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

Abstract

To provide a light diffusion sheet having high luminance uniformizing ability.SOLUTION: The first surface 43a of the light diffusion sheet 43 is provided with a plurality of recesses 105 each having a substantially inverted quadrangular pyramid shape. A plurality of linear structures 106 extending in a predetermined direction are provided on the second surface 43b of the light diffusion sheet 43. The plurality of linear structures 106 constitute a prism, and an apex angle of the plurality of recesses 105 is 130° or more and 150° or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

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

[0003] When a direct backlight is used, a light diffusion sheet is used to diffuse light from a light source such as an LED (Light Emitting Diode) and improve the uniformity of brightness and chromaticity across the entire screen (see, for example, Patent Document 1).

[0004] Light diffusion sheets diffuse light incident from the light incident surface by using the diffusion caused by providing an uneven shape on the light exit surface or by dispersing fine particles with a different refractive index than the substrate in the sheet substrate. In addition, multiple light diffusion sheets may be stacked to improve the uniformity of brightness within the screen (in-plane brightness uniformity).

[0005] Patent Document 1 discloses a light diffusion sheet having a plurality of quadrangular pyramids formed on one surface and a plurality of parallel linear prisms formed on the other surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Application Publication No. 2021 / 0072598A1 Summary of the Invention [Problem to be solved by the invention]

[0007] In the backlights of LCD displays, there is a demand for thinner displays, which requires a reduction in the thickness of the light diffusion sheet and the number of layers of light diffusion sheet. In addition, in direct-type backlights, the light source is placed directly below the display screen, so there is also a need to reduce the distance between the light source and the light diffusion sheet. Therefore, in order to maintain in-plane brightness uniformity even as the display becomes thinner, it is necessary to improve the brightness uniformity per light diffusion sheet.

[0008] An object of the present disclosure is to provide a light diffusion sheet with high luminance uniformity. [Means for solving the problem]

[0009] To achieve the above object, the light diffusion sheet according to the present disclosure is a light diffusion sheet having a first surface serving as a light exit surface and a second surface serving as a light entrance surface. One of the first surface and the second surface is provided with a plurality of recesses each having a substantially inverted square pyramid shape. The other of the first surface and the second surface is provided with a plurality of linear structures extending in a predetermined direction. The apex angle of the recesses is 100° or greater.

[0010] The light diffusion sheet according to the present disclosure has a plurality of recesses each having a substantially inverted quadrangular pyramid shape on one side and a plurality of linear structures extending in a predetermined direction on the other side, with the apex angle of the recesses set to 100° or greater. This enhances the synergistic effect of the light diffusion effect of the plurality of recesses and the light diffusion effect of the plurality of linear structures. This improves the luminance uniformity per light diffusion sheet, thereby enabling reductions in the thickness and number of stacked light diffusion sheets to be achieved as the light diffusion sheet becomes thinner.

[0011] In the present disclosure, the term "light diffusion sheet" encompasses a plate-shaped "light diffusion plate" and a film-shaped "light diffusion film."

[0012] In the light diffusion sheet according to the present disclosure, the plurality of linear structures may form prisms, hairlines, lenticulars, or diffraction gratings, which, in combination with the substantially inverted square pyramidal recesses, can reliably enhance the synergistic effect of light diffusion.

[0013] In the light diffusion sheet according to the present disclosure, the linear structures may form prisms with an apex angle of 95° or less, and the apex angle of the recesses may be 110° or more and 130° or less. This can particularly enhance the synergistic effect of the light diffusion effect of the recesses and the light diffusion effect of the linear structures.

[0014] In the light diffusion sheet according to the present disclosure, the linear structures may form prisms, and the apex angles of the recesses may be 130° or more and 150° or less. This can increase the luminance while improving the luminance uniformity.

[0015] In the light diffusion sheet according to the present disclosure, the recesses may be arranged in a two-dimensional matrix, and the arrangement direction may intersect with the predetermined direction (the direction in which the linear structures extend). In this way, the synergistic effect of the light diffusion effect can be increased over a wide range of apex angles of the recesses.

[0016] Another aspect of the light diffusion sheet according to the present disclosure is a light diffusion sheet having a first surface serving as a light exit surface and a second surface serving as a light entrance surface. One of the first surface and the second surface is provided with a plurality of recesses each having a substantially inverted square pyramid shape. The other of the first surface and the second surface is provided with a plurality of linear structures extending in a predetermined direction. The linear structures form prisms with an apex angle of 95° or more, and the apex angles of the recesses are between 85° and 95°.

[0017] According to another aspect of the light diffusion sheet of the present disclosure, one surface is provided with a plurality of recesses having a substantially inverted quadrangular pyramid shape, and the other surface is provided with a plurality of linear structures extending in a predetermined direction, each linear structure forming a prism with an apex angle of 95° or more, and the apex angle of the recesses is set to be between 85° and 95°. This enhances the synergistic effect of the light diffusion effect of the plurality of recesses and the light diffusion effect of the plurality of linear structures. This improves the luminance uniformity per light diffusion sheet, thereby enabling reductions in the thickness and number of stacked light diffusion sheets to be achieved as the light diffusion sheet becomes thinner.

[0018] The backlight unit according to the present disclosure is incorporated into a liquid crystal display device and directs light emitted from multiple light sources toward a display screen, and includes the light diffusion sheet according to the present disclosure (including other embodiments; the same applies below) between the display screen and the multiple light sources.

[0019] The backlight unit according to the present disclosure includes the light diffusion sheet according to the present disclosure, which improves the luminance uniformity per light diffusion sheet, thereby enabling reductions in the thickness and number of light diffusion sheets required to achieve further slimmer designs.

[0020] In the backlight unit according to the present disclosure, the plurality of light sources may be disposed on a reflecting sheet provided on the opposite side of the display screen from the light diffusing sheet, whereby light is further diffused by multiple reflections between the light diffusing sheet and the reflecting sheet, thereby further improving in-plane luminance uniformity.

[0021] In the backlight unit according to the present disclosure, a plurality of the light diffusion sheets may be stacked and disposed between the display screen and the plurality of light sources. In this manner, the use of the plurality of light diffusion sheets can further improve in-plane luminance uniformity. In this case, the stacked plurality of light diffusion sheets may include a first light diffusion sheet and a second light diffusion sheet, and the extension direction of the plurality of linear structures on the first light diffusion sheet may intersect with the extension direction of the plurality of linear structures on the second light diffusion sheet. In this manner, the occurrence of moiré (interference fringes) can be suppressed.

[0022] The backlight unit according to the present disclosure may further include another light diffusion sheet between the display screen and the light diffusion sheet, and a plurality of other recesses each having a substantially inverted square pyramid shape may be provided on one surface of the other light diffusion sheet, and the apex angle of the plurality of other recesses may be smaller than the apex angle of the plurality of recesses. In this way, in a backlight unit using a combination of light diffusion sheets with different configurations, it is possible to increase brightness and improve in-plane brightness uniformity.

[0023] In the backlight unit according to the present disclosure, the distance between the plurality of light sources and the light diffusion sheet may be 0 mm or more and 1 mm or less. In this way, even if a sufficient distance cannot be ensured between the light sources and the sheet due to a thin design, the diffusion performance of the light diffusion sheet according to the present disclosure can suppress deterioration of in-plane luminance uniformity.

[0024] A liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure described above and a liquid crystal display panel.

[0025] According to the liquid crystal display device of the present disclosure, since it is equipped with the backlight unit of the present disclosure described above, it is possible to maintain in-plane brightness uniformity even when the thickness of the light diffusion sheet or the number of layers is reduced as a result of further slimming.

[0026] An information device according to the present disclosure includes the liquid crystal display device according to the present disclosure.

[0027] According to the information device according to the present disclosure, since it includes the liquid crystal display device according to the present disclosure, it is possible to maintain in-plane luminance uniformity even when the device is made thinner. [Effects of the Invention]

[0028] According to the present disclosure, it is possible to provide a light diffusion sheet having a high ability to uniform brightness, as well as a backlight unit, a liquid crystal display device, and an information device that use the light diffusion sheet. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a cross-sectional view of a liquid crystal display device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a backlight unit according to the embodiment. [Figure 3] 1 is a cross-sectional view of a light diffusion sheet according to an embodiment. [Figure 4] FIG. 1 is a perspective view of a light diffusion sheet according to an embodiment. [Figure 5] 3A and 3B are diagrams showing the planar and cross-sectional configurations of a recess having a substantially inverted quadrangular pyramid shape provided on one surface of a light diffusion sheet according to an embodiment. [Figure 6] 1A and 1B are diagrams showing the relationship between the arrangement direction of recesses and the extension direction of linear structures in a light diffusion sheet according to an embodiment, where (a) shows the case where the directions are aligned, and (b) shows the case where the directions intersect at 45°. [Figure 7] 1A and 1B are cross-sectional views showing variations of multiple linear structures provided on the other surface of the light diffusion sheet according to the embodiment, in which (a) shows a case where the linear structures form hairlines, (b) shows a case where the linear structures form lenticulars, and (c) shows a case where the linear structures form a diffraction grating. [Figure 8] FIG. 10 is a diagram showing the evaluation results of in-plane luminance uniformity of the light diffusion sheets of the first example and the comparative example. [Figure 9] FIG. 10 is a cross-sectional view of a backlight unit incorporating the light diffusion sheets of the second and third embodiments. [Figure 10]FIG. 10 is a cross-sectional view of a light diffusion sheet according to a second embodiment. [Figure 11] FIG. 10 is a diagram showing the evaluation results of the in-plane luminance uniformity of the light diffusion sheet of the second example. [Figure 12] FIG. 10 is a diagram showing the evaluation results of the luminance (average value) of the light diffusion sheet of the second example. [Figure 13] FIG. 10 is a diagram showing the evaluation results of the in-plane luminance uniformity of the light diffusion sheet of the third example. [Figure 14] FIG. 10 is a diagram showing the evaluation results of the luminance (average value) of the light diffusion sheet of the third example. DETAILED DESCRIPTION OF THE INVENTION

[0030] (Embodiment) Hereinafter, a light diffusion sheet, a backlight unit, a liquid crystal display device, and an information device according to embodiments will be described with reference to the drawings. Note that the scope of the present disclosure is not limited to the following embodiments and can be arbitrarily modified within the scope of the technical concept of the present disclosure.

[0031] <Liquid crystal display device> FIG. 1 is an example of a cross-sectional view of a liquid crystal display device according to this embodiment.

[0032] 1, a liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the back side of the liquid crystal display panel 5 via the first polarizing plate 6. The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 arranged to face each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a frame-shaped sealant (not shown) for enclosing the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

[0033] The shape of the display screen 50a of the liquid crystal display device 50 when viewed from the front (top of Figure 1) is, in principle, rectangular or square, but is not limited to this and may be any shape such as a rectangle with rounded corners, an oval, a circle, a trapezoid, or an automobile instrument panel.

[0034] In the liquid crystal display device 50, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 in each sub-pixel corresponding to each pixel electrode to change the alignment state of the liquid crystal layer 3. This adjusts the transmittance of light incident from the backlight unit 40 through the first polarizer 6. The light with the adjusted transmittance is then emitted through the second polarizer 7 to display an image.

[0035] The liquid crystal display device 50 of this embodiment is used as a display device incorporated into various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, mobile phones, personal digital assistants, portable game machines, copy machines, ticket vending machines, automated teller machines, etc.).

[0036] The TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film covering each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and connected to each of the plurality of TFTs, and an alignment film covering each pixel electrode. The CF substrate 2 includes, for example, a black matrix arranged in a grid pattern on the glass substrate, color filters including red, green, and blue layers arranged between each grid of the black matrix, a common electrode covering the black matrix and the color filters, and an alignment film covering the common electrode. The liquid crystal layer 3 is made of a nematic liquid crystal material containing liquid crystal molecules with electro-optical properties. The first polarizer 6 and the second polarizer 7 include, for example, a polarizer layer having a unidirectional polarization axis and a pair of protective layers sandwiching the polarizer layer.

[0037] <Backlight unit> FIG. 2 is an example of a cross-sectional view of the backlight unit according to this embodiment.

[0038] As shown in Figure 2, the backlight unit 40 includes a reflective sheet 41, a plurality of light sources 42 arranged two-dimensionally on the reflective sheet 41, a light diffusion sheet (lower light diffusion sheet) 43 provided above the plurality of light sources 42, a color conversion sheet 44 provided above the light diffusion sheet 43, a first prism sheet 45 and a second prism sheet 46 provided in this order above the color conversion sheet 44, and a light diffusion sheet (upper light diffusion sheet) 47 provided above the second prism sheet 46.

[0039] Although Figure 2 illustrates an example in which three layers of light diffusion sheets 43 having the same structure are stacked and provided in the backlight unit 40, the light diffusion sheets 43 may be used in a single layer, or may be stacked in two or four or more layers.

[0040] The reflective sheet 41 is made of, for example, a white polyethylene terephthalate resin film, a silver vapor deposition film, or the like.

[0041] The type of light source 42 is not particularly limited, but may be, for example, an LED element or a laser element. From the viewpoint of cost, productivity, and the like, an LED element may be used. The light source 42 may have a rectangular shape in a plan view, in which case, the length of one side may be 10 μm or more (preferably 50 μm or more) and 20 mm or less (preferably 10 mm or less, more preferably 5 mm or less). When an LED is used as the light source 42, multiple LED chips, each several millimeters square, may be arranged on the reflective sheet 41 at regular intervals. A lens may be attached to the LED to adjust the light output angle characteristics of the LED serving as the light source 42. The number of light sources 42 to be arranged is not particularly limited, but when multiple light sources 42 are arranged in a dispersed manner, it is preferable to arrange them regularly on the reflective sheet 41. "Regularly arranged" means arranging the light sources 42 according to a certain rule, such as arranging the light sources 42 at equal intervals. When the light sources 42 are arranged at equal intervals, the center-to-center distance between two adjacent light sources 42 may be 0.5 mm or more (preferably 2 mm or more) and 20 mm or less.

[0042] The light diffusion sheet (lower light diffusion sheet) 43 diffuses light rays incident from the light source 42 while concentrating the light toward the normal direction (i.e., concentrating and diffusing the light). The matrix resin constituting the light diffusion sheet 43 is not particularly limited as long as it is made of a material that transmits light, but may be, for example, 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 may be, for example, 50 μm to 3 mm. If the thickness of the light diffusion sheet 43 exceeds 3 mm, it becomes difficult to achieve a thin LCD display, while if the thickness of the light diffusion sheet 43 is less than 50 μm, it becomes difficult to achieve a sufficient light diffusion effect. As shown in FIG. 2, when multiple light diffusion sheets 43 with the same structure are stacked, the stack thickness may be several hundred μm to several mm. The light diffusion sheet 43 may be in the form of a film or a plate. The detailed structure and manufacturing method of the light diffusion sheet 43 will be described later.

[0043] The color conversion sheet 44 is a wavelength conversion sheet that converts light from the light source 42 (e.g., blue light) into light whose peak wavelength is a wavelength of a given color (e.g., green or red). For example, the color conversion sheet 44 converts blue light with a wavelength of 450 nm into green light with a wavelength of 540 nm and red light with a wavelength of 650 nm. In this case, if a light source 42 that emits blue light with a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet 44, and the light that passes through the color conversion sheet 44 becomes white light. For example, a QD (quantum dot) sheet, a fluorescent sheet, or the like may be used as the color conversion sheet 44.

[0044] The first prism sheet 45 and the second prism sheet 46 refract light rays incident from the color conversion sheet 44 side toward the normal direction. For example, a plurality of grooves having an isosceles triangular cross section are arranged adjacent to each other on the light exit surface of each of the prism sheets 45 and 46, and a prism is formed by a triangular prism portion sandwiched between a pair of adjacent grooves. The apex angle of the prism is, for example, approximately 90°. The grooves formed on the first prism sheet 45 and the grooves formed on the second prism sheet 46 may be arranged perpendicular to each other. In this manner, light rays incident from the color conversion sheet 44 side can be refracted toward the normal direction by the first prism sheet 45, and light rays emitted from the first prism sheet 45 can be refracted by the second prism sheet 45 so as to travel approximately perpendicular to the light entrance surface of the light diffusion sheet 47. The prism sheets 45 and 46 may be laminated as separate members or may be formed integrally. The total thickness of the prism sheets 45 and 46 may be, for example, about 100 to 400 μm. The prism sheets 45 and 46 may be, for example, a PET (polyethylene terephthalate) film with a prism shape formed by using a UV-curable acrylic resin.

[0045] The light diffusion sheet (upper light diffusion sheet) 47 slightly diffuses light rays incident from the second prism sheet 46 side, thereby suppressing brightness unevenness caused by the shape of the prism portions of the prism sheets 45 and 46. The light diffusion sheet 47 may be laminated directly on the surface of the prism sheet 4. The thickness of the light diffusion sheet 47 is not particularly limited, but may be, for example, 50 μm to 3 mm. If the thickness of the light diffusion sheet 47 exceeds 3 mm, it becomes difficult to achieve a thin LCD display, while if the thickness of the light diffusion sheet 47 is less than 50 μm, it becomes difficult to achieve a sufficient light diffusion effect. The light diffusion sheet 47 may be in the form of a film or a plate. For example, the light diffusion sheet 47 may be a PET film having an uneven surface formed on at least one side using a UV-curable acrylic resin.

[0046] <Detailed structure of the light diffusion sheet (lower light diffusion sheet)> 3 and 4 are an example of a cross-sectional view and a perspective view of the light diffusion sheet according to this embodiment.

[0047] As shown in Fig. 3, the light diffusion sheet 43 has a first surface 43a serving as a light exit surface and a second surface 43b serving as a light entrance surface. That is, the light diffusion sheet 43 is disposed with the second surface 43b facing the light source 42. The light diffusion sheet 43 is composed of a base layer 101, a first diffusion layer 102 provided on the first surface 43a side of the base layer 101, and a second diffusion layer 103 provided on the second surface 43b side of the base layer 101. The first diffusion layer 102 is provided with a plurality of recesses 105 having a substantially inverted polygonal pyramid shape, specifically a substantially inverted square pyramid shape (inverted pyramid shape). The second diffusion layer 103 is provided with a plurality of linear structures 106 extending in a predetermined direction.

[0048] In this embodiment, the first surface 43a on which the first diffusion layer 102 is formed is the light exit surface, and the second surface 43b on which the second diffusion layer 103 is formed is the light incident surface. Alternatively, the first surface 43a may be the light incident surface, and the second surface 43b may be the light exit surface.

[0049] Since the base layer 101 needs to transmit light, it is formed primarily from a transparent (e.g., colorless and transparent) synthetic resin. The main component of the base layer 101 is not particularly limited, and may be, for example, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polystyrene, polyolefin, cellulose acetate, weather-resistant vinyl chloride, or the like. The term "main component" refers to the component with the highest content, e.g., a content of 50% by mass or more. The base layer 101 may contain a diffusing agent or other additives, or may be substantially additive-free. The additives that can be contained are not particularly limited, and may be, for example, inorganic particles such as silica, titanium oxide, aluminum hydroxide, or barium sulfate, or organic particles such as acrylic, acrylonitrile, silicone, polystyrene, or polyamide.

[0050] The lower limit of the average thickness of the base layer 101 is preferably about 10 μm, more preferably about 35 μm, and even more preferably about 50 μm. The upper limit of the average thickness of the base layer 101 is preferably about 500 μm, more preferably about 250 μm, and even more preferably about 180 μm. If the average thickness of the base layer 101 is less than the lower limit, curling may occur when the diffusion layers 102 and 103 are formed. Conversely, if the average thickness of the base layer 101 exceeds the upper limit, the brightness of the liquid crystal display device 50 may decrease, and the liquid crystal display device 50 may not meet the demand for a thinner design. Note that the "average thickness" refers to the average value of thicknesses at any 10 points.

[0051] The first diffusion layer 102 needs to transmit light, and therefore may be formed mainly from a transparent (e.g., colorless and transparent) synthetic resin. The first diffusion layer 102 may be molded integrally with the base material layer 101 during extrusion molding of the base material resin that will become the base material layer 101, or may be molded separately using an ultraviolet-curable resin after molding the base material layer 101.

[0052] The plurality of recesses 105, each having a substantially inverted quadrangular pyramid shape, provided on the first diffusion layer 102 (the first surface 43a of the light diffusion sheet 43) may be arranged in a two-dimensional matrix, as shown in FIG. 4, for example. In other words, the plurality of recesses 105 may be arranged along two directions perpendicular to each other. Adjacent recesses 105 are separated by ridge lines 111. The ridge lines 111 extend along the two directions in which the recesses 105 are arranged. The arrangement pitch of the recesses 105 may be, for example, not less than approximately 50 μm and not more than approximately 500 μm. The center 112 of each recess 105 (the apex of the inverted pyramid) is the deepest part of the recess 105. The center (deepest part) 112 of each recess 105 may reach the surface (light emission surface) of the base layer 101. In other words, the depth of the recess 105 may be equal to the thickness of the first diffusion layer 102. For simplicity, FIG. 4 illustrates an example in which the recesses 105 are arranged in a 5×5 matrix, but the actual number of recesses 105 arranged is much greater.

[0053] As one of the features of this embodiment, the apex angle θ of the recess 105 is set to 100° or more. To prevent a decrease in light diffusion due to the first diffusion layer 102, the upper limit of the apex angle θ of the recess 105 may be set to, for example, 170°. Here, the apex angle θ of the recess 105 refers to the angle formed between the inclined surfaces of the recess 105 in a cross section (lower view of FIG. 5 ) that appears when the recess 105 is cut in a plane (longitudinal cross section) perpendicular to the mounting surface (horizontal plane) of the light diffusion sheet 43, passing through the apex 112 of the inverted pyramid and perpendicularly intersecting a pair of ridgelines 111 that face each other across the apex 112, as shown in FIG. 5 . The upper view of FIG. 5 shows the planar configuration of the recess 105. In FIG. 5 , "H" indicates the depth of the recess 105 (the height of the pyramid shape), and "P" indicates the horizontal width of the recess 105 (i.e., the arrangement pitch of the recess 105). The depth H of the recesses 105 is determined by the arrangement pitch P of the recesses 105 and the apex angle θ of the recesses 105.

[0054] In this embodiment, the recesses 105 are arranged in a two-dimensional matrix, forming a concave-convex shape. However, the recesses 105 may be arranged randomly to the extent that the effects of the present invention are not lost. When the recesses 105 are arranged regularly in two dimensions, gaps may or may not be provided between the recesses 105. The recesses 105 may have a substantially inverted polygonal pyramid shape other than a substantially inverted square pyramid shape. For example, the "inverted polygonal pyramid" shape of the recesses 105 may be an inverted triangular pyramid or an inverted hexagonal pyramid, which can be arranged two-dimensionally without gaps, similar to an inverted square pyramid. When the "inverted polygonal pyramid" shape of the recesses 105 is an inverted square pyramid, it is easy to improve the accuracy of the surface cutting operation of the mold (metal roll) used in manufacturing processes such as extrusion molding and injection molding when forming the recesses 105.

[0055] In this disclosure, the term "approximately inverted polygonal pyramid" is used in consideration of the difficulty of forming a geometrically strict inverted polygonal pyramid recess using conventional shape transfer technology. However, "approximately" means that it can be approximated; for example, "approximately inverted square pyramid" refers to a shape that can be approximated to an inverted square pyramid. For example, "inverted polygonal pyramid truncated shapes" with flat apexes are also included in the "approximately inverted polygonal pyramid" category if the apex area is small enough that the effects of the present invention are not lost. Furthermore, shapes that deform from an "inverted polygonal pyramid" within the range of unavoidable shape variations due to processing accuracy in industrial production are also included in the "approximately inverted polygonal pyramid" category.

[0056] The second diffusion layer 103 needs to transmit light, and therefore may be formed mainly from a transparent (e.g., colorless and transparent) synthetic resin. The second diffusion layer 103 may be molded integrally with the base material layer 101 during extrusion molding of the base material resin that will become the base material layer 101, or may be molded separately using an ultraviolet-curable resin after molding the base material layer 101.

[0057] The linear structures 106 provided on the second diffusion layer 103 (the second surface 43b of the light diffusion sheet 43) so as to extend in a predetermined direction may be, for example, striped prisms (triangular pillars). The lower limit of the thickness of the second diffusion layer 103 (the height from the surface (light incident surface) of the base layer 101 to the apex of the prism that becomes the linear structures 106) may be, for example, about 5 μm, more preferably about 10 μm. The upper limit of the thickness of the second diffusion layer 103 may be, for example, about 200 μm, more preferably about 100 μm. The lower limit of the pitch of the linear structures 106 may be, for example, about 10 μm, more preferably about 20 μm. The upper limit of the pitch of the linear structures 106 may be, for example, about 200 μm, more preferably about 100 μm. The lower limit of the refractive index of the prism that becomes the linear structures 106 may be, for example, 1.5, more preferably 1.55, and the upper limit of the refractive index may be, for example, 1.7.

[0058] As shown in FIG. 6, when a plurality of recesses 105 are arranged in a two-dimensional matrix, the linear structures 106 may extend along one of the arrangement directions (i.e., the extension direction of the ridge lines 111) (see FIG. 6(a)), or the arrangement direction may intersect with the extension direction of the linear structures 106 (see FIG. 6(b)). When the arrangement direction of the recesses 105 intersects with the extension direction of the linear structures 106, the intersection angle may be, for example, 30° or more and 60° or less, preferably 40° or more and 50° or less. Note that FIG. 6 is a plan view of a part of the light diffusion sheet 43 as viewed from the recesses 105 (first diffusion layer 102) side.

[0059] When multiple light diffusion sheets 43 are stacked and used in the backlight unit 40, the extension direction of the linear structure 106 in one light diffusion sheet 43 may be the same as or may intersect with the extension direction of the linear structure 106 in another light diffusion sheet 43.

[0060] In the light diffusion sheet 43 shown in FIG. 3, striped prisms are provided as the plurality of linear structures 106. However, the linear structures 106 are not particularly limited as long as they include convex structures extending in a predetermined direction on the second diffusion layer 103 (the second surface 43b of the light diffusion sheet 43). For example, as shown in FIG. 7, the plurality of linear structures 106 may be hairlines (FIG. 7(a)), lenticulars (FIG. 7(b)), diffraction gratings (FIG. 7(c)), or the like. The hairlines forming the linear structures 106 may be, for example, elongated stripes formed by polishing the surface of the base layer 101 in a single direction. The lenticulars forming the linear structures 106 may be, for example, fine, elongated, semi-cylindrical convex lenses provided on the surface of the base layer 101. The diffraction grating forming the linear structures 106 may be, for example, a grating pattern consisting of linear concaves and convexities periodically arranged on the surface of the base layer 101. 7A to 7C show variations of the cross-sectional configuration of the second diffusion layer 103 of the light diffusion sheet 43 shown in FIG.

[0061] Furthermore, when prisms are provided as the linear structures 106, the height of the prisms may be periodically changed along the vertical direction. That is, the apexes (ridges) of the prisms that form the linear structures 106 may be wavy, moving up and down in the vertical direction. Furthermore, the width of the prisms may be changed along with the height of the prisms. Specifically, the width of the prisms may be wider where the prisms are taller and narrower where the prisms are shorter. Furthermore, the height and repetition period of the peaks that repeatedly appear on the prism ridges may be the same. Varying the height of the prisms in this way reduces the contact area between the prisms and another light diffusion sheet 43 that is overlaid, thereby reducing the inclusion of foreign matter, scratches due to contact, and poor user visibility.

[0062] Furthermore, when prisms are provided as the linear structures 106, the prisms may be extended in a predetermined direction while periodically meandering horizontally. Specifically, the arrangement of prism ridges may be periodically meandered without changing the shape (height, pitch, apex angle) of the prisms. In other words, when the second surface 43b of the light diffusion sheet 43 is viewed from the front, the prisms that form the linear structures 106 may extend in a wavy manner. This makes it possible to suppress the occurrence of interference patterns caused by the combination of the inverted pyramid-shaped recesses 105 and the prisms that form the linear structures 106.

[0063] <Manufacturing method for light diffusion sheets (underwear light diffusion sheets)> The method for manufacturing the light diffusion sheet 43 is not particularly limited, but for example, the light diffusion sheet 43 can be manufactured using any of the following four manufacturing methods.

[0064] In the first manufacturing method, first, pellet-shaped base resin (plastic resin) is formed into a resin film using an extruder. Then, two metal rolls are used: one with a convex pyramid shape on its surface, and the other with a plurality of linear concave shapes extending in a predetermined direction on its surface. These rolls are then pressed onto the resin film to produce a light diffusion sheet 43 having an inverted pyramid shape (concave portions 105) on one side and linear convex shapes (linear structures 106) on the other side. In this manufacturing method, the base layer 101, the first diffusion layer 102, and the second diffusion layer 103 are integrally formed.

[0065] In the second manufacturing method, first, pellet-shaped base resin (plastic resin) is formed into a resin film using an extrusion molding machine. Then, two metal rolls are used, one of which has a convex pyramidal shape on its surface, and the other a mirror-finished roll. These rolls are then pressed against the resin film to produce a sheet (a sheet in which the base layer 101 and the first diffusion layer 102 are integrated) with an inverted pyramidal shape (recesses 105) on one side and a mirror-finished surface on the other side. Next, the sheet is fed between a pair of pressure rolls, and an ultraviolet-curable resin (a resin composition for forming protrusions) is supplied to the back side of the base layer 101 (for example, the light incident surface side when incorporated into a liquid crystal display device 50) just before the pair of pressure rolls. Here, the pressure roll that comes into contact with the ultraviolet-curable resin has a plurality of linear recesses extending in a predetermined direction on its outer circumferential surface. The sheet supplied with the ultraviolet curable resin is pressed with a pair of pressure rolls, and then the ultraviolet curable resin is cured by irradiating it with ultraviolet light, and a plurality of linear protrusions (linear structures 106), which are the inverse shape of the plurality of linear recesses, are transferred to the opposite side of the sheet to which the inverted pyramid shapes (recesses 105) have been imparted. In this manufacturing method, only the second diffusion layer 103 is formed separately.

[0066] In the third manufacturing method, first, pellet-shaped base resin (plastic resin) is formed into a resin film using an extrusion molding machine. Then, two metal rolls are used: one roll with a plurality of linear recesses extending in a predetermined direction on its surface, and the other roll with a mirror finish. These rolls are then pressed against the resin film to produce a sheet (a sheet in which the base layer 101 and the second diffusion layer 103 are integrated) with a plurality of linear protrusions (linear structures 106) on one side, which are the inverse shape of the linear recesses, and a mirror finish on the other side. Next, the sheet is fed between a pair of pressure rolls, and a UV-curable resin (a protrusion-forming resin composition) is applied to the surface side of the base layer 101 (e.g., the light-emitting surface side when incorporated into a liquid crystal display device 50) just before the pair of pressure rolls. Here, the pressure roll that comes into contact with the UV-curable resin has a plurality of approximately square pyramidal protrusions on its outer circumferential surface. The sheet supplied with the ultraviolet-curable resin is pressed with a pair of pressure rolls, and then the ultraviolet-curable resin is cured by irradiating it with ultraviolet light, and a plurality of inverted pyramid shapes (depressions 105), which are the inverted shapes of the plurality of approximately square pyramidal convex portions, are transferred to the opposite side of the sheet to which the plurality of linear protrusions (linear structures 106) have been added. In this manufacturing method, only the first diffusion layer 102 is formed separately.

[0067] In the fourth manufacturing method, first, a base layer 101 containing, for example, polyethylene terephthalate as a main component is prepared. While this base layer 101 is fed between a pair of first pressure rolls, a first ultraviolet-curable resin (a resin composition for forming protrusions) is supplied to the back side of the base layer 101 (for example, the light incident surface side when incorporated into a liquid crystal display device 50) just before the pair of first pressure rolls. Here, the first pressure roll that comes into contact with the first ultraviolet-curable resin has a plurality of linear recesses extending in a predetermined direction on its outer circumferential surface. After pressing the base layer 101 to which the first ultraviolet-curable resin has been supplied with the first ultraviolet-curable resin between the pair of first pressure rolls, the first ultraviolet-curable resin is cured by irradiating it with ultraviolet light, and a sheet (a sheet in which the base layer 101 and the second diffusion layer 103 are laminated) is produced on the back side of the base layer 101, on which a plurality of linear protrusions (linear structures 106), which are the inverse shapes of the linear recesses, have been transferred. Next, while the sheet is fed between a pair of second pressure rolls, a second ultraviolet-curable resin (a protrusion-forming resin composition) is supplied to the front side of the sheet (e.g., the light-emitting surface side when incorporated into a liquid crystal display device 50) onto which the multiple linear protrusions (linear structures 106) have been transferred, just before the pair of second pressure rolls. The second pressure roll that comes into contact with the second ultraviolet-curable resin has multiple approximately square pyramidal protrusions on its outer circumferential surface. After pressing the sheet onto which the second ultraviolet-curable resin has been supplied with the second ultraviolet-curable resin between the pair of second pressure rolls, the second ultraviolet-curable resin is cured by irradiating it with ultraviolet light, and multiple inverted pyramidal shapes (recesses 105), which are the inverse shapes of the multiple approximately square pyramidal protrusions, are transferred to the opposite side of the sheet onto which the multiple linear protrusions (linear structures 106) have been transferred. In this manufacturing method, the base layer 101, the first diffusion layer 102, and the second diffusion layer 103 are each formed as separate bodies.

[0068] In the fifth manufacturing method, first, pellet-shaped base resin (plastic resin) is formed into a resin film using an extruder. Then, two flat metal plates are used: one with a convex pyramidal shape on its surface, and the other with a plurality of linear concave shapes extending in a predetermined direction on its surface. These two flat metal plates are then pressed (heat-pressed) onto the resin film to produce a light diffusion sheet 43 having an inverted pyramidal shape (concave portions 105) on one side and linear convex shapes (linear structures 106) on the other side. In this manufacturing method, the base layer 101, the first diffusion layer 102, and the second diffusion layer 103 are integrally formed.

[0069] <Features of the embodiment> According to the light diffusion sheet 43 of the present embodiment described above, one surface is provided with a plurality of recesses 105 each having a substantially inverted quadrangular pyramid shape, and the other surface is provided with a plurality of linear structures 106 extending in a predetermined direction, with the apex angle of the recesses 105 set to 100° or more. This increases the synergistic effect of the light diffusion effect of the plurality of recesses 105 and the light diffusion effect of the plurality of linear structures 106. This improves the luminance uniformity of the light diffusion sheet 43, thereby enabling reductions in the thickness of the light diffusion sheet 43 and the number of layers to be reduced as the sheet becomes thinner.

[0070] In the light diffusion sheet 43 of this embodiment, the linear structures 106 may form prisms, hairlines, lenticulars, or diffraction gratings. In this way, by combining them with the recesses 105 having an approximately inverted square pyramid shape, it is possible to reliably increase the synergistic effect of the light diffusion effect.

[0071] In the light diffusion sheet 43 of this embodiment, the recesses 105 are arranged in a two-dimensional matrix, and the arrangement direction may intersect with the extension direction of the linear structures 106. In this way, the synergistic effect of the light diffusion effect can be increased over a wide range of the apex angle θ of the recesses 105.

[0072] The backlight unit 40 of this embodiment is incorporated into a liquid crystal display device 50, and guides light emitted from a plurality of light sources 42 toward the display screen 50a. The backlight unit 40 includes a light diffusion sheet 43 of this embodiment between the display screen 50a and the light sources 42. This improves the luminance uniformity of the light diffusion sheet 43, and therefore allows for reductions in the thickness of the light diffusion sheet 43 and the number of layers thereof as the display device becomes thinner.

[0073] In the backlight unit 40 of this embodiment, the plurality of light sources 42 may be disposed on a reflecting sheet 41 provided on the opposite side of the display screen 50a from the light diffusing sheet 43. In this case, the light is further diffused by multiple reflections between the light diffusing sheet 43 and the reflecting sheet 41, further improving the in-plane luminance uniformity.

[0074] In the backlight unit 40 of this embodiment, a plurality of light diffusion sheets 43 may be stacked and disposed between the display screen 50a and the plurality of light sources 42. In this way, the use of a plurality of light diffusion sheets 43 can further improve in-plane luminance uniformity. In this case, in the stacked light diffusion sheets 43, the extension direction of the plurality of linear structures 106 in one light diffusion sheet 43 may intersect with the extension direction of the plurality of linear structures 106 in another light diffusion sheet 43. In this way, the occurrence of moiré (interference fringes) can be suppressed.

[0075] In the backlight unit 40 of this embodiment, the distance between the plurality of light sources 42 and the light diffusion sheet 43 may be 0 mm or more and 1 mm or less. In this way, even if a sufficient distance cannot be secured between the light sources and the sheet due to a thin design, the diffusion performance of the light diffusion sheet 43 of this embodiment can prevent deterioration of in-plane luminance uniformity.

[0076] The liquid crystal display device 50 of this embodiment includes the backlight unit 40 of this embodiment and a liquid crystal display panel 5. Therefore, the backlight unit 40 can improve in-plane luminance uniformity, and therefore the in-plane luminance uniformity can be maintained even when the thickness of the light diffusion sheet 43 or the number of layers is reduced as a result of further thinning. The same effect can be obtained in information devices (personal computers, mobile phones, etc.) incorporating the liquid crystal display device 50 of this embodiment.

[0077] In this embodiment, a direct-type backlight unit in which a plurality of light sources 42 are distributed on the rear 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 sources 42 and the light diffusion sheet 43. However, reducing this distance can easily cause a phenomenon in which the brightness of the display screen 50a in the areas between the distributed light sources 42 is lower than that of other areas (brightness unevenness).

[0078] In contrast, use of the light diffusion sheet 43 of this embodiment is useful for suppressing brightness unevenness. In particular, in view of future thinning of small and medium-sized liquid crystal displays, the usefulness of the light diffusion sheet 43 of this embodiment is considered to become even more pronounced when the distance between the light source 42 and the light diffusion sheet (lower light diffusion sheet) 43 is set to 15 mm or less, preferably 10 mm or less, more preferably 5 mm or less, even more preferably 2 mm or less, and ultimately 0 mm.

[0079] <First Example> A first example will be described below. As evaluation samples serving as the first example of the above-mentioned light diffusion sheet 43, samples with apex angles θ of the inverted pyramid shapes forming the recesses 105 of 100° and 120° were prepared, as shown in Table 1. In each sample, the inverted pyramid shapes and linear structures 106 (prism shapes) were transferred onto the base layer 101 made of polycarbonate using an acrylate UV-curable resin.

[0080] [Table 1]

[0081] As shown in Table 1, the height of the inverted pyramid shape was set to 50 μm for all evaluation samples. As a result, the arrangement pitch of the inverted pyramid shapes was 119 μm for samples with an inverted pyramid apex angle θ of 100°, and the arrangement pitch of the inverted pyramid shapes was 180 μm for samples with an inverted pyramid apex angle θ of 120°.

[0082] Furthermore, for each sample with an inverted pyramid shape apex angle θ of 100° and 120°, two types were prepared: one with a base layer 101 thickness of 70 μm and a prism shape apex angle (hereinafter also referred to as prism angle) of 64° that constitutes linear structure 106, and the other with a base layer 101 thickness of 90 μm and a prism angle of 90°. In the sample with a prism angle of 64°, the height of the prism shapes was 50 μm and the arrangement pitch of the prism shapes was 62 μm. In the sample with a prism angle of 90°, the height of the prism shapes was 12.5 μm and the arrangement pitch of the prism shapes was 25 μm.

[0083] In Table 1, the apex angle θ, height, and pitch of the inverted pyramid shape, as well as the apex angle, height, and pitch of the prism shape, are values ​​obtained from the dimensions of the mold used to produce those shapes.

[0084] As an evaluation sample serving as a comparative example, one was prepared in which the apex angle θ of the inverted pyramid shape was 80° (height: 50 μm, pitch: 84 μm) and the prism angles were 64° and 90° (the height and pitch of the prism shape were the same as those described above), as shown in Table 1. Furthermore, as another evaluation sample serving as a comparative example, one was prepared in which the apex angle θ of the inverted pyramid shape was 80°, 90°, 100°, and 120° (the height and pitch of the inverted pyramid shape were the same as those described above except for 90°), the thickness of the base layer 101 was 70 μm, and there were no prisms (corresponding to a prism angle of 180°), i.e., no second diffusion layer 103 was formed, as shown in Table 1. In the sample in which the apex angle θ of the inverted pyramid shape was 90°, the height and arrangement pitch of the inverted pyramid shape were 50 μm and 100 μm, respectively.

[0085] The in-plane luminance uniformity of the evaluation samples of the first example and comparative example shown in Table 1 was evaluated using the backlight unit 40 shown in Figure 2 configured as follows. A blue LED array arranged at a 3 mm pitch was used as the multiple light sources 42. Three evaluation samples (light diffusion sheets 43) with the same configuration and in the same orientation (with the same extension direction of the linear structures 106) were stacked and used. The total thickness of each sample when the three sheets were stacked is shown in Table 1. A transparent glass plate was placed on the light diffusion sheet (upper light diffusion sheet) 47 to prevent the sheets constituting the backlight unit 40 from floating.

[0086] The luminance of the backlight unit 40 constructed as described above was measured in the vertically upward direction (from the LED array toward the glass plate) using a 2D colorimeter UA-200 manufactured by Topcon Technohouse. The obtained 2D luminance distribution image was then corrected for variations in the luminance intensity of each LED and filtered to suppress bright and dark spot noise caused by foreign matter, after which the average and standard deviation of the luminance of all pixels were calculated. Finally, the "in-plane luminance uniformity" was defined as "average luminance value / standard deviation of luminance" and the in-plane luminance uniformity of the evaluation samples of the first example and the comparative example was calculated. The in-plane luminance uniformity was evaluated both when the samples were stacked with the inverted pyramid shape (recess 105) facing the light exit surface (in the orientation shown in Figure 3 ) and when the samples were stacked with the inverted pyramid shape (recess 105) facing the light entrance surface (inverted from the orientation shown in Figure 3 ).

[0087] Figure 8 and Table 2 show the results of evaluating the in-plane luminance uniformity of the evaluation samples of the first example and the comparative example. Note that "upper inverted pyramid" in Figure 8 and "(top)" in Table 2 indicate that the inverted pyramid shape is on the light exit surface side, and "lower inverted pyramid" in Figure 8 and "(bottom)" in Table 2 indicate that the inverted pyramid shape is on the light entrance surface side. Furthermore, Table 2 omits the calculated value of in-plane luminance uniformity when the apex angle θ of the inverted pyramid shape is 90°.

[0088] [Table 2]

[0089] As shown in FIG. 8 and Table 2, the in-plane luminance uniformity of the first example, which included inverted pyramids with apex angles of 100° and 120° and prisms, was generally higher than that of the comparative examples, which included inverted pyramids with apex angles of 80° or no prisms. Specifically, in the comparative example without prisms (a sample with a flat surface and a prism angle of 180°), the in-plane luminance uniformity decreased as the inverted pyramid apex angle increased. In contrast, when prisms were included, the in-plane luminance uniformity increased as the inverted pyramid apex angle and the prism angle increased. In particular, in the first example, which included inverted pyramids with apex angles of 120° and prisms with prism angles of 90°, the in-plane luminance uniformity was high, exceeding 200, regardless of whether the inverted pyramids were located on the light exit surface or the light entrance surface.

[0090] <Second Example> A second example will now be described. As evaluation samples of the second example of light diffusion sheet 43, samples were prepared in which the apex angle θ of the inverted pyramid shape forming recesses 105 (hereinafter also referred to as pyramid apex angle) was 80°, 90°, 100°, 120°, 140°, and 160°, as shown in Table 3. In each sample, the inverted pyramid shape or linear structure 106 (prism shape) was transferred onto base layer 101 made of polycarbonate using an acrylate UV-curable resin.

[0091] [Table 3]

[0092] As shown in Table 3, the height of the inverted pyramid shapes was set to 50 μm for all evaluation samples. As a result, the arrangement pitch of the inverted pyramid shapes was 84 μm for the sample with a pyramid apex angle of 80°, 100 μm for the sample with a pyramid apex angle of 90°, 118 μm for the sample with a pyramid apex angle of 100°, 172 μm for the sample with a pyramid apex angle of 120°, 275 μm for the sample with a pyramid apex angle of 140°, and 568 μm for the sample with a pyramid apex angle of 160°.

[0093] Furthermore, for each sample with a pyramid apex angle of 80° to 160°, four types were prepared, each having a base layer 101 thickness of 50 μm and apex angles of the prism shapes forming linear structures 106 (hereinafter also referred to as prism apex angles) of 80°, 90°, 100°, and 120°. For each sample with a prism apex angle, the height of the prism shapes was 50 μm, and the sample with an 80° prism apex angle had an arrangement pitch of 84 μm, the sample with a 90° prism apex angle had an arrangement pitch of 100 μm, the sample with a 100° prism apex angle had an arrangement pitch of 118 μm, and the sample with a 120° prism apex angle had an arrangement pitch of 172 μm.

[0094] In Table 3, the apex angle, height, and pitch of the inverted pyramid shape and the apex angle, height, and pitch of the prism shape are values ​​obtained from the dimensions of the mold used to produce those shapes.

[0095] The in-plane luminance uniformity of the evaluation sample of Example 2 shown in Table 3 was evaluated using a backlight unit 40 configured as shown in FIGS. 9 and 10 . In FIGS. 9 and 10 , the same components as those in the backlight unit 40 shown in FIG. 2 and the light diffusion sheet 43 shown in FIG. 3 are denoted by the same reference numerals. In the backlight unit 40 shown in FIG. 2 , three light diffusion sheets 43 with the same structure were laminated, whereas in the backlight unit 40 shown in FIG. 9 , two light diffusion sheets 43 with the same structure were laminated. In the backlight unit 40 shown in FIG. 2 , the light diffusion sheet 43 was arranged so that its first surface 43 a (the surface on which the recesses 105 were formed) served as the light exit surface, as shown in FIG. 3 . In the backlight unit 40 shown in FIG. 9 , the light diffusion sheet 43 was arranged so that its first surface 43 a (the surface on which the recesses 105 were formed) served as the light entrance surface, as shown in FIG. 10 . For each evaluation sample (light diffusion sheet 43), two sheets were laminated with the linear structures 106 extending in the same direction. The total thickness of each sample when two sheets were stacked is shown in Table 3. A blue LED array arranged at a pitch of 3 mm was used as the multiple light sources 42, and a transparent glass plate was placed on top of the light diffusion sheet (upper light diffusion sheet) 47 to prevent the sheets that make up the backlight unit 40 from floating.

[0096] In the backlight unit 40 configured as above, the luminance (average value) and in-plane luminance uniformity were calculated in the same manner as in Example 1. Figures 11 and 12 show the results of evaluating the in-plane luminance uniformity and luminance (average value) of the evaluation sample of Example 2.

[0097] As shown in Figure 11, when the prism apex angle is 95° or less, it was found that excellent in-plane luminance uniformity can be obtained by setting the pyramid apex angle between 110° and 130°. From a practical standpoint, the prism apex angle may be set to approximately 60° or more.

[0098] Furthermore, as shown in FIG. 11, when the prism apex angle is 95° or more, it was found that excellent in-plane luminance uniformity can be obtained by setting the pyramid apex angle to be between 85° and 95°.

[0099] Furthermore, as shown in Figure 12, for all evaluation samples with different prism apex angles, it was found that by setting the pyramid apex angle to between 130° and 150°, it was possible to increase the luminance while improving the luminance uniformity capability.

[0100] <Third Example> Hereinafter, a description will be given of Example 3. As an evaluation sample of Example 3 of the light diffusion sheet 43, similar to Example 2, each sample shown in Table 3 was used.

[0101] The in-plane luminance uniformity of the evaluation sample of Example 3 was evaluated using a backlight unit 40 configured as shown in FIG. 9. In Example 3, similar to Example 2, two layers of light diffusion sheets 43 with the same structure were laminated on the backlight unit 40 shown in FIG. 9. In Example 2, the light diffusion sheet 43 was positioned so that the first surface 43a (the surface on which the recesses 105 were formed) served as the light incident surface, as shown in FIG. 10. In Example 3, similar to Example 1, the light diffusion sheet 43 was positioned so that the first surface 43a (the surface on which the recesses 105 were formed) served as the light exit surface, as shown in FIG. 3. For each evaluation sample (light diffusion sheet 43), two sheets were laminated so that the extension directions of the linear structures 106 were aligned. The total thickness of each sample when two sheets were laminated is shown in Table 3. A blue LED array arranged at a 3 mm pitch was used as the multiple light sources 42. A transparent glass plate was placed on the light diffusion sheet (upper light diffusion sheet) 47 to prevent the sheets constituting the backlight unit 40 from floating.

[0102] In the backlight unit 40 configured as above, the luminance (average value) and in-plane luminance uniformity were calculated in the same manner as in Example 1. Figures 13 and 14 show the results of evaluating the in-plane luminance uniformity and luminance (average value) of the evaluation sample of Example 3.

[0103] As shown in Figure 13, when the prism apex angle is 95° or less, it was found that excellent in-plane luminance uniformity can be obtained by setting the pyramid apex angle between 110° and 130°. From a practical standpoint, the prism apex angle may be set to approximately 60° or more.

[0104] Furthermore, as shown in FIG. 13, when the prism apex angle is 95° or more, it was found that excellent in-plane luminance uniformity can be obtained by setting the pyramid apex angle to be between 85° and 95°.

[0105] 14, when the prism apex angle is 110° or less, the brightness is slightly reduced when the pyramid apex angle is set to 150° or more, whereas when the prism apex angle is 110° or more, the brightness is increased when the pyramid apex angle is set to 130° or more. Thus, the brightness of the third embodiment showed a different tendency from that of the second embodiment shown in FIG.

[0106] Next, Tables 4 and 5 show the results of evaluating the in-plane luminance uniformity and luminance (average value) for various combinations of evaluation samples of the third embodiment, including configurations in which the pyramid apex angle or prism apex angle is different between the light diffusion sheet 43 on the light incident side (lower side) and the light diffusion sheet 43 on the light output side (upper side). The unit of luminance shown in Table 5 is cd / m. 2 is.

[0107] [Table 4]

[0108] [Table 5]

[0109] As shown in Tables 4 and 5, in the third embodiment, it was found that both the in-plane brightness uniformity and brightness tended to improve overall when the pyramid apex angle of the light diffusion sheet 43 on the light output side was made smaller than the pyramid apex angle of the light diffusion sheet 43 on the light input side.

[0110] Similar evaluations of in-plane luminance uniformity and luminance (average value) were carried out for various combinations of the evaluation samples of the second embodiment described above, and the results are shown in Tables 6 and 7. The unit of luminance shown in Table 7 is cd / m 2 is.

[0111] [Table 6]

[0112] [Table 7]

[0113] As shown in Tables 6 and 7, in the second embodiment, the same tendency as in the third embodiment shown in Table 5 was observed in terms of luminance, but the same tendency as in the third embodiment shown in Table 4 was not observed in terms of in-plane luminance uniformity.

[0114] (Other embodiments) Although embodiments (including examples; the same applies hereinafter) of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the disclosure. In other words, the description of the above-described embodiments is merely illustrative in nature and is not intended to limit the present disclosure, its applications, or its uses. [Explanation of symbols]

[0115] 1 TFT substrate 2 CF board 3 Liquid crystal layer 5 LCD display panel 6 First polarizing plate 7 Second polarizing plate 40 Backlight unit 41 Reflective sheet 42 Light source 43 Light diffusion sheet (lower light diffusion sheet) 43a 1st page 43b 2nd side 44 Color Conversion Sheet 45 First prism sheet 46 Second prism sheet 47 Light diffusion sheet (upper light diffusion sheet) 50 LCD display device 50a display screen 101 Base material layer 102 First diffusion layer 103 Second diffusion layer 105 Recess 106 Linear Structure

Claims

1. A light diffusion sheet used in a backlight unit incorporated in a liquid crystal display device to guide light emitted from a plurality of light sources toward a display screen, It has a first surface that serves as a light exit surface and a second surface that serves as a light entrance surface, a plurality of recesses having a substantially inverted quadrangular pyramid shape are provided on one of the first surface and the second surface; a plurality of linear structures extending in a predetermined direction are provided on the other of the first surface and the second surface; the plurality of linear structures form a prism, The apex angle of the plurality of recesses is equal to or greater than 130° and equal to or less than 150°. Light diffusion sheet.

2. The plurality of recesses are arranged in a two-dimensional matrix, and the arrangement direction intersects with the predetermined direction. The light diffusing sheet according to claim 1 .

3. A backlight unit that is incorporated into a liquid crystal display device and guides light emitted from a plurality of light sources to a display screen, The light diffusing sheet according to claim 1 or 2 is provided between the display screen and the plurality of light sources. Backlight unit.

4. The plurality of light sources are disposed on a reflecting sheet provided on the opposite side of the display screen from the light diffusing sheet. The backlight unit according to claim 3 .

5. The light diffusion sheet is a laminate of a plurality of sheets and is disposed between the display screen and the plurality of light sources. The backlight unit according to claim 3 .

6. the light diffusion sheets stacked in plurality include a first light diffusion sheet and a second light diffusion sheet, The extending direction of the plurality of linear structures in the first light diffusion sheet intersects with the extending direction of the plurality of linear structures in the second light diffusion sheet. The backlight unit according to claim 5 .

7. Further, another light diffusion sheet is provided between the display screen and the light diffusion sheet, a plurality of other recesses each having a substantially inverted quadrangular pyramid shape are provided on one surface of the other light diffusion sheet; The apex angles of the other recesses are smaller than the apex angles of the recesses. The backlight unit according to claim 3 .

8. The distance between the plurality of light sources and the light diffusion sheet is 1 mm or less. The backlight unit according to claim 3 .

9. The backlight unit according to claim 3; A liquid crystal display panel is provided. LCD display device.

10. An information device comprising the liquid crystal display device according to claim 9.

Images