CN110622050A

CN110622050A - Light guide plate, surface light source device, display device, and electronic apparatus

Info

Publication number: CN110622050A
Application number: CN201880030641.8A
Authority: CN
Inventors: 渡边正太郎; 矢部卫
Original assignee: Omron Corp
Current assignee: Northeast Electronics Co.,Ltd.
Priority date: 2017-07-31
Filing date: 2018-06-28
Publication date: 2019-12-27
Also published as: JP2019029334A; TW201910834A

Abstract

The brightness of light emitted from the light-emitting surface of the light guide plate is prevented from being increased. A light guide plate having a substantially flat plate shape and having a light incident surface on a side thereof, into which light is incident, and a light exit surface from which light incident from the light incident surface exits, the light guide plate comprising: a flat plate portion; and at least one of the plurality of convex strips and concave strips, which are provided on the plane of the flat plate portion and extend in a vertical direction perpendicular to the light incident surface when viewed from a normal direction of the plane, wherein the plurality of convex strips and concave strips have inclined surfaces inclined with respect to the plane, the light exit surface is formed by the inclined surfaces of at least one of the plurality of convex strips and concave strips, and an angle formed by the plane and a tangent line of the inclined surfaces of at least one of the convex strips and concave strips is 30 degrees or more and 70 degrees or less.

Description

Light guide plate, surface light source device, display device, and electronic apparatus

Technical Field

The invention relates to a light guide plate, a surface light source device, a display device and an electronic apparatus.

Background

In recent years, electronic devices have been reduced in size and thickness. A liquid crystal display device mounted on such an electronic device is required to have a narrow frame and a thin display region with a large area. As the backlight of the display panel, for example, a surface Light source device of a side Light source type (also referred to as an edge Light type) using an LED (Light Emitting Diode) Emitting white Light as a Light source and a Light guide plate (also referred to as a Light guide) is used. In a liquid crystal display device, a screen is divided into a plurality of regions (lighting regions) and light emission luminance is controlled in accordance with each of the plurality of regions. Such control is called local dimming control. A surface light source device of an edge light system capable of applying local dimming is proposed (see patent document 1). A light guide plate and an edge light type backlight capable of improving the efficiency of local dimming have been proposed (see patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-069668

Patent document 2: japanese patent laid-open publication No. 2013-127966

Disclosure of Invention

Problems to be solved by the invention

Light emitted from the light source enters the light guide plate, repeats reflection in the light guide plate, and enters the light guide plate. When light incident on the light-emitting surface of the light guide plate is incident at an incident angle smaller than the critical angle, the light is emitted from the light-emitting surface of the light guide plate to the outside. When the brightness of light emitted from the light exit surface of the light guide plate is greatly expanded, it is difficult to control the light emission brightness in a narrow region in the local dimming control.

In view of such circumstances, an object of the present invention is to suppress the increase in luminance of light emitted from the light exit surface of the light guide plate.

Means for solving the problems

In order to solve the above problems, the present invention adopts the following means. That is, the present invention is a light guide plate having a substantially flat plate shape and having a light incident surface on a side to which light is incident, and light incident from the light incident surface is emitted from a light emitting surface, the light guide plate including: a flat plate portion; and at least one of the plurality of convex strips and concave strips, which is arranged on the plane of the flat plate part and extends in the vertical direction perpendicular to the light incident surface when viewed from the normal direction of the plane, wherein at least one of the plurality of convex strips and concave strips has an inclined surface inclined relative to the plane, the light emergent surface is formed by the inclined surface of at least one of the plurality of convex strips and concave strips, and the angle formed by the tangent line of the plane and the inclined surface of the end part of at least one of the convex strips and concave strips is more than 30 degrees and less than 70 degrees.

According to the light guide plate of the present invention, by setting the angle formed by the plane of the flat plate portion provided in the light guide plate and the tangent to the inclined surface of the end portion of at least one of the convex strip and the concave strip to 30 degrees or more and 70 degrees or less, it is possible to suppress the brightness of light emitted from the light exit surface of the light guide plate from increasing.

In the light guide plate of the present invention, an angle formed by a plane of the flat plate portion and a tangent line to an inclined surface of at least one of the end portions of the convex strip and the concave strip may be 45 degrees or more and 60 degrees or less. In the light guide plate of the present invention, the inclined surface may include a curved surface. In the light guide plate of the present invention, the inclined surface may include a curved surface and a flat surface, and an angle formed by the flat surface and the flat surface at the end of at least one of the convex strip and the concave strip may be 30 degrees or more and 70 degrees or less. In the light guide plate of the present invention, the inclined surface may include a curved surface and a flat surface, and an angle formed by the flat surface and the flat surface at the end portion of at least one of the convex strip and the concave strip may be 45 degrees or more and 60 degrees or less. In the light guide plate of the present invention, the thickness of the light guide plate excluding at least one of the plurality of convex stripes and concave stripes may be 0.2mm or more and 1.0mm or less. In the light guide plate of the present invention, at least one of the plurality of convex stripes and the plurality of concave stripes may be arranged on the plane of the flat plate portion without a gap. In the light guide plate of the present invention, at least one of the plurality of convex strips and the plurality of concave strips may be disposed on the plane of the flat plate portion at predetermined intervals, and the light exit surface may be formed by the inclined surface and the plane of at least one of the plurality of convex strips and the plurality of concave strips.

Further, the present invention is a light guide plate having a substantially flat plate shape, a light incident surface on a side of the light guide plate, and a light exit surface through which light incident from the light incident surface exits, the light guide plate including: a flat plate portion; and at least one of a plurality of ridges and grooves provided on a plane of the flat plate portion and extending in a vertical direction perpendicular to the light incident surface when viewed in a normal direction of the plane, wherein at least one of the plurality of ridges and grooves is arranged on the plane at predetermined intervals, at least one of the plurality of ridges and grooves has an inclined surface inclined with respect to the plane, the light exit surface is formed by the inclined surface of at least one of the plurality of ridges and grooves and the plane, and an angle formed by the plane and a tangent line to the inclined surface of an end portion of at least one of the ridges and grooves is 30 degrees to 80 degrees.

According to the light guide plate of the present invention, at least one of the plurality of convex strips and the plurality of concave strips is arranged on the flat plate portion provided in the light guide plate with a predetermined interval, and the angle formed by the plane of the flat plate portion and the tangent to the inclined surface of the end portion of at least one of the convex strips and the concave strips is set to 30 degrees or more and 80 degrees or less, thereby suppressing the brightness of light emitted from the light exit surface of the light guide plate from being increased.

The surface light source device of the present invention includes: the light guide plate of the present invention; and a light source disposed at a position opposite to the light incident surface. The surface light source device of the present invention includes the light guide plate of the present invention, a 1 st light source and a 2 nd light source, the light incident surfaces include a 1 st light incident surface and a 2 nd light incident surface, the 1 st light incident surface is opposed to the 2 nd light incident surface, the 1 st light source is disposed at a position opposed to the 1 st light incident surface, and the 2 nd light source is disposed at a position opposed to the 2 nd light incident surface. The display device of the present invention includes: the surface light source device of the present invention; and a display panel receiving the light emitted from the surface light source device. The electronic device of the present invention has the display device of the present invention.

Effects of the invention

According to the present invention, it is possible to suppress the increase in luminance of light emitted from the light exit surface of the light guide plate.

Drawings

Fig. 1 is a perspective view illustrating a structure of a liquid crystal display device of an embodiment.

Fig. 2 is a perspective view illustrating a structure of a surface light source device of the embodiment.

Fig. 3A is a diagram illustrating a light guide plate of an embodiment.

Fig. 3B is a diagram illustrating a light guide plate of an embodiment.

Fig. 4A is a diagram illustrating a relationship between the width of a light beam emitted from the upper surface of the light guide plate and the angle of the lenticular lens.

Fig. 4B is a diagram illustrating a relationship between the width of the light beam emitted from the upper surface of the light guide plate and the angle of the lenticular lens.

Fig. 4C is a diagram illustrating a relationship between the width of the light beam emitted from the upper surface of the light guide plate and the angle of the lenticular lens.

Fig. 5A is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 5B is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 5C is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 6 is a graph showing a relationship between the luminance of light emitted from the upper surface of the light guide plate and the angle of the lenticular lens.

Fig. 7 is an explanatory view of the full width at half maximum of the luminance of light emitted from the upper surface of the light guide plate.

Fig. 8 is a graph showing a relationship between the contrast ratio and the angle of the lenticular lens.

Fig. 9 is an explanatory diagram of the contrast ratio.

Fig. 10 is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 11 is a graph showing the relationship between the thickness of the light guide plate, the contrast ratio, and the angle of the lenticular lens.

Fig. 12A is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 12B is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 13A is a view illustrating a light guide plate of an embodiment.

Fig. 13B is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 13C is a diagram showing contrast ratios in the light guide plate not provided with the flat portion and the light guide plate provided with the flat portion.

Fig. 14A is a view illustrating a light guide plate of an embodiment.

Fig. 14B is a diagram illustrating a light guide plate of an embodiment.

Fig. 15 is a view showing a light guide plate of an embodiment.

Fig. 16A is a diagram illustrating a light guide plate according to an embodiment.

Fig. 16B is a diagram illustrating a light guide plate according to an embodiment.

Fig. 17 is a view showing a light guide plate of an embodiment.

Fig. 18 is a view showing a light guide plate of an embodiment.

Fig. 19A is a view illustrating a light guide plate of an embodiment.

Fig. 19B is a diagram illustrating a light guide plate according to an embodiment.

Fig. 19C is a diagram illustrating a light guide plate according to an embodiment.

Fig. 19D is a diagram illustrating a light guide plate according to an embodiment.

Fig. 19E is a diagram illustrating a light guide plate according to an embodiment.

Fig. 20A is a diagram illustrating a luminance distribution of light emitted from the upper surface of the light guide plate.

Fig. 20B is a graph showing a contrast ratio in the light guide plate.

Fig. 21A is a view illustrating a light guide plate of an embodiment.

Fig. 21B is a diagram illustrating a light guide plate according to an embodiment.

Fig. 21C is a diagram illustrating a light guide plate according to an embodiment.

Fig. 22A is a view illustrating a light guide plate of an embodiment.

Fig. 22B is a diagram illustrating a light guide plate of an embodiment.

Fig. 22C is a diagram illustrating a light guide plate according to an embodiment.

Fig. 23A is a view illustrating a light guide plate of an embodiment.

Fig. 23B is a diagram illustrating a light guide plate of an embodiment.

Fig. 23C is a diagram illustrating a light guide plate according to an embodiment.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are merely examples of the present invention, and the present invention is not limited to the specific configurations described below.

In the following embodiments, a "display device" will be described as a liquid crystal display device, and a "surface light source device" will be described as a backlight unit of the liquid crystal display device. The "surface light source device" can be used for applications other than a backlight unit, such as a front light source disposed on the front surface of a display device formed of a display panel or electronic paper.

(Structure of liquid Crystal display device)

Fig. 1 is a perspective view illustrating a structure of a liquid crystal display device of an embodiment. As shown in fig. 1, the liquid crystal display device includes: a surface light source device 1 configured as a backlight unit; and a display panel 2 that receives the light emitted from the surface light source device 1. The display panel 2 displays an image by applying a voltage to liquid crystal sealed between glass plates to increase or decrease the transmittance of light. Hereinafter, the surface light source device 1 will be described with the side closer to the display panel 2 being the upper surface side and the opposite side being the lower surface side.

(Structure of surface light source device 1)

Fig. 2 is a perspective view illustrating the structure of the surface light source device 1 of the embodiment. The surface light source device 1 of the embodiment includes a light guide plate 10, a light source 11, a flexible printed circuit board (hereinafter also referred to as "FPC") 12, a fixing member 13, and a frame 14. Further, the surface light source device 1 includes: a reflection sheet 15 disposed on the lower surface side of the light guide plate 10; a diffusion sheet 16 sequentially stacked on the upper surface side of the light guide plate 10; a prism sheet 17; and a light-shielding double-sided adhesive tape 18.

The light guide plate 10 is substantially flat and is formed of a light-transmitting material such as a polycarbonate resin or a polymethyl methacrylate resin. The upper surface of the light guide plate 10 is a light exit surface through which light exits, and is a surface facing the display panel 2. The light guide plate 10 guides light incident into the light guide plate 10 from the light source 11 to a light exit surface, and the whole or a part of the light exit surface emits light. The light guide plate 10 may include a light guide plate body and a light introduction part having a height greater than that of the light guide plate body. The light emitted from the light source 11 is efficiently incident into the light guide plate main body from the light introduction part, and the light use efficiency of the light guide plate 10 is improved. The light guide plate body is thinner than the light introduction portion, thereby improving the thinning of the surface light source device 1 and the thinning of the liquid crystal display device having the surface light source device 1. However, the light guide plate 10 according to the embodiment may have a flat plate shape without a light introduction portion.

The light source 11 emits white light from the fluorescent portion. The light source 11 is, for example, an LED package, but a light source other than an LED package may be used. The light source 11 is formed by sealing an LED chip as a light emitting element with a translucent resin (resin layer) containing a phosphor. Alternatively, the phosphor layer may be disposed on the light exit surface of the light guide plate 10 without disposing the phosphor on the LED chip, or the phosphor layer may be disposed on the reflective sheet 15. The light source 11 is driven and lighted by receiving power supply from the FPC 12. As the light source 11, an LED light source other than white may be used. The light source 11 is disposed at a position facing the light incident surface of the light guide plate 10. For example, the light source 11 is mounted on the FPC 12 such that a light emitting surface of the light source 11 faces the light incident surface of the light guide plate 10. The plurality of light sources 11 may be mounted on the FPC 12 in a row at a predetermined interval.

The FPC 12 is a wiring substrate in which wiring is provided on a base material which is a flexible insulating film via a conductor foil, and a cover or a resin (photosensitive resin) which is an insulating film for protection is bonded to the surface of the base material. A wiring is provided on the FPC 12. The wiring of the FPC 12 is used to supply power to the light source 11 and the like. The fixing member 13 is disposed on the lower surface of the FPC 12, for example, and fixes the FPC 12 to the light guide plate 10. The fixing member 13 is, for example, a double-sided adhesive tape having an upper surface and a lower surface as adhesive surfaces.

The frame 14 houses the light guide plate 10, the light source 11, the FPC 12, the fixing member 13, the reflective sheet 15, the diffusion sheet 16, and the prism sheet 17. The frame 14 may be a frame (frame-shaped member) surrounding the side surface of the light guide plate 10, or may be a case (box-shaped member) having a frame surrounding the side surface of the light guide plate 10 and a bottom plate on which the frame is erected. The frame body may be formed of a 4-sided side wall member, a circular side wall member having an opening, or an oval side wall member having an opening. In addition, the corner portions of the 4-sided side wall members of the frame body may be formed in a right-angled shape, and the corner portions of the 4-sided side wall members of the frame body may be formed in an R-shape.

The reflective sheet 15 is disposed in contact with the lower surface of the light guide plate 10. The lower surface of the light guide plate 10 is a surface on the opposite side to the upper surface of the light guide plate 10. The reflective sheet 15 is a smooth sheet made of a high reflective film having a multilayer film structure, a white resin sheet or a metal foil having a high reflectance, or the like, and reflects light in the light guide plate 10 so that the light does not leak from the lower surface of the surface light source device 1. When the frame 14 is a case having a frame body and a bottom plate, the reflection sheet 15 is disposed between the light guide plate 10 and the bottom plate of the frame 14.

A diffusion sheet 16 and 1 or 2 prism sheets 17 are disposed on the light guide plate 10. The diffusion sheet 16 is a translucent resin film, and diffuses light emitted from the light exit surface of the light guide plate 10 to improve the directivity of the light. The prism sheet 17 is a transparent resin film having a triangular prism-like fine pattern formed on the upper surface thereof, and concentrates light diffused by the diffusion sheet 16 to increase the brightness when the surface light source device 1 is viewed from the upper surface side. The light-shielding double-sided tape 18 is a black adhesive tape having adhesive surfaces on both upper and lower surfaces. The light-shielding double-sided tape 18 has a frame shape (ring shape). The light-shielding double-sided tape 18 is disposed along the outer peripheral portion of the frame 14, and suppresses light from leaking to the outside of the surface light source device 1.

(Structure of light guide plate 10)

Fig. 3A and 3B are views illustrating the light guide plate 10 of the embodiment. The light guide plate 10 includes: a light incident surface 20 on which light emitted from the light source 11 is incident; and a light exit surface that emits light incident from the light entrance surface 20. The light exit surface of the light guide plate 10 faces the display panel 2, and hereinafter, the light exit surface of the light guide plate 10 will be described as an upper surface 21 of the light guide plate 10, and a surface (opposite surface) opposite to the light exit surface of the light guide plate 10 will be described as a lower surface 22 of the light guide plate 10. The lower surface 22 of the light guide plate 10 is inclined at approximately 90 degrees with respect to the light incident surface 20 of the light guide plate 10. The light emitted from the light source 11 enters the light guide plate 10 through the light incident surface 20 of the light guide plate 10, repeats total reflection on the upper surface 21 and the lower surface 22 of the light guide plate 10, and enters the light guide plate 10. When light incident to the upper surface 21 of the light guide plate 10 is incident at an incident angle less than the critical angle, the light is emitted from the upper surface 21 of the light guide plate 10 to the outside.

As shown in fig. 3B, the light guide plate 10 includes: a flat plate portion 30; and a plurality of lenticular lenses 23 provided on the flat surface 31 of the flat plate portion 30. Fig. 3B is a diagram illustrating the light guide plate 10 according to the embodiment, and fig. 3B illustrates the light guide plate 10 when viewed from the light incident surface 20 side of the light guide plate 10. The plurality of lenticular lenses 23 have curved surfaces 23A. The curved surface 23A is inclined with respect to the plane 31. Therefore, the lenticular lens 23 has an inclined surface inclined with respect to the flat surface 31. The upper surface 21 of the light guide plate 10 is formed by the curved surfaces 23A of the plurality of lenticular lenses 23. When viewed from the normal direction of the plane 31 of the flat plate portion 30, each of the lenticular lenses 23 is a ridge extending in the direction perpendicular to the light incident surface 20 of the light guide plate 10. Therefore, the curved surface 23A of the lenticular lens 23 protrudes from the flat surface 31 of the flat plate portion 30 in the normal direction of the flat surface 31 of the flat plate portion 30. Since the light guide plate 10 has the lenticular lenses 23, the distribution of light emitted from the upper surface 21 of the light guide plate 10 can be controlled, and the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 can be controlled. The plurality of lenticular lenses 23 are arranged in parallel with each other. The plurality of lenticular lenses 23 are continuously arranged, and 2 adjacent lenticular lenses 23 are connected to each other. Therefore, the plurality of lenticular lenses 23 are arranged on the flat surface 31 of the flat plate portion 30 without any gap. The width of the lenticular lens 23 (the length of the lenticular lens 23 in the short side direction) is the same as the pitch of the lenticular lens 23. The lenticular lens 23 may be integrally formed with the light guide plate 10 manufactured by injection molding.

Fig. 4A to 4C are diagrams illustrating a relationship between the width of the light flux emitted from the upper surface 21 of the light guide plate 10 and the angle of the lenticular lens 23. Fig. 4A and 4B show the light guide plate 10 when viewed from the light incident surface 20 side of the light guide plate 10. The angle of the lenticular lens 23 shown in fig. 4A is smaller than the angle of the lenticular lens 23 shown in fig. 4B. The angle of the lenticular lens 23 is the contact angle of the lenticular lens 23. That is, the angle of the lenticular lens 23 is an angle (θ) formed by the flat surface 31 of the flat plate portion 30 and a tangent line L1 of the curved surface 23A of the end portion of the lenticular lens 23 (see fig. 4C). For example, when the angle of the lenticular lens 23 is small, the angle of the curved surface of the lenticular lens 23 with respect to the incident light incident on the upper surface 21 of the light guide plate 10 is small, and therefore, the incident angle of the light hardly exceeds the critical angle, and the light hardly exits from the upper surface 21 of the light guide plate 10. Therefore, as shown in fig. 4A, when the angle of the lenticular lens 23 is made smaller, the width W1 of the light beam emitted from the upper surface 21 of the light guide plate 10 becomes larger. For example, when the angle of the lenticular lens 23 is increased, the angle of the curved surface of the lenticular lens 23 with respect to the incident light incident on the upper surface 21 of the light guide plate 10 is increased, and therefore, the incident angle easily exceeds the critical angle, and the light is easily emitted from the upper surface 21 of the light guide plate 10. As shown in fig. 4B, when the angle of the lenticular lens 23 is increased, the width W2 of the light beam emitted from the upper surface 21 of the light guide plate 10 is narrowed. As described above, the larger the angle of the lenticular lens 23, the more easily the light is emitted from the upper surface 21 of the light guide plate 10, and therefore, the luminance distribution of the light emitted from the upper surface 21 of the light guide plate 10 can be easily controlled.

Fig. 5A to 5C show the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10. The angle of the lenticular lenses 23 of the light guide plate 10 shown in fig. 5A is smaller than the angle of the lenticular lenses 23 of the light guide plate 10 shown in fig. 5B. In fig. 5A and 5B, light emitted from one light source 11 is incident on the light guide plate 10. As shown in fig. 5A, the luminance of the light emitted from the upper surface 21 of the light guide plate 10 is increased in the lateral width direction (X direction in fig. 5A) of the light guide plate 10. The lateral width direction of the light guide plate 10 is a direction perpendicular to the optical axis of the light source 11.

In contrast, as shown in fig. 5B, the luminance of the light emitted from the upper surface 21 of the light guide plate 10 is suppressed from increasing in the lateral width direction (X direction in fig. 5B) of the light guide plate 10. Fig. 5C shows the expansion of the luminance of the light emitted from the upper surface 21 of the light guide plate 10. The vertical axis of fig. 5C represents the luminance of light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 5C represents the horizontal width (mm) of the light guide plate 10. A broken line C of fig. 5C is the brightness of light emitted from the upper surface 21 of the light guide plate 10 at the one-dot chain line a-a of fig. 5A. A solid line D of fig. 5C is the brightness of light exiting from the upper surface 21 of the light guide plate 10 at the one-dot chain line B-B of fig. 5B.

Fig. 6 is a graph showing a relationship between the luminance of light emitted from the upper surface 21 of the light guide plate 10 and the angle of the lenticular lens 23. The vertical axis of fig. 6 indicates the full width at half maximum of the luminance of the light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 6 indicates the angle of the lenticular lens 23. As shown in fig. 7, the full width at half maximum of the luminance of the light emitted from the upper surface 21 of the light guide plate 10 is the width at half the peak of the luminance of the light emitted from the upper surface 21 of the light guide plate 10 (W3). The vertical axis of fig. 7 represents the luminance of light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 7 represents the distance from the optical axis of the light source 11. In fig. 6, the full width at half maximum in the case where the angle of the lenticular lens 23 is 15 degrees is depicted as 1.0. The full width at half maximum in the case where the angle of the lenticular lens 23 in fig. 6 is 30 degrees, 45 degrees, 60 degrees, or 75 degrees is a ratio to the full width at half maximum in the case where the angle of the lenticular lens 23 is 15 degrees. As shown in fig. 6, the full width at half maximum when the angle of the lenticular lens 23 is 35 degrees to 75 degrees is equal to or less than half of the full width at half maximum when the angle of the lenticular lens 23 is 15 degrees.

Fig. 8 is a graph showing the relationship between the contrast ratio and the angle of the lenticular lens 23. The vertical axis of fig. 8 indicates the contrast ratio, and the horizontal axis of fig. 8 indicates the angle of the lenticular lens 23. Fig. 8 shows a contrast ratio in the case where the thickness of the light guide plate 10 is 0.4 mm. The thickness of the light guide plate 10 is the thickness of the cylindrical lens 23 removed. That is, the thickness of the light guide plate 10 except for the portion of the lenticular lens 23 is 0.4 mm. The contrast ratio is a value obtained by dividing a portion (low-luminance portion, point a in fig. 9) where the luminance of the light emitted from the upper surface 21 of the light guide plate 10 is low by a peak value (luminance peak value, point B in fig. 9) of the luminance of the light emitted from the upper surface 21 of the light guide plate 10. The vertical axis of fig. 9 represents the luminance of light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 9 represents the distance from the optical axis of the light source 11. The distance from the optical axis of the light source 11 to the point a of fig. 9 is 100 mm. As shown in fig. 8, the contrast ratio is 1/5000 or less in the range where the angle of the lenticular lens 23 is 30 degrees or more and 70 degrees or less, and the contrast ratio is a value near 1/10000 in the range where the angle of the lenticular lens 23 is 45 degrees or more and 60 degrees or less. As shown in fig. 8, in the range where the angle of the lenticular lens 23 is 30 degrees or more and 70 degrees or less, the contrast ratio is improved by 3 times or more as compared with the case where the angle of the lenticular lens 23 is 15 degrees.

Fig. 10 shows the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 when the angle of the lenticular lens 23 is 45 degrees, and the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 when the angle of the lenticular lens 23 is 75 degrees. The vertical axis of fig. 10 indicates the luminance of light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 10 indicates the distance from the optical axis of the light source 11. As shown in fig. 10, as the distance from the optical axis of the light source 11 increases, the luminance of light when the angle of the lenticular lens 23 is 75 degrees is greater than the luminance of light when the angle of the lenticular lens 23 is 45 degrees. The contrast ratio in the case where the angle of the lenticular lens 23 is 75 degrees is larger than that in the case where the angle of the lenticular lens 23 is 45 degrees. As shown in fig. 8, when the angle of the lenticular lens 23 is larger than 70 degrees, the contrast ratio is larger than 1/5000.

Fig. 11 is a diagram illustrating a relationship between the thickness of the light guide plate 10, the contrast ratio, and the angle of the lenticular lens 23. The vertical axis of fig. 11 indicates the contrast ratio, and the horizontal axis of fig. 11 indicates the angle of the lenticular lens 23. Fig. 11 shows contrast ratios in the case where the thickness of the light guide plate 10 is 0.2mm, 0.3mm, 0.5mm, 1.0 mm. The thickness of the light guide plate 10 is the thickness of the cylindrical lens 23 removed. That is, the thickness of the light guide plate 10 except for the portion of the lenticular lens 23 is 0.2mm, 0.3mm, 0.5mm, 1.0 mm. In fig. 11, the contrast ratio is expressed logarithmically. As shown in fig. 11, in the range where the angle of the lenticular lens 23 is 30 degrees to 75 degrees, the contrast ratio is improved as compared with the case where the angle of the lenticular lens 23 is 15 degrees. In this way, when the thickness of the light guide plate 10 is 0.2mm to 1.0mm, the angle of the lenticular lens 23 is 30 degrees to 75 degrees, thereby improving the contrast ratio compared to the case where the angle of the lenticular lens 23 is 15 degrees.

When the pitch of the lenticular lens 23 is narrow, moire is more likely to occur in the screen of the liquid crystal display device. In addition, when the moire pitch is narrow, it is more difficult to visually recognize the moire in the screen of the liquid crystal display device. For example, when the thickness of the light guide plate 10 is 1.0mm, the angle of the lenticular lens 23 is 65 degrees, the height of the lenticular lens 23 is 0.012mm, the pitch of the lenticular lens 23 is 0.042mm, and the curvature radius ratio is 0.012, the moire pitch is 1mm or less. For example, when the thickness of the light guide plate 10 is 1.0mm, the angle of the lenticular lens 23 is 65 degrees, the height of the lenticular lens 23 is 0.04mm, the pitch of the lenticular lens 23 is 0.126mm, and the curvature radius ratio is 0.04, the moire pitch is about 3 mm. The curvature radius ratio R is a value obtained by dividing the height H of the lenticular lens 23 by the thickness T of the light guide plate 10 (R ═ H/T).

As shown in fig. 12A, a plurality of light sources 11 may be arranged on the light incident surface 20 side of the light guide plate 10. As shown in fig. 12B, a plurality of light sources 11 may be arranged on the light incident surface 20 side of the light guide plate 10, and a plurality of light sources 41 may be arranged on the light incident surface 24 side of the light guide plate 10. The light incident surface 24 of the light guide plate 10 is a surface opposite to the light incident surface 20 of the light guide plate 10. The structure of the light source 41 is the same as that of the light source 11. The light incident surface 20 is an example of the 1 st light incident surface. The light incident surface 24 is an example of the 2 nd light incident surface. The light source 11 is an example of the 1 st light source. The light source 41 is an example of the 2 nd light source. The light source 11 is disposed at a position facing the light incident surface 20 of the light guide plate 10, and the light source 41 is disposed at a position facing the light incident surface 24 of the light guide plate 10. The light emitted from the light source 11 enters the light guide plate 10 through the light incident surface 20 of the light guide plate 10, and the light emitted from the light source 41 enters the light guide plate 10 through the light incident surface 24 of the light guide plate 10.

Fig. 12A and 12B show the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10. In fig. 12A, light emitted from one light source 11 enters the light guide plate 10. In fig. 12B, light emitted from one light source 11 and one light source 41 enters the light guide plate 10. In fig. 12B, the light guide distance in the light guide plate 10 is shortened by the light incident from the light incident surface 20 and the light incident surface 24 of the light guide plate 10. Therefore, as shown in fig. 12B, the luminance of the light emitted from the upper surface 21 of the light guide plate 10 is suppressed from being increased in the lateral width direction (X direction in fig. 12B) of the light guide plate 10.

For example, the light guide plate 10 shown in fig. 3A and 3B shows the following example: a plurality of lenticular lenses 23 are arranged in series, and 2 adjacent lenticular lenses 23 are connected. The configuration of the light guide plate 10 shown in fig. 3A and 3B is not limited to the above, and the plurality of lenticular lenses 23 may be arranged at predetermined intervals. For example, as shown in fig. 13A, a flat portion (flat surface) 25 may be provided between adjacent lenticular lenses 23 among the plurality of lenticular lenses 23. In the configuration example of the light guide plate 10 shown in fig. 13A, the plurality of lenticular lenses 23 are arranged in parallel with each other at predetermined intervals. In the configuration example of the light guide plate 10 shown in fig. 13A, the upper surface 21 of the light guide plate 10 is formed by the curved surfaces 23A of the plurality of lenticular lenses 23 and the plurality of flat portions 25. The flat portion (flat surface) 25 is coplanar with the plane 31 of the flat plate portion 30. Therefore, in the configuration example of the light guide plate 10 shown in fig. 13A, the upper surface 21 of the light guide plate 10 is formed by the curved surfaces 23A of the plurality of lenticular lenses 23 and the flat surface 31 of the flat plate portion 30. The flat portion 25 may be parallel to the lower surface 22 of the light guide plate 10. The angle of the lenticular lens 23 shown in fig. 13A is, for example, 80 degrees. By providing a plurality of lenticular lenses 23 on the upper surface 21 of the light guide plate 10 and providing the flat portion 25 between the adjacent lenticular lenses 23, the contrast ratio can be made smaller than 1/5000 even in the case where the angle of the lenticular lenses 23 is larger than 70 degrees. The angle of the lenticular lens 23 shown in fig. 13A may be an angle other than 80 degrees, and may be, for example, 30 degrees to 70 degrees, or 45 degrees to 60 degrees.

Fig. 13B shows the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 provided with the flat portion 25 and the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 provided with the flat portion 25. In the light guide plate 10 not provided with the flat portion 25, the plurality of lenticular lenses 23 are arranged on the flat surface 31 of the flat plate portion 30 without a gap. A plurality of lenticular lenses 23 are arranged at predetermined intervals on the light guide plate 10 provided with the flat portion 25. The vertical axis of fig. 13B represents the luminance of light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 13B represents the distance from the optical axis of the light source 11. The angle of the lenticular lens 23 on the light guide plate 10 not provided with the flat portion 25 is 60 degrees, and the angle of the lenticular lens 23 on the light guide plate 10 provided with the flat portion 25 is 80 degrees. The thickness of the light guide plate 10 except for the portions of the lenticular lenses 23 was 0.4 mm. As shown in fig. 13B, the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 provided with the flat portion 25 is the same as the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 provided with the flat portion 25. In this way, even when the angle of the lenticular lenses 23 is 80 degrees, the control of the luminance distribution of the light emitted from the upper surface 21 of the light guide plate 10 can be improved by providing a plurality of lenticular lenses 23 on the upper surface 21 of the light guide plate 10 and providing the flat portion 25 between the adjacent lenticular lenses 23.

Fig. 13C shows the contrast ratio of the light guide plate 10 not provided with the flat portion 25 and the contrast ratio of the light guide plate 10 provided with the flat portion 25. The thickness of the light guide plate 10 except for the portions of the lenticular lenses 23 was 0.4 mm. From fig. 13C it can be confirmed that: by providing a plurality of lenticular lenses 23 on the upper surface 21 of the light guide plate 10 and providing the flat portion 25 between the adjacent lenticular lenses 23, the contrast ratio can be made smaller than 1/5000 even in the case where the angle of the lenticular lenses 23 is 80 degrees. With respect to the light guide plate 10 provided with the flat portion 25, even in the case where the thickness of the light guide plate 10 other than the portion of the lenticular lens 23 is 0.2mm, 0.3mm, 0.5mm, 1.0mm, the same effect as that in the case where the thickness of the light guide plate 10 other than the portion of the lenticular lens 23 is 0.4mm can be obtained. Further, the light guide plate 10 provided with the flat portion 25 can obtain the same effect as the light guide plate 10 not provided with the flat portion 25 in the range where the angle of the lenticular lens 23 is 30 degrees or more and 70 degrees or less. That is, according to the light guide plate 10 provided with the flat portion 25, the contrast ratio is 1/5000 or less in the range where the angle of the lenticular lens 23 is 30 degrees or more and 80 degrees or less, and the contrast ratio is a value near 1/10000 in the range where the angle of the lenticular lens 23 is 45 degrees or more and 60 degrees or less.

The angle of the lenticular lens 23 can be adjusted by changing the height and the curvature radius of the lenticular lens 23. The angle of the lenticular lens 23 may be adjusted by fixing the height of the lenticular lens 23 and changing the radius of curvature of the lenticular lens 23. The angle of the lenticular lens 23 can also be adjusted by changing the height of the lenticular lens 23 by fixing the radius of curvature of the lenticular lens 23.

For example, the light guide plate 10 shown in fig. 3A and 3B shows the following example: the plurality of lenticular lenses 23 are provided on the plane 31 of the flat plate portion 30, and each lenticular lens 23 is a convex strip extending in a direction perpendicular to the light incident surface 20 of the light guide plate 10 when viewed from a direction normal to the plane 31 of the flat plate portion 30. Without being limited to the configuration example of the light guide plate 10 shown in fig. 3A and 3B, as shown in fig. 14A, a plurality of lenticular lenses 33 may be provided on the plane 32 of the flat plate portion 30, and each lenticular lens 33 may be a convex strip extending in a direction perpendicular to the light incident surface 20 of the light guide plate 10 when viewed from the normal direction of the plane 32 of the flat plate portion 30. The flat surface 32 of the flat plate portion 30 is a surface on the opposite side of the flat surface 31 of the flat plate portion 30. The plurality of lenticular lenses 33 have curved surfaces 33A. The curved surface 33A is inclined with respect to the flat surface 32. Therefore, the lenticular lens 33 has an inclined surface inclined with respect to the flat surface 32.

In the configuration example of the light guide plate 10 shown in fig. 14A, the upper surface 21 of the light guide plate 10 is formed by the plane of the flat plate portion 30, and light is emitted from the upper surface 21 of the light guide plate 10. In the configuration example of the light guide plate 10 shown in fig. 14A, the lower surface 22 of the light guide plate 10 is formed by the curved surfaces 33A of the plurality of lenticular lenses 33. The angle of the lenticular lens 33 is an angle (θ) formed by the flat surface 32 of the flat plate portion 30 and a tangent line L2 of the curved surface 33A at the end of the lenticular lens 33 (see fig. 14B). Even when the lenticular lens 33 is provided on the lower surface 22 side of the light guide plate 10, the brightness of the light emitted from the upper surface 21 of the light guide plate 10 can be suppressed from increasing, as in the case where the lenticular lens 23 is provided on the upper surface 21 side of the light guide plate 10. Further, the lenticular lens 23 may be provided on the upper surface 21 side of the light guide plate 10 and the lenticular lens 33 may be provided on the lower surface 22 side of the light guide plate 10. The plurality of lenticular lenses 33 may be disposed on the flat surface 32 of the flat plate portion 30 at predetermined intervals.

For example, the light guide plate 10 shown in fig. 3A and 3B shows an example in which the lenticular lenses 23 are convex stripes provided on the flat surface 31 of the flat plate portion 30. Without being limited to the configuration example of the light guide plate 10 shown in fig. 3A and 3B, as shown in fig. 15 and 16A, the plurality of lenticular lenses 23 may be provided on the plane 31 of the flat plate portion 30, and each lenticular lens 23 may be a concave stripe extending in a direction perpendicular to the light incident surface 20 of the light guide plate 10 when viewed from the normal direction of the plane 31 of the flat plate portion 30. The plurality of lenticular lenses 23 have curved surfaces 23B. The curved surface 23B is inclined with respect to the plane 31. Therefore, the lenticular lens 23 has an inclined surface inclined with respect to the flat surface 31. The upper surface 21 of the light guide plate 10 is formed by the curved surfaces 23B of the plurality of lenticular lenses 23. The curved surface 23B of the lenticular lens 23 is recessed from the flat surface 31 of the flat plate portion 30 toward the normal direction of the flat surface 31 of the flat plate portion 30.

Since the light guide plate 10 has the lenticular lenses 23, the distribution of light emitted from the upper surface 21 of the light guide plate 10 can be controlled, and the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 can be controlled. The plurality of lenticular lenses 23 are arranged in parallel with each other. In the configuration example of the light guide plate 10 shown in fig. 15, 16A, and 16B, a plurality of lenticular lenses 23 are arranged in series, and 2 adjacent lenticular lenses 23 are connected to each other. Therefore, in the configuration example of the light guide plate 10 shown in fig. 15, 16A, and 16B, the plurality of lenticular lenses 23 are arranged on the flat surface 31 of the flat plate portion 30 without a gap. In the configuration examples of the light guide plate 10 shown in fig. 15, 16A, and 16B, the width of the lenticular lenses 23 is the same as the pitch of the lenticular lenses 23. The angle of the lenticular lens 23 is an angle (θ) formed by the flat surface 31 of the flat plate portion 30 and a tangent L3 of the curved surface 23B at the end of the lenticular lens 23 (see fig. 16B).

Even if the plurality of lenticular lenses 23 are concave stripes, the contrast ratio can be 1/5000 or less in the range where the angle of the lenticular lens 23 is 30 degrees or more and 70 degrees or less. Even if the plurality of lenticular lenses 23 are concave, the contrast ratio can be set to a value near 1/10000 in the range where the angle of the lenticular lens 23 is 45 degrees or more and 60 degrees or less. Even if the plurality of lenticular lenses 23 are concave strips, the contrast ratio can be improved by setting the angle of the lenticular lenses 23 to 30 degrees or more and 75 degrees or less when the thickness of the light guide plate 10 is 0.2mm or more and 1.0mm or less except for the portions of the lenticular lenses 23.

The present invention is not limited to the configuration examples of the light guide plate 10 shown in fig. 15, 16A, and 16B, and the plurality of lenticular lenses 23 may be arranged at predetermined intervals. For example, as shown in fig. 17, the flat portion 25 may be provided between adjacent lenticular lenses 23 among the plurality of lenticular lenses 23. In the configuration example of the light guide plate 10 shown in fig. 17, the plurality of lenticular lenses 23 are arranged in parallel with each other at predetermined intervals. In the configuration example of the light guide plate 10 shown in fig. 17, the upper surface 21 of the light guide plate 10 is formed by the curved surfaces 23B of the plurality of lenticular lenses 23 and the plurality of flat portions 25. The flat portion (flat surface) 25 is coplanar with the plane 31 of the flat plate portion 30. Therefore, in the configuration example of the light guide plate 10 shown in fig. 17, the upper surface 21 of the light guide plate 10 is formed by the curved surfaces 23B of the plurality of lenticular lenses 23 and the flat surface 31 of the flat plate portion 30. The flat portion 25 may be parallel to the lower surface 22 of the light guide plate 10. The angle of the lenticular lens 23 shown in fig. 17 is, for example, 80 degrees. By providing a plurality of lenticular lenses 23 on the upper surface 21 of the light guide plate 10 and providing the flat portion 25 between the adjacent lenticular lenses 23, the contrast ratio can be made smaller than 1/5000 even in the case where the angle of the lenticular lenses 23 is larger than 70 degrees. The angle of the lenticular lens 23 shown in fig. 17 may be an angle other than 80 degrees, and may be, for example, 30 degrees to 70 degrees, or 45 degrees to 60 degrees.

As shown in fig. 18, the plurality of lenticular lenses 23 may be provided on the flat surface 31 of the flat plate portion 30, and a part of the plurality of lenticular lenses 23 may be convex stripes and another part of the plurality of lenticular lenses 23 may be concave stripes. As shown in fig. 18, the convex stripes are arranged adjacent to each other, and the concave stripes are arranged adjacent to each other. In the configuration example of the light guide plate 10 shown in fig. 18, the plurality of lenticular lenses 23 are arranged on the flat surface 31 of the flat plate portion 30 without a gap. That is, the plurality of convex stripes and the plurality of concave stripes are arranged on the flat surface 31 of the flat plate portion 30 without a gap. The present invention is not limited to the configuration example of the light guide plate 10 shown in fig. 18, and for example, one or more convex stripes and one or more concave stripes may be alternately arranged on the flat surface 31 of the flat plate portion 30. Similarly to the configuration example of the light guide plate 10 shown in fig. 13A and 17, the flat portion 25 may be provided between adjacent lenticular lenses 23 among the lenticular lenses 23, and the plurality of convex stripes and the plurality of concave stripes may be arranged on the flat surface 31 of the flat plate portion 30 with a predetermined interval. The plurality of convex strips may be disposed on the flat surface 31 of the flat plate portion 30 at predetermined intervals, and the plurality of concave strips may be disposed on the flat surface 31 of the flat plate portion 30 without any gap. The plurality of ridges may be disposed on the flat surface 31 of the flat plate portion 30 without any gap, and the plurality of ridges may be disposed on the flat surface 31 of the flat plate portion 30 with a predetermined interval. Further, the plurality of convex stripes and the plurality of concave stripes may be arranged on the flat surface 32 of the flat plate portion 30 at predetermined intervals. The plurality of convex strips may be disposed on the flat surface 32 of the flat plate portion 30 at predetermined intervals, and the plurality of concave strips may be disposed on the flat surface 32 of the flat plate portion 30 without any gap. The plurality of ridges may be disposed on the flat surface 32 of the flat plate portion 30 without any gap, and the plurality of ridges may be disposed on the flat surface 32 of the flat plate portion 30 with a predetermined interval.

According to the light guide plate 10 of the above-described embodiment, by setting the angle of the lenticular lens 23 to 30 degrees or more and 70 degrees or less, it is possible to suppress the increase in luminance of light emitted from the upper surface 21 of the light guide plate 10, and thus, the contrast ratio is improved. Since the increase in luminance of the light emitted from the upper surface 21 of the light guide plate 10 can be suppressed, the control of the emission luminance in a narrow region is facilitated in the local dimming control. In addition, according to the light guide plate 10 of the embodiment, the contrast ratio is further improved by making the angle of the lenticular lens 23 45 degrees or more and 60 degrees or less. Therefore, by mounting the surface light source device 1 having the light guide plate 10 as a backlight, a liquid crystal display device having an improved contrast ratio can be provided.

Fig. 19A and 19B are views illustrating the light guide plate 10 of the embodiment. In the configuration example of the light guide plate 10 shown in fig. 19A and 19B, the light guide plate 10 has a plurality of lenticular lenses 23 provided on the flat surface 31 of the flat plate portion 30, and each lenticular lens 23 has a curved surface 23A and a flat surface 51A. When viewed from the normal direction of the plane 31 of the flat plate portion 30, each of the lenticular lenses 23 is a ridge extending in the direction perpendicular to the light incident surface 20 of the light guide plate 10. The curved surface 23A and the flat surface 51A are inclined with respect to the flat surface 31. Therefore, the lenticular lens 23 has an inclined surface inclined with respect to the flat surface 31.

In the configuration example of the light guide plate 10 shown in fig. 19A, a plurality of lenticular lenses 23 are continuously provided, and the adjacent lenticular lenses 23 are connected to each other. The opposing 2 flat surfaces 51A in the adjacent 2 lenticular lenses 23 are connected to each other. Therefore, the plurality of lenticular lenses 23 are arranged on the flat surface 31 of the flat plate portion 30 without any gap. In the configuration example of the light guide plate 10 shown in fig. 19B, the flat portion 25 is provided between the adjacent lenticular lenses 23. The flat portion 25 is connected to each flat surface 51A of the adjacent lenticular lens 23. Therefore, the plurality of lenticular lenses 23 are arranged in parallel with each other at predetermined intervals.

Fig. 19C to 19E are views showing the light guide plate 10 according to the embodiment. In the configuration examples of the light guide plate 10 shown in fig. 19C to 19E, the angle of the lenticular lens 23 is 60 degrees, but the angle of the lenticular lens 23 may be an angle other than 60 degrees. The angle of the lenticular lens 23 may be, for example, 30 degrees to 80 degrees, 30 degrees to 70 degrees, or 45 degrees to 60 degrees. The angle of the lenticular lens 23 is an angle (θ) formed by the flat surface 31 of the flat plate portion 30 and the flat surface 51A of the end portion of the lenticular lens 23.

As shown in fig. 19C to 19E, the lenticular lens 23 includes a trapezoidal portion 52A and an arc portion 53A in contact with the top and bottom of the trapezoidal portion 52A when viewed from the normal direction of the light incident surface 20 of the light guide plate 10. The length of the upper base of the trapezoidal section 52A is shorter than the length of the lower base of the trapezoidal section 52A. The trapezoidal portion 52A contacts the flat surface 31 of the flat plate portion 30, and the circular arc-shaped portion 53A is separated from the flat surface 31 of the flat plate portion 30. In the configuration example of the light guide plate 10 shown in fig. 19C, the height of the trapezoidal portion 52A is 50% of the total value of the height of the trapezoidal portion 52A and the height of the circular arc-shaped portion 53A. In the configuration example of the light guide plate 10 shown in fig. 19D, the height of the trapezoidal portion 52A is 80% of the total of the height of the trapezoidal portion 52A and the height of the arc-shaped portion 53A. In the configuration example of the light guide plate 10 shown in fig. 19E, the height of the trapezoidal portion 52A is 90% of the total of the height of the trapezoidal portion 52A and the height of the arc-shaped portion 53A. The ratio of the height of the trapezoidal portion 52A to the total of the height of the trapezoidal portion 52A and the height of the circular arc-shaped portion 53A is not limited to 50%, 80%, and 90%. The ratio of the height of the trapezoidal portion 52A to the total of the height of the trapezoidal portion 52A and the height of the arc-shaped portion 53A may be 0% to 100%.

Fig. 20A shows the luminance distribution of light emitted from the upper surface 21 of the light guide plate 10 when the angle of the lenticular lens 23 is 60 degrees. The vertical axis of fig. 20A represents the luminance of light emitted from the upper surface 21 of the light guide plate 10, and the horizontal axis of fig. 20A represents the distance from the optical axis of the light source 11. Fig. 20A shows the luminance distribution of light in the case where the ratio of the height of the trapezoidal portion 52A to the total value of the height of the trapezoidal portion 52A and the height of the circular arc-shaped portion 53A is 0%, 50%, 80%, and 90%. When the ratio of the height of the trapezoidal portion 52A to the total value of the height of the trapezoidal portion 52A and the height of the circular arc-shaped portion 53A is 0%, the lenticular lens 23 has the circular arc-shaped portion 53A but does not have the trapezoidal portion 52A. When the ratio of the height of the trapezoidal portion 52A to the total of the height of the trapezoidal portion 52A and the height of the arc-shaped portion 53A is 0%, the lenticular lens 23 has the curved surface 23A but does not have the flat surface 51A.

As can be seen from fig. 20A, the luminance distribution of the light emitted from the upper surface 21 of the light guide plate 10 has almost no difference between the case where the lenticular lens 23 has only the curved surface 23A and the case where the lenticular lens 23 has the curved surface 23A and the flat surface 51A. In this way, when the lenticular lens 23 has the curved surface 23A and the flat surface 51A, the same effect as that of the case where the lenticular lens 23 has only the curved surface 23A can be obtained. Further, the same effect as that in the case where the lenticular lens 23 has only the curved surface 23A can be obtained even when the angle of the lenticular lens 23 is 30 degrees or more and 80 degrees or less and the lenticular lens 23 has the curved surface 23A and the flat surface 51A.

Fig. 20B shows the contrast ratio in the case where the angle of the lenticular lens 23 is 60 degrees. Fig. 20B shows contrast ratios in the case where the ratio of the height of the trapezoidal portion 52A to the total value of the height of the trapezoidal portion 52A and the height of the circular arc-shaped portion 53A is 0%, 50%, 80%, and 90%. As can be seen from fig. 20B, with respect to the contrast ratio, there is almost no difference between the case where the lenticular lens 23 has only the curved surface 23A and the case where the lenticular lens 23 has the curved surface 23A and the flat surface 51A. In this way, in the case where the lenticular lens 23 has the curved surface 23A and the flat surface 51A, the same effect as that in the case where the lenticular lens 23 has only the curved surface 23A can be obtained. Therefore, the angle of the lenticular lens 23 is 30 degrees or more and 80 degrees or less, and the lenticular lens 23 has the curved surface 23A and the flat surface 51A, whereby the contrast ratio can be improved.

Fig. 21A and 21B are views illustrating a light guide plate 10 of an embodiment. In the configuration example of the light guide plate 10 shown in fig. 21A and 21B, the light guide plate 10 has a plurality of lenticular lenses 23 provided on the flat surface 31 of the flat plate portion 30, and each lenticular lens 23 has a curved surface 23B and a flat surface 51B. When viewed from the normal direction of the plane 31 of the flat plate portion 30, each of the lenticular lenses 23 is a concave stripe extending in the direction perpendicular to the light incident surface 20 of the light guide plate 10. The curved surface 23B and the flat surface 51B are inclined with respect to the flat surface 31. Therefore, the lenticular lens 23 has an inclined surface inclined with respect to the flat surface 31.

In the configuration example of the light guide plate 10 shown in fig. 21A, a plurality of lenticular lenses 23 are continuously provided, and the adjacent lenticular lenses 23 are connected to each other. The 2 flat surfaces 51B of the adjacent 2 lenticular lenses 23 are connected to each other. Therefore, the plurality of lenticular lenses 23 are arranged on the flat surface 31 of the flat plate portion 30 without any gap. In the configuration example of the light guide plate 10 shown in fig. 21B, the flat portion 25 is provided between the adjacent lenticular lenses 23. The flat portion 25 is connected to each flat surface 51B of the adjacent lenticular lens 23. Therefore, the plurality of lenticular lenses 23 are arranged in parallel with each other at predetermined intervals.

Fig. 21C is a diagram illustrating the light guide plate 10 of the embodiment. In the configuration example of the light guide plate 10 shown in fig. 21C, the angle of the lenticular lens 23 is 60 degrees, but the angle of the lenticular lens 23 may be an angle other than 60 degrees. The angle of the lenticular lens 23 may be, for example, 30 degrees to 80 degrees, 30 degrees to 70 degrees, or 45 degrees to 60 degrees. The angle of the lenticular lens 23 is an angle (θ) formed by the flat surface 31 of the flat plate portion 30 and the flat surface 51B of the end portion of the lenticular lens 23. The angle of the lenticular lens 23 is 30 degrees to 80 degrees, and the lenticular lens 23 has the curved surface 23B and the flat surface 51B, whereby the contrast ratio can be improved.

As shown in fig. 21C, the lenticular lens 23 includes a trapezoidal portion 52B and an arc-shaped portion 53B in contact with a lower base of the trapezoidal portion 52B when viewed from a normal direction of the light incident surface 20 of the light guide plate 10. The length of the lower base of the trapezoidal section 52B is shorter than the length of the upper base of the trapezoidal section 52B. The trapezoidal portion 52B contacts the flat surface 31 of the flat plate portion 30, and the circular arc-shaped portion 53B is separated from the flat surface 31 of the flat plate portion 30. In the configuration example of the light guide plate 10 shown in fig. 21C, the height of the trapezoidal portion 52B is 50% of the total of the height of the trapezoidal portion 52B and the height of the arc-shaped portion 53B. The ratio of the height of the trapezoidal portion 52B to the total of the height of the trapezoidal portion 52B and the height of the circular arc portion 53B is not limited to 50%. The ratio of the height of the trapezoidal portion 52B to the total of the height of the trapezoidal portion 52B and the height of the arc-shaped portion 53B may be 0% to 100%.

Fig. 22A and 22B are views illustrating the light guide plate 10 of the embodiment. In the configuration example of the light guide plate 10 shown in fig. 22A and 22B, the light guide plate 10 includes a plurality of lenticular lenses 33 provided on the flat surface 32 of the flat plate portion 30, and each lenticular lens 33 has a curved surface 33A and a flat surface 61A. When viewed from the normal direction of the plane 32 of the flat plate portion 30, each of the lenticular lenses 33 is a convex strip extending in the direction perpendicular to the light incident surface 20 of the light guide plate 10. The curved surface 33A and the flat surface 61A are inclined with respect to the flat surface 32. Therefore, the lenticular lens 33 has an inclined surface inclined with respect to the flat surface 32.

In the configuration example of the light guide plate 10 shown in fig. 22A, a plurality of lenticular lenses 33 are continuously provided, and the adjacent lenticular lenses 33 are connected to each other. The opposing 2 flat surfaces 61A in the adjacent 2 lenticular lenses 33 are connected to each other. Therefore, the plurality of lenticular lenses 33 are arranged on the flat surface 32 of the flat plate portion 30 without any gap. In the configuration example of the light guide plate 10 shown in fig. 22B, the flat portion 25 is provided between the adjacent lenticular lenses 33. The flat portion 25 is connected to each flat surface 61A of the adjacent lenticular lens 33. Therefore, the plurality of lenticular lenses 33 are arranged in parallel with each other at predetermined intervals.

Fig. 22C is a diagram illustrating the light guide plate 10 of the embodiment. In the configuration example of the light guide plate 10 shown in fig. 22C, the angle of the lenticular lens 33 is 60 degrees, but the angle of the lenticular lens 33 may be an angle other than 60 degrees. The angle of the lenticular lens 33 may be, for example, 30 degrees to 80 degrees, 30 degrees to 70 degrees, or 45 degrees to 60 degrees. The angle of the lenticular lens 33 is an angle (θ) formed by the flat surface 32 of the flat plate portion 30 and the flat surface 61A of the end portion of the lenticular lens 33. The angle of the lenticular lens 33 is 30 degrees or more and 80 degrees or less, and the lenticular lens 33 has the curved surface 33A and the flat surface 61A, whereby the contrast ratio can be improved.

As shown in fig. 22C, the lenticular lens 33 includes a trapezoidal portion 62A and an arc-shaped portion 63A in contact with a lower base of the trapezoidal portion 62A when viewed from a normal direction of the light incident surface 20 of the light guide plate 10. The length of the lower base of the trapezoidal section 62A is shorter than the length of the upper base of the trapezoidal section 62A. The trapezoidal portion 62A contacts the flat surface 32 of the flat plate portion 30, and the circular-arc shaped portion 63A is separated from the flat surface 32 of the flat plate portion 30. In the configuration example of the light guide plate 10 shown in fig. 22C, the height of the trapezoidal portion 62A is 50% of the total of the height of the trapezoidal portion 62A and the height of the circular arc portion 63A. The ratio of the height of the trapezoidal portion 62A to the total of the height of the trapezoidal portion 62A and the height of the circular arc-shaped portion 63A is not limited to 50%. The ratio of the height of the trapezoidal portion 62A to the total of the height of the trapezoidal portion 62A and the height of the circular arc portion 63A may be 0% to 100%.

Fig. 23A and 23B are views illustrating a light guide plate 10 of an embodiment. In the configuration example of the light guide plate 10 shown in fig. 23A and 23B, the light guide plate 10 has a plurality of lenticular lenses 33 provided on the flat surface 32 of the flat plate portion 30, and each lenticular lens 33 has a curved surface 33B and a flat surface 61B. When viewed from the normal direction of the plane 32 of the flat plate portion 30, each of the lenticular lenses 33 is a concave stripe extending in the direction perpendicular to the light incident surface 20 of the light guide plate 10. The curved surface 33B and the flat surface 61B are inclined with respect to the flat surface 32. Therefore, the lenticular lens 33 has an inclined surface inclined with respect to the flat surface 32.

In the configuration example of the light guide plate 10 shown in fig. 23A, a plurality of lenticular lenses 33 are continuously provided, and the adjacent lenticular lenses 33 are connected to each other. The opposing 2 flat surfaces 61B in the adjacent 2 lenticular lenses 33 are connected to each other. Therefore, the plurality of lenticular lenses 33 are arranged on the flat surface 32 of the flat plate portion 30 without any gap. In the configuration example of the light guide plate 10 shown in fig. 23B, the flat portion 25 is provided between the adjacent lenticular lenses 33. The flat portion 25 is connected to each flat surface 61B of the adjacent lenticular lens 33. Therefore, the plurality of lenticular lenses 33 are arranged in parallel with each other at predetermined intervals.

Fig. 23C is a diagram illustrating the light guide plate 10 of the embodiment. In the configuration example of the light guide plate 10 shown in fig. 23C, the angle of the lenticular lens 33 is 60 degrees, but the angle of the lenticular lens 33 may be an angle other than 60 degrees. The angle of the lenticular lens 33 may be, for example, 30 degrees to 80 degrees, 30 degrees to 70 degrees, or 45 degrees to 60 degrees. The angle of the lenticular lens 33 is an angle (θ) formed by the flat surface 32 of the flat plate portion 30 and the flat surface 61B of the end portion of the lenticular lens 33. The angle of the lenticular lens 33 is 30 degrees to 80 degrees, and the lenticular lens 33 has the curved surface 33B and the flat surface 61B, whereby the contrast ratio can be improved.

As shown in fig. 23C, the lenticular lens 33 includes a trapezoidal portion 62B and an arc portion 63B in contact with the top and bottom of the trapezoidal portion 62B when viewed from the normal direction of the light incident surface 20 of the light guide plate 10. The length of the upper base of the trapezoidal section 62B is shorter than the length of the lower base of the trapezoidal section 62B. The trapezoidal portion 62B contacts the flat surface 32 of the flat plate portion 30, and the circular-arc shaped portion 63B is separated from the flat surface 32 of the flat plate portion 30. In the configuration example of the light guide plate 10 shown in fig. 23C, the height of the trapezoidal portion 62B is 50% of the total of the height of the trapezoidal portion 62B and the height of the circular arc portion 63B. The ratio of the height of the trapezoidal portion 62B to the total of the height of the trapezoidal portion 62B and the height of the circular arc portion 63B is not limited to 50%. The ratio of the height of the trapezoidal portion 62B to the total of the height of the trapezoidal portion 62B and the height of the circular arc portion 63B may be 0% to 100%.

When a moving image is displayed on the liquid crystal display device, by bringing a part of the plurality of light sources 11 and 41 into a non-lighting state in conjunction with scanning of the liquid crystal and making the inside of the screen partially black, it is possible to reduce afterimages in the moving image so that switching of the liquid crystal is not visually recognized. A technique for reducing such afterimages in a moving image is called backlight scanning. According to the liquid crystal display device of the embodiment, since the increase in luminance of the light emitted from the upper surface 21 of the light guide plate 10 can be suppressed, the display control of the black region in a part of the screen can be improved. In addition, such a liquid crystal display device can also be used to display content using VR (Virtual Reality) technology.

Such a liquid crystal display device can be mounted on various electronic apparatuses. Examples of electronic devices having such a liquid crystal display device include a smartphone, a digital camera, a tablet terminal, an electronic book, a wearable device, a car navigation device, an electronic dictionary, and an electronic billboard.

Description of the reference symbols

1: a surface light source device; 2: a display panel; 10: a light guide plate; 11. 41: a light source; 12: FPC; 13: a fixing member; 14: a frame; 15: a reflective sheet; 16: a diffusion sheet; 17: a prism sheet; 18: a light-shielding double-sided tape; 23. 33: a lenticular lens; 23A, 23B, 33A, 33B: a curved surface; 30: a flat plate portion; 31. 32: a plane; 51A, 51B, 61A, 61B: a flat surface.

Claims

1. A light guide plate having a substantially flat plate shape and having a light incident surface on a side thereof, into which light is incident, and from which light incident from the light incident surface exits, the light guide plate comprising:

a flat plate portion; and

at least one of a plurality of convex strips and concave strips which are provided on the plane of the flat plate portion and extend in a vertical direction perpendicular to the light incident surface when viewed from a normal direction of the plane,

at least one of the plurality of convex strips and concave strips has an inclined surface inclined with respect to the plane,

the light exit surface is formed by the inclined surface of at least one of the convex strips and the concave strips,

an angle formed by the plane and a tangent to the inclined surface at an end of at least one of the plurality of convex strips and concave strips is 30 degrees or more and 70 degrees or less.

2. The light guide plate according to claim 1,

an angle formed by the plane and a tangent to the inclined surface at an end of at least one of the plurality of convex strips and concave strips is 45 degrees or more and 60 degrees or less.

3. The light guide plate according to claim 1 or 2,

the inclined surface includes a curved surface.

4. The light guide plate according to claim 1,

the inclined surface comprises a curved surface and a flat surface,

an angle formed by the flat surface and the flat surface at an end portion of at least one of the plurality of convex strips and concave strips is 30 degrees or more and 70 degrees or less.

5. The light guide plate according to claim 1,

the inclined surface comprises a curved surface and a flat surface,

an angle formed by the flat surface and the flat surface at an end portion of at least one of the plurality of convex strips and concave strips is 45 degrees or more and 60 degrees or less.

6. The light guide plate according to any one of claims 1 to 5,

the thickness of the light guide plate excluding at least one of the plurality of convex strips and concave strips is 0.2mm to 1.0 mm.

7. The light guide plate according to any one of claims 1 to 6,

at least one of the plurality of convex strips and concave strips is arranged on the plane without a gap.

8. The light guide plate according to any one of claims 1 to 3,

at least one of the plurality of convex strips and concave strips is arranged on the plane at a predetermined interval,

the light emitting surface is formed by the inclined surface and the plane of at least one of the convex strips and the concave strips.

9. A light guide plate having a substantially flat plate shape and having a light incident surface on a side thereof, into which light is incident, and from which light incident from the light incident surface exits, the light guide plate comprising:

a flat plate portion; and

the light emitting surface is formed by the inclined surface and the plane of at least one of the convex strips and the concave strips,

an angle formed by the plane and a tangent to the inclined surface at an end of at least one of the plurality of convex strips and concave strips is 30 degrees or more and 80 degrees or less.

10. The light guide plate according to claim 9,

11. The light guide plate according to claim 9 or 10,

the inclined surface includes a curved surface.

12. The light guide plate according to claim 9,

the inclined surface comprises a curved surface and a flat surface,

an angle formed by the flat surface and the flat surface at an end portion of at least one of the plurality of convex strips and concave strips is 30 degrees or more and 80 degrees or less.

13. The light guide plate according to claim 9,

the inclined surface comprises a curved surface and a flat surface,

14. The light guide plate according to any one of claims 9 to 13,

15. A surface light source device includes:

the light guide plate according to any one of claims 1 to 14; and

and a light source disposed at a position facing the light incident surface.

16. A surface light source device includes:

the light guide plate according to any one of claims 1 to 14;

1 st light source; and

a 2 nd light source for emitting light from the light source,

the light incident surface comprises a 1 st light incident surface and a 2 nd light incident surface,

the 1 st light incident surface is opposite to the 2 nd light incident surface,

the 1 st light source is arranged at a position opposite to the 1 st light incident surface,

the 2 nd light source is disposed at a position facing the 2 nd light incident surface.

17. A display device, having:

the surface light source device of claim 15 or 16; and

a display panel receiving the light emitted from the surface light source device.

18. An electronic device having the display device according to claim 17.