the prism portion of the prism sheets (45, 46). The other light-diffusing sheet (47) may be directly laminated on the surface of the second prism sheet (46). The thickness of the other light-diffusing sheet (47) is not particularly limited, but, for example, may be 50 μm or more and 1.5 mm or less. If the thickness of the other light-diffusing sheet (47) exceeds 1.5 mm, it becomes difficult to achieve thinness of the liquid crystal display. If the thickness of the other light-diffusing sheet (47) is less than 50 μm, it becomes difficult to obtain a sufficient light-diffusing effect, and problems such as a decrease in the rigidity of the other light-diffusing sheet (47) are likely to occur. The other light-diffusing sheet (47) may be in the shape of a film or a plate. As for other light-diffusing sheets (47), for example, a PET film with an uneven shape formed by using a UV-curable acrylic resin on at least one surface may be used.

[0058] [Polarizing Sheet]

[0059] Although the city is omitted, a polarizing sheet may be placed on the upper side (display screen (50a) side) of another light diffusion sheet (47). The polarizing sheet improves the brightness of the display screen (50a) by preventing light emitted from the backlight unit (40) from being absorbed by the first polarizing plate (6) of the liquid crystal display device (50).

[0060] <Print Pattern>

[0061] In the backlight unit (40) shown in FIG. 2, light emitted from a point light source (42) is diffused by a concave portion (22) or a diffuser (not shown) when passing through a light diffusion sheet (43). Accordingly, for example, the brightness in the area directly above the point light source (42) is suppressed. However, if the backlight unit (40) is made thin by reducing the distance between the point light source (42) and the light diffusion sheet (43), or by reducing the thickness of the light diffusion sheet (43), or if the number of point light sources (42) is reduced to reduce costs, it is easy for brightness non-uniformity to occur between the area directly above the light source and the area between the light sources (areas where the light source is not placed).

[0062] In contrast, the aforementioned luminance non-uniformity can be suppressed by forming a printing pattern (101) that at least partially suppresses light transmission from a plurality of point light sources (42) on the light-emitting surface (21b) of a light-diffusing sheet (43) (lower light-diffusing sheet (43)), as in the comparative example shown in FIG. 5. The printing pattern (101) is composed of, for example, white ink that reflects light. The printing pattern (101) is formed, for example, with a high density in the area directly above the light source and a low density in the area between the light sources. Alternatively, the printing pattern (101) is formed with a high occupancy rate in the area directly above the light source and a low occupancy rate in the area between the light sources, as shown in FIG. 6, for example. Here, occupancy rate refers to the ratio of the area of ​​the printing pattern (ink-coated portion) to the unit area, and in the case shown in FIG. 6, the occupancy rate in the area directly above the light source is 100%.

[0063] FIG. 7 shows the relationship between the printing pattern (101) and the placement of the point light source (42) in a comparative example where the printing pattern (101) shown in FIG. 6 is formed on the lower light diffusion sheet (43). The point light source (42) is an LED and is arranged two-dimensionally without localization. The printing pattern (101) is arranged in a gradient shape such that the degree of suppression of light transmission is reduced from the vicinity directly above the point light source (42) toward the outside. Specifically, the gradient density of the printing pattern (101) changes continuously from 100% in the vicinity directly above the LED to 0% in the area between the LEDs.

[0064] However, as shown in the comparative example in FIGS. 5 to 7, when attempting to improve luminance uniformity by suppressing luminance non-uniformity with a single printing pattern (101), luminance uniformity is significantly reduced when the printing pattern (101) is misaligned with the placement position of the point light source (42).

[0065] FIG. 8(a) shows a plurality of point light sources (42) arranged two-dimensionally on a reflective sheet (41). FIG. 8(b) shows a printed pattern (101) having a pattern corresponding to the luminance distribution (luminance non-uniformity) caused by the plurality of point light sources (42) formed on a light-diffusing sheet (43) (substrate layer (21)). FIG. 8(c) shows a position where the arrangement location of the point light sources (42) coincides with the formation location of the printed pattern (101). FIG. 8(d) shows a positional misalignment of the printed pattern (101) with respect to the arrangement location of the point light sources (42).

[0066] As shown in FIG. 8(c), when a printing pattern (101) is formed to correspond to the arrangement of a plurality of point light sources (42), light transmission in the region directly above the light source is suppressed, thereby reducing the brightness in the region directly above the light source and eliminating brightness non-uniformity.

[0067] However, as shown in FIG. 8(d), if the position of the printed pattern (101) is misaligned with respect to the placement position of the point light source (42), the light transmission in the area directly above the high-brightness light source cannot be sufficiently suppressed, and as a result of excessively suppressing the light transmission in the area between the low-brightness light sources, the brightness non-uniformity cannot be resolved, and the brightness uniformity is reduced.

[0068] In order to suppress the deterioration of luminance uniformity caused by the positional misalignment of printing patterns as described above, the inventors of the present invention have arrived at an invention that suppresses luminance non-uniformity by combining multiple printing patterns. When luminance non-uniformity is suppressed by combining multiple printing patterns, the amount of change in printing density (tone change) in each of the multiple printing patterns can be reduced compared to the case where a single printing pattern is used. Therefore, even if there is a printing pattern among the multiple printing patterns that is misaligned with respect to the position of the light source, the deterioration of luminance uniformity can be suppressed.

[0069] In the following description, examples are provided for cases where two printing patterns are formed on each side of two light-diffusing sheets or on both sides of one light-diffusing sheet, but three or more printing patterns may be formed, and printing patterns may be formed on optical sheets other than light-diffusing sheets.

[0070] In the configuration of the present embodiment shown in FIG. 9, a first printing pattern (101A) that at least partially suppresses light transmission from a plurality of point light sources (42) is formed on the light-emitting surface (21b) of the lower light-diffusing sheet (43), and a second printing pattern (101B) that at least partially suppresses light transmission from a plurality of point light sources (42) is formed on the light-emitting surface (21b) of the upper light-diffusing sheet (43). In the configuration of the present embodiment shown in FIG. 9, the luminance non-uniformity caused by the plurality of point light sources (42) is suppressed by the first printing pattern (101A) and the second printing pattern (101B), and the luminance is made uniform.

[0071] The printing pattern (101A, 101B) may be formed with a high density in the area directly above the light source and a low density in the area between the light sources, for example. Alternatively, the printing pattern (101A, 101B) may be formed with a high occupancy rate in the area directly above the light source and a low occupancy rate in the area between the light sources, for example, as shown in FIG. 10. The printing unit of the printing pattern (101A, 101B) may be a dot shape, such as a circle, for example, or a line shape. In addition, the printing pattern (101A, 101B) may be formed as a solid shape in the area directly above the light source.

[0072] In addition, in the present disclosure, a shape recognized as a granular shape such as a circle, triangle, or square is referred to as a "dot shape," a shape recognizable as a straight line shape or a dashed line shape is referred to as a "line shape," and a shape having a surface (two-dimensional diffusion) other than a "dot shape" and a "line shape" is referred to as a "solid shape" (meaning the background of the background printing).

[0073] FIG. 11 illustrates the relationship between the printing patterns (101A, 101B) and the placement of point light sources (42) in the configuration of the present embodiment in which the printing patterns (101A, 101B) shown in FIG. 10 are formed on lower and upper light diffusion sheets (43). The point light sources (42) are LEDs and are arranged two-dimensionally without uneven distribution. The printing patterns (101A, 101B) are a collection of unit patterns in a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one point light source (42) toward the intermediate region between the adjacent point light source (42), and the printing patterns (101A, 101B) are formed by arranging the unit patterns two-dimensionally without uneven distribution. Specifically, the gradient density of the printing pattern (101) of the comparative example shown in FIG. 7 directly above the LED is set to 100%, and the gradient density of the printing patterns (101A, 101B) changes continuously from 50% near the LED directly to 0% in the area between LEDs. In addition, the printing pattern (101A), the printing pattern (101B), and the pattern formed by overlapping the printing pattern (101A) and the printing pattern (101B) are each patterns having a printing density according to the luminance in the luminance distribution generated by the point light source (42) when the printing patterns (101A, 101B) are not formed, and said luminance and said printing density have a positive correlation.

[0074] And, only one of the printing pattern (101A) or the printing pattern (101B) is a pattern having a printing density according to the luminance in the luminance distribution described above, and said luminance and said printing density may have a positive correlation.

[0075] Instead of the configuration shown in FIGS. 9 to 11 of the present embodiment, as in the configuration of the modified example shown in FIG. 12, a first printing pattern (101A) may be formed on the light-emitting surface (21b) of the lower light-diffusing sheet (43), and a second printing pattern (101B) may be formed on the light-receiving surface (21a) of the same lower light-diffusing sheet (43). Here, the second printing pattern (101B) is arranged so as to fill in a plurality of concave portions (22) formed on the light-receiving surface (21a) of the light-diffusing sheet (43). In the configuration of the modified example shown in FIG. 12, the luminance non-uniformity caused by the plurality of point light sources (42) is suppressed by the first printing pattern (101A) and the second printing pattern (101B), and the luminance is made uniform. In the configuration of the modified example shown in FIG. 12, printing patterns (101A, 101B) are formed on both sides of the lower light-diffusing sheet (43), but instead, printing patterns (101A, 101B) may be formed on both sides of the upper light-diffusing sheet (43).

[0076] In the present embodiment (including variations thereof; hereinafter the same), the material of the printing pattern (101A, 101B) is not particularly limited as long as it is a material that is printable and capable of suppressing light transmission, but may be an ink material that reflects, absorbs, or diffuses light, specifically a white ink with high reflectivity. The white ink may be composed of a medium (a base resin), a white pigment, a white dye, a curing component, etc. In addition, the type of ink may be a thermal curing ink such as a heat-reactive type or a solvent-evaporating type that is cured using a heat source, a UV-curing ink that is cured using ultraviolet rays, or a mixture of both. The white pigment may be, for example, titanium oxide. The solvent may be, for example, an organic solvent such as toluene. The adhesive resin may be, for example, an acrylic resin.

[0077] Additionally, in the present embodiment, the printing pattern (101A, 101B) is a collection of unit patterns in a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the point light sources (42) to the intermediate region between the adjacent point light source (42), and the printing pattern (101A, 101B) may be formed by arranging the unit patterns two-dimensionally without localization. Alternatively, at least one of the printing pattern (101A, 101B) is a pattern having a printing density according to the luminance in the luminance distribution (hereinafter simply referred to as "luminance distribution") generated by the multiple point light sources (42) when the printing pattern (101A, 101B) is not formed, and the luminance and the printing density may have a positive correlation. In other words, the printing pattern (101A, 101B) may be formed with a relatively high density or high occupancy rate in a high-luminance region of the luminance distribution. The high-luminance region may be, for example, a region directly above a point light source (42). Alternatively, the pattern formed by overlapping the printing pattern (101A) and the printing pattern (101B) is a pattern having a printing density according to the luminance in the luminance distribution generated by a plurality of point light sources (42) when the printing pattern (101A, 101B) is not formed, and the luminance and the printing density may have a positive correlation.

[0078] When a printing pattern (101A, 101B) is formed by dot printing with white ink, the total light transmittance, i.e., brightness, decreases as the area ratio of the dot printing increases. Therefore, by adjusting the area ratio of the dot printing, the total light transmittance according to the degree of brightness suppression required in the high-brightness region can be easily realized. In other words, by identifying the location of the high-brightness region or the degree of brightness suppression required in the high-brightness region, and forming a printing pattern (101A, 101B) by performing dot printing with white ink in the high-brightness region of the light diffusion sheet (43) at an area ratio according to the degree of brightness suppression required, brightness uniformity can be improved.

[0079] In the embodiment described above, the high-brightness region of the brightness distribution is exemplified as being the region directly above the light source. However, depending on the configuration of the backlight unit (40) (optical sheet laminate (100)), the structure of the light diffusion sheet (43), the characteristics of the reflective member (41) or the point light source (42), the high-brightness region may be the region between adjacent point light sources (42) rather than the region directly above the light source. In this case, brightness non-uniformity can be suppressed by forming a printing pattern (101A, 101B) in the region between light sources that becomes the high-brightness region. Furthermore, the region between light sources includes not only the region between adjacent point light sources (42) along the two directions in which the point light sources (42) are arranged, but also the region between adjacent point light sources (42) along a direction inclined with respect to the arrangement direction of the point light sources (42) (diagonal direction).

[0080] In this embodiment, the printing pattern (101A, 101B) may be arranged in a gradient shape such that the arrangement density increases as the luminance in the luminance distribution increases. Arranging the printing pattern in a gradient shape means changing the arrangement density of the printing pattern. The arrangement density of the printing pattern refers to the ratio of the area occupied by the printing pattern in a unit area. For example, in the case of a dot-shaped gradient, the area ratio is calculated based on "the area of ​​one dot in the unit area" × "the number of dots in the unit area (if multiple dot sizes exist, that is also taken into account)." For example, in the case of a line-shaped gradient, the area ratio is calculated based on "the area of ​​one line in the unit area" × "the number of lines in the unit area (if multiple line sizes exist, that is also taken into account)." For example, in the case of a solid-shaped gradient, the area ratio is calculated based on "the area of ​​one solid in the unit area" × "the number of solids in the unit area (if multiple solid sizes exist, that is also taken into account)." The arrangement density of the printing pattern arranged in a gradient shape varies between 100% (completely solid) and 0%. The range of batch density from 100% to 0% includes 100% and 0%, but the maximum and minimum values ​​of the batch density of the printed pattern do not necessarily have to be 100% and 0%. The change in batch density may be linear or curvilinear. The change in batch density may be a unidirectional change such as monotonic increase or monotonic decrease (e.g., 100%→0%), or a change involving increase or decrease (e.g., 100%→50%→70%→0%). The "unit area" used to represent the batch density of the printed pattern may be set arbitrarily.

[0081] The printing pattern (101A, 101B) may be formed in a dot shape or an inverted shape thereof. The shape of the dot is not limited to a circle and may be a triangle, square, hexagon, etc. Alternatively, the dot may have multiple different shapes. Alternatively, multiple dots having different sizes may be used. The size of the dot or the dot spacing, etc., are appropriately set according to the luminance distribution, for example, by adjusting the placement density of white ink. In the printing pattern (101A, 101B), parts of the dot shape or an inverted shape thereof may be mixed with parts of the line shape or solid shape.

[0082] The printing pattern (101A, 101B) may be formed as a line shape, such as a straight line or a dashed line, or as an inverted shape thereof. The line shape is not particularly limited and may have multiple shapes with different dimensions. Alternatively, multiple lines with different dimensions may be used. The width, length, and spacing of the lines are appropriately set according to the luminance distribution, for example, by adjusting the placement density of white ink. In the printing pattern (101A, 101B), parts of the line shape or an inverted shape thereof may be mixed with parts of the dot shape or solid shape.

[0083] Method for manufacturing an optical sheet laminate

[0084] The method for manufacturing an optical sheet laminate (100) of the present embodiment comprises: a process A of forming a first printing pattern (101A) that at least partially suppresses light transmission from a plurality of point light sources (42) on a first surface (e.g., a light-emitting surface (21b)) of a first optical sheet (e.g., a lower light-diffusing sheet (43)); and a process B of forming a second printing pattern (101B) that at least partially suppresses light transmission from a plurality of point light sources (42) on a second optical sheet (e.g., an upper light-diffusing sheet (43)) different from the first optical sheet, or on a second surface (e.g., a light-receiving surface (21a)) of the first optical sheet. Processes A and B are performed such that the brightness non-uniformity caused by the plurality of point light sources (42) is suppressed by the printing patterns (101A, 101B) and the brightness is made uniform.

[0085] In the method for manufacturing the optical sheet laminate (100) of the present embodiment, the printing pattern (101A, 101B) is a collection of unit part patterns of a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the point light sources (42) among the plurality of point light sources (42) toward the intermediate region next to it, and the printing pattern (101A, 101B) may be formed by arranging the unit patterns two-dimensionally without localization. Alternatively, at least one of the printing pattern (101A, 101B) is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources (42) when the printing pattern (101A, 101B) is not formed, and the luminance and the printing density may have a positive correlation. Alternatively, the pattern formed by overlapping the printing pattern (101A) and the printing pattern (101B) is a pattern having a printing density according to the brightness in the brightness distribution generated by the plurality of point light sources (42) when the printing patterns (101A, 101B) are not formed, and the brightness and the printing density may have a positive correlation. In this case, the region with high brightness in the brightness distribution may be a region directly above the plurality of point light sources (42) depending on the configuration of the optical sheet laminate (100) or the characteristics of the point light source (42), or it may be a region between adjacent point light sources (42) among the plurality of point light sources (42).

[0086] The printing method of the printing pattern (101A, 101B) is not particularly limited, but, for example, screen printing, offset printing, inkjet printing, etc., may be used. In addition, the printing ink constituting the printing pattern (101A, 101B) is not particularly limited as long as it is usable for printing, but, for example, UV-curing ink, heat-curing ink, evaporative drying ink, oxidative polymerization ink, etc. may be used. Also, from the viewpoint of suppressing light transmission, the printing ink is preferably white ink or gray ink, etc.

[0087] The method of giving shape, such as the concave portion (22) in the light diffusion sheet (43), is not particularly limited, but, for example, extrusion molding, injection molding, laser processing, mold transfer, etc. may be used.

[0088] The procedure for manufacturing a single-layer light-diffusing sheet having an uneven surface shape using an extrusion molding method is as follows. First, a pellet-shaped plastic resin (which may have a diffusing agent added) is fed into a single-axis extruder and melted and kneaded while heating. Then, the molten resin extruded by a T-die is placed between two metal rolls to cool, then conveyed using guide rolls, and cut into a single-sheet plate using a sheet cutter to produce a light-diffusing sheet. Here, by using metal rolls having a surface shape that is an inverted version of the desired uneven shape and placing the molten resin between them, the inverted shape of the roll surface is transferred to the resin, thereby allowing the desired uneven shape to be formed on the surface of the light-diffusing sheet. Furthermore, since the shape transferred to the resin does not necessarily transfer 100% of the shape of the roll surface, the shape of the roll surface may be designed by working backward from the degree of transfer. In addition, instead of cutting the extruded resin into single-sheet plates using a sheet cutter, it may be wound into a roll shape first and then cut into single-sheet plates in a subsequent process (cutting process after printing).

[0089] When manufacturing a two-layer light-diffusing sheet having an uneven surface using an extrusion molding method, for example, pellet-shaped plastic particles required for forming each layer are fed into each of two single-screw extruders, and then the sequence described above is performed for each layer, and the manufactured sheets are laminated.

[0090] Alternatively, a light-diffusing sheet with a two-layer structure having an uneven surface may be manufactured as follows. First, pellet-shaped plastic particles required for forming each layer are fed into each of two single-axis extruders, and are melted and kneaded while heating. Then, the molten resin to be each layer is fed into a single T-die, laminated within the T-die, and the laminated molten resin extruded by the T-die is cooled by sandwiching it between two metal rolls. After that, the laminated molten resin is conveyed using guide rolls and cut into a single-sheet plate using a sheet cutter to manufacture a light-diffusing sheet with a two-layer structure having an uneven surface. Alternatively, instead of cutting the laminated resin into a single-sheet plate using a sheet cutter, it may be wound into a roll shape and then cut into a single-sheet plate in a subsequent process (cutting process after printing).

[0091] In addition, a light-diffusing sheet may be manufactured as follows by a mold transfer using UV (ultraviolet) light. First, an uncured UV-curing resin is filled into a roll having an inverted shape of the uneven surface to be transferred, and a substrate is placed against the resin and pressed. Next, with the roll filled with the UV-curing resin and the substrate in a state where they are integrated, UV light is irradiated to cure the resin. Next, the sheet with the uneven surface transferred by the resin is peeled off from the roll. Finally, UV light is irradiated onto the sheet again to completely cure the resin, thereby producing a light-diffusing sheet having an uneven surface.

[0092] <Features of the Embodiment>

[0093] The optical sheet laminate (100) of the present embodiment is embedded in a liquid crystal display device (50) in which a plurality of point light sources (42) are dispersed on the back side of a display screen (50a). The optical sheet laminate (100) has a first optical sheet (lower light diffusion sheet (43)) having a first printing pattern (101A) formed on a first surface (light-emitting surface (21b)) that at least partially suppresses light transmission from the plurality of point light sources (42). A second printing pattern (101B) that at least partially suppresses light transmission from the plurality of point light sources (42) is formed on a second optical sheet (upper light diffusion sheet (43)) different from the first optical sheet, or on a second surface (light-receiving surface (21a)) of the first optical sheet. By the first printing pattern (101A) and the second printing pattern (101B), the luminance non-uniformity caused by a plurality of point light sources (42) is suppressed, and the luminance is made uniform.

[0094] According to the optical sheet laminate (100) of the present embodiment, a first printing pattern (101A) and a second printing pattern (101B) for suppressing luminance non-uniformity are arranged on both sides of a plurality of different optical sheets (lower light-diffusing sheet (43) and upper light-diffusing sheet (43)), or on the same optical sheet (lower light-diffusing sheet (43)). Accordingly, compared to the case where luminance non-uniformity is suppressed by a single printing pattern, the amount of change (tone change) in the printing density (placement density) in the first printing pattern (101A) and the second printing pattern (101B) can be reduced. Therefore, even if the first printing pattern (101A) and / or the second printing pattern (101B) are misaligned with respect to the light source placement position, the deterioration of luminance uniformity can be suppressed.

[0095] FIG. 13(a) shows an example of a luminance distribution when no printed pattern is formed on the optical sheet laminate (100). The point light source (42) is an LED. As shown in FIG. 13(a), the luminance of the LED-side region is relatively high, and the luminance of the LED-side region is relatively low. That is, luminance non-uniformity occurs.

[0096] FIGS. 13(b) and (c) show an example of a placement density of a printing pattern that resolves the luminance non-uniformity shown in FIG. 13(a). The placement density is represented as a relative density in which the placement density of the LED-direction region of a single printing pattern (101) in the comparative example is set to 100.

[0097] FIG. 13(d) shows a printed pattern formed on an optical sheet laminate (100) so that the position is not misaligned, thereby resolving the non-uniformity of brightness.

[0098] In a single printing pattern (101) that is a comparative example, as shown in FIG. 13(b), a large tone change occurs from a density of 100 in the LED area to a density of 0 in the LED area. Therefore, when the printing pattern (101) is misaligned with respect to the LED placement position, the degree of degradation of brightness uniformity increases.

[0099] In this regard, as shown in FIG. 13(b) and (c), in the first printing pattern (101A) (first layer) and the second printing pattern (101B) (second layer) of the present embodiment, the tone change is suppressed by half compared to the comparative example, from a density of 50 in the LED upper region to a density of 0 in the LED inter-regional region. Therefore, even if the position of the first printing pattern (101A) and / or the second printing pattern (101B) is misaligned with respect to the LED placement position, the degree of degradation of brightness uniformity can be reduced.

[0100] And, in the example shown in FIG. 13, half of the luminance difference (hereinafter simply referred to as "luminance difference") between the LED upper region and the LED inter-region is suppressed by each of the first printing pattern (101A) and the second printing pattern (101B). However, within a range where luminance non-uniformity is substantially eliminated by the combination of the first printing pattern (101A) and the second printing pattern (101B), each of the first printing pattern (101A) and the second printing pattern (101B) may suppress the luminance difference by about 20% to 80%, preferably about 30% to 70%, and more preferably about 40% to 60%.

[0101] In the optical sheet laminate (100) of the present embodiment, the printing pattern (101A, 101B) is a collection of unit patterns in a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the point light sources (42) among the plurality of point light sources (42) toward the intermediate region next to it, and the printing pattern (101A, 101B) may be formed by arranging the unit patterns two-dimensionally without localization. Alternatively, at least one of the first printing pattern (101A) and the second printing pattern (101B) is a pattern having a printing density according to the brightness in the brightness distribution generated by the plurality of point light sources (42) when the first printing pattern (101A) and the second printing pattern (101B) are not formed, and the brightness and the printing density may have a positive correlation. Alternatively, the pattern formed by overlapping the first printing pattern (101A) and the second printing pattern (101B) is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources (42) when the first printing pattern (101A) and the second printing pattern (101B) are not formed, and the luminance and the printing density may have a positive correlation. In this way, the luminance non-uniformity caused by the plurality of point light sources (42) is suppressed by the first printing pattern (101A) and the second printing pattern (101B), thereby improving luminance uniformity. In this case, the region with high luminance in the luminance distribution may be an area directly above the plurality of point light sources (42), or an area between adjacent point light sources (42) among the plurality of point light sources (42), depending on the configuration of the optical sheet laminate (100) or the characteristics of the point light sources (42). By doing this, the brightness in the area directly above the point light source (42) or the area between the point light sources (42) can be suppressed, thereby improving brightness uniformity.

[0102] In the optical sheet laminate (100) of the present embodiment, the optical sheet on which the first printing pattern (101A) is formed may be a light-diffusing sheet (43) (lower light-diffusing sheet (43)). By doing so, the non-uniformity of brightness can be further suppressed by the light-diffusing sheet (43). In this case, the second printing pattern (101B) is formed on another optical sheet (upper light-diffusing sheet (43)), and in the lower light-diffusing sheet (43), the first surface (output surface (21b)) where the first printing pattern (101A) is formed is a flat surface or a matte surface, and in the second surface (input surface (21a)), a plurality of concave portions (22) arranged two-dimensionally are formed, and in the upper light-diffusing sheet (43), when the second printing pattern (101B) is formed on the output surface (21b) which is a flat surface or a matte surface, the first printing pattern (101A) and the second printing pattern (101B) can be easily formed on a flat surface or a matte surface with small undulations. Alternatively, a second printing pattern (101B) may also be formed on the lower light-diffusing sheet (43), and a plurality of concave portions (22) arranged two-dimensionally are formed on one of the first and second surfaces of the lower light-diffusing sheet (43) (light-receiving surface (21a)). If the other of the first and second surfaces (light-emitting surface (21b)) is a flat surface or a matte surface, then one of the first printing pattern (101A) or the second printing pattern (101B) (the second printing pattern (101B)) is formed thickly by filling the concave portions (22), thereby further suppressing light transmission. Additionally, the plurality of concave portions (22) may have an inverted polygonal pyramid shape, an inverted polygonal frustum shape, or a lower hemisphere shape. By doing so, the light-diffusing properties of the light-diffusing sheet (43) can be improved.

[0103] The backlight unit (40) of the present embodiment is embedded in the liquid crystal display device (50) and guides light emitted from a plurality of point light sources (42) toward the display screen (50a), and the optical sheet laminate (100) of the present embodiment is provided between the display screen (50a) and the plurality of point light sources (42). Accordingly, brightness uniformity can be improved.

[0104] In the backlight unit (40) of the present embodiment, the distance between the plurality of point light sources (42) and the optical sheet laminate (100) may be 2 mm or less. This allows for improved brightness uniformity even in configurations where non-uniformity in brightness distribution is likely to occur in conventional light-diffusing sheets. That is, the backlight unit (40) of the present embodiment is a direct-type backlight unit in which a plurality of point light sources (42) are distributed on the back side of the display screen (50a) of the liquid crystal display device (50). Therefore, in order to thin or miniaturize the liquid crystal display device (50), it is necessary to reduce the distance between the point light sources (42) and the optical sheet laminate (100). However, if this distance is reduced, for example, a phenomenon (brightness non-uniformity) is likely to occur in which the brightness of the display screen (50a) located in the area between the light sources distributed among the point light sources (42) becomes lower than that of other parts. In contrast, using the optical sheet laminate (100) of the present embodiment, having a first printing pattern (101A) and a second printing pattern (101B) formed thereon, is useful for suppressing brightness non-uniformity. In particular, aiming for the thinning of future small and medium-sized liquid crystal display devices, if the distance between the point light source and the optical sheet laminate is set to 10 mm or less, more preferably 5 mm or less, even more preferably 2 mm or less, and ultimately 0 mm, the usefulness of the optical sheet laminate (100) of the present embodiment is expected to become even more significant.

[0105] In the backlight unit (40) of the present embodiment, the point light source (42) may be an LED element. By doing so, sufficient brightness can be obtained across the entire screen even if the number of light sources is reduced.

[0106] In the backlight unit (40) of the present embodiment, the point light source (42) may be placed on a reflective member (41) positioned on the opposite side of the display screen (50a) when viewed from the optical sheet laminate (100). By doing so, the brightness uniformity is further improved.

[0107] The liquid crystal display device (50) of the present embodiment is equipped with the backlight unit (40) of the present embodiment and the liquid crystal display panel (5), thereby improving brightness uniformity. The same effect is obtained in an information device equipped with the liquid crystal display device (50) of the present embodiment.

[0108] The method for manufacturing an optical sheet laminate (100) according to the present embodiment is a method for manufacturing an optical sheet laminate (100) embedded in a liquid crystal display device (50) in which a plurality of point light sources (42) are dispersed on the back side of a display screen (50a). The method for manufacturing an optical sheet laminate (100) according to the present embodiment comprises: a process A for forming a first printing pattern (101A) that at least partially suppresses light transmission from a plurality of point light sources (42) on a first surface (output surface (21b)) of a first optical sheet (lower light diffusion sheet (43)); and a process B for forming a second printing pattern (101B) that at least partially suppresses light transmission from a plurality of point light sources (42) on a second optical sheet (upper light diffusion sheet (43)) different from the first optical sheet, or on a second surface (input surface (21a)) of the first optical sheet. Processes A and B are carried out such that the luminance non-uniformity caused by a plurality of point light sources (42) is suppressed by the first printing pattern (101A) and the second printing pattern (101B), thereby making the luminance uniform.

[0109] According to the manufacturing method of the optical sheet laminate (100) of the present embodiment, a first printing pattern (101A) and a second printing pattern (101B) for suppressing luminance non-uniformity are formed on both sides of a plurality of different optical sheets (lower light-diffusing sheet (43) and upper light-diffusing sheet (43)) or the same optical sheet (lower light-diffusing sheet (43)). Accordingly, compared to the case where luminance non-uniformity is suppressed by a single printing pattern, the tone change in the first printing pattern (101A) and the second printing pattern (101B) can be reduced. Therefore, even if the first printing pattern (101A) and / or the second printing pattern (101B) are misaligned with respect to the placement position of the point light source (42), the decrease in luminance uniformity can be suppressed.

[0110] In the method for manufacturing the optical sheet laminate (100) of the present embodiment, the printing pattern (101A, 101B) is a collection of unit patterns in a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the point light sources (42) among the plurality of point light sources (42) toward the intermediate region next to it, and the printing pattern (101A, 101B) may be formed by arranging the unit patterns two-dimensionally without localization. Alternatively, at least one of the first printing pattern (101A) and the second printing pattern (101B) is a pattern having a printing density according to the brightness in the brightness distribution generated by the plurality of point light sources (42) when the first printing pattern (101A) and the second printing pattern (101B) are not formed, and the brightness and the printing density may have a positive correlation. Alternatively, the pattern formed by overlapping the first printing pattern (101A) and the second printing pattern (101B) is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources (42) when the first printing pattern (101A) and the second printing pattern (101B) are not formed, and the luminance and the printing density may have a positive correlation. In this way, the luminance non-uniformity caused by the plurality of point light sources (42) is suppressed by the first printing pattern (101A) and the second printing pattern (101B), thereby improving luminance uniformity. In this case, the region with high luminance in the luminance distribution may be an area directly above the plurality of point light sources (42), or an area between adjacent point light sources (42) among the plurality of point light sources (42), depending on the configuration of the optical sheet laminate (100) or the characteristics of the point light sources (42). By doing this, the brightness in the area directly above the point light source (42) or the area between the point light sources (42) can be suppressed, thereby improving brightness uniformity.

[0111] (Example)

[0112] Below, the results of investigating the effect of positional misalignment of printing patterns on luminance uniformity in the examples and comparative examples are described.

[0113] As an evaluation sample for the example, the configuration of the backlight unit (40) shown in FIG. 2 was used. Specifically, as a plurality of point light sources (42), a blue LED array was used in which blue mini LEDs were arranged at a pitch of 2.5 mm. Two light-diffusing sheets (43) were stacked and used, with the thickness of the lower light-diffusing sheet (43) being 130 μm and the thickness of the upper light-diffusing sheet (43) being 190 μm. On the light-input surface (21a) of each light-diffusing sheet (43), a plurality of concave portions (22) having an inverted pyramid shape were arranged in a two-dimensional manner, and the light-output surface (21b) of each light-diffusing sheet (43) was made into a matte surface. Each light-diffusing sheet (43) was formed by processing the polycarbonate that serves as the substrate layer (21) by extrusion molding and arranging the concave portions (22) in a two-dimensional manner. No diffusing agent was added to each light-diffusing sheet (43). In the lower light-diffusing sheet (43), inverted pyramid-shaped concave portions (22) with a depth of about 50 μm were arranged at a pitch of 100 μm. In the upper light-diffusing sheet (43), inverted pyramid-shaped concave portions (22) with a depth of about 100 μm were arranged at a pitch of 180 μm. The first printing pattern (101A) and the second printing pattern (101B) were formed on each of the two light-diffusing sheets (43), as shown in FIGS. 9 and FIGS. 11. As a comparative example, an evaluation sample was also prepared in which a single printing pattern (101) was formed only on the lower light-diffusing sheet (43), as shown in FIGS. 5 and FIGS. 7. Additionally, as comparative examples, two types of comparative examples, Comparative Example 1 and Comparative Example 2, were prepared in which the printing patterns (101) were different. The first printing pattern (101A) and the second printing pattern (101B) of the example, and the printing pattern (101) of the comparative example were all formed by gradient printing using white ink. As the white ink, a two-component reaction-curing ink (thermal-curing ink) was used, which has a reflectance of about 88% for light of a wavelength of 460 nm when the printing thickness is about 18 μm. Screen printing was used for the gradient printing, and the printing thickness was set to about 18 μm.The placement density (printing density) of the first printing pattern (101A) and the second printing pattern (101B) of the example was set to half the placement density (printing density) of the printing pattern (101) of the comparative example. In addition, to suppress floating of the sheets constituting the backlight unit (40), a transparent glass plate was placed on another light-diffusing sheet (47).

[0114] In addition, to evaluate the effect of the positional misalignment of the printing pattern relative to the light source placement position on luminance uniformity, in “pattern position misalignment 1,” the first printing pattern (101A) and the second printing pattern (101B) were offset together by 300㎛ and 500㎛ from a predetermined position (a position without positional misalignment. The same applies hereinafter) in a diagonal 45-degree direction (hereinafter also referred to as the θ direction) with respect to the two-dimensional arrangement direction of the point light source (42). In addition, in “pattern position misalignment 2,” only the first printing pattern (101A) was offset by 300㎛ and 500㎛ in the θ direction from a predetermined position, while the second printing pattern (101B) was formed at a predetermined position without positional misalignment. In addition, in "pattern position misalignment 3," the first printing pattern (101A) is misaligned by 300 μm and 500 μm in the θ direction from a predetermined position, while the second printing pattern (101B) is misaligned by 300 μm and 500 μm in the opposite direction of 180 degrees in the θ direction from a predetermined position. And, for the comparative example, the printing pattern (101) is misaligned by 300 μm and 500 μm in the θ direction from a predetermined position.

[0115] For the evaluation samples of the examples and comparative examples configured as described above, the luminance in the vertical upward direction (the direction from the LED array toward the glass plate) was measured using a 2D colorimeter UA-200 manufactured by TOPCON TECHNOHOUSE. Next, for the obtained 2D luminance distribution image, correction was performed on the deviation of the luminance intensity of individual LEDs, and filtering processing was performed to suppress bright spot and dark spot noise caused by foreign substances, etc., and then the average value and standard deviation were calculated for the luminance of all pixels. Finally, "luminance uniformity" was defined as "average value of luminance / standard deviation of luminance," and the luminance uniformity of the evaluation samples of the examples and comparative examples was calculated. Furthermore, for the calculation of luminance uniformity, the luminance measurement results were 2D mapped, and an area of ​​16 LEDs (4 vertical x 4 horizontal) without LED defects or non-uniformity was extracted, and the calculation was performed each time in that area.

[0116] Figure 14 and Table 1 show the results of investigating the effect of positional misalignment of the printing patterns of the evaluation samples of the examples and comparative examples on luminance uniformity.

[0117]

[0118] As shown in FIG. 14 and Table 1, in the examples, in any of the pattern position misalignments 1 to 3, there was almost no decrease in luminance uniformity compared to the case where there was no position misalignment. In contrast, in the comparative examples, compared to the case where there was no position misalignment, the luminance uniformity was significantly reduced in both cases of the θ-direction position misalignment of 300 μm and 500 μm.

[0119] From the above results, it was found that by combining multiple printing patterns (101A, 101B) as in the example to suppress luminance non-uniformity, even when positional misalignment occurs in multiple printing patterns (101A, 101B), the decrease in luminance uniformity can be suppressed compared to the case where a single printing pattern (101) is used as in the comparative example.

[0120] (Other embodiments)

[0121] Although embodiments of the present disclosure (including embodiments, hereinafter the same) have been described above, the present disclosure is not limited to the aforementioned embodiments and various modifications are possible within the scope of the disclosure. That is, the description of the aforementioned embodiments is essentially merely illustrative and is not intended to limit the present disclosure, its applications, or its uses. Explanation of the symbols

[0122] 1 : TFT substrate 2 : CF substrate 3: Liquid crystal layer 5 : Liquid crystal display panel 6: First polarizer 7 : Second polarizer 21 : Base layer 21a : Light-entering surface 21b : Emitting surface 22 : Concave part 40: Backlight unit 41 : Reflective element 42 : Point light source 43 : Light diffusion sheet 44 : Color Conversion Sheet 45: 1st prism sheet 46: Second prism sheet 47 : Other light-diffusing sheets 50 : Liquid Crystal Display 50a : Display screen 100 : Optical sheet laminate 101A: First printing pattern 101B: Second printing pattern 111 : Ridge 112 : Center of the depression (vertex of the inverted pyramid)

Claims

Claim 1 An optical sheet laminate embedded in a liquid crystal display device having a plurality of point light sources two-dimensionally dispersed on the back side of a display screen, comprising: a first optical sheet having a first printing pattern formed on a first surface that suppresses at least partially light transmission from the plurality of point light sources; a second optical sheet different from the first optical sheet having a second printing pattern formed thereon that suppresses at least partially light transmission from the plurality of point light sources; and by the first printing pattern and the second printing pattern, brightness non-uniformity caused by the plurality of point light sources is suppressed and brightness is uniformized; wherein the first optical sheet is a first light-diffusing sheet, wherein a plurality of two-dimensionally arranged concave portions are formed on the first surface where the first printing pattern is formed in the first light-diffusing sheet, and a second surface opposite to the first surface is a flat surface or a matte surface; and wherein the second optical sheet is a second light-diffusing sheet having a plurality of two-dimensionally arranged concave portions on the surface where the second printing pattern is formed. Claim 2 An optical sheet laminate according to claim 1, wherein the first printing pattern and the second printing pattern are a collection of unit patterns having a gradient shape in which the degree of suppression of light transmission is reduced from the immediate vicinity of one of the plurality of point light sources toward an intermediate region with the adjacent point light source, and the first printing pattern and the second printing pattern are formed by arranging the unit patterns two-dimensionally without localization. Claim 3 An optical sheet laminate according to claim 1, wherein at least one of the first printing pattern or the second printing pattern is a pattern having a printing density according to the luminance in a luminance distribution generated by the plurality of point light sources when the first printing pattern and the second printing pattern are not formed, and the luminance and the printing density have a positive correlation. Claim 4 In claim 1, the pattern formed by overlapping the first printing pattern and the second printing pattern is a pattern having a printing density according to the luminance in the luminance distribution generated by the plurality of point light sources when the first printing pattern and the second printing pattern are not formed, and the luminance and the printing density have a positive correlation, an optical sheet laminate. Claim 5 In paragraph 3, the region with the highest luminance in the luminance distribution is an optical sheet laminate that is a region directly above the plurality of point light sources. Claim 6 In paragraph 3, the region with the highest luminance in the luminance distribution is an optical sheet laminate, which is a region between adjacent point light sources among the plurality of point light sources. Claim 7 An optical sheet laminate according to claim 1, wherein the plurality of concave portions have an inverted polygonal pyramid shape, an inverted polygonal frustum shape, or a lower hemisphere shape. Claim 8 A backlight unit embedded in the liquid crystal display device and guiding light emitted from the plurality of point light sources toward the display screen, wherein the backlight unit comprises an optical sheet laminate described in any one of claims 1 to 7 between the display screen and the plurality of point light sources. Claim 9 A backlight unit according to claim 8, wherein the distance between the plurality of point light sources and the optical sheet laminate is 2 mm or less. Claim 10 In paragraph 8, the plurality of point light sources are backlight units, which are LED elements. Claim 11 In claim 8, the plurality of point light sources are backlight units disposed on a reflective member positioned on the opposite side of the display screen as viewed from the optical sheet laminate. Claim 12 A liquid crystal display device comprising a backlight unit and a liquid crystal display panel as described in paragraph 8. Claim 13 An information device having a liquid crystal display device as described in paragraph 12.

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