Light diffusers, backlight units, liquid crystal displays, and information tools.

Abstract

A plurality of substantially inverted quadrangular pyramid-shaped recesses 44c are provided on one surface of a light-diffusing sheet 44, and a plurality of linear structures 64 extending in a predetermined direction are provided on the other surface. The opening shapes of the plurality of recesses 44c are substantially quadrilateral shapes having a pair of opposing angles of 95° or more and 130° or less.

Description

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

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

[0002] Liquid crystal display devices (hereinafter also referred to as LCDs) are widely used as display devices for various information devices such as smartphones, tablet devices, virtual reality (VR) goggles, etc. The most common backlights for LCD displays are either edge-light, in which a light source is placed near the side of the LCD panel, or direct-light, in which a light source is placed behind the LCD panel.

[0003] An edge-lit backlight unit includes a light guide plate, a light source that directs light into the edge of the light guide plate, and an optical sheet laminated on the light guide plate (see Patent Document 1). The optical sheet has functions such as changing the angle of light from the light source and diffusing light, and multiple optical sheets including a light diffusion sheet may be used in combination.

[0004] Japanese Patent Application Laid-Open No. 2017-22059

[0005] Light diffusion sheets utilize the diffusion that occurs when an uneven surface is given to the sheet surface or when fine particles with a refractive index different from that of the sheet substrate are dispersed within the sheet substrate to diffuse light and make the brightness on the display screen uniform.

[0006] However, conventionally, when an attempt is made to improve the luminance uniformity of a light diffusion sheet, there has been a problem in that the luminance itself is reduced.

[0007] An object of the present disclosure is to provide a light diffusion sheet that can suppress a decrease in brightness.

[0008] In order to achieve the above-mentioned object, the light diffusion sheet according to the present disclosure is a light diffusion sheet having a first surface which serves as a light exit surface and a second surface which serves as a light entrance surface, wherein one of the first surface and the second surface has a plurality of recesses each having a substantially inverted quadrangular pyramid shape, and the other of the first surface and the second surface has a plurality of linear structures extending in a predetermined direction, and the opening shapes of the recesses are substantially quadrilaterals, each of a pair of opposing angles of 95° or more and 130° or less.

[0009] The light diffusion sheet according to the present disclosure can increase brightness compared to when a pair of opposing angles in the substantially quadrilateral opening shape of the recess are each less than 95° or more than 130°.

[0010] In the present disclosure, the term "light diffusion sheet" encompasses a plate-shaped "light diffusion plate" and a film-shaped "light diffusion film."

[0011] In the light diffusion sheet according to the present disclosure, when each of the pair of angles is 100° or more and 120° or less, the brightness can be further increased.

[0012] In the light diffusion sheet according to the present disclosure, if the approximate quadrilateral is an approximate rhombus, the light diffusion sheet can be easily manufactured.

[0013] In the light diffusion sheet according to the present disclosure, when the plurality of linear structures form a prism, a hairline, a lenticular, or a diffraction grating, when the sheet is placed in an edge-lit backlight unit, light emitted from a light source provided at the end in a direction approximately parallel to the display screen can be guided to the display screen.

[0014] The backlight unit according to the present disclosure is an edge-lit backlight unit that is incorporated into a liquid crystal display device and guides light emitted from a light source to a display screen, and comprises a light-guiding member having the light source provided at its side edge, and a light-diffusing sheet according to the present disclosure that is provided between the display screen and the light-guiding member, and the light-diffusing sheet is arranged with the multiple recesses facing toward the display screen.

[0015] The backlight unit according to the present disclosure includes the light diffusion sheet according to the present disclosure described above, and therefore can make the brightness uniform while suppressing a decrease in brightness.

[0016] In the backlight unit according to the present disclosure, if the light guide member is disposed on a reflecting member provided on the opposite side of the display screen from the light diffusion sheet, the brightness can be further increased.

[0017] In the backlight unit according to the present disclosure, when the longer of the two diagonals of the approximate quadrangle is substantially parallel to the light emission direction of the light source, brightness can be increased compared to other arrangements.

[0018] In the backlight unit according to the present disclosure, when the direction in which the plurality of linear structures extend is substantially parallel to the light emission direction of the light source, light incident on the light diffusion sheet from the light-guiding member can be refracted toward the display screen at a more favorable angle compared to other arrangements.

[0019] In the backlight unit according to the present disclosure, the angle formed by the longer of the two diagonals of the approximately quadrangle and the light output direction of the light source may be between 5° and 20°. In this way, even when the angle formed by the extension direction of the plurality of linear structures and the light output direction of the light source is between 5° and 20° in order to suppress the occurrence of moire, it is possible to increase the brightness compared to other arrangements.

[0020] In the backlight unit according to the present disclosure, when the angle between the direction in which the plurality of linear structures extend and the light output direction of the light source is between 5° and 20°, the occurrence of moire can be suppressed and brightness uniformity can be improved compared to other arrangements.

[0021] In the backlight unit according to the present disclosure, if a brightness enhancing sheet is provided between the display screen and the light diffusing sheet, the brightness can be further increased.

[0022] 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.

[0023] The liquid crystal display device according to the present disclosure includes the backlight unit according to the present disclosure described above, and therefore can achieve uniform brightness while suppressing a decrease in brightness.

[0024] An information device according to the present disclosure includes the liquid crystal display device according to the present disclosure.

[0025] According to the information device according to the present disclosure, since the information device includes the liquid crystal display device according to the present disclosure, it is possible to make the brightness uniform while suppressing a decrease in brightness.

[0026] According to the technology of the present disclosure, it is possible to provide a light diffusion sheet capable of suppressing a decrease in brightness, as well as a backlight unit, a liquid crystal display device, and an information device that use the light diffusion sheet.

[0027] FIG. 1 is a schematic cross-sectional view illustrating a liquid crystal display device according to an embodiment. FIG. 2 is a schematic cross-sectional view and a plan view illustrating the configuration of a backlight unit according to an embodiment. FIG. 3 is a schematic cross-sectional view of a light diffusion sheet according to an embodiment. FIG. 4 is a perspective view illustrating an inverted pyramid layer of a light diffusion sheet according to an embodiment. FIG. 5 is a diagram illustrating the shape of the inverted pyramid layer of a light diffusion sheet according to an embodiment. FIG. 6 is a diagram illustrating the opening shape of recesses in the inverted pyramid layer of a light diffusion sheet according to an embodiment. FIG. 7 is a diagram illustrating the shape of a linear structure layer (when the linear structures form prisms) of a light diffusion sheet according to an embodiment. FIG. 8 is a cross-sectional view illustrating variations of the linear structure layer of a light diffusion sheet according to an embodiment, where (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. FIG. 9 is a diagram illustrating a structure for suppressing moiré in a light diffusion sheet according to an embodiment. FIG. 10 is a diagram illustrating another structure for suppressing moiré in a light diffusion sheet according to an embodiment. FIG. 11 is a diagram showing the results of examining the change in brightness when the quadrilateral shape of the recessed opening of the inverted pyramid layer of the light diffusion sheet is changed in the example.

[0028] 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.

[0029] <Liquid Crystal Display Device> FIG. 1 is a schematic cross-sectional view illustrating a liquid crystal display device 50 according to this embodiment.

[0030] As shown in Figure 1, the liquid crystal display device 50 of this embodiment includes a liquid crystal display panel 5, a first polarizer 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizer 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 polarizer 6.

[0031] The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 that are disposed so as to face each other, and a liquid crystal layer 3 that is disposed between the TFT substrate 1 and the CF substrate 2 .

[0032] 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 respectively 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.

[0033] The backlight unit 40 is an edge-light type backlight unit that guides light 48 emitted from a light source 41 provided at an end portion and directed generally parallel to the liquid crystal display panel 5 toward the liquid crystal display panel 5 .

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

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

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

[0037] <Backlight Unit> FIG. 2 shows an example of the configuration of the backlight unit 40 according to this embodiment.

[0038] As shown in Fig. 2 (left cross-sectional view), the backlight unit 40 is configured by laminating a surface light-emitting section 47, a light diffusion sheet 44, a first prism sheet 45, and a second prism sheet 46 in this order. Although Fig. 2 shows the components spaced apart, the components may be substantially in contact with each other in the backlight unit 40. Furthermore, Fig. 2 shows a schematic cross section of each component, but the cutting direction of some components may differ from the direction shown in the drawing.

[0039] The first prism sheet 45 and the second prism sheet 46 concentrate the light from the surface light-emitting portion 47 toward the display screen 50a, thereby contributing to high brightness over the entire surface of the liquid crystal display panel 5. However, in order for the prism sheets 45 and 46 to function as brightness-enhancing sheets, it is desirable that light be incident on the prism sheets 45 and 46 at an angle within a predetermined range.

[0040] On the other hand, since the surface light emitting unit 47 is an edge light type having the light source 41 at its edge, the light emitted from the surface light emitting unit 47 is emitted at an angle nearly parallel to the display screen 50a. Therefore, if the first prism sheet 45 and the second prism sheet 46 were provided directly on the surface light emitting unit 47, the angle at which the light is incident on the prism sheets 45 and 46 would not necessarily be a desirable angle, which could result in a decrease in brightness.

[0041] Therefore, in this embodiment, the light diffusion sheet 44 is disposed between the surface light emitting section 47 and the first prism sheet 45, and a linear structure layer 63 (described later) is provided on the light incident surface of the light diffusion sheet 44, thereby refracting the light emitted from the surface light emitting section 47 toward the first prism sheet 45 and causing the light to enter the prism sheets 45 and 46 at a desired angle. This enables the backlight unit 40 to achieve uniform and high-brightness light emission.

[0042] The right diagram of FIG. 2 schematically shows a planar configuration of the stacked components as viewed from the stacking direction (the vertical direction of the cross-sectional view on the left of FIG. 2 ). These plan views are shown according to the orientation in which the components are actually stacked in the backlight unit 40. Details of the individual components will be described later, but the orientation of the stacked components is set as follows. First, the direction in which light 48 is emitted from the light source 41, the extension direction of the lenticular lenses 43 a in the light guide plate 43 of the surface-emitting unit 47, and the extension direction of the prism ridges 44 b in the linear structure layer 63 of the light diffusion sheet 44 are all parallel to one another. Furthermore, the longer of the two diagonals of the quadrilateral (diamond-shaped in this example) that forms the opening shape of the recess 44 c in the inverted pyramid layer 62 of the light diffusion sheet 44 is parallel to the prism ridges 44 b in the linear structure layer 63. Furthermore, the prism ridges 45a of the first prism sheet 45 and the prism ridges 46a of the second prism sheet 46 are perpendicular to each other, and the prism ridges 45a and the prism ridges 44b of the linear structure layer 63 of the light diffusion sheet 44 are perpendicular to each other.

[0043] In addition, the terms "parallel" and "orthogonal" used in this disclosure include not only geometrically strict parallel and orthogonal, but also cases where they can be considered to be substantially parallel and orthogonal within the range of industrial tolerance or within the range where the effects of the technology of this disclosure are not lost. In other words, it is permissible for the angle formed by the two directions to deviate from 0° (in the case of parallel) or 90° (in the case of orthogonal). The permissible degree of "deviation" is 10° or less, preferably 5° or less, more preferably 3° or less, and even more preferably 1° or less.

[0044] Each component of the backlight unit 40 will be described in detail below.

[0045] <Surface Light Emitting Unit> The surface light emitting unit 47 includes a reflective sheet 42, which is a reflective member, a light guide plate 43, which is a light guide member, laminated thereon, and a light source 41 provided on a side edge of the light guide plate 43. The light source 41, reflective sheet 42, and light guide plate 43 may be housed in close contact inside a frame without being adhered to each other. The light source 41 causes light 48 to enter the light guide plate 43 substantially parallel to the surface of the light guide plate 43. The light guide plate 43 guides the light 48 in the opposite direction from the light source 41 and emits the light toward the light diffusion sheet 44 at a relatively small angle relative to the surface of the light guide plate 43. The reflective sheet 42 reflects the light emitted in the opposite direction from the light diffusion sheet 44 and directs it toward the light diffusion sheet 44.

[0046] The reflective sheet 42 is made of, for example, a white polyethylene terephthalate resin film, a silver-deposited film, or the like. The light guide plate 43 may be a lenticular lens sheet made of, for example, polycarbonate, polyethylene terephthalate, acrylic resin, or the like. In this case, each lenticular lens 43a (see the plan view in FIG. 2 ) preferably extends in the direction of incidence of the light 48. Since the light 48 is emitted from the light source 41 with a certain degree of divergence, the direction of incidence of the light 48 is the direction in which the center of the light 48 emitted from the light source 41 travels, which is, for example, a direction perpendicular to the side end face of the light guide plate 43 on which the light source 41 is provided.

[0047] The planar shape of the light guide plate 43 may be basically rectangular, but may also be octagonal with chamfered corners. The light guide plate 43 may have an edge of, for example, several centimeters, and a plurality of light sources 41 may be arranged in a row along the edge.

[0048] The type of light source 41 is not particularly limited, and may be, for example, an LED element or a laser element. From the viewpoint of cost, productivity, etc., an LED element may be used. When an LED element is used, it may include multiple LED chips. The light source 41 may be a white light source. When a colored light source such as a blue light source is used, a color conversion sheet is arranged in the backlight unit 40 in addition to the light diffusion sheet 44 and the prism sheets 45 and 46.

[0049] <Light Diffusion Sheet> As shown in Figures 2 and 3 , the first surface (the light-emitting surface in this example) of the light diffusion sheet 44 is provided with a plurality of recesses 44c formed in the shape of an approximately inverted quadrangular pyramid, and the second surface (the light-receiving surface in this example) is provided with a plurality of linear structures 63 formed adjacent to each other and having an isosceles triangular cross section. In the example shown in Figure 3 , the light diffusion sheet 44 has a base layer 61, an inverted pyramid layer 62 provided on one surface of the base layer 61, and a linear structure layer 63 provided on the other surface of the base layer 61. In this example, the linear structure layer 63 is arranged so as to face the surface light-emitting portion 47. The overall thickness of the light diffusion sheet 44 may be, for example, approximately 50 μm or more and approximately 300 μm or less.

[0050] [Substrate Layer] The substrate layer 61 must transmit light, and is formed primarily from a transparent (e.g., colorless and transparent) synthetic resin. The primary component of the substrate layer 61 is not particularly limited, and examples thereof include polycarbonate, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polystyrene, polyolefin, cellulose acetate, and weather-resistant vinyl chloride. The term "primary component" refers to the component with the highest content, e.g., a content of 50% by mass or more. The substrate layer 61 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 include, for example, inorganic particles such as silica, titanium oxide, aluminum hydroxide, and barium sulfate, or organic particles such as acrylic, acrylonitrile, silicone, polystyrene, and polyamide.

[0051] The lower limit of the average thickness of the substrate layer 61 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 substrate layer 61 is preferably about 500 μm, more preferably about 250 μm, and even more preferably about 180 μm. If the average thickness of the substrate layer 61 is less than the lower limit, curling may occur when the inverted pyramid layer 62 or the linear structure layer 63 is formed. Conversely, if the average thickness of the substrate layer 61 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.

[0052] [Inverted Pyramid Layer] The inverted pyramid layer 62 has a concave-convex shape that diffuses light, and in this example, a plurality of recesses 44c that are approximately inverted square pyramid-shaped (inverted pyramid-shaped). Since the inverted pyramid layer 62 needs to transmit light, it may be formed primarily from a transparent (e.g., colorless and transparent) synthetic resin. The inverted pyramid layer 62 may be molded integrally with the base material layer 61 during extrusion molding of the base resin that forms the base material layer 61, or may be molded separately using an ultraviolet-curable resin or the like after molding the base material layer 61.

[0053] The recesses 44c may be arranged in a two-dimensional matrix, as shown in FIG. 4 , for example. Adjacent recesses 44c are separated by ridges 44a. The ridges 44a extend along the direction in which the recesses 44c are arranged. The arrangement pitch of the recesses 44c may be, for example, approximately 50 μm or more and approximately 500 μm or less. The center 44e of each recess 44c (the apex of the inverted pyramid that is the deepest part) is the deepest part of the recess 44c. The center 44e of each recess 44c may reach the surface of the base layer 61. In other words, the depth of each recess 44c may be equal to the thickness of the inverted pyramid layer 62. Note that, for simplicity, FIG. 4 illustrates an example in which the recesses 44c are arranged in a 4×4 matrix, but the actual number of recesses 44c arranged is much greater.

[0054] 5 shows the shape of the inverted pyramid layer 62. Fig. 5 shows a plan view of the inverted pyramid layer 62 and a cross-sectional view (the position of the cross-section is indicated by a dashed line in the plan view) parallel to one edge line 44 a and passing through the center 44 e of the recess 44 c. In this cross-section, the remaining portion 65 from which the recess 44 c has been removed is triangular, and the side that contacts the base layer 61 is the base.

[0055] The height h of the remaining portions 65 (depth of the recesses 44c) may be approximately 10 μm or more and approximately 200 μm or less. The pitch p of the remaining portions 65 (arrangement pitch of the recesses 44c) may be approximately 20 μm or more and approximately 400 μm or less. The apex angle θ of the remaining portions 65 may be approximately 60° or more and approximately 150° or less.

[0056] In the present embodiment, the concave and convex portions 44c are arranged in a two-dimensional matrix, each having an inverted pyramid shape (approximately an inverted square pyramid shape), but the concave portions 44c may be arranged randomly to the extent that the effects of the technology of the present disclosure are not lost. In the present example, the concave portions 44c are arranged regularly in two dimensions without gaps, but instead, for example, the ridges 44a may be formed wide to provide gaps between the concave portions 44c.

[0057] In this disclosure, the term "approximately inverted square pyramid" is used in consideration of the difficulty of forming a geometrically strict inverted square pyramid recess using conventional shape transfer technology. However, "approximately" means that it can be approximated, and "approximately inverted square pyramid" refers to a shape that can be approximated to an inverted square pyramid. For example, an "inverted square pyramid trapezoid" with a flat bottom is also included in the "approximately inverted polygonal pyramid" as long as the effect of the technology disclosed herein is not lost. Furthermore, shapes that deform from an "inverted square pyramid" within the range of unavoidable shape variations due to processing accuracy in industrial production are also included in the "approximately inverted square pyramid."

[0058] One feature of this embodiment is that the opening shape of the recess 44c is a substantially quadrilateral (e.g., a substantially rhombus) with a pair of opposing corners each having an angle of 95° to 130°, preferably 100° to 120°. The opening shape of the recess 44c is a shape surrounded by the ridge lines 44a of the recess 44c. In the example shown in FIG. 6 , the quadrilateral that is the opening shape of the recess 44c is a rhombus 100. The rhombus 100 has a long diagonal line (hereinafter also referred to as a long axis) 101 and a short diagonal line (hereinafter also referred to as a short axis) 102. As described above, in this example, the recesses 44c are arranged so that the long axis 101 of the rhombus 100 is substantially parallel to the prism ridge lines 44b of the linear structure layer 63, i.e., the direction in which light 48 is emitted from the light source 41. The angle φ between the minor axis 102 and the ridge line 44a of the rhombus 100 is 47.5° or more and 65° or less, preferably 50° or more and 60° or less. The rhombus 100 does not have to be a true rhombus as long as the angle φ is within the above-mentioned angle range. For example, the rhombus 100 may be a quadrilateral that is asymmetric with respect to the major axis 101 or the minor axis 102, depending on the light emission characteristics of the surface light-emitting unit 47.

[0059] In this disclosure, the terms "approximately quadrilateral" or "approximately rhombus" are used in consideration of the difficulty of forming recesses with geometrically strict quadrilateral or rhombus openings using conventional shape transfer techniques. However, "approximately quadrilateral" or "approximately rhombus" includes shapes that can be considered to be true or substantially quadrilateral or rhombus. Furthermore, "approximately" means that it can be approximated, and "approximately quadrilateral" or "approximately rhombus" refers to a shape that can be approximated to a quadrilateral or rhombus. For example, quadrilaterals or rhombus with chipped or rounded corners are also included in the "approximately quadrilateral" or "approximately rhombus" definition, provided that the effects of the technology disclosed herein are not lost. Furthermore, shapes that deform from a quadrilateral or rhombus within the range of unavoidable shape variations due to processing accuracy in industrial production are also included in the "approximately quadrilateral" or "approximately rhombus" definition.

[0060] In addition, in a cross section that appears when the recess 44c is cut along the long axis 101 of the rhombus 100 in a plane (longitudinal cross section) perpendicular to the placement surface (horizontal plane) of the light diffusion sheet 44, the angle formed by the oblique sides of the recess 44c is preferably 110° or more and 135° or less, and more preferably 113° or more and 128° or less. This has the effect of improving brightness.

[0061] [Linear Structure Layer] In the linear structure layer 63 of this example, a plurality of grooves having an isosceles triangular cross section are arranged adjacent to each other, and a triangular prism portion sandwiched between a pair of adjacent grooves forms a linear structure (a prism in this example) 64. The linear structure layer 63 is formed using, for example, a UV-curable acrylic resin.

[0062] As described above, the prism ridges 44 b of each linear structure 64 are arranged so as to extend in the same direction as the lenticular lenses 43 a of the surface light emitting unit 47 , that is, the direction in which light 48 is emitted from the light source 41 .

[0063] 7 shows the shapes of the linear structure layer 63 and the linear structures 64. Fig. 7 shows a plan view of the linear structure layer 63 and a cross-sectional view perpendicular to the prism ridge line 44b (the position of the cross-section is indicated by a dashed line in the plan view). The cross-sectional shape of the prism that constitutes each linear structure 64 is an isosceles triangle, and the side that contacts the base layer 61 is the base.

[0064] The height h of the linear structures 64 may be approximately 8 μm or more and approximately 100 μm or less. The pitch p of the linear structures 64 may be approximately 15 μm or more and approximately 200 μm or less. The apex angle θ of the linear structures 64 is preferably approximately 60° or more and approximately 120° or less, and more preferably approximately 80° or more and approximately 100° or less.

[0065] In the example shown in FIG. 7 , the cross-sectional shape of the linear structure 64 is shown as a geometrically strict isosceles triangle, and adjacent linear structures 64 are shown as being in contact with each other. However, the shape may differ from the illustrated shape as long as the effects of the technology disclosed herein are not lost or within the range of unavoidable shape variations due to processing accuracy in industrial production. For example, the apex (prism ridge 44b) may be rounded or may be a flat trapezoid. In this case, the apex angle θ is the intersection angle when the sides extending from both ends of the base are extended, assuming a triangle. Furthermore, adjacent linear structures 64 may be arranged with a gap between them.

[0066] In the example shown in FIG. 7 , prisms are provided as the linear structures 64, but the linear structures 64 are not particularly limited as long as they include convex bodies extending in a predetermined direction. For example, as shown in FIG. 8 , the linear structures 64 may be hairlines ( FIG. 8( a) ), lenticulars ( FIG. 8( b) ), diffraction gratings ( FIG. 8( c) ), or the like. The hairlines forming the linear structures 64 may be, for example, elongated stripes created by polishing the surface of the base layer 61 in a single direction. The lenticulars forming the linear structures 64 may be, for example, fine, elongated, semi-cylindrical convex lenses provided on the surface of the base layer 61. The diffraction grating forming the linear structures 64 may be, for example, a grating pattern consisting of linear concaves and convexities periodically arranged on the surface of the base layer 61.

[0067] In the case of any shape of linear structure 64, including the prism in this example, if the direction in which each linear structure 64 extends is substantially parallel to the light emission direction of light source 41, light incident on light diffusion sheet 44 from light guide plate 43 can be refracted toward prism sheets 45 and 46 at a more preferable angle than in other arrangements.

[0068] In the backlight unit 40 of this embodiment, moiré may occur on the light-emitting surface, resulting in a decrease in brightness uniformity. Modifications of the linear structure layer 63 for suppressing this are shown in Figures 9 and 10 . The configurations shown in Figures 9 and 10 can suppress the occurrence of moiré and improve brightness uniformity. Note that, because moiré occurs due to, for example, the dimensional relationship between the various components, such as the surface light-emitting section 47, the light guide plate 43, and the light diffusion sheet 44, the configurations shown in Figures 9 and 10 may not be necessary.

[0069] 9, the grooves and the resulting linear structures (prisms) 64 are formed in a repeatedly curved wave shape in the linear structure layer 63 of the light diffusion sheet 44. As a result, the prism ridges 44b also become wave-shaped.

[0070] In Fig. 10, the extension direction of the grooves and linear structures 64 (prism ridges 44b) is not parallel to the emission direction of light 48 from the surface-emitting unit 47 (indicated by the arrow in the figure), but forms an angle of, for example, about 5° to 20°. Compared to the configuration shown in Fig. 2 and other figures, the configuration shown in Fig. 10 has the linear structure layer 63 arranged on the base layer 61 rotated by a slight angle (for example, 5° to 20°) around the sheet normal direction as its central axis. In this case, in the inverted pyramid layer 62 of the light diffusion sheet 44, if the extension direction of the long axes 101 of the rhombuses 100 also forms an angle of, for example, about 5° to 20° with respect to the emission direction of light 48, similar to the extension direction of the prism ridges 44b, then brightness can be improved compared to other arrangements.

[0071] <Method for Manufacturing Light Diffusion Sheet> The method for manufacturing the light diffusion sheet 44 is not particularly limited, but the light diffusion sheet 44 can be manufactured using, for example, any of the manufacturing methods described below.

[0072] In the first manufacturing method, a pellet-shaped base resin (plastic resin) is first formed into a resin film using an extruder. Then, two metal rolls are used, one of which has a convex pyramid shape on its surface, and the other of which has a plurality of linear concave shapes extending in a predetermined direction on its surface. These rolls are then pressed against the resin film to produce a light diffusion sheet 44 having an inverted pyramid shape (concave portions 44c) on one side and linear convex shapes (linear structures 64) on the other side. In this manufacturing method, the base layer 61, the inverted pyramid layer 62, and the linear structure layer 63 are integrally formed.

[0073] In the second manufacturing method, pellet-shaped base resin (plastic resin) is first 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 is a mirror-finished roll. These rolls are then pressed against the resin film to produce a sheet (a sheet in which the base layer 61 and the inverted pyramidal layer 62 are integrated) with an inverted pyramidal shape (recess 44c) on one side and a mirror-finished surface on the other side. The sheet is then fed between a pair of pressure rolls, and a UV-curable resin (a resin composition for forming protrusions) is applied to the back surface of the base layer 61 just before the pair of pressure rolls. Here, the pressure roll that comes into contact with the UV-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 64), which are the inverse shapes of the plurality of linear recesses, are transferred to the opposite side of the sheet to which the inverted pyramid shapes (recesses 44c) have been imparted. In this manufacturing method, only the linear structure layer 63 is formed separately.

[0074] In the third manufacturing method, pelletized base resin (plastic resin) is first formed into a resin film using an extrusion molding machine. Then, two metal rolls are used: one with a surface having a plurality of linear recesses extending in a predetermined direction, and the other with a mirrored surface. These rolls are then pressed against the resin film to produce a sheet (a sheet in which the base layer 61 and the linear structure layer 63 are integrated) with a plurality of linear protrusions (linear structures 64) on one side, which are the inverse shape of the linear recesses, and a mirrored surface on the other side. Next, the sheet is fed between a pair of pressure rolls, and an ultraviolet-curable resin (a protrusion-forming resin composition) is supplied to the surface side of the base layer 61 just before the pair of pressure rolls. Here, the pressure roll that contacts the ultraviolet-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 (recesses 44c), which are the inverted shapes of the plurality of substantially square pyramid-shaped protrusions, are transferred to the opposite surface of the sheet to which the plurality of linear protrusions (linear structures 64) have been added. In this manufacturing method, only the inverted pyramid layer 62 is formed separately.

[0075] In the fourth manufacturing method, a base layer 61 containing, for example, polyethylene terephthalate as a main component is first prepared. While feeding the base layer 61 between a pair of first pressure rolls, a first ultraviolet-curable resin (a protrusion-forming resin composition) is supplied to the back surface of the base layer 61 immediately before the pair of first pressure rolls. Here, the first pressure roll that contacts 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 61 with the supplied first ultraviolet-curable resin between the pair of first pressure rolls, the first ultraviolet-curable resin is cured by irradiating it with ultraviolet light, thereby producing a sheet (a sheet in which the base layer 61 and the linear structure layer 63 are laminated) on the back surface of the base layer 61, on which a plurality of linear protrusions (linear structures 64) that are the inverse shapes of the linear recesses are transferred. Next, while feeding the sheet between a pair of second pressure rolls, a second ultraviolet-curable resin (a protrusion-forming resin composition) is supplied to the surface side of the sheet onto which the multiple linear protrusions (linear structures 64) have been transferred, just before the pair of second pressure rolls. The second pressure roll that contacts 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 pyramid shapes (recesses 44c), which are the inverted shapes of the multiple approximately square pyramidal protrusions, are transferred to the opposite surface of the sheet onto which the multiple linear protrusions (linear structures 64) have been transferred. In this manufacturing method, the base layer 61, the inverted pyramid layer 62, and the linear structure layer 63 are each formed as separate bodies.

[0076] In the fifth manufacturing method, a pellet-shaped base resin (plastic resin) is first formed into a resin film using an extrusion molding machine. Then, two flat metal plates are used: one having a convex pyramidal shape on its surface, and the other having a plurality of linear concave shapes extending in a predetermined direction on its surface. These flat metal plates are then heat-pressed onto the resin film to produce a light diffusion sheet 44 having an inverted pyramidal shape (concave portions 44c) on one side and linear convex shapes (linear structures 64) on the other side. In this manufacturing method, the base layer 61, the inverted pyramidal layer 62, and the linear structure layer 63 are integrally formed.

[0077] 2, a first prism sheet 45 and a second prism sheet 46 are provided as brightness enhancement sheets on the light diffusion sheet 44. The prism sheets 45 and 46 have a configuration in which a plurality of grooves each having an isosceles triangular cross section are arranged adjacent to each other, and a prism is formed by a triangular prism portion sandwiched between a pair of adjacent grooves. The prism sheets 45 and 46 may be, for example, a polyethylene terephthalate (PET) film with a prism shape formed using a UV-curable acrylic resin.

[0078] As shown in the cross-sectional view of FIG. 2, the prisms of the first and second prism sheets 45 and 46 are both arranged on the opposite side of the surface light-emitting portion 47 .

[0079] 2, the first prism sheet 45 is disposed so that its prism ridges 45a are perpendicular to the prism ridges 44b of the light diffusion sheet 44, and the second prism sheet 46 is disposed so that its prism ridges 46a are parallel to the prism ridges 44b of the light diffusion sheet 44. Therefore, the first and second prism sheets 45 and 46 are disposed so that their respective prism ridges 45a and 46a are perpendicular to each other. A plurality of protrusions 46b may be provided on the rear surface of the second prism sheet 46 (the surface opposite to the surface on which the prisms are provided) to prevent the occurrence of moire and the visibility of foreign matter.

[0080] Instead of using the two prism sheets 45 and 46 as described above as brightness enhancement sheets, one or more prism sheets may be used, or a brightness enhancement sheet of a different type than the prism sheets may be used.

[0081] <Features of the embodiment> According to the light diffusion sheet 44 of the present embodiment described above, a plurality of recesses 44c having a substantially inverted quadrangular pyramid shape are provided on one surface, a plurality of linear structures 64 extending in a predetermined direction are provided on the other surface, and the opening shape of each recess 44c is configured as a substantially quadrangle with a pair of opposing angles of 95° to 130°. Therefore, it is possible to increase the brightness compared to when a pair of opposing angles in the substantially quadrangle opening shape of the recess 44c are each less than 95° or more than 130°.

[0082] In the light diffusion sheet 44 of this embodiment, if each of the pair of angles is 100° or more and 120° or less, the brightness can be further increased.

[0083] In the light diffusion sheet 44 of this embodiment, if the opening shape of the recesses 44c is substantially rhombic, the light diffusion sheet 44 can be easily manufactured.

[0084] In the light diffusion sheet 44 of this embodiment, if the linear structures 64 form a prism, hairline, lenticular, or diffraction grating, when the light diffusion sheet 44 is placed in an edge-lit backlight unit 40, light emitted from the light source 41 approximately parallel to the display screen 50a can be guided to the display screen 50a.

[0085] The edge-lit backlight unit 40 of this embodiment is incorporated into a liquid crystal display device 50 and guides light emitted from a light source 41 to a display screen 50a. The backlight unit 40 includes a light guide plate 43 having the light source 41 provided at its side edge, and a light diffusion sheet 44 provided between the display screen 50a and the light guide plate 43, with the recess 44c of the light diffusion sheet 44 facing the display screen 50a.

[0086] According to the backlight unit 40 of this embodiment, since the light diffusion sheet 44 is provided, it is possible to make the brightness uniform while suppressing a decrease in brightness.

[0087] In the backlight unit 40 of this embodiment, if the light guide plate 43 is disposed on the reflective sheet 42 provided on the opposite side of the display screen 50a from the light diffusion sheet 44, the brightness can be further increased.

[0088] In the backlight unit 40 of this embodiment, when the longer diagonal 101 of the two diagonals 101, 102 in the approximately quadrilateral opening shape of the recess 44c is substantially parallel to the light emission direction of the light source 41, the brightness can be increased compared to other arrangements.

[0089] In the backlight unit 40 of this embodiment, when the direction in which the linear structure 64 extends and the light emission direction of the light source 41 are substantially parallel, the light incident on the light diffusion sheet 44 from the light guide plate 43 can be refracted at a more preferable angle toward the display screen 50a compared to other arrangements.

[0090] In the backlight unit 40 of the present embodiment, the angle formed by the longer diagonal 101 of the two diagonals 101, 102 of the approximately quadrilateral opening shape of the recess 44c and the light output direction of the light source 41 may be 5° or more and 20° or less. In this way, even when the angle formed by the extension direction of the linear structure 64 and the light output direction of the light source 41 is 5° or more and 20° or less to suppress the occurrence of moire, it is possible to increase the brightness compared to other arrangements.

[0091] In the backlight unit 40 of this embodiment, when the angle between the extension direction of the linear structure 64 and the light emission direction of the light source 41 is 5° or more and 20° or less, the occurrence of moire can be suppressed and brightness uniformity can be improved compared to other arrangements.

[0092] In the backlight unit 40 of this embodiment, if a brightness improving sheet (prism sheets 45, 46 in this example) is provided between the display screen 50a and the light diffusing sheet 44, the brightness can be further increased.

[0093] The liquid crystal display device 50 of this embodiment includes the backlight unit 40, and therefore can achieve uniform brightness while suppressing a decrease in brightness. The same applies to various information devices that include the liquid crystal display device 50.

[0094] In the examples, evaluation samples of the light diffusion sheet 44 were prepared by varying the angle φ shown in FIG. 6 from 5° to 85° in increments of 5°, and the luminance of each sample sheet was evaluated in a configuration basically similar to that of the backlight unit 40 shown in FIG. 2 .

[0095] Specifically, the thickness of the base layer 61 of the light diffusion sheet 44 was set to 82 μm, and an inverted pyramid layer 62 was provided on one surface of the base layer 61, and a linear structure layer 63 was provided on the other surface.

[0096] The depth of each recess 44c in the inverted pyramid layer 62 (the height of the remaining portion 65) was set to 20 μm, and the direction of the diagonal line corresponding to the long axis 101 shown in Fig. 6 was aligned with the light output direction of the light source 41. The inverted pyramid shape of each recess 44c was formed by preparing prisms with a height of 20 μm and a pitch of 40 μm (i.e., an apex angle of 90°) and combining these prisms by intersecting them at an angle 2φ, which is twice the angle φ shown in Fig. 6. Therefore, in the opening shape of the recess 44c of each sample sheet (see Figure 6), the length of each diagonal line corresponding to the major axis 101 and the minor axis 102 changes depending on the angle φ, and specifically, the "length of the diagonal line corresponding to the major axis 101" = 2 x (depth 20 μm) / cos φ = 40 / cos φ [μm], and the "length of the diagonal line corresponding to the minor axis 102" = 2 x (depth 20 μm) / sin φ = 40 / sin φ [μm].

[0097] The linear structures 64 of the linear structure layer 63 were prisms with an apex angle of 90° and a height of 12 μm, and the direction in which the prism ridges 44 b extended was aligned with the light output direction of the light source 41 .

[0098] The first prism sheet 45 was prepared by providing a 66 μm thick base layer with a mirrored light entrance surface and a prism with a 90° apex angle and a height of 12 μm (refractive index 1.68) on the light exit surface, with the prism ridge 45 a perpendicular to the light exit direction of the light source 41.

[0099] The second prism sheet 46 was prepared by providing a 96 μm thick base layer with a mirrored light entrance surface and a prism with a 90° apex angle and a height of 12 μm (refractive index 1.67) on the light exit surface, with the prism ridge 46 a aligned with the light exit direction of the light source 41.

[0100] In addition, to evaluate the brightness of each sample sheet, instead of an edge-light type surface light emitting unit 47 in which a light source 41 is provided at the side edge of a light guide plate 43, a monochromatic surface light source (LED) with a wavelength of 450 nm and a light emitting area of ​​10 mm x 10 mm, which has the same light distribution characteristics (light output angle characteristics) and brightness value as the surface light emitting unit 47, was used without placing a reflective sheet.

[0101] In the backlight unit configuration described above, sample sheets with different angles φ shown in FIG. 6 were placed, and the luminance in the vertically upward direction (the direction from the surface light source toward the display screen) was measured over an 8 mm x 8 mm area using a two-dimensional spectroradiometer SR-5000HS manufactured by Topcon Technohouse Corporation. The average luminance value of all pixels was then calculated for the obtained two-dimensional luminance distribution image. The results are shown in FIG. 11. Note that in FIG. 11, the luminance is shown as a relative luminance based on the value when φ is 45° (when the opening shape of the recess 44c is square). For reference, FIG. 11 also shows the relationship between the planar configuration shown in FIG. 6 and the traveling direction of light 48 emitted from the light source 41.

[0102] 11 , the brightness was improved when φ was in the range of 47.5° to 65° (wherein each of a pair of opposing angles in the quadrilateral opening shape of recess 44c was in the range of 95° to 130°) compared to the brightness when φ was 45°. In particular, when φ was in the range of 50° to 60° (wherein each of a pair of opposing angles in the quadrilateral opening shape of recess 44c was in the range of 100° to 120°), the brightness was improved by 10% or more compared to the brightness when φ was 45°, and the maximum brightness when φ was 55° was improved by 12% or more.

[0103] (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 descriptions of the above-described embodiments are merely exemplary in nature and are not intended to limit the present disclosure, its applications, or its uses.

[0104] According to the technology of the present disclosure, a light diffusion sheet capable of suppressing a decrease in brightness can be provided, and therefore, the light diffusion sheet is useful as a backlight unit, a liquid crystal display device, and an information device.

[0105] REFERENCE SIGNS LIST 1 TFT substrate 2 CF substrate 3 Liquid crystal layer 5 Liquid crystal display panel 6 First polarizer 7 Second polarizer 40 Backlight unit 41 Light source 42 Reflective sheet 43 Light guide plate 43a Lenticular lens 44 Light diffusion sheet 44a Ridge line 44b Prism ridge line 44c Recess 44e Recess center 45 First prism sheet 45a Prism ridge line 46 Second prism sheet 46a Prism ridge line 46b Protrusion 47 Surface emitting portion 48 Light 50 Liquid crystal display device 50a Display screen 61 Base layer 62 Inverted pyramid layer 63 Linear structure layer 64 Linear structure 65 Remaining portion 100 Diamond 101 Long diagonal 102 Short diagonal

Claims

DEPCT691. A diffuser plate with a first surface acting as the emitting surface and a second surface acting as the light-entry surface, in which a number of significant inverted square pyramid-shaped concave sections are arranged on one of the first and second surfaces, a number of linear structures extending in predetermined directions are arranged on the other of the first and second surfaces, and a number of open shapes of the concave sections hold significant tetralateral shapes with pairs of opposite angles of 95 degrees or more and 130 degrees or less, respectively.

2. A diffuser plate according to claim 1, in which pairs of angles are 100 degrees or more and 120 degrees or less, respectively.

3. A diffuser plate according to claim 1, in which the significant tetralateral shapes are significant rhombuses.

4. A diffuser plate according to claim 1, in which a number of linear structures form prisms, slender lines, lenticulars, or diffraction gratings. 5.An edge-light backlight unit integrated into a liquid crystal display device to guide light emitted from a light source to the display screen, comprising: a light-guiding element with the light source provided on its side end; and a diffuser plate under one of claims 1 through 4, provided between the display screen and the light-guiding element, where the diffuser plate is used in such a manner that a number of notches are oriented toward the display screen.

6. A backlight unit under claim 5, where the light-guiding element is used on a reflective element provided on the opposite side of the display screen as seen in the diffuser plate.

7. A backlight unit under claim 5, where the longer lines in the two diagonals of a tetrahedron are significantly parallel and the emission direction of the light source is significantly parallel.

8. A backlight unit under claim 5, where the protrusion directions of a number of linear structures and the emission direction of the light source are significantly parallel. 9.Backlit unit under claim 5, where the angle formed by the longer line in the two diagonals of a tetrahedron is significantly greater and the emission direction of the light source is 5 degrees or greater and 20 degrees or less.

10. Backlit unit under claim 5, where the angle formed by the projection direction of a number of linear structures and the emission direction of the light source is 5 degrees or greater and 20 degrees or less.

11. Backlit unit under claim 5, where an illuminating plate is provided between the display screen and the light diffuser plate.

12. Liquid crystal display device incorporating: a backlit unit under claim 5; and a liquid crystal display panel.

13. Information device incorporating a liquid crystal display device under claim 12;

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