Backlight unit, liquid crystal display device, and information apparatus

Abstract

The purpose of the present disclosure is to provide a novel backlight unit. A backlight unit (40) according to one aspect of the present disclosure comprises: a light guide plate (43); at least one light source (41); a first sheet (44) having a plurality of prisms (64a) extending in a first direction (d12); a second sheet (45) having a plurality of prisms (45a) extending in a second direction (d13); and a third sheet (46) having a plurality of prisms (46a) extending in a third direction (d14). The second direction and the third direction are substantially orthogonal to each other in a plan view. Angles X1 and X3 between the direction (d11) of extension of a light incident surface of the light guide plate and the first direction and the third direction in a plan view satisfy at least one of the following. 0°≦X3<95° and -10°≦X1-X3≦10° (1), 95°≦X3≦135° and -45°≦X1-X3≦45° (2), 135°<X3<180° and -10°≦X1-X3≦10° (3).

Description

Backlight unit, liquid crystal display device, and information equipment

[0001] This disclosure relates to a backlight unit, a liquid crystal display device, and information equipment.

[0002] Liquid crystal displays (LCDs) are widely used as display devices for various information equipment, including in-vehicle systems such as car navigation systems, personal computers, monitors, mobile phones, smartphones, laptops and tablets, portable game consoles, photocopiers, ticket vending machines, ATMs, and VR goggles. Two types of backlights are used for LCDs: the direct-lit type, where the light source is located behind the LCD panel, and the light guide plate type. In recent years, efforts have been actively made to reduce the thickness of LCDs, and many designs employing the light guide plate type have been proposed as they are suitable for thinning.

[0003] Furthermore, various backlight units have been developed from various viewpoints such as brightness intensity, brightness uniformity, and ease of assembly (for example, Patent Document 1 and Patent Document 2).

[0004] U.S. Patent Application Publication No. 2020 / 0379159

[0005] The characteristics required of a backlight unit vary depending on its application. Therefore, the development of new backlight units remains essential.

[0006] One aspect of this disclosure aims to provide a novel backlight unit.

[0007] In order to achieve the above object, the backlight unit according to Embodiment 1 of the present disclosure includes a light guide plate having a light incident surface and a light exit surface, at least one light source disposed on the light incident surface side of the light guide plate, and a first sheet laminated on the light exit surface side of the light guide plate. The first sheet has a light incident surface and a light exit surface facing each other, a first prism structure including a plurality of prisms extending in a first direction provided on the light incident surface side of the first sheet, and a light diffusion structure provided on the light exit surface side of the first sheet. A second sheet laminated on the light exit surface side of the first sheet, the second sheet having a light incident surface and a light exit surface facing each other, and a second prism structure including a plurality of prisms extending in a second direction provided on the light exit surface side of the second sheet. A third sheet laminated on the light exit surface side of the second sheet, the third sheet having a light incident surface and a light exit surface facing each other, and a third prism structure including a plurality of prisms extending in a third direction provided on the light exit surface side of the third sheet. The second direction and the third direction are substantially orthogonal to each other in a plan view, and the angles between the direction in which the light incident surface of the light guide plate extends in a plan view and the first direction and the third direction are X １ , , ３ ,

[0009] , ３ , , ３ ,

[0008] and X ３ When set as, X １ and X ３ Satisfy at least one of the following. (1) 0°≦X ３ <95°, and -10°≦X １ -X ３ ≦10° (2) 95°≦X ３ ≦135°, and -45°≦X １ -X ３ ≦45° (3) 135°<X ３ <180°, and -10°≦X １ -X ３ ≦10°

[0008] According to one aspect of the present disclosure, a novel backlight unit, a liquid crystal display device, and an information device can be provided.

[0009] Figure 1 is a schematic cross-sectional view illustrating an example of a liquid crystal display device according to an embodiment. Figure 2 is a schematic cross-sectional view and a plan view showing an example of the configuration of a backlight unit according to an embodiment. Figure 3 is a schematic cross-sectional view of the first sheet according to an embodiment. Figure 4 is a perspective view of a prism constituting the first prism structure according to an embodiment. Figure 5 is a schematic diagram showing how each layer of the backlight unit according to an embodiment overlaps. Figure 6 is a perspective view showing another example of the light diffusion structure according to an embodiment. Figure 7 is a perspective view showing another example of the light diffusion structure according to an embodiment. Figure 8 is a diagram showing another example of the shape of the edge of a prism constituting the first prism structure according to an embodiment. Figure 9 is a diagram showing another example of the shape of the edge of a prism constituting the first prism structure according to an embodiment. Figure 10 is a schematic cross-sectional view illustrating the configuration of a backlight unit according to an embodiment.

[0010] (Embodiment 1) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, 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.

[0011] In this disclosure, "sheet" refers to a general term for relatively thin, generally flattened shapes, and includes both plate-like and film-like materials.

[0012] <Liquid Crystal Display Device> As shown in Figure 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 back side of the liquid crystal display panel 5 via the first polarizing plate 6.

[0013] The liquid crystal display panel 5 comprises a TFT substrate 1 and a CF substrate 2 arranged facing each other, a liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) provided in the shape of a frame between the TFT substrate 1 and the CF substrate 2 to enclose the liquid crystal layer 3.

[0014] The backlight unit 40 is a side-edge type backlight unit that guides light 48 emitted substantially parallel to the liquid crystal display panel 5 by a light source 41 provided at the edge towards the liquid crystal display panel 5.

[0015] The shape of the display screen 50a of the liquid crystal display device 50, when viewed from the front (above in Figure 1), is generally a rectangle or a square, but is not limited to these; it may be a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or any other shape such as that of an instrument panel in an automobile.

[0016] In the liquid crystal display device 50, a predetermined voltage is applied to the liquid crystal layer 3 at each subpixel corresponding to each pixel electrode to change the orientation state of the liquid crystal layer 3. This adjusts the transmittance of the light incident from the backlight unit 40 through the first polarizing plate 6. The light with adjusted transmittance is emitted through the second polarizing plate 7 to display an image.

[0017] The liquid crystal display device 50 of this embodiment is used as a display device incorporated into various information devices (for example, in-vehicle devices such as car navigation systems, personal computers, monitors, mobile phones, smartphones, portable information terminals such as laptops and tablets, portable game consoles, photocopiers, ticket vending machines, ATMs, VR goggles, etc.).

[0018] The TFT substrate 1 comprises, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film provided to cover each TFT, a plurality of pixel electrodes provided in a matrix on the interlayer insulating film and connected to each of the plurality of TFTs, and an alignment film provided to cover each pixel electrode. The CF substrate 2 comprises, for example, a black matrix provided in a grid on a glass substrate, a color filter including a red layer, a green layer, and a blue layer provided between each grid of the black matrix, a common electrode provided to cover the black matrix and the color filter, and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is made of a nematic liquid crystal material or the like containing liquid crystal molecules having electro-optic properties. The first polarizer plate 6 and the second polarizer plate 7 each comprise, for example, a polarizer layer having a polarization axis in one direction and a pair of protective layers provided to sandwich the polarizer layer.

[0019] <Backlight Unit> Figure 2 is a schematic cross-sectional view and plan view showing an example of the configuration of the backlight unit 40 according to this embodiment, and Figure 3 is a schematic cross-sectional view of the first sheet 44 of this embodiment. In Figures 2 and 3, the upper side of the figures is the side of the liquid crystal display panel 5 shown in Figure 1.

[0020] The left side of Figure 2 shows a schematic cross-sectional view of the backlight unit 40. The backlight unit 40 comprises a side-edge type light source layer 47, a first sheet 44 laminated on the light-emitting surface (upper part of Figure 2) side of the light source layer 47, a second sheet 45 laminated on the light-emitting surface (upper part of Figure 2) side of the first sheet 44, and a third sheet 46 laminated on the light-emitting surface (upper part of Figure 2) side of the second sheet 45. The first sheet 44 is laminated on the light-emitting surface side of the light guide plate 43. However, for clarity, the gaps between each layer are shown to be large. In other words, in the backlight unit 40, each layer is actually in substantial contact. Furthermore, while the cross-section of each layer is schematically shown, for layers with a prism structure, the cross-section is shown cut perpendicular to the direction in which the prism extends.

[0021] The second sheet 45 and the third sheet 46 are prism sheets having a prism structure provided on the light-emitting surface side (upper side in Figure 2), and contribute to high-brightness and uniform light emission across the entire surface of the liquid crystal display panel 5 by diffusing light from the light source layer 47. However, for these prism sheets to function properly, it is desirable that light be incident at an angle within a predetermined range.

[0022] In contrast, as will be explained in detail later, the light from the light source 41 in the light source layer 47 is emitted at an angle that is nearly parallel to the second sheet 45 and the third sheet 46. Therefore, if the second sheet 45 and the third sheet 46 were to be placed directly on the light source layer 47, the angle at which light is incident on these prism sheets would not necessarily be desirable. As a result, the light would not be properly diffused, leading to low uniformity and brightness.

[0023] Therefore, the backlight unit 40 includes a first sheet 44 between the light source layer 47 and the second sheet 45. The first sheet 44 functions as a light diffusion sheet, refracting the light emitted from the light source layer 47 toward the second sheet 45, causing the light to enter the second sheet 45 and the third sheet 46 at a desirable angle. As a result, the backlight unit 40 achieves uniform and high-brightness light emission.

[0024] The right side of Figure 2 schematically shows a plan view of each stacked layer as seen from a vertical direction (up and down direction on the left side of Figure 2) (i.e., a plan view). These plan views are shown in accordance with the orientation in which the layers are actually stacked in the backlight unit 40. Note that d11 indicates the direction in which the light incident surface of the light guide plate 43 extends horizontally. The direction d11 in which the light incident surface of the light guide plate 43 extends is along the arrangement direction of the multiple light sources 41. Each element will be described in detail later. In this disclosure, descriptions such as "plan view" or "in a plan view" refer to observing each element in the stacking direction of the backlight unit 40 (i.e., the up and down direction on the left side of Figure 2).

[0025] Furthermore, in the backlight unit 40 according to this embodiment, components other than the laminate consisting of the light guide plate 43, the light source 41, and the first sheet 44 may be appropriately changed, modified, or replaced without departing from the spirit of this disclosure. In other words, the laminate in which the reflective sheet 42, the second sheet 45, and the third sheet 46 of the backlight unit 40 are removed is also within the scope of this disclosure.

[0026] <Light source layer> The light source layer 47 comprises a light source 41, a reflective sheet 42, and a light guide plate 43. The light guide plate 43 is laminated on the reflective sheet 42.

[0027] The light source 41 is at least one light source positioned on the light incident surface side of the light guide plate 43, and causes light 48 to be incident on the light guide plate 43 substantially parallel to the light guide plate 43. In this embodiment, there are multiple side-edge type LED chips, that is, multiple LED chips arranged along the direction in which the light incident surface of the light guide plate 43 extends.

[0028] The type of light source 41 is not particularly limited, but may be an LED element or a laser element, for example, and an LED element may be used from the viewpoint of cost, productivity, etc. If an LED element is used, it may include multiple LED chips. The number of light sources 41 may be one or multiple. If there are multiple light sources 41, it is preferable to arrange the multiple light sources 41 in a linear fashion on the light incident surface side of the light guide plate 43. Also, the light sources 41 may be point sources or linear sources. If the light sources 41 are linear sources, it is preferable to arrange the light sources 41 so that the longitudinal axis direction of the light source 41 is along the light incident surface of the light guide plate 43.

[0029] In this embodiment, a side-edge type light source is described, but the backlight unit of this disclosure is not limited to this form, and the light source may be any light guide plate type light source.

[0030] The light guide plate 43 guides light 48 toward the opposite side of the light source 41 and emits it toward the liquid crystal display panel 5 at a relatively small angle with respect to the light emission surface of the light guide plate 43 (i.e., an angle nearly parallel to the second sheet 45 and the third sheet 46). The light guide plate 43 has its main surface toward the liquid crystal display panel 5 as the light emission surface, and the light emission surface of the light guide plate 43 is also the light emission surface of the light source layer 47. The light guide plate 43 also has a side surface that functions as a light incident surface. In this embodiment, the light guide plate 43 is a rectangular parallelepiped lenticular lens sheet. Of the four side surfaces of the light guide plate 43, two side surfaces perpendicular to the direction in which the lenticular lens 43a extends can function as light incident surfaces. In this embodiment, since the light source 41 is provided on one of these two side surfaces, the side surface on which the light source 41 is provided functions as a light incident surface.

[0031] This disclosure is not limited to such configurations, and any configuration that allows light to be incident on the side of the light guide plate 43 may be adopted. For example, at least one light source 41 may be provided on both of the two sides perpendicular to the direction in which the lenticular lens extends. Also, if a light guide plate 43 without a lenticular lens is used, at least one light source 41 may be provided on any side, so that the side on which the at least one light source 41 is provided functions as the light incident surface.

[0032] The light guide plate 43 is a sheet made of, for example, polycarbonate, polyethylene terephthalate, or acrylic resin. It may also be a sheet having a lenticular structure on one side. In this case, the direction in which each lenticular lens 43a (see the plan view in Figure 2) extends coincides with the direction in which light 48 is incident from the light source 41 to the light guide plate 43. Hereinafter, the direction in which light 48 is incident from the light source 41 to the light guide plate 43 may be referred to as the "light guiding direction d1".

[0033] The light guide direction d1 of the light guide plate 43 is determined by the arrangement of the light source 41 relative to the light guide plate 43. In this embodiment, since the light source 41 consists of a plurality of LED chips arranged along the direction in which the light incident surface of the light guide plate 43 extends, the light guide direction d1 is perpendicular to the direction in which the plurality of LED chips are arranged in a plan view. As another example, if the light source 41 consists of a single point light source, the light guide direction d1 refers to the direction of radiation centered on the point light source. As yet another example, if the light source 41 consists of a single linear light source arranged along the direction in which the light incident surface of the light guide plate 43 extends, the light guide direction d1 is perpendicular to the direction in which the light incident surface extends in a plan view.

[0034] The reflective sheet 42 reflects light 48 that would otherwise be emitted away from the liquid crystal display panel 5, directing it towards the liquid crystal display panel 5. The reflective sheet 42 is made of, for example, a white polyethylene terephthalate resin film, a silver vapor-deposited film, or the like.

[0035] <First Sheet> As shown in Figure 2, the first sheet 44 has two opposing light-emitting surfaces 62a (upper part of Figure 2) and a light-incident surface 63a (lower part of Figure 2). A light-diffusing structure 65 is provided on the light-emitting surface 62a side of the first sheet 44. A first prism structure 64, consisting of a plurality of prisms 64a extending in a first direction d12, is provided on the light-incident surface 63a side of the first sheet 44.

[0036] Figure 3 shows the first sheet 44 of this embodiment by itself. The first sheet 44 comprises a base layer 61, a light diffusion structure 65, and a first prism structure 64.

[0037] The overall thickness of the first sheet 44 is approximately 50 μm or more and approximately 300 μm or less.

[0038] [Base Layer] The base layer 61 needs to transmit light, so it is formed mainly from a transparent (e.g., colorless and transparent) synthetic resin. The main component of the base layer 61 is not particularly limited, and for example, polycarbonate, polyethylene terephthalate (PET), polyethylene naphthalate, acrylic resin, polystyrene, polyolefin, cellulose acetate, weather-resistant polyvinyl chloride, etc. may be used. The "main component" refers to the component with the highest content, for example, a component with a content of 50% by mass or more. The base layer 61 may contain additives other than the main component, or it may not contain additives at all.

[0039] 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, from the viewpoint of suppressing curling. 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, from the viewpoint of further improving brightness and making the layer thinner. Note that "average thickness" refers to the average value of the thicknesses of any 10 points.

[0040] [First Prism Structure] The first prism structure 64 consists of a plurality of prisms 64a extending in a first direction d12. In the plurality of prisms 64a, each prism 64a extends in the first direction d12 and is substantially parallel to one another. The cross-sectional shape of each prism 64a cut by a plane perpendicular to the first direction d12 is an isosceles triangle, and one side of the triangle having a different length from the other two sides (hereinafter also referred to as the "base") is located on the substrate layer 61 side. The first prism structure 64 may be formed using, for example, an ultraviolet (UV) curable acrylic resin.

[0041] The shape of the cross-section perpendicular to the longitudinal direction of the prism 64a of the first prism structure 64 (i.e., the direction in which the prism extends, and in the case of the prism 64a of the first prism structure 64, the first direction d12) is indicated by the height h1 and the vertex angle θ1. The spacing between the multiple prisms 64a is indicated by the pitch p1. The pitch is the distance between the vertices corresponding to the vertex angles of the triangles in the cross-section perpendicular to the longitudinal direction of each prism. Hereafter, the cross-section perpendicular to the longitudinal direction of the prism may be simply referred to as the "prism cross-section," and the vertex angle and height of the prism cross-section may be simply referred to as the "prism vertex angle" and the "prism height," respectively. In the cross-section of the prism 64a of the first prism structure 64, each vertex is not limited to an angle consisting of two straight lines as in this embodiment, but may also be a rounded angle.

[0042] In this embodiment, since we are describing a configuration in which there are no gaps between adjacent prisms, the pitch of each prism is equal to the length of the base of each prism. In another embodiment, the prisms may be arranged with gaps between them. In this case, the length of the base of the triangle and the pitch will not be equal.

[0043] The length of the pitch p1 of the prism 64a of the first prism structure 64 is preferably 5 μm or more, more preferably 10 μm or more, and more preferably 50 μm or less, and more preferably 40 μm or less, from the viewpoint of suppressing moiré and ensuring good brightness.

[0044] The apex angle θ1 of the prism 64a of the first prism structure 64 is preferably 70° or more, more preferably 80° or more, and preferably 110° or less, and more preferably 100° or less, from the viewpoint of suppressing moiré and ensuring good brightness.

[0045] The height h1 of the prism 64a of the first prism structure 64 is preferably 5 μm or more, more preferably 6 μm or more, and more preferably 30 μm or less, and more preferably 20 μm or less, from the viewpoint of suppressing moiré and ensuring good brightness.

[0046] In Figure 3, etc., the prism 64a is shown as a geometrically precise isosceles triangle, and adjacent prisms are shown touching each other. However, the prism may differ from the example described in Figure 3, as long as the effects of this disclosure are not lost, or within the range of unavoidable shape variations due to processing accuracy in industrial production. For example, the vertex may be rounded, or it may be a flat trapezoid. In this case, the vertex angle of the cross section perpendicular to the length direction of the prism 64a is the angle obtained by extending the sides assuming that the cross section is a triangle.

[0047] Furthermore, the shape of the ridge of the prism 64a will be explained using Figure 4. As shown in Figure 4, the ridge of the prism 64a of the first prism structure 64 has a constant height h1 (that is, the ridge is a straight line substantially parallel to the base material layer 61).

[0048] [Light Diffusion Structure] The light diffusion structure 65 has the function of diffusing light passing through the first sheet 44 from the light incident surface 63a to the light emission surface 62a. Any known structure can be used as the light diffusion structure 65, as long as it exhibits such a function. For example, the light diffusion structure 65 may be an uneven structure spreading on the light emission surface 62a, or an island-like phase separation structure inside the first sheet 44, or a combination of these.

[0049] In this embodiment, the light diffusion structure 65 contains a light diffusing agent 651 and a matrix resin 652. The light diffusing agent 651 is granular and, in this embodiment, is dispersed on the surface of the substrate layer 61 on the light-emitting surface 62a side. The matrix resin 652 is a cured resin that exists between the light diffusing agents 651 and between the substrate layer 61 and the light diffusing agents 651, and binds them together. The matrix resin 652 spreads out in a generally planar manner on the light-emitting surface 62a side of the substrate layer 61, but some parts of the light diffusing agents 651 protrude from the matrix resin 652, forming an uneven structure.

[0050] In the light-diffusing structure 65, light diffusion occurs at the interface between the island-like phase made of the light-diffusing agent 651 and the sea-like phase made of the substrate layer 61 or the matrix resin 652. Furthermore, light diffusion occurs at the interface between the uneven structure formed by a portion of the light-diffusing agent 651 and the environment outside the first sheet 44.

[0051] The light diffusion structure 65 only needs to be provided on the light-emitting surface 62a side of the first sheet 44 than the first prism structure 64. In other words, the light diffusion structure 65 does not need to be located on the outermost layer on the light-emitting surface 62a side of the first sheet 44, and the first sheet 44 may have any additional components on the light-emitting surface 62a side of the light diffusion structure 65.

[0052] Examples of light diffusing agents 651 include: inorganic particles such as silica, titanium oxide, aluminum hydroxide, barium sulfate, barium sulfide, aluminum oxide, zinc oxide, and magnesium silicate; and organic particles such as acrylic, acrylonitrile, silicone, polystyrene, and polyamide.

[0053] The average particle diameter of the light diffusing agent 651 is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more, from the viewpoint of suppressing moiré patterns in the backlight unit 40 and ensuring good brightness by improving the light diffusion effect. Furthermore, the average particle diameter of the light diffusing agent 651 is preferably 50 μm or less, more preferably 25 μm or less, and even more preferably 15 μm or less, from the viewpoint of suppressing moiré patterns in the backlight unit 40 and ensuring good brightness by improving the light diffusion effect. Note that the average particle diameter of the light diffusing agent 651 refers to the volume average particle diameter.

[0054] The average particle size of the light diffusing agent 651 can be determined by measuring the particle size of the light diffusing agent at a magnification of 1000x using a laser microscope VK-X3050 (manufactured by Keyence) and averaging the particle sizes of 30 particles.

[0055] The shape of the light diffusing agent 651 is not particularly limited and may be spherical, bead-shaped, flake-shaped, cubic, needle-shaped, rod-shaped, spindle-shaped, plate-shaped, scale-shaped, fibrous, etc. Of these, spherical and bead-shaped are more preferred as they have excellent light diffusing properties.

[0056] The refractive index of the light diffusing agent 651 is preferably 1.40 or higher, more preferably 1.45 or higher, and even more preferably 1.50 or higher, from the viewpoint of refracting light and ensuring good brightness uniformity. Furthermore, there is no particular upper limit to the refractive index of the light diffusing agent 651, but it is preferably 1.60 or lower, and more preferably 1.57 or lower.

[0057] From the viewpoint of ensuring good brightness uniformity by reflecting and refracting light with the light diffuser, the content of the light diffuser 651 is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of matrix resin 652. Furthermore, from the viewpoint of ensuring good brightness and brightness uniformity, the content of the light diffuser 651 is preferably 200 parts by mass or less, preferably 100 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of matrix resin 652.

[0058] Since the matrix resin 652 needs to transmit light, it is formed mainly from a transparent (especially colorless and transparent) resin. Examples of usable resins include thermosetting resins and UV-curing resins. Examples of usable thermosetting resins include epoxy resins, silicone resins, phenolic resins, urea resins, unsaturated polyester resins, melamine resins, alkyd resins, polyimide resins, acrylic resins, amide-functional copolymers, and urethane resins. For UV-curing resins, we can use UV-curing resins that harden by crosslinking when irradiated with ultraviolet light. Examples of UV-curing resins include acrylic, polyurethane, urethane acrylate, polyester, fluorine-based, silicone-based, polyamide-imide, and epoxy. These resins can be used individually or in combination of two or more. Of these, acrylic resin and urethane acrylate resin are more preferred as highly transparent optical materials.

[0059] Furthermore, electron beam-curable resins that harden by crosslinking upon irradiation with an electron beam can also be used, and polymerizable monomers and polymerizable oligomers can be appropriately selected and used.

[0060] The matrix resin 652 may contain, as appropriate, plasticizers, dispersants, various leveling agents, ultraviolet absorbers, antioxidants, viscosity modifiers, lubricants, light stabilizers, antistatic agents, and the like.

[0061] The full width at half maximum (FWHM) of the first sheet 44 with respect to linearly transmitted light is preferably 2° or more and 30° or less. Here, the full width at half maximum (FWHM) refers to the full width at half maximum (FWHM) of the angle of the spread of the emitted light. With this configuration, moiré patterns can be further suppressed. In addition, sufficient brightness can be ensured.

[0062] Thus, in the first sheet 44 of this disclosure, brightness uniformity can be improved by appropriately adopting preferred values ​​for the pitch, apex angle, and height of the prism 64a, the average particle diameter of the light diffusing agent 651, and the full width at half maximum of the first sheet 44 with respect to linearly transmitted light. The backlight unit 40 used in the liquid crystal display device 50 faces an urgent challenge in terms of improving brightness uniformity due to the demand for thinner designs, but this problem can also be solved by using the first sheet 44 of this disclosure.

[0063] <Prism Sheet> As shown in Figure 2, a second sheet 45 is laminated on the light-emitting surface 62a side of the first sheet 44. The second sheet 45 has a light-incident surface (lower side in Figure 2) and a light-emitting surface (upper side in Figure 2) that are opposite to each other. The second sheet 45 is a prism sheet and has a second prism structure consisting of a plurality of prisms 45a extending in the second direction d13. A third sheet 46 is also laminated on the light-emitting surface side of the second sheet 45. The third sheet 46 has a light-incident surface (lower side in Figure 2) and a light-emitting surface (upper side in Figure 2) that are opposite to each other. The third sheet 46 is a prism sheet and has a third prism structure consisting of a plurality of prisms 46a extending in the third direction d14.

[0064] For the second sheet 45 and the third sheet 46, for example, a PET (polyethylene terephthalate) film may be used with a prism shape formed using a UV-curing acrylic resin.

[0065] The configuration of the multiple prisms in the second sheet 45 and the third sheet 46 may be set as appropriate, except that their extending directions (second direction d13 and third direction d14) are as described later in the section [Orientation of each layer]. For example, the configuration of the multiple prisms in the second sheet 45 and the third sheet 46 may be the same as that of the multiple prisms 64a in the first sheet 44, except for their extending directions. For example, the height, apex angle, and pitch of the multiple prisms in the second sheet 45 and the third sheet 46 may be the same as the height h1, apex angle θ1, and pitch p1 of the multiple prisms 64a in the first sheet 44.

[0066] While it is preferable to laminate two prism sheets 45 and 46 on the first sheet 44 as in this embodiment, this is not essential. Only one prism sheet may be laminated on the first sheet 44, or three or more sheets may be used, or a light diffusion sheet with a different structure from one containing a prism may be used.

[0067] Furthermore, a projection 46b may be provided on the light incident surface side of the third sheet 46. The projection 46b may be shaped, for example, as part of a sphere. This configuration can suppress the prism sheet from sticking to other sheets.

[0068] <Color Conversion Sheet> Although not shown in the figures, the backlight unit 40 of this disclosure may further include a color conversion sheet. The color conversion sheet is a wavelength conversion sheet that converts light from a light source 41 (for example, blue light) into light with a peak wavelength of any color (for example, green or red). For example, the color conversion sheet converts blue light with a wavelength of 450 nm into green light with a wavelength of 540 nm and red light with a wavelength of 650 nm. In this case, if a light source 41 that emits blue light with a wavelength of 450 nm is used, the blue light is partially converted into green light and red light by the color conversion sheet, so the light transmitted through the color conversion sheet becomes white light. For example, a QD (quantum dot) sheet or a fluorescent sheet may be used as the color conversion sheet.

[0069] The position where the color conversion sheet is provided is not particularly limited, but in this embodiment, for example, it could be between the light guide plate 43 and the first sheet 44, between the first sheet 44 and the second sheet 45, or on the light-emitting surface side of the third sheet 46. The color conversion sheet may be provided in one of these locations or in multiple locations. In this embodiment, the case in which only one first sheet 44 is provided as the light diffusion sheet is described, but additional light diffusion sheets may be provided as described later, and in this case, the color conversion sheet may be provided between the first sheet 44 and the additional light diffusion sheet.

[0070] [Orientation of Each Layer] Next, the way in which the layers of the backlight unit 40 overlap will be explained using Figure 5. Figure 5 is a schematic diagram showing how the layers overlap, and schematically shows the orientation of each layer when viewed from above. In Figure 5, the X-axis is set to coincide with the direction d11 in which the light incident surface of the light guide plate 43 extends, and the Y-axis is set to be perpendicular to the X-axis. As shown in Figure 5, it is preferable that the layers of the backlight unit 40 overlap so that the angles in the following directions are as follows.

[0071] In this embodiment, the angle θ111 between the light guide direction d1 and the direction d11 in which the light incident surface of the light guide plate 43 extends is 90°, meaning that these two directions are orthogonal in a plan view.

[0072] The second direction d13 in which the prism 45a of the second prism structure extends and the third direction d14 in which the prism 46a of the third prism structure extends are substantially orthogonal in a plan view. In other words, the angle θ1314 between the second direction d13 and the third direction d14 is substantially a right angle. With this configuration, moiré patterns (interference fringes) can be further suppressed, and the uniformity of the brightness of the backlight unit 40 is improved.

[0073] In this disclosure, “substantially parallel” means that the angle between the two directions is 0° or an angle that produces the same effect in the application of the backlight unit as if it were 0°. Without limiting this disclosure, “substantially parallel” may also mean that the angle is within the range of 0° ± 5°. Similarly, in this disclosure, “substantially orthogonal” or “substantially right-angled” means that the angle between the two directions is 90° or an angle that produces the same effect in the application of the backlight unit as if it were 90°. Without limiting this disclosure, “substantially orthogonal” or “substantially right-angled” may also mean that the angle is within the range of 90° ± 5°.

[0074] In Figure 5, X １ This refers to the angle, viewed counterclockwise from the direction d11 in which the light incident surface of the light guide plate 43 extends, to the first direction d12 in which the prism 64a of the first prism structure 64 extends, in a plan view. ３This refers to the angle viewed counterclockwise from direction d11 in a plan view, toward the third direction d14, to which the prism 46a of the third prism structure extends. In this embodiment, X １ and X ３ It satisfies at least one of the following conditions (1), (2), and (3).

[0075] (1) 0° ≤ X ３ <95° and -10° ≤ X １ -X ３ ≤10° (2) 95° ≤X ３ ≤ 135° and -45° ≤ X １ -X ３ ≦45° (3) 135°<X ３ <180° and -10° ≤ X １ -X ３ ≤10°

[0076] X １ and X ３ It is advantageous from the viewpoint of improving the brightness of the backlight unit 40 if it satisfies at least one of the following (1), (2), and (3).

[0077] From the perspective of further improving the brightness of the backlight unit 40, X １ and X ３ It is preferable that the following conditions (1), (2-1), (2-2), (2-3), (2-4), (2-5), and (3) are met. (2-1), (2-2), (2-3), (2-4), and (2-5) are specific embodiments of (2) above.

[0078] (1) 0° ≤ X ３ <95° and -10° ≤ X １ -X ３ ≤10° (2-1) 95° ≤X ３ <100° and -10° ≤ X １ -X ３ ≤10° (2-2) 100° ≤X ３ <110° and -20° ≤ X １ -X ３ ≤20° (2-3) 110° ≤X ３ <120° and -25° ≤ X １ -X ３≤25° (2-4) 120° ≤X ３ <130° and -35° ≤ X １ -X ３ ≤35° (2-5) 130° ≤X ３ ≤ 135° and -20° ≤ X １ -X ３ ≦20° (3) 135°<X ３ <180° and -10° ≤ X １ -X ３ ≤10°

[0079] Among them, X １ and X ３ It is preferable that it satisfies (2) of the above (1), (2), and (3), more preferably that it satisfies at least one of the above (2-1), (2-2), (2-3), (2-4), and (2-5), and even more preferably that it satisfies (2-3).

[0080] X １ and X ３ When the above (2) is satisfied, from the viewpoint of improving the brightness of the backlight unit 40, X １ (4) 90° ≤ X １ It is preferable that the angle is further satisfied with ≤135°.

[0081] Furthermore, from the viewpoint of improving the brightness of the backlight unit 40, X １ -X ３ The angle is preferably -45° to 45°, more preferably -35° to 35°, even more preferably -25° to 25°, even more preferably -15° to 15°, preferably -10° to 10°, and particularly preferably -5° to 5°.

[0082] The angle θ1213 between the first direction d12 in which the prism 64a of the first prism structure 64 extends and the second direction d13 in which the prism 45a of the second prism structure extends is preferably 25° or more and preferably 115° or less in a plan view, from the viewpoint of suppressing moiré and ensuring good brightness. In this disclosure, the angle θ1213 refers to the angle viewed counterclockwise from the first direction d12 to the second direction d13.

[0083] It is more preferable that the light guide directions d1, the first direction d12, the second direction d13, and the third direction d14 of the light guide plate 43 are all different. By configuring it in this way, the backlight unit 40 will have sufficiently high brightness and moiré will be further suppressed.

[0084] Furthermore, it is more preferable that the first direction d12, the second direction d13, and the light guide direction d1 of the light guide plate 43 are positioned in this order when viewed counterclockwise. This relationship may also be satisfied when viewed clockwise. This helps to suppress moiré patterns.

[0085] Furthermore, it is more preferable that the second direction d13 in which the prism 45a of the second sheet 45 extends, or the third direction d14 in which the prism 46a of the third sheet 46 extends, is 10° or more and 30° or less with respect to the light guide direction d1 of the light guide plate 43, and it is even more preferable that the third direction d14 is 10° or more and 30° or less with respect to the light guide direction d1 of the light guide plate 43. This results in better brightness and suppression of moiré patterns.

[0086] [Another Example of Light Diffusion Structure] Next, another example of the light diffusion structure 65 will be described using Figures 6 and 7. Figures 6 and 7 are schematic cross-sectional views of the first sheets 44a and 44b having another example of the light diffusion structure 65, 65a and 65b, respectively. Members having the same function as those described in the above example are denoted by the same reference numerals, and their descriptions are not repeated.

[0087] As shown in Figure 6, the first sheet 44a may contain a light-diffusing structure 65a made of a light-diffusing agent 651 inside the base layer 61a. Here, the light-emitting surface 62a of the first sheet 44a may be the light-emitting surface of the base layer 61a (upper side in Figure 6), or it may be flat.

[0088] As shown in Figure 7, the first sheet 44b may have a plurality of uneven structures 653 provided on the light-emitting surface side of the base layer 61b as a light-diffusing structure 65b.

[0089] (Another example of the prism edge shape) In this embodiment, as shown in Figure 4, a configuration in which the height h1 of the prism 64a of the first prism structure 64 is constant (i.e., the edge is a straight line parallel to the plane direction of the substrate layer 61) is described, but the first sheet 44 of this disclosure is not limited to this configuration. For example, the height is not constant, and the edge may be straight, stepped, non-straight, wavy, or other curved shape. With these shapes, moiré can be further improved.

[0090] A linear change means raising or lowering using a single straight line; a stepped change means raising or lowering using two or more straight lines; a non-linear change means raising or lowering using a combination of straight lines and curves; and a curved change means raising or lowering using one or more curves. These ridge shapes may be a single shape or a combination of two or more ridge shapes. If the ridge is a wavy curve, the wave may have regularity in wavelength and width, or it may be a random wave.

[0091] Figures 8 and 9 show other examples of the shape of the ridge line. As shown in Figure 8, the first prism structure 64 may have a plurality of prisms 64b whose ridge lines are wavy. The plurality of prisms 64b may each have the same wavy shape, for example, as shown in Figure 8, a plurality of identical shapes may be arranged in a row. Also, as shown in Figure 9, in the first prism structure 64, the shape of the ridge line may be randomly different for each prism, such as prisms 64b and prisms 64c. With these shapes, moiré can be further improved.

[0092] (Embodiment 2) The backlight unit 140 of this embodiment will be described with reference to Figure 10. For the sake of convenience of explanation, components having the same function as those described in the above embodiment will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0093] As shown in Figure 10, the backlight unit 140 further comprises a fourth sheet 54 laminated between the first sheet 44 and the second sheet. The fourth sheet 54 is a light-diffusing sheet, similar to the first sheet 44; in other words, the backlight unit 140 comprises two light-diffusing sheets. Thus, the backlight unit of this disclosure may comprise two light-diffusing sheets. Although not shown, it may also comprise three or more sheets.

[0094] The fourth sheet 54 has a light incident surface 73a and a light emission surface 72a that face each other. The light emission surface 72a is provided with a fourth prism structure consisting of a plurality of prisms extending in a fourth direction. The fourth sheet 54 according to this embodiment is identical to the first sheet 44, except that the fourth direction in which the prisms of the fourth prism structure extend is different from the first direction d12 in which the prisms of the first prism structure 64 of the first sheet 44 extend.

[0095] The first and fourth directions are substantially orthogonal in a plan view. With this configuration, the combination of the first prism structure 64 and the fourth prism structure, which are arranged to be substantially orthogonal to each other, performs a function similar to that of an inverted pyramid structure, thereby improving the brightness of the backlight unit 140.

[0096] The first sheet 44 and the fourth sheet 54 may be bonded together. The method of bonding is not particularly limited, but one example is to provide an adhesive layer using a known adhesive sheet or the like between the first sheet 44 and the fourth sheet 54 and bond these sheets together.

[0097] (Additional Notes) The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0098] (Summary) As can be understood from the above description, this disclosure encompasses the following aspects:

[0099] A backlight unit according to Embodiment 1 of the present disclosure includes: a light guide plate having a light incident surface and a light emission surface; at least one light source disposed on the light incident surface side of the light guide plate; a first sheet laminated on the light emission surface side of the light guide plate, the first sheet having a light incident surface and a light emission surface facing each other, a first prism structure consisting of a plurality of prisms extending in a first direction provided on the light incident surface side of the first sheet, and a light diffusion structure provided on the light emission surface side of the first sheet; and a second sheet laminated on the light emission surface side of the first sheet, the second sheet having a light incident surface and a light emission surface facing each other, The present invention provides a second sheet having a second prism structure consisting of a plurality of prisms extending in a second direction, provided on the light-emitting surface side of the second sheet, and a third sheet laminated on the light-emitting surface side of the second sheet, having a light-incident surface and a light-emitting surface facing each other, and a third prism structure consisting of a plurality of prisms extending in a third direction, provided on the light-emitting surface side of the third sheet, wherein the second direction and the third direction are substantially orthogonal in a plan view, and the angle between the direction in which the light-incident surface of the light guide plate extends and the first direction and the third direction in a plan view is X １ and X ３ In that case, X １ and X ３ It satisfies at least one of the following conditions: (1) 0° ≤ X ３ <95° and -10° ≤ X １ -X ３ ≤10° (2) 95° ≤X ３ ≤ 135° and -45° ≤ X １ -X ３ ≦45° (3) 135°<X ３ <180° and -10° ≤ X １ -X ３ ≤10°

[0100] According to this embodiment, a novel backlight unit can be provided. Furthermore, according to this embodiment, the brightness of the backlight unit is improved.

[0101] Aspect 2 of this disclosure is the backlight unit of Aspect 1, where X １ and X ３satisfies any one of the following: (1) 0° ≤ X ３ <95°, and -10° ≤ X １ -X ３ ≤ 10° (2-1) 95° ≤ X ３ <100°, and -10° ≤ X １ -X ３ ≤ 10° (2-2) 100° ≤ X ３ <110°, and -20° ≤ X １ -X ３ ≤ 20° (2-3) 110° ≤ X ３ <120°, and -25° ≤ X １ -X ３ ≤ 25° (2-4) 120° ≤ X ３ <130°, and -35° ≤ X １ -X ３ ≤ 35° (2-5) 130° ≤ X ３ ≤ 135°, and -20° ≤ X １ -X ３ ≤ 20° (3) 135° < X ３ <180°, and -10° ≤ X １ -X ３ ≤ 10° According to this aspect, the luminance of the backlight unit is improved.

[0102] Aspect 3 of the present disclosure is the backlight unit of Aspect 1 or 2, where X １ and X ３ satisfy (2) 95° ≤ X ３ ≤ 135°, and -45° ≤ X １ -X ３ ≤ 45°, and X １ further satisfies (4) 90° ≤ X １ ≤ 135°. According to this aspect, the luminance of the backlight unit is improved.

[0103] Aspect 4 of the present disclosure is the backlight unit of any one of Aspects 1 to 3, where the angle between the first direction and the second direction is 25° or more and 115° or less in plan view. According to this aspect, the luminance of the backlight unit is improved.

[0104] Embodiment 5 of the present disclosure is a backlight unit in any one of embodiments 1 to 4, wherein the light diffusion structure contains a light diffusing agent. According to this embodiment, the first sheet can be easily manufactured in roll form, and manufacturing costs can be greatly reduced.

[0105] Embodiment 6 of this disclosure is a backlight unit of Embodiment 5 in which the average particle size of the light diffusing agent is 0.5 μm or more and 50 μm or less. According to this embodiment, the function of the light diffusing agent is improved, and the brightness of the backlight unit is further improved.

[0106] Aspect 7 of the present disclosure is a backlight unit in any one of aspects 1 to 6, wherein the backlight unit further comprises a fourth sheet laminated between the first sheet and the second sheet, the fourth sheet having a light incident surface and a light emission surface facing each other, and a fourth prism structure consisting of a plurality of prisms extending in a fourth direction, provided on the light incident surface side of the fourth sheet, wherein the first direction and the fourth direction are substantially orthogonal in a plan view. According to this aspect, the combination of the first prism structure and the fourth prism structure, which are provided to be substantially orthogonal to each other, performs a function similar to an inverted pyramid structure, thereby improving the brightness of the backlight unit.

[0107] Embodiment 8 of this disclosure comprises a backlight unit from any one of embodiments 1 to 7 and a liquid crystal display panel. According to this embodiment, a novel liquid crystal display device can be provided.

[0108] The information device according to aspect 9 of this disclosure comprises the liquid crystal display device of aspect 8. According to this aspect, a novel information device can be provided.

[0109] (Brightness Evaluation) An embodiment of the present invention will be described below. In each example, the brightness was measured using a color luminance meter BM-7AC (Topcon Techno House Co., Ltd.) with the backlight unit 40 configured as shown in Figure 2, and X １ = 0° and X ３ = Brightness at 115° is 2878 cd / m² ２ This is expressed as a relative value with a baseline (100%).

[0110] In each embodiment, the light source layer 47 was a laminate of a light guide plate 43 and a reflective sheet 42, in which multiple LED chips were arranged on one side surface that served as the light incident surface.

[0111] In each embodiment, the first sheet 44, which is a light-diffusing sheet, was manufactured as follows. First, a light-diffusing structure was formed on the surface of a 50 μm thick substrate layer mainly composed of PET by wet coating with a UV-curable acrylic matrix resin containing a light-diffusing agent. An acrylic resin with an average particle size of 3 μm was used as the light-diffusing agent. In the light-diffusing structure, the content of the light-diffusing agent was 30 parts by mass per 100 parts by mass of matrix resin. Next, a first prism structure made of UV-curable acrylic resin was formed on a surface of the substrate layer separate from the surface on which the light-diffusing structure was formed. The first prism structure had a prism height of 6.5 μm, a pitch of 13 μm, and an apex angle of 90°. The light-diffusing structure of the first sheet 44 was then placed on the backlight unit 40 with the light-emitting surface 62a side and the first prism structure on the light-incident surface 63a side.

[0112] Furthermore, the second sheet 45 and the third sheet 46 were prepared as prism sheets, respectively, with PET (base layer) and UV-curable acrylic resin (prism) as the materials, and with prism heights of 10 μm, pitches of 24 μm, and apex angles of 90°, in which the constituent prisms were arranged without gaps.

[0113] Table 1 shows the angle X in a plan view of the first direction d12 in which the prism of the first sheet 44 extends, with respect to the direction d11 in which the light incident surface of the light guide plate 43 extends in the backlight unit 40 of each embodiment. １ , and the angle X in the third direction d14 to which the prism of the third sheet 46 extends ３ This shows the angles. Each angle is a counterclockwise angle from the plane of incident light. Note that the second direction in which the prism of the second sheet extends is set to be perpendicular to the third direction.

[0114] The results are shown in Table 1. A relative luminance value of 95% or higher (2734 cd / m² in absolute value) is considered a luminance value of 95% or higher. ２While a brightness of 98% or higher (equivalent to 2820 cd / m² in absolute terms) is sufficient for practical use as a backlight unit, in order to achieve both low power consumption and high brightness, the relative brightness must be 98% or higher. ２ (As stated above) the brightness can be considered sufficiently high for practical use as a backlight unit.

[0115]

[0116] As shown in Table 1, (2) 95° ≤ X ３ ≤ 135° and -45° ≤ X １ -X ３ Backlight units that satisfy ≤45° exhibited brightness that is practically sufficient. Also, 95° ≤ X ３ -10° ≤ X within the range of ≤ 135° １ -X ３ When ≤ 10° was satisfied, the backlight unit showed particularly high brightness. From this, 95° ≤ X ３ Even outside the range of ≤135°, -10° ≤ X １ -X ３ It was suggested that the backlight unit exhibits higher brightness when ≤ 10° is satisfied. Therefore, it was found that the backlight unit according to this disclosure that satisfies at least one of the following conditions exhibits a brightness that is practically sufficient: (1) 0° ≤ X ３ <95° and -10° ≤ X １ -X ３ ≤10° (2) 95° ≤X ３ ≤ 135° and -45° ≤ X １ -X ３ ≦45° (3) 135°<X ３ <180° and -10° ≤ X １ -X ３ ≤10°

[0117] 1 TFT substrate, 2 CF substrate, 3 liquid crystal layer, 5 liquid crystal display panel, 6 first polarizer, 7 second polarizer, 40, 140 backlight unit, 41 light source, 42 reflective sheet, 43 light guide plate, 43a lenticular lens, 44, 44a, 44b first sheet, 45 second sheet, 45a, 46a, 64a, 64b, 64c prism, 46 third sheet, 46b projection, 47 light source layer, 50 liquid crystal display device, 50a display screen, 54 fourth sheet, 61, 61a, 61b substrate layer, 62a, 72a light emission surface, 63a, 73a light incident surface, 64 first prism structure, 65, 65a, 65b light diffusion structure, 651 light diffusion agent, 652 matrix resin, 653 uneven structure, d1 Light guide direction, d11: Direction in which the light incident surface of the light guide plate extends, d12: First direction, d13: Second direction, d14: Third direction

Claims

1. A light guide plate having a light incident surface and a light exit surface, at least one light source disposed on the light incident surface side of the light guide plate, and a first sheet laminated on the light exit surface side of the light guide plate, the first sheet having a light incident surface and a light exit surface facing each other, a first prism structure including a plurality of prisms extending in a first direction provided on the light incident surface side of the first sheet, and a light diffusion structure provided on the light exit surface side of the first sheet, a second sheet laminated on the light exit surface side of the first sheet, the second sheet having a light incident surface and a light exit surface facing each other, and a second prism structure including a plurality of prisms extending in a second direction provided on the light exit surface side of the second sheet, a third sheet laminated on the light exit surface side of the second sheet, the third sheet having a light incident surface and a light exit surface facing each other, and a third prism structure including a plurality of prisms extending in a third direction provided on the light exit surface side of the third sheet, wherein the second direction and the third direction are substantially orthogonal to each other in a plan view, and the angles between the direction in which the light incident surface of the light guide plate extends in a plan view and the first direction and the third direction are X １ and X ３ When set as, X １ and X ３ satisfy at least one of the following: (1) 0° ≤ X ３ < 95°, and -10° ≤ X １ -X ３ ≤ 10° (2) 95° ≤ X ３ ≤ 135°, and -45° ≤ X １ -X ３ ≤ 45° (3) 135° < X ３ < 180°, and -10° ≤ X １ -X ３ ≤ 10° A backlight unit.

2. X １ and X ３ (1) 0° ≤ X ３ <95° and -10° ≤ X １ -X ３ ≤10° (2-1) 95° ≤X ３ <100° and -10° ≤ X １ -X ３ ≤10° (2-2) 100° ≤X ３ <110° and -20° ≤ X １ -X ３ ≤20° (2-3) 110° ≤X ３ <120° and -25° ≤ X １ -X ３ ≤25° (2-4) 120° ≤X ３ <130° and -35° ≤ X １ -X ３ ≤35° (2-5) 130° ≤X ３ ≤ 135° and -20° ≤ X １ -X ３ ≦20° (3) 135°<X ３ <180° and -10° ≤ X １ -X ３ ≤10° The backlight unit according to claim 1.

3. X １ and X ３ (2) 95° ≤ X ３ ≤ 135° and -45° ≤ X １ -X ３ Satisfying ≤ 45°, X １ (4) 90° ≤ X １ The backlight unit according to claim 1 or 2, further satisfying ≤135°.

4. The backlight unit according to claim 1 or 2, wherein the angle between the first direction and the second direction is 25° or more and 115° or less in a plan view.

5. The backlight unit according to claim 1 or 2, wherein the light diffusing structure contains a light diffusing agent.

6. The backlight unit according to claim 5, wherein the average particle size of the light diffusing agent is 0.5 μm or more and 50 μm or less.

7. The backlight unit according to claim 1 or 2, further comprising a fourth sheet laminated between the first sheet and the second sheet, the fourth sheet having a light incident surface and a light emission surface facing each other, and a fourth prism structure consisting of a plurality of prisms extending in a fourth direction, provided on the light incident surface side of the fourth sheet, wherein the first direction and the fourth direction are substantially orthogonal in a plan view.

8. A liquid crystal display device comprising a backlight unit according to claim 1 or 2 and a liquid crystal display panel.

9. An information device comprising the liquid crystal display device described in claim 8.

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