Composite light diffusion sheet, backlight unit, liquid crystal display device, and information device

Abstract

To improve brightness uniformity of a backlight unit.SOLUTION: A composite light diffusion sheet 100 comprises a light reflective layer 101 for reflecting visible light and a light diffusion layer 43. Th light reflective layer 101 has an average light reflectance in a range of 50% to 90%, inclusive. The light reflective layer 101 may be provided on the same base material as that of the light diffusion layer 43 or on a different base material from that of the light diffusion layer 43.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a composite light-diffusing sheet, a backlight unit, a liquid crystal display device, and an information device. [Background technology]

[0002] In recent years, liquid crystal display devices (hereinafter also referred to as liquid crystal displays) have been widely used as display devices for various information devices such as smartphones, tablet terminals, etc. The main types of backlights for liquid crystal displays are direct-type, in which a light source is placed on the back surface of the liquid crystal panel, and edge-light type, in which a light source is placed near the side of the liquid crystal panel.

[0003] When a direct-type backlight is used, a light diffusion member (light diffusion plate, light diffusion sheet, light diffusion film) is used to eliminate the image of a light source such as an LED (Light Emitting Diode) on the light-emitting surface and increase the uniformity of in-plane brightness (see, for example, Patent Document 1).

[0004] In direct backlight units for thin displays such as those for notebook computers and tablets, attempts have been made to improve brightness uniformity by using a plurality of light diffusion sheets stacked one on top of the other. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-129277 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional light diffusion sheets have not yet achieved sufficient brightness uniformity.

[0007] The present disclosure aims to improve the luminance uniformity of a backlight unit. [Means for solving the problem]

[0008] In order to achieve the above object, the first composite light-diffusing sheet according to the present disclosure includes a light-reflecting layer that reflects visible light and a light-diffusing layer provided on the same substrate as the light-reflecting layer, and the average light reflectance of the light-reflecting layer for visible light is 50% or more and 90% or less.

[0009] The first composite light diffusion sheet according to the present disclosure includes a light-reflecting layer that reflects visible light, and thus the light from the light source is reflected multiple times, thereby improving brightness uniformity compared to when no light-reflecting layer is provided.

[0010] In the first composite light-diffusing sheet according to the present disclosure, the light-diffusing layer may have a first surface provided with a plurality of recesses each having a substantially inverted polygonal pyramid shape or a substantially inverted polygonal truncated pyramid shape, and a second surface that is a flat or matte surface, and the light-reflecting layer may be provided on the second surface. In this way, the light-reflecting layer can be easily provided on the second surface of the light-diffusing layer by, for example, printing with ink.

[0011] In addition, in the light diffusion sheet according to the present disclosure, the terms "approximately inverted polygonal pyramid" or "approximately inverted polygonal pyramid truncated shape" are used in consideration of the difficulty of forming recesses in a geometrically strict inverted polygonal pyramid shape or inverted polygonal pyramid truncated shape using conventional shape transfer techniques, but it goes without saying that these terms also include shapes that can be considered to be true or substantially inverted polygonal pyramids or inverted polygonal pyramid truncated shapes.

[0012] A second composite light-diffusing sheet according to the present disclosure includes a light-reflecting layer that reflects visible light and a light-diffusing layer provided on a substrate different from the light-reflecting layer, and the average light reflectance of the light-reflecting layer for visible light is 50% or more and 90% or less.

[0013] The second composite light diffusion sheet according to the present disclosure includes a light-reflecting layer that reflects visible light, and therefore the light from the light source is reflected multiple times, thereby improving brightness uniformity compared to when no light-reflecting layer is provided.

[0014] In the first or second composite light-diffusing sheet according to the present disclosure, the light-reflecting layer may have an average light reflectance of 60% or more and 90% or less for visible light, thereby further improving luminance uniformity.

[0015] In the first or second composite light-diffusing sheet according to the present disclosure, two or more light-diffusing layers may be provided, thereby further improving the luminance uniformity.

[0016] In the first or second composite light-diffusing sheet according to the present disclosure, two or more light-reflecting layers may be provided, thereby further improving the luminance uniformity.

[0017] In the first or second composite light diffusion sheet according to the present disclosure, the light diffusion layer may have a thickness of 50 μm or more and 1200 μm or less, thereby enabling a thinner liquid crystal display to be achieved while still obtaining the light diffusion effect of the light diffusion layer.

[0018] In the first or second composite light diffusion sheet according to the present disclosure, the "light diffusion layer" may be a "light diffusion sheet", or may be a plate-shaped "light diffusion plate" or a film-shaped "light diffusion film".

[0019] The backlight unit according to the present disclosure is a backlight unit incorporated into a liquid crystal display device so as to guide light emitted from multiple light sources toward a display screen via a brightness enhancement sheet that increases the brightness of the light, and includes the first or second composite light diffusion sheet according to the present disclosure described above between the brightness enhancement sheet and the multiple light sources.

[0020] The backlight unit according to the present disclosure includes the first or second composite light-diffusing sheet according to the present disclosure, and therefore improves brightness uniformity.

[0021] The backlight unit according to the present disclosure may further include a color conversion sheet between the brightness enhancement sheet and the plurality of light sources, which converts the wavelength of light emitted from the plurality of light sources. In this way, the backlight unit can be configured even when a light source other than a white light source is used as the light source.

[0022] In the backlight unit according to the present disclosure, the plurality of light sources may be disposed on a reflecting sheet disposed on the opposite side of the display screen from the composite light-diffusing sheet, thereby further improving brightness uniformity by multiple reflections of light between the reflecting sheet and the composite light-diffusing sheet.

[0023] In the backlight unit according to the present disclosure, the composite light diffusion sheet may include a plurality of the light diffusion layers, and the light reflecting layer may be disposed closer to the brightness enhancing sheet than the light diffusion layer closest to the light sources. This configuration allows the light reflecting layer to achieve a sufficient effect of improving brightness uniformity. In this case, if three or more light diffusion layers are provided and the light reflecting layer is disposed closer to the brightness enhancing sheet than the light diffusion layer next closest to the light sources, the brightness uniformity improving effect of the light reflecting layer is further enhanced. In particular, if the light reflecting layer is disposed closer to the brightness enhancing sheet than the light diffusion layer farthest from the light sources, the brightness uniformity improving effect of the light reflecting layer can be further enhanced.

[0024] In the backlight unit according to the present disclosure, the composite light-diffusing sheet may include a plurality of the light-diffusing layers, and the light-reflecting layer may be provided on the light-incident surface of the light-diffusing layer that is farthest from the plurality of light sources, thereby more significantly improving the luminance uniformity due to the light-reflecting layer.

[0025] In the backlight unit according to the present disclosure, the composite light-diffusing sheet may include a plurality of the light-diffusing layers provided on a substrate different from that of the light-reflecting layer, and the light-reflecting layer may be disposed between the light-diffusing layer farthest from the light sources and the light-diffusing layer second farthest from the light sources, thereby enabling the light-reflecting layer to exhibit a more pronounced effect of improving brightness uniformity.

[0026] A liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure described above and a liquid crystal display panel.

[0027] According to the liquid crystal display device according to the present disclosure, the brightness uniformity is improved since the liquid crystal display device includes the backlight unit according to the present disclosure described above.

[0028] An information device according to the present disclosure includes the liquid crystal display device according to the present disclosure.

[0029] According to the information device according to the present disclosure, brightness uniformity is improved because it includes the liquid crystal display device according to the present disclosure described above. [Effects of the Invention]

[0030] According to the present disclosure, it is possible to improve the luminance uniformity of the backlight unit. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a cross-sectional view of a liquid crystal display device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a backlight unit according to the embodiment. [Figure 3] 3 is a plan view showing an example of the arrangement of light sources in the backlight unit shown in FIG. 2. FIG. [Figure 4] FIG. 2 is a perspective view of a light diffusion layer constituting the composite light diffusion sheet according to the embodiment. [Figure 5] FIG. 10 is a cross-sectional view of a backlight unit according to Modification 1. [Figure 6] FIG. 10 is a cross-sectional view of a backlight unit according to Modification 2. [Figure 7] FIG. 11 is a cross-sectional view of a backlight unit according to Modification 3. [Figure 8] FIG. 10 is a cross-sectional view of a backlight unit according to a fourth modification. [Figure 9] FIG. 11 is a cross-sectional view of a backlight unit according to Modification 5. [Figure 10] FIG. 2 is a diagram showing the shape of a regular square pyramid on a roll used to mold a resin sheet that becomes a light diffusion layer in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0032] (Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments and can be modified as desired within the scope of the technical concept of the present disclosure.

[0033] <Liquid crystal display device> 1, a liquid crystal display device 50 of this embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the back side of the liquid crystal display panel 5 via the first polarizing plate 6. The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 arranged to face each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a frame-shaped sealant (not shown) for enclosing the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0034] The shape of the display screen 50a of the liquid crystal display device 50 when viewed from the front (top of Figure 1) is, in principle, rectangular or square, but is not limited to this and may be any shape such as a rectangle with rounded corners, an oval, a circle, a trapezoid, or an automobile instrument panel.

[0035] In the liquid crystal display device 50, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 in each sub-pixel corresponding to each pixel electrode to change the alignment state of the liquid crystal layer 3. This adjusts the transmittance of light incident from the backlight unit 40 through the first polarizer 6, and the light is then emitted through the second polarizer 7, thereby displaying an image.

[0036] The liquid crystal display device 50 of this embodiment is used as a display device incorporated into various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, personal digital assistants, portable game machines, copy machines, ticket vending machines, automated teller machines, etc.).

[0037] The TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film covering each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and connected to each of the plurality of TFTs, and an alignment film covering each pixel electrode. The CF substrate 2 includes, for example, a black matrix arranged in a grid pattern on the glass substrate, color filters including red, green, and blue layers arranged between each grid of the black matrix, a common electrode covering the black matrix and the color filters, and an alignment film covering the common electrode. The liquid crystal layer 3 is made of a nematic liquid crystal material containing liquid crystal molecules with electro-optical properties. The first polarizer 6 and the second polarizer 7 include, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers sandwiching the polarizer layer.

[0038] <Backlight unit> 2, the backlight unit 40 of this embodiment includes a reflecting sheet 41, a plurality of small light sources 42 arranged two-dimensionally on the reflecting sheet 41, a composite light diffusing sheet 100 provided above the plurality of small light sources 42, a color conversion sheet 44 provided above the composite light diffusing sheet 100, and a brightness enhancement sheet 47 provided above the color conversion sheet 44. Details of the composite light diffusing sheet 100 will be described later.

[0039] [Reflection sheet] The reflection sheet 41 is composed of, for example, a film made of white polyethylene terephthalate resin, a silver vapor deposition film, or the like.

[0040] [Light source] The type of the small light source 42 is not particularly limited, and it may be, for example, an LED element, a laser element, or the like, and an LED element may be used from the viewpoints of cost, productivity, etc. In order to adjust the light emission angle characteristics of the LED element serving as the small light source 42, a lens may be attached to the LED element. For example, as shown in FIG. 3, a plurality of small light sources 42 each composed of an LED element having a size of several millimeters square may be arranged on the reflection sheet 41 in a two-dimensional array with a certain interval. The small light source 42 may have a rectangular shape in plan view, 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 number of the small light sources 42 arranged is not particularly limited, but when a plurality of small light sources 42 are arranged dispersedly, it is preferable to arrange them regularly on the reflection sheet 41. Arranging regularly means arranging with a certain regularity, and for example, the case where the small light sources 42 are arranged at equal intervals corresponds to this. When the small light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent small light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0041] In this example, a blue light source is used as the small light source 42. The blue light source may emit light with x < 0.24 and y < 0.18 in the chromaticity coordinates of CIE1931. Incidentally, a white light source may be used as the small light source 42. The white light source is composed of an LED element having a peak wavelength in the blue region, an LED element having a peak wavelength in the green region, and an LED element having a peak wavelength in the red region, and may emit light with 0.24 < x < 0.42 and 0.18 < y < 0.48 in the chromaticity coordinates of CIE1931, for example.

[0042] [Color conversion sheet] The color conversion sheet 44 is a wavelength conversion sheet that converts light from the compact light source 42, which is, for example, a blue light source, into light with a peak wavelength of a desired 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 compact light source 42 emitting blue light with a wavelength of 450 nm is used, the color conversion sheet 44 partially converts the blue light into green light and red light, so that the light transmitted through the color conversion sheet 44 becomes white light. The color conversion sheet 44 may be, for example, a quantum dot (QD) sheet or a fluorescent sheet. Note that, if a white light source is used as the compact light source 42, the color conversion sheet 46 may not be provided. Furthermore, the color conversion sheet 46 may be disposed above or below the composite light diffusion sheet 100, or between the sheets that constitute the composite light diffusion sheet 100, as long as it is located between the compact light source 42 and the brightness enhancement sheet 47 (described later).

[0043] [Brightness enhancement sheet] The brightness enhancement sheet 47 has a structure in which a first prism sheet 45 and a second prism sheet 46 are sequentially laminated from the side closest to the compact light source 42. The first prism sheet 45 and the second prism sheet 46 are, for example, films in which a plurality of grooves having an isosceles triangular cross section are formed adjacent to each other, and the apex angle of the prisms sandwiched between a pair of adjacent grooves is approximately 90°. Here, the grooves formed in the first prism sheet 45 and the grooves formed in the second prism sheet 46 are arranged so as to be perpendicular to each other. The first prism sheet 45 and the second prism sheet 46 may be integrally formed. For example, the first prism sheet 45 and the second prism sheet 46 may be formed by forming a prism shape on a PET (polyethylene terephthalate) film using a UV-curable acrylic resin.

[0044] Although not shown, a polarizing sheet may be provided above the second prism sheet 46. The polarizing sheet prevents the 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.

[0045] In this example, a prism sheet is used as the brightness enhancing sheet 47, but instead of this, other optical sheets capable of increasing the brightness of the light emitted from the small light source 42 may be used.

[0046] <Composite light diffusion sheet> The composite light diffusion sheet 100 has a structure in which three light diffusion layers 43 having the same structure are stacked, and the uppermost light diffusion layer 43, which is the farthest from the compact light source 42, is provided with a light reflecting layer 101 that reflects visible light. The type and number of light diffusion layers 43 constituting the composite light diffusion sheet 100 are not particularly limited. For example, the composite light diffusion sheet 100 may have only one light diffusion layer 43, or may have a structure in which two or four or more light diffusion layers 43 are stacked. The composite light diffusion sheet 100 may also include multiple light diffusion layers 43 with different structures. The light diffusion layer 43 constituting the composite light diffusion sheet 100 may be a "light diffusion sheet," or may be a plate-shaped "light diffusion plate" or a film-shaped "light diffusion film."

[0047] [Light diffusion layer] The light diffusion layer 43 has a base layer 21. A plurality of recesses 22 are provided on a first surface 43a (surface facing the compact light source 42) of the light diffusion layer 43. In this example, the plurality of recesses 22 are formed in the shape of a substantially inverted regular quadrangular pyramid. Adjacent recesses 22 are separated by ridge lines 23. The arrangement pitch of the recesses 22 is, for example, from about 50 μm to about 500 μm. The angle formed by the wall surface of the recesses 22 (the slope of the substantially inverted polygonal pyramid or the truncated shape of the substantially inverted polygonal pyramid) and the sheet surface of the light diffusion layer 43 (a virtual mirror surface without recesses 22) is, for example, from 40 degrees to 65 degrees. In other words, the apex angle of the recesses 22 is, for example, from 50 degrees to 100 degrees. The second surface 43b of the light diffusion layer 43 may be a mirror surface, or may be a matte surface to improve diffusion. FIG. 4 illustrates an example in which recesses 22 formed in the shape of approximately inverted square pyramids are arranged in a 5×5 matrix on the first surface 43a of the light diffusion layer 43, but the actual number of recesses 22 arranged is much greater.

[0048] In the example shown in Figure 2, multiple recesses 22 are formed on the first surface 43a (the surface facing the small light source 42) of the light diffusion layer 43, but instead of this, or in addition to this, multiple other recesses similar to the recesses 22 may be formed on the second surface 43b of the light diffusion layer 43.

[0049] The plurality of recesses 22 may be formed in the shape of a substantially inverted polygonal pyramid or a substantially inverted polygonal truncated pyramid. The plurality of recesses 22 may be regularly arranged two-dimensionally. As the "inverted polygonal pyramid (trapezoid)", a triangular pyramid (trapezoid), a square pyramid (trapezoid), or a hexagonal pyramid (trapezoid) is preferred, as they can be arranged two-dimensionally without gaps. A mold (metal roll) is used in the manufacturing process such as extrusion molding or injection molding to form the recesses 22, and in consideration of the precision of the cutting work on the surface of this mold (metal roll), an inverted square pyramid (trapezoid) may be selected as the "inverted polygonal pyramid (trapezoid)".

[0050] In consideration of the difficulty of forming a recess having a geometrically strict inverted polygonal pyramid or inverted polygonal truncated pyramid shape using ordinary shape transfer technology, the terms "approximately inverted polygonal pyramid" or "approximately inverted polygonal truncated pyramid" are used, but it goes without saying that these terms also include shapes that can be regarded as true or substantially inverted polygonal pyramids or inverted polygonal truncated pyramids. Furthermore, "approximately" means that it can be approximated; for example, "approximately square pyramid" refers to a shape that can be approximated to a square pyramid. Furthermore, shapes that are deformed from an "inverted polygonal pyramid" or "inverted polygonal truncated pyramid" within the range of unavoidable shape variations due to processing accuracy in industrial production are also included in the "approximately inverted polygonal pyramid" or "approximately inverted polygonal pyramid" shapes.

[0051] When the plurality of recesses 22 are regularly arranged two-dimensionally, the recesses 22 may be provided without gaps across the entire surface of the light diffusion layer 43, or may be provided at a fixed interval (pitch). Furthermore, some of the recesses 22 may be arranged randomly to the extent that the light diffusion effect is not impaired.

[0052] The light diffusion layer 43 may be formed from a substrate layer 21 that does not contain a diffusing agent, for example, a substrate layer 21 made of clear polycarbonate. When a diffusing agent is contained in the substrate layer 21, the material of the diffusing agent is not particularly limited, and inorganic particles such as silica, titanium oxide, aluminum hydroxide, barium sulfate, etc., and organic particles such as acrylic, acrylonitrile, silicone, polystyrene, polyamide, etc., may be used. From the viewpoint of light diffusion effect, the particle size of the diffusing agent may be, for example, 0.1 μm or more (preferably 1 μm or more) and 10 μm or less (preferably 8 μm or less).

[0053] From the viewpoints of the reflection and refraction effects of the substantially inverted polygonal pyramid shape and the light diffusion effect of the diffusing agent, it is preferable that the light diffusion layer 43 does not contain a diffusing agent. However, the content of the diffusing agent may be, for example, 0.1% by mass or more (preferably 0.3% by mass or more) and 10% by mass or less (preferably 8% by mass or less), where the material (matrix) constituting the base layer 21 is 100% by mass. The difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base layer 21 may be 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and most preferably 0.15 or more. If the difference between the refractive index of the diffusing agent and the refractive index of the matrix of the base layer 21 is less than 0.01, the diffusion effect of the diffusing agent will be insufficient.

[0054] The resin that forms the matrix of the base layer 21 is not particularly limited as long as it is a material that transmits light, but for example, acrylic, polystyrene, polycarbonate, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. may be used.

[0055] The thickness of the light diffusion layer 43 is not particularly limited, but may be, for example, 1200 μm or less and 50 μm or more. If the thickness of the light diffusion layer 43 exceeds 1200 μm, it becomes difficult to achieve a thin liquid crystal display. On the other hand, if the thickness of the light diffusion layer 43 is less than 50 μm, it becomes difficult to achieve the effect of improving brightness uniformity.

[0056] The light diffusion layer 43 may have a multilayer structure, for example, a two-layer structure consisting of a first base material layer and a second recess-forming layer. In this case, the base material layer and the recess-forming layer may each be configured as independent sheets and laminated together to form the light diffusion layer 43, or the base material layer and the recess-forming layer may each be disposed separately to form the light diffusion layer 43. The thickness of the recess-forming layer is greater than the maximum depth of the recesses 22. For example, if a recess with a depth of 20 μm is to be formed, the thickness of the recess-forming layer is set to be greater than 20 μm. The light diffusion layer 43 may have a three-layer or more structure including the base material layer and the recess-forming layer.

[0057] [Method of manufacturing the light diffusion layer] Hereinafter, a method for manufacturing the light diffusion layer 43 will be described using an example in which the light diffusion layer 43 is formed into a sheet. The method for manufacturing the light diffusion layer 43 is not particularly limited, and may be, for example, an extrusion molding method, a compression molding method, an injection molding method, or the like. When extrusion molding the light diffusion layer 43, for example, the line speed may be set to 2 m / min or more and 30 m / min or less, and the compression linear pressure may be set to 100 kgf / cm or more and 500 kgf / cm or less.

[0058] The procedure for manufacturing a single-layer light diffusion sheet having a textured surface using extrusion molding is as follows: First, pellet-shaped plastic particles (to which a diffusing agent may be added) are fed into a single-screw extruder and melted and kneaded while being heated. The molten resin extruded through a T-die is then sandwiched between two metal rolls and cooled, then conveyed using guide rolls and cut into individual flat plates using a sheet cutter. Alternatively, the continuous sheet is wound into a roll using a winder and then cut into individual flat plates using a sheet cutter, thereby producing a light diffusion sheet. Here, by sandwiching the molten resin between metal rolls having a surface with an inverted shape of the desired textured shape, the inverted shape of the roll surface is transferred to the resin, allowing the desired textured shape to be formed on the diffusion sheet surface. Furthermore, the shape transferred to the resin is not necessarily a 100% transfer of the shape of the roll surface, so the shape of the roll surface may be designed by calculating backwards from the degree of transfer.

[0059] When using an extrusion molding method to manufacture a two-layer light diffusion sheet having an uneven surface, for example, the pellet-shaped plastic particles required to form each layer are fed into each of two single-screw extruders, and then the same procedure as described above is carried out for each layer, and the resulting sheets are laminated.

[0060] Alternatively, a two-layer light diffusion sheet having an uneven surface may be produced as follows. First, pellet-shaped plastic particles required for forming each layer are fed into two single-screw extruders, and melted and kneaded while heated. The molten resins for each layer are then fed into a T-die and laminated within the T-die. The laminated molten resin extruded through the T-die is sandwiched between two metal rolls and cooled. The laminated molten resin is then transported using guide rolls and cut into individual flat plates using a sheet cutter, thereby producing a two-layer light diffusion sheet having an uneven surface.

[0061] Alternatively, a light diffusion sheet may be manufactured by shape transfer using UV (ultraviolet rays) as follows. First, a roll having an inverse shape of the concave-convex shape to be transferred is filled with uncured UV-curable resin, and a substrate is pressed against the resin. Next, while the roll filled with the UV-curable resin and the substrate are integrated, UV light is irradiated to cure the resin. Next, the sheet onto which the concave-convex shape has been transferred by the resin is peeled off from the roll. Finally, the sheet is again irradiated with UV light to completely cure the resin, producing a light diffusion sheet having a concave-convex shape on its surface.

[0062] [Light reflective layer] 2, a light reflecting layer 101 that reflects visible light is provided on the second surface (light output surface) 43b of the uppermost light diffusing layer 43, which is the farthest from the compact light source 42. That is, in this example, the light reflecting layer 101 is provided on the same substrate as the uppermost light diffusing layer 43. The second surface 43b of the light diffusing layer 43 may be a flat surface or a matte surface.

[0063] The average light reflectance of the light-reflecting layer 101 for visible light is 50% or more and 90% or less, preferably 60% or more and 90% or less, more preferably 70% or more and 85% or less, and particularly preferably 75% or more and 85% or less. When the average light reflectance is 90% or less, a decrease in brightness can be suppressed, and when the average light reflectance is 50% or more, brightness uniformity can be improved.

[0064] The light reflecting layer 101 can be formed, for example, by printing a light-reflective ink (e.g., white ink) on the second surface 43b of the light diffusing layer 43. In this case, the thickness of the light reflecting layer 101 may be, for example, about 20 μm. The light reflectance can be adjusted by the type of ink, the type and composition of the reflecting agent added to the ink, the printing thickness of the ink, etc. The light reflecting layer 101 can also be configured as an inorganic reflective layer having a multilayer structure, for example, a metal oxide layer.

[0065] In the present example shown in Fig. 2, the light reflecting layer 101 is provided on the second surface 43b of the uppermost (third) light diffusing layer 43. However, instead of this, as shown in Fig. 5, the light reflecting layer 101 may be provided on the second surface 43b of the second light diffusing layer 43. Alternatively, although not shown, the light reflecting layer 101 may be provided on the second surface 43b of the lowermost (first) light diffusing layer 43.

[0066] 2, only one light-reflecting layer 101 is provided in the composite light-diffusing sheet 100. However, instead of this, as shown in FIG. 6, two light-reflecting layers 101 may be provided on the second surfaces 43b of the second and third light-diffusing layers 43. Alternatively, although not shown, two light-reflecting layers 101 may be provided on the second surfaces 43b of the first and third light-diffusing layers 43 or the first and second light-diffusing layers 43. Alternatively, three light-reflecting layers 101 may be provided on the second surfaces 43b of the first to third light-diffusing layers 43.

[0067] 2, 5, and 6, the light diffusion layer 43 has the recesses 22 on the first surface 43a, which serves as the light incident surface, and the light reflecting layer 101 on the second surface 43b, which serves as the light exit surface. However, instead of this, at least one light diffusion layer 43 may have the recesses 22 on the light exit surface and the light reflecting layer 101 on the light incident surface. For example, as shown in FIG. 7, the uppermost light diffusion layer 43 may have the recesses 22 on the first surface 43a, which serves as the light exit surface, and the light reflecting layer 101 on the second surface 43b, which serves as the light incident surface.

[0068] In the examples shown in FIGS. 2 and 5 to 7, the light-reflecting layer 101 is provided on the same substrate as the light-diffusing layer 43. However, instead, as shown in FIG. 8, the light-reflecting layer 101 may be provided on a substrate different from that of the light-diffusing layer 43. For example, a light-reflecting sheet 103 having a light-reflecting layer 101 provided on a substrate layer 102 may be disposed between the uppermost light-diffusing layer 43 and the brightness-enhancing sheet 47 (first prism sheet 45). The configuration shown in FIG. 8 can be employed as an alternative configuration, for example, when the light-diffusing layer 43 has unevenness on both sides and it is difficult to provide the light-reflecting layer 101 on the light-diffusing layer 43 by ink printing or the like. In the example shown in FIG. 8, the light-reflecting sheet 103 having the light-reflecting layer 101 is disposed between the third light-diffusing layer 43 and the brightness-enhancing sheet 47. However, instead, as shown in FIG. 9, the light-reflecting sheet 103 having the light-reflecting layer 101 may be disposed between the third and second light-diffusing layers 43. Alternatively, a light reflecting sheet 103 having a light reflecting layer 101 may be disposed between the second and first light diffusing layers 43. When the light reflecting sheet 103 is disposed between the light diffusing layers 43, the light diffusing layer 43 on the upper side of the light reflecting sheet 103 may be disposed so that the first surface 43a on which the recesses 22 are formed becomes the light emitting surface. A plurality of light reflecting sheets 103 may be disposed between the light diffusing layer 43 and the brightness improving sheet 47 or between the light diffusing layers 43.

[0069] 2 and 5 to 9, three light diffusion layers 43 are provided. However, instead of this, one, two, or four or more light diffusion layers 43 may be provided, and the light reflecting layer 101 may be provided on any of the light diffusion layers 43. Alternatively, the light reflecting sheet 103 may be provided at any position between the first light diffusion layer 43 and the brightness improving sheet 47.

[0070] <Effects of the embodiment> As described above, the composite light-diffusing sheet 100 of this embodiment includes the light-reflecting layer 101 that reflects visible light and the light-diffusing layer 43. The average light reflectance of the light-reflecting layer 101 for visible light is 50% or more and 90% or less. The light-reflecting layer 101 may be provided on the same substrate as the light-diffusing layer 43, or may be provided on a substrate different from that of the light-diffusing layer 43.

[0071] The composite light diffusion sheet 100 of this embodiment includes a light reflecting layer 101 that reflects visible light, and therefore the light from the small light source 42 is reflected multiple times, thereby improving brightness uniformity compared to when the light reflecting layer 101 is not provided.

[0072] In the composite light-diffusing sheet 100 of this embodiment, the light-diffusing layer 43 has a first surface 43a provided with a plurality of recesses 22 each having a substantially inverted polygonal pyramid shape or a substantially inverted polygonal truncated pyramid shape, and a second surface 43b that is a flat or matte surface, and the light-reflecting layer 101 may be provided on the second surface 43b. In this way, the light-reflecting layer can be easily provided on the second surface of the light-diffusing layer by, for example, printing with ink.

[0073] In the composite light-diffusing sheet 100 of this embodiment, the average light reflectance of the light-reflecting layer 101 for visible light may be 60% or more and 90% or less, which can further improve the luminance uniformity.

[0074] The composite light-diffusing sheet 100 of this embodiment may be provided with two or more light-diffusing layers 43. In this way, the luminance uniformity can be further improved.

[0075] The composite light-diffusing sheet 100 of this embodiment may be provided with two or more light-reflecting layers 101. In this way, the luminance uniformity can be further improved.

[0076] In the composite light-diffusing sheet 100 of the present embodiment, the thickness of the light-diffusing layer 43 may be 50 μm or more and 1200 μm or less. In this way, the liquid crystal display 50 can be made thinner while still obtaining the light-diffusing effect of the light-diffusing layer 43.

[0077] The backlight unit 40 of this embodiment is incorporated into a liquid crystal display device 50 so as to guide light emitted from a plurality of small light sources 42 toward a display screen 50a via a brightness enhancing sheet 47 that enhances the brightness of the light. The backlight unit 40 of this embodiment includes the composite light diffusing sheet 100 of this embodiment between the brightness enhancing sheet 47 and the plurality of small light sources 42.

[0078] The backlight unit 40 of this embodiment includes the composite light-diffusing sheet 100 of this embodiment, and therefore improves luminance uniformity.

[0079] The backlight unit 40 of this embodiment may further include a color conversion sheet 44 between the brightness enhancement sheet 46 and the small light source 42, which converts the wavelength of light emitted from the small light source 42. In this way, the backlight unit 40 can be configured even when a light source other than a white light source is used as the small light source 42.

[0080] In the backlight unit 40 of this embodiment, the small light source 42 may be disposed on the reflective sheet 41 provided on the opposite side of the display screen 50a from the composite light-diffusing sheet 100. In this case, multiple reflections of light between the reflective sheet 41 and the composite light-diffusing sheet 100 further improve the brightness uniformity.

[0081] In the backlight unit 40 of this embodiment, the composite light diffusion sheet 100 includes multiple light diffusion layers 43, and the light reflecting layer 101 may be disposed closer to the brightness enhancing sheet 47 than the light diffusion layer 43 that is closest to the compact light source 42 among the multiple light diffusion layers 43. In this manner, the brightness uniformity improving effect of the light reflecting layer 101 can be sufficiently obtained. In this case, if three or more light diffusion layers 43 are provided and the light reflecting layer 101 is disposed closer to the brightness enhancing sheet 47 than the light diffusion layer 43 that is second closest to the compact light source 42 among the multiple light diffusion layers 43, the brightness uniformity improving effect of the light reflecting layer 101 can be further enhanced. In particular, if the light reflecting layer 101 is disposed closer to the brightness enhancing sheet 47 than the light diffusion layer 43 that is farthest from the compact light source 42 among the multiple light diffusion layers 43, the brightness uniformity improving effect of the light reflecting layer 101 can be further enhanced.

[0082] In the backlight unit 40 of this embodiment, the composite light-diffusing sheet 100 includes a plurality of light-diffusing layers 43, and the light-reflecting layer 101 may be provided on the light-receiving surface of the light-diffusing layer 43 that is farthest from the compact light source 42 among the plurality of light-diffusing layers 43. In this way, the effect of the light-reflecting layer 101 in improving brightness uniformity can be more significantly exhibited.

[0083] In the backlight unit 40 of this embodiment, the composite light-diffusing sheet 100 includes a plurality of light-diffusing layers 43 provided on a substrate different from that of the light-reflecting layer 101, and the light-reflecting layer 101 may be disposed between the light-diffusing layer 43 farthest from the compact light source 42 among the plurality of light-diffusing layers 43 and the light-diffusing layer 43 second farthest from the compact light source 42 among the plurality of light-diffusing layers 43. In this way, the effect of improving brightness uniformity by the light-reflecting layer 101 can be more significantly exhibited.

[0084] The liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and a liquid crystal display panel 5.

[0085] The liquid crystal display device 50 of this embodiment and an information device equipped with the liquid crystal display device 50 have improved luminance uniformity because they are equipped with the backlight unit 40 of this embodiment.

[0086] (Example) Examples and Reference Examples will be explained below in comparison with Comparative Examples.

[0087] <Measurement of average light reflectance> As the optical properties of the light diffusing layer 43 and the light reflecting layer 101 in each of the examples, reference examples, and comparative examples described below, the average light reflectance in the visible light region, specifically in the wavelength range of 400 nm to 700 nm, was measured as follows.

[0088] Test pieces measuring approximately 50 mm × 50 mm were prepared for measurement. As described below, a light diffusion layer 43 on which a light reflection layer 101 was printed, a light diffusion layer 43 without printing, and a light reflection sheet 103 in which the light reflection layer 101 was printed on a biaxially stretched polyethylene terephthalate film (PET film) serving as a base layer 102 were prepared.

[0089] A V-670 manufactured by JASCO Corporation was used as a measuring device to measure the light reflectance at each wavelength in 2 nm increments in the wavelength range of 400 nm to 700 nm, and the average of these measurements was used as the average light reflectance of the test piece (sample). For the light diffusion layer 43 on which the light reflecting layer 101 was printed, the average light reflectance of light incident from the printed surface (second surface 43 b) was measured, for the light diffusion layer 43 without printing, the average light reflectance of light incident from the second surface 43 b (the surface opposite to the first surface 43 a on which the inverted square pyramidal recesses 22 were formed) was measured, and for the light reflecting sheet 103 on which the light reflecting layer 101 was printed on the base layer 102, the average light reflectance of light incident from the printed surface was measured.

[0090] <Measurement of luminance and luminance uniformity> In each of the examples, reference examples, and comparative examples described below, measurements of luminance and luminance uniformity were carried out using an LED array in which compact light sources 42 were arranged as shown in Fig. 3, with a configuration similar to that of the backlight unit 40 described above (see, for example, Figs. 2, 5 to 9). That is, measurements of luminance and luminance uniformity were carried out by placing a light diffusion sheet 43, a color conversion sheet 44, and a luminance enhancement film 47 on top of the compact light sources (LEDs) 42 arranged in an array.

[0091] Specifically, the bottom (first) light diffusion layer 43 having the recesses 22 in the shape of an inverted square pyramid was placed on an LED array composed of compact light sources 42 so that the first surface 43a on which the recesses 22 were formed was in contact with the top surface of the LED array. The second light diffusion layer 43 was placed on the first light diffusion layer 42 with the first surface 43a on which the recesses 22 were formed facing toward the compact light sources 42. Furthermore, the third light diffusion layer 43 was placed on the second light diffusion layer 42 with the first surface 43a on which the recesses 22 were formed or the second surface 43b facing toward the compact light sources 42. A brightness enhancement sheet 47 (a pair of prism sheets 45 and 46) was placed on the three-layered light diffusion layer 43 with a color conversion sheet 44 interposed between them so that the ridges of the prism sheets 45 and 46 were perpendicular to each other, and the brightness and brightness uniformity were measured. The LED array used was a compact light source 42 made by Cree, and was made up of blue LEDs (product number XPGDRY-L1-0000-00501) arranged at a pitch of 12.5 mm.

[0092] To measure brightness uniformity, we first measured the two-dimensional brightness distribution on the brightness enhancement film surface on the top surface of the backlight unit film configuration described above using an LED array (6 × 6) as shown in Figure 3. We then calculated the average value and standard deviation for the brightness of all 22,500 pixels (pixel pitch 0.25 mm, 150 × 150 pixels) within an area of ​​3 LEDs vertically × 3 horizontally in the LED array.

[0093] Brightness uniformity is Luminance uniformity = (average luminance (cd / m 2 ))÷(Standard deviation of luminance (cd / m 2 )) The higher the luminance uniformity value calculated in this way, the more uniform the luminance is.

[0094] <Examples 1 to 17, Reference Examples 1 and 2, Comparative Examples 1 to 4> The resin sheets used to form the light diffusion layers 43 in Examples 1 to 17, Reference Examples 1 and 2, and Comparative Examples 1 to 4 were manufactured by the following method.

[0095] First, aromatic polycarbonate resin with a melt mass-flow rate of 15 g / 10 min measured in accordance with ISO 1133 is fed into an extruder, melt-kneaded, and then extruded through a T-die. One of the two metal rolls has a surface with the shape shown in Figure 10 (A) and (B) ((B) is a cross-sectional view of (A) along the XY line) (a regular square pyramid shape with a height of 107 μm, a pitch of 180 μm, and an apex angle of 80 degrees), and the other roll has a random matte surface (surface roughness Ra = 2.5 μm). The molten resin extruded from the T-die is sandwiched between the two rolls and cooled while the shape is transferred. As a result, a light diffusion layer 43 (resin sheet) was produced by extrusion molding, which was composed of a single-layer substrate layer 21 with a thickness of 650 μm, having a concave (inverted) pyramid shape with a depth of 87 μm, which depends on the height of the regular square pyramid on the roll, on one surface (first surface 43a), and a matte surface with a surface roughness Ra = 0.5 μm on the remaining surface (second surface 43b).

[0096] Next, in Examples 1 to 7, Reference Examples 1 and 2, and Comparative Examples 1 to 3, UV-curable inks (Raycure 6100 Series SL6107 High Density White and Raycure 6100 Series SL6100 Medium, manufactured by Jujo Chemical Co., Ltd.) were used, and the ratio of each ink was adjusted so that the average light reflectance (%) was the target value. Then, the white ink was solid-printed by screen printing on the entire matte surface (second surface 43b) of the light diffusion layer 43 prepared as described above to form the light-reflecting layer 101. Furthermore, in Examples 8 to 10, thermosetting inks (Teikoku Ink Mfg. Co., Ltd. two-component insert molding inks XIP-HF679 White and XIP-HF001 Victoria) were used, and the ratio of the white ink to the transparent ink was adjusted so that the average light reflectance (%) was the target value. Then, the white ink was solid-printed on the entire matte surface (second surface 43b) of the light diffusion layer 43 prepared as described above to form the light-reflecting layer 101.

[0097] Specifically, in Examples 1 to 3, a light-reflecting layer 101 having an average light reflectance of approximately 68% was printed on the matte surface (second surface 43b) of the light-diffusing layer 43. In Example 1, the light-reflecting layer 101 was printed on the first (lowest) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 2, the light-reflecting layer 101 was printed on the second light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 3, the light-reflecting layer 101 was printed on the third (uppermost) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. The brightness and brightness uniformity were measured as described above in Examples 1 to 3, and the results are shown in Table 1 together with the average light reflectance (the average light reflectance of the light-diffusing layer 43 alone, on which the light-reflecting layer 101 was formed by solid printing with white ink).

[0098] [Table 1]

[0099] In Examples 4 to 6, a light-reflecting layer 101 having an average light reflectance of approximately 74% was printed on the matte surface (second surface 43b) of the light-diffusing layer 43. In Example 4, the light-reflecting layer 101 was printed on the first (lowest) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 5, the light-reflecting layer 101 was printed on the second light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 6, the light-reflecting layer 101 was printed on the third (uppermost) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. The brightness and brightness uniformity were measured as described above in Examples 4 to 6, and the results are shown in Table 1 together with the average light reflectance (the average light reflectance of the light-diffusing layer 43 alone, on which the light-reflecting layer 101 was formed by solid printing with white ink).

[0100] In Reference Examples 1 and 2 and Example 7, a light-reflecting layer 101 having an average light reflectance of about 53% was printed on the matte surface (second surface 43b) of the light-diffusing layer 43. In Reference Example 1, the light-reflecting layer 101 was printed on the first (lowest) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Reference Example 2, the light-reflecting layer 101 was printed on the second light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 7, the light-reflecting layer 101 was printed on the third (uppermost) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. The results of measuring the brightness and brightness uniformity as described above in Reference Examples 1 and 2 are shown in Table 2 together with the average light reflectance (average light reflectance of the light diffusion layer 43 alone in which the light-reflecting layer 101 was formed by solid printing with white ink), and the results of measuring the brightness and brightness uniformity as described above in Example 7 are shown in Table 1 together with the average light reflectance (average light reflectance of the light diffusion layer 43 alone in which the light-reflecting layer 101 was formed by solid printing with white ink).

[0101] [Table 2]

[0102] In Examples 8 to 10, a light-reflecting layer 101 having an average light reflectance of approximately 82% was printed on the matte surface (second surface 43b) of the light-diffusing layer 43. In Example 8, the light-reflecting layer 101 was printed on the first (lowest) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 9, the light-reflecting layer 101 was printed on the second light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. In Example 10, the light-reflecting layer 101 was printed on the third (uppermost) light-diffusing layer 43, and the other light-diffusing layers 43 were left unprinted. The brightness and brightness uniformity were measured as described above in Examples 8 to 10, and the results are shown in Table 1 together with the average light reflectance (the average light reflectance of the light-diffusing layer 43 alone, on which the light-reflecting layer 101 was formed by solid printing with white ink).

[0103] In Comparative Examples 1 to 3, a light-reflecting layer 101 having an average light reflectance of about 40% was printed on the matte surface (second surface 43b) of the light diffusion layer 43. In Comparative Example 1, the light-reflecting layer 101 was printed on the first (lowest) light diffusion layer 43, and the other light diffusion layers 43 were left unprinted. In Comparative Example 2, the light-reflecting layer 101 was printed on the second light diffusion layer 43, and the other light diffusion layers 43 were left unprinted. In Comparative Example 3, the light-reflecting layer 101 was printed on the third (uppermost) light diffusion layer 43, and the other light diffusion layers 43 were left unprinted. The brightness and brightness uniformity were measured as described above for Comparative Examples 1 to 3, and the results are shown in Table 2 together with the average light reflectance (the average light reflectance of the light diffusion layer 43 alone, on which the light-reflecting layer 101 was formed by solid printing with white ink).

[0104] In Comparative Example 4, three unprinted light diffusion layers 43 were laminated, without using a light diffusion layer 43 on which printing was performed to form the light reflection layer 101. The results of measuring the brightness and brightness uniformity in Comparative Example 4 as described above are shown in Table 2, along with the average light reflectance. The average light reflectance in Comparative Example 4 was measured for light incident on one light diffusion layer 43 from the second surface 43b (matte surface), which is the surface opposite to the first surface 43a on which the inverted square pyramidal recesses 22 are formed.

[0105] In Example 11, a 38 μm-thick biaxially oriented polyethylene terephthalate film (product name: Cosmoshine) manufactured by Toyobo Co., Ltd. was used as the base layer 102, which was different from the light diffusion layer 43. One surface of the film was solid-printed with white ink using the same ink as in Examples 1 to 7 so that the average light reflectance was 80%, forming a light-reflecting layer 101, thereby obtaining a light-reflecting sheet 103. Measurements of luminance and luminance uniformity were performed in a state where the light-reflecting sheet 103 was placed between a structure in which three unprinted light-diffusing layers 43 were stacked (the structure used in Comparative Example 4) and a color conversion sheet 44, with its printed surface facing the color conversion sheet 44 (see FIG. 8 ). The results of measuring luminance and luminance uniformity as described above in Example 11 are shown in Table 1, along with the average light reflectance of the light-reflecting sheet 103 alone obtained by solid-printing with white ink.

[0106] In Examples 12 and 13, similarly to Examples 1 to 7, UV-curable inks (Jujo Chemical Co., Ltd.'s Raycure 6100 Series SL6107 High Density White and Raycure 6100 Series SL6100 Medium) were used, and the ratio of each ink was adjusted so that the average light reflectance (%) would be the target value. Then, by screen printing, the white ink was solid printed over the entire matte surface (second surface 43b) of the light diffusion layer 43 prepared as described above to form a light-reflecting layer 101. Specifically, in Example 12, the third (top) light diffusion layer 43 was positioned so that the first surface 43a, on which the recesses 22 were formed, served as the light-emitting surface. A light-reflecting layer 101 having an average light reflectance of approximately 53% was printed on the matte surface (second surface 43b, the light-incident surface) of the third light diffusion layer 43, and the other light diffusion layers 43 were left unprinted. In Example 13, the third (top) light diffusion layer 43 was disposed so that the first surface 43a, on which the recesses 22 were formed, was the light output surface, and a light reflecting layer 101 having an average light reflectance of approximately 74% was printed on the matte surface (the second surface 43b, which was the light input surface) of the third light diffusion layer 43, with no printing being performed on the other light diffusion layers 43. The results of measuring the brightness and brightness uniformity as described above in Examples 12 and 13 are shown in Table 3, along with the average light reflectance (the average light reflectance of the light diffusion layer 43 alone, on which the light reflecting layer 101 was formed by solid printing with white ink).

[0107] [Table 3]

[0108] In Example 14, similarly to Examples 8 to 10, thermosetting inks (Two-component insert molding inks XIP-HF679 White and XIP-HF001 Victoria manufactured by Teikoku Ink Mfg. Co., Ltd.) were used, and the ratio of white ink to transparent ink was adjusted so that the average light reflectance (%) was the target value. Then, the white ink was solid printed on the entire matte surface (second surface 43b) of the light diffusion layer 43 prepared as described above to form a light-reflecting layer 101. Specifically, in Example 14, the third (top) light diffusion layer 43 was arranged so that the first surface 43a provided with the recesses 22 was the light-emitting surface, and a light-reflecting layer 101 with an average light reflectance of approximately 82% was printed on the matte surface (second surface 43b, which is the light-receiving surface) of the third light diffusion layer 43, and the other light diffusion layers 43 were left unprinted. The results of measuring the brightness and brightness uniformity in Example 14 as described above are shown in Table 3, along with the average light reflectance (average light reflectance of the light diffusion layer 43 alone on which the light-reflecting layer 101 was formed by solid printing with white ink).

[0109] In Example 15, as in Example 11, a 38 μm-thick biaxially oriented polyethylene terephthalate film (product name: Cosmoshine) manufactured by Toyobo Co., Ltd. was used as the base layer 102 different from the light diffusion layer 43, and a white ink was solid-printed on the entire surface of one side of the film using the same ink as in Examples 1 to 7 so that the average light reflectance was 80%, thereby forming a light-reflecting layer 101, thereby obtaining a light-reflecting sheet 103. Measurements of luminance and luminance uniformity were performed in a structure in which three unprinted light diffusion layers 43 were stacked (the structure used in Comparative Example 4), with the third (uppermost) light diffusion layer 43 being positioned so that the first surface 43a, on which the recesses 22 were formed, served as the light-emitting surface, and the light-reflecting sheet 103 was positioned between the second and third light diffusion layers 43 so that its printed surface faced the third light diffusion layer 43. The results of measuring the brightness and brightness uniformity as described above in Example 15 are shown in Table 3 together with the average light reflectance of the light reflecting sheet 103 alone obtained by solid printing with white ink.

[0110] In Example 16, a 125 μm-thick biaxially oriented polyethylene terephthalate film (product name: Cosmoshine) manufactured by Toyobo Co., Ltd. was used as the base layer 102, which was different from the light diffusion layer 43. One surface of the film was solid-printed with white ink using the same ink as in Examples 1 to 7 so that the average light reflectance was 80%, forming a light-reflecting layer 101, thereby obtaining a light-reflecting sheet 103. Measurements of luminance and luminance uniformity were performed, as in Example 11, with the light-reflecting sheet 103 positioned between a structure in which three unprinted light-diffusing layers 43 were stacked (the structure used in Comparative Example 4) and a color conversion sheet 44, with the printed surface facing the color conversion sheet 44 (see FIG. 8 ). The results of measuring luminance and luminance uniformity as described above in Example 16 are shown in Table 3, along with the average light reflectance of the light-reflecting sheet 103 alone obtained by solid-printing with white ink.

[0111] In Example 17, as in Example 16, a 125 μm-thick biaxially oriented polyethylene terephthalate film (product name: Cosmoshine) manufactured by Toyobo Co., Ltd. was used as the base layer 102 different from the light diffusion layer 43, and a white ink was solid-printed on the entire surface of one side of the film using the same ink as in Examples 1 to 7 so that the average light reflectance was 80%, thereby forming a light-reflecting layer 101, thereby obtaining a light-reflecting sheet 103. As in Example 15, measurements of luminance and luminance uniformity were performed using a structure (the structure used in Comparative Example 4) in which three unprinted light diffusion layers 43 were stacked, with the third (uppermost) light diffusion layer 43 being positioned so that the first surface 43a, on which the recesses 22 were formed, served as the light-emitting surface, and the light-reflecting sheet 103 being positioned between the second and third light diffusion layers 43 so that its printed surface faced the third light diffusion layer 43. The results of measuring the brightness and brightness uniformity in Example 17 as described above are shown in Table 3 together with the average light reflectance of the light reflecting sheet 103 alone obtained by solid printing with white ink.

[0112] <Evaluation of Examples 1 to 17, Reference Examples 1 and 2, and Comparative Examples 1 to 4> As shown in Tables 1 to 3, in Examples 1 to 17, the luminance uniformity was improved compared to Comparative Example 4, which used only the light diffusion layer 43 without the light reflecting layer 101, and it was found that a composite light diffusion sheet 100 with good luminance uniformity was obtained. Furthermore, even when the average light reflectance of the light reflecting layer 101 exceeded 80%, the decrease in luminance was small compared to Comparative Example 4, which did not use the light reflecting layer 101.

[0113] Furthermore, as shown in Tables 1 and 2, comparisons between Examples 2 and 3 and Example 1, comparisons between Examples 5 and 6 and Example 4, comparisons between Example 7 and Reference Examples 1 and 2, and comparisons between Examples 9 and 10 and Example 8 show that providing a light-reflecting layer 101 on the second or third light-diffusing layer 43 significantly improves brightness uniformity compared to providing a light-reflecting layer 101 on the first light-diffusing layer 43, and it is particularly preferable to provide a light-reflecting layer 101 on the third light-diffusing layer 43.

[0114] Furthermore, as shown in Tables 1 and 3, comparisons between Example 7 and Example 12, between Example 6 and Example 13, and between Example 10 and Example 14 show that by providing a light-reflecting layer 101 on the light-entering surface of the third light-diffusing layer 43, the effect of improving brightness uniformity by the light-reflecting layer 101 can be obtained more significantly.

[0115] Furthermore, as shown in Tables 1 and 3, a comparison between Example 11 and Example 15 and a comparison between Example 16 and Example 17 reveals that the effect of improving brightness uniformity by the light reflecting layer 101 can be more significantly obtained by arranging the third light diffusion layer 43 so that the first surface 43a where the recesses 22 are provided becomes the light output surface, and by arranging the light reflecting sheet 103 provided with the light reflecting layer 101 between the second and third light diffusion layers 43. Furthermore, a comparison between Example 11 and Example 16 and a comparison between Example 15 and Example 17 reveals that, when the base layer 102 of the light reflecting sheet 103 is made thicker, brightness decreases slightly, but brightness uniformity is further improved.

[0116] (Other embodiments) Although the embodiments of the present disclosure (including variations and examples; the same applies hereinafter) have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the disclosure. In other words, the description of the above-described embodiments is essentially merely illustrative and is not intended to limit the present disclosure, its applications, or its uses. For example, it goes without saying that the configuration (layer structure, materials, etc.) of the composite light diffusion sheet is not limited to the configuration of the composite light diffusion sheet 100 in the above-described embodiments. It also goes without saying that the configuration of the backlight unit to which the composite light diffusion sheet is applied and the configuration of the liquid crystal display device equipped with the backlight unit are not limited to the configuration of the backlight unit 40 and the liquid crystal display device 50 in the above-described embodiments. [Explanation of symbols]

[0117] 1 TFT substrate 2 CF board 3 Liquid crystal layer 5 LCD display panel 6 First polarizing plate 7 Second polarizing plate 21 Base material layer 22 recess 23 Ridgeline 40 Backlight unit 41 Reflective sheet 42 Small light source 43 Light diffusion layer 43a 1st page 43b 2nd side 44 Color Conversion Sheet 45 First prism sheet 46 Second prism sheet 47 Brightness enhancement sheet 50 LCD display device 50a display screen 100 Composite light diffusion sheet 101 Light reflective layer 102 Base material layer 103 Light reflective sheet

Claims

1. A composite light-diffusing sheet that is incorporated between a display screen and a plurality of light sources in a direct-type backlight unit in which the plurality of light sources are provided on the rear side of the display screen, a light reflective layer that reflects visible light; a light diffusing layer provided on the same substrate as the light reflecting layer, the average light reflectance of the light-reflecting layer for visible light is 50% or more and 90% or less (excluding the range of 80% or more); the light-reflecting layer is formed from a light-reflecting ink printed on one surface of the base material, the light diffusion layer has a first surface that serves as one of a light exit surface and a light incident surface, and a second surface that is located on the opposite side of the first surface and serves as the other of the light exit surface and the light incident surface, the light incident surface faces the plurality of light sources, the light reflecting layer is formed to be exposed on the second surface, Two or more light diffusion layers are provided, and the two or more light diffusion layers include a light diffusion layer provided on a substrate different from that on which the light reflection layer is provided. Composite light diffusion sheet.

2. the light diffusion layer has a first surface on which a plurality of recesses each having a substantially inverted polygonal pyramid shape or a substantially inverted polygonal truncated pyramid shape is provided, and a second surface which is a flat surface or a matte surface; The light reflecting layer is provided on the second surface. The composite light-diffusing sheet according to claim 1 .

3. A composite light-diffusing sheet that is incorporated between a display screen and a plurality of light sources in a direct-type backlight unit in which the plurality of light sources are provided on the rear side of the display screen, a light reflective layer provided on the first substrate and reflecting visible light; a light diffusing layer provided on a second substrate different from the first substrate of the light reflecting layer, the average light reflectance of the light-reflecting layer for visible light is 50% or more and 90% or less (excluding the range of 80% or more); the light-reflecting layer is made of a light-reflecting ink printed on the entire surface of one surface of the first substrate, the one surface or the opposite surface of the first base material faces the plurality of light sources; the light reflecting layer is formed and exposed on the one surface of the first substrate, Two or more light diffusion layers are provided. Composite light diffusion sheet.

4. The average light reflectance of the light-reflecting layer for visible light is 60% or more and 90% or less (excluding the range of 80% or more). The composite light-diffusing sheet according to any one of claims 1 to 3.

5. Two or more light reflecting layers are provided. The composite light-diffusing sheet according to any one of claims 1 to 3.

6. The thickness of the light diffusion layer is 50 μm or more and 1200 μm or less. The composite light-diffusing sheet according to any one of claims 1 to 3.

7. A direct-type backlight unit that is incorporated into a liquid crystal display device so as to guide light emitted from a plurality of light sources toward a display screen via a brightness enhancement sheet that increases the brightness of the light, The composite light-diffusing sheet according to any one of claims 1 to 3 is provided between the brightness enhancement sheet and the plurality of light sources. Backlight unit.

8. a color conversion sheet that converts the wavelength of light emitted from the plurality of light sources, between the brightness enhancement sheet and the plurality of light sources; The backlight unit according to claim 7 .

9. the plurality of light sources are disposed on a reflecting sheet provided on the opposite side of the display screen from the composite light diffusing sheet; The backlight unit according to claim 7 .

10. the composite light diffusion sheet includes a plurality of the light diffusion layers, The light reflecting layer is provided closer to the brightness enhancing sheet than the light diffusing layer that is closest to the light sources among the plurality of light diffusing layers. The backlight unit according to claim 7 .

11. The light diffusion layer is provided in three or more layers, The light reflecting layer is provided closer to the brightness enhancing sheet than the light diffusing layer that is second closest to the plurality of light sources among the plurality of light diffusing layers. The backlight unit according to claim 10.

12. The light reflecting layer is provided closer to the brightness enhancing sheet than the light diffusing layer farthest from the light sources among the plurality of light diffusing layers. The backlight unit according to claim 10.

13. the composite light diffusion sheet includes a plurality of the light diffusion layers, The light reflecting layer is provided on a light incident surface of the light diffusing layer that is farthest from the light sources among the plurality of light diffusing layers. The backlight unit according to claim 7 .

14. the composite light-diffusing sheet includes a plurality of the light-diffusing layers provided on a substrate different from the light-reflecting layer, The light reflecting layer is disposed between the light diffusing layer farthest from the light sources among the plurality of light diffusing layers and the light diffusing layer second farthest from the light sources among the plurality of light diffusing layers. The backlight unit according to claim 7 .

15. The backlight unit according to claim 7; A liquid crystal display panel. LCD display device.

16. A liquid crystal display device comprising the liquid crystal display device according to claim 15. Information equipment.

Images