JP4963726B2 - Surface illumination device and liquid crystal display device - Google Patents

Description

The present invention relates to a planar illumination device and a liquid crystal display device including a transparent light guide plate that diffuses light incident from a rod-shaped light source in a direction substantially parallel to the light emission surface and emits more uniform illumination light from the light emission surface. About.

A liquid crystal display device uses a backlight unit that irradiates light from the back side of a liquid crystal panel (LCD) to illuminate the liquid crystal panel. At present, the so-called direct type is the mainstream for backlight units of large-sized liquid crystal televisions (see, for example, Patent Document 1). The direct type backlight unit has a configuration in which a plurality of cold cathode tubes, which are light sources, are arranged on the back surface of the liquid crystal panel, and the inside of the casing in which the cold cathode tubes are arranged has a white reflecting surface as a liquid crystal panel Lighting up.
However, in order to make the light quantity distribution uniform in this method, in principle, the liquid crystal panel requires a thickness of about 30 mm in the vertical direction. In recent years, thinning, low power consumption, and large size of liquid crystal display devices have been demanded. However, in the direct backlight unit described above, when the thickness is 10 mm or less, unevenness in the amount of light occurs. There was a limit to reducing the thickness.

  As a backlight unit that realizes a reduction in thickness, a backlight unit called a sidelight type is known. The sidelight type backlight unit includes a light source for illumination and a plate-shaped light guide plate having a rectangular light exit surface, and has a structure in which the light source is arranged on the side surface of the light guide plate. In such a sidelight-type backlight unit, light from a light source is taken in from the side surface of the light guide plate and propagated while reflecting the light on the surface opposite to the light emitting side. The liquid crystal panel is illuminated by emitting light from the surface on the side where the liquid crystal is disposed. Since the sidelight type backlight unit has a structure in which the light source is arranged on the side surface of the light guide plate, it can be made thinner than the direct type backlight unit. In the sidelight type backlight unit, optical components such as a prism sheet and a diffusion sheet are provided in order to improve luminance and make light emitted from the light guide plate uniform.

As one of such sidelight type backlight units, a so-called tandem type system is known in which a plurality of units each having a light guide plate arranged on the side surface of an illumination light source are arranged (for example, Patent Documents). 2). In this method, the backlight unit can be made thin by connecting a plurality of light guide plates and allowing light to enter from the side surfaces of the light guide plates. However, since this method has lower light utilization efficiency than a direct backlight unit, high power is required to emit high-luminance light.
Therefore, light guide plates having various shapes have been proposed in order to realize thinning, low power consumption, and large size of liquid crystal display devices (Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, and Patent). Reference 7).

FIG. 30 is a schematic cross-sectional view of a surface light source device having a light guide plate 100 disclosed in Patent Document 3.
In the surface light source device (backlight unit) shown in the figure, after the fluorescent lamp 102 is embedded in the light guide plate 100, the reflection sheet 104 is disposed on the back surface of the light guide plate 100, and the transmitted light amount correction sheet is provided on the exit surface of the light guide plate 100. 106, a light diffusion plate 108, and a prism sheet 110 are laminated.
The light guide plate 100 has a substantially rectangular shape and is formed using a resin in which fine particles that diffuse illumination light are dispersed and mixed. In addition, the upper surface of the light guide plate 100 is flat and assigned to the exit surface. Further, a groove 100a having a U-shaped cross-section for embedding the fluorescent lamp 102 is formed on the back surface (surface opposite to the emission surface) of the light guide plate 100, and the emission surface of the light guide plate 100 is directly above the fluorescent lamp 102. Avoiding this, a light amount correction surface 100b that prompts emission of illumination light is formed.
As described above, in Patent Document 3, the light guide plate 100 is formed by mixing fine particles, and the illumination light is corrected by the light amount correction surface 100b formed on a part or all of the emission surface except directly above the fluorescent lamp 102. It is described that by promoting the emission, the entire thickness can be reduced and unnatural luminance unevenness of the emitted light can be reduced.

Further, Patent Document 4 provides a backlight of a liquid crystal display device that can realize a reduction in size and weight and a reduction in cost and power consumption of the liquid crystal display device without reducing the amount of backlight irradiation. For this purpose, a rectangular irradiation surface, a rectangular cross section grooved in parallel with the long side at the center of the short side, and a groove with a rectangular cross-section for inserting the light source, facing both sides of the long side across this groove A light guide plate having a back surface formed so that the plate thickness is gradually reduced is disclosed.
In Patent Document 5, the frame of the liquid crystal display device can be narrowed, the thickness can be reduced, and in order to obtain a bright backlight unit with high light utilization efficiency, in the width direction of the recess for arranging the light source. A light guide (light guide plate) is disclosed in which the parallel cross-sectional shape is a parabolic shape with the depth direction as the main axis.

  Further, in Patent Document 6, in order to keep the in-plane brightness of the display panel uniform and to provide high-intensity illumination, a plurality of refractive indexes are sequentially increased on the C-shaped highly reflective layer. A light guide plate is disclosed in which the plate-like optical waveguide layers are stacked and the light diffusion layer is brightened by the light emitted from the respective light emission end faces. Here, the recess for arranging the light source has a triangular shape.

  Further, in Patent Document 7, in order to improve the liquid crystal backlight for a large liquid crystal display surface of a wall-mounted television, a plurality of light guide plates are arranged in parallel, and a predetermined number of linear light sources are arranged between the light guide plates. It achieves a large and uniform large-sized backlight with high brightness.

  The light guide plates disclosed in each of the above patent documents are intended to achieve some of the thinning, size and weight reduction, power consumption, cost reduction, etc. of the liquid crystal display device. One or a plurality of grooves are provided, and a rod-shaped light source is accommodated in the grooves, and preferably, the plate thickness is gradually reduced from the groove portion toward the end surface to achieve a reduction in thickness. .

Japanese Utility Model Publication No. 5-4133 JP-A-11-288611 Japanese Patent Laid-Open No. 9-304623 JP-A-8-62426 JP 10-1333027 A JP-A-5-249320 JP 2001-42327 A

  However, in the light guide plate 100 disclosed in Patent Document 3, a light amount correction surface 100b such as a rough surface or a microprism surface is formed on the surface of the light emission surface avoiding the light source (fluorescent lamp) 102, and the light emission surface is formed on the light emission surface. On the other hand, although the emission of the illumination light incident at an angle greater than the critical angle is urged, as shown in FIG. 29, the solid line with respect to the luminance N1 of the illumination light from the light guide plate not having the light quantity correction surface indicated by the dotted line The effect of improving the luminance N2 of the illumination light from the light guide plate 100 having the light amount correction surface 100b shown in FIG. 5 is little, so the luminance improvement effect by the light amount correction surface 100b is not great, and the light source light utilization efficiency is low. Since the diffusion of the light source light is insufficient, there is a problem that uniform and high-intensity light cannot be emitted from the emission surface.

  In the light guide plate 100 disclosed in Patent Document 3, the light source (fluorescent lamp) 102 is embedded in the groove 100a having a circular cross-sectional shape, and the luminance peak due to the light source 102 remains as shown in FIG. In order to use as a surface light source device, it is necessary to remove the unnatural luminance unevenness on the exit surface by using the transmitted light amount correction sheet 106, the light diffusion plate 108, the prism sheet 110, etc. arranged on the exit side of the light guide plate. Therefore, there is a problem that the cost of the surface light source device increases.

  Further, in the backlight of the liquid crystal display device disclosed in Patent Document 4, by disposing the components on the electronic circuit board in the gap generated by tilting the back surface of the light guide plate, the liquid crystal display is inexpensive and has low power consumption. Although the apparatus can be reduced in size, weight, and thickness, the unevenness of illumination light emitted from the exit surface of the light guide plate is not considered at all.

Further, in the backlight unit of the liquid crystal display device disclosed in Patent Document 5, the cross-sectional shape of the concave portion on the groove provided in the light guide (light guide plate) is a parabola, so that light diffusion in the light guide is substantially reduced. Although light is incident on the light guide to be uniform and the light use efficiency can be increased, the unevenness of light emitted from the light exit surface of the light guide is not considered at all.
In addition, the light guide plate disclosed in Patent Document 6 has a complicated structure in which a plurality of plate-like optical waveguide plates are stacked. Therefore, it is possible to obtain a uniform brightness with less attenuation of brightness than in the past. However, there is a problem that the manufacturing cost becomes high.

  In addition, in the light guide plate disclosed in Patent Document 7, since the luminance increases immediately above the linear light source, a transmission suppression pattern that suppresses transmission of light from the linear light source must be provided, and the linear light source Since the light from the light is transmitted in the in-plane direction from one end to the other end inside the light guide plate, the amount of light gradually attenuates, which is insufficient for increasing the brightness.

The present invention has been made to solve the above problems, and a first object of the present invention is to solve the above-mentioned problems of the prior art, and to be thin, lightweight, and manufactured at a lower cost. It can emit light with higher light utilization efficiency, more uniformity, less unevenness and higher brightness, and can be used as a large-sized illumination surface, or a liquid crystal display such as a wall-mounted TV An object of the present invention is to provide a planar lighting device that can be applied as a backlight of the device.

In addition, the second problem of the present invention is to solve the above-mentioned problems of the prior art, and is thin and lightweight, can be manufactured at a lower cost, has high light utilization efficiency, is more uniform, and has less unevenness. It is another object of the present invention to provide a liquid crystal display device that can perform display with higher brightness, can be a large-sized display screen, or can be a wall-mounted type such as a wall-mounted television.

To solve the above first problem, the first state like the present invention has a rectangular outer shape, and a light exit surface having a concave portion formed substantially parallel to one side, substantially parallel to the one side The rectangular light exit surface at a substantially central portion of the rectangular light emitting surface, a pair of thin end portions formed substantially parallel to the thick portion, and the rectangular light at a substantially central portion of the thick portion. on the exit surface on the opposite side, the side substantially parallel to form a parallel groove for accommodating the rod-shaped light sources, the thin end of the pair of opposite sides in the orthogonal direction substantially orthogonal to the one side from the thick portion thickness towards the respective parts becomes thin, the the inclined rear portions of the pair forming the inclined rear planes of each pair on either side of the parallel grooves, and a transparent light guide plate to have a, the parallel of the light guide plate A rod-shaped light source housed in the groove, a reflector provided behind the rod-shaped light source so as to close the parallel groove, and the light guide plate A reflection sheet attached to the inclined back surface of the inclined back surface on both sides of the thick wall portion, a diffusion sheet disposed on the rectangular light emission surface of the light guide plate, and the rectangular light emission of the light guide plate In order to effectively suppress the occurrence of uneven brightness of illumination light, including a halftone dot sheet laminated on a surface, and a halftone dot plate arranged in parallel to the halftone dot sheet at a predetermined interval Further, the halftone dot pattern of the halftone dot sheet is configured with a pattern for suppressing high-frequency luminance unevenness, and the halftone dot pattern of the halftone plate is configured with a pattern for suppressing low-frequency luminance unevenness. A planar lighting device is provided.

In the planar illumination device of the present invention, the parallel grooves are formed by a pair of contour lines that intersect at the vertices with a narrower interval toward the rectangular light exit surface in the cross-sectional shape in the orthogonal direction. Each contour line of the parallel groove in the cross-sectional shape in the orthogonal direction has a portion where an inclination angle with respect to a line perpendicular to the rectangular light exit surface changes, and the apex side is closer to the apex than the apex side. It is preferable that the base end side of the parallel groove far from the center is formed with an acute angle.

Further, the pair of inclined rear surface portions are symmetrical with respect to a plane that includes the axis of the rod-shaped light source and is perpendicular to the rectangular light exit surface, and a pair of the parallel grooves in the cross-sectional shape in the orthogonal direction. The outline of the parallel groove is symmetric with respect to a plane that includes the center of the parallel groove and is perpendicular to the rectangular light exit surface, and a tip portion of the parallel groove has a cross-sectional shape in the orthogonal direction of the parallel groove. It is preferable that the interval between the parallel grooves is symmetrically narrower toward the rectangular light exit surface with respect to a center line perpendicular to the rectangular light exit surface.
In addition, the luminance peak value formed in the portion corresponding to the parallel grooves on the rectangular light emitting surface is 3 of the average value of luminance formed in the portion corresponding to the inclined back surface on the rectangular light emitting surface. It is preferable to taper the tip end shape of the parallel groove in the cross-sectional shape in the orthogonal direction so as to be less than double.
The parallel grooves are formed by a pair of distal end surfaces constituting a distal end portion and a pair of proximal end surfaces constituting a proximal end portion in the cross-sectional shape in the orthogonal direction, and the pair of distal end surfaces are formed by the rectangular shape. Formed by a line segment having a predetermined angle with respect to a line perpendicular to the shape light exit surface and passing through the center of the rod-shaped light source, the top is formed in a curved shape, and the pair of base end surfaces are A line segment perpendicular to the rectangular light exit surface or a curved line that is concave toward the center of the parallel groove, and further extends a line segment of the pair of tip surfaces, and the rectangular light exit It is preferable that a parallel surface is provided between the intersection of the line parallel to the surface and passing through the lower end of the light guide plate and the lower end of the pair of base end surfaces.
The parallel grooves are formed by a pair of distal end surfaces constituting a distal end portion and a pair of proximal end surfaces constituting a proximal end portion in the cross-sectional shape in the orthogonal direction, and the pair of distal end surfaces are hyperbolic. The pair of base end surfaces are formed by a line segment perpendicular to the rectangular light exit surface or a concave curve toward the center of the parallel groove, and further, a hyperbola of the pair of distal end surfaces It is preferable that a parallel plane is provided between an intersection of a line extending from the line, a line parallel to the rectangular light exit surface and passing through the lower end of the light guide plate, and a lower end of the pair of base end surfaces.
The parallel grooves are formed by a pair of distal end surfaces constituting a distal end portion and a pair of proximal end surfaces constituting a proximal end portion in the cross-sectional shape in the orthogonal direction, and the pair of distal end surfaces are hyperbolic. Preferably, the pair of base end surfaces are formed by line segments perpendicular to the rectangular light exit surface.

Further, there is provided a planar illumination device characterized in that the light guide plate is a single light guide plate block, which is composed of a plurality of light guide plate blocks, and the thin end surfaces of the light guide plate blocks are connected to each other. .

The concave portion is formed in a luminance unevenness generation region of the rectangular light emitting surface, and the rectangular light emitting surface includes a curved surface forming the concave portion and two flat surfaces located on both sides thereof. Is preferred .

Also, the dot sheet is flexible, wherein said curved surface forming the rectangular light exit plane of the light guide plate be disposed in close contact on two planes preferable.

Moreover, in order to solve the said 2nd subject, the 2nd aspect of this invention is arrange | positioned at the light emission surface side of the planar illuminating device according to the 1st aspect of this invention, and the said planar illuminating device. A liquid crystal display device comprising: a liquid crystal display panel; and a drive unit for driving the liquid crystal display panel.

According to a first aspect of the present invention, a lightweight thin type can be manufactured at lower cost, high utilization efficiency of light, less unevenness in a more uniform and higher intensity illumination light It is possible to provide a planar illumination device that can emit light, have a large illumination surface, or can be applied to a liquid crystal display device such as a wall-mounted television.

Moreover, according to the 2nd aspect of this invention, it is thin and lightweight by using the planar illuminating device of the said 1st aspect, can be manufactured at lower cost, and the utilization efficiency of light is high. Liquid crystal lighting device that can display more uniform, less unevenness, and higher brightness, can have a large display screen, or can be a wall-mounted type such as a wall-mounted TV Can be provided.

It is a schematic structure sectional view at the time of arranging a plurality of light guide plates provided in the planar lighting device of the present invention in parallel. (A) and (b) are respectively a schematic perspective view and a schematic sectional view of a liquid crystal display device using the bus click light unit of the present invention. It is a schematic structure sectional view of the light guide plate in which the concave part was formed in the light emission surface. It is a schematic structure sectional drawing of the light- guide plate which laminated | stacked the dot sheet | seat on the light emission surface. (A) is a schematic sectional drawing which shows a mode that the prism sheet is arrange | positioned between a reflective sheet and the inclined surface of a light-guide plate, (b) is between a reflective sheet and the inclined surface of a light-guide plate. It is the schematic plan view and schematic cross-sectional view which looked at the arrange | positioned prism sheet from the light-guide plate side. It is a schematic structure sectional drawing of the light- guide plate in which the convex part was formed in the light-projection surface, and is the example by which the several lenticular lens is arrange | positioned in the center area | region of the light-projection surface. It is a schematic structure sectional view of a light guide plate in which a convex part was formed in the light emission surface, and is an example in which a plurality of prism rows are arranged in the central region of the light emission surface. It is a schematic structure sectional view of a light guide plate in which a convex part was formed in the light emission surface, and is an example in which a plurality of dimples were formed in the central region of the light emission surface. It is a schematic structure sectional view of the light guide plate in which the convex part was formed in the light emission surface, and is an example in which a plurality of hemispherical lenses were arranged in the central area of the light emission surface. It is a schematic diagram of the halftone dot pattern when the halftone dot pattern is directly formed on the light exit surface of the light guide plate by printing. In this configuration example, a halftone dot sheet is arranged on the light exit surface of the light guide plate, and the halftone dot plate is supported by a convex portion thereon. Luminance distribution A on the light exit surface of the light guide plate, brightness distribution B when only a halftone dot sheet on which a halftone dot pattern for suppressing high-frequency brightness unevenness is formed on the light exit surface side of the light guide plate, and the light guide plate This is an example of the luminance distribution C when a halftone dot sheet and a halftone dot plate on which a halftone dot pattern that suppresses low frequency luminance unevenness is arranged on the light exit surface side of FIG. It is the elements on larger scale of the edge part of a light-guide plate, and is the figure which showed typically the shape of the convex part formed in the edge part of a light-guide plate. (A) is schematic sectional drawing of the parallel groove periphery of the light guide plate whose cross-sectional shape perpendicular | vertical to the length direction of a pair of front end surface of a parallel groove is a hyperbola, (b) is a pair of front end of a parallel groove FIG. 4C is a schematic cross-sectional view of the periphery of a parallel groove of a light guide plate having an elliptical cross-sectional shape perpendicular to the surface length direction, and FIG. 5C is a cross-sectional shape perpendicular to the length direction of a pair of front end surfaces of the parallel groove. FIG. 6 is a schematic cross-sectional view of the periphery of the parallel groove of the light guide plate formed from a part of two circular arc curves that are symmetric with respect to the center line that passes through the center of the parallel groove and is perpendicular to the light exit surface of the light guide plate; ) Is a part of two parabolas in which the cross-sectional shape perpendicular to the length direction of the pair of tip surfaces of the parallel grooves is symmetrical with respect to the center line passing through the center of the parallel grooves and perpendicular to the light exit surface of the light guide plate It is a schematic sectional drawing of the parallel groove periphery of the light-guide plate currently formed from. (A) is a schematic cross section around the parallel groove of the light guide plate in which the cross-sectional shape perpendicular to the length direction of the pair of front end surfaces of the parallel groove is formed from two curves convex toward the center of the parallel groove (B) is a cross-sectional shape perpendicular to the length direction of a pair of tip surfaces of a parallel groove formed from a curve combining a convex curve and a concave curve toward the center of the parallel groove. It is a schematic sectional drawing of the parallel groove periphery of a light guide plate. (A) is a schematic sectional view around the parallel groove of the light guide plate in which the cross-sectional shape perpendicular to the length direction of the pair of base end faces of the parallel groove is formed by a line segment having an acute angle than the pair of front end faces (B) is a schematic cross-section around the parallel groove of the light guide plate in which the cross-sectional shape perpendicular to the length direction of the pair of base end faces of the parallel groove is formed as a concave curve toward the center of the parallel groove. FIG. It is a schematic sectional drawing which shows another example of the light-guide plate with which the planar illuminating device of this invention is equipped . (A) is a parallel groove of a light guide plate in which the cross-sectional shape of a pair of distal end surfaces of a parallel groove is a hypotenuse and the cross-sectional shape of a pair of base end surfaces of the parallel groove is a line segment perpendicular to the light exit surface. FIG. 4B is a schematic cross-sectional view of the periphery, and FIG. 5B is a line segment in which the cross-sectional shape of the pair of distal end surfaces of the parallel grooves is the hypotenuse and the cross-sectional shape of the pair of base end surfaces of the parallel grooves is the same as the pair of distal end surfaces FIG. 4C is a schematic cross-sectional view of the periphery of the parallel groove of the light guide plate formed in step (c), in which the cross-sectional shape of the pair of front end surfaces of the parallel groove is a hypotenuse and the cross-sectional shape of the pair of base end surfaces of the parallel groove is a pair; It is a schematic sectional drawing of the parallel groove periphery of the light-guide plate formed with the line segment of a steep inclination rather than the front end surface of (a), (d) is a pair of front end surface and a pair of base end surfaces rather than (a). FIG. 6E is a schematic cross-sectional view of the periphery of the parallel groove of the light guide plate formed with the connecting portion on the parallel portion side, and FIG. 8E is a cross-sectional shape of a pair of tip surfaces of the parallel groove is a hypotenuse and a pair of bases of the parallel groove End face break Shape is a schematic cross-sectional view of parallel grooves around the concave of the light guide plate formed with a curve toward the center of the parallel groove. (A)-(d) are the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate shown to FIG.18 (a), FIG.18 (c), FIG.18 (d), and FIG.18 (e), respectively. It is a graph which shows. (A)-(c) is a schematic block diagram of the parallel groove periphery of a light-guide plate when not providing the parallel surface of the light-guide plate shown in FIG.18 (a), FIG.18 (c), and FIG.18 (d), respectively. is there. (A)-(c) is a graph which shows the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate shown to Fig.20 (a), FIG.20 (b), and FIG.20 (c), respectively. (A) is a parallel groove of a light guide plate in which the cross-sectional shape of a pair of front end surfaces of a parallel groove is a hyperbola and the cross-sectional shape of a pair of base end surfaces of the parallel groove is a line segment perpendicular to the light exit surface. FIG. 4B is a schematic cross-sectional view of the periphery, in which (b) is formed by a hyperbola having a cross-sectional shape of a pair of front end surfaces of parallel grooves and a hyperbola having a cross-sectional shape of a pair of base end surfaces of parallel grooves. FIG. 6C is a schematic cross-sectional view of the periphery of the parallel groove of the light guide plate, and FIG. 8C is a pair of distal end surfaces of a pair of distal end surfaces of the parallel groove and a pair of distal end surfaces of a pair of proximal end surfaces of the parallel groove. FIG. 4D is a schematic cross-sectional view of the periphery of a parallel groove of a light guide plate formed by a steeper hyperbola, and FIG. 4D is a cross-sectional shape of a pair of front end surfaces of the parallel groove; It is a schematic sectional drawing of the periphery of the parallel groove of the light guide plate in which the cross-sectional shape of the end surface is formed as a concave curve toward the center of the parallel groove. (A)-(c) is a graph which shows the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate shown to Fig.22 (a), FIG.22 (c), and FIG.22 (d), respectively. (A) And (b) is a schematic block diagram of the parallel groove periphery of a light-guide plate when not providing the parallel surface of the light-guide plate shown to FIG. 22 (a) and FIG.22 (c), respectively. (A) And (b) is a graph which shows the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate shown to Fig.24 (a) and FIG.24 (b), respectively. It is a schematic sectional drawing of another example when the light-guide plate with which the planar illuminating device of this invention is equipped is arrange | positioned in parallel. (A) is the structural example which has arrange | positioned the reflecting plate in the side surface of the light guide plate with which the planar illuminating device of this invention is equipped , (b) is the light guide plate with which the planar illuminating device of this invention is equipped in parallel. It is the structural example which has arrange | positioned the reflecting plate in the side surface of the light-guide plate when it arrange | (A) is a schematic sectional drawing which shows a mode that the prism is formed in the inclined surface of a light-guide plate, (b) looked at the inclined surface of the light-guide plate in which the prism was formed from the light-projection surface side. It is a schematic plan view and a schematic cross-sectional view. It is a schematic sectional drawing which shows a mode that the prism is formed in the inclined surface and light-projection surface of a light-guide plate. It is a schematic sectional drawing of the surface light source device which has the conventional light-guide plate. It is a graph of the brightness | luminance in the output surface of the light-guide plate of the surface light source device of FIG.

Hereinafter, the planar illumination device and a liquid crystal display device of the present invention, based on preferred embodiments shown in the accompanying drawings and will be described in detail.

FIG. 1 shows a schematic cross-sectional view of a planar illumination device 2 (hereinafter also referred to as a backlight unit) according to the first aspect of the present invention in which a plurality of light guide plates 18 are arranged in parallel. Such a planar illumination device 2 is used as a backlight unit of the liquid crystal display device according to the second aspect of the present invention. 2 (a) and 2 (b), a part of one light guide plate 18 of the backlight unit 2 shown in FIG. 1, and a schematic partial perspective view and a schematic of a liquid crystal display device 10 using the backlight unit 2 are shown. A partial sectional view is shown. As shown in FIGS. 2A and 2B, the liquid crystal display device 10 basically includes a backlight unit 2, a liquid crystal display panel 4 disposed on the light emission surface side of the backlight unit 2, and those And a drive unit 6 for driving the motor.

  In the liquid crystal display device shown in FIGS. 2A and 2B, the liquid crystal display panel 4 includes, for example, GH, PC, TN, STN, ECB, PDLC, IPS (In-Plane Switching), VA (Vertical Aligned). ) Liquid crystal display panels in accordance with liquid crystal display modes such as various types (MVA, PVA, EVA), OCB, ferroelectric liquid crystal, and anti-ferroelectric liquid crystal can be used. The driving method of the liquid crystal display panel 4 is not particularly limited, and a known driving method such as a simple matrix method or an active matrix method can be used.

The backlight unit 2 is a planar illumination device for irradiating the entire surface of the liquid crystal display panel 4 with uniform light from behind the liquid crystal display panel 4. The backlight unit 2 is light having substantially the same size as the image display surface of the liquid crystal display panel 4. It has an emission surface (light emitting surface). As shown in FIG. 2, the backlight unit 2 basically includes a light source 12, a diffusion sheet 14, two prism sheets 16 and 17 , a light guide plate 18, a reflector 20, and a reflection sheet 22. Have

The driving method of the backlight unit 2 is not particularly limited. For example, the backlight unit 2 may be driven to perform luminance modulation by monitoring the surrounding environment. For example, the brightness may be modulated according to the brightness or temperature by providing an ambient light sensor to detect ambient brightness, or providing a temperature sensor to detect ambient temperature. Also, the driving method of the backlight unit 2 is not particularly limited. For example, R (red), G (green), and B (blue) light sources (for example, LED light sources) are used, and these light sources are displayed on a liquid crystal display. It may be driven by a field sequential method of sequentially lighting in accordance with the display on the panel 4, or may be driven by an intermittent lighting method of sequentially emitting light or turning off in accordance with a liquid crystal scanning display. If the backlight unit 2 is driven using the field sequential method, the R, G, and B color filters can be removed, so that the loss of light quantity due to the color filters can be eliminated. In addition, if the light source is turned on for a short time according to the intermittent lighting method, the display performance of the moving image can be improved.
Hereinafter, components of the backlight unit 2 will be described.

First, the light guide plate 18 will be described. FIG. 3 shows a schematic cross-sectional view of the light guide plate in a state where the light source 12 is accommodated.
The light guide plate 18 in FIG. 3 is a light guide plate provided in the planar illumination device according to the present invention. The light guide plate 18 includes a rectangular light exit surface 18a, a thick portion 18b parallel to one side thereof, a pair of thin end portions 18c formed in parallel to the one side on both sides of the thick portion 18b, and a thickness. thickness toward both sides of the thin end portions 18c from the wall portion 18b in the direction of Cartesian to the one side becomes thin, and inclined rear portion 18e of the pair of forming an inclined surface 18 d, to the one side in the thick portion 18b A parallel groove 18f for accommodating the light sources 12 formed in parallel.
The light guide plate 18 is a flat plate having a rectangular outer shape on the surface, and is formed of a transparent resin. The light guide plate 18 is configured such that one surface forms a light emission surface 18a for emitting light, and the other surface is thinned toward the one side from the thick portion 18b toward both sides. The pair of inclined surfaces 18d are inclined with respect to one surface. Here, the inclined surface 18d is formed as a flat surface, but may be a curved surface.

As shown in FIG. 3, have you to this embodiment, the light guide plate 18, a concave portion 18k is formed on the light exit surface 18a. That is, as shown in FIG. 3, the light exit surface 18a of the light guide plate 18 is a curved surface region Wc located substantially at the center in the width direction of the light guide plate (the direction parallel to the light exit surface and perpendicular to the parallel grooves). And two planar regions Wf positioned so as to sandwich the curved surface region Wc. The recess 18k is formed with a constant width in the width direction of the light guide plate 18. Further, the concave portion 18k is formed so as to gradually become deeper toward the central portion.
Such a recess 18k is a region where unevenness in luminance is generated on the light exit surface 18a of the light guide plate 18 when the brightness of the light exit surface of the light guide plate 18 having a flat light exit surface is measured. (Hereinafter, referred to as a luminance unevenness generation region). Here, the luminance unevenness means a difference in luminance between any two points on the light exit surface. For example, the distance between any point x1 and x2 on the light exit surface of the light guide plate is dx (mm). , the luminance of points ^{x1 B1 (cd / m 2)} , as the luminance at the point ^{x2 B2 (cd / m 2)} , when the brightness difference between two points was dB, be defined in dB / dx it can.
By forming such a recess 18k in a region of the light exit surface 18a of the light guide plate 18 where luminance unevenness that is visible is generated, a film member for a backlight unit (see FIG. 2 (a) and (b), a space is secured between the prism sheet 16). As a result, the light emitted from the recess 18k is mixed and diffused in the space formed between the recess 18k and the member disposed thereon. That is, light emitted from a region where uneven brightness occurs is scattered. For this reason, in the backlight unit 2 (planar illumination device) including the light guide plate 18, occurrence of uneven brightness is reduced.

The shape of the concave portion 18k of the light exit surface 18a may be any shape as long as the height difference is formed on the light exit surface 18a according to the uneven brightness generation region. A preferable shape is shown in FIG. The cross-sectional shape when cut along a plane perpendicular to the length direction of the parallel grooves 18f is an arc shape.
The optical component disposed on the light exit surface 18a of the light guide plate 18 can be supported in contact with the flat portions 18m located on both sides of the recess 18a in the width direction of the light guide plate 18. The optical component may be a member having a certain degree of rigidity so that it does not sag due to its own weight in the region of the recess 18k, or in close contact with the light emitting surface 18a in order to suppress the generation of bright lines on the light emitting surface 18a. It may be a member having flexibility (for example, a halftone dot sheet). FIG. 4 shows an example in which a halftone dot sheet 32 is laminated on the light exit surface 18 a of the light guide plate 18. As shown in FIG. 4, the halftone dot sheet 32 is provided so as to be substantially in close contact with the light exit surface 18a, and is arranged along the shape of the recess 18k in the region where the recess 18k is formed. Yes. Thus, when the halftone dot sheet 32 is formed on the light exit surface 18a of the light guide plate 18, a space formed between the position of the concave portion 32a of the halftone dot sheet 32 and the optical member disposed thereon. Thus, the light emitted through the halftone sheet 32 is mixed and diffused. That is, the planar illumination light emitted from the light exit surface 18a of the light guide plate 18 is further suppressed by the generation of uneven brightness in the halftone dot sheet 32, and further, due to the mixing effect of the space formed by the recess 32a. Generation of bright lines is effectively suppressed. As described above, in the present invention , the light guide plate suppresses the occurrence of luminance unevenness by forming a level difference in the light emission surface by making the luminance unevenness generation region on the light emission surface recessed from other regions. Yes.

In the light guide plate 18, a parallel surface 18g parallel to the light exit surface 18a is formed between the inclined surface 18d and the base end surface 18i on the other surface. That is, the thick portion 18b of the light guide plate 18 is provided with a parallel surface 18g extending from the inclined surface 18d. In the present invention, such a parallel surface 18g is not necessarily provided, but is preferably provided because it can improve the light utilization efficiency.

On the opposite side of the light emitting surface 18a of the thick portion 18b of the light guide plate 18, a parallel groove 18f for accommodating the light source 12 is formed extending in the longitudinal direction. The depth of the parallel groove 18f is preferably determined so that a part of the light source 12 does not protrude from the lower surface of the light guide plate 18, and takes into account the dimensions of the light source 12, the mechanical strength of the light guide plate 18, and changes over time. Is preferably determined. Further, the thickness of the thick portion 18 b and the thin end portion 18 c of the light guide plate 18 can be arbitrarily changed according to the dimensions of the light source 12. Here, the parallel grooves 18f of the light guide plate 18 may be formed in a direction perpendicular to the longitudinal direction of the light guide plate 18, but in order to increase the light use efficiency from the light source 12 accommodated in the parallel grooves 18f. Is preferably formed in the longitudinal direction.
In the present embodiment, the parallel groove 18f is formed by a pair of distal end surfaces 18h constituting the distal end portion and a pair of proximal end surfaces 18i constituting the proximal end portion, and the distal end surface 18h with respect to the light emitting surface 18a is formed. The inclination of the base end face 18i is steeper than the inclination. That is, the maximum value of the angle formed by the tangential plane of the distal end surface 18h and the light emitting surface 18a, that is, the angle (tilt angle) Φn formed by the tangential plane of the proximal end surface 18i and the light emitting surface 18a is greater than the maximum inclination angle Φm. large.

In the light guide plate 18 having the structure shown in FIG. 3, among the light emitted from the light source 12 arranged in the parallel groove 18f, the light incident on the inside of the light guide plate 18 from the side surface forming the parallel groove 18f is guided. After being reflected by the inclined surface 18d of the light plate 18, it is emitted from the light exit surface 18a. At this time, a part of the light leaks from the lower surface of the light guide plate 18, but the leaked light is reflected by the reflection sheet 22 formed on the inclined surface 18 d side of the light guide plate 18 and again inside the light guide plate 18. And exits from the light exit surface 18a. Thus, uniform light is emitted from the light exit surface 18a of the light guide plate 18.
In the present invention, in order to make the light emitted from the light exit surface 18a uniform, the light flux is effective in a direction (depth direction) parallel to the light exit surface 18a and perpendicular to the parallel grooves. The angle (taper) of the inclined surface 18d is limited so as to reach. That is, the angle (taper) of the inclined surface 18d is set such that the light beam emitted from the light source 12 and incident on the light guide plate 18 is totally reflected by the inclined surface 18d (back surface).

  In FIG. 3, the parallel groove 18 f of the light guide plate 18 has a cross-sectional shape perpendicular to the length direction of the parallel groove 18 f, a tip portion of which forms a triangle, a base end portion of which forms a rectangle, and the light emission surface as a whole. It is formed to have a convex home base shape on the 18a side. Accordingly, the pair of front end surfaces 18h of the parallel grooves 18f are inclined at a predetermined angle with respect to a vertical plane perpendicular to the light exit surface 18a and passing through the center of the light source, with one end of each pair intersecting each other. The cross-sectional shape is formed by two line segments (slanted sides) having a predetermined angle of inclination forming one vertex of the triangle. The pair of base end surfaces 18i of the parallel grooves 18f of the light guide plate 18 has one end connected to the other end of the pair of front end surfaces 18h, and is parallel and symmetrical to the vertical surface. The cross-sectional shape is formed by line segments that are respectively in contact with the remaining two vertices of the triangle and perpendicular to the light exit surface 18a connected to the parallel surface 18g of the light guide plate 18, respectively.

  In the present invention, the shape of the parallel groove 18f of the light guide plate 18 is not particularly limited, and can be various shapes. Although the shape of the parallel grooves 18f of the light guide plate 18 will be described in detail later, by optimizing the cross-sectional shape of the parallel grooves 18f of the light guide plate 18, unevenness in luminance on the light exit surface 18a can be suppressed. Therefore, the shape of the parallel groove 18f is designed to be an optimal shape, and the occurrence of uneven brightness is further effectively suppressed by forming the recess 18k on the light exit surface 18a as described above. Therefore, by configuring the backlight unit using such a light guide plate, illumination light with reduced luminance unevenness can be emitted from the backlight unit.

And have you the present invention, the light guide plate 18, for example, a method of molding by extrusion or injection molding a heated material resin, monomers in a mold, a casting polymerization method of forming by polymerization of oligomers with production can do. Examples of the material of the light guide plate 18 include acrylic resins such as PMMA (polymethyl methacrylate), PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), benzyl methacrylate and MS resins, other acrylic resins, Alternatively, a transparent resin such as COP (cycloolefin polymer) can be used. Further, the transparent resin may be mixed with fine particles for scattering light, whereby the light emission efficiency from the light emission surface 18a can be further enhanced.

The light guide plate 18 constituting the backlight unit 2 has been described above.
Next, the light source 12 will be described with reference to FIGS.
2A and 2B, a light source 12 is a thin rod-like cold cathode tube, and is used for illuminating the liquid crystal display panel 4. The light source 12 is disposed in a parallel groove 18f formed in the light guide plate 18, and is connected to the drive unit 6 including a light source drive unit. Here, a cold cathode tube is used as the light source 12, but the present invention is not limited to this, and any rod-shaped light source may be used. As the light source 12, for example, a normal fluorescent tube (hot cathode tube), LED (light emitting diode), or the like can also be used.
For example, instead of the light source 12, an LED light source having a columnar or prismatic transparent light guide having a length equivalent to the parallel groove 18f of the light guide plate 18 and LEDs arranged on the top and bottom surfaces of the light guide is used. You may use for. Such an LED light source can emit LED light from the side surface of the light guide by entering LED light from the top and bottom surfaces of the light guide.

Next, the diffusion sheet 14 of the backlight unit 2 will be described.
2 (a) and 2 (b), the diffusion sheet 14 is for diffusing and uniformizing the light emitted from the light exit surface 18a of the light guide plate 18. For example, PET (polyethylene terephthalate), PP For flat plate members made of optically transparent resin such as (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, other acrylic resins, or COP (cycloolefin polymer) It is formed with light diffusibility. The method is not particularly limited. For example, the surface of the flat plate member is subjected to surface roughening by fine unevenness processing or polishing (hereinafter, the surface on which these are applied is referred to as “sand-rubbed surface”) to impart diffusibility. Or pigments such as silica, titanium oxide or zinc oxide that scatter light on the surface, or the above-mentioned pigments that apply beads such as resin, glass or zirconia together with a binder, or scatter light into the resin. It is formed by kneading beads. In the present invention, as the diffusion sheet 14, a mat type or coating type diffusion sheet can be used.
In the present invention, as the diffusion sheet 14, it is also preferable to use a film-like member having a thickness of 500 μm or less that uses the above-mentioned material and imparts light diffusibility.

The diffusion sheet 14 is preferably arranged at a predetermined distance from the light exit surface 18 a of the light guide plate 18, and the distance can be appropriately changed according to the light amount distribution from the light exit surface 18 a of the light guide plate 18. Thus, by separating the diffusion sheet 14 from the light exit surface 18 a of the light guide plate 18 by a predetermined distance, light emitted from the light exit surface 18 a of the light guide plate 18 is further between the light exit surface 18 a and the diffusion sheet 14. Mixed (mixed). Thereby, the brightness | luminance of the light which permeate | transmits the diffusion sheet 14 and illuminates the liquid crystal display panel 4 can be made further uniform. As a method of separating the diffusion sheet 14 from the light exit surface 18 a of the light guide plate 18 by a predetermined distance, for example, a method of providing a spacer between the diffusion sheet 14 and the light guide plate 18 can be used.
In particular, when the thickness of the backlight unit 2 may be slightly increased, the peak value of the luminance at the light exit surface 18a of the light guide plate 18 corresponding to the parallel grooves 18f, depending on the cross-sectional shape of the parallel grooves 18f of the light guide plate 18. Is not required to be sufficiently reduced, and the brightness distribution of the illumination light emitted from the diffusion sheet 14 is made uniform by partially reducing and providing a gap between the diffusion sheet 14 and the light exit surface 18a of the light guide plate 18. Anyway. In addition, there is a limit to the improvement of the cross-sectional shape of the parallel groove 18f of the light guide plate 18 (the taper of the tip portion of the parallel groove), and the luminance peak value on the light exit surface 18a of the light guide plate 18 corresponding to the parallel groove 18f is completely reduced. Even when it cannot be reduced to a sufficient level or when it cannot be reduced sufficiently, a gap is provided between the diffusion sheet 14 and the light exit surface 18a of the light guide plate 18 to make the luminance distribution of the illumination light emitted from the diffusion sheet 14 uniform. Also good.

Next, the prism sheets 16 and 17 will be described.
The prism sheets 16 and 17 are transparent sheets formed by arranging a plurality of prisms in parallel, and improve the light collecting property of the light emitted from the light exit surface 18a of the light guide plate 18 to improve the luminance. Can do. One of the prism sheets 16 and 17 is arranged so that the extending direction of the prism row is parallel to the parallel groove 18f of the light guide plate 18, and the other is arranged to be vertical. That is, the prism sheets 16 and 17 are arranged so that the extending directions of the prism rows are perpendicular to each other. The prism sheet 16 is disposed so that the apex angle of the prism faces the light exit surface 18 a of the light guide plate 18. Here, the arrangement order of the prism sheets 16 and 17 is that a prism sheet 16 having a prism extending in a direction parallel to the parallel groove of the light guide plate is arranged immediately above the light guide plate, and on the prism sheet 16, A prism sheet 17 having prisms extending in a direction perpendicular to the parallel grooves 18f of the light guide plate 18 may be disposed, or vice versa.

  In the illustrated example, a prism sheet is used, but a sheet in which optical elements similar to prisms are regularly arranged may be used instead of the prism sheet. In addition, a sheet that regularly includes an optical element such as a lens effect, for example, a lenticular lens, a concave lens, a convex lens, or a pyramid type can be used instead of the prism sheet.

  In the present invention, as shown in FIGS. 5A and 5B, a prism sheet 19 is also provided between the reflection sheet 22 and the inclined surface 18d opposite to the light exit surface 18a of the light guide plate 18. It is preferable. FIG. 5A is a schematic cross-sectional view showing a state in which the prism sheet 19 is disposed between the reflection sheet 22 and the inclined surface 18d of the light guide plate 18, and FIG. It is the schematic plan view and schematic cross-sectional view which looked at the prism sheet 19 arrange | positioned between 18 d of inclined surfaces of the light-guide plate 18 from the light-guide plate side. The prism sheet 19 provided between the reflection sheet 22 and the inclined surface 18d of the light guide plate 18 is disposed so that the extending direction of the prism 19a is perpendicular to the parallel groove 18f of the light guide plate 18, and the prism 19a. It is preferable to arrange so that the apex angle of the light guide plate 18 faces the inclined surface 18 d of the light guide plate 18.

Although a prism sheet is used here, an optical element having the same effect as the prism sheet may be used, and an optical element having a lens effect, for example, an optical element such as a lenticular lens, a concave lens, a convex lens, or a pyramid type is regularly formed. Arranged sheets may be provided.
In the illustrated example, the prism sheets 16 and 17, more preferably the prism sheet 19, are used. However, when the luminance on the light exit surface 18a by the parallel grooves 18f of the light guide plate 18 is more uniform, Of course, the prism sheet 19 is unnecessary, and either one or both of the prism sheets 16 and 17 may not be used. The cost of the apparatus can be reduced by reducing the number of expensive prism sheets used or by stopping the use of prism sheets.

Next, the reflection sheet 22 will be described with reference to FIGS. 2 (a) and 2 (b).
2 (a) and 2 (b), the reflection sheet 22 is for reflecting light leaking from the inclined surface 18d (lower surface in the drawing) of the light guide plate 18 so as to enter the light guide plate 18 again. Light utilization efficiency can be improved. The reflection sheet 22 is formed so as to cover the inclined surface 18 d of the light guide plate 18. The reflector 20 is provided behind the light source 12 so as to close the parallel groove 18 f of the light guide plate 18. The reflector 20 can reflect light from the lower surface of the light source 12 and make light incident from the side wall surface of the parallel groove 18 f of the light guide plate 18.

  The reflection sheet 22 may be formed of any material as long as it can reflect light leaking from the inclined surface 18d of the light guide plate 18. For example, a filler is kneaded with PET, PP (polypropylene), or the like. Resin sheet with increased reflectivity by forming voids by post-stretching, transparent or white resin sheet surface as described above, mirror-coated by aluminum vapor deposition, etc., carrying metal foil or metal foil such as aluminum It is possible to form the resin sheet or a thin metal plate having sufficient reflectivity on the surface. In addition, the reflector 20 can be formed of, for example, the same material as that of the reflection sheet 22, that is, a resin material, a metal foil, or a metal plate that imparts sufficient reflectivity to the surface.

The example of the configuration of the backlight unit 2 of the present invention has been described above with reference to the drawings.
Next, it will be described with reference to the drawings another configuration example of the obtained that the light guide plate used in the backlight unit 2.

As described above, in FIG. 3, the light guide plate in which the concave portion 18 is formed on the light emission surface 18a is shown as an example of the light guide plate. However, in the present invention, as shown in FIG. You may comprise the light-guide plate 118 so that it may have the convex part 18p. In FIG. 3, the cross-sectional shape of the parallel groove 18f of the light guide plate 18 is a home base shape, but in the light guide plate 118 (18A, 18B and 18C) shown in FIG. It has a triangular shape. However, the shape of the parallel groove 18f in which the rod-shaped light source is arranged is not particularly limited, and can be various shapes. As shown in FIG. 6, the light exit surface 18a has a convex portion 18p. Even if it is a light-guide plate, the cross-sectional shape of a parallel groove | channel can be made into a home base type similarly to FIG.
The light guide plate 118 shown in FIG. 6 is an example of a light guide plate block obtained by molding the three light guide plates 18A, 18B, and 18C so as to be integrated. Although FIG. 6 shows a configuration in which three light guide plates are integrally formed, a configuration in which two or four or more light guide plates are integrally formed may be used.

In FIG. 6, the convex portion 18p formed on the light exit surface 18a of the light guide plate 118 is disposed at the boundary between the light guide plates 18A, 18B, and 18C in parallel with the parallel groove 18f. As shown in FIG. 6, the convex portion 18p has a rounded shape such as an ellipse cut in half, and is formed with a certain height and width in a direction parallel to the parallel grooves. The height of the convex portion 18p is not particularly limited as long as the luminance unevenness on the light exit surface 18a of the light guide plate 18 can be sufficiently reduced by the film member disposed thereon. Further, the shape of the convex portion 18p is not particularly limited, and the cross-sectional shape of the convex portion 18p may be, for example, a rectangle, a trapezoid, a semicircle, or a triangle. Moreover, the position of the convex part 18p formed in the light-projection surface 18a of the light-guide plate 18 is not limited to the position shown in FIG. 6, but can be provided in arbitrary positions. Further, the number of the convex portions 18p is not limited, and three or more convex portions 18p can be formed for each of the light guide plates 18A, 18B, and 18C.
The convex portions formed on the light exit surface of the light guide plate may be formed integrally with the light guide plate during the manufacture of the light guide plate, or after the light guide plate having the flat light exit surface is manufactured, the flat light exit surface You may arrange | position the components used as a convex part to. From the viewpoint of ease of manufacture, it is preferable to form it integrally with the light guide plate.
Moreover, the convex part formed in a light emission surface can be utilized as a spacer for ensuring a space between the optical member which comprises a backlight unit, and a light emission surface. That is, it can be used as a spacer for separating a film-like optical member such as a prism sheet or a diffusion sheet disposed on the light emission surface by a predetermined distance from the flat portion of the light emission surface.

In FIG. 6, as a preferred embodiment, a plurality of lenticular lenses 34 are formed on the light exit surface 18a located above the parallel groove 18f in which the light source 12 is disposed. In other words, a plurality of lenticular lenses 34 are arranged in a predetermined region substantially at the center of the light exit surface 18a. Such a lenticular lens 34 is preferably arranged in a luminance unevenness generation region.
In the case of the light guide plate 18 in which the light source 12 is disposed in the parallel groove 18f as shown in FIG. 6, bright lines are generated from the light emission surface 18a above the parallel groove 18f, and uneven brightness is generated on the light emission surface 18a. Give rise to Therefore, the light guide plate 18 shown in FIG. 6 employs a configuration in which an optical element is disposed on the light exit surface 18a above the parallel groove 18f.

In FIG. 6, a plurality of lenticular lenses 34 are arranged, but other optical elements may be arranged. 7 to 9 show configuration examples of other light guide plates in which optical elements other than the lenticular lens are arranged. FIG. 7 shows a light guide plate in which a plurality of prism rows 36 are arranged in the approximate center of the light exit surface 18 a of the light guide plate 118 instead of the lenticular lens 34 shown in FIG. 6. 8A and 8B are a schematic plan view of a light guide plate in which a plurality of dimples 37 are formed at substantially the center of the light exit surface 18a of the light guide plate 118 instead of the lenticular lens 34 shown in FIG. It is a schematic sectional drawing. FIG. 9 is a schematic cross-sectional view of a light guide plate in which a plurality of hemispherical lenses 38 are formed at substantially the center of the light exit surface of the light guide plate instead of the lenticular lens 34 shown in FIG. In the present invention, the size and optical characteristics of these optical elements can be arbitrarily set according to the luminance unevenness generated on the light exit surface.
Thus, in the case of forming the protrusions on the light exit surface of the light guide plate, the Brightness unevenness generation area of the light exit surface of the light guide plate, a lenticular lens, prism row, dimples, pyramidal optical element, or hemisphere By arranging or forming various optical components such as a shaped optical element, luminance unevenness can be further suppressed.

  6 to 9 show a configuration in which optical elements are arranged at a constant density in a region where luminance unevenness occurs, the optical elements may be arranged with a distribution in the width direction of the light guide plate. For example, the number of optical elements may be increased or decreased in the width direction of the light guide plate in accordance with the occurrence position of luminance unevenness. Moreover, you may arrange | position a some optical element so that size may differ in the width direction of a light-guide plate. Also, different types of optical elements can be arranged.

  In the above example, a configuration in which an optical element such as a lenticular lens or a prism array is arranged in a predetermined region of the light exit surface of the light guide plate is shown. Light diffusibility may be imparted by surface roughening (rubbing surface) by polishing. Further, when such a rubbing surface is formed on the light exit surface, the surface roughness of the light exit surface may be distributed in the width direction of the light guide plate.

Further, in the present invention, a halftone dot pattern can also be formed in a portion where luminance unevenness is generated instead of arranging an optical element in a region where luminance unevenness occurs in the light guide plate, or making that region a sand-rubbed surface. As a method of forming the halftone dot pattern, for example, a sheet on which the halftone dot pattern is formed may be laminated on the light emitting surface, or the halftone dot pattern may be directly formed on the light emitting surface 18a of the light guide plate 18 by printing. Also good. An example of the halftone dot pattern is shown in FIG. FIG. 10 is a diagram schematically showing a halftone dot pattern when a halftone dot pattern is directly formed on the light exit surface 18a of the light guide plate 18 by printing. In the halftone dot pattern 92, as shown in FIG. 10, the density of halftone dots is high at a certain centerline X, and the density of halftone dots gradually increases from the centerline X toward both sides (perpendicular to the centerline). The halftone dot pattern is low. In this case, it is preferable to laminate the halftone sheet so that the center line X coincides with the position of the parallel groove in the width direction of the light guide plate 18. The shape of the halftone dots can be any shape such as a rectangle, a circle, or an ellipse, and the density of the halftone dots can be appropriately selected according to the intensity and spread of the bright line in the region where the luminance unevenness occurs. it can.
Thus, when a halftone dot pattern is formed immediately above the light exit surface of the light guide plate, the halftone dot plate on which the halftone dot pattern is formed is further supported by the convex portion. Furthermore, it is preferable to arrange on the light exit surface side of the light guide plate. Such a halftone dot plate is configured, for example, by forming a halftone dot pattern on at least one surface of a transparent acrylic plate having a predetermined rigidity.

FIG. 11 shows a configuration in which the halftone dot sheet 32 is arranged on the light exit surface 18a of the light guide plate 18 and the halftone dot plate 39 is supported by the convex portion 18p thereon. In FIG. 11, the convex portion 18p formed on the light exit surface 18a is an independent member that is not formed integrally with the light guide plate 18, and has a rectangular cross-sectional shape. As shown in FIG. 11, when adopting a configuration in which two halftone dot patterns are arranged on the optical path of the light emitted from the light exit surface 18 a of the light guide plate 18, the light guide plate 18 is closer to the light exit surface 18 a. The halftone dot pattern of the halftone dot sheet 32 to be arranged is a pattern for suppressing high-frequency luminance unevenness, and the halftone dot plate 39 arranged away from the light exit surface 18a by the height of the convex portion 18p. It is preferable to configure the halftone dot pattern with a pattern that suppresses low-frequency luminance unevenness. By comprising in this way, generation | occurrence | production of the brightness nonuniformity of illumination light can be suppressed effectively.
Here, the high-frequency luminance unevenness is, as described above, the distance between an arbitrary point x1 and the point x2 on the light exit surface of the light guide plate is dx (mm), and the luminance B1 (cd / m ² ) at the point x1. As the difference dB between the brightness B2 (cd / m ² ) and the brightness B2 (cd / m ² ) at the point x2, when the brightness unevenness is defined as dB / dx, the distance dx between the two points is 0.1 mm <dx <3 mm. It means a change in luminance such that dB / dx |> 5. On the other hand, low-frequency luminance unevenness means a change in luminance that satisfies | dB / dx | ≦ 5 when the distance dx between two points is 3 mm ≦ dx.

FIG. 12 shows the luminance distribution A when only the luminance distribution A on the light exit surface of the light guide plate and the halftone dot sheet 32 on which the halftone dot pattern that suppresses high-frequency luminance unevenness is formed on the light exit surface side of the light guide plate. As shown in FIG. 11, the distribution B and the halftone dot sheet 32 and the halftone dot plate 39 in which a halftone dot pattern for suppressing low frequency luminance unevenness is formed on the light exit surface 18a side of the light guide plate 18. An example of the luminance distribution C when arranged is shown. In FIG. 12, the vertical axis represents relative luminance, and the horizontal axis represents the distance from the origin in a direction (width direction of the light guide plate) orthogonal to the central axis of the light source. As shown in the luminance distribution A of FIG. 12, in the light guide plate having the shape shown in FIG. 11, the luminance of the light exit surface changes significantly in the width direction of the light guide plate. That is, high-frequency luminance unevenness defined by the above relational expression exists in a predetermined region on the light exit surface of the light guide plate. On the other hand, when the halftone dot sheet 32 on which the halftone dot pattern for suppressing high-frequency luminance unevenness is arranged on the light exit surface side of the light guide plate, the light guide plate as shown in the luminance distribution B of FIG. The change in luminance in the width direction is reduced, and the occurrence of high-frequency luminance unevenness is suppressed. However, in the luminance distribution B of FIG. 12, the luminance is slightly high near the origin (position of the light source), and the luminance gradually decreases in the direction toward the end of the light guide plate, and is low as defined by the above relational expression. It can be seen that the luminance unevenness of the frequency exists. This indicates that the luminance unevenness on the light emitting surface of the light guide plate includes low frequency luminance unevenness in addition to the high frequency luminance unevenness, and the halftone dot sheet 32 is provided on the light emitting surface of the light guide plate. Although the arrangement can suppress the occurrence of high-frequency luminance unevenness, the low-frequency luminance unevenness still remains. Such low-frequency luminance unevenness may be visually recognized when the planar lighting device is thinned.
Therefore, in the present invention, as shown in FIG. 11, a halftone dot sheet 32 is disposed on the light emission surface 18 a side of the light guide plate 18, and furthermore, low-frequency luminance unevenness on the light emission side of the halftone dot sheet 32. It is preferable to dispose a halftone dot plate 39 on which a halftone dot pattern is formed. By adopting such a configuration, as shown in the luminance distribution C of FIG. 12, it is possible to suppress the occurrence of low-frequency luminance unevenness, and to emit uniform light whose luminance hardly changes in the width direction of the light guide plate. Obtainable. As described above, in the present invention, the halftone dot sheet 32 on which the high-frequency luminance unevenness is formed and the halftone dot pattern that suppresses the low-frequency luminance unevenness are formed on the light exit surface side of the light guide plate. By arranging the halftone dot plate, not only high-frequency luminance unevenness but also low-frequency luminance unevenness can be suppressed, so that uniform illumination light with almost no luminance unevenness can be obtained. .
In the structure shown in FIG. 11, it is preferable to disperse the light further by disposing a diffusion sheet or the like on the surface of the halftone plate 39 on the light emitting side. Thereby, more uniform illumination light can be obtained.

  6 to 9 show a form in which the three light guide plates 18A, 18B, and 18C are integrally formed. However, the light guide plates are independently manufactured, and the end faces of the light guide plates are brought into close contact with each other and connected to each other. You can also. In this case, it is preferable to form a convex portion 18 p ′ as shown in FIG. 13 at the end portion of each light guide plate 18. In this case, the protrusions 18p 'may be provided at both ends in the width direction of the light guide plate, or may be provided only at one end. When providing a convex portion only on one end of the light guide plate, when the light guide plate block is configured by connecting the respective light guide plates, the end portion on the side where the convex portion of the light guide plate is provided, and the convex portion What is necessary is just to connect the edge part of the side which is not provided.

  In the light guide plate in which the convex portion is formed on the light exit surface as described above, the region other than the convex portion of the light exit surface is basically configured as a flat surface, but similarly to the light guide plate shown in FIG. A recess may be formed in the approximate center in the width direction of the light guide plate.

Next , the shape of the parallel grooves of the light guide plate will be described in detail.
In the light guide plate shown in FIG. 3, the cross-sectional shape of the parallel groove 18f is a home base shape in which the tip end portion is triangular and the base end portion is rectangular. However, the present invention is not limited to this. In order to effectively suppress the occurrence of luminance unevenness on the light exit surface, it is preferable that the tip portions intersect with each other and the slope of the base end portion connected to the tip portion is steeper than the tip portion. . That is, the cross-sectional shape of the parallel groove 18f is composed of a pair of contour lines whose intervals are narrowed toward the light exit surface 18a at the tip portion and intersect at the apex, and each contour line is perpendicular to the light exit surface 18a. As long as it has a portion where the inclination angle with respect to a straight line changes, the base end side (base end face 18i) of the parallel groove far from the apex has a sharper angle than the tip end side (tip end face 18h) close to the apex. . In other words, in the cross-sectional shape of the parallel groove 18f, the base end of the parallel groove farther from the vertex than the inclination angle (maximum inclination angle Φm) formed by the contour line on the tip side (tip surface 18h) close to the vertex and the light exit surface 18a. Any shape may be used as long as the inclination angle (inclination angle Φn) formed by the contour line on the side (base end face 18i) and the light exit surface 18a is larger. For example, as shown in FIG. 14 (a), the pair of tip surfaces 40 of the parallel grooves 18f have a hyperbolic shape, and as shown in FIG. 14 (b), the pair of tip surfaces 42 of the parallel grooves 18f have an elliptical shape. Can be. Alternatively, the cross-sectional shape of the pair of tip surfaces of the parallel grooves 18f of the light guide plate 18 may be a catenary line shape.

  Further, in the present invention, the cross-sectional shape of the parallel groove may be such that the apex of the parallel groove, that is, the deepest portion (the connection portion of the side wall forming the parallel groove) is a cusp. That is, two cross-sectional shapes of the pair of front end surfaces of the parallel grooves are symmetrical with respect to a center line perpendicular to the light exit surface of the light guide plate through the center of the parallel grooves, having one sharp intersection intersecting each other. It can be formed from a part of a curve or straight line. In the present invention, even if the cross-sectional shape of the parallel groove of the light guide plate is any of the above shapes, uniform light can be emitted from the light exit surface of the light guide plate.

  In FIG. 14 (c), the cross-sectional shape of the pair of front end surfaces 50 of the parallel grooves has a sharp point of intersection that intersects each other and passes through the center of the parallel grooves 18f and is perpendicular to the light exit surface of the light guide plate. An example in the case of consisting of a part of two curves symmetrical to a line is shown. The light guide plate 18 shown in FIG. 14 (c) has two symmetrical curves that form a pair of tip surfaces 50 with respect to a center line X passing through the center of the parallel groove 18f and perpendicular to the light exit surface 18a of the light guide plate 18. This is the case where 51a and 51b are arcs. In this case, as shown in FIG. 14C, the center position of the arc 51a corresponding to one side wall forming the parallel groove 18f is different from the center position of the arc 51b corresponding to the other side wall. Is done. Thereby, the part 52 where the arc-shaped side walls intersect each other has a sharp shape as shown in FIG.

  Further, in FIG. 14D, the cross-sectional shape of the pair of front end surfaces 53 of the parallel grooves is perpendicular to the light exit surface of the light guide plate through the center of the parallel grooves having one sharp intersection that intersects each other. Still another example in the case of consisting of a part of two curves symmetrical with respect to the center line is shown. The light guide plate 18 shown in FIG. 14 (d) has two symmetrical two end surfaces 53 that are paired with the center line X perpendicular to the light exit surface 18a of the light guide plate 18 through the center of the parallel groove 18f. The curves 54a and 54b are parabolic. In FIG. 14 (d), a pair of tip surfaces of the parallel groove 18f so that the focal point of the parabola 54a corresponding to one side wall of the parallel groove 18f is different from the focal point of the parabola 54b corresponding to the other side wall. 53 is formed.

  As shown in FIG. 14 (d), when the cross-sectional shape of the pair of tip surfaces 53 of the parallel groove 18f is formed by two curves 54a and 54b that intersect at the intersection 56, it is formed on one side wall of the parallel groove 18f. The angle θ between the tangent line at the intersection (point) 56 of the corresponding curve 54a and the tangent line at the intersection 56 of the curve 54b corresponding to the other side wall is preferably 90 degrees or less, and more preferably 60 degrees or less. .

FIG. 14D shows an example of a light guide plate in which the curved line forming the pair of front end surfaces of the parallel grooves is concave toward the center of the parallel grooves in the cross-sectional shape of the parallel grooves. FIGS. 15A and 15B show another example of the light guide plate. FIG. 15A is an example of a light guide plate in which the cross-sectional shape of the pair of front end surfaces 60 of the parallel grooves 18f is formed from two curves 61a and 61b that are convex toward the center of the parallel grooves 18f. 15 (b), the cross-sectional shape of the pair of front end surfaces 62 of the parallel grooves 18f is formed from a curve obtained by combining convex curves 64a and 64b and concave curves 66a and 66b toward the center of the parallel groove 18f. It is an example of a light-guide plate. The light guide plate having the parallel grooves having the cross-sectional shape as shown in FIGS. 15A and 15B can also emit light with sufficient luminance from the light exit surface while suppressing generation of bright lines.

  In FIG. 15B, in the cross-sectional shape of the parallel groove, the pair of base end surfaces of the parallel groove is a line segment perpendicular to the light emitting surface 18a in contact with the tip surface 62 and the parallel surface 18g. The cross-sectional shape of the parallel groove 18f is composed of a pair of contour lines whose intervals are narrowed toward the light exit surface 18a, and each contour line has an inclination angle with respect to a line perpendicular to the light exit surface. The shape may be any shape as long as the base end side (base end face) of the parallel groove far from the apex has a sharper angle than the front end side (tip end face) close to the apex. When the cross-sectional shape of the distal end surface of the prism is triangular, as shown in FIG. 16A, the cross-sectional shape of the pair of base end surfaces 70 of the parallel grooves is perpendicular to the light exit surface 18a and the center of the light source. A line segment having a predetermined angle of inclination with an angle formed with a line passing through the tip surface 18h that is an acute angle. It may be formed by the hypotenuse). Further, the cross-sectional shape of each base end face of the parallel groove is not limited to a straight line, and a curved line can also be used. As shown in FIG. 16B, the cross-sectional shape of the pair of base end faces 72 of the parallel groove 18f is parallel. It is good also as a concave curve toward the center of the groove | channel 18f. Here, as a curve, various curves used for a pair of front end surfaces of parallel grooves, such as a hyperbola shape, an ellipse shape, and a parabola shape, can be used.

  The shape of the parallel grooves is not limited to this, and may be various shapes such as a combination of the shapes of the pair of distal end surfaces and the pair of proximal end surfaces described above. In addition, the size of the pair of distal end surfaces and the pair of proximal end surfaces of the parallel grooves is sufficient if the light source can be disposed inside the parallel grooves, and the boundary position (contact position) between the pair of distal end surfaces and the pair of proximal end surfaces. Is not particularly limited.

  Here, a joint (connecting portion) between a pair of distal end surfaces and a pair of proximal end surfaces of the parallel grooves, a joint between the pair of proximal end surfaces and the parallel surfaces of the parallel grooves, and a joint between the parallel surfaces and the inclined surface, A smooth shape with a curvature R> 0.01 [mm] is preferable. By making the seam a smooth shape, irregular reflection of light at the seam can be prevented, and generation of bright lines and uneven brightness can be prevented.

Further, the surface of the light guide plate excluding the side surfaces (a pair of front end surfaces and a pair of base end surfaces) of the parallel grooves, for example, a plurality of predetermined edges whose ridges are parallel to the axis of the rod-shaped light source on the light emission surface and / or the inclined surface. It is preferable to form a very small prism. When a planar illumination device such as a backlight is formed by forming a large number of minute prisms having a predetermined shape on the surface of the light guide plate excluding the side surfaces of the parallel grooves (a pair of front end surfaces and a pair of base end surfaces). The prism sheet can be dispensed with, the light use efficiency as the planar illumination device can be improved, the device can be made compact, and the cost can be reduced. It is more preferable to form a large number of minute prisms having a predetermined shape on either the inclined surface or the light exit surface, but it is also preferable to form such prisms on both the inclined surface and the light exit surface. More preferred.
Here, the prism formed on the inclined surface preferably has an apex angle θ _p1 of 100 ° ≦ θ _p1 ≦ 140 °. The prism formed on the light exit surface more preferably has an apex angle θ _p2 of 40 ° ≦ θ _p2 ≦ 70 °.

  In the light guide plate shown in FIG. 3, a pair of parallel surfaces are provided between the pair of inclined surfaces and the pair of base end surfaces of the parallel grooves. However, in the present invention, the parallel surfaces are not necessarily provided. Alternatively, as shown in FIG. 17, a structure may be adopted in which the inclined surface 80 and the base end surface 18i of the parallel groove 18f are directly connected without providing a parallel surface.

Here, the luminance distribution of light emitted through the light exit plane is dependent largely on the shape of the distal end portion of the parallel groove of the light guide plate, designing the shape of the parallel groove of the light guide plate, so that the above-mentioned shape By simply doing this, the brightness on the light exit surface of the light guide plate can be optimally adjusted and made uniform.
As an example, when the cross-sectional shape of the parallel groove of the light guide plate is a hyperbola, the peak value of the relative luminance in the portion corresponding to the parallel groove is the average value of the relative luminance formed by the light emitted from the inclined back surface portion. It becomes 10 times or less, and the luminance from the light exit surface becomes substantially uniform. On the other hand, in a conventional light guide plate in which the cross-sectional shape of the parallel grooves is semicircular or parabolic, the relative luminance increases at the central portion of the parallel grooves, that is, the position immediately above the light source, and bright lines are generated. That is, in the conventional light guide plate having a semicircular or parabolic cross-sectional shape of the parallel grooves, the luminance on the light exit surface is not uniform.

Also, in a light guide plate with a parallel groove having a triangular cross-sectional shape, the relative brightness of the central portion is low. Therefore, by flattening the apex with a predetermined width or a curved surface with a relatively small radius of curvature, The brightness on the exit surface can be made uniform.
Here, when flattening the apex of the parallel groove with a predetermined width, the relative luminance in the portion corresponding to the parallel groove of the light guide plate changes according to the length of the flat portion. For this reason, in the present invention, the brightness can be increased by lengthening the flat end portion of the deepest part of the parallel groove, but if it is too long, there is a possibility that a bright line may be formed. The diameter is preferably 20% or less, more preferably 10% or less.

Further, on the surface of the light guide plate, the luminance and illuminance can be handled in substantially the same manner. In the present invention, it is presumed that there is a similar tendency in illuminance. Therefore, it is considered that the illuminance on the light exit surface of the light guide plate can be made uniform by designing the shape of the parallel grooves of the light guide plate to be the above-described shape.
In addition, the cross-sectional shape of the top part (deepest part) of the tip of the parallel groove is a chamfered flat or rounded circle at one sharp intersection so as to be symmetric with respect to the center line of the parallel groove Of course, not only the shape but also an elliptical shape, a parabolic shape, or a hyperbolic shape may be used. In addition to this, as described above, the peak value of illuminance or luminance may be reduced by using a top portion (deepest portion) of the tip of the parallel groove as a rubbing surface.

From the above, Oite the present onset bright, non-parallel groove 18f in the light exit plane 18a of the light guide plate 18, i.e. to the average value of luminance is formed in the portion (second portion) corresponding to the inclined surface 18 d, the light guide plate Depending on the ratio of the peak value (peak value of luminance) of the bright line formed in the portion corresponding to the parallel groove 18f (first portion) on the 18 light exit surfaces 18a, the tip shape of the parallel groove 18f of the light guide plate 18 Tapering is performed, that is, the degree of tapering of the tip shape of the parallel groove 18f of the light guide plate 18 can be controlled according to the value of this ratio. In this case, as in the case of the second embodiment to be described later, this ratio is preferably 3 or less, more preferably 2 or less.

  This ratio is the thickness of the backlight unit 2 (the distance between the light exit surface 18a of the light guide plate 18 and the diffusion sheet 14), the diffusion efficiency and the number of the diffusion sheets 14 used in the backlight unit 2, It is preferable to set according to the diffusion efficiency, the number of sheets used, etc. of the prism sheets 16, 17 and 19. That is, when the thickness of the backlight unit 2 (the distance between the light exit surface 18 a of the light guide plate 18 and the diffusion sheet 14) can be increased to a certain extent (or larger), or the diffusion sheet 14 used in the backlight unit 2. When the diffusion efficiency is high and the number of used sheets can be increased, or when the diffusion efficiency of the prism sheets 16, 17 and 19 is high and the number of used sheets can be increased, the illumination light emitted from the light exit surface 18a of the light guide plate 18 can be increased. Diffusion (mixing, etc.) can be performed sufficiently, so that the cost is high. However, the second light emission surface 18a of the light guide plate 18 with respect to the average value of the luminance of the second portion of the light output surface 18a of the light guide plate 18 can be obtained. The ratio of the luminance peak values of one portion can be set large to some extent. However, if this is not the case, the cost can be reduced, but the value of this ratio needs to be set small.

On the other hand, Oite this onset Ming, the peak value of the luminance of the first portion of the light exit plane 18a of the light guide plate 18, 3 times or less the average value of the brightness of the second portion of the light exit plane 18a of the light guide plate 18 More preferably, the tip of the parallel groove 18f of the light guide plate 18 is tapered so as to be twice or less. Here, the peak value of the luminance of the first portion of the light exit surface 18a of the light guide plate 18 is set to be not more than three times the average value of the brightness of the second portion of the light exit surface 18a of the light guide plate 18. This is because the luminance distribution of the illumination light emitted from the light exit surface 18a of the light guide plate 18 is made more uniform than before, and as a result, the diffusion of the illumination light emitted from the light exit surface 18a of the light guide plate 18 ( Mixing, etc.) does not need to be performed sufficiently, and a low-cost diffusion sheet 14 having a low diffusion efficiency can be used, the number of sheets used can be reduced, and expensive prism sheets 16, 17 and 19 can be used. This is because the use of the prism sheets 16, 17 and 19 with low diffusion efficiency can be used or the number of sheets used can be reduced.

In the present onset bright, in the cross-sectional shape of the parallel groove 18f of the light guide plate 18, the tip part for tapering of the parallel groove 18f is at an angle relative to the vertical line directed from the center of the rod-shaped light sources 12 to the light exit plane 18a, both sides It is preferable that the portion be within 90 degrees, and more preferably be a portion within 60 degrees. That is, in the present invention, in order to reduce the peak luminance value of the first portion corresponding to the parallel groove 18f of the light exit surface 18a of the light guide plate 18, the portion where the parallel groove 18f is tapered is the portion of the parallel groove 18f. The whole may be sufficient, but if the peak value can be reduced, a predetermined tip portion is sufficient.

  Further, according to the present invention, the shape of the parallel grooves of the light guide plate is made up of a pair of contour lines whose intervals are narrowed toward the light exit surface, and each contour line is perpendicular to the light exit surface. And the base end side (one pair of base end faces) of the parallel groove far from the apex is more acute than the tip end side (a pair of tip end faces) near the apex. By adopting such a shape, the luminance unevenness can be further reduced, and the emission efficiency can be improved. In other words, the cross-sectional shape of the parallel groove is a combination of curves having other inclination angles Φn (> Φm) with respect to the maximum inclination angle Φm of other hyperbola, parabola, and other curved segments. The uneven brightness can be reduced, and the emission efficiency can be improved.

Next, when the cross-sectional shape of the parallel groove of the light guide plate was changed to various shapes, the luminance distribution of light emitted from the light exit surface of the light guide plate was simulated and examined. In the following, in order to examine the luminance distribution of light emitted from the light exit surface of the light guide plate according to the cross-sectional shape of the parallel grooves of the light guide plate, the shape of the light exit surface of the light guide plate is a flat shape. .
First, the luminance distribution of light emitted from the light exit surface of the light guide plate 18 shown in FIG. Here, in the parallel groove 18f of the light guide plate 18 shown in FIG. 18A, the cross-sectional shape of the tip surface 18h is perpendicular to the light exit surface 18a and has a predetermined angle with respect to a line passing through the center of the light source 12. It is formed by a line segment having an inclination (the hypotenuse), and the cross-sectional shape of the base end surface 18i is formed by a line segment that is in contact with the tip surface 18h and the parallel surface 18g and is perpendicular to the light exit surface 18a, and the top portion has a curved surface shape. It is formed. Further, the parallel surface 18g is an intersection of a line obtained by extending the line segment of the front end surface 18h of the parallel groove 18 and a line parallel to the light emitting surface and passing through the lower end of the light guide plate, and a pair of base end surfaces of the parallel groove It is provided between the lower end of.
Here, the light guide plate 18 shown in FIG. 18A has a diameter of the light source 12 of 3 mm, an inclination angle of the tip surface 18h with respect to a line perpendicular to the light exit surface 18a and passing through the center of the light source 12, and 30 degrees. The top curved surface has a curvature R = 0.25 mm, and the joint between the distal end surface 18h and the base end surface 18i has a curvature R = 15 mm.
For reference, the luminance distribution of light emitted from the light exit surface 18a was also examined for the light guide plate 18 in which the cross-sectional shape of the parallel groove 18f shown in FIG. Here, in the light guide plate 18 shown in FIG. 18B, the side surface 74 of the parallel groove 18f, that is, the cross-sectional shape of the pair of distal end surfaces and the pair of proximal end surfaces is a shape formed by only the oblique sides. Except for this, it has the same shape as the light guide plate shown in FIG.

  FIG. 19A shows the luminance distribution on the light emitting side surface of the light guide plate shown in FIG. 18A and the light guide plate shown in FIG. In FIG. 19A, the vertical axis represents luminance, and the horizontal axis represents the distance from the center position of the light guide plate (the central portion of the parallel groove). Further, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18A is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 18B is indicated by a dotted line.

As can be seen from FIG. 19A, the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18A is the same as that on the light exit surface of the light guide plate shown in FIG. It is smaller than the difference between the maximum value and the minimum value of the luminance distribution. That is, the light guide plate shown in FIG. 18A can emit light with less uneven brightness than the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Further, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the light emission efficiency of the light guide plate having the shape shown in FIG. 18A is 65.9%, and the light guide plate having the shape shown in FIG. The emission efficiency of was 59.7%. Further, the incident efficiency of the light guide plate having the shape shown in FIG. 18A was 84.0%, and the incident efficiency of the light guide plate having the shape shown in FIG. 18B was 95.5%. As described above, the light guide plate shown in FIG. 18A can have higher emission efficiency and incidence efficiency than the light guide plate shown in FIG.

As another example of the light guide plate, a pair of base end surfaces 70 of parallel grooves as shown in FIG. 18C are half of the inclination of the front end surface 18h, that is, perpendicular to the light exit surface 18a. The light guide plate having the same shape as the light guide plate in FIG. 18A is emitted from the light exit surface except that it is a line segment (slanted side) having an inclination of 30 degrees with respect to a line passing through the center of the light source. The brightness distribution of the light was examined.
FIG. 19B shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 19B, the vertical axis indicates the luminance, and the horizontal axis indicates the distance from the center position of the light guide plate (the central portion of the parallel groove). Further, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18C is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 18B is indicated by a dotted line for comparison.

As can be seen from FIG. 19B, the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18C is the difference in the light exit surface of the light guide plate shown in FIG. It is smaller than the difference between the maximum value and the minimum value of the luminance distribution. That is, the light guide plate shown in FIG. 18C can emit light with less uneven brightness than the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the emission efficiency of the light guide plate having the shape shown in FIG. 18C was 61.9%. As described above, the light guide plate shown in FIG. 18C can have the emission efficiency higher than that of the light guide plate shown in FIG.

As still another example of the light guide plate, as shown in FIG. 18 (d), the connecting portion between the distal end surface 18h ′ and the base end surface 18i ′ of the parallel groove 18f is more than the light guide plate shown in FIG. 18 (a). The brightness distribution of light emitted from the light exit surface of the light guide plate having the same shape as that of the light guide plate in FIG.
FIG. 19C shows a luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 19C, the vertical axis indicates the luminance, and the horizontal axis indicates the distance from the center position of the light guide plate (the central portion of the parallel groove). In addition, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18D is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 18B is indicated by a dotted line for comparison.

As can be seen from FIG. 19 (c), the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18 (d) is the same as that on the light exit surface of the light guide plate shown in FIG. 18 (b). This is substantially the same as the difference between the maximum value and the minimum value of the luminance distribution. That is, the light guide plate shown in FIG. 18D can emit light with reduced luminance unevenness equivalent to the light guide plate shown in FIG.
Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the output efficiency of the light guide plate having the shape shown in FIG. 18D was 61.5%. Thus, the light guide plate shown in FIG. 18 (d) can have higher emission efficiency than the light guide plate shown in FIG. 18 (b).

As yet another example of the light guide plate, except that the cross-sectional shape of the pair of base end faces 72 of the parallel groove 18f shown in FIG. 18 (e) is a concave curve toward the center of the parallel groove 18f, The brightness distribution of the light emitted from the light exit surface was examined for the light guide plate having the same shape as the light guide plate in FIG.
FIG. 19D shows a luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 19D, the vertical axis represents luminance, and the horizontal axis represents the distance from the center position of the light guide plate (the central portion of the parallel groove). In addition, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18E is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 18B is indicated by a dotted line for comparison.

As can be seen from FIG. 19 (d), the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 18 (e) is the same as that on the light exit surface of the light guide plate shown in FIG. It is smaller than the difference between the maximum value and the minimum value of the luminance distribution. That is, the light guide plate shown in FIG. 18 (e) can emit light with less uneven brightness than the light guide plate shown in FIG. 18 (b). That is, the luminance on the light exit surface can be made more uniform.
Further, as a result of calculating the emission efficiency of the light guide plate from the measured luminance distribution, the emission efficiency of the light guide plate having the shape shown in FIG. 18E was 70.9%. Thus, the light guide plate shown in FIG. 18 (e) can have higher emission efficiency than the light guide plate shown in FIG. 18 (b).

  From the results shown in FIGS. 19A to 19D, the parallel grooves of the light guide plate are formed into the shapes shown in FIGS. 18A and 18C, so that the parallel grooves are obtained. It can be seen that the luminance unevenness equivalent to that in the case where the shape is a triangular shape that can reduce the luminance unevenness compared to the conventional shape, or the luminance unevenness can be further reduced, and the emission efficiency can be improved. Therefore, the occurrence of uneven brightness can be more effectively suppressed by forming such a parallel groove shape and forming a concave or convex portion on the light exit surface. Therefore, by selecting the shape of the parallel grooves that can reduce the luminance unevenness and improve the emission efficiency, and forming the concave portion or the convex portion on the light exit surface, the luminance unevenness is more effectively achieved. Can be suppressed.

Next, the base end face 18i of the parallel groove 18f shown in FIGS. 20 (a) to 20 (c) is directly connected to the inclined surface 80, and the light is emitted from the light exit surfaces of the light guide plates having various shapes without providing parallel faces. The brightness distribution of the light was investigated.
Here, the light guide plate shown in FIG. 20A is not provided with a parallel surface, except that the inclination angle of the inclined surface 80 is changed and the base end face 18i of the parallel groove 18f and the inclined surface 80 are directly connected. The shape is the same as that of the light guide plate shown in FIG. Also, the light guide plates shown in FIG. 20B and FIG. 20C also do not have a parallel surface, the inclination angle of the inclined surface 80 is changed, and the pair of proximal end surfaces 70 or 18i ′ of the parallel groove 18f and the inclined surface. Except for being directly connected to 80, it has the same shape as the light guide plate shown in FIGS. 18 (c) and 18 (d).

21 (a) to 21 (c) show the luminance distributions on the light exit side surfaces of the light guide plates shown in FIGS. 20 (a) to 20 (c), respectively. 21A to 21C, the vertical axis represents luminance, and the horizontal axis represents the distance from the center position of the light guide plate (the central portion of the parallel groove). 21 (a) to 21 (c) show the luminance distribution on the light exit surface of the light guide plate shown in FIGS. 20 (a) to 20 (c) with a solid line, and FIG. The luminance distribution on the light exit surface of the light guide plate having the shape shown in b) is indicated by a dotted line.
As shown in FIGS. 21 (a) to 21 (c), it can be seen that in any light guide plate, the luminance unevenness and the light guide plate shown in FIG. 18 (b) can be equal or more reduced. Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the emission efficiency of the light guide plate shown in FIG. 20A is 61.5%, and the emission efficiency of the light guide plate shown in FIG. The emission efficiency of the light guide plate shown in FIG. Thereby, it turns out that any light-guide plate can improve radiation | emission efficiency rather than the light-guide plate shown in FIG.18 (b).
As described above, from FIGS. 21A to 21C, the parallel grooves of the light guide plate are shaped as shown in FIG. It can be seen that the luminance unevenness equivalent to the triangular shape that can reduce the luminance unevenness or the luminance unevenness can be further reduced, and the emission efficiency can be improved. Therefore, by selecting the shape of the parallel grooves that can reduce the luminance unevenness and improve the emission efficiency, and forming the concave portion or the convex portion on the light exit surface, the luminance unevenness is more effectively achieved. Can be suppressed.

Next, the luminance distribution of the light emitted from the light exit surface of the light guide plate in which the cross-sectional shape of the pair of front end surfaces of the parallel grooves of the light guide plate shown in FIGS. 22 (a) to 22 (d) is a hyperbolic shape is examined. It was.
Here, the light guide plate 18 shown in FIG. 22A is the same as the light guide plate shown in FIG. 18A except that the cross-sectional shape of the pair of tip surfaces 40 of the parallel grooves 18f is a hyperbola. Shape. For comparison, the luminance distribution of light emitted from the light exit surface 18a was also examined for the light guide plate 18 in which the cross-sectional shape of the side surface 78 of the parallel groove 18f shown in FIG. . Here, the light guide plate shown in FIG. 22B is a figure except that one of the side surfaces 78 of the parallel grooves 18f, that is, the cross-sectional shapes of the front end surface and the base end surface are each formed by one hyperbola. The shape is the same as that of the light guide plate shown in FIG.

  FIG. 23 (a) shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. 22 (a) and the light guide plate shown in FIG. 22 (b). In FIG. 23A, the vertical axis represents luminance, and the horizontal axis represents the distance from the center position of the light guide plate (the central portion of the parallel groove). Further, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 22A is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 22B is indicated by a dotted line.

As can be seen from FIG. 23A, the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 22A is the same as that on the light exit surface of the light guide plate shown in FIG. It is smaller than the difference between the maximum value and the minimum value of the luminance distribution. That is, the light guide plate shown in FIG. 22A can emit light with reduced luminance unevenness more than that of the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the output efficiency of the light guide plate having the shape shown in FIG. 22A is 63.1%, and the light guide plate having the shape shown in FIG. The emission efficiency was 56.6%. As described above, the light guide plate shown in FIG. 22A can have higher emission efficiency than the light guide plate shown in FIG.

As another example of the light guide plate, the cross-sectional shape of the pair of base end faces 76 of the parallel grooves 18f as shown in FIG. 22C is a hyperbola having a half inclination of the hyperbola of the front end face 40. That is, it is the same as the light guide plate of FIG. 22A except that the angle formed by the line perpendicular to the light exit surface 18a and passing through the center of the light source is a hyperbola smaller than the hyperbola of the tip surface 40. The luminance distribution of light emitted from the light exit surface of the light guide plate having the shape was examined.
FIG. 23B shows a luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 23B, the vertical axis represents luminance, and the horizontal axis represents the distance from the center position of the light guide plate (the central portion of the parallel groove). Further, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 22C is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 22B is indicated by a dotted line for comparison.

As can be seen from FIG. 23 (b), the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 22 (c), and the light exit surface of the light guide plate shown in FIG. 22 (b). The difference between the maximum value and the minimum value of the luminance distribution is substantially the same. That is, the light guide plate shown in FIG. 22C can emit light with reduced luminance unevenness equivalent to the light guide plate shown in FIG.
Further, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the emission efficiency of the light guide plate having the shape shown in FIG. 22C was 59.1%. As described above, the light guide plate shown in FIG. 22C can have higher emission efficiency than the light guide plate shown in FIG.

As still another example of the light guide plate, as shown in FIG. 22 (d), the cross-sectional shape of a pair of base end faces of the parallel grooves is a concave curve toward the center of the parallel grooves. The light intensity distribution of the light emitted from the light exit surface of the light guide plate having the same shape as the light guide plate 22 (a) was examined.
FIG. 23C shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 23C, the vertical axis indicates the luminance, and the horizontal axis indicates the distance from the center position of the light guide plate (the central portion of the parallel groove). In addition, the luminance distribution on the light exit surface of the light guide plate shown in FIG. 22D is indicated by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 22B is indicated by a dotted line for comparison.

As can be seen from FIG. 23 (c), the difference between the maximum value and the minimum value of the luminance distribution on the light exit surface of the light guide plate shown in FIG. 22 (d) is the difference in the light exit surface of the light guide plate shown in FIG. 22 (b). It is smaller than the difference between the maximum value and the minimum value of the luminance distribution. That is, the light guide plate shown in FIG. 22 (d) can emit light with less uneven brightness than the light guide plate shown in FIG. 22 (b). That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the light emission efficiency of the light guide plate from the measured luminance distribution, the light emission efficiency of the light guide plate having the shape shown in FIG. 22D was 67.8%. In this way, the light guide plate shown in FIG. 22D can have higher emission efficiency than the light guide plate shown in FIG.
As described above, according to FIGS. 23A to 23C, the parallel grooves of the light guide plate are shaped as shown in FIGS. 22A, 22C, or 22D, so that the parallel grooves are shaped. It can be seen that the luminance unevenness equivalent to the case of the hyperbolic shape that can reduce the luminance unevenness compared to the conventional case, or the luminance unevenness can be further reduced, and the emission efficiency can be improved. Therefore, by selecting the shape of the parallel grooves that can reduce the luminance unevenness and improve the emission efficiency, and forming the concave portion or the convex portion on the light exit surface, the luminance unevenness is more effectively achieved. Can be suppressed.

Next, as shown in FIGS. 24A and 24B, a pair of base end faces and inclined surfaces of the parallel grooves are directly connected to each other, and are emitted from the light exit surfaces of the light guide plates having various shapes without providing parallel surfaces. The brightness distribution of the light was investigated.
Here, the light guide plate shown in FIG. 24A does not have a parallel surface, except that the inclined angle of the inclined surface is changed and the pair of base end surfaces of the parallel groove and the inclined surface are directly connected to each other. The shape is the same as that of the light guide plate shown in FIG. In addition, the light guide plate shown in FIG. 24 (b) also does not provide a parallel surface, except that the inclined angle of the inclined surface is changed and the pair of base end surfaces of the parallel groove and the inclined surface are directly connected, respectively. The shape is the same as that of the light guide plate shown in FIG.

FIGS. 25A and 25B show luminance distributions on the light exit side surfaces of the light guide plate shown in FIGS. 24A and 24B, respectively. In FIGS. 25A and 25B, the vertical axis indicates the luminance, and the horizontal axis indicates the distance from the center position of the light guide plate (the central portion of the parallel groove). 25 (a) and 25 (b) show the luminance distribution on the light exit surface of the light guide plate shown in FIGS. 24 (a) and 24 (b) with a solid line, and FIG. 22 (b) shows for comparison. The luminance distribution on the light exit surface of the shaped light guide plate is indicated by a dotted line.
It can be seen that in any light guide plate shown in FIGS. 25A and 25B, the luminance unevenness and the light guide plate shown in FIG. Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the emission efficiency of the light guide plate shown in FIG. 24A is 63.9%, and the emission efficiency of the light guide plate shown in FIG. Was 58.9%. Thereby, it turns out that any light-guide plate can improve an output efficiency rather than the light-guide plate shown in FIG.22 (b).
As described above, from FIGS. 25A and 25B, the parallel grooves of the light guide plate are shaped as shown in FIG. It can be seen that the luminance unevenness equivalent to that of a hyperbolic shape that can be made, or the luminance unevenness can be further reduced, and the emission efficiency can be improved. Therefore, by selecting the shape of the parallel grooves that can reduce the luminance unevenness and improve the emission efficiency, and forming the concave portion or the convex portion on the light exit surface, the luminance unevenness is more effectively achieved. Can be suppressed.

  As described above, the shape of the parallel groove of the light guide plate is made up of a pair of contour lines whose intervals are narrowed toward the light exit surface and intersect at the vertices, and each contour line corresponds to a line perpendicular to the light exit surface. It has a part where the angle of inclination changes, and the base end side (a pair of base end surfaces) of the parallel groove far from the apex has a sharper angle than the front end side (a pair of front end surfaces) near the apex. Thus, more uniform light can be emitted, and the emission efficiency can be increased.

Further, even when a halftone dot pattern is arranged on the light exit surface, the dynamic range of the halftone dot density can be narrowed, and the halftone dot pattern can be designed more easily. Accordingly, ink having various transmittances can be used as the ink used for forming the halftone dot pattern, and the selection range of the ink material for halftone dots can be widened, that is, the transmittance range depending on the ink type. Can be widened.
Moreover, since the luminance adjustment control range of the halftone dot can be narrowed, the transmittance of the halftone dot film itself can be improved. That is, since the uniform light can be emitted from the light emitting surface, the range of brightness to be adjusted can be narrowed. That is, the arrangement density of halftone dots can be reduced, and the transmittance of the halftone dot pattern can be increased. As a result, even when a halftone dot pattern is arranged, it is possible to emit more uniform light while suppressing a reduction in luminance of light emitted from the light emitting surface, that is, maintaining high luminance.

  Further, by providing a plane (parallel plane) parallel to the light exit plane between the parallel groove and the inclined plane, the emission efficiency can be further increased. Here, the size of the parallel surface is not particularly limited, and an intersection of a line obtained by extending a cross-sectional line of a pair of tip surfaces of the parallel groove and a line passing through the lower end of the light guide plate and parallel to the light exit surface, It is preferable to provide between the lower ends of the pair of base end faces of the parallel grooves.

Having described in detail the planar lighting device and a liquid crystal display device of the present invention, the present invention is limited to the upper Kitai like is not the sole, without departing from the scope and spirit of the present invention, and that various improvements and modifications Of course.

For example, in the present invention, when a large-sized light guide plate is configured by arranging a plurality of light guide plates 18 so that all the light exit surfaces 18a of the light guide plate 18 form the same plane, as shown in FIG. In addition, a tangential line at the contact point between the inclined surface 18d of one light guide plate 18 and the inclined surface 18d 'of the other light guide plate 18' connected thereto is not crossed, that is, a smooth flat surface at the connecting portion of the inclined surfaces. Alternatively, the inclination angle of the inclined surface 18d of the light guide plate 18 can be adjusted so that a curved surface is formed. In the light guide plate shown in FIG. 26, the surfaces formed by the inclined surfaces 18d and 18d ′ of the light guide plates 18 and 18 ′ are formed in an arch shape.
By using such a light guide plate having a large light emitting surface, a backlight unit having a large light emitting surface can be obtained, and therefore, it can be applied to a liquid crystal display device having a large display screen. In particular, the present invention can be applied to a wall-mounted liquid crystal display device such as a wall-mounted television.
Here, when a plurality of light guide plates 18 are configured in parallel, the shape and angle of the inclined surface are not emitted by one block, but are emitted for several blocks and emitted from the light emitting surface. It is preferable that the luminance distribution be uniform.
As described above, the light incident on the adjacent light guide plate is also emitted from the light exit surface, so that more uniform light can be emitted and the emission efficiency can be improved.

Coupled as one unit light guide plate as described above to form a large-size light guide plate is arranged separately molded light guide plate such thin portions are in contact with or be formed by joining In order to improve the uniformity of the emitted light, it is preferable to integrally form the two or more light guide plates in a connected shape.
From the viewpoint of manufacturing efficiency, it is preferable to integrally form a number of light guide plate units necessary for forming a light guide plate corresponding to a required screen size.

Further , in the light guide plate, the reflecting plate 24 may be arranged on the side surface of the light guide plate 18 as shown in FIG. In the case where a plurality of light guide plates 18 are arranged, as shown in FIG. 27B, the reflection plate 24 may be arranged on the side surface of the light guide plate 18 arranged on the outermost side. By disposing such a reflecting plate 24 on the side surface, leakage of light from the side surface of the light guide plate 24 can be prevented, and light utilization efficiency can be further enhanced. The reflection plate 24 can be formed using the same material as the above-described reflection sheet and reflector.

In the embodiment shown in FIGS. 1 to 3, the prism sheet is disposed on the light exit surface side of the light guide plate and / or between the inclined surface of the light guide plate and the reflection sheet, but the present invention is not limited to this. First, a prism whose groove is parallel to the axis of the rod-shaped light source directly on the surface of the light guide plate excluding the side surfaces (a pair of front end surfaces and a pair of base end surfaces) of the parallel grooves, for example, the light exit surface and / or the inclined surface. It may be engraved.
For example, the prism 25 may be directly formed on the inclined surface 18d of the light guide plate 18 as shown in FIGS. 28A and 28B, and the prism 26 is formed on the light exit surface 18a of the light guide plate 18 as shown in FIG. The prism 25 may be formed on the inclined surface 18d.
As described above, by forming the prism on the surface of the light guide plate excluding the side surfaces (a pair of front end surfaces and a pair of base end surfaces) of the parallel grooves, the same effect as in the case of arranging the prism sheet can be obtained. . Furthermore, since there is no need to provide a prism sheet, the arrangement of the sheet makes it possible to eliminate light attenuation (decrease in luminance) caused by the formed gap, and the light use efficiency as a planar illumination device, that is, light The emission efficiency can be made higher than when a prism sheet is arranged. Furthermore, since it is not necessary to provide a prism sheet, the apparatus can be further downsized (thinned).
In the present embodiment, the interval is narrowed toward the light exit surface, and is configured by a pair of contour lines that intersect at the apex, and each contour line is a portion where the inclination angle with respect to a line perpendicular to the light exit surface changes. The light guide plate having a shape in which the base end side (a pair of base end surfaces) of the parallel groove far from the apex has a sharper angle than the front end side (a pair of front end surfaces) close to the apex is used. For example, in the case of using a light guide plate having a parallel groove having a shape that narrows toward a tip portion that faces a light exit surface, such as a triangle or a hyperbola, the side surfaces of the parallel grooves (a pair of tip surfaces and one pair of tip surfaces) By forming a prism on the surface of the light guide plate excluding the pair of base end faces, the same effect as described above can be obtained.

Here, the prism formed on the inclined surface preferably has an apex angle θ _p1 of 100 ° ≦ θ _p1 ≦ 140 °. The prism formed on the light exit surface preferably has an apex angle θ _p2 of 40 ° ≦ θ _p2 ≦ 70 °. By setting the apex angle θ _p1 and apex angle θ _p2 of the prism to be formed within the above ranges, the emission efficiency as the planar illumination device can be more suitably improved.

2 Backlight unit 4 Liquid crystal display panel 6 Drive unit 10 Liquid crystal display device 12 Light source 14 Diffusion sheet 16, 17, 19 Prism sheet 18 Light guide plate 18a, 52 Light exit surface 18b Thick portion 18c Thin end portion 18d Inclined surface 18e, 80 Inclined back surface portion 18f Parallel groove 18g Parallel surfaces 18h, 18h ', 40 One pair of tip surfaces 18i, 18i', 70, 72, 76 One pair of base end surfaces 20 Reflector 22 Reflective sheet 24 Reflector 25, 26 Prism 54a, 54b Arc curve 56 Intersection point 64a, 64b Parabola 72a, 72b, 82a, 82b, 84a, 84b Curve 74, 78 Side surface 92 Halftone dot pattern

Claims (11)

A light emitting surface having a rectangular outer shape and having a recess formed substantially parallel to one side thereof; a thick wall portion substantially parallel to the one side and positioned at a substantially central portion of the rectangular light emitting surface; A pair of thin-walled end portions formed substantially parallel to the portion, and substantially at the center of the thick-walled portion, on the opposite side of the rectangular light emitting surface, and substantially parallel to the one side, and accommodates a rod-shaped light source. parallel grooves for the wall thickness becomes thin toward each of the thin end portions on both sides of the pair of thick portions in the orthogonal direction substantially orthogonal to the one side, respectively a pair on both sides of the parallel groove and inclined rear portions of the pair forming the inclined rear planes of the transparent light guide plate to have a,
A rod-shaped light source housed in the parallel groove of the light guide plate;
A reflector provided behind the bar light source so as to close the parallel grooves;
A reflective sheet attached to the inclined back surface of the inclined back surface on both sides of the thick portion of the light guide plate;
A diffusion sheet disposed on the rectangular light exit surface of the light guide plate;
A halftone dot sheet laminated on the rectangular light exit surface of the light guide plate;
A halftone dot plate arranged in parallel with the halftone dot sheet at a predetermined interval, and
In order to effectively suppress the occurrence of luminance unevenness of the illumination light, the halftone dot pattern of the halftone sheet is configured with a pattern for suppressing high-frequency luminance unevenness, and the halftone dot pattern of the halftone dot plate, A planar illumination device comprising a pattern that suppresses low-frequency luminance unevenness . The parallel groove, in the cross-sectional shape in the orthogonal direction, is configured with a pair of contour lines that are narrowed toward the rectangular light exit surface and intersect at the apex,
Each contour line of the parallel groove in the cross-sectional shape in the orthogonal direction has a portion in which an inclination angle with respect to a line perpendicular to the rectangular light exit surface changes, and is farther from the vertex than the tip side near the vertex. 2. The planar lighting device according to claim 1, wherein the base end side of the parallel groove has an acute angle. The pair of inclined back surface portions are symmetric with respect to a plane that includes an axis of the rod-shaped light source and is perpendicular to the rectangular light exit surface;
A pair of contour lines of the parallel grooves in the cross-sectional shape in the orthogonal direction is symmetric with respect to a plane that includes the center of the parallel grooves and is perpendicular to the rectangular light exit surface;
The front end portion of the parallel groove is spaced from the center line perpendicular to the rectangular light exit surface of the parallel groove toward the rectangular light exit surface in the cross-sectional shape of the parallel groove in the orthogonal direction. The planar illumination device according to claim 1 or 2, wherein becomes narrower symmetrically. The luminance peak value formed in the portion corresponding to the parallel groove on the rectangular light emitting surface is not more than three times the average value of the luminance formed in the portion corresponding to the inclined back surface on the rectangular light emitting surface. The planar illumination device according to any one of claims 1 to 3, wherein the tip shape of the parallel groove in the cross-sectional shape in the orthogonal direction is tapered. The parallel grooves are formed by a pair of distal end surfaces constituting a distal end portion and a pair of proximal end surfaces constituting a proximal end portion in the cross-sectional shape in the orthogonal direction,
The pair of tip surfaces are formed as line segments that are perpendicular to the rectangular light exit surface and have a predetermined angle with respect to a line passing through the center of the rod-shaped light source, and the tops are formed in a curved shape. ,
The pair of base end surfaces are formed by a line segment perpendicular to the rectangular light exit surface or a concave curve toward the center of the parallel groove,
Further, an intersection of a line obtained by extending a line segment of the pair of distal end surfaces, a line parallel to the rectangular light exit surface and passing through the lower end of the light guide plate, and a lower end of the pair of proximal end surfaces The planar illumination device according to any one of claims 1 to 4 , wherein a parallel plane is provided therebetween . The parallel grooves are formed by a pair of distal end surfaces constituting a distal end portion and a pair of proximal end surfaces constituting a proximal end portion in the cross-sectional shape in the orthogonal direction,
The pair of tip surfaces is formed by a hyperbola,
The pair of base end surfaces are formed by a line segment perpendicular to the rectangular light exit surface or a concave curve toward the center of the parallel groove,
Further, between the intersection of a line obtained by extending the hyperbola of the pair of distal end surfaces, a line parallel to the rectangular light exit surface and passing through the lower end of the light guide plate, and the lower end of the pair of proximal end surfaces a spread illuminating apparatus according to any one of claims 1 to 4, parallel surfaces is provided. The parallel grooves are formed by a pair of distal end surfaces constituting a distal end portion and a pair of proximal end surfaces constituting a proximal end portion in the cross-sectional shape in the orthogonal direction,
The pair of tip surfaces is formed by a hyperbola,
The planar illumination device according to any one of claims 1 to 4 , wherein the pair of base end surfaces are formed by line segments perpendicular to the rectangular light exit surface. The light guide plate as a light guide plate blocks, made of a plurality of light guide plate blocks, any of claims 1 to 7, wherein the thin end face of each of the light guide plate blocks is characterized in that it is connected to each other one The surface illumination device according to item . The said recessed part is formed in the brightness | luminance unevenness generation | occurrence | production area | region of the said rectangular light emission surface, The said rectangular light emission surface consists of the curved surface which forms the said recessed part, and two planes located in the both sides. The planar illumination device according to claim 8.   The planar lighting device according to claim 9, wherein the halftone dot sheet has flexibility and is disposed in close contact with the curved surface forming the rectangular light emission surface of the light guide plate and the two planes. A surface illumination device according to any one of claims 1 to 10 ,
A liquid crystal display panel disposed on the light exit surface side of the planar illumination device;
And a drive unit for driving the liquid crystal display panel.

Images