Light diffusion sheet, backlight unit, liquid crystal display device, and information device

Abstract

A light diffusion sheet (43) has a first surface (43a) serving as one of a light emission surface and a light incidence surface, and a second surface (43b) serving as the other of the light emission surface and the light incidence surface. A plurality of inverted substantially quadrangular pyramid-shaped recesses 22 are provided in the first surface 43a. The arithmetic average roughness of the second surface 43b is 1.5 [mu] m or less. The transfer rate of the plurality of recesses 22 is 87% or more.

Description

Technical Field

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

[0002] Liquid crystal display devices are widely used as display devices in various information devices including smartphones and tablet terminals. As a backlight device for a liquid crystal display device, a direct - type system in which a light source is arranged on the rear surface of a liquid crystal panel is mainly used.

[0003] When a direct - type backlight device is adopted, a light diffusing sheet is used to erase an image of a light source (such as an LED (light - emitting diode)) and to improve the brightness uniformity on a display screen (see PTL 1).

[0004] In a thin - type display for a laptop computer, a tablet terminal, etc., for example, a sheet formed with concave portions having an inverted pyramid shape is used as the light diffusing sheet.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] PTL 1: Japanese Patent Application Laid - Open No. 2011 - 129277 Summary of the Invention

[0008] Technical Problem

[0009] In a direct - type backlight device, since the light source is arranged directly below the display screen, as the display becomes thinner, both the distance from the light source to the light diffusing sheet and the thickness of the light diffusing sheet decrease, making it difficult to sufficiently diffuse light using the light diffusing sheet. As a result, a problem of deterioration in brightness uniformity in the display screen has occurred.

[0010] An object of the present disclosure is to provide a light diffusing sheet capable of improving brightness uniformity, and a backlight unit, a liquid crystal display device, and an information device using the light diffusing sheet.

[0011] Solution to the Problem

[0012] To achieve the above object, the light diffusing sheet according to the present disclosure has a first surface and a second surface, the first surface serving as one of a light - emitting surface and a light - incident surface, and the second surface serving as the other of the light - emitting surface and the light - incident surface. A plurality of inverted substantially quadrangular - pyramidal concave portions are provided in the first surface. The arithmetic mean roughness of the second surface is 1.5 μm or less. The transfer rate of the plurality of concave portions is 87% or more.

[0013] For the light diffusing sheet according to the present disclosure, a plurality of inverted substantially quadrangular pyramid-shaped recesses are provided on a first surface serving as a light emitting surface or a light incident surface, and the transfer rate of these recesses is 87% or more. Thus, the light emitted or incident can be uniformly diffused by these recesses. Further, by setting the arithmetic mean roughness of the second surface to 1.5 μm or less, it is possible to suppress the impairment of the brightness uniformity effect achieved by the recesses due to light diffusion on the second surface. Therefore, with the light diffusing sheet according to the present disclosure, the brightness uniformity can be improved.

[0014] In the present disclosure, the "transfer rate of the recesses" is a value expressed as a percentage (%) of "(the depth of the actually formed recesses) / (the depth of the recesses when formed as geometrically true inverted quadrangular pyramids)".

[0015] In the light diffusing sheet according to the present disclosure, when the transfer rate is 90% or more, the brightness uniformity effect of the recesses can be further improved.

[0016] In the light diffusing sheet according to the present disclosure, when the arithmetic mean roughness is 1.0 μm or less, it is possible to further suppress the impairment of the brightness uniformity effect of the recesses.

[0017] The backlight unit according to the present disclosure is built into a liquid crystal display device to guide the light emitted from a plurality of light sources to a display screen. The backlight unit includes the above-described light diffusing sheet according to the present disclosure, and the light diffusing sheet is disposed between the display screen and the plurality of light sources.

[0018] Since the backlight unit according to the present disclosure includes the above-described light diffusing sheet according to the present disclosure, the brightness uniformity can be improved even when the thickness of the liquid crystal display device is further reduced.

[0019] In the backlight unit according to the present disclosure, the light diffusing sheets can be stacked in multiple layers and disposed between the display screen and the plurality of light sources. Thus, the multiple layers of the light diffusing sheets can further improve the brightness uniformity. In this case, the plurality of light sources can be white light sources, and the arithmetic mean roughness can be 1.0 μm or less. Alternatively, the plurality of light sources can be blue light sources, a color conversion sheet for converting the wavelength of light can be further provided, and the transfer rate can be 90% or more. The color conversion sheet can be disposed between the display screen and the multiple stacked layers of the light diffusing sheets, and in this case, in the light diffusing sheet having multiple stacked layers, the first surface can be the light incident surface.

[0020] The liquid crystal display device according to the present disclosure includes a liquid crystal display panel and the above-described backlight unit according to the present disclosure.

[0021] Since the liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure as described above, even when the thickness is further reduced, the brightness uniformity can be improved.

[0022] The information device according to the present disclosure includes the liquid crystal display device according to the present disclosure as described above.

[0023] Since the information device according to the present disclosure includes the liquid crystal display device according to the present disclosure as described above, even when the thickness is further reduced, the brightness uniformity can be improved.

[0024] Advantageous Effects of the Present Invention

[0025] According to the present disclosure, it is possible to provide a light diffusion sheet capable of improving brightness uniformity, and a backlight unit, a liquid crystal display device, and an information device using the light diffusion sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a cross-sectional view of a liquid crystal display device according to an embodiment.

[0027] Figure 2 is a view showing a first example of a cross-sectional structure of a backlight unit according to an embodiment.

[0028] Figure 3 is a view showing a second example of a cross-sectional structure of a backlight unit according to an embodiment.

[0029] Figure 4 is a view showing a third example of a cross-sectional structure of a backlight unit according to an embodiment.

[0030] Figure 5 is a perspective view of a light diffusion sheet according to an embodiment.

[0031] Figure 6 is a schematic view showing an example of a cross-sectional structure of a light diffusion sheet according to an embodiment when cut along a plane that passes through the respective centers of adjacent recesses and the midpoint of a ridge line positioned between the recesses and is perpendicular to the sheet surface.

[0032] Figure 7 is a view showing evaluation results regarding brightness and brightness uniformity obtained in a first test (using a configuration in which a color conversion sheet is not provided).

[0033] Figure 8 is a view showing evaluation results regarding brightness and brightness uniformity obtained in a second test (using a configuration in which a color conversion sheet is provided on the upper side of the light diffusion sheet).

[0034] Figure 9This is a view showing the evaluation results regarding brightness and brightness uniformity obtained in the second test (using the configuration in which the color conversion sheet is disposed on the lower side of the light diffusing sheet).

[0035] Figure 10 This is a view showing the evaluation results regarding brightness and brightness uniformity obtained in the third test (using the configuration in which the color conversion sheet is disposed on the upper side of the light diffusing sheet).

[0036] Figure 11 This is a view showing the evaluation results regarding brightness and brightness uniformity obtained in the third test (using the configuration in which the color conversion sheet is disposed on the lower side of the light diffusing sheet). Detailed Description

[0037] (Example)

[0038] Hereinafter, a light diffusing sheet, a backlight unit, a liquid crystal display device, and an information device according to an embodiment will be described with reference to the drawings. It should be noted that the scope of the present disclosure is not limited to the embodiments described below, and any modifications can be made without departing from the scope of the technical idea of the present disclosure.

[0039] <Liquid Crystal Display Device>

[0040] Figure 1 This is an exemplary cross-sectional view of a liquid crystal display device according to an embodiment.

[0041] As Figure 1 shown, the liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizing plate 6 adhered to the bottom surface of the liquid crystal display panel 5, a second polarizing plate 7 adhered to the top surface of the liquid crystal display panel 5, and a backlight unit 40 disposed on the rear surface 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 disposed to face each other, a liquid crystal layer 3 disposed between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) disposed in a frame shape between the TFT substrate 1 and the CF substrate 2 to seal the liquid crystal layer 3.

[0042] Although when viewed from the front ( Figure 1 the upper side in ), the shape of the display screen 50a of the liquid crystal display device 50 is substantially rectangular or square, the shape is not limited thereto, and it can be any shape, such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or the shape of an automotive dashboard.

[0043] In the liquid crystal display device 50, in each sub-pixel corresponding to each pixel electrode, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3. Accordingly, the transmittance of light entering from the backlight unit 40 through the first polarizing plate 6 is adjusted. The light whose transmittance is adjusted is emitted through the second polarizing plate 7, thereby displaying an image.

[0044] The liquid crystal display device 50 of this embodiment is used as a display device built in different information devices (for example, in-vehicle devices for car navigation etc., personal computers, mobile phones, portable information terminals, portable game machines, copying machines, ticket vending machines or automated teller machines).

[0045] For example, the TFT substrate 1 includes: a plurality of TFTs arranged in a matrix pattern on a glass substrate; an interlayer insulating film provided to cover each TFT; a plurality of pixel electrodes arranged in a matrix pattern on the interlayer insulating film and respectively connected to the plurality of TFTs; and an alignment film provided to cover each pixel electrode. For example, the CF substrate 2 includes: a black matrix arranged in a grid pattern on a glass substrate; a color filter including a red layer, a green layer, and a blue layer respectively provided between corresponding grids of the black matrix; a common electrode provided to cover the black matrix and the color filter; and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is composed of a nematic liquid crystal material containing liquid crystal molecules having electro-optical characteristics etc. For example, the first polarizing plate 6 and the second polarizing plate 7 include a polarizer layer with a polarization axis in one direction and a pair of protective layers provided to sandwich the polarizer layer therebetween.

[0046] <Backlight unit>

[0047] Figure 2 A first example of a cross-sectional structure of the backlight unit 40 according to an embodiment is shown.

[0048] As Figure 2 shown, the backlight unit 40 includes a reflection sheet 41, a plurality of light sources 42 arranged in a two-dimensional pattern on the reflection sheet 41, a light diffusion sheet 43 provided on the upper side of the plurality of light sources 42, a color conversion sheet 44 provided on the upper side of the light diffusion sheet 43, a first prism sheet 45 and a second prism sheet 46 provided in sequence on the upper side of the color conversion sheet 44, and an upper light diffusion sheet 47 provided on the upper side of the second prism sheet 46.

[0049] In Figure 2 the example shown, the light diffusion sheet 43 is provided on the backlight unit 40 as a three-layer stack, but the light diffusion sheet 43 can be used as a single layer, or can be used as a stack of two, four or more layers.

[0050] For example, the reflection sheet 41 is composed of a film made of white polyethylene terephthalate resin, a silver-deposited film etc.

[0051] The type of the light source 42 is not particularly limited. For example, the light source 42 can be an LED element, a laser element, etc. From the perspectives of cost, productivity, etc., an LED element can be used. In Figure 2 the example shown, a blue LED element is used as the light source 42. For example, the blue LED element emits light with CIE 1931 chromaticity coordinates of x < 0.24 and y < 0.18. The light source 42 can have a rectangular shape in a plan view, and in this case, the length of one side can be greater than or equal to 10 μm (preferably, greater than or equal to 50 μm) and less than or equal to 10 mm (preferably, less than or equal to 5 mm). When an LED element is used as the light source 42, a plurality of LED elements can be arranged on the reflection sheet 41 at fixed intervals. In order to adjust the output angle characteristics of the LED element used as the light source 42, a lens can be mounted on the LED element. Although the number of the arranged light sources 42 is also not particularly limited, in the case where a plurality of light sources 42 are arranged in a distributed manner, the light sources 42 are preferably arranged regularly on the reflection sheet 41. Regular arrangement means arranging in a fixed rule. For example, arranging the light sources 42 at equal intervals constitutes a regular arrangement. When the light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent light sources 42 can be greater than or equal to 0.5 mm (preferably, greater than or equal to 2 mm) and less than or equal to 20 mm.

[0052] The light diffusion sheet 43 diffuses and emits the light entering from the light source 42. As long as the matrix resin constituting the light diffusion sheet 43 is formed of a material that transmits light, there is no particular limitation thereto, and for example, the matrix resin can be polycarbonate, acrylic, polystyrene, MS (methyl methacrylate-styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. The thickness of the light diffusion sheet 43 is also not particularly limited, but for example, it can be greater than or equal to 50 μm and less than or equal to 3 mm. When the thickness of the light diffusion sheet 43 exceeds 3 mm, it becomes more difficult to achieve a reduction in the thickness of the liquid crystal display, while when the thickness of the light diffusion sheet 43 drops below 50 μm, it becomes difficult to obtain a sufficient light diffusion effect. When the light diffusion sheets 43 are stacked in multiple layers, as Figure 2 shown, the total thickness of the stacked sheets can be approximately several hundred μm to several mm. The light diffusion sheet 43 can be in the form of a film or a plate. The configuration and manufacturing method of the light diffusion sheet 43 will be described in detail later.

[0053] The color conversion sheet 44 is a wavelength conversion sheet for converting the light from the light source 42 (in Figure 2In the illustrated example, blue light is converted into light having a desired color (e.g., green or red) as a peak wavelength. For example, the color conversion sheet 44 converts blue light having a wavelength of 450 nm into green light having a wavelength of 540 nm and red light having a wavelength of 650 nm. In this case, when using a light source 42 that emits blue light with a wavelength of 450 nm, the blue light is partially converted into green light and red light by the color conversion sheet 44, and thus the light passing through the color conversion sheet 44 becomes white light. For example, a QD (quantum dot) sheet, a fluorescent sheet, etc. can be used as the color conversion sheet 44.

[0054] The first prism sheet 45 and the second prism sheet 46 are brightness enhancement sheets that refract the light entering from the color conversion sheet 44 toward the normal direction side. For example, a plurality of grooves having an isosceles triangle cross-section are disposed adjacent to each other on the light emitting surface side of each of the prism sheets 45 and 46, and the prism is formed by a triangular prism portion sandwiched between adjacent groove pairs. For example, the apex angle of the prism is about 90 degrees. The grooves formed in the first prism sheet 45 and the grooves formed in the second prism sheet 46 may be alternately arranged. Thus, the light entering from the color conversion sheet 44 can be refracted by the first prism sheet 45 toward the normal direction side, and the light emitted from the first prism sheet 45 can be further refracted by the second prism sheet 45 so as to advance substantially perpendicular to the light incident surface of the upper light diffusion sheet 47. The prism sheets 45 and 46 may be stacked as separate bodies or integrally formed. For example, the total thickness of the prism sheets 45 and 46 may be about 100 μm to 400 μm. For example, a PET (polyethylene terephthalate) film having a prism shape presented by a UV curable acrylic resin can be used as the prism sheets 45 and 46.

[0055] It should be noted that a single-layer prism sheet can be used as the brightness enhancement sheet instead of using the prism sheets 45 and 46. Alternatively, another type of optical sheet that can increase the brightness of the light emitted from the light source 42 can be used.

[0056] The overcoat diffusion sheet 47 suppresses the brightness non-uniformity caused by the shape of the prism portions of the prism sheets 45, 46, etc. by slightly diffusing the light entering from the side of the second prism sheet 46. The overcoat diffusion sheet 47 can be directly stacked on the front surface of the second prism sheet 46. The thickness of the light diffusion sheet 47 is not particularly limited, and can be, for example, greater than or equal to 50 μm and less than or equal to 3 mm. When the thickness of the overcoat diffusion sheet 47 exceeds 3 mm, it becomes more difficult to reduce the thickness of the liquid crystal display, and when the thickness of the overcoat diffusion sheet 47 drops below 50 μm, it becomes difficult to obtain a sufficient light diffusion effect. The overcoat diffusion sheet 47 can be in the form of a film or a plate. The overcoat diffusion sheet 47 can be configured to include a substrate layer and a light diffusion layer, the light diffusion layer being stacked on the light-emitting surface of the substrate layer and containing a resin matrix and resin beads. Alternatively, for example, a PET film having at least one surface with an uneven shape using a UV-curable acrylic resin can be used as the overcoat diffusion prism sheet 47.

[0057] <Modification of the backlight unit>

[0058] In Figure 2 the example configuration of the backlight unit 40 shown, the color conversion sheet 44 is provided on the upper side of the light diffusion sheet 43, or more specifically, between the uppermost layer of the light diffusion sheet 43 and the first prism sheet 45. Alternatively, as Figure 3 shown, the color conversion sheet 44 can be provided on the lower side of the light diffusion sheet 43, or more specifically, between the lowermost layer of the light diffusion sheet 43 and the plurality of light sources 42.

[0059] Furthermore, in Figure 2 or Figure 3 the example configuration of the backlight unit 40 shown, a blue light source is used as the light source 42, and the color conversion sheet 44 is used. Alternatively, as Figure 4 shown, a configuration using a white light source as the light source 42 and not providing the color conversion sheet can be adopted. In this case, as in the example shown in Figure 4 the overcoat diffusion sheet 47 can also be omitted. The white light source can be 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 can emit light having CIE 1931 chromaticity coordinates of 0.24 < x < 0.42, 0.18 < y < 0.48, for example.

[0060] <Light diffusion sheet>

[0061] Figure 5 is an example perspective view of the light diffusion sheet 43 according to an embodiment.

[0062] As Figure 5As shown, the light diffusing sheet 43 includes a first surface 43a and a second surface 43b. The first surface serves as one of a light emitting surface and a light incident surface, and the second surface serves as the other of the light emitting surface and the light incident surface. A plurality of inverted substantially quadrangular pyramid-shaped (inverted pyramid-shaped) recesses 22 are provided in the first surface 43a. The second surface 43b is a flat surface or a matte surface. When using a plurality of sheets as the light diffusing sheet 43, sheets with the first surface 43a serving as the light emitting surface and sheets with the first surface 43a serving as the light incident surface can coexist, and various types of sheets with different sizes, shapes, and arrangement pitches of the recesses 22 and different surface shapes of the second surface 43b can be used.

[0063] The plurality of recesses 22 can be arranged on the first surface 43a in a two-dimensional matrix pattern. In other words, the plurality of recesses 22 can be arranged along two mutually orthogonal directions. Adjacent recesses 22 are separated by ridge lines 23. The ridge lines 23 extend along the two directions in which the recesses 22 are arranged. The arrangement pitch of the recesses 22 can be, for example, greater than or equal to about 50 μm and less than or equal to about 500 μm. The deepest part of the recess 22 is located at the center of the recess 22 (the apex of the inverted pyramid). The angle formed by the wall surface of the recess 22 (the inclined surface of the inverted substantially quadrangular pyramid) and the sheet surface of the light diffusing sheet 43 (the imaginary specular surface when the recess 22 is absent) can be, for example, greater than or equal to 40 degrees and less than or equal to 65 degrees, preferably greater than or equal to 45 degrees and less than or equal to 60 degrees. In other words, the apex angle of the recess 22 can be, for example, greater than or equal to 50 degrees and less than or equal to 100 degrees, preferably greater than or equal to 60 degrees and less than or equal to 90 degrees.

[0064] In Figure 5 In the example shown, for simplicity, the recesses 22 are shown arranged in a 5 by 5 matrix pattern, but the actual number of the arranged recesses 22 is much larger. In the two-dimensional arrangement of the plurality of recesses 22, the recesses 22 can be provided in the first surface 21a without gaps, or can be provided at a predetermined interval. In addition, a part of the recesses 22 can be randomly arranged to such an extent that the light diffusion effect is not affected.

[0065] Although the expression "inverted substantially quadrangular pyramid" is used in consideration of the fact that it is difficult to form recesses in a geometrically strict inverted quadrangular pyramid shape using ordinary shape transfer techniques, this expression of course includes shapes that can be regarded as true or substantially inverted quadrangular pyramids. In other words, "substantially" means "can be approximated". For example, "substantially quadrangular pyramid" means a shape that can be approximated as a quadrangular pyramid. In addition, within the inevitable shape variability range caused by machining accuracy during industrial production, shapes deformed from the "inverted quadrangular pyramid" are also included in the "substantially inverted quadrangular pyramid".

[0066] The light diffusing sheet 43 is formed by machining the base material layer 21. The base material layer 21 must transmit light, and thus is formed using a transparent (e.g., colorless and transparent) synthetic resin as the main component. The main component of the base material layer 21 is not particularly limited, and for example, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polystyrene, polyolefin, cellulose acetate, weather-resistant polyvinyl chloride, etc. may be used. It should be noted that the term "main component" refers to the component having the largest content, for example, the component having a content of 50 mass% or more. The base material layer 21 may contain a diffusing agent and other additives, or may be substantially free of additives. The additives that may be included are not particularly limited, but may be, for example, inorganic particles such as silica, titanium oxide, aluminum hydroxide, barium sulfate, or organic particles such as acrylic, acrylonitrile, silicone, polystyrene, polyamide, etc. The light diffusing sheet 43 may have a single-layer structure composed of the base material layer 21, or may have a structure of two or more layers including a layer formed with the recess 22.

[0067] The method for manufacturing the light diffusing sheet 43 is not particularly limited, and for example, an extrusion molding method, an injection molding method, etc. may be used.

[0068] The procedure for manufacturing a single-layer light diffusing sheet having an uneven shape on its surface using the extrusion molding method is as follows. First, plastic pellets in a pellet shape (to which a diffusing agent may be added) are fed into a single-screw extruder and melted and kneaded while applying heat. Subsequently, after sandwiching the melted resin extruded from a T-die between two metal rolls and cooling the melted resin, the light diffusing sheet is manufactured by conveying the resin using guide rolls and cutting the resin into a flat sheet with a slicer. In this case, since the melted resin is sandwiched by an inverted-shaped metal roll having a desired uneven shape on its surface and the inverted shape on the roll surface is transferred to the resin, a desired uneven shape can be formed on the surface of the light diffusing sheet. In addition, since the shape transferred to the resin does not necessarily represent 100% transfer of the roll surface shape, the shape of the roll surface can be reverse-designed according to the transfer degree.

[0069] When manufacturing a light diffusing sheet having a two-layer structure with an uneven shape on its surface using an extrusion molding method, for example, after feeding plastic particles in pellet form required for forming each layer into each of two single-screw extruders, similar procedures to those for the single-layer light diffusing sheet described above can be performed on each layer, and then the correspondingly formed sheets can be stacked. Alternatively, a light diffusing sheet having a two-layer structure with an uneven shape on its surface can be manufactured as follows. First, plastic particles in pellet form required for forming each layer are fed into each of two single-screw extruders, and while applying heat, they are melted and kneaded. Next, the melted resin for forming each layer is fed into a T-die, and the stacked melted resin that has been stacked in the T-die and extruded from the T-die is sandwiched between two metal rollers and cooled. Subsequently, a diffusing sheet having a two-layer structure with an uneven shape on its surface can be manufactured by conveying the stacked melted resin using guide rollers and cutting the resin into flat sheets with a slicing machine.

[0070] In addition, a light diffusing sheet 43 can be manufactured by shape transfer using UV (ultraviolet light) as follows. First, an inverted-shaped roller having an uneven shape to be transferred is filled with uncured ultraviolet-curable resin, and then a substrate is pressed onto the resin. Next, ultraviolet light is emitted so that the ultraviolet-curable resin cures to a state where the roller filled with resin and the substrate are integrated. Next, the sheet on which the uneven shape has been shape-transferred by the resin is separated from the roller. Finally, the sheet is irradiated again with ultraviolet light to completely cure the resin, thereby manufacturing a light diffusing sheet having an uneven shape on its surface.

[0071] <Transfer rate of recesses in the light diffusing sheet and arithmetic mean roughness of the second surface>

[0072] In the light diffusing sheet 43 according to the embodiment, the transfer rate of a plurality of inverted substantially quadrangular pyramid-shaped (inverted pyramid-shaped) recesses 22 provided in a first surface 43a serving as one of a light emitting surface and a light incident surface is set to 87% or more, and the arithmetic mean roughness of a second surface 43b serving as the other of the light emitting surface and the light incident surface is set to 1.5 μm or less.

[0073] Figure 6 An example of a cross-sectional structure of the light diffusing sheet 43 according to the embodiment is shown in the case of being cut along a plane that passes through corresponding centers (vertices) 22a of recesses 22 adjacent to each other in the arrangement direction (A - B line) of the recesses 22 and the midpoint of a ridge line 23 positioned between the recesses 22 and is perpendicular to the sheet surface.

[0074] In this disclosure, the "transfer rate of the recess 22" is expressed as a percentage (%) of the value "(depth H of the actually formed recess 22) / (depth (target depth) H of the recess 22 when geometrically formed as a true inverted quadrangular pyramid)". For example, the average value of the transfer rates of a predetermined number of recesses determined statistically can be used as the "transfer rate of the recess 22". 0 )". For example, the average value of the transfer rates of a predetermined number of recesses determined statistically can be used as the "transfer rate of the recess 22".

[0075] The depth H of the recess 22 is measured by a laser microscope or the like. The dimensions of the mold used to manufacture the recess 22 can be used as the target depth H of the recess 22 0 . When the recess 22 is formed by extrusion molding, for example, the height of the pyramid shape (inverted shape of the recess 22) formed in the extrusion roll used for molding can be used. When the dimensions of the mold used to manufacture the recess 22 are unknown, the target depth H can be obtained by the following method 0 : Using the actual measurement data obtained by a laser microscope or the like to identify the position of the intersection point R between the virtual lines L, which are obtained by extending the straight line portions of the wall surfaces (inclined surfaces) 22b of the adjacent recesses 22 on both sides of the ridge line 23; calculating the height difference between the intersection point R and the ridge line 23; and adding the depth H of the recess 22 to this difference. Alternatively, a laser microscope or the like can be used to measure the angle θ formed by the straight line portions of the respective inclined surfaces 22b of the adjacent recesses 22 on both sides of the ridge line 23 and the arrangement pitch P of the recesses 22, and the target depth H of the recess 22 0 can be determined based on the calculation formula H 0 =(P / 2) / tan(θ / 2).

[0076] It should be noted that when the apex angles of the recesses 22 are the same, as the arrangement pitch of the recesses 22 increases, the filling rate of the resin in the mold increases, making it easier for the transfer rate of the recess 22 to increase. In addition, when the height of the pyramid shape (inverted shape of the recess 22) formed in the mold is the same, as the apex angle of the recess 22 increases, the filling rate of the resin in the mold increases, making it easier for the transfer rate of the recess 22 to increase.

[0077] From the perspective of the mechanical strength of the light diffusing sheet 43 (damage resistance of the recess formation surface), the transfer rate of the recess 22 can be set to 99% or less, or more preferably 98% or less. In addition, as the transfer rate of the recess 22 increases, or in other words, as the filling rate of the resin in the mold increases, mass production of the light diffusing sheet 43 becomes more difficult. Therefore, conventionally, a light diffusing sheet with a transfer rate of the recesses of about 80% or less is used.

[0078] The inventors of the present application found that as the transfer rate of the concave portion 22 increases, the brightness uniformity effect achieved by the light diffusion sheet 43 is significantly improved. The inventors of the present application also found that in order to prevent the brightness uniformity effect of the concave portion 22 from being impaired due to light diffusion on the second surface 43b, the arithmetic mean roughness Ra of the second surface 43b is preferably set to 1.5 μm or less. However, it should be noted that when the arithmetic mean roughness Ra of the second surface 43b is set to 0, or in other words, when the second surface 43b is a mirror surface, defects tend to occur on the mirror surface, resulting in a decrease in both the manufacturing yield and the brightness of the light diffusion sheet 43. In addition, when stacking various optical sheets during the manufacture of the backlight unit, the mirror surface sheet is more likely to adhere to another optical sheet, which can easily cause a decrease in manufacturing efficiency. Accordingly, the arithmetic mean roughness Ra of the second surface 43b can be set to 0.01 μm or more.

[0079] <Characteristics of the embodiment>

[0080] For the light diffusion sheet 43 of the above embodiment, a plurality of inverted substantially quadrangular pyramid-shaped concave portions 22 are provided on the first surface 43a serving as a light emitting surface or a light incident surface, and the transfer rate of these concave portions is 87% or more, so that the emitted or incident light can be uniformly diffused by the concave portions 22. In addition, the arithmetic mean roughness of the second surface 43b is 1.5 μm or less, so that the brightness uniformity effect of the concave portion 22 can be prevented from being impaired due to light diffusion on the second surface 43b. Therefore, even when the display is made thinner, an improvement in brightness uniformity can be achieved by using the light diffusion sheet 43 of the present embodiment.

[0081] More specifically, for the configuration of the example to be described below, in which the light diffusion sheet is composed of three stacked sheets, the transfer rate of the concave portion is set to 95%, and the arithmetic mean roughness Ra of the second surface is set to 0.3 μm, an 8% to 61% improvement in brightness uniformity is obtained compared to the configuration of the comparative example to be described below, in which the light diffusion sheet is composed of three stacked sheets, the transfer rate of the concave portion is set to 87%, and the arithmetic mean roughness Ra of the second surface is set to 1.8 μm.

[0082] In the light diffusion sheet 43 of the embodiment, when the transfer rate of the concave portion 22 is 90% or more, preferably 92% or more, and more preferably 94% or more, the brightness uniformity effect of the concave portion 22 can be further improved.

[0083] In the light diffusion sheet 43 of the embodiment, when the arithmetic mean roughness Ra of the second surface 43b is 1.0 μm or less, preferably 0.5 μm or less, and more preferably 0.3 μm or less, the impairment of the brightness uniformity effect of the concave portion 22 can be further suppressed.

[0084] The backlight unit 40 of the embodiment is built in the liquid crystal display device 50 to guide the light emitted from the plurality of light sources 42 to the display screen 50a. In the backlight unit 40, the light diffusion sheet 43 of the embodiment is disposed between the display screen 50a and the light source 42. Therefore, even when the thickness of the liquid crystal display device 50 is further reduced, the brightness uniformity can be improved.

[0085] In the backlight unit 40 of the embodiment, the plurality of light sources 42 may be arranged on the reflective sheet 41, which is disposed on the side opposite to the display screen 50a when viewed from the light diffusion sheet 43. Therefore, the light is further diffused by multiple reflections between the light diffusion sheet 43 and the reflective sheet 41, thereby further improving the brightness uniformity.

[0086] In the backlight unit 40 of the embodiment, the light diffusion sheets 43 may be stacked in multiple layers and disposed between the display screen 50a and the light source 42. Therefore, the multiple layers of the light diffusion sheets 43 can further improve the brightness uniformity. In this case, the plurality of light sources 42 may be white light sources, and the arithmetic mean roughness Ra of the second surface 43b may be 1.0 μm or less. Alternatively, the plurality of light sources 42 may be blue light sources, and the transfer rate of the concave portions 22 may be 90% or more. When the plurality of light sources 42 are blue light sources, the color conversion sheet 43 may be disposed between the display screen 50a and the multiple stacked layers of the light diffusion sheets 43, and in this case, the first surface 43a of the multiple stacked layers of the light diffusion sheets 43 may be the light incident surface.

[0087] In the backlight unit 40 of the embodiment, the distance between the plurality of light sources 42 and the light diffusion sheet 43 may be greater than or equal to 0 mm and less than or equal to 1 mm. Therefore, even when it is impossible to ensure a sufficient distance between the light source and the sheet due to the thickness reduction, the deterioration of the brightness uniformity can be suppressed by the diffusion performance of the light diffusion sheet 43.

[0088] The liquid crystal display device 50 of the embodiment includes the liquid crystal display panel 5 and the backlight unit 40 of the embodiment. Therefore, even when the thickness or the number of the stacked layers of the light diffusion sheet 43 is reduced in response to the thickness reduction or in a similar situation, the brightness uniformity can be improved. Similar effects can be obtained in the information devices (personal computers, mobile phones, etc.) in which the liquid crystal display device 50 of the embodiment is built.

[0089] It should be noted that in this embodiment, a direct - type backlight unit in which a plurality of light sources 42 are arranged in a distributed manner on the rear - surface side of the display screen 50a of the liquid - crystal display device 50 is used as the backlight unit 40. Therefore, in order to reduce the size of the liquid - crystal display device 50, it is necessary to reduce the distance between the light source 42 and the light - diffusing sheet 43. However, when this distance is reduced, a phenomenon (brightness non - uniformity) is more likely to occur, that is, the brightness of the portion of the display screen 50a in the area between the distributed light sources 42 is reduced to be lower than that of other portions.

[0090] However, the light - diffusing sheet 43 of this embodiment effectively suppresses brightness non - uniformity. More specifically, in view of the future reduction in the thickness of small and medium - sized liquid - crystal displays, it is considered that by setting the distance between the light source 42 and the light - diffusing sheet 43 to 15 mm or less, preferably 10 mm or less, more preferably 5 mm or less, even more preferably 2 mm or less, and finally 0 mm, the effectiveness of the light - diffusing sheet 43 of this embodiment will become even more obvious.

[0091] (Examples and Comparative Examples)

[0092] Examples and comparative examples will be described below.

[0093] In the examples and comparative examples, a light - diffusing sheet 43 is used, which has a substrate layer 21 formed using transparent polycarbonate as the substrate, and the thickness of the substrate layer is 110 μm. In both the examples and comparative examples, no diffusing agent is added to the substrate layer 21, and a plurality of inverted substantially quadrangular - pyramidal (inverted - pyramid - shaped) recesses 22 having a target depth of 50 μm and an apex angle of 90° are two - dimensionally arranged on the first surface 43a at an arrangement pitch of 100 μm.

[0094] The method for manufacturing the light - diffusing sheets 43 of the examples and comparative examples is as follows. First, pellet - shaped substrate resin (plastic resin) is formed into a resin film using an extruder. Next, a roll having a convex pyramid shape on its surface is used as one of the two metal rolls, and an embossing roll or a mirror roll having a random matte shape is used as the other roll, and these two rolls are pressed (thermally pressed) on the resin film to produce a single - layer light - diffusing sheet 43 having inverted - pyramid - shaped recesses 22 on the first surface 43a and a matte surface or a mirror surface on the second surface 43b. The transfer rate of the recesses 22 is controlled by the pressing conditions of the rolls, etc., and the arithmetic mean roughness Ra of the second surface 43b (in the case of a matte surface) is controlled by the roughness of the embossing - roll surface.

[0095] More specifically, as an example of the light diffusing sheet 43, samples are prepared in which the transfer rate of the concave portions 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 0 μm, 0.3 μm, and 1.3 μm, respectively, samples in which the transfer rate of the concave portions 22 is 94% and the arithmetic mean roughness Ra of the second surface 43b is 0 μm, 0.3 μm, and 1.3 μm, respectively, and samples in which the transfer rate of the concave portions 22 is 100% and the arithmetic mean roughness Ra of the second surface 43b is 0 μm, 0.3 μm, and 1.3 μm, respectively.

[0096] Furthermore, as a comparative example of the light diffusing sheet 43, samples are prepared in which the transfer rate of the concave portions 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and 4.2 μm, respectively, samples in which the transfer rate of the concave portions 22 is 77% and the arithmetic mean roughness Ra of the second surface 43b is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm, respectively, samples in which the transfer rate of the concave portions 22 is 94% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and 4.2 μm, respectively, and samples in which the transfer rate of the concave portions 22 is 100% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and 4.2 μm, respectively.

[0097] The arithmetic mean roughness Ra of the second surface 43b of the light diffusing sheet 43 of the example and the comparative example is measured according to JIS B 0601 - 1994 using an SJ - 210 manufactured by Mitutoyo Corp. The measurement speed is set to 0.5 mm / s, the measurement distance is set to 4 mm, and the cut - off value λc is set to 0.8 mm.

[0098] In the first to fourth tests described below, the brightness and brightness uniformity of the light diffusing sheet 43 of the example and the comparative example are evaluated as follows. First, light diffusing sheets 43 having the same structure are stacked in three layers in the same orientation and arranged on the upper side of a plurality of two - dimensionally arranged light sources 42. Prismatic sheets 45, 46 are arranged on the upper side of the light diffusing sheet, and a transparent glass plate is placed on the upper side of the prismatic sheets to prevent these sheets from lifting. Then, using a 2D spectro - radiometer SR - 5000HS manufactured by Topcon Technohouse Corp., the brightness in the vertically upward direction (from the light source 42 toward the glass plate) is measured. Next, a two - dimensional brightness distribution within a range of 40 square millimeters is obtained using a brightness non - uniformity measuring device, and after correcting the total brightness balance, the average value and standard deviation of the brightness are calculated. The calculated average brightness value is set as the brightness of the light diffusing sheet 43, and “(average brightness value) / (standard deviation of brightness)” is defined as the brightness uniformity of the light diffusing sheet 43, thereby evaluating these performances.

[0099] <First Test>

[0100] In the first test, the Figure 4 configuration of the backlight unit 40 shown was used to evaluate the brightness and brightness uniformity of the light diffusion sheet 43, where a white light source was used as the light source 42, and the color conversion sheet 44 and the upper light diffusion sheet 47 were not provided.

[0101] Therefore, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 87%, when the brightness of the sample in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightnesses of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 98%, 96%, 99%, and 99% respectively, and when the first surface 43a is set as the light emitting surface, the brightnesses of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 83%, 91%, 91%, and 99% respectively.

[0102] Furthermore, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 87%, when the brightness uniformity of the sample in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 85%, 92%, 98%, and 82% respectively, and when the first surface 43a is set as the light emitting surface, the brightness uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 122%, 101%, 99%, and 76% respectively.

[0103] In other words, in the example in which the transfer rate of the concave portion 22 is 87%, when the first surface 43a is set as the light emitting surface and the arithmetic mean roughness Ra of the second surface 43b is set to 0 μm, the brightness uniformity is greatly improved.

[0104] Further, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, when the brightness of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 101%, 101%, 100%, 101%, and 101% respectively, and when the first surface 43a is set as the light emission surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 91%, 97%, 96%, 102%, and 102% respectively.

[0105] In addition, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, when the brightness uniformity of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 89%, 95%, 92%, 98%, and 98% respectively, and when the first surface 43a is set as the light emission surface, the brightness uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 101%, 99%, 84%, 95%, and 92% respectively.

[0106] In other words, in the comparative example where the transfer rate of the concave portion 22 is 77%, even when the arithmetic mean roughness Ra of the second surface 43b is decreased, the brightness uniformity is not improved.

[0107] In addition, regarding the examples and comparative examples where the transfer rate of the concave portion 22 is 94%, when the brightness of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 99%, 99%, 99%, 100%, and 100% respectively, and when the first surface 43a is set as the light emission surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 74%, 88%, 87%, 98%, and 98% respectively.

[0108] Furthermore, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 94%, when the luminance uniformity of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 85%, 94%, 103%, 99%, and 89% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 117%, 103%, 93%, 102%, and 80% respectively.

[0109] In other words, in the example in which the transfer rate of the concave portion 22 is 94%, when the first surface 43a is set as the light emitting surface and the arithmetic mean roughness Ra of the second surface 43b is set to 0 μm, the luminance uniformity is greatly improved.

[0110] In addition, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 100%, when the luminance of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 91%, 96%, 97%, 99%, and 99% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 61%, 81%, 85%, 96%, and 97% respectively.

[0111] Furthermore, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 100%, when the luminance uniformity of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 78%, 108%, 97%, 102%, and 99% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 107%, 117%, 88%, 102%, and 79% respectively.

[0112] In other words, in an example where the transfer rate of the concave portion 22 is 100%, when the first surface 43a is set as the light-emitting surface and the arithmetic mean roughness Ra of the second surface 43b is set to 0.3 μm, the brightness uniformity is greatly improved.

[0113] The Figure 7 summarizes the evaluation results regarding brightness and brightness uniformity obtained in the above first test. In the Figure 7 , the white circles, white triangles, white inverted triangles, and white squares represent the results obtained when the first surface 43a is set as the light-incident surface (lower pyramid), while the black circles, black triangles, black inverted triangles, and black squares represent the results obtained when the first surface 43a is set as the light-emitting surface (upper pyramid). Further, the numerical values on the graph represent the arithmetic mean roughness Ra (μm) of the second surface 43b. In addition, the + symbol represents the evaluation results (both brightness and brightness uniformity are 100%) of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, which is used as an evaluation reference (reference) for the lower pyramid, and the * symbol represents the evaluation results of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, which is used as an evaluation reference (reference) for the upper pyramid. However, the evaluation reference for the upper pyramid is 6.4% lower in brightness and 39% higher in brightness uniformity than that for the lower pyramid, and thus, in the Figure 7 , the evaluation results for the upper pyramid are converted to the values obtained when the evaluation reference for the lower pyramid is set to 100%.

[0114] As Figure 7 shows, it is understood that for the configuration of the backlight unit 40 shown in the Figure 4 , where the white light source is used as the light source 42 and the color conversion sheet 44 and the upper light diffusion sheet 47 are not provided, when the transfer rate of the concave portion 22 of the light diffusion sheet 43 is set to 87% or more and the arithmetic mean roughness Ra of the second surface 43b is set to 1.5 μm or less, preferably 1.0 μm or less, and more preferably close to 0 μm, the brightness uniformity can be improved. It is also understood that the overall brightness uniformity when the first surface 43a is set as the light-emitting surface (upper pyramid) is better than when the first surface 43a is set as the light-incident surface (lower pyramid).

[0115] <Second Test>

[0116] In the second test, use Figure 2 and Figure 3The configuration of the backlight unit 40 shown is used to evaluate the brightness and brightness uniformity of the light diffusing sheet 43, where a blue light source is used as the light source 42, and a color conversion sheet 44 and an upper light diffusing sheet 47 are provided. It should be noted that in the second test, blue LED elements arranged in a square at intervals of 3.5 mm and 4.5 mm are used as the plurality of light sources 42.

[0117] Therefore, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 87%, for Figure 2 the backlight unit configuration shown, when the brightness of a sample in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 90%, 95%, 94%, and 99% respectively, and when the first surface 43a is set as the light emitting surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 94%, 97%, 96%, and 99% respectively.

[0118] Meanwhile, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 87%, for Figure 3 the backlight unit configuration shown, when the brightness of a sample in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and having Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 92%, 93%, 94%, and 99% respectively, and when the first surface 43a is set as the light emitting surface, the brightnesses of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 90%, 93%, 94%, and 99% respectively.

[0119] Furthermore, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 87%, for Figure 2 the backlight unit configuration shown, when the brightness uniformity of a sample in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 110%, 108%, 105%, and 86% respectively, and when the first surface 43a is set as the light emitting surface, the brightness uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 100%, 103%, 99%, and 89% respectively.

[0120] Meanwhile, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 87%, forFigure 3 The backlight unit configuration shown, when the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and has Figure 2 When the luminance uniformity of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 95%, 101%, 98%, and 89% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 116%, 117%, 111%, and 82% respectively.

[0121] In other words, in the example where the transfer rate of the concave portion 22 is 87%, when the arithmetic mean roughness Ra of the second surface 43b approaches 0 μm, the luminance uniformity is improved.

[0122] Furthermore, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 2 The backlight unit configuration shown, when the luminance of the sample with the transfer rate of the concave portion 22 being 87% and the arithmetic mean roughness Ra of the second surface 43b being 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 98%, 101%, 100%, 104%, and 104% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 100%, 101%, 101%, 102%, and 102% respectively.

[0123] Meanwhile, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 3 The backlight unit configuration shown, when the luminance of the sample with the transfer rate of the concave portion 22 being 87% and the arithmetic mean roughness Ra of the second surface 43b being 1.8 μm and having Figure 2 The luminance of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 96%, 98%, 97%, 100%, and 100% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 95%, 98%, 97%, 100%, and 100% respectively.

[0124] Furthermore, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 2 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the luminance uniformity of the sample is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 91%, 92%, 92%, 93%, and 93% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 89%, 89%, 89%, 94%, and 95% respectively.

[0125] Meanwhile, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the luminance uniformity of the sample with Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 86%, 92%, 92%, 102%, and 105% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 106%, 105%, 106%, 103%, and 101% respectively.

[0126] In other words, in the comparative example where the transfer rate of the concave portion 22 is 77%, even when the arithmetic mean roughness Ra of the second surface 43b decreases, the luminance uniformity is not improved.

[0127] In addition, regarding the examples and comparative examples where the transfer rate of the concave portion 22 is 94%, for Figure 2 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the luminance of the sample is set to 100% and the first surface 43a is set as the light incident surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 84%, 91%, 90%, 97%, and 96% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 90%, 94%, 94%, 98%, and 98% respectively.

[0128] Meanwhile, for the example and the comparative example in which the transfer rate of the concave portion 22 is 94%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and having Figure 2 the luminance of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 90%, 94%, 93%, 99%, and 98% respectively, and when the first surface 43a is set as the light emitting surface, the luminance of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 87%, 94%, 94%, 99%, and 99% respectively.

[0129] In addition, for the example and the comparative example in which the transfer rate of the concave portion 22 is 94%, for Figure 2 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, the luminance uniformity of the sample is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 142%, 132%, 135%, 120%, and 103% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 125%, 119%, 121%, 116%, and 101% respectively.

[0130] Meanwhile, for the example and the comparative example in which the transfer rate of the concave portion 22 is 94%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and having Figure 2 the luminance uniformity of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 108%, 112%, 114%, 114%, and 100% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 127%, 126%, 127%, 115%, and 93% respectively.

[0131] In other words, in an example where the transfer rate of the concave portion 22 is 94%, when the arithmetic mean roughness Ra of the second surface 43b approaches 0 μm, the luminance uniformity is greatly improved.

[0132] In addition, regarding the example and the comparative example where the transfer rate of the concave portion 22 is 100%, for Figure 2 the backlight unit configuration shown, when the luminance of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminances of samples where Ra is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 76%, 84%, 86%, 94%, and 93% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of samples where Ra is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 83%, 89%, 92%, 95%, and 96% respectively.

[0133] Meanwhile, regarding the example and the comparative example where the transfer rate of the concave portion 22 is 100%, for Figure 3 the backlight unit configuration shown, when the luminance of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and having Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminances of samples where Ra is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 82%, 89%, 92%, 98%, and 97% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of samples where Ra is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 80%, 90%, 92%, 97%, and 98% respectively.

[0134] In addition, regarding the example and the comparative example where the transfer rate of the concave portion 22 is 100%, for Figure 2 the backlight unit configuration shown, when the luminance uniformity of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of samples where Ra is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 161%, 152%, 150%, 125%, and 110% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of samples where Ra is 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 136%, 134%, 137%, 119%, and 108% respectively.

[0135] Meanwhile, for an example and a comparative example in which the transfer rate of the concave portion 22 is 100%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and having Figure 2 the backlight unit configuration shown, the luminance uniformity of the sample is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 120%, 125%, 126%, 114%, and 103% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 126%, 132%, 129%, 107%, and 92% respectively.

[0136] In other words, in the example where the transfer rate of the concave portion 22 is 100%, when the arithmetic mean roughness Ra of the second surface 43b approaches 0 μm, the luminance uniformity is greatly improved.

[0137] Regarding the evaluation results of luminance and luminance uniformity obtained in the above second test, Figure 8 shows the evaluation results obtained using Figure 2 the backlight unit configuration shown (where the color conversion sheet 44 is disposed on the upper side of the light diffusing sheet 43), Figure 9 shows the evaluation results obtained using Figure 3 the backlight unit configuration shown (where the color conversion sheet 44 is disposed on the lower side of the light diffusing sheet 43). In Figure 8 and Figure 9 , the white circles, white triangles, white inverted triangles, and white squares represent the results obtained when the first surface 43a is set as the light incident surface (lower pyramid), while the black circles, black triangles, black inverted triangles, and black squares represent the results obtained when the first surface 43a is set as the light emitting surface (upper pyramid). Further, the numerical values on the graph represent the arithmetic mean roughness Ra (μm) of the second surface 43b. In addition, Figure 8 the + sign in represents the evaluation results of the sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm (both luminance and luminance uniformity are 100%), which is used as the evaluation reference (reference) for the lower pyramid, while Figure 8The "*" symbol in [reference] indicates the evaluation result of a sample where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, which is used as the evaluation reference for the upper pyramid. However, the evaluation reference for the upper pyramid is approximately 5% higher in brightness and approximately 20% lower in brightness uniformity than that for the lower pyramid. Therefore, in Figure 8 and Figure 9 , the evaluation result of the upper pyramid is converted to the value obtained when the evaluation reference for the lower pyramid is set to 100%.

[0138] As Figure 8 and Figure 9 show, it is understood that for the configuration of the backlight unit 40 shown in Figure 2 and Figure 3 , where a blue light source (blue LED elements arranged in a square at intervals of 3.5 mm and 4.5 mm) is used as the light source 42 and a color conversion sheet 44 and an upper light diffusion sheet 47 are provided, when the transfer rate of the concave portion 22 of the light diffusion sheet 43 is set to 87% or more, preferably 90% or more, and more preferably close to 100% and the arithmetic mean roughness Ra of the second surface 43b is set to 1.5 μm or less, preferably 1.0 μm or less, and more preferably close to 0 μm, the brightness uniformity can be improved. It is also understood that for the total brightness uniformity of the configuration of the backlight unit shown in Figure 2 (where the color conversion sheet 44 is provided on the upper side of the light diffusion sheet 43) is better than that for the configuration of the backlight unit shown in Figure 3 (where the color conversion sheet 44 is provided on the lower side of the light diffusion sheet 43). More specifically, as Figure 8 shows, when the first surface 43a is set as the light incident surface (lower pyramid), for the configuration of the backlight unit shown in Figure 2 (where the color conversion sheet 44 is provided on the upper side of the light diffusion sheet 43), a significant improvement effect in brightness uniformity is obtained.

[0139] <Third Test>

[0140] In the third test, the configurations of the backlight unit 40 shown in Figure 2 and Figure 3 are used to evaluate the brightness and brightness uniformity of the light diffusion sheet 43, where a blue light source is used as the light source 42 and a color conversion sheet 44 and an upper light diffusion sheet 47 are provided. It should be noted that in the third test, blue LED elements arranged in a square at intervals of 2.8 mm and 2.8 mm are used as the plurality of light sources 42.

[0141] Therefore, regarding the example and the comparative example where the transfer rate of the concave portion 22 is 87%, for Figure 2In the backlight unit configuration shown, when the luminance of a sample with an arithmetic mean roughness Ra of 1.8 μm of the second surface 43b is set to 100% and the first surface 43a is set as the light incident surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 91%, 95%, 95%, and 100% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 94%, 97%, 97%, and 99% respectively.

[0142] Meanwhile, regarding an example and a comparative example in which the transfer rate of the recess 22 is 87%, for Figure 3 the backlight unit configuration shown, when the luminance of a sample with an arithmetic mean roughness Ra of 1.8 μm of the second surface 43b, having Figure 2 the luminance of a sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 92%, 93%, 95%, and 99% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 90%, 93%, 94%, and 99% respectively.

[0143] Furthermore, regarding an example and a comparative example in which the transfer rate of the recess 22 is 87%, for Figure 2 the backlight unit configuration shown, when the luminance uniformity of a sample with an arithmetic mean roughness Ra of 1.8 μm of the second surface 43b is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 96%, 94%, 97%, and 89% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 94%, 96%, 94%, and 87% respectively.

[0144] Meanwhile, regarding an example and a comparative example in which the transfer rate of the recess 22 is 87%, for Figure 3 the backlight unit configuration shown, when the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, having Figure 2When the luminance uniformity of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 80%, 87%, 87%, and 93% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, and 4.2 μm are 101%, 102%, 104%, and 81% respectively.

[0145] In other words, in the example where the transfer rate of the concave portion 22 is 87%, the influence of the arithmetic mean roughness Ra of the second surface 43b on the luminance uniformity is small.

[0146] Furthermore, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 2 the backlight unit configuration shown, when the luminance of the sample with the transfer rate of the concave portion 22 being 87% and the arithmetic mean roughness Ra of the second surface 43b being 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 98%, 101%, 100%, 104%, and 103% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 100%, 101%, 101%, 102%, and 102% respectively.

[0147] Meanwhile, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the luminance of the sample with Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 96%, 98%, 97%, 101%, and 101% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 94%, 98%, 97%, 101%, and 100% respectively.

[0148] Furthermore, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 2In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, the brightness uniformity of the sample is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 80%, 79%, 79%, 87%, and 90% respectively. And when the first surface 43a is set as the light emitting surface, the brightness uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 79%, 80%, 80%, 89%, and 90% respectively.

[0149] Meanwhile, regarding the comparative example where the transfer rate of the concave portion 22 is 77%, for Figure 3 In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the brightness uniformity of the sample having Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 74%, 79%, 78%, 97%, and 104% respectively. And when the first surface 43a is set as the light emitting surface, the brightness uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 96%, 93%, 94%, 97%, and 100% respectively.

[0150] In other words, in the comparative example where the transfer rate of the concave portion 22 is 77%, even when the arithmetic mean roughness Ra of the second surface 43b decreases, the brightness uniformity is not improved.

[0151] In addition, regarding the examples and comparative examples where the transfer rate of the concave portion 22 is 94%, for Figure 2 In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the brightness of the sample is set to 100% and the first surface 43a is set as the light incident surface, the brightnesses of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 84%, 91%, 90%, 96%, and 97% respectively. And when the first surface 43a is set as the light emitting surface, the brightnesses of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 90%, 95%, 94%, 98%, and 98% respectively.

[0152] Meanwhile, for the example and the comparative example where the transfer rate of the concave portion 22 is 94%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and having Figure 2 the luminance of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 90%, 94%, 94%, 99%, and 100% respectively, and when the first surface 43a is set as the light emitting surface, the luminance of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 87%, 94%, 93%, 99%, and 100% respectively.

[0153] In addition, for the example and the comparative example where the transfer rate of the concave portion 22 is 94%, for Figure 2 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the luminance uniformity of the sample is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 129%, 126%, 129%, 130%, and 117% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 119%, 121%, 122%, 125%, and 109% respectively.

[0154] Meanwhile, for the example and the comparative example where the transfer rate of the concave portion 22 is 94%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and having Figure 2 the luminance uniformity of the sample of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 92%, 105%, 105%, 117%, and 107% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 121%, 126%, 122%, 126%, and 103% respectively.

[0155] In other words, in an example where the transfer rate of the concave portion 22 is 94%, an overall improvement in luminance uniformity is obtained regardless of the arithmetic mean roughness Ra of the second surface 43b.

[0156] In addition, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 100%, for Figure 2 the backlight unit configuration shown, when the luminance of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 77%, 85%, 86%, 94%, and 95% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 84%, 89%, 92%, 96%, and 96% respectively.

[0157] Meanwhile, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 100%, for Figure 3 the backlight unit configuration shown, when the luminance of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and having Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 82%, 90%, 92%, 98%, and 98% respectively, and when the first surface 43a is set as the light emitting surface, the luminances of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 80%, 90%, 92%, 98%, and 98% respectively.

[0158] In addition, regarding the example and the comparative example in which the transfer rate of the concave portion 22 is 100%, for Figure 2 the backlight unit configuration shown, when the luminance uniformity of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 147%, 153%, 151%, 143%, and 135% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 135%, 147%, 146%, 140%, and 127% respectively.

[0159] Meanwhile, for an example and a comparative example in which the transfer rate of the concave portion 22 is 100%, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and having Figure 2 the backlight unit configuration shown, when the luminance uniformity of the sample is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 109%, 122%, 120%, 124%, and 119% respectively, and when the first surface 43a is set as the light emitting surface, the luminance uniformities of the samples with Ra of 0 μm, 0.3 μm, 1.3 μm, 1.8 μm, and 4.2 μm are 108%, 128%, 127%, 118%, and 105% respectively.

[0160] In other words, in the example where the transfer rate of the concave portion 22 is 100%, an overall improvement in luminance uniformity is obtained regardless of the arithmetic mean roughness Ra of the second surface 43b.

[0161] Regarding the evaluation results of luminance and luminance uniformity obtained in the above third test, Figure 10 shows the evaluation results obtained using Figure 2 the backlight unit configuration shown (where the color conversion sheet 44 is disposed on the upper side of the light diffusion sheet 43), Figure 11 shows the evaluation results obtained using Figure 3 the backlight unit configuration shown (where the color conversion sheet 44 is disposed on the lower side of the light diffusion sheet 43). In Figure 10 and Figure 11 , the white circles, white triangles, white inverted triangles, and white squares represent the results obtained when the first surface 43a is set as the light incident surface (lower pyramid), while the black circles, black triangles, black inverted triangles, and black squares represent the results obtained when the first surface 43a is set as the light emitting surface (upper pyramid). Further, the numerical values on the graph represent the arithmetic mean roughness Ra (μm) of the second surface 43b. In addition, Figure 10 the + sign in represents the evaluation results (both luminance and luminance uniformity are 100%) of the sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, which is used as the evaluation reference (reference) for the lower pyramid, while Figure 10The "*" symbol in represents the evaluation result of a sample in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, which is used as an evaluation reference (reference) for the upper pyramid. However, the evaluation reference for the upper pyramid is about 5% higher in brightness and about 20% lower in brightness uniformity than the evaluation reference for the lower pyramid, and thus, in Figure 10 and Figure 11 the evaluation result of the upper pyramid is converted to a value obtained when the evaluation reference of the lower pyramid is set to 100%.

[0162] As Figure 10 and Figure 11 shown, it is understood that for the configuration of the backlight unit 40 shown in Figure 2 and Figure 3 wherein a blue light source (blue LED elements arranged in a square at pitches of 2.8 mm and 2.8 m) is used as the light source 42 and a color conversion sheet 44 and an upper light diffusion sheet 47 are provided, when the transfer rate of the concave portion 22 of the light diffusion sheet 43 is set to 87% or more, preferably 90% or more, and more preferably close to 100% and the arithmetic mean roughness Ra of the second surface 43b is set to 1.5 μm or less, and preferably about 1.0 μm, the brightness uniformity can be improved. It is also understood that for the total brightness uniformity of the configuration of the backlight unit shown in Figure 2 (wherein the color conversion sheet 44 is provided on the upper side of the light diffusion sheet 43) is better than that of the configuration of the backlight unit shown in Figure 3 (wherein the color conversion sheet 44 is provided on the lower side of the light diffusion sheet 43).

[0163] <Effect of the light source in the first to third tests>

[0164] For the light source 42 used in the first test, a small amount of light components are emitted from the light source 42 in the directly upward direction, while a large amount of light components are emitted in the obliquely upward direction. For the light source 42 used in the second test, slightly more light components are emitted from the light source 42 in the directly upward direction, while slightly fewer light components are emitted in the obliquely upward direction. For the light source 42 used in the third test, a large amount of light components are emitted from the light source 42 in the directly upward direction, while a small amount of light components are emitted in the obliquely upward direction.

[0165] When using a light source 42 in which the number of light components emitted in a directly upward direction (hereinafter referred to as directly upward light) is greater than the number of light components emitted in an obliquely upward direction (hereinafter referred to as oblique light), and when the transfer rate of the concave portion 22 is low, the directly upward light is more likely to pass through the light diffusing sheet 43 as it is. Therefore, it is considered that the arithmetic mean roughness Ra of the second surface 43b should be increased to a certain extent in order to improve the light diffusion performance of the second surface 43b. Further, when using a light source 42 that emits more directly upward light than oblique light and increasing the transfer rate of the concave portion 22, it is considered that the arithmetic mean roughness Ra of the second surface 43b should be decreased so as not to hinder the total reflection of the concave portion 22, which improves the brightness uniformity. It should be noted that in the third test (where a light source 42 that emits more directly upward light than oblique light is used), in some cases, both the brightness and the brightness uniformity can be improved by setting the arithmetic mean roughness Ra of the second surface 43b to a larger value.

[0166] Meanwhile, when using a light source 42 that emits less directly upward light than oblique light, the degree to which the brightness uniformity increases with an increase in the transfer rate of the concave portion 22 decreases. Therefore, it is considered that the arithmetic mean roughness Ra of the second surface 43b should be decreased in order to prevent an increase in the oblique light component. It should be noted that the directly upward light is less likely to be affected by the thickness of the base material layer 21, while the oblique light is more likely to be affected by the thickness of the base material layer 21. Therefore, it is believed that a change in the thickness of the base material layer 21 has a similar effect on the oblique light as a change in the arithmetic mean roughness Ra of the second surface 43b.

[0167] From the above description, it can be considered that in order to improve the brightness uniformity of the backlight unit 40, when using a light source 42 that emits more directly upward light than oblique light, (1) the transfer rate of the concave portion 22 should be as close to 100% as possible, (2) when the transfer rate of the concave portion 22 is close to 100%, the arithmetic mean roughness Ra of the second surface 43b should be steadily decreased, and (3) when the transfer rate of the concave portion 22 and the number of light diffusing sheets 43 arranged are limited, both the arithmetic mean roughness Ra of the second surface 43b and the thickness of the base material layer 21 should be increased.

[0168] Further, in order to improve the brightness uniformity of the backlight unit 40, when using a light source 42 that emits less directly upward light than oblique light, it can be considered that (1) the transfer rate of the concave portion 22 should be set to 87% or more, and (2) the arithmetic mean roughness Ra of the second surface 43b should be set as small as possible.

[0169] In addition, in order to improve the brightness uniformity of the backlight unit 40, a light source 42 that emits both light directly upward and oblique light is used, and it can be considered that (1) the transfer rate of the concave portion 22 should be set to be close to 100%, and (2) the arithmetic mean roughness Ra of the second surface 43b should be set to 1.5 μm or less.

[0170] <Fourth Test>

[0171] The difference between the fourth test and the second and third tests is that the thickness of the base material layer 21 of the light diffusing sheet 43 is reduced to 90 μm. In the fourth test, as an example of the light diffusing sheet 43, samples in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 0 μm, and samples in which the transfer rate of the concave portion 22 is 100% and the arithmetic mean roughness Ra of the second surface 43b is 0 μm are prepared. Further, as a comparative example of the light diffusing sheet 43, samples in which the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and samples in which the transfer rate of the concave portion 22 is 100% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm are prepared.

[0172] In the fourth test, first, Figure 2 and Figure 3 The configuration of the backlight unit 40 shown is used to evaluate the brightness and brightness uniformity of the light diffusing sheet 43, where the same blue light source as those in the second test is used as the light source 42, and the color conversion sheet 44 and the upper light diffusing sheet 47 are provided.

[0173] Therefore, in the case where the transfer rate of the concave portion 22 is 87%, for Figure 2 the backlight unit configuration shown, when the brightness of the comparative example in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightness of the example in which Ra is 0 μm is 93%, and when the first surface 43a is set as the light emitting surface, the brightness of the example in which Ra is 0 μm is 96%. At the same time, for Figure 3 the backlight unit configuration shown, when the brightness of the comparative example in which the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and has Figure 2 the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the brightness of the example in which Ra is 0 μm is 94%, and when the first surface 43a is set as the light emitting surface, the brightness of the example in which Ra is 0 μm is 92%.

[0174] Further, in the case where the transfer rate of the concave portion 22 is 87%, for Figure 2The backlight unit configuration shown, when the luminance uniformity of the comparative example where the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the example where Ra is 0 μm is 111%, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the example where Ra is 0 μm is 104%. At the same time, for Figure 3 the backlight unit configuration shown, when the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and has Figure 2 the luminance uniformity of the comparative example of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the example where Ra is 0 μm is 98%, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the example where Ra is 0 μm is 115%.

[0175] In addition, in the case where the transfer rate of the concave portion 22 is 100%, for Figure 2 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, and the luminance of the comparative example is set to 100%, and the first surface 43a is set as the light incident surface, the luminance of the example where Ra is 0 μm is 81%, and the luminance of the comparative example where Ra is 1.8 μm is 96%, and when the first surface 43a is set as the light emitting surface, the luminance of the example where Ra is 0 μm is 86%, and the luminance of the comparative example where Ra is 1.8 μm is 96%. At the same time, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and has Figure 2 the luminance of the comparative example of the backlight unit configuration shown is set to 100%, and the first surface 43a is set as the light incident surface, the luminance of the example where Ra is 0 μm is 89%, and the luminance of the comparative example where Ra is 1.8 μm is 101%, and when the first surface 43a is set as the light emitting surface, the luminance of the example where Ra is 0 μm is 88%, and the luminance of the comparative example where Ra is 1.8 μm is 102%.

[0176] In addition, in the case where the transfer rate of the concave portion 22 is 100%, for Figure 2In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, the brightness uniformity of the comparative example is set to 100%, and when the first surface 43a is set as the light incident surface, the brightness uniformity of the example with Ra of 0 μm is 158%, and the brightness uniformity of the comparative example with Ra of 1.8 μm is 122%. And when the first surface 43a is set as the light emitting surface, the brightness uniformity of the example with Ra of 0 μm is 137%, and the brightness uniformity of the comparative example with Ra of 1.8 μm is 118%. At the same time, for Figure 3 In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, having Figure 2 In the backlight unit configuration shown, when the brightness uniformity of the comparative example is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformity of the example with Ra of 0 μm is 130%, and the brightness uniformity of the comparative example with Ra of 1.8 μm is 114%. And when the first surface 43a is set as the light emitting surface, the brightness uniformity of the example with Ra of 0 μm is 139%, and the brightness uniformity of the comparative example with Ra of 1.8 μm is 112%.

[0177] Next, in the fourth test, use Figure 2 and Figure 3 The configuration of the backlight unit 40 shown to evaluate the brightness and brightness uniformity of the light diffusing sheet 43, where the same blue light source as those in the third test is used as the light source 42, and the color conversion sheet 44 and the upper light diffusing sheet 47 are provided.

[0178] Therefore, in the case where the transfer rate of the concave portion 22 is 87%, for Figure 2 In the backlight unit configuration shown, when the brightness of the comparative example with the arithmetic mean roughness Ra of the second surface 43b being 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the brightness of the example with Ra of 0 μm is 93%, and when the first surface 43a is set as the light emitting surface, the brightness of the example with Ra of 0 μm is 96%. At the same time, for Figure 3 In the backlight unit configuration shown, when the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, having Figure 2 In the backlight unit configuration shown, when the brightness of the comparative example is set to 100% and the first surface 43a is set as the light incident surface, the brightness of the example with Ra of 0 μm is 94%, and when the first surface 43a is set as the light emitting surface, the brightness of the example with Ra of 0 μm is 92%.

[0179] Further, when the transfer rate of the concave portion 22 is 87%, for Figure 2 the backlight unit configuration shown, when the luminance uniformity of the comparative example where the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the example where Ra is 0 μm is 97%, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the example where Ra is 0 μm is 93%. At the same time, for Figure 3 the backlight unit configuration shown, when the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and has Figure 2 the luminance uniformity of the comparative example of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance uniformity of the example where Ra is 0 μm is 87%, and when the first surface 43a is set as the light emitting surface, the luminance uniformity of the example where Ra is 0 μm is 103%.

[0180] In addition, when the transfer rate of the concave portion 22 is 100%, for Figure 2 the backlight unit configuration shown, when the luminance of the comparative example where the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm is set to 100% and the first surface 43a is set as the light incident surface, the luminance of the example where Ra is 0 μm is 81%, and the luminance of the comparative example where Ra is 1.8 μm is 96%, and when the first surface 43a is set as the light emitting surface, the luminance of the example where Ra is 0 μm is 87%, and the luminance of the comparative example where Ra is 1.8 μm is 97%. At the same time, for Figure 3 the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm and has Figure 2 the luminance of the comparative example of the backlight unit configuration shown is set to 100% and the first surface 43a is set as the light incident surface, the luminance of the example where Ra is 0 μm is 88%, and the luminance of the comparative example where Ra is 1.8 μm is 100%, and when the first surface 43a is set as the light emitting surface, the luminance of the example where Ra is 0 μm is 87%, and the luminance of the comparative example where Ra is 1.8 μm is 101%.

[0181] In addition, when the transfer rate of the concave portion 22 is 100%, for Figure 2In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, the brightness uniformity of the comparative example is set to 100%, and when the first surface 43a is set as the light incident surface, the brightness uniformity of the example where Ra is 0 μm is 152%, and the brightness uniformity of the comparative example where Ra is 1.8 μm is 142%. When the first surface 43a is set as the light emitting surface, the brightness uniformity of the example where Ra is 0 μm is 138%, and the brightness uniformity of the comparative example where Ra is 1.8 μm is 133%. At the same time, for Figure 3 In the backlight unit configuration shown, when the transfer rate of the concave portion 22 is 87% and the arithmetic mean roughness Ra of the second surface 43b is 1.8 μm, having Figure 2 In the backlight unit configuration shown, when the brightness uniformity of the comparative example is set to 100% and the first surface 43a is set as the light incident surface, the brightness uniformity of the example where Ra is 0 μm is 117%, and the brightness uniformity of the comparative example where Ra is 1.8 μm is 124%. When the first surface 43a is set as the light emitting surface, the brightness uniformity of the example where Ra is 0 μm is 134%, and the brightness uniformity of the comparative example where Ra is 1.8 μm is 117%.

[0182] As described above, in the fourth test (where the thickness of the base material layer 21 of the light diffusing sheet 43 is reduced compared to the second and third tests), when the same light source 42 as that in the second test is used, evaluation results similar to those in the second test are obtained, and when the same light source 42 as that in the third test is used, evaluation results similar to those in the third test are obtained.

[0183] (Other embodiments)

[0184] Although embodiments of the present disclosure have been described above (including examples: the same applies below), the present disclosure is not limited to the above embodiments and can be variously modified within the scope of the present disclosure. In other words, the foregoing description of the embodiments is illustrative in nature and is not intended to limit the present disclosure, its application, or its use.

[0185] List of reference numerals

[0186] 1 TFT substrate

[0187] 2 CF substrate

[0188] 3 Liquid crystal layer

[0189] 5 Liquid crystal display panel

[0190] 6 First polarizing plate

[0191] 7. Second polarizing plate

[0192] 21. Substrate layer

[0193] 22. Recess

[0194] 22a. Center (vertex)

[0195] 22b. Wall surface (tilted surface)

[0196] 23. Ridge line

[0197] 40. Backlight unit

[0198] 41. Reflective sheet

[0199] 42. Light source

[0200] 43. Light diffusing sheet

[0201] 43a. First surface

[0202] 43b. Second surface

[0203] 44. Color conversion sheet

[0204] 45. First prism sheet

[0205] 46. Second prism sheet

[0206] 47. Upper light diffusing sheet

[0207] 50. Liquid crystal display device

[0208] 50a. Display screen

Claims

1. A light diffuser having a first surface and a second surface, the first surface serving as one of a light emitting surface and a light incident surface, the second surface serving as the other of the light emitting surface and the light incident surface, in, A plurality of inverted substantially quadrangular pyramidal recesses are provided in the first surface, The second surface has an arithmetic mean roughness of 1.5 μm or less, and The transfer rate of the plurality of concave portions was 87% or more.

2. The light diffuser according to claim 1, in, The transfer rate was 90% or more.

3. The light diffuser according to claim 1, in, The arithmetic mean roughness is 1.0 μm or less.

4. A backlight unit built into a liquid crystal display device so as to guide light emitted from a plurality of light sources to a display screen, The backlight unit comprises the light diffusion sheet according to claim 1, and the light diffusion sheet is disposed between the display screen and the plurality of light sources.

5. The backlight unit according to claim 4, in, The light diffusion sheet is stacked into a plurality of layers and is arranged between the display screen and the plurality of light sources.

6. The backlight unit according to claim 5, in, The plurality of light sources are white light sources, and The arithmetic mean roughness is 1.0 μm or less.

7. The backlight unit according to claim 5, in, The plurality of light sources are blue light sources, The backlight unit further includes a color conversion sheet that converts the wavelength of the light, and The transfer rate was 90% or more.

8. The backlight unit according to claim 7, in, The color conversion sheet is disposed between the display screen and the plurality of stacked layers of the light diffusion sheet.

9. The backlight unit according to claim 8, in, In the plurality of stacked layers of the light diffusion sheet, the first surface is a light incident surface.

10. A liquid crystal display device, the liquid crystal display device include: The backlight unit according to any one of claims 4 to 9; as well as Liquid crystal display panel.

11. An information device comprising the liquid crystal display device according to claim 10.

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