Backlight unit, liquid crystal display device, and information device

Abstract

To provide a light diffusion sheet that can suppress deterioration in luminance.SOLUTION: A light diffusion sheet 44 is provided with: a plurality of recesses 44c having a substantially inverted quadrangular pyramid shape on one side; and a plurality of linear structures 64 extending in a predetermined direction on the other side. The recesses 44c have an opening shape that is a substantially quadrilateral shape where a pair of opposite angles are respectively 95° or more and 130° 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] Liquid crystal display devices (hereinafter sometimes referred to as liquid crystal displays) are widely used as display devices for various information devices such as smartphones, tablet terminals, VR (Virtual Reality) goggles, etc. The mainstream backlights for liquid crystal displays are either the edge-light type, in which a light source is placed near the side of the liquid crystal panel, or the direct type, in which a light source is placed on the back of the liquid crystal panel.

[0003] An edge-light type 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 are sometimes used in combination. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-22059 A Summary of the Invention [Problem to be solved by the invention]

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

[0006] However, in the past, when an attempt was made to improve the luminance uniformity capability of a light diffusion sheet, there was a problem that the luminance itself was reduced.

[0007] An object of the present disclosure is to provide a light diffusion sheet capable of suppressing a decrease in luminance. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the light diffusion sheet of 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, wherein one of the first surface and the second surface has a plurality of recesses having an approximately inverted 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 shape of the plurality of recesses is an approximately quadrilateral with a pair of opposing angles each of which is equal to or greater than 95° and equal to or less than 130°.

[0009] The light diffusion sheet according to the present disclosure can increase luminance compared to a case in which a pair of opposing angles in the approximate quadrilateral shape of the opening 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 equal to or greater than 100° and equal to or less than 120°, the luminance can be further increased.

[0012] In the light diffusion sheet according to the present disclosure, when 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 multiple linear structures form a prism, hairline, lenticular, or diffraction grating, when the sheet is placed in an edge-light type 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 end, and a light diffusion sheet according to the present disclosure provided between the display screen and the light-guiding member, and the light diffusion sheet is positioned with the multiple recesses facing towards 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 achieve uniform brightness while suppressing a decrease in brightness.

[0016] In the backlight unit according to the present disclosure, when 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, the brightness can be increased compared to other arrangements.

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

[0019] In the backlight unit according to the present disclosure, the angle between the longer diagonal of the two diagonals of the approximate quadrangle and the light output direction of the light source may be 5° to 20°. In this way, even if the angle between the extension direction of the multiple linear structures and the light output direction of the light source is set to 5° to 20° in order to suppress the occurrence of moire, the luminance can be increased compared to other arrangements.

[0020] In the backlight unit according to the present disclosure, when the angle between the direction in which the multiple linear structures extend and the light emission direction of the light source is between 5° or more and 20° or less, 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] According to the liquid crystal display device according to the present disclosure, since the liquid crystal display device includes the backlight unit according to the present disclosure described above, it is possible to make the brightness uniform while suppressing a decrease in the brightness.

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

[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 described above, it is possible to make the brightness uniform while suppressing a decrease in the brightness. Effect of the Invention

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

[0027] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a liquid crystal display device according to an embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view and a plan view illustrating the configuration of the backlight unit of the embodiment. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a light diffusion sheet according to an embodiment. [Figure 4] FIG. 4 is a perspective view showing an inverted pyramid layer of the light diffusion sheet according to the embodiment. [Diagram 5] FIG. 5 is a diagram illustrating the shape of an inverted pyramid layer of a light diffusion sheet according to an embodiment. [Figure 6] FIG. 6 is a diagram illustrating the shape of an opening of a recess in an inverted pyramid layer of a light diffusion sheet according to an embodiment. [Figure 7] FIG. 7 is a diagram for explaining the shape of a linear structure layer (when the linear structures form prisms) of a light diffusion sheet according to an embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing variations of the linear structure layer of the light diffusion sheet of the embodiment, where (a) shows the case where the linear structure forms a hairline, (b) shows the case where the linear structure forms a lenticular, and (c) shows the case where the linear structure forms a diffraction grating. [Figure 9] FIG. 9 is a diagram illustrating a structure for suppressing moire in the light diffusion sheet according to the embodiment. [Figure 10] FIG. 10 is a diagram illustrating another structure for suppressing moire in the light diffusion sheet according to the embodiment. [Figure 11] FIG. 11 is a diagram showing the results of investigating changes in luminance when the quadrilateral shape of the recessed opening of the inverted pyramid layer of the light diffusion sheet is changed in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] (Embodiment) Hereinafter, a light diffusion sheet, a backlight unit, a liquid crystal display device, and an information device according to the 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 idea of ​​the present disclosure.

[0029] <Liquid crystal display device> FIG. 1 is a schematic cross-sectional view illustrating a liquid crystal display device 50 of the present embodiment.

[0030] As shown in FIG. 1, the liquid crystal display device 50 of this embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 provided on the rear side of the liquid crystal display panel 5 via the first polarizing plate 6.

[0031] The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 disposed to face each other, and a liquid crystal layer 3 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 arranged to cover 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 arranged to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix arranged in a lattice on a glass substrate, color filters including a red layer, a green layer, and a blue layer arranged between each lattice of the black matrix, a common electrode arranged to cover the black matrix and the color filter, and an alignment film arranged to cover the common electrode. The liquid crystal layer 3 is made of a nematic liquid crystal material containing liquid crystal molecules having electro-optical properties. The first polarizing plate 6 and the second polarizing plate 7 include, for example, a polarizer layer having a polarization axis in one direction and a pair of protective layers arranged to sandwich 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, a rectangle or a square, but is not limited to this and may be any shape, such as a rectangle with rounded corners, an ellipse, 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 polarizing plate 6. The light with the adjusted transmittance is emitted through the second polarizing plate 7 to display an image.

[0036] The liquid crystal display device 50 of this embodiment is used as a display device incorporated into various information devices (e.g., in-vehicle devices such as car navigation systems, personal computers, mobile phones, portable information terminals such as notebook computers 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 a backlight unit 40 according to this embodiment.

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

[0039] The first prism sheet 45 and the second prism sheet 46 concentrate the light from the surface 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 improving 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 emitting unit 47 is an edge light type having the light source 41 at the end, the light emitted from the surface 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 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 may result in a decrease in brightness.

[0041] Therefore, in this embodiment, a light diffusion sheet 44 is disposed between the surface emission 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, so that the light emitted from the surface emission section 47 is refracted toward the first prism sheet 45, and the light is made to enter the prism sheets 45 and 46 at a desired angle. This enables the backlight unit 40 to achieve uniform and high-luminance light emission.

[0042] The right diagram of FIG. 2 shows a schematic planar configuration of each stacked component 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 direction in which each component is actually stacked in the backlight unit 40. Details of each component will be described later, but the direction of each stacked component is set as follows. First, the direction in which light 48 is emitted from the light source 41, the extension direction of the lenticular lens 43a in the light guide plate 43 of the surface light emitting section 47, and the extension direction of the prism ridge 44b in the linear structure layer 63 of the light diffusion sheet 44 are parallel to each other. In addition, the longer diagonal of the two diagonals of the quadrilateral (diamond in this example) that is the opening shape of the recess 44c in the inverted pyramid layer 62 of the light diffusion sheet 44 and the prism ridge 44b of the linear structure layer 63 are parallel to each other. 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 diffusing sheet 44 are perpendicular to each other.

[0043] In addition, the terms "parallel" and "orthogonal" in this disclosure include not only strict geometric parallel and orthogonal, but also substantially parallel and orthogonal within the range of industrial error or within the range in which the effect of the technology of this disclosure is not lost. In other words, it is permissible for the angle between the two directions to deviate from 0° (parallel) or 90° (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 now be described in detail.

[0045] <Surface emitting part> The surface light emitting unit 47 includes a reflection sheet 42 which is a reflection member, a light guide plate 43 which is a light guide member laminated thereon, and a light source 41 provided at a side end of the light guide plate 43. The light source 41, the reflection sheet 42, and the light guide plate 43 may be stored in close contact with each other inside a frame body without being bonded to each other. The light source 41 causes light 48 to enter the light guide plate 43 in a state substantially parallel to the surface of the light guide plate 43. The light guide plate 43 guides the light 48 in the opposite direction to the light source 41, and causes the light to exit toward the light diffusion sheet 44 at a relatively small angle with respect to the surface of the light guide plate 43. The reflection sheet 42 reflects the light exiting in the opposite direction to the light diffusion sheet 44, directing 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, for example, a lenticular lens sheet made of polycarbonate, polyethylene terephthalate, acrylic resin, or the like. In this case, it is preferable that each lenticular lens 43a (see the plan view of FIG. 2) extends in the direction in which the light 48 enters. Since the light 48 is emitted from the light source 41 with a certain degree of spread, the direction in which the light 48 enters is the direction in which the center of the light 48 emitted from the light source 41 advances, and 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 basically be a rectangle, but may also be an octagon with chamfered corners. The light guide plate 43 may have an edge of, for example, about several centimeters, and a plurality of light sources 41 may be arranged in a line 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, and may be an LED element from the viewpoint of cost, productivity, etc. When an LED element is used, it may include a plurality of 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 FIG. 2 and FIG. 3, a first surface (light output surface in this example) of the light diffusion sheet 44 is provided with a plurality of recesses 44c formed in a substantially inverted quadrangular pyramid shape, and a second surface (light input 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 FIG. 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 disposed so as to face the surface light emitting portion 47. The total thickness of the light diffusion sheet 44 may be, for example, about 50 μm or more and about 300 μm or less.

[0050] [Base material layer] The base layer 61 is formed mainly from a transparent (e.g., colorless and transparent) synthetic resin, since it is necessary to transmit light. The main component of the base layer 61 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, for example, a component with a content of 50 mass % or more. The base layer 61 may contain a diffusing agent or other additives, or may substantially not contain additives. The additives that can be contained are not particularly limited, and may be, for example, inorganic particles such as silica, titanium oxide, aluminum hydroxide, barium sulfate, or organic particles such as acrylic, acrylonitrile, silicone, polystyrene, polyamide, or the like.

[0051] The lower limit of the average thickness of the base 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 base 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 base 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 base 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 thickness. The "average thickness" refers to the average value of thicknesses at any 10 points.

[0052] [Inverted pyramid layer] The inverted pyramid layer 62 is provided with a concave-convex shape that diffuses light, in this example, a plurality of concave portions 44c each having a substantially inverted quadrangular pyramid shape (inverted pyramid shape). The inverted pyramid layer 62 needs to transmit light, so it may be formed mainly 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 material resin that becomes the base material layer 61, or may be molded separately using an ultraviolet curing resin or the like after molding of the base material layer 61.

[0053] The recesses 44c may be arranged in a two-dimensional matrix, for example, as shown in FIG. 4. Adjacent recesses 44c are partitioned 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, about 50 μm or more and about 500 μm or less. The center 44e of the 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 the recess 44c may reach the surface of the base layer 61. In other words, the depth of the 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 the recesses 44c arranged is much greater.

[0054] Fig. 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 parallel to one edge line 44a and passing through the center 44e of the recess 44c (the position of the cross-section is indicated by a dashed line in the plan view). In this cross-section, the remaining portion 65 from which the recess 44c is removed is triangular, and the side in contact with the base layer 61 is the base.

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

[0056] In this embodiment, the concave and convex shapes are provided by arranging the inverted pyramid-shaped (approximately inverted square pyramid-shaped) concaves 44c in a two-dimensional matrix, but the concaves 44c may be arranged randomly to the extent that the effect of the technology of the present disclosure is not lost. In this example, the concaves 44c are regularly arranged two-dimensionally without gaps, but instead, for example, the ridge 44a may be formed wide to provide gaps between the concaves 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 by a normal shape transfer technique, but the term "approximately inverted square pyramid" includes shapes that can be regarded as genuine or substantially inverted square pyramids. Furthermore, "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 of the present disclosure is not lost. Furthermore, shapes that are deformed from an "inverted square pyramid" within the range of unavoidable shape variations due to the processing accuracy of industrial production are also included in the "approximately inverted square pyramid".

[0058] As one of the features of this embodiment, 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° or more and 130° or less, preferably 100° or more and 120° or less. The opening shape of the recess 44c is a shape surrounded by the ridge line 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 line 44b of the linear structure layer 63, that is, the direction in which the light 48 is emitted from the light source 41. In the rhombus 100, the angle φ between the short axis 102 and the edge line 44a 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, depending on the light emission characteristics of the surface light-emitting unit 47, the rhombus 100 may be a quadrilateral that is asymmetric with respect to the long axis 101 or the short axis 102.

[0059] In this disclosure, in consideration of the difficulty of forming a recess having a geometrically strict quadrilateral or rhombus opening by a normal shape transfer technique, the term "approximate quadrilateral" or "approximate rhombus" is used, but "approximate quadrilateral" or "approximate rhombus" includes a shape that can be regarded as a true or substantial quadrilateral or rhombus. In addition, "approximate" means that it can be approximated, and "approximate quadrilateral" or "approximate rhombus" refers to a shape that can be approximated to a quadrilateral or rhombus. For example, a quadrilateral or rhombus with chipped or rounded corners is also included in the "approximate quadrilateral" or "approximate rhombus" as long as the effect of the technology of the present disclosure is not lost. In addition, a shape that is deformed from a quadrilateral or rhombus within the range of unavoidable shape variation due to the processing accuracy of industrial production is also included in the "approximate quadrilateral" or "approximate rhombus".

[0060] In addition, in a cross section that appears when cutting the recess 44c 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 between 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 provides the effect of improving the brightness.

[0061] [Linear structure layer] In the linear structure layer 63 of this example, a plurality of grooves having a cross section of an isosceles triangle are arranged adjacent to each other, and a triangular prism portion sandwiched between a pair of adjacent grooves constitutes 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 44b of each linear structure 64 are arranged so as to extend in the same direction as the extension direction of the lenticular lenses 43a of the surface emission unit 47, that is, the direction in which the light 48 is emitted from the light source 41.

[0063] Fig. 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 constituting each linear structure 64 is an isosceles triangle, and the side in contact with the base layer 61 is the base.

[0064] The height h of the linear structures 64 may be about 8 μm or more and about 100 μm or less. The pitch p of the linear structures 64 may be about 15 μm or more and about 200 μm or less. The apex angle θ of the linear structures 64 is preferably about 60° or more and about 120° or less, and more preferably about 80° or more and about 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 to be in contact with each other. However, the shape may be different from the illustrated shape as long as the effect of the technology of the present disclosure is not lost or the shape is within the range of inevitable variation 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. In addition, adjacent linear structures 64 may be arranged with a gap between them.

[0066] In the example shown in FIG. 7, a prism is provided as the linear structure 64, but the linear structure 64 is not particularly limited as long as it includes a convex body extending in a predetermined direction. For example, as shown in FIG. 8, the linear structure 64 may be configured as a hairline (FIG. 8(a)), a lenticular (FIG. 8(b)), a diffraction grating (FIG. 8(c)), or the like. The hairline that becomes the linear structure 64 may be, for example, a long and thin stripe generated by polishing the surface of the base layer 61 in a single direction. The lenticular that becomes the linear structure 64 may be, for example, a fine and long, semi-cylindrical convex lens body provided on the surface of the base layer 61. The diffraction grating that becomes the linear structure 64 may be, for example, a grating pattern consisting of linear concaves and convexes 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, when the extension direction of each linear structure 64 is substantially parallel to the light emission direction of light source 41, light entering light diffusion sheet 44 from light guide plate 43 can be refracted toward prism sheets 45, 46 at a more preferable angle than in other arrangements.

[0068] In the backlight unit 40 of the present embodiment, moire 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 Figs. 9 and 10. The configurations shown in Figs. 9 and 10 can suppress the occurrence of moire and improve brightness uniformity. Note that since moire occurs due to, for example, the relationship between the dimensions of each component such as the surface light-emitting section 47, the light guide plate 43, and the light diffusion sheet 44, the configurations shown in Figs. 9 and 10 may not be necessary.

[0069] 9, the grooves and the linear structures (prisms) 64 left by them 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 the light 48 from the surface light emitting unit 47 (indicated by an arrow in the figure), but forms an angle of, for example, about 5° to 20°. Compared to the configuration shown in FIG. 2, etc., the configuration shown in FIG. 10 is configured such that the linear structure layer 63 is arranged on the base material layer 61 by rotating a small angle (for example, 5° to 20°) with the sheet normal direction as the central axis. In this case, in the inverted pyramid layer 62 of the light diffusion sheet 44, if the extension direction of the long axis 101 of the rhombus 100 is also at an angle of, for example, about 5° to 20° with respect to the emission direction of the light 48, similar to the extension direction of the prism ridges 44b, the luminance can be improved compared to other arrangements.

[0071] <Manufacturing method of light diffusion sheet> The method for producing the light diffusion sheet 44 is not particularly limited, but for example, the light diffusion sheet 44 can be produced using any of the production methods described below.

[0072] In the first manufacturing method, first, a pellet-shaped base resin (plastic resin) is made into a resin film by an extrusion molding machine. Then, one of two metal rolls is used, one of which has a convex pyramid shape on its surface, and the other roll is used, one of which has a plurality of linear concave shapes extending in a predetermined direction on its surface, and both rolls are pressed against the resin film to produce a light diffusion sheet 44 having an inverted pyramid shape (concave 44c) on one side and linear convex shapes (linear structure 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, first, a pellet-shaped base resin (plastic resin) is made into a resin film by an extrusion molding machine. Then, one of two metal rolls is a roll having a convex pyramid shape on its surface, and the other roll is a mirror roll. The two rolls are pressed against the resin film to produce a sheet (a sheet in which the base layer 61 and the inverted pyramid layer 62 are integrated) having an inverted pyramid shape (recess 44c) on one side and a mirror surface on the other side. Next, while the sheet is sent between a pair of pressing rolls, an ultraviolet-curable resin (a resin composition for forming protrusions) is supplied to the back side of the base layer 61 just before the pair of pressing rolls. Here, a pressing roll that contacts the ultraviolet-curable resin has a plurality of linear recesses extending in a predetermined direction on its outer circumferential surface. The sheet to which the ultraviolet-curable resin has been applied is pressed by a pair of pressing 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 shape 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, first, a pellet-shaped base resin (plastic resin) is made into a resin film by an extrusion molding machine. Then, one of two metal rolls is a roll having a surface with a plurality of linear recesses extending in a predetermined direction, and the other roll is a mirror roll. The two rolls are 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) having a plurality of linear protrusions (linear structures 64) that are the inverted shape of the plurality of linear recesses on one side and a mirror surface on the other side. Next, while the sheet is sent between a pair of pressing rolls, an ultraviolet-curable resin (a resin composition for forming protrusions) is supplied to the surface side of the base layer 61 just before the pair of pressing rolls. Here, a pressing roll having a plurality of approximately square pyramid-shaped protrusions on the outer circumferential surface is used as the pressing roll that contacts the ultraviolet-curable resin. The sheet to which the ultraviolet-curable resin has been supplied is pressed by a pair of pressing 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, first, a base layer 61 mainly composed of, for example, polyethylene terephthalate is prepared. While sending this base layer 61 between a pair of first pressing rolls, a first ultraviolet curable resin (a resin composition for forming protrusions) is supplied to the back side of the base layer 61 immediately before the pair of first pressing rolls. Here, a first pressing roll having a plurality of linear recesses extending in a predetermined direction on its outer circumferential surface is used as the first pressing roll on the side in contact with the first ultraviolet curable resin. After pressing the base layer 61 to which the first ultraviolet curable resin has been supplied with the first ultraviolet curable resin with the pair of first pressing rolls, the first ultraviolet curable resin is cured by irradiating it with ultraviolet light, and a sheet (a sheet in which the base layer 61 and the linear structure layer 63 are laminated) is produced on the back side of the base layer 61, on which a plurality of linear convex shapes (linear structures 64) that are the inverted shapes of the linear concave shapes are transferred. Next, while the sheet is sent between a pair of second pressing rolls, a second ultraviolet curing resin (a resin composition for forming protrusions) is supplied to the surface side of the sheet to which the multiple linear convex shapes (linear structures 64) have been transferred just before the pair of second pressing rolls. The second pressing roll on the side in contact with the second ultraviolet curing resin has multiple approximately square pyramid-shaped convex portions on its outer circumferential surface. After pressing the sheet to which the second ultraviolet curing resin has been supplied with the second ultraviolet curing resin with the pair of second pressing rolls, the second ultraviolet curing resin is cured by irradiating ultraviolet light, and multiple inverted pyramid shapes (recesses 44c), which are the inverted shapes of the multiple approximately square pyramid-shaped convex portions, are transferred to the opposite surface side of the sheet to which the multiple linear protrusions (linear structures 64) have been imparted. In this manufacturing method, the base layer 61, the inverted pyramid layer 62, and the linear structure layer 63 are each formed as a separate body.

[0076] In the fifth manufacturing method, first, a pellet-shaped base resin (plastic resin) is made into a resin film by an extrusion molding machine. Then, one of the two metal flat plates is a metal flat plate having a convex pyramid shape on its surface, and the other is a metal flat plate having a plurality of linear concave shapes extending in a predetermined direction on its surface. The two metal flat plates are pressed (heat pressed) to the resin film to produce a light diffusion sheet 44 having an inverted pyramid shape (concave 44c) on one side and linear convex shapes (linear structure 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.

[0077] <Prism sheet> 2, a first prism sheet 45 and a second prism sheet 46 are provided as brightness enhancing 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 provided 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 PET (polyethylene terephthalate) film having a prism shape formed by 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 to 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) in order to prevent the occurrence of moire and the visibility of foreign objects.

[0080] Incidentally, instead of using the two prism sheets 45 and 46 as described above as the brightness enhancing sheets, only one prism sheet or three or more prism sheets may be used, or a brightness enhancing 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, one surface is provided with a plurality of recesses 44c having a substantially inverted pyramidal shape, the other surface is provided with a plurality of linear structures 64 extending in a predetermined direction, and the opening shape of each recess 44c is configured as a substantially quadrilateral with a pair of opposing angles each having an angle of 95° or more and 130° or less. Therefore, the brightness can be increased compared to the case where the opening shape of the recess 44c, which is a substantially quadrilateral, has a pair of opposing angles each less than 95° or more than 130°.

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

[0083] In the light diffusion sheet 44 of the present 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, when the linear structures 64 form a prism, a hairline, a lenticular, or a diffraction grating, when the light diffusion sheet 44 is arranged in an edge-light type 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-light type backlight unit 40 of this embodiment is incorporated in 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 one side thereof, and a light diffusion sheet 44 provided between the display screen 50a and the light guide plate 43, and the light diffusion sheet 44 is disposed with the recess 44c facing the display screen 50a.

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

[0087] In the backlight unit 40 of this embodiment, when 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 the present 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 extension direction of the linear structure 64 is substantially parallel to the light emission direction of the light source 41, the light incident on the light diffusion sheet 44 from the light guide plate 43 can be refracted toward the display screen 50a at a more preferable angle compared to other arrangements.

[0090] In the backlight unit 40 of the present embodiment, the angle between the longer diagonal 101 of the two diagonals 101, 102 in the substantially quadrilateral opening shape of the recess 44c and the light emission direction of the light source 41 may be 5° or more and 20° or less. In this way, even when the angle between the extension direction of the linear structure 64 and the light emission direction of the light source 41 is set to 5° or more and 20° or less in order to suppress the occurrence of moire, it is possible to increase the luminance 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 the present embodiment, if a brightness improving sheet (in this example, prism sheets 45, 46) is provided between the display screen 50a and the light diffusion sheet 44, the brightness can be further increased.

[0093] The liquid crystal display device 50 of the present embodiment includes the backlight unit 40, and therefore is capable of uniforming the luminance while suppressing a decrease in the luminance. The same is true for various information devices that include the liquid crystal display device 50.

[0094] <Example> 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 brightness 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 in which the diagonal line corresponding to the long axis 101 shown in Fig. 6 extends 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 corresponding to the long axis 101 and the short axis 102 changes depending on the angle φ, and specifically, the "length of the diagonal corresponding to the long axis 101" = 2 × (depth 20 μm) / cos φ = 40 / cos φ [μm], and the "length of the diagonal corresponding to the short axis 102" = 2 × (depth 20 μm) / sin φ = 40 / sin φ [μm].

[0097] As the linear structures 64 of the linear structure layer 63, prisms with an apex angle of 90° and a height of 12 μm were provided, and the extending direction of the prism ridge lines 44 b was aligned with the light output direction of the light source 41.

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

[0099] The second prism sheet 46 was prepared by preparing a 96 μm-thick base layer with a mirror-finished 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 46a 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 end 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, each sample sheet with different angles φ shown in FIG. 6 was placed, and the luminance in the vertical upward direction (direction from the surface light source toward the display screen) was measured in an area of ​​8 mm×8 mm using a two-dimensional spectroradiometer SR-5000HS manufactured by Topcon Technohouse. Next, the average value of the luminance of all pixels was calculated for the obtained two-dimensional luminance distribution image. The result is shown in FIG. 11. 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 luminance was improved when φ was in the range of 47.5° to 65° (wherein each of a pair of opposing corners in the quadrilateral opening shape of recess 44c is in the range of 95° to 130°) compared to when φ was 45°. In particular, when φ was in the range of 50° to 60° (wherein each of a pair of opposing corners in the quadrilateral opening shape of recess 44c is in the range of 100° to 120°), the luminance was improved by 10% or more compared to when φ was 45°, and the maximum luminance when φ was 55° was improved by 12% or more.

[0103] (Other embodiments) Although the embodiments of the present disclosure (including examples; the same applies below) have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the disclosure. In other words, the description of the above-described embodiments is essentially merely illustrative, and is not intended to limit the present disclosure, its applications, or its uses. [Industrial Applicability]

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

[0105] 1 TFT substrate 2 CF board 3 Liquid crystal layer 5 Liquid crystal display panel 6 First polarizing plate 7 Second polarizing plate 40 Backlight unit 41 Light source 42 Reflective sheet 43 Light guide plate 43a Lenticular lens 44 Light diffusion sheet 44a Ridgeline 44b Prism Ridge 44c Recess 44e Center of recess 45 First prism sheet 45a Prism Ridge 46 Second Prism Sheet 46a Prism Ridge 46b protrusion 47 Surface emitting part 48 light 50 LCD display device 50a display screen 61 Base material layer 62 Inverted Pyramid Layer 63 Linear structure layer 64 Linear Structure 65 Remainder 100 rhombus 101 Long Diagonal 102 Short Diagonal

Claims

1. An edge-lit backlight unit incorporated in a liquid crystal display device for guiding light emitted from a light source to a display screen, comprising: a light guide member provided with the light source at a side end; a light diffusion sheet provided between the display screen and the light guide member; and the light diffusion sheet has a first surface serving as a light emitting surface and a second surface serving as a light incident surface; a plurality of substantially inverted quadrangular recesses 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 opening shape of the plurality of recesses is a substantially quadrilateral with a pair of opposing angles each being 95° or more and 130° or less; the light diffusion sheet is arranged with the plurality of recesses facing the display screen; a backlight unit.

2. each of the pair of angles is 100° or more and 120° or less; the backlight unit according to Claim 1.

3. the substantially quadrilateral is a substantially rhombus; the backlight unit according to Claim 1.

4. the plurality of linear structures constitute a prism, a hairline, a lenticular, or a diffraction grating; the backlight unit according to Claim 1.

5. the light guide member is arranged on a reflection member provided on the opposite side of the display screen when viewed from the light diffusion sheet; the backlight unit according to Claim 1.

6. the longer diagonal of the two diagonals in the substantially quadrilateral is substantially parallel to the light emission direction of the light source; the backlight unit according to Claim 1.

7. the direction in which the plurality of linear structures extend is substantially parallel to the light emission direction of the light source; the backlight unit according to Claim 1.

8. the angle formed by the longer diagonal of the two diagonals in the substantially quadrilateral and the light emission direction of the light source is 5° or more and 20° or less; the backlight unit according to Claim 1.

9. the angle formed by the direction in which the plurality of linear structures extend and the light emission direction of the light source is 5° or more and 20° or less; the backlight unit according to Claim 1.

10. a brightness enhancement sheet is provided between the display screen and the light diffusion sheet; the backlight unit according to Claim 1.

11. a backlight unit according to any one of Claims 1 to 10, and a liquid crystal display panel; a liquid crystal display device.

12. an information device including the liquid crystal display device according to Claim 11.

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