Edge light type backlight unit, liquid crystal display device, and information apparatus

Abstract

An edge light type backlight unit (40) is provided with: a light guide plate (43) that guides light entering through one end toward the end on the opposite side; a light refraction sheet (44) stacked on one surface of the light guide plate (43); and a light diffusion layer (45, 46) that is stacked on the light refraction sheet. The first surface of the light refracting sheet (44) includes a plurality of recesses (44c) formed in an inverted substantially polygonal pyramid shape or an inverted substantially truncated polygonal pyramid shape. The second surface of the light refracting sheet (44) includes a plurality of groove lines formed adjacent to each other and having an isosceles triangle cross-section.

Description

Technical Field

[0001] The present disclosure relates to an edge-lit backlight unit, a liquid crystal display device, and an information device. Background Art

[0002] A display device (such as a liquid crystal display device) used in a liquid crystal display, VR (virtual reality) goggles, etc. includes a display panel and a backlight unit provided on the back side of the display panel. The backlight unit includes types such as edge-lit and direct-lit. The edge-lit backlight unit includes a light guide plate, a light source that inputs light into an end portion of the light guide plate, and optical sheets stacked on the light guide plate. The optical sheets are used to change the angle of light from the light source, diffuse light, etc., and may be composed of multiple layers. In addition, for the purpose of light diffusion, a light diffusing agent (such as resin beads) is used on the optical sheet, for example.

[0003] Citation List

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-052493 Summary of the Invention

[0006] Technical Problem

[0007] The backlight unit needs to emit light uniformly and with high brightness over the entire screen of the display device. Conventionally, there is a trade-off between increasing brightness and increasing brightness uniformity.

[0008] An object of the present disclosure is to provide an edge-lit backlight unit that achieves increased brightness while maintaining brightness uniformity, as well as a liquid crystal display device and an information device including the edge-lit backlight unit.

[0009] Solution to the Problem

[0010] The edge-lit backlight unit of the present disclosure includes: a light guide plate that guides light entering through one end portion toward the end portion on the opposite side; a light refraction sheet stacked on one surface of the light guide plate; and a light diffusion layer stacked on the light refraction sheet. The first surface of the light refraction sheet includes a plurality of concave portions formed in an inverted substantially polygonal pyramid shape or an inverted substantially truncated polygonal pyramid shape. The second surface of the light refraction sheet includes a plurality of groove lines formed adjacent to each other and having an isosceles triangle cross-section.

[0011] According to the edge-lit backlight unit of the present disclosure, by providing a light refraction sheet between the light diffusion layer and the light source layer having the light guide plate, brightness can be increased while maintaining uniformity. The reason is that the light refraction sheet refracts the light entering through the end portion of the light guide plate toward the light diffusion layer side, and thus, the light can enter the light diffusion layer at a desired angle.

[0012] Note that the groove lines provided in the second surface of the light refraction sheet may be parallel to the direction in which light enters the light guide plate.

[0013] The recesses provided on the first surface of the light refraction sheet may be formed in an inverted substantially quadrangular pyramid shape or an inverted substantially frustum of a quadrangular pyramid shape having a rectangular or square bottom surface, and the ridge lines separating adjacent recesses may form an angle of 30° or more and 60° or less with respect to the direction in which light enters the light guide plate.

[0014] With these configurations, a remarkable brightness improvement effect is obtained.

[0015] The light diffusion layer may include a first light diffusion sheet and a second light diffusion sheet, and the first light diffusion sheet may be positioned closer to the light guide plate side than the second light diffusion sheet. Further, each of the first light diffusion sheet and the second light diffusion sheet may include a plurality of groove lines formed adjacent to each other on the surface on the side opposite to the light guide plate and having an isosceles triangle cross-section. The groove lines in the first light diffusion sheet may be orthogonal to the direction in which light enters the light guide plate, and the groove lines in the second light diffusion sheet may be parallel to the direction in which light enters the light guide plate.

[0016] This configuration can be used as a desired exemplary configuration of the light diffusion layer combined with the light refraction sheet of the present disclosure.

[0017] The second surface of the light refraction sheet is preferably on the light guide plate side. Thus, a remarkable brightness improvement effect is obtained.

[0018] The apex angle of the recesses formed in the light refraction sheet may be 80° or more and 100° or less. This angle is preferred in order to achieve a remarkable brightness improvement effect.

[0019] The groove lines provided in the second surface of the light refraction sheet may form an angle of 5° or more and 10° or less with respect to the direction in which light enters the light guide plate. Further, the groove lines provided in the second surface of the light refraction sheet may be formed in a repeatedly bent wavy shape.

[0020] These configurations can be used to suppress the occurrence of moiré fringes in the edge-lit backlight unit.

[0021] The liquid crystal display device according to the present disclosure includes a liquid crystal display panel and the edge-lit backlight unit of the present disclosure.

[0022] Since the liquid crystal display device of the present disclosure includes the above-described edge-lit backlight unit, the brightness can be increased while maintaining the light emission uniformity over the entire screen.

[0023] The information device according to the present disclosure includes the liquid crystal display device of the present disclosure.

[0024] Since the information device of the present disclosure includes the above liquid crystal display device, the brightness can be increased while maintaining the light emission uniformity over the entire screen.

[0025] Advantageous Effects of the Invention

[0026] According to the technology of the present disclosure, improved brightness can be achieved in a side-light type backlight unit, a liquid crystal display device using the side-light type backlight unit, and an information device, while maintaining brightness uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Figure 1 is a schematic cross-sectional view showing an example of a liquid crystal display device according to an embodiment.

[0028] Figure 2 Figure 2 is a schematic cross-sectional view and a schematic plan view showing the configuration of a backlight unit according to an embodiment.

[0029] Figure 3 Figure 3 is a schematic cross-sectional view of a light refraction sheet according to an embodiment.

[0030] Figure 4 Figure 4 is a perspective view showing an inverted pyramid layer of a light refraction sheet according to an embodiment.

[0031] Figure 5 Figure 5 is a view showing the shape of an inverted pyramid layer of a light refraction sheet according to an embodiment.

[0032] Figure 6 Figure 6 is a view showing the shape of a prism layer of a light refraction sheet according to an embodiment.

[0033] Figure 7 Figure 7 is a view showing a structure for suppressing moiré fringes in a light refraction sheet according to an embodiment.

[0034] Figure 8 Figure 8 is a view showing another structure for suppressing moiré fringes in a light refraction sheet according to an embodiment. DETAILED DESCRIPTION

[0035] (Embodiment)

[0036] Embodiments of the present disclosure will be described below with reference to the drawings. It should be noted that the scope of the present disclosure is not limited to the embodiments described below, and any modifications can be made without departing from the scope of the technical concept of the present disclosure. ​​​​​​​​​​​​​​​​

[0037] <Liquid Crystal Display Device>

[0038] As Figure 1 shown, the liquid crystal display device 50 according to this embodiment includes a liquid crystal display panel 5, a first polarizing plate 6 adhered to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 adhered to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 disposed on the rear surface side of the liquid crystal display panel 5 via the first polarizing plate 6.

[0039] The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 disposed to face each other, a liquid crystal layer 3 disposed between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) disposed in a frame shape between the TFT substrate 1 and the CF substrate 2 to seal the liquid crystal layer 3.

[0040] The backlight unit 40 is a side-light type backlight unit that guides light 48 emitted from a light source 41 disposed at an end substantially parallel to the liquid crystal display panel 5 toward the liquid crystal display panel 5 side.

[0041] From the front ( Figure 1 above in the figure), the shape of the display screen 50a of the liquid crystal display device 50 is generally rectangular or square, but the shape is not limited thereto and can be any desired shape, such as a rectangular shape with rounded corners, an oval shape, a circular shape, or a trapezoidal shape, or the shape of an instrument panel of an automobile.

[0042] In the liquid crystal display device 50, in each sub-pixel corresponding to each pixel electrode, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3. Accordingly, the transmittance of light entering through the first polarizing plate 6 from the backlight unit 40 is adjusted. The light with the adjusted transmittance passes through the second polarizing plate 7 and is emitted, thereby displaying an image.

[0043] The liquid crystal display device 50 according to this embodiment is used as a display device built in any one of different information devices (for example, in-vehicle devices for car navigation, personal computers, mobile phones, portable information terminals (such as laptop computers or tablet computers), portable game consoles, copiers, ticket vending machines, automated teller machines, VR goggles, etc.).

[0044] For example, the TFT substrate 1 includes: a plurality of TFTs arranged in a matrix pattern on a glass substrate; an interlayer insulating film provided to cover the TFTs; a plurality of pixel electrodes arranged in a matrix pattern on the interlayer insulating film and respectively connected to the plurality of TFTs; and an alignment film provided to cover the pixel electrodes. For example, the CF substrate 2 includes: a black matrix arranged in a grid pattern on a glass substrate; a color filter including a red layer, a green layer, and a blue layer respectively provided between the grids of the black matrix; a common electrode provided to cover the black matrix and the color filter; and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is formed of a nematic liquid crystal material containing liquid crystal molecules having electro-optical properties, etc. For example, the first polarizing plate 6 and the second polarizing plate 7 include a polarizer layer with a polarization axis in one direction and a pair of protective layers provided to sandwich the polarizer layer therebetween.

[0045] <Backlight unit>

[0046] Figure 2 An exemplary configuration of a backlight unit 40 according to an embodiment is shown.

[0047] Figure 2 The left cross-sectional view of shows that the backlight unit 40 includes a light source layer 47, a light refraction sheet 44, a first light diffusion sheet 45, and a second light diffusion sheet 46, and the respective layers are stacked in this order. However, it should be noted that, for easier viewing of the drawings, large gaps are shown between the layers. In other words, in the backlight unit 40, these layers are substantially in contact with each other. In addition, the cross-sections of each layer are schematically shown, but as will be described below, some layers are cut in different directions. It should be noted that in Figure 3 the light refraction sheet 44 is shown separately and in an enlarged form.

[0048] The first light diffusion sheet 45 and the second light diffusion sheet 46 diffuse the light from the light source layer 47, thereby helping to achieve high brightness and uniform light emission over the entire surface of the liquid crystal display panel 5. It should be noted that, in order to demonstrate the function of the light diffusion sheet, it is desirable for the light to enter at an angle within a specified range.

[0049] However, since the light source layer 47 is a side-light type in which the light source 41 is provided at its end, the light emitted from the light source layer 47 forms an angle close to parallel with the light source layer 47. Therefore, if the first light diffusion sheet 45 and the second light diffusion sheet 46 are directly provided on the light source layer 47, the light may not enter the light diffusion sheets 45 and 46 at a desired angle. As a result, the light is less likely to be properly diffused, which leads to a reduction in uniformity and brightness.

[0050] Therefore, the light refraction sheet 44 is disposed between the light source layer 47 and the first light diffusion sheet 45. The light refraction sheet 44 refracts the light emitted from the light source layer 47 to the first light diffusion sheet 45 side, so that the light enters the first light diffusion sheet 45 and the second light diffusion sheet 46 at a desired angle. Therefore, the backlight unit 40 achieves uniform and high-brightness light emission.

[0051] Figure 2 The right side of () shows a schematic plan view of the corresponding stacked layers as seen from the vertical direction ( Figure 2 the up-and-down direction in). These plan views are shown according to the orientation in which the respective layers are actually stacked in the backlight unit 40. Each element will be described in detail later, but first, the orientation of each layer in the stacked layers will be described as follows. First, the extending direction of the cylindrical lens 43a in the light source layer 47, the emission direction of the light 48 from the light source 41, and the direction of the ridge line 44b on the prism layer 63 of the light refraction sheet 44 are parallel to each other. Further, the ridge line 44a on the inverted pyramid layer 62 of the light refraction sheet 44 forms an angle of 45° with respect to the ridge line 44b of the prism layer 63. In addition, the ridge line 45a of the prism on the first light diffusion sheet 45 and the ridge line 45b of the prism on the second light diffusion sheet 46 are orthogonal to each other, and the ridge line 45a is orthogonal to the ridge line 44b on the prism layer 63 of the light refraction sheet 44.

[0052] It should be noted that the terms "parallel" and "orthogonal" as used herein include not only strictly geometric parallelism and orthogonality, but also substantially parallel and orthogonal within the range of industrial errors or within the range where the functions and effects of the present invention are not lost. For example, it is allowed that the angle formed by two directions deviates from 0° (in the case of parallel) or 90° (in the case of orthogonal). The deviation is preferably 10° or less.

[0053] The constituent elements are further described below.

[0054] <Light source layer>

[0055] The light source layer 47 includes a reflection sheet 42, a light guide plate 43 stacked on the reflection sheet, and a light source 41. The light source 41 inputs the light 48 through the end of the light guide plate 43 substantially parallel to the light guide plate 43. The light guide plate 43 guides the light 48 toward the side opposite to the light source 41 and emits the light 48 to the liquid crystal display panel 5 side at a relatively small angle with respect to the surface of the light guide plate 43. The reflection sheet 42 reflects the light that is about to exit to the side opposite to the liquid crystal display panel 5 so as to guide the light to the liquid crystal display panel 5 side.

[0056] The reflective sheet 42 is composed of, for example, a white polyethylene terephthalate resin film, a silver vapor deposition film, etc. The light guide plate 43 can also be a lenticular lens sheet made of, for example, polycarbonate, polyethylene terephthalate, acrylic resin, etc. In this case, each lenticular lens 43a (see Figure 2 for the plan view) preferably extends in the incident direction of the light 48. It should be noted that when the light guide plate 43 (and thus the display screen 50a) is rectangular, the incident direction of the light 48 is generally perpendicular to the side where the light source layer 47 is provided. Although the light 48 is emitted from the light source 41 with a certain degree of diffuseness, its incident direction can be considered as the direction indicated by the center of the light 48.

[0057] It should be noted that the term "sheet" (such as a light refraction sheet and a light diffusion sheet) generally refers to a relatively thin flat shape and includes plate-shaped components, film-shaped components, etc.

[0058] The type of the light source 41 is not particularly limited, and for example, an LED element, a laser element, etc. can be used, and from the perspectives of cost, productivity, etc., an LED element can be used. When an LED element is used, the LED element can include a plurality of LED chips.

[0059] <Light refraction sheet>

[0060] The first surface of the light refraction sheet 44 ( Figure 2 the surface on the side of the light source layer 47 at the bottom) includes a plurality of concave portions formed in an inverted substantially polyhedral pyramid shape or an inverted substantially truncated polyhedral pyramid shape. The second surface of the light refraction sheet 44 includes a plurality of groove lines formed adjacent to each other and having an isosceles triangle cross-section. As an example, the light refraction sheet 44 of this embodiment (which is shown individually and in an enlarged form in Figure 3 ) includes a substrate layer 61, an inverted pyramid layer 62 provided on one surface (the first surface) of the substrate layer 61, and a prism layer 63 provided on the other surface (the second surface) of the substrate layer 61. In the example of this embodiment, the prism layer 63 is provided on the side of the light source layer 47, and the inverted pyramid layer 62 is provided on the opposite side.

[0061] The total thickness of the light refraction sheet 44 is about 50 μm or more and 300 μm or less.

[0062] [Substrate layer]

[0063] The base material layer 61 needs to transmit light, and thus is formed using a transparent (e.g., colorless and transparent) synthetic resin as the main component. The main component of the base material layer 61 is not particularly limited, and for example, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polystyrene, polyolefin, cellulose acetate, weather-resistant vinyl chloride, etc. may be used. Note that the term "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 material layer 61 may contain a diffusing agent or other additives, or may be substantially free of additives. The additives that may be included 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, etc.

[0064] The lower limit of the average thickness of the base material 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 material layer 61 is preferably about 500 μm, more preferably about 250 μm, and even more preferably about 180 μm.

[0065] When the average thickness of the base material layer 61 is less than the lower limit, curling may occur when forming the inverted pyramid layer 62 and the prism layer 63. Conversely, when the average thickness of the base material layer 61 exceeds the upper limit, the brightness of the liquid crystal display device 50 may decrease, and it may be difficult to meet the requirement of making the liquid crystal display device 50 thinner. It should be noted that the term "average thickness" refers to the average of the thicknesses at any ten points.

[0066] [Prism layer]

[0067] The prism layer 63 is configured such that a plurality of groove lines having an isosceles triangle cross-section are arranged adjacent to each other, and the prism 64 is formed by a triangular prism portion sandwiched between adjacent pairs of groove lines. Further, the prism layer 63 may be formed using, for example, a UV curable acrylic resin.

[0068] In addition, the triangular prism-shaped prisms 64 are arranged to extend in the same direction as the extending direction of the cylindrical lens 43a of the light source layer 47. This also matches the direction in which the light 48 is emitted from the light source layer 47 in the light source layer 47. In Figure 2 the plan view, this direction is indicated by the ridge line 44b of the prism 64.

[0069] Figure 6 The shape of the prism 64 is shown. Figure 6 The plan view and a cross-sectional view perpendicular to the ridge line 44b (the position of the cross-section is shown by a dashed line) of the prism layer 63 are shown. Each individual prism 64 is an isosceles triangle, and on the side of the base material layer 61 ( Figure 6The edges on the lower side (in the figure) form the base. The shape of the prism 64 can be represented by the height h, the pitch p, and the apex angle θ.

[0070] The height h of the prism 64 is preferably about 8 μm or greater and 100 μm or less. The pitch p of the prism 64 is preferably about 15 μm or greater and 200 μm or less. The apex angle θ of the prism 64 is preferably about 60° or greater and 120° or less, and more preferably about 80° or greater and 100° or less.

[0071] Note that in Figure 6 etc., the prism 64 is shown as a geometrically strict isosceles triangle, and adjacent prisms 64 are shown as being in contact with each other. However, shapes different from the Figure 6 example shown can be used as long as the functions and effects of the present invention are not lost, or within the inevitable shape variability caused by machining accuracy during industrial production. For example, the vertex (ridge line 44b) portion can be rounded, or the prism 64 can have a flat trapezoidal shape. In this case, the apex angle θ is the angle formed when the sides of the imaginary triangle are extended. In addition, adjacent prisms 64 can be arranged with a small gap therebetween. In this case, the length of the base of the triangle does not match the pitch p.

[0072] [Inverted pyramid layer]

[0073] The inverted pyramid layer 62 is provided with a plurality of concave portions 44c for diffusing light, and these concave portions have an uneven shape, such as an inverted substantially polyhedral shape (in this example, an inverted substantially quadrangular pyramid shape (inverted pyramid shape)). The inverted pyramid layer 62 needs to transmit light, and thus a transparent (e.g., colorless transparent) synthetic resin can be used as the main component to form it. For example, the inverted pyramid layer 62 can be integrally formed with the base layer 61 during the extrusion molding of the base resin to be used as the base layer 61, or can be separately formed using a UV curable resin or the like after molding the base layer 61.

[0074] As Figure 4 shown, for example, the plurality of concave portions 44c can be arranged in a two-dimensional matrix pattern. In other words, the plurality of concave portions 44c can be arranged along two mutually orthogonal directions. Adjacent concave portions 44c are separated by ridge lines 44a. The ridge lines 44a extend along the two directions in which the concave portions 44c are arranged. The arrangement pitch of the concave portions 44c can be, for example, about 50 μm or greater and about 500 μm or less. The center 44e (the vertex of the inverted pyramid) of the concave portion 44c is the deepest part of the concave portion 44c. The center 44e (the deepest part) of the concave portion 44c can reach the surface of the base layer 61. In other words, the depth of the concave portion 44c can be equal to the thickness of the inverted pyramid layer 62. Note that, for the sake of brevity,Figure 4 shows a state in which the recesses 44c are arranged in a 5×5 matrix pattern, but the actual number of the arranged recesses 44c is much larger.

[0075] In this embodiment, the recess 44c has a quadrangular pyramid shape with a square bottom surface. Further, the ridge line 44a in the inverted pyramid layer 62 forms a 45° angle with respect to the ridge line 44b in the prism layer 63. It should be noted that although 45° is the desired angle, this angle is not limited thereto. In order to enhance the brightness improvement effect, it is desirable that the ridge line 44a and the ridge line 44b form an angle rather than being parallel, and this angle is preferably 30° or greater and 60° or less, and more preferably 40° or greater and 50° or less.

[0076] The shape of the inverted pyramid layer 62 is shown in Figure 5 . Figure 5 shows a plan view of the inverted pyramid layer 62 and a cross-sectional view perpendicular to the ridge line 44b and passing through the center 44e of the recess 44c (the position of the cross-sectional view is shown by the dashed line). In this cross-section, the remaining portion 65 after the recess 44c has been removed is an isosceles triangle, and its side on the substrate layer 61 side ( Figure 6 the lower side in) forms the base. Similar to the prism 64 of the prism layer 63, the shape of the remaining portion 65 can be represented by the height h, the pitch p, and the apex angle θ.

[0077] The height h of the remaining portion 65 is preferably about 10 μm or greater and 200 μm or less. The pitch p of the remaining portion 65 is preferably about 20 μm or greater and 400 μm or less. The apex angle θ of the remaining portion 65 is preferably about 60° or greater and 150° or less, and more preferably about 80° or greater and 100° or less.

[0078] It should be noted that in this embodiment, the inverted pyramid-shaped (inverted approximate quadrangular pyramid shape) recesses 44c are arranged in a two-dimensional matrix pattern to provide an uneven shape, but as long as the functions and effects of the present invention are not lost, the recesses 44c can be randomly arranged. When the recesses 44c are regularly arranged two-dimensionally, a gap may or may not be provided between the recesses 44c. The recess 44c may have another inverted approximate polyhedron shape different from the inverted approximate quadrangular pyramid shape. For example, the "inverted polyhedron" shape of the recess 44c may be an inverted triangular pyramid or an inverted hexagonal pyramid, which can be arranged two-dimensionally without a gap, similar to the inverted quadrangular pyramid.

[0079] When the "inverted polyhedron" shape of the recess 44c is an inverted quadrangular pyramid, it is easy to improve the accuracy of the surface cutting operation of the metal mold (metal roll) for providing the recess 44c in the manufacturing process (such as extrusion molding or injection molding).

[0080] In addition, although the term "inverted substantially polygonal pyramid" is used in the present disclosure in view of the fact that it is difficult to form geometrically strict inverted polygonal pyramid-shaped recesses using ordinary shape transfer techniques, it is considered that the term "inverted substantially polygonal pyramid" includes shapes that can be regarded as true or substantially inverted polygonal pyramids. Further, the term "substantially" means "can be approximated", such that, for example, an "inverted substantially quadrangular pyramid" refers to a shape that can be approximated as an inverted quadrangular pyramid. For example, also with respect to an "inverted frustum of a polygonal pyramid" having a flat top, a shape with a small top area is also considered to be included within the "inverted substantially polygonal pyramid" as long as the functions and effects of the present invention are not lost. In addition, shapes deformed from an "inverted polygonal pyramid" within the inevitable shape variability range caused by machining accuracy in industrial production are also considered to be included within the "inverted substantially polygonal pyramid".

[0081] <Light diffusion layer>

[0082] The first light diffusion sheet 45 and the second light diffusion sheet 46 are provided on the light refraction sheet 44 as a light diffusion layer. Each of the light diffusion sheets is configured such that a plurality of groove lines having an isosceles triangle cross-section are provided adjacent to each other, and a prism is formed by a triangular prism portion sandwiched between a pair of adjacent groove lines. For example, a PET (polyethylene terephthalate) film (on which a prism shape has been formed using a UV curable acrylic resin) can be used as the light diffusion sheets 45 and 46.

[0083] As Figure 2 shown in the cross-sectional view, the first light diffusion sheet 45 and the second light diffusion sheet 46 are arranged such that the side on which the prism is provided faces the side opposite to the light source layer 47.

[0084] Furthermore, as Figure 2 shown in the plan view, the first light diffusion sheet 45 is arranged such that the ridge line 45a of the prism is orthogonal to the ridge line 44b of the prism on the light refraction sheet 44. In the second light diffusion sheet 46, the ridge line 45b of the prism is arranged parallel to the ridge line 44b of the prism on the light refraction sheet 44. Accordingly, the first light diffusion sheet 45 and the second light diffusion sheet 46 are arranged such that their respective ridge lines 45a and 45b are orthogonal to each other.

[0085] It should be noted that it is preferable but not essential to use the two light diffusion sheets 45 and 46 as described above as the light diffusion layer. Only one light diffusion sheet or three or more light diffusion sheets can be used, or a light diffusion sheet having a structure different from that of the sheet provided with a prism can be used.

[0086] In addition, a protrusion 46b can be provided on the rear surface (light source layer 47 side) of the second light diffusion sheet 46. For example, the protrusion 46b can have a shape similar to a part of a sphere.

[0087] Example

[0088] Examples that are mainly different in the configuration of the light refraction sheet 44 and comparative examples using an optical sheet different from the light refraction sheet 44 of this embodiment will be described below. The brightness in each example was measured using a luminance meter in the state where the backlight unit 40 was configured as shown in Figure 2 and the brightness is expressed as a relative value with the comparative example as a reference (100%).

[0089] <Vertex angle of the inverted pyramid layer and the base material>

[0090] Examples 1 to 4 and comparative examples to be described below are also shown in Table 1. In Table 1, the first surface refers to the surface of the light refraction sheet 44 (and the optical sheet of the comparative example) on the side opposite to the light source layer 47, and the second surface refers to the surface on the light source layer 47 side.

[0091] (Example 1)

[0092] In the light refraction sheet 44 of Example 1, the pitch p of the remaining portion 65 on the inverted pyramid layer 62 serving as the first surface is 100 μm, the height h is 50 μm, and the vertex angle θ is 90°. Here, if the remaining portions 65 having a strictly geometrically isosceles triangle shape are arranged adjacent to each other without a gap, as shown in Figure 5 it is not possible to obtain these values. However, as described above, shape deformation and gaps between the remaining portions 65 are allowed, and thus these values can be obtained (the same applies to the following examples; this also applies to the prism layer 63).

[0093] Furthermore, the base material layer 61 is made of polyethylene terephthalate (PET) and has a thickness of 75 μm.

[0094] In addition, the pitch p of the prisms 64 on the prism layer 63 serving as the second surface is 100 μm, the height h is 50 μm, and the vertex angle θ is 90°.

[0095] Both the inverted pyramid layer 62 and the prism layer 63 are made of a UV curable resin (described as UV resin in Table 1).

[0096] Regarding the light refraction sheet 44 of Example 1, the actual total thickness is 169 μm. The reason why this value does not match the sum of the height of the remaining portion 65, the thickness of the base material layer 61, and the height of the prism layer 63 as described above is that each dimension is a design value, while the total thickness is an actual dimension. In other words, the reason for the mismatch is the variation in the thickness of the base material layer 61, the manufacturing variation of the inverted pyramid layer 62 and the prism layer 63, etc., and this also applies to the examples described below.

[0097] In Example 1, using the comparative example as a reference, the brightness is 126.0%.

[0098] (Example 2)

[0099] Example 2 is similar to Example 1, except that the base material layer 61 is formed of polycarbonate (PC) with a thickness of 100 μm. The total thickness of the light refraction sheet 44 in Example 2 is 195 μm. In Example 2, the brightness is 125.0%.

[0100] (Example 3)

[0101] The light refraction sheet 44 of Example 3 is similar to that of Example 1, except for the following points. That is, regarding the remaining portion 65 of the inverted pyramid layer 62, the pitch p is 275 μm, the height h is 50 μm, and the apex angle θ is 140°. The total thickness of the light refraction sheet 44 is 168 μm. In Example 3, the brightness is 110.0%.

[0102] (Example 4)

[0103] The light refraction sheet 44 of Example 4 is similar to that of Example 2, except for the following points. That is, regarding the remaining portion 65 of the inverted pyramid layer 62, the pitch p is 275 μm, the height h is 50 μm, and the apex angle θ is 140°. The total thickness of the light refraction sheet 44 is 196 μm. In Example 4, the brightness is 103.8%.

[0104] (Comparative Example)

[0105] In the comparative example, an optical sheet having a different structure is used instead of the light refraction sheet 44 of this embodiment. The base material layer is made of PET with a thickness of 38 μm, and both the first surface and the second surface are coated with a coating containing beads made of a thermosetting resin.

[0106] (Comparison of Examples)

[0107] As shown in Table 1, in all of Examples 1 to 4, compared with the comparative example, the brightness is increased. Further, in Examples 1 and 2 in which the apex angle θ of the inverted pyramid layer 62 is 90°, the effect is more obvious than in Examples 3 and 4 in which the apex angle θ is 140°.

[0108] Paying attention to the differences in the base material layer 61 while keeping the shape the same, the brightness in Examples 1 and 3 using PET is higher than that in Examples 2 and 4 using PC. Specifically, there are obvious differences between Example 3 and Example 4 in which the apex angle θ is 140°.

[0109] Further, in Examples 1 to 4 and the comparative example, the light emission uniformity is substantially the same. Note that the brightness uniformity is evaluated based on the variation of the brightness measured at multiple positions on the light emission surface.

[0110] [Table 1]

[0111]

[0112] [Spacing and Height of Inverted Pyramid Layer and Prism Layer]

[0113] Examples 5 to 7 below are also shown in Table 2. Similarly in this case, the brightness is based on the values of the comparative examples shown in Table 1.

[0114] (Example 5)

[0115] In the light refraction sheet 44 of Example 5, the spacing p of the remaining portion 65 on the inverted pyramid layer 62 is 100 μm, the height h is 50 μm, and the apex angle θ is 90°. The base material layer 61 is made of polyethylene terephthalate (PET) and has a thickness of 75 μm. The spacing p of the prisms 64 on the prism layer 63 is 100 μm, the height h is 50 μm, and the apex angle θ is 90°. The total thickness is 169 μm. In Example 5, the brightness is 122.1%.

[0116] (Example 6)

[0117] In the light refraction sheet 44 of Example 6, the spacing p of the remaining portion 65 on the inverted pyramid layer 62 is 40 μm, the height h is 20 μm, and the apex angle θ is 90°. The base material layer 61 is made of polyethylene terephthalate (PET) and has a thickness of 50 μm. The spacing p of the prisms 64 on the prism layer 63 is 24 μm, the height h is 12 μm, and the apex angle θ is 90°. The total thickness is 83 μm. In Example 6, the brightness is 121.8%.

[0118] (Example 7)

[0119] In the light refraction sheet 44 of Example 7, the spacing p of the remaining portion 65 on the inverted pyramid layer 62 is 40 μm, the height h is 20 μm, and the apex angle θ is 90°. The base material layer 61 is made of polyethylene terephthalate (PET) and has a thickness of 50 μm. The spacing p of the prisms 64 on the prism layer 63 is 24 μm, the height h is 12 μm, and the apex angle θ is 90°. The total thickness is 82 μm. In Example 6, the brightness is 123.8%.

[0120] (Comparison of Examples)

[0121] In all of Examples 5 to 7 in which the sizes (spacing p and height h) of the prisms 64 and the remaining portion 65 are different, the brightness is significantly improved compared to the comparative examples.

[0122] [Table 2]

[0123]

[0124] <Materials and Refractive Indexes of Inverted Pyramid Layer and Prism Layer>

[0125] Table 3 shows the effect of material differences of a light refraction sheet 44 having the same shape as that in Example 6 (the pitch p, height h, apex angle θ of the inverted pyramid layer 62 and prism layer 63, and the thickness of the substrate layer 61).

[0126] More specifically, a light refraction sheet 44 was prepared by using PET or PC as the substrate layer 61 and using three types of resin materials having refractive indexes of 1.5, 1.58, and 1.65, respectively, to form the inverted pyramid layer 62 and prism layer 63. Table 3 shows the corresponding brightness. It should be noted that the refractive index is a value at a wavelength of 589 nm.

[0127] Here, the refractive index of polyethylene terephthalate is about 1.5, and the refractive index of polycarbonate is about 1.6.

[0128] As shown in Table 3, from the viewpoint of improving brightness, it is preferable that the difference between the refractive index of the substrate layer 61 and the refractive index of the prism layer 63 is small. When the substrate layer 61 is made of PC and the refractive index of the resin material is 1.58 (i.e., close to the refractive index of the substrate layer 61), the improvement in brightness is excellent. Similarly, when the substrate layer 61 is made of PET and the refractive index of the resin material is 1.5 (i.e., close to the refractive index of the substrate layer 61), the improvement in brightness is excellent.

[0129] [Table 3]

[0130] Refractive index of the resin 1.5 1.58 1.65 Base material layer PET 126.3％ 102.9％ 114.1％ Base material layer PC 126.7％ 131.1％ 128.5％

[0131] <Light Diffusion Layer>

[0132] Examples of the configurations of the first light diffusion sheet 45 and the second light diffusion sheet 46 constituting the light diffusion layer are shown in Table 4.

[0133] In the light diffusion sheets 45 and 46 as well, it can be assumed that the pitch p, height h, and apex angle θ of the formed prism shapes are the same as those of Figure 6 The thickness is the total thickness obtained by combining the thicknesses of the prism part, the film on which the prism is formed, and the like.

[0134] The brightness was measured in the case of using the light diffusion sheets having the following Configurations A and B and using the same components as those of Figure 6 the light refraction sheet 44 as the components.

[0135] In Configuration A, regarding Figure 2The second light diffusion sheet 46 on the upper side has a thickness of 100 μm, a pitch p of 24 μm, a height h of 11.5 μm, and a vertex angle θ of 90°, and is estimated to have a refractive index of 1.7 at a wavelength of 450 nm and 1.68 at a wavelength of 532 nm. Regarding the first light diffusion sheet 45 on the lower side, the thickness is 75 μm, the pitch p is 24 μm, the height h is 11.5 μm, the vertex angle θ is 90°, and the refractive index is estimated to be 1.68 at a wavelength of 450 nm and 1.65 at a wavelength of 532 nm. In this configuration, the brightness is 113.1%.

[0136] In Configuration B, regarding the second light diffusion sheet 46, the thickness is 95 μm, the pitch p is 24 μm, the height h is 12 μm, the vertex angle θ is 90°, and the refractive index is estimated to be 1.67 at a wavelength of 450 nm and 1.64 at a wavelength of 532 nm. Regarding the first light diffusion sheet 45, the thickness is 65 μm, the pitch p is 24 μm, the height h is 12 μm, the vertex angle θ is 90°, and the refractive index is estimated to be 1.68 at a wavelength of 450 nm and 1.64 at a wavelength of 532 nm. In this configuration, the brightness is 126.3%.

[0137] From the perspective of brightness improvement, it is preferable that the refractive index of the light refraction sheet 44 is less than that of the light diffusion sheet. The refractive index difference is preferably 0.05 or more and approximately 0.18.

[0138] Note that the "estimated refractive index" is the refractive index calculated based on the shape of the prism and the angle of the light emitted from the light diffusion sheet.

[0139] [Table 4]

[0140]

[0141] [Configuration for preventing moiré fringes]

[0142] In the backlight unit 40 of this embodiment, moiré fringes may appear on the light emitting surface, resulting in a reduction in brightness uniformity. Figure 7 and Figure 8 An exemplary configuration of the prism layer 63 for suppressing the appearance of moiré fringes is shown. It should be noted that moiré fringes may occur due to, for example, the dimensional relationships of the corresponding parts in the light guide plate 43, the light refraction sheet 44, the light emitting layer, etc. In the backlight unit 40 of this embodiment, the following configuration is not necessary for achieving moiré - free light emission.

[0143] In Figure 7 , the groove lines in the prism layer 63 of the light refraction sheet 44 and the prisms 64 left by the groove lines are formed in the shape of a repeatedly bent wave. Therefore, the ridge line 44b also becomes wavy.

[0144] InFigure 8 In this case, the extending direction of the groove line and the prism 64 (ridge line 44b) is not parallel to the emission direction of the light 48 from the light source layer 47 (indicated by the upward arrow), but forms an angle of, for example, about 5° to 10°. It should be noted that in this case as well, the angle between the ridge line 44a of the inverted pyramid layer 62 and the ridge line 44b of the prism layer 63 is preferably 45°. Compared with Figure 2 the desired configuration shown, the structure of the light refraction sheet 44 itself is the same, but the light refraction sheet 44 is slightly rotated (e.g., 5° to 10°) when in use.

[0145] Therefore, the appearance of moiré fringes can be suppressed, and the brightness uniformity can be improved.

[0146] <Other configurations>

[0147] When Figure 2 the light refraction sheet 44 in is turned upside down so that the inverted pyramid layer 62 faces the light source layer 47 side, the effect of improving brightness can also be achieved. However, when the prism layer 63 faces the light source layer 47 side, as described above, the effect is more obvious.

[0148] Industrial applicability

[0149] According to the technology of the present disclosure, uniform and high-brightness light emission is achieved, and thus the technology of the present disclosure can be used as a side light type backlight unit, as well as a liquid crystal display device and an information device using the side light type backlight unit.

[0150] List of reference numerals

[0151] 1 TFT substrate

[0152] 2 CF substrate

[0153] 3 Liquid crystal layer

[0154] 5 Liquid crystal display panel

[0155] 6 First polarizing plate

[0156] 7 Second polarizing plate

[0157] 40 Backlight unit

[0158] 41 Light source

[0159] 42 Reflective sheet

[0160] 43 Light guide plate

[0161] 43a Cylindrical lens

[0162] 44 Light refraction sheet

[0163] 44a Ridge line

[0164] 44b Ridge line

[0165] 44c Concave portion

[0166] 44e Center (of the concave portion)

[0167] 45 First light diffusing sheet

[0168] 45a Ridge line

[0169] 45b Ridge line

[0170] 46 Second light diffusing sheet

[0171] 47 Light source layer

[0172] 48 Light

[0173] 50 Liquid crystal display device

[0174] 50a Display screen

[0175] 61 Substrate layer

[0176] 62 Inverted pyramid layer

[0177] 63 Prism layer

[0178] 64 Prism

[0179] 65 Remaining part

Claims

1. A side light type backlight unit, comprising: A light guide plate that guides light entering through one end to the end side on the opposite side; A light refraction sheet stacked on one surface of the light guide plate; And A light diffusion layer stacked on the light refraction sheet, Wherein, the first surface of the light refraction sheet includes a plurality of concave portions formed in an inverted substantially polyhedral pyramid shape or an inverted substantially truncated polyhedral pyramid shape, and The second surface of the light refraction sheet includes a plurality of groove lines formed adjacent to each other and having an isosceles triangle cross-section.

2. The side light type backlight unit according to claim 1, Among them, The groove lines provided on the second surface of the light refraction sheet are parallel to the direction in which the light enters the light guide plate.

3. The side light type backlight unit according to claim 1 or 2, Among them, The concave portions provided on the first surface of the light refraction sheet are formed in an inverted substantially quadrangular pyramid shape or an inverted substantially truncated quadrangular pyramid shape having a rectangular or square bottom surface, and The ridge lines separating adjacent concave portions form an angle of 30° or more and 60° or less with respect to the direction in which the light enters the light guide plate.

4. The side light type backlight unit according to claim 1 or 2, Among them, The light diffusion layer includes a first light diffusion sheet and a second light diffusion sheet, and the first light diffusion sheet is positioned closer to the light guide plate side than the second light diffusion sheet, Each of the first light diffusion sheet and the second light diffusion sheet includes a plurality of groove lines formed adjacent to each other on the surface on the side opposite to the light guide plate and having an isosceles triangle cross-section, The groove lines in the first light diffusion sheet are orthogonal to the direction in which the light enters the light guide plate, and The groove lines in the second light diffusion sheet are parallel to the direction in which the light enters the light guide plate.

5. The side light type backlight unit according to claim 1 or 2, Among them, The second surface of the light refraction sheet is on the light guide plate side.

6. The side light type backlight unit according to claim 1 or 2, Among them, The apex angle of the concave portions formed in the light refraction sheet is 80° or more and 100° or less.

7. The side light type backlight unit according to claim 1, Among them, The groove lines provided on the second surface of the light refraction sheet form an angle of 5° or more and 10° or less with respect to the direction in which the light enters the light guide plate.

8. The side light type backlight unit according to claim 1, Among them, The groove lines provided on the second surface of the light refraction sheet are formed in a repeatedly curved wavy shape.

9. A liquid crystal display device, the liquid crystal display device comprising: The side light type backlight unit according to claim 1; And A liquid crystal display panel.

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

Images