Light guide plate, surface light source device, display device, and method for manufacturing light guide plate

Abstract

The present invention relates to a light guide plate, a surface light source device, a display device, and a method for manufacturing a light guide plate. The light guide plate (12) is characterized in that it has: a light incident surface (12a) for light to enter; a light exit surface (12c) intersecting the light incident surface (12a) and from which light exits; and an opposing surface (12b) opposing the light incident surface (12a). The light guide plate guides light incident from the light incident surface (12a) toward the opposing surface (12b) while exiting from the light exit surface (12c). The refractive index (Nx) in a direction perpendicular to the light incident surface (12a) is greater than the refractive index (Ny) in a direction parallel to the light exit surface (12c) and parallel to the light incident surface (12a).

Description

[0001] This application is a divisional application. The application number of the original application is 201880092408.2, the application date is April 16, 2018, and the name of the invention is "Light guide plate, surface light source device, display device, and manufacturing method of light guide plate." Technical Field

[0002] The present invention relates to a light guide plate, a surface light source device, a display device and a method for manufacturing the light guide plate. Background Art

[0003] Conventionally, there is known a display device that displays an image by illuminating a display portion such as an LCD (Liquid Crystal Display) panel using a surface light source device.

[0004] Surface light source devices are broadly classified into the following types: direct-light type, in which the light source is positioned directly below optical components such as optical sheets; and edge-light type, in which the light source is positioned to the side of the optical component. Edge-light type surface light source devices, because they place the light source to the side of an optical component such as a light guide plate, offer the advantage of being thinner than direct-light type surface light source devices, leading to their widespread use in recent years.

[0005] Generally speaking, in an edge-light type surface light source device, the light source is arranged at a position facing the side of the light guide plate, that is, the light incident surface. The light emitted by the light source enters the light guide plate from the light incident surface, and is repeatedly reflected by the light emitting surface and the back surface opposite to the light emitting surface, while traveling from the light incident surface toward the opposite surface opposite to the light incident surface in a direction perpendicular to the light incident surface (light guiding direction).

[0006] Furthermore, the traveling direction of light is changed by using a concave-convex shape provided on the light guide plate, so that light is emitted toward the LCD panel from various positions along the light guide direction of the light exit surface (for example, Patent Document 1).

[0007] A portion of such a light guide plate is sometimes manufactured by extrusion molding, in which a resin is extruded and formed. However, in this case, there is a possibility that light incident from the light incident surface leaks, thereby causing so-called brightness unevenness such as bright lines on the light exiting surface.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-217283 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] An object of the present invention is to provide a light guide plate, a surface light source device, a display device, and a method for manufacturing a light guide plate, which are capable of suppressing the occurrence of uneven brightness.

[0013] Means for solving problems

[0014] The present invention solves the problem by the following solution. Furthermore, for ease of understanding, the present invention is described using reference numerals corresponding to the embodiments thereof, but the present invention is not limited thereto. Furthermore, the structures described with reference numerals may be modified as appropriate, or at least a portion thereof may be replaced with other structures.

[0015] The first invention is a light guide plate (12), which has: a light incident surface (12a) for light incident; a light emitting surface (12c) intersecting the light incident surface and from which light is emitted; and an opposite surface (12b) opposite to the light incident surface, wherein the light guide plate guides light incident from the light incident surface toward the opposite surface while emitting light from the light emitting surface, and is characterized in that a refractive index Nx in a direction perpendicular to the light incident surface is greater than a refractive index Ny in a direction parallel to the light emitting surface and parallel to the light incident surface.

[0016] The second invention is a surface light source device (10), wherein the surface light source device comprises: a light guide plate (12) of the first invention; and a light source portion (11) which is arranged at a position facing the light incident surface (12a) of the light guide plate and projects light onto the light incident surface.

[0017] The third invention is a display device (1), wherein the display device comprises: the surface light source device (10) of the second invention; and a display portion (2) which is arranged on the light emitting surface (12c) side of the light guide plate (12) provided in the surface light source device.

[0018] A fourth invention is a display device characterized in that, in the display device (1) of the third invention, the display portion (2) is a reflective display portion.

[0019] The fifth invention is a method for manufacturing a light guide plate, which manufactures the light guide plate (12) of the first invention by an extrusion molding method, and is characterized in that the method for manufacturing the light guide plate comprises: a resin extrusion process, in which the resin forming the light guide plate is extruded onto a molding plate (70) having a concave-convex portion (73) corresponding to the shape of the light guide plate; and a light guide plate molding process, in which the resin extruded by the resin extrusion process is conveyed while being pressed on the molding plate to form the light guide plate, and the molding plate is arranged in such a manner that the surface (73a) of the concave-convex portion corresponding to the light incident surface (12a) is perpendicular to the conveying direction (S) of the resin.

[0020] Effects of the Invention

[0021] According to the present invention, the occurrence of uneven brightness can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1 is a schematic diagram illustrating the display device 1 .

[0023] Figure 2 It is a diagram for explaining the light guide plate 12 .

[0024] Figure 3 This is a diagram illustrating details of a shaped sheet used in manufacturing the light guide plate 12 .

[0025] Figure 4 It is a diagram for explaining a method of manufacturing the light guide plate 12 .

[0026] Figure 5 These are photographs showing how light incident on the light guide plates of the embodiment and the comparative example exits from the light exit surface.

[0027] Description of labels

[0028] 1: Display device;

[0029] 10: Surface light source device;

[0030] 11: Light source;

[0031] 12: Light guide plate;

[0032] 12a: light incident surface;

[0033] 13: concave and convex part;

[0034] 70: excipient tablets;

[0035] 71: base material portion;

[0036] 72: forming layer;

[0037] 73: Concavo-convex shape portion. DETAILED DESCRIPTION

[0038] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, the technical scope of the present invention is not limited to these embodiments. In addition, in the drawings used to illustrate the embodiments, the sizes and proportions of the components may be changed or exaggerated as needed.

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings and the like. Figure 1 The drawings shown below are schematic diagrams, and the sizes and shapes of the parts are appropriately exaggerated for easier understanding.

[0040] In this specification, the terms "plate" and "sheet" are used. However, as a general rule, they are used in the order of thickness, plate, sheet, and film, and this is also used in this specification. However, this distinction is not technically meaningful, so these terms can be appropriately replaced.

[0041] The numerical values, material names, and the like of the dimensions of each component described in this specification are examples of the embodiment and are not limiting, and can be appropriately selected and used.

[0042] In this specification, terms specifying shapes or geometric conditions, such as parallel or perpendicular, include, in addition to their strict meanings, states in which the same optical function is achieved and there is an error to the extent that they are considered to be parallel or perpendicular.

[0043] In this specification, a sheet surface (plate surface, film surface) refers to a surface in the plane direction of each sheet (plate, film) when the sheet (plate, film) is viewed from the entire sheet (plate, film).

[0044] (Implementation Method)

[0045] Figure 1 It is a diagram for explaining the display device 1 according to this embodiment.

[0046] Figure 2 It is a diagram for explaining the light guide plate 12 of this embodiment. Figure 2 (a) is a top view of the light guide plate 12 observed from the light emitting surface 12c side, Figure 2 (b) is Figure 2 A partial cross-sectional view of part b of (a).

[0047] And, in the included Figure 1 For ease of understanding in the following figures and descriptions, when the display device 1 is in use, the direction perpendicular to the light incident surface 12a of the light guide plate 12, of the two directions parallel to and perpendicular to the screen of the display device 1, is referred to as the X direction, and the direction perpendicular to the X direction is referred to as the Y direction. Furthermore, the direction perpendicular to the screen of the display device 1 (the thickness direction) is referred to as the Z direction. Furthermore, the +Z side of the thickness direction (Z direction) is referred to as the observer side, and the -Z side is referred to as the back side.

[0048] The display device 1 of this embodiment includes an LCD panel 2 and a surface light source device 10. The display device 1 illuminates the LCD panel 2 from the viewer's side using the surface light source device 10 and displays image information formed on the LCD panel 2.

[0049] The screen of the display device 1 of this embodiment is equivalent to the surface (hereinafter referred to as the display surface) 10a on the +Z side (observer side) of the surface light source device 10. The "front direction" of the display device 1 refers to the normal direction of the display surface 10a, which is parallel to the Z direction and consistent with the normal direction of the plate surface of the light guide plate 12 described later.

[0050] The LCD panel 2 is formed of a liquid crystal display element and is a reflective display unit that displays image information on its display surface. The LCD panel 2 is formed in a generally flat plate shape. When viewed in the Z direction, the LCD panel 2 has a rectangular shape with two opposing sides parallel to the X direction and two opposing sides parallel to the Y direction.

[0051] The surface light source device 10 illuminates the LCD panel 2 from the viewer side (+Z side), and includes a light source unit 11 and a light guide plate 12. The surface light source device 10 is an edge light type surface light source device (front light).

[0052] The light source unit 11 emits light for illuminating the LCD panel 2. The light source unit 11 is arranged along the Y direction so as to face a light incident surface 12a (described later) on one side (+X side) of the light guide plate 12 in the X direction.

[0053] The light source unit 11 is formed by arranging multiple point light sources at predetermined intervals in the Y direction. These point light sources utilize LEDs (Light Emitting Diodes). Furthermore, the light source unit 11 can be a linear light source, such as a cold-cathode tube, or it can be configured as a light source arranged on the end face of a light guide extending in the Y direction.

[0054] In order to improve the efficiency of utilizing the light emitted by the light source unit 11 , a reflective plate (not shown) may be provided to cover the outside of the light source unit 11 .

[0055] The light guide plate 12 constituting the surface light source device 10 has a rectangular shape when viewed from the front direction (Z direction), and has two opposing sides parallel to the X direction and two opposing sides parallel to the Y direction.

[0056] The light guide plate 12 is a substantially flat plate-shaped member that guides light. The light emitted from the light source 11 enters the light incident surface 12 a , is guided within the light guide plate 12 , and then is emitted from the light emitting surface 12 c .

[0057] In this embodiment, the light incident surface 12a and the opposing surface 12b are located at the two ends of the light guide plate 12 in the X direction (the +X side end and the -X side end), and are two sides extending parallel to the Y direction when viewed from the normal direction of the plate surface (the Z direction).

[0058] Furthermore, the light emitting surface 12c and the back surface 12d, which are opposed to each other, are located at the two Z-direction end portions (-Z side end portion and +Z side end portion) of the light guide plate 12. The plate surface of the light guide plate 12 is parallel to the XY plane, and the back surface 12d, which becomes the display surface 10a of the display device 1, is a surface parallel to the plate surface.

[0059] The first side surface 12e and the second side surface 12f facing each other are located at the two ends of the light guide plate 12 in the Y direction (-Y side end and +Y side end), and are two sides extending parallel to the X direction when viewed from the normal direction of the plate surface (Z direction).

[0060] The light guide plate 12 allows the light emitted from the light source portion 11 to be incident from the light incident surface 12a, and while being totally reflected on the light emitting surface 12c and the back surface 12d, it mainly guides the light in the X direction toward the opposite surface 12b side (X2 side) opposite to the light incident surface 12a, and is appropriately emitted from the light emitting surface 12c to the LCD panel 2 side (-Z side).

[0061] Regarding the light guide plate 12 of this embodiment, the shape observed from the thickness direction (Z direction) is formed into a rectangular shape. From the perspective of guiding more light, among the surfaces parallel to the thickness direction, the surfaces parallel to the length direction (Y direction) are used as the light incident surface 12a and the opposing surface 12b.

[0062] In this embodiment, if Figure 2 As shown, a concave-convex portion 13 is formed on the light exit surface 12c of the light guide plate 12. The concave-convex portion 13 is composed of tiny concave and convex portions formed alternately in a direction (X direction) perpendicular to the light incident surface 12a. As a result, the light guided in the light guide plate 12 can be appropriately emitted from the light exit surface 12c.

[0063] like Figure 2 As shown in (b), the concavo-convex portion 13 is composed of convex portions 13a with a rectangular cross-section and concave portions 13b with a rectangular cross-section. These extend in the Y direction of the light guide plate 12 and are alternately formed in the X direction. The concavo-convex portions constituting the concavo-convex portion 13 are finely formed. For example, the depth of the concave portion 13b is approximately 0.1 μm to 3.0 μm. In addition, the bottom width of the concave portion 13b and the top width of the convex portion 13a are approximately 1 μm to 30 μm.

[0064] Furthermore, the shape of the concavo-convex portion 13 is not limited to the above-described example, and other forms may be applied, or a plurality of forms may be applied in combination.

[0065] As other forms of concave and convex portions, for example, the following forms can be listed: a form having a predetermined cross-section and extending in an inclined manner relative to the width direction (Y direction) of the light guide plate 12; a form having a two-dimensional shape in which a plurality of conical convex portions are arranged vertically and horizontally when viewed from above; and a form in which a plurality of convex portions are arranged in the shape of dots when viewed from above.

[0066] The light guide plate 12 can be formed from a variety of materials. For example, in addition to thermoplastic resins such as alicyclic polymer resins, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyethersulfone, reactive resins such as epoxy acrylates and urethane acrylates can also be used. These materials are widely used for optical components such as light guide plates, have excellent mechanical and optical properties, stability, and processability, and are readily available at low cost.

[0067] The light guide plate 12 of this embodiment is formed such that the refractive index Nx in the direction perpendicular to the light incident surface 12a (the X direction, the direction from the light incident surface 12a toward the opposing surface 12b) is greater than the refractive index Ny in the width direction parallel to the light exit surface 12c and parallel to the light incident surface 12a (the Y direction, the direction from the first side surface 12e toward the second side surface 12f) (Nx>Ny). As a result, the light guide plate 12 of this embodiment can uniformly emit light incident from the light incident surface 12a and guided within the light guide plate 12 from the light exit surface.

[0068] When the refractive index Nx in the direction perpendicular to the light incident surface 12a is smaller than the refractive index Ny in the width direction (Nx<Ny), light incident from the light incident surface may leak. In this case, bright lines are seen on the light emitting surface, resulting in uneven brightness, which is not desirable.

[0069] This is thought to be because, when the refractive index (Nx) in the X direction (light guiding direction) perpendicular to the light incident surface is lower than the refractive index (Ny) in the Y direction (Nx < Ny), light incident from the incident surface tends to travel in the light guiding direction (X direction), and the light is excessively concentrated in the X direction, making it more likely to be seen as a bright line. On the other hand, it is thought that when the refractive index in the X direction (light guiding direction) is higher than the refractive index in the Y direction (Nx > Ny), part of the light incident from the incident surface is dispersed and travels in a direction intersecting the X direction, suppressing excessive light concentration in the X direction and, therefore, suppressing the occurrence of bright lines.

[0070] The light guide plate 12 of this embodiment is formed of a polycarbonate resin having optical anisotropy, and has a refractive index Nx of 1.59 in a direction perpendicular to the light incident surface 12 a and a refractive index Ny of 1.58 in a direction perpendicular to the first side surface 12 e .

[0071] Here, the light guide plate 12 is particularly effective when used as a front light as in the display device 1 of the present embodiment.

[0072] Regarding the light guide plate used for backlighting, there is a case where the light exiting surface of the light guide plate is not only equipped with an LCD panel but also with a diffuser plate or prism sheet. Therefore, even if the above-mentioned bright lines are generated on the light exiting surface of the light guide plate, they are not easily noticeable due to the diffuser plate and other factors. In contrast, for the light guide plate 12 used for frontlighting, since the back surface 12d of the light guide plate directly serves as the display surface 10a of the display device 1, the possibility of bright lines being visible when they are generated is very high. Therefore, by providing a light guide plate 12 in the surface light source device 10 that satisfies Nx>Ny, as in the display device 1 of this embodiment, the above-mentioned bright lines can be suppressed from being visible.

[0073] Furthermore, since the display device 1 of this embodiment includes a reflective LCD panel 2 as described above, when the amount of incident light such as external light incident on the LCD panel 2 is sufficient, the light source unit 11 provided in the surface light source device 10 is used in a turned-off state. On the other hand, when the amount of incident light incident on the LCD panel 2 is insufficient, resulting in a dark image displayed on the display surface 10a, the display device 1 is used with the light source unit 11 emitting light.

[0074] Therefore, if the display device 1 is to be placed in a relatively bright location, the light source unit 11 is illuminated for a very short time. Therefore, from the perspective of reducing the cost or energy consumption of the display device 1, the number of point light sources used in the light source unit 11 may be reduced. In such a case, if the refractive index in the light guiding direction (X direction) is lower than that in the Y direction (Nx < Ny), the spacing between the point light sources increases, which may cause bright lines to be more noticeable. However, by making the refractive index in the light guiding direction (X direction) higher than that in the Y direction (Nx > Ny) as in this embodiment, the bright lines can be suppressed from being noticeable even in such a case.

[0075] The thickness of the light guide plate 12 (the distance from the light emitting surface 12c (the top of the convex portion) to the back surface 12d in the thickness direction of the light guide plate) is preferably 0.1 mm to 1.0 mm. When the thickness of the light guide plate 12 is less than 0.1 mm, the number of reflections of the light guided within the light guide plate becomes too many. On the other hand, when the thickness is greater than 1.0 mm, the number of reflections of the light guided within the light guide plate becomes too few. Therefore, in either case, it is difficult to uniformly emit light from the light emitting surface of the light guide plate, which is not desirable. In addition, the thickness of the light guide plate 12 of this embodiment is, for example, 0.4 mm.

[0076] Furthermore, to more effectively suppress the visibility of the aforementioned bright lines, the refractive index difference (Nx - Ny) between the refractive index Nx and the refractive index Ny of the light guide plate 12 is preferably 0.002 or greater, more preferably 0.005 or greater, and even more preferably 0.01 or greater. This refractive index difference tends to vary depending on the thickness of the light guide plate. More specifically, as the thickness of the light guide plate decreases, the refractive index difference decreases. Therefore, when the thickness of the light guide plate 12 is 0.1 mm, the lower limit of the aforementioned preferred range, the refractive index difference is preferably 0.002 or greater.

[0077] (Regarding the Manufacturing Method of the Light Guide Plate 12)

[0078] Here, before describing the method for manufacturing the light guide plate 12 , the shaping sheet 70 used for molding the light guide plate 12 will be described.

[0079] Figure 3 This is a diagram for explaining a shaping sheet 70 used for molding the light guide plate 12 .

[0080] like Figure 3 As shown, the shaping sheet 70 is a long, flexible resin-formed plate in which a base material 71 and a shaping layer 72 are laminated. The shaping sheet 70 is wound before the light guide plate 12 is manufactured.

[0081] The base material portion 71 is a base material serving as a base of the shaped sheet 70 and is formed of, for example, polyethylene terephthalate (PET) resin.

[0082] Furthermore, in addition to PET resin, transparent resins such as polycarbonate (PC) resin, methyl methacrylate-butadiene-styrene (MBS) resin, methyl methacrylate-styrene (MS) resin, acrylonitrile-styrene (AS) resin, and acrylonitrile-butadiene-styrene (ABS) resin may also be used.

[0083] The shaping layer 72 is a layer having concavo-convex portions 73 corresponding to the concavo-convex portions 13 of the light guide plate 12 formed on the surface (surface) opposite to the substrate portion 71. The shaping layer 72 is formed, for example, from a urethane acrylate-based UV-curable resin. In addition to urethane acrylate-based UV-curable resins, other UV-curable resins such as polyester acrylates, epoxy acrylates, polyether acrylates, polythiol resins, and butadiene acrylates can also be used. Furthermore, in addition to the aforementioned UV-curable resins, electron beam-curable resins can also be used as energy ray-curable resins.

[0084] In order to simultaneously mold multiple light guide plates 12, a plurality of concavo-convex portions 73 are arranged on the surface of the shaping layer 72. In this embodiment, three rows of concavo-convex portions 73 are formed in a direction parallel to the short sides of the long shaped sheet 70, and the concavo-convex portions 73 are formed in multiple stages in a direction parallel to the long sides.

[0085] Next, a method for manufacturing the light guide plate 12 by extrusion molding will be described.

[0086] Figure 4 It is a diagram for explaining a method of manufacturing the light guide plate 12 .

[0087] First, if Figure 4 As shown, the wound shaped sheet 70 is unwound and sequentially conveyed between a first roller 81 and a second roller 82, wherein the second roller 82 is arranged with a predetermined gap relative to the first roller 81. Here, the conveying direction S of the shaped sheet 70 is a direction parallel to the direction perpendicular to the short side of the shaped sheet 70.

[0088] Then, the molten thermoplastic resin composition 85 (resin forming the light guide plate) is extruded from the nozzle 86 between the surface of the shaping sheet 70 on the side where the concavo-convex portion 73 is formed and the second roller 82 (resin extrusion step).

[0089] Next, the extruded thermoplastic resin composition 85 is fed together with the shaping sheet 70 and is sandwiched between the first roller 81 and the second roller 82 for extrusion to form the light guide plate 12 (light guide plate forming step). Thus, the thermoplastic resin composition 85 is filled in the shaping layer 72 (see FIG. 1 ) of the shaping sheet 70. Figure 3 ) is placed in the concave-convex portion 73 provided on the surface of the shaped sheet 70, and is cooled by the second roller 82 and the atmosphere (external air, the working environment of the manufacturing device, etc.), thereby solidifying into the shape of the concave-convex portion 73 along the shaped sheet 70.

[0090] The thermoplastic resin composition 85 is further cooled by passing through the third roller 83 and the fourth roller 84, and its final shape is fixed. Thus, a light guide plate assembly sheet 10' having multiple light guide plates 12 in the vertical and horizontal regions can be obtained.

[0091] Next, the light guide plate imposition sheet 10 ′ is released from the shaping sheet 70 by the peeling roller 87 .

[0092] Finally, the light guide plate assembly sheet 10' is punched out, cut, etc., thereby obtaining a plurality of individual light guide plates 12 (see Figure 2 (a)).

[0093] The inventors of the present invention conducted intensive research and found that since the thermoplastic resin composition 85 extruded from the nozzle 86 extends in the conveying direction S, the refractive index in the conveying direction S tends to be higher than the refractive index in a direction perpendicular to the conveying direction S.

[0094] Therefore, in this embodiment, if Figure 3 As shown, each of the concave-convex portions 73 provided on the shaping sheet 70 is formed such that a surface 73a corresponding to the light incident surface 12a of the light guide plate 12 (a surface parallel to the longitudinal direction of the light guide plate 12) is parallel to the short side w1 of the shaping sheet 70. In other words, each of the concave-convex portions 73 provided on the shaping sheet 70 is arranged on the shaping layer 72 such that a surface 73a corresponding to the light incident surface 12a of the light guide plate 12 is perpendicular to the conveying direction S of the shaping sheet 70.

[0095] Therefore, the thermoplastic resin composition 85 extruded from the nozzle 86 extends in a direction perpendicular to the surface 73a of the concavo-convex portion 73, which serves as the light incident surface 12a of the light guide plate 12. As a result, the manufactured light guide plate panel 10' (light guide plate 12) is formed such that the refractive index Nx in the direction perpendicular to the light incident surface 12a of the light guide plate 12 (light guiding direction) is higher than the refractive index Ny in the direction perpendicular to the first side surface 12e.

[0096] Through the above steps, a light guide plate 12 is manufactured that satisfies the refractive index Nx>refractive index Ny. Furthermore, the refractive index difference between refractive index Nx and refractive index Ny can be adjusted by appropriately adjusting the resin temperature or cooling temperature of the thermoplastic resin composition 85 extruded from the nozzle 86, the conveying speed of the shaping sheet 70, the tension in the conveying direction S, and the like.

[0097] Conventionally, light guide plates have been manufactured using injection molding, as described in Japanese Patent Application Laid-Open No. 10-142601, and thus it has been impossible to manufacture a light guide plate satisfying Nx>Ny, as in the light guide plate 12 of this embodiment. Furthermore, while it is possible to manufacture a light guide plate 12 satisfying Nx>Ny by machining the concave-convex portion 13 on one surface of an optically anisotropic resin film, in this case, machining the desired concave-convex portion with high precision is sometimes very difficult, and this can increase manufacturing costs. In contrast, by using the shaped sheet 70 and employing an extrusion molding method as described above, it is possible to manufacture a light guide plate 12 satisfying Nx>Ny more easily and more cheaply.

[0098] (Evaluation of brightness unevenness)

[0099] Next, evaluation results of the relationship between the refractive index of the light guide plate in a direction perpendicular to the light incident surface and the refractive index in a direction perpendicular to each side surface, and the occurrence of brightness unevenness on the light exit surface of the light guide plate will be described.

[0100] Figure 5 These are photographs showing how light incident on the light guide plates of the embodiment and the comparative example exits from the light exit surface. Figure 5 (a) is a photograph taken from a direction perpendicular to the light emitting surface of the light guide plate of the embodiment. Figure 5 (b) is a photograph taken from a direction inclined 45 degrees relative to the light emitting surface of the light guide plate of the embodiment. Figure 5 (c) is a photograph taken from a direction perpendicular to the light emitting surface of the light guide plate of the comparative example. Figure 5 (d) is a photograph taken from a direction inclined at 45 degrees with respect to the light emitting surface of the light guide plate of the comparative example.

[0101] The light guide plate of the example used in the evaluation was formed similarly to the light guide plate 12 of the aforementioned embodiment and was made of polycarbonate resin. The light guide plate of the example was configured such that the refractive index Nx in the direction perpendicular to the light incident surface (light guiding direction) was 1.59, and the refractive index Ny in the direction from the first side surface toward the second side surface (the direction perpendicular to each side surface) was 1.58, with the refractive index Nx being greater than the refractive index Ny (Nx>Ny).

[0102] The light guide plate of the comparative example is formed of polycarbonate resin and is constructed as follows: the refractive index Nx in the direction perpendicular to the light incident surface (light guiding direction) is 1.58, the refractive index Ny in the direction from the first side surface toward the second side surface (the direction perpendicular to each side surface) is 1.59, and the refractive index Nx is less than the refractive index Ny (Nx<Ny).

[0103] The refractive indices Nx and Ny of each light guide plate were measured using a KOBRA series measuring instrument (KOBRA-WR) manufactured by Oji Instruments Co., Ltd. For the refractive index measurements of the light guide plates of the Examples and Comparative Examples, flat-plate samples without concave or convex portions on the light-emitting surface were used.

[0104] The measurement apparatus described above consists of a light source, a polarizer, an analyzer, and a light receiving unit, arranged in this order. A sample placement stage is placed between the polarizer and analyzer. Each sample is placed on the stage, and a single-wavelength beam is irradiated from the light source. With the polarizer and analyzer held parallel to the Nicol, the sample is rotated one revolution about the optical axis. The angular dependence of the transmitted light intensity at this time is used to determine the sample's phase difference and orientation angle, thereby determining the refractive index in the X and Y directions. A 590nm wavelength beam is used as the light source.

[0105] like Figure 5 (c) and Figure 5 As shown in (d), regarding the light guide plate of the comparative example, it was confirmed that leakage of light incident from the light incident surface was seen as bright lines on the light exit surface.

[0106] In contrast, regarding the light guide plate of the embodiment, as shown in FIG. Figure 5 (a) and Figure 5 As shown in (b), it was confirmed that the leakage of light incident from the light incident surface was suppressed as much as possible, the bright line visible on the light emitting surface was greatly suppressed, and the light was emitted uniformly.

[0107] Based on the above, the light guide plate 12 of this embodiment is formed such that the refractive index Nx in the direction from the light incident surface 12a toward the opposing surface 12b (a direction perpendicular to the light incident surface 12a) is greater than the refractive index Ny in the direction from the first side surface 12e toward the second side surface 12f (a direction perpendicular to each side surface) (Nx>Ny). This prevents uneven brightness of light emitted from the light exit surface 12c and ensures that the guided light is emitted uniformly from the light exit surface 12c.

[0108] In addition, in the manufacturing method of the light guide plate 12 of the present embodiment, since the surface 73a of the concave-convex shaped portion 73 of the shaping sheet 70 corresponding to the light incident surface 12a of the light guide plate 12 is configured to be perpendicular to the conveying direction S of the resin, it is possible to easily manufacture a light guide plate 12 that satisfies the refractive index Nx>refractive index Ny.

[0109] While the embodiments of the present invention have been described above, the present invention is not limited to the aforementioned embodiments. Various modifications and alterations, such as those described below, are possible, and these modifications and alterations are also within the technical scope of the present invention. Furthermore, the effects described in the embodiments are merely examples of the best effects produced by the present invention, and the effects of the present invention are not limited to those described in the embodiments. Furthermore, the aforementioned embodiments and the modifications described below can be appropriately combined for utilization, but detailed descriptions are omitted.

[0110] (Deformation method)

[0111] (1) In the above embodiment, the light guide plate 12 is used as a front light for a display device. However, the light guide plate 12 is not limited to this and may also be used as a backlight for a transmissive display device. In this case, the LCD panel needs to be a transmissive type that transmits light from the back side. Alternatively, a light control sheet such as a prism sheet or a light diffuser sheet may be provided between the LCD panel and the light guide plate.

[0112] (2) In the above embodiment, the light guide plate 12 is formed from the unwound shaping sheet 70, but the present invention is not limited thereto. For example, a roller having concave and convex portions formed on the cylindrical circumferential side surface may be used instead of the shaping sheet for manufacturing.

[0113] (3) In the above-mentioned embodiment, an example is shown in which the display surface 10a of the display device 1 is the back surface 12d of the light guide plate 12, but it is not limited to this. It may also be that a transparent protective sheet for preventing damage to the light guide plate is pasted on the back surface 12d of the light guide plate 12, and the surface of the protective sheet is used as the display surface.

[0114] In this case, for the bonding layer that bonds the back surface 12d of the light guide plate 12 and the protective sheet together, it is preferable to use a material having a lower refractive index than the material used for the light guide plate 12 from the viewpoint of more efficiently achieving total reflection of light within the light guide plate 12. When the light guide plate 12 is formed of a polycarbonate resin as in the above-mentioned embodiment, it is desirable to use a material having a lower refractive index than the polycarbonate resin, such as an acrylic resin, for the bonding layer.

[0115] (4) Alternatively, the light-emitting surface 12c of the light guide plate 12 and the LCD panel 2 may be joined together by a transparent joining member. In this case, the joining member may be provided so as to bury the concave-convex shape formed on the light-emitting surface 12c of the light guide plate 12. Furthermore, even in this case, from the perspective of efficiently performing total reflection of light within the light guide plate 12, it is desirable to use a material having a lower refractive index than the material used in the light guide plate 12 for the joining member.

Claims

1. A light guide plate comprising: a light incident surface for light to be incident on; a light emitting surface, intersecting the light incident surface, and through which light is emitted; a back surface, which is opposite to the light emitting surface and parallel to the plate surface of the light guide plate; and an opposite surface, which is opposite to the light incident surface, and the light guide plate guides the light incident from the light incident surface toward the opposite surface side while emitting it from the light emitting surface. The refractive index Nx in the direction perpendicular to the light incident surface is greater than the refractive index Ny in the direction parallel to the light exit surface and parallel to the light incident surface. The thickness of the light guide plate is 0.1 mm to 1.0 mm.

2. A display device, wherein: The display device comprises: A surface light source device comprising the light guide plate and a light source unit according to claim 1, wherein the light source unit is provided at a position facing a light incident surface of the light guide plate and projects light onto the light incident surface; and The display unit is arranged on the light emitting surface side of the light guide plate provided in the surface light source device.

3. The display device according to claim 2, wherein: The display portion is a reflective display portion.

4. A method for manufacturing a light guide plate, comprising manufacturing the light guide plate according to claim 1 by an extrusion molding method. It is characterized in that The method for manufacturing the light guide plate comprises: a resin extrusion step of extruding a resin for forming the light guide plate onto a forming plate having a concave-convex portion corresponding to the shape of the light guide plate; and a light guide plate forming step of conveying the resin extruded in the resin extrusion step while pressing it on the forming plate to form the light guide plate; The molding plate is arranged such that the surface of the concavo-convex portion corresponding to the light incident surface is perpendicular to the conveying direction of the resin.

Images