JP2007059164A - Light guide plate, and planar lighting system and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate that is small in thickness and weight, high in light utilization efficiency (light emission efficiency) from the light-emitting surface, and capable of emitting further uniform and high-luminance illumination light small in irregularities. <P>SOLUTION: This transparent light guide plate includes the rectangular light-emitting surface; a thick part nearly parallel with its one side and located nearly at the center part of the rectangular light-emitting surface; a pair of thin ends formed nearly in parallel with the thick part; a parallel groove formed at the center of the thick part and nearly in parallel with the one side thereof on the side opposite to the rectangular light emitting surface for housing a rod-like light source; and a pair of tilting back face part reduced in thickness as going toward the pair of respective thin ends on both sides, in a direction nearly perpendicular to the one side from the thick part and respectively forming a pair of tilted back faces on both sides of the parallel groove. The light guide plate has a diffusion part for making the light entered in at least a part facing the parallel groove diffuse on the light-emitting surface side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

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 amount distribution uniform in this method, in principle, the liquid crystal panel needs to have 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 above-described direct type backlight unit, when the thickness is made 10 mm or less, unevenness in the amount of light occurs, so the thickness is reduced. There were limits.
Here, as a backlight unit that can be thinned, there is a so-called tandem type in which a plurality of units each having a light guide plate arranged on the side surface of an illumination light source are arranged (see, for example, Patent Document 2). In this conventional method, the backlight unit can be made thin by making light incident from the side surface of the light guide plate. However, since this conventional method has lower light use efficiency than a direct backlight unit, high power is required to emit high-luminance light.
In view of this, light guide plates having various shapes have been proposed in order to realize thinning, low power consumption, and large size of the liquid crystal display device (Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, and Patent). Reference 7).

FIG. 33 is a schematic cross-sectional view of a surface light source device having a light guide plate 100 disclosed in Patent Document 3. As shown in FIG.
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 while 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. 34, a 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 Since 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. 2 is slight, the effect of improving the luminance 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.
Further, 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 section, 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 low in cost and low in power consumption. Although the device 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 first problem of the present invention is to solve the above-mentioned problems of the prior art, is thin and lightweight, has high light utilization efficiency (light emission efficiency) from the light emission surface, is more uniform and has less unevenness, and An object of the present invention is to provide a light guide plate capable of emitting illumination light with higher brightness.
Another object of the present invention is to provide a light guide plate that can have a larger light exit surface in addition to the first problem.

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. A planar illumination device that can emit illumination light with higher brightness, can be used as a large-sized illumination surface, or can be applied as a backlight to a liquid crystal display device such as a wall-mounted television. It is to provide.
The third problem of the present invention is to solve the above-mentioned problems of the prior art, and is thin and light, 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.

  In order to solve the first problem described above, a first form of the first aspect of the present invention is a rectangular light exit surface, and is substantially parallel to one side of the rectangular light exit surface and located at a substantially central portion of the rectangular light exit surface. A thick portion, a pair of thin end portions formed substantially parallel to the thick portion, and a substantially center of the thick portion, on the opposite side to the rectangular light exit surface, and substantially parallel to the one side. And a parallel groove for accommodating the rod-shaped light source, and the thickness decreases from the thick portion toward each of the pair of thin end portions on both sides in a direction substantially perpendicular to the one side. A transparent light guide plate having a pair of inclined back surface portions that form a pair of inclined back surfaces on both sides of the groove, respectively, and the light incident on at least a portion facing the parallel groove on the light emitting surface side It is an object of the present invention to provide a light guide plate having a diffusing portion for diffusing.

Here, it is preferable that the diffusion portion is disposed on the entire surface of the light exit surface.
Moreover, it is preferable that the said spreading | diffusion part is a shape from which the thickness of the direction perpendicular | vertical to the said light emission surface differs according to the position on the said light emission surface.
Furthermore, the adjustment amount of the thickness in the direction perpendicular to the light exit surface with respect to the reference thickness tx at an arbitrary position x on the light exit surface of the diffuser is dt (x), and the diffuser has the reference thickness tx. When the intensity of light emitted from the arbitrary position x of the light guide plate is Ip (x), the target light intensity is I (target_ave), and a constant determined according to the material of the diffusion portion is A. The thickness T (x) of the diffusion part at any position x preferably satisfies the following formula.
I (target_ave) / Ip (x) = Exp (−A · dt (x))
T (x) = t (x) + dt (x)
Here, A is preferably a constant determined based on the scattering cross section and particle density of the particles mixed in the diffusion portion.

Furthermore, it is preferable to have a polarization separation part on the light exit surface side.
Furthermore, it is preferable to have a prism portion on the light exit surface side.

  Here, in the cross-sectional shape in the orthogonal direction, the parallel groove is composed of a pair of contour lines whose intervals are narrowed toward the rectangular light exit surface and intersect at the apex, and the cross-sectional shape in the orthogonal direction Each of the contour lines of the parallel grooves has a portion in which an inclination angle with respect to a line perpendicular to the rectangular light exit surface changes, and the base end side of the parallel grooves farther from the apex side than the apex side close to the apex It is preferable to configure so as to have an acute angle.

That is, the light guide plate of the present invention is a bridge-type light guide plate in which the cross-sectional shape of the parallel groove serving as the light incident portion is combined with a curve having a cross section with a larger inclination with respect to the slope of the curve near the top. Thus, the cross section of the lower part of the light incident part is formed by a line segment having the same angle as the angle of the taper part.
Here, in the cross-sectional shape of the parallel groove serving as the light incident portion of the light guide plate, it is preferable that an intermediate portion of the joint portion between the tapered portion and the parallel groove serving as the light incident portion is parallel to the light emitting surface.

  Here, in the cross-sectional shape of the parallel groove in the orthogonal direction, the tip portion of the parallel groove is a rod-shaped light source housed in the parallel groove in a first portion corresponding to the parallel groove of the rectangular light emitting surface. Depending on the ratio of the peak value of illuminance or luminance formed by the emitted light to the average value of illuminance or luminance formed by the emitted light in the second portion corresponding to the pair of inclined back surface portions. It is preferable to be configured by a pair of contour lines whose intervals become narrower toward the shaped light exit surface.

  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 center line perpendicular to the rectangular light exit surface of the parallel groove, and the tip of the parallel groove has the parallel groove in the cross-sectional shape in the orthogonal direction. It is preferable that the distance between the central light line and the center line perpendicular to the rectangular light exit surface is symmetrically narrowed toward the rectangular light exit surface.

In addition, the pair of contour lines at the tip portions of the parallel grooves has a peak value of illuminance (relative illuminance) or luminance (relative luminance) of the first portion of the rectangular light exit surface. It is preferable that the interval be narrow so that the average value of (relative illuminance) or luminance (relative luminance) is three times or less.
The peak value of illuminance (relative illuminance) or luminance (relative luminance) of the first portion of the rectangular light exit surface is an average value of illuminance (relative illuminance) or luminance (relative luminance) of the second portion. It is preferably 2 times or less.

Moreover, it is preferable that the pair of inclined back surface portions each have a portion parallel to the rectangular light exit surface in the vicinity of the parallel groove.
Preferably, a plurality of minute prisms are formed on at least one of the rectangular light exit surface and the pair of inclined back surface portions.

Further, it is preferable that a plurality of minute prisms are formed on the pair of inclined back surface portions.
Here, it is preferable that the prisms formed on the pair of inclined back surface portions have different shapes depending on positions in the orthogonal direction.
Moreover, it is preferable that the prisms formed on the pair of inclined rear surface portions have an asymmetric shape with respect to a surface perpendicular to the bottom surface and passing through the apex.
Moreover, it is preferable that the prism formed in the pair of inclined back surface portions has an asymmetric shape with respect to a plane that passes through the apexes and is perpendicular to the inclined back surface portion when there is no prism.
The prisms formed on the pair of inclined back surface portions are perpendicular to the line connecting the contact points with adjacent prisms in the cross-sectional shape in the orthogonal direction, and are asymmetrical with respect to the line passing through the apex. It is preferable to have a different shape.
Further, the prism formed on the pair of inclined back surface portions has a length of a contour line connecting the vertex and the end portion on the parallel groove side in the cross-sectional shape in the orthogonal direction, and the vertex and the thin end portion side. It is preferable to have a shape in which the length of the contour line connecting the end portions of the two is different.

Moreover, it is preferable that the prism formed in the pair of inclined back surface portions has an apex angle of 70 degrees or more and 140 degrees or less.
In addition, the prism formed on the pair of inclined back surface portions has an angle formed by a surface perpendicular to the bottom surface and passing through the apex thereof and the surface on the parallel groove side is not less than 0 degrees and not more than 70 degrees. The angle formed between the surface perpendicular to the bottom surface and passing through the apex thereof and the surface on the thin end portion side is preferably 45 degrees or more and 70 degrees or less.
In addition, the prism formed on the pair of inclined rear surface portions has an angle formed by a surface perpendicular to the bottom surface and passing through the apex thereof and the surface on the parallel groove side is not less than 30 degrees and not more than 70 degrees. More preferably.
Moreover, it is preferable that the prism formed in the pair of inclined back surface portions has a base length of 0.1 mm or less in the orthogonal direction.

Moreover, in the cross-sectional shape of the parallel groove, the tip portion is preferably a portion where an angle formed by the pair of contour lines is within 90 degrees.
Moreover, in the cross-sectional shape of the parallel groove, the tip portion is preferably a portion where an angle formed by the pair of contour lines is within 60 degrees.

Further, it is preferable that at least a pair of contour lines of at least the tip portion of the parallel groove is composed of two straight lines or a part of a curve that is symmetrical with respect to the center line and has one sharp intersection intersecting each other.
In addition, it is preferable that the two curved lines serving as a pair of contour lines of at least the tip portion of the parallel groove are convex or concave toward the center of the parallel groove.
In addition, it is preferable that the two curves having a cross-sectional shape of at least the tip portion of the parallel groove can be approximated by a tenth-order function and are convex or concave toward the center of the parallel groove.
In addition, a pair of contour lines of at least the tip portion of the parallel groove, or the two curves serving as a pair of contour lines of the parallel groove are convex or concave toward the center of the parallel groove. , Ellipse, parabola, or part of a hyperbola.

Moreover, it is preferable that the cross-sectional shape of at least the tip portion of the parallel groove or the cross-sectional shape of the parallel groove is a triangle.
Moreover, it is preferable that the cross-sectional shape of the top part of the tip portion of the parallel groove is a shape connected with a straight line or a curve symmetrical with respect to the center line before the two symmetrical straight lines or curves intersect. .

It is preferable that the cross-sectional shape of the top portion of the tip portion of the parallel groove is a shape having a portion parallel to the rectangular light exit surface in which one sharp intersection is chamfered.
The cross-sectional shape of at least the tip portion of the parallel groove or the cross-sectional shape of the parallel groove is a triangle, and the cross-sectional shape of the top portion of the tip portion of the parallel groove is symmetric with respect to the center line. A trapezoidal shape is preferable.
Moreover, it is preferable that the cross-sectional shape of the top portion of the tip portion of the parallel groove is a curved shape that is convex or concave with respect to the rectangular light exit surface and symmetrical with respect to the center line.

Further, the cross-sectional shape of the top portion of the tip portion of the parallel groove is a circular shape, an elliptical shape, a parabolic shape, or a hyperbolic shape in which one sharp intersection is rounded symmetrically with respect to the center line. Is preferred.
Moreover, it is preferable that at least one pair of contour lines of the tip portion of the parallel groove is an oval or a part of a hyperbola.
Moreover, it is preferable that the said top part of the said front-end | tip part of the said parallel groove | channel is a sand-slipping surface.
Moreover, it is preferable to have a halftone dot in the part corresponding to the top part of the front-end | tip part of the said parallel groove of the said rectangular light emission surface.

In order to solve other problems in addition to the first problem, the second mode of the first aspect of the present invention is that the light guide plate of the first mode is used as one light guide plate block. The present invention provides a light guide plate comprising a plurality of light guide plate blocks, the thin end surfaces of which are connected to each other.
Here, it is preferable that the inclined back surfaces of the thin end surfaces of the two light guide plate blocks connected to each other have portions that are gently inclined with respect to each other at the connecting portions.

  In order to solve the second problem, the second aspect of the present invention includes a light guide plate according to any one of the first aspect, a rod-shaped light source housed in the parallel groove of the light guide plate, A reflector provided behind the rod-shaped light source so as to close the parallel groove, and a reflection 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 planar illumination device is provided.

Here, the second aspect of the present invention is the above planar illumination device, and preferably further includes a diffusion sheet disposed on the rectangular light exit surface of the light guide plate.
In addition, the ratio of the relative illuminance or relative luminance peak value of the first part of the rectangular light exit surface of the light guide plate to the average value of the relative illuminance or relative luminance of the second part is the ratio of the light guide plate It is preferable to set according to the space allowed between the rectangular light exit surface and the diffusion sheet or the thickness allowed for the planar lighting device.

  In order to solve the third problem, a third aspect of the present invention includes a backlight unit including the planar illumination device according to any one of the second aspects, and a light emission surface of the backlight unit. The present invention provides a liquid crystal display device comprising a liquid crystal display panel arranged on the side, and a drive unit for driving the backlight unit and the liquid crystal display panel.

Since the light guide plate according to the first aspect of the present invention has a diffusion portion at least in a portion facing the parallel groove on the light exit surface side, light incident on the light guide plate can be suitably diffused, and uneven brightness is reduced. Can be made. In addition, by providing the light guide plate with a diffusing portion, it is possible to increase the light utilization efficiency as compared with the case where the light guide plate and the diffusion sheet are provided as separate members. Furthermore, even if the light guide plate is made thinner than the prior art by providing a diffusion portion, the occurrence of uneven brightness can be suppressed. Therefore, the light guide plate of the present invention can be reduced in thickness and weight, and the light emission surface has high light utilization efficiency (light emission efficiency), more uniform, less unevenness, and high brightness illumination light. Can be emitted.
Furthermore, by adopting a configuration having a polarization separation section and / or a prism section, it is possible to further reduce luminance unevenness and increase the light utilization efficiency. Moreover, it can also prevent that each member mutually shifts by setting a light-guide plate as a structure which has a spreading | diffusion part, a polarization separation part, and / or a prism part. As a result, it is possible to suitably reduce luminance unevenness.

  Further, according to the second aspect of the present invention, by using the light guide plate of the first aspect, it is thin and lightweight, can be manufactured at a lower cost, has high light utilization efficiency, and more Uniform, non-uniform, and brighter illumination light can be emitted, the illumination surface can be made large, or can be applied to liquid crystal display devices such as wall-mounted televisions A lighting device can be provided.

  Moreover, according to the 3rd aspect of this invention, by using the planar illuminating device of the said 2nd aspect, it is thin and lightweight, 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.

  Hereinafter, the light guide plate of the present invention, a planar illumination device using the same, and a liquid crystal display device will be described in detail on the basis of preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view of a planar illumination device 2 (hereinafter also referred to as a backlight unit) according to a second aspect of the present invention in which a plurality of light guide plates 18 according to the first aspect of the present invention 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 third 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 FIGS. 2A and 2B, the backlight unit 2 basically includes a light source 12, a diffusion sheet 14, a prism sheet 16, a light guide plate 18, a reflector 20, and a reflection sheet. 22.

  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.

The light source 12 is a rod-shaped cold cathode tube having a small diameter, and is used for illuminating the liquid crystal display panel 4. The light source 12 is disposed in a parallel groove 18 f formed in the light guide plate 18 and is connected to the drive unit 6. 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 light source such as a normal fluorescent tube, a cold cathode tube, a hot cathode tube, an external electrode tube, a light emitting diode (LED), or a semiconductor laser can be used. Or a light emitting diode is preferable.
Further, instead of the light source 12, an LED light source in which a cylindrical or prismatic transparent light guide having a length equivalent to the parallel groove 18f of the light guide plate 18 is used and LEDs are 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.

In FIG. 2, a 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 (polypropylene), PC (polycarbonate). ), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, other acrylic resin, or a flat member made of optically transparent resin such as COP (cycloolefin polymer) It is formed. 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 a pigment such as silica, titanium oxide or zinc oxide that scatters light on the surface, or the above-mentioned pigment that coats beads such as resin, glass or zirconia together with a binder, or scatters 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.

The prism sheet 16 is a transparent sheet formed by arranging a plurality of prisms in parallel. The prism sheet 16 can improve the concentration of light emitted from the light exit surface 18a of the light guide plate 18 and improve the luminance. . The prism sheet 16 is arranged so that the extending direction of the prism row is parallel to the parallel groove 18 f of the light guide plate 18. The prism sheet 16 is arranged so that the apex angle of the prism faces the diffusion sheet 14 (the liquid crystal display panel 4).
Further, in addition to the prism sheet 16, a prism sheet in which the prism rows extend may be arranged so that the extending direction of the prism rows is perpendicular to the parallel grooves 18 f of the light guide plate 18. Here, when arranging two prism sheets, the arrangement order is such that a prism sheet 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. A prism sheet 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. 3A, 3B and 3C, a prism 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 to provide the sheet 19. FIG. 3A 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. FIG. 3C is a schematic plan view of the prism sheet 19 disposed between the inclined surface 18d of the light guide plate 18 as viewed from the light guide plate side, and FIG. 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 sheet 16 is more preferably used, but the prism sheet 19 is of course unnecessary if the luminance on the light exit surface 18a of the light guide plate 18 is made more uniform. There is no need to use the prism sheet 16. 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.

  In FIG. 2, the reflection sheet 22 is for reflecting light leaking from the back surface (lower surface in the drawing) of the light guide plate 18 and making it incident on the light guide plate 18 again, and can improve the light use efficiency. it can. The reflection sheet 22 is formed so as to cover the lower surface (inclined surface) 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 back surface (the lower surface in the drawing) of the light guide plate 18, for example, PET, PP (polypropylene), or the like. Resin sheet with increased reflectivity by forming voids by kneading and stretching filler, transparent or white resin sheet surface as described above, with a mirror surface formed by aluminum vapor deposition, metal foil such as aluminum or the like It can be formed of a resin sheet carrying a metal foil 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.

Moreover, you may affix a reflection sheet directly on the part except the parallel groove | channel of the surface of the side facing the light-projection surface of a light-guide plate, for example, an inclined surface. Moreover, it is not limited to sticking a reflective sheet directly to a light guide plate, You may apply | coat the coating material which has a function equivalent to a reflective sheet directly to a light guide plate.
In this way, by directly attaching the reflective sheet or directly applying the paint, it is possible to improve the emission efficiency, and it is possible to prevent uneven brightness due to an attachment error of the reflective sheet.

In FIG. 2B, the light guide plate 18 includes a rectangular light exit surface 18a, a thick portion 18b parallel to one side thereof, and a pair of sides formed on both sides of the thick portion 18b in parallel to the one side. A pair of inclined back surface portions 18e that form a sloping surface 18d, with a thickness decreasing toward the thin end portions 18c on both sides in a direction perpendicular to the one side from the thick wall portion 18b, The part 18b has a parallel groove 18f for accommodating the light source 12 formed parallel to the one side.
That is, the light guide plate 18 is a flat plate having a rectangular outer shape, and one surface is flat to form the light emission surface 18a, and the other surface is on both sides from the thick portion 18b. A pair of inclined surfaces 18d are formed so as to be inclined with respect to one surface so that the plate thickness becomes thinner toward one side. Here, the inclined surface 18d is formed as a flat surface, but may be a curved surface.
Further, in the light guide plate 18 of the present embodiment, 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 use 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. 2, of 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 angle of the inclined surface 18d so that the light beam effectively reaches the light exit surface 18a at a right angle and in a parallel direction (depth direction). (Taper) is limited. That is, the angle (taper) of the inclined surface 18d is set such that a part of the light beam emitted from the light source 12 and incident on the light guide plate 18 is totally reflected by the light emitting surface 18a (back surface).

  In FIG. 2, 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 grooves 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.

The light guide plate 18 having such a shape includes a transparent portion 21 and a diffusion portion 23 provided in a predetermined region of the transparent portion 21 on the light emission surface 18a side. That is, the parallel grooves 18 f and the inclined back surface portion 18 of the light guide plate 18 are formed by the transparent portion 21, and the light exit surface 18 of the light guide plate 18 is formed by the diffusion portion 23. That is, the transparent portion 21 has a structure in which the diffusion portion 23 is laminated on the light exit surface 18a side.
The light guide plate 18 composed of the transparent portion 21 and the diffusing portion 23 is formed by, for example, a method of molding a heated raw material resin by extrusion molding or injection molding, and a casting weight that is molded by polymerizing monomers, oligomers, and the like in a mold. It can be manufactured using legal methods.
Alternatively, the transparent portion 21 and the diffusing portion 23 may be separately manufactured and bonded by an adhesive having a refractive index equal to that of the transparent portion 21 and the diffusing portion 23.

  Examples of the transparent portion 21 include acrylic resins such as PMMA (polymethyl methacrylate), PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, and others. Acrylic resin or transparent resin such as COP (cycloolefin polymer) can be used.

In the diffusing part 23, fine particles for scattering light, for example, pigments such as silica, titanium oxide or zinc oxide, or beads such as resin, glass or zirconia are mixed in the transparent resin used for the transparent part 21. Alternatively, a kneaded material can be used. In addition, as the fine particles to be mixed into the transparent resin, isotropic fine particles and anisotropic fine particles can be suitably used.
By making the diffusing portion 23 have a configuration in which fine particles are mixed in a transparent resin, incident light can be diffused, and the emission efficiency of light from the light exit surface 18a can be further increased. Moreover, by providing the light guide plate 18 with the diffusing portion 23, the light emitted from the transparent portion can enter the diffusing portion without passing through the air layer, and the light can be diffused. Thereby, the utilization efficiency of light can be made higher.

The diffusing section 23 of the present embodiment is provided so that the thickness in the direction perpendicular to the light exit surface varies depending on the position on the light exit surface. By changing the thickness of the diffusing unit 23 according to the position, specifically, by changing the thickness according to the intensity (luminance) of the light incident on the diffusing unit 23, the light emitted from the light exit surface The luminance unevenness can be further reduced. In addition, since the light-guide plate of this invention is a structure which unites a diffusion part and a transparent part, the thickness of a transparent part also changes according to the change of the thickness of a diffusion part. That is, the light guide plate of the present embodiment has a shape in which the boundary surface between the diffusion portion and the transparent portion is changed according to the position.
The relationship between the thickness of the diffusion portion and the reduction in luminance unevenness will be described in detail later.

Here, in this embodiment, although the thickness of the diffusion part was changed according to the position, the present invention is not limited to this, and the diffusion part may have a uniform thickness, for example.
FIG. 4A is a schematic cross-sectional view showing an example of a light guide plate in which a diffusing portion having a uniform thickness is provided on the entire light emission surface. A halftone dot, which will be described later, is formed directly on the surface of the light guide plate by printing.
From the point that luminance unevenness can be suitably reduced, it is preferable to use a diffusion portion having a distribution in thickness as shown in FIG. 2, but as shown in FIG. 4A, the diffusion portion 23a having a uniform thickness is replaced with a transparent portion 21a. Even if it is set as the structure provided in this light-projection surface, the utilization efficiency of light can be made high by providing the diffusion part 23a in the light-guide plate 18. FIG. Specifically, a backlight unit using a light guide plate provided with a diffusion portion having a uniform thickness is 1 in comparison with a backlight unit in which a light guide plate, a diffusion film (diffusion plate), and a prism sheet are laminated as separate members. Can output 1x light quantity. That is, in the backlight unit in which each part is laminated as a separate member, when 16 cold cathode fluorescent lamps (CCFL) are used to illuminate a 32-inch screen, by using the backlight unit 220, Fifteen CCFLs can achieve the same brightness. By improving the light utilization efficiency in this way, the number of necessary parts can be reduced, and it can be manufactured at a lower price.

In each of the above embodiments, the diffusing portion is provided in the entire area of the light emitting surface. However, the present invention is not limited to this, and the diffusing portion may be provided in a part of the light emitting surface.
FIGS. 4B and 4C are schematic cross-sectional views showing examples of the light guide plate in which a diffusion portion is provided only on a part of the light exit surface of the light guide plate.

FIG. 4B shows a flat plate shape in which the boundary line between the transparent portion 21b and the diffusing portion 23b is a straight line at the portion directly above the parallel groove 18f of the light guide plate 18, that is, the portion facing the parallel groove 18f of the light exit surface 18a. This is a case where the diffusion portion 23b is provided.
Here, in the light guide plate as in the present embodiment, light having higher luminance than the other portions is emitted from the portion directly above the parallel groove 18f. Therefore, as shown in FIG. 4B, by providing the diffusion portion 23b directly above the parallel groove 18f, the light incident on the parallel groove 18f is diffused, and the bright line directly above the parallel groove is suppressed. can do. Furthermore, the light beam component that has passed through the portion directly above the parallel groove and caused the luminance unevenness can be divided into line segments in the total reflection direction so that the light can reach a position farther from the light source. As a result, luminance unevenness can be reduced.

In the light guide plate shown in FIG. 4B, the diffusing portion has a flat plate shape in which the boundary line between the transparent portion and the diffusing portion in the cross-sectional shape of the light guide plate is a straight line, but the present invention is not limited to this.
FIG. 4C shows a flat plate shape in which the boundary line between the transparent portion 21c and the diffusing portion 23c is curved at a portion immediately above the parallel groove 18f of the light guide plate 18, that is, a portion facing the parallel groove 18f of the light exit surface 18a. This is a case where the diffusion portion 23c is provided.
Further, the boundary line between the transparent part and the diffusing part can be a curved line, for example, an arc, a hyperbola, a parabola, etc., and the boundary line between the transparent part and the diffusing part is a corrugated, straight line and curved line. Various shapes such as composite shapes can be used.

  Next, an example of the thickness distribution of the diffusion part of the light guide plate that can suitably reduce the luminance unevenness will be described together with a method for determining the thickness distribution.

Next, the attenuation factor (transmittance) of the material used as the diffusion part is measured.
Here, the attenuation rate is a numerical value that can be adjusted in accordance with the material used for the diffusion part and the thickness of the diffusion part. The predetermined thickness is t, the optical characteristic value of the material used for the diffusion part is A, and the incident light intensity. If I is I and the transmitted light intensity is I0, the relationship between the values can be expressed by the following equation (1).
I / I0 = Exp (−A · t) Formula (1)
Here, the optical property value A of the material used for the diffusion part is a constant determined according to the scattering cross section Φ, particle density Np and coefficient K of the particles dispersed in the diffusion part, and A = K · Φ · Np.
The optical characteristic value A can be calculated by making light incident on a diffusion portion having a constant thickness t, measuring the incident light intensity I and the emitted light intensity I0, and substituting the measurement results into the above equation.
Here, since the measured value in the case of the thickness t = 2 is I / I0 = 0.35, A = 0.52 in the diffusing portion used in this example.
Therefore, the attenuation factor of the diffusion unit used in the present embodiment can be expressed as the following formula (2).
I / I0 = Exp (−0.52 · t) Equation (2)

  As shown in the above equation (2), the attenuation factor can be adjusted by changing the thickness t of the diffusion portion. That is, by changing the thickness t according to the incident light intensity I, light having a uniform emitted light intensity I0 can be emitted from the entire light exit surface.

A more specific example of the method for determining the thickness distribution of the diffusion portion is shown below.
First, as shown in FIG. 5 (a), the light emitted from the light emission surface of the backlight unit in which the prism sheet is arranged on the surface of the light guide plate provided with the diffusion portion having a uniform thickness on the entire surface of the light emission surface. Luminance distribution, that is, transmitted light intensity Ip (x) is measured.
Here, in the light guide plate 18 shown in FIG. 5, the thickness of the diffusion portion is 2 mm, and the thickness of the thickest portion of the transparent portion is 5.5 mm. The distance from the center of the light guide plate 18 to the surface where the thickness of the light guide plate 18 is the thinnest, that is, the joint surface with the adjacent light guide plate 18 was 15 mm. The width of the end of the parallel groove 18f opposite to the light exit surface 18a was 7.5 mm, and the shape of the parallel groove was a hyperbolic shape.
Further, a prism sheet 16 is provided on the light exit surface side of the light guide plate 18, a light source 12 is provided on the parallel groove 12 of the light guide plate 18, a reflection plate 22 is provided on the inclined surface 18d side of the light guide plate 18, and a parallel groove 18f is provided. The reflector 20 was arrange | positioned so that it might block.
In the present embodiment, the transparent portion and the diffusing portion of the light guide plate are bonded together by using an adhesive having a refractive index substantially equal to that of the transparent portion and the diffusing portion.

Next, the target transmitted light intensity I (target_ave) is determined, the measured transmitted light intensity Ip (x), the thickness tx of the diffusion portion at an arbitrary position at the time of measurement, and the target transmitted light intensity I (target_ave) Based on the above, the light guide plate thickness adjustment amount dt (x) necessary for setting the transmitted light intensity Ip (x) at each position on the light exit surface to the target transmitted light intensity I (target_ave) is calculated. .
By substituting I (target_ave) for I0 in the above equation (2) and Ip (x) for I, as shown in the following equation (3), the adjustment amount dt of the thickness of the diffusion portion is calculated.
Ip (x) / I (target_ave) = Exp (−0.52 · dt (x)) Equation (3)
The thickness t of the diffuser plate whose transmitted light intensity is measured is adjusted according to the adjustment amount dt calculated by the above equation (3). That is, the thickness T (x) of the diffusion portion at an arbitrary position x is set to t (x) + dt (x).
FIG. 6 shows the thickness distribution of the diffusion portion calculated and adjusted using the above equation (3), that is, the calculated T (x) at an arbitrary position. In FIG. 6, the vertical axis indicates the thickness of the diffusion portion, and the horizontal axis indicates the distance from the center position of the light guide plate (the central portion of the parallel groove).
As shown in FIG. 6, the diffusion portion of the present embodiment has a thin center at the light guide plate (a portion directly above the light source), and becomes thicker as the distance from the center of the light guide plate increases. The shape is as follows.
Next, the luminance distribution of the light emitted from the light exit surface of the light guide plate having the diffusion portion produced so as to have the thickness distribution shown in FIG. 6 was measured. Here, the measurement of the luminance distribution was performed under the same conditions as the measurement of the luminance distribution of the light guide plate shown in FIG. 5 except that the thickness of the diffusion portion of the light guide plate was different.

FIG. 7 shows the measurement results. In FIG. 7, the vertical axis represents relative luminance, and the horizontal axis represents the distance (mm) from the center position of the light guide plate (the central portion of the parallel groove). Here, the luminance distribution of light emitted from the light exit surface of the light guide plate in which the shape of the diffusion portion shown in FIG. 6 has a distribution in thickness is shown by a solid line, and for comparison, FIG. The luminance distribution of the light emitted from the light exit surface of the light guide plate having a shape having the diffusion portion having the uniform thickness shown is indicated by a dotted line.
As shown in FIG. 7, the luminance unevenness of the light emitted from the light exit surface of the light guide plate having the diffusion portion having no thickness distribution was 14%. On the other hand, the luminance unevenness of the light emitted from the light exit surface of the light guide plate having a thickness distribution in the diffusion portion was 15%.

Further, the luminance distribution of the light guide plate having the diffusion part having the thickness distribution shown in FIG. 6, that is, the transmitted light intensity is set to Ip (x), and the target transmitted light intensity I (target_ave) is determined, and the above formula (3) And the thickness adjustment amount dt (x) at an arbitrary position x is calculated.
Based on the calculated thickness adjustment amount dtx, the thickness of the diffusion portion having a distribution in the thickness shown in FIG. 6 is adjusted. That is, the thickness of the diffusion part is adjusted twice using the above formula (3).
FIG. 8 shows the thickness Tx distribution of the diffusing portion of the adjusted light guide plate. In FIG. 8, the vertical axis indicates the thickness (mm) of the diffusion portion, and the horizontal axis indicates the distance (mm) from the center of the light guide plate. Here, the thickness distribution of the diffusing portion that has been adjusted twice is indicated by a solid line, and for comparison, is based on the luminance distribution of light emitted from the light guide plate having the diffusing portion having the uniform thickness described above. The thickness distribution of the diffusion part whose thickness has been adjusted, that is, the diffusion part whose thickness has been adjusted once is indicated by a dotted line.

The brightness distribution of the light emitted from the light exit surface of the light guide plate having the diffusing portion where the thickness was adjusted twice was measured. The luminance distribution was measured under the same conditions as the above measurement except that the thickness of the diffusion part of the light guide plate was different.
FIG. 9 shows the measurement results. In FIG. 9, the vertical axis represents relative luminance, and the horizontal axis represents the distance (mm) from the center position of the light guide plate (the central portion of the parallel groove). Here, in FIG. 9, the luminance distribution of the light emitted from the light exit surface of the light guide plate having the diffusing portion that has been subjected to the thickness adjustment twice is shown by a solid line, and for comparison, the thickness of the thickness shown in FIG. Luminance distribution of light emitted from the light exit surface of the light guide plate having a diffusing portion having no distribution is indicated by a dotted line, and the light emitted from the light exit surface of the light guide plate having the diffusing portion subjected to thickness adjustment once. The luminance distribution is indicated by a one-dot chain line.
As shown in FIG. 9, the luminance unevenness of the light emitted from the light exit surface of the light guide plate having the diffusing portion where the thickness was adjusted twice was 12%.
In this way, the unevenness of luminance is reduced without increasing the thickness of the diffusing portion by making the diffusing portion of the light guide plate a diffusing portion in which the thickness is adjusted twice using the above formula (3). Can do. As described above, according to the present invention, it is possible to realize a light guide plate with reduced luminance unevenness and reduced thickness.

Next, the entire thickness of the diffusion portion is made thicker, and the thickness adjustment amount dt is the same as that when the thickness is adjusted once, that is, the thickness distribution shown in FIG. The luminance distribution was measured for the light guide plate having a diffusion portion uniformly thickened by 2 mm. The luminance distribution was measured under the same conditions as the above measurement except that the thickness of the diffusion part of the light guide plate was different.
The measurement results are shown in FIG. In FIG. 10, the vertical axis represents relative luminance, and the horizontal axis represents the distance (mm) from the center position of the light guide plate (the central portion of the parallel groove).
Here, in FIG. 10, the luminance distribution of light emitted from the light exit surface of the light guide plate having the diffusion portion in which the thickness distribution shown in FIG. 6 is further uniformly increased by 2 mm is indicated by a solid line, and for comparison, FIG. The luminance distribution of light emitted from the light exit surface of the light guide plate having a diffusion portion (t = 2) having no distribution in the thickness shown in FIG. The luminance distribution of light emitted from the light exit surface of the light plate is indicated by a one-dot chain line. In addition, the luminance distribution of light emitted from the light exit surface of the light guide plate having a diffusion portion having a thickness t = 4 and no thickness distribution is indicated by a two-dot chain line.

As shown in FIG. 10, the luminance unevenness of the light emitted from the light exit surface of the light guide plate having the diffusion portion in which the thickness of the diffusion portion is uniformly increased by 2 mm was 6%. Further, the luminance unevenness of the light emitted from the light exit surface of the light guide plate having a diffusion portion having a thickness t = 4 and no thickness distribution was 9%.
By increasing the thickness of the diffusion portion in this way, it is possible to further reduce luminance unevenness. In addition, even when the diffusion layer is thickened, luminance unevenness can be reduced by forming the diffusion portion in a shape having a distribution in thickness.

Here, as described above, the light attenuation rate by the diffusing portion is determined by the optical property value A of the material used for the diffusing portion (the scattering cross section Φ and particle density Np of the particles dispersed in the diffusing portion) and the thickness of the diffusing portion. It can be adjusted by t.
Therefore, in the above embodiment, the thickness of the diffusing portion is uniformly increased. However, the same effect can be obtained by increasing the optical characteristic value A of the material used for the diffusing portion, that is, the particle scattering cross section Φ and the particle density Np. Can be obtained.
Furthermore, by increasing the optical characteristic value A of the material used for the diffusion part, it is possible to suitably reduce the uneven brightness even when the diffusion part has a smaller thickness adjustment amount and a thinner overall thickness. it can.
Here, the particle density Np is preferably Np> 4% wt.
By making the particle density Np larger than 4% wt, the attenuation rate can be made a certain level or more, and uneven brightness can be suitably suppressed.

Next, another configuration example of the light guide plate according to the present invention and a backlight unit using the light guide plate will be described with reference to the drawings.
As described above, in FIG. 2, the light guide plate in which the transparent portion and the diffusion portion are integrally formed is shown as the light guide plate of the present invention. However, in the present invention, as shown in FIG. The light guide plate 202 may be configured to have the prism portion 208 on the 18a side.
Here, the backlight unit 200 shown in FIG. 11 includes a light guide plate 202, a light source 12, a reflector 20, a reflection plate 22, and a diffusion film 14. The light source 12 is disposed in the parallel groove 18 f of the light guide plate 302, the reflector 20 and the reflection plate 22 are disposed on the inclined surface 18 d side of the light guide plate 202, and the diffusion film 14 is disposed on the light exit surface 18 a side of the light guide plate 202. This is the same as the backlight unit 2 of FIG. 2 described above.

The light guide plate 202 shown in FIG. 11 includes a transparent portion 204 on the inclined back surface 18d side, a diffusion portion 206 laminated on the light emission surface 18a side of the transparent portion 204, and a light emission surface 18a of the transparent portion 204 and the diffusion portion 206. And a prism portion 208 stacked on the side.
Thus, by using the configuration in which the diffusing unit 206 and the prism unit 208 are integrated, light utilization efficiency can be further improved. As an example, the backlight unit 200 using the light guide plate 202 outputs a light amount 1.3 times that of the backlight unit in which the light guide plate, the diffusion film (diffusion plate), and the prism sheet are laminated as separate members. be able to. That is, in the backlight unit in which each part is laminated as a separate member, when 16 cold cathode fluorescent lamps (CCFL) are used to illuminate a 32-inch screen, by using the backlight unit 200, The same brightness can be achieved with 12 CCFLs. By improving the light utilization efficiency in this way, the number of necessary parts can be reduced, and it can be manufactured at a lower price.
Here, the prism portion formed on the light exit surface preferably has an apex angle θ _p2 of 40 ° ≦ θ _p2 ≦ 70 °.

  In the backlight unit shown in FIG. 11, the diffusion film is disposed on the light exit surface side of the light guide plate. However, the present invention is not limited to this, and the light guide plate 18 may be replaced with or in addition to the diffusion film 14. In order to improve the luminance of the light emitted from the polarizing plate, a polarization separation film (luminance improving film) may be disposed.

  As the polarization separation film, a reflective polarizing film, a cholestic polarizing film, a scattering polarizing film, or the like can be used.

As the reflective polarizing sheet, for example, as described in JP-A-6-331824, the refractive index higher than the refractive index of the light guide plate on the light exit surface of the light guide plate for at least one polarization plane. A birefringent material having a refractive index lower than the average refractive index of the light guide plate can be used for the plane of polarization perpendicular to the plane of polarization.
Moreover, a stretched film as described in JP-A-11-281975 can also be used. Here, when using a stretched film, as described in JP-A-11-281975, it is preferable that the stretched film is attached to one side of the light guide plate via an adhesive layer or an adhesive layer.
Moreover, as described in JP-A-7-49496, a multilayer structure in which transparent media having a relatively high refractive index and transparent media having a relatively low refractive index are alternately laminated, In addition, at least one dielectric film having a thickness of preferably 1000 nm or less is formed on at least one surface of the planar transparent support, or a plurality of types of transparent types having different refractive indexes What laminated | stacked the polymer can also be used.
Further, as described in JP-A-7-72475, a transparent support having a substantially W-shaped cross section is provided with at least one dielectric thin film having a thickness equal to or less than a visible light wavelength, and a predetermined thickness. It is also possible to use a polarization separator that transmits the p-polarized component and reflects at least a part of the s-polarized component with respect to the light rays in the vicinity of the incident direction.
And a structured surface consisting of a linear array of essentially right-angled isosceles prisms arranged side by side as described in Japanese Patent Application Laid-Open No. 2004-78234. A first material having a plane of perpendicular modulus forming an angle of approximately 45 ° with respect to the tangent to the opposite smooth surface, a second material essentially the same as the first material, and at least one Comprising at least one optical deposit of alternating layers of high and low refractive index materials of a selected optical thickness on a structured plane of the material, the first and second Are all optically bonded to form a single unit in which the refractive index of the first and second materials and the refractive index and optical of the multiple layers of the optical deposit The thickness is a selective counter-current of polarized light. In the interior of the part of the optical stack, the mixed polarized incident light is separated into an s-polarized component and a p-polarized component, and the s-polarized component is , Reflected by other parts of the optical deposit and reflected parallel to the incident light in that part, but proceeding in the opposite direction to the incident light, the p-polarized component is parallel to the incident light. A retroreflective polarizer that transmits light can also be used.
Further, as described in JP-A-61-262705, a polarizing filter function and a phase difference are formed on a transparent material in which A-shaped ridges and V-shaped grooves are alternately provided to form a triangular waveform surface. A polarizing element provided with a dielectric multilayer film having a plate function can also be used.
In addition, a polarizing film as described in US Pat. No. 3,610,729 can be used by continuously laminating a material having birefringence into a layer having a thickness of ¼ of various wavelengths. it can.
Further, as described in US Pat. No. 5,867,316, an optical film formed of a polymer having a continuous phase having birefringence and a small amount of a dispersed phase inside the continuous phase can also be used.
Further, a polarization separation film having a structure in which a metal thin film using surface plasmon is sandwiched with a low refractive index transparent medium as described in JP-A-2003-295183 can also be used.
Furthermore, in addition to the arrangement of the polarization separation film using surface plasmons that transmit only the P-polarized light component parallel to the incident surface and reflect the S-polarized light component perpendicular to the incident surface, the polarization direction of the light is changed, for example, orthogonal By forming a polarization direction changing film such as a λ / 4 phase film or a diffusion film having a slight birefringence that causes a difference of λ / 4 in the optical thickness between the polarization components with the light guide plate. , The luminance can be further improved.

As the scattering type polarizing film, for example, an anisotropic scatterer formed by stretching a composite of a liquid crystal and a polymer as described in JP-A-8-76114 can be used.
Also, a haze anisotropic layer having a different haze value depending on the vibration direction of linearly polarized light as described in JP-A-2001-343612 can be used. In this case, it is further preferable to attach a first retardation plate to the surface opposite to the light exit surface of the light guide plate, and to install a second retardation plate between the light guide plate and the reflection plate.
Further, as described in JP-A-9-274108, minute regions made of different materials are uniformly dispersed in a transparent polymer film, and the polymer film and the minute regions are orthogonal to each other. Polarization elements having substantially the same refractive index for one of the linearly polarized light and different refractive indexes for the other of the linearly polarized light can be used.

  As the cholesteric polarizing film, for example, as described in JP-A-6-281814, the molecular helix is oriented so that the axis of the molecular helix extends across the film, and the pitch of the molecular helix in the film is Films that have been varied so that the difference between the maximum and minimum pitch is at least 100 nm can be used.

In the above embodiment, a configuration using a brightness enhancement film having a polarization separation function has been described. However, the present invention is not limited to this, and is described in JP-A-2001-201746 and JP-A-2001-228474. In addition, the luminance of light emitted from the light exit surface can also be improved by forming a fine uneven portion having a polarization separation function on the light exit surface of the light guide plate.
Further, as described in JP-A-9-134607, the first refractive index substantially equal to or higher than the refractive index of the light guide plate and the light guide plate between the light guide plate and the reflecting member (reflecting plate). Even if an anisotropic layer having a second refractive index smaller than the refractive index and separating substantially all of the first polarization state from the second polarization state orthogonal to the first polarization state is disposed, Can be improved.
In addition, as described in Japanese Patent Application Laid-Open No. 2004-363062, the luminance can also be improved by forming a rough surface pattern that is formed of fine protrusions and has a polarization separation function on the inclined back surface of the light guide plate. .
Further, as described in JP-A-10-508151, a concave portion filled with a material different from the material of the optical waveguide is provided in the optical waveguide (light guide plate), and one of these two materials has a refractive index. Is an isotropic material with np, and the other material is an anisotropic material with refractive indices no and ne. Here, regarding the refractive index, no or ne is equal to or substantially equal to np. As a result, polarized light can be separated at the interface between the isotropic material and the anisotropic material, and most of the light irradiated by the light source is changed to light having the same polarization direction before exiting the optical waveguide. Can do. Thus, the luminance can also be improved by applying the configuration described in JP-T-10-508151 to the present invention.
Further, as described in JP-A-9-292530, the light guide plate is composed of two or more layers having a light guide function, and at least one of the first layer and the second layer is provided. The brightness can also be increased by providing a birefringent material, providing an interface between the first layer and the second layer, and emitting light scattered, refracted or diffracted at the interface from the surface of the light guide plate. Can be improved.

  In the above-described polarization separation film, the backlight unit in the present invention may be provided in the backlight unit 2 having the configuration shown in FIGS. In this case, the polarization separation film is preferably disposed between the light guide plate 18 and the liquid crystal display panel 4 (lower surface polarizing plate), and in particular, disposed on the light incident side surface of the liquid crystal display panel 4 (lower surface polarizing plate). It is preferable.

Another configuration example of the light guide plate according to the present invention and a backlight unit using the light guide plate will be described with reference to the drawings.
The backlight unit 220 illustrated in FIG. 12 includes a light guide plate 222, the light source 12, the reflector 20, and the reflection plate 22. The light source 12 is disposed in the parallel groove of the light guide plate 222, and the reflector 20 and the reflection plate 22 are disposed on the inclined surface side of the light guide plate 222, similar to the backlight unit 2 in FIG. .
The light guide plate 222 shown in FIG. 12 includes a transparent part 224 on the inclined back side, a diffusion part 226 laminated on the light emission surface side of the transparent part 224, and a polarization separation laminated on the light emission surface side of the diffusion part 226. Part 228 and a prism part 230 stacked on the light exit surface side of the polarization separation part 228. That is, the light guide plate 222 has a configuration in which the transparent portion 224, the diffusion portion 226, the polarization separation portion 228, and the prism portion 230 are laminated in this order from the inclined back surface side to the light emission surface side.
Here, as the polarization separation portion, films of various materials and configurations exemplified as the polarization separation film described above can be used. As the prism portion, a sheet similar to the prism sheet described above can be used.
In this manner, the light utilization efficiency can be further improved by integrally forming the diffusion unit 226, the polarization separation unit 228, and the prism unit 230.
As an example, the backlight unit 220 using the light guide plate 222 outputs 1.6 times the amount of light compared to the backlight unit in which the light guide plate, the diffusion film (diffusion plate), and the prism sheet are laminated as separate members. be able to. That is, in the backlight unit in which each part is laminated as a separate member, when 16 cold cathode fluorescent lamps (CCFL) are used to illuminate a 32-inch screen, by using the backlight unit 220, The same luminance can be obtained with ten CCFLs. By improving the light utilization efficiency in this way, the number of necessary parts can be reduced, and it can be manufactured at a lower price.

Here, in the backlight unit 220 shown in FIG. 12, the transparent unit, the diffusing unit, the polarization separating unit, and the prism unit are configured, but the present invention is not limited to this, and does not include the prism unit. A backlight unit having a transparent part, a diffusing part, and a polarization separating part can also be suitably used.
FIG. 13A is a cross-sectional view illustrating an example of a backlight unit 240 having a light guide plate 242 in which a polarization separation unit 248 is provided on the light exit surface 18a side of the diffusion unit 246, and FIG. It is a top view of 13 (a).
The backlight unit 240 shown in FIG. 13 includes a light guide plate 242, the light source 12, the reflector 20, and the reflection plate 22. The light source 12 is arranged in the parallel groove 18f of the light guide plate 242, and the reflector 20 and the reflection plate 22 are arranged on the inclined surface 18d side of the light guide plate 242, as in the backlight unit 2 in FIG. It is.
The light guide plate 242 illustrated in FIG. 13 is laminated on the transparent portion 244 on the inclined surface 18d side, the diffusion portion 246 laminated on the light emission surface 18a side of the transparent portion 244, and the light emission surface 18a side of the diffusion portion 246. And a polarization separation unit 248. That is, the light guide plate 242 has a configuration in which the transparent portion 244, the diffusion portion 246, and the polarization separation portion 248 are laminated in this order from the inclined surface 18d side to the light emission surface 18a side.
Here, the polarization separation unit 248 used for the light guide plate 242 will be described in detail.
The polarization separation unit 248 shown in FIG. 13 is a plate-like member in which acicular crystals are oriented in a predetermined direction and dispersed in a transparent resin.
By aligning the needle-shaped crystals in a predetermined direction and dispersing in the transparent resin, only the predetermined polarized light is transmitted and the other polarized light is absorbed and / or reflected. .

  Here, as the acicular crystal, calcium carbonate, strontium carbonate, silicic acid, calcium, aluminum hydroxide, or the like can be used. In addition, as a material of the transparent resin, acrylic resin such as PMMA (polymethyl methacrylate), PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, Other acrylic resins or COP (cycloolefin polymer) can be used.

  Here, the polarization separation unit 248 is not limited to a member in which needle-like crystals are dispersed in a transparent resin, and members having various configurations having the polarization separation function described above can be used.

  Further, the backlight unit in the present invention is not limited to the above-described configuration, and an optical compensation film for widening the viewing angle can be provided. As the optical compensation film, for example, an optical compensation film using a discotic liquid crystal or a nematic liquid crystal, an optical compensation film using a collimating film, or the like can be used. 2A and 2B, the optical compensation film is preferably provided by being attached to the upper surface or the lower surface of the liquid crystal display panel 4.

  Further, an optical member having functions such as diffusion, condensing, scattering, or diffraction is used as the light exit side of the light guide plate 18 in FIGS. 2A and 2B, for example, the light exit surface of the light guide plate 18 or the light guide plate. It can also be arranged between the liquid crystal display panel 4 and the liquid crystal display panel 4. As such an optical component, only one optical component having any one of the above functions may be disposed, or a plurality of optical members having the same or different functions may be disposed in combination. When a plurality of optical components are used in combination, the arrangement order of the plurality of optical components is arbitrary, and the arrangement order can be adjusted as appropriate according to the desired optical characteristics.

  One or more optical members such as the diffusion film, prism sheet, and polarization separation film described above may be used. Further, such optical members can be used by being attached to each other. Further, it can be directly attached to the light guide plate, or can be attached to the light incident side surface of the liquid crystal display panel. Also, the arrangement of the prism sheet is not particularly limited. For example, when the light emission direction is upward, the prism may be disposed upward or downward, and the two prism sheets may be overlapped. It can also be used.

2A and 2B, optical components such as the diffusion sheet 14 and the prism sheet 16 are arranged between the light guide plate 18 and the liquid crystal display panel 4 as described above. The configuration of the components is not limited to such a configuration example, and can be configured as shown below, for example. For example, on the light exit surface side of the light guide plate, a diffusion sheet in which a halftone dot for suppressing the generation of bright lines is formed by printing, a prism sheet, and the above-described polarization separation film are arranged in order. Can do. In this case, it is preferable that a halftone dot is formed on the light incident side surface of the diffusion sheet, that is, the surface facing the light exit surface of the light guide plate, and the prism sheet has a prism row arranged on the light output side. Preferably it is.
As another configuration example, a diffusion sheet in which halftone dots are formed by printing and a polarization separation film can be arranged on the light exit surface side of the light guide plate. In this case, similarly to the above, it is preferable that a halftone dot is formed on the light incident side surface of the diffusion sheet. As another configuration example, a halftone dot is formed on the light exit surface of the light guide plate by printing, and a diffusion sheet and a polarization separation film are arranged in this order on the light exit surface side of the light guide plate. You can also. In this case, since the halftone dots are formed on the light exit surface of the light guide plate, a diffusion sheet having no halftone dots is used.
Further, a halftone dot is formed on the light exit surface of the light guide plate by printing, and on the light exit surface side of the light guide plate, two diffusion sheets having the same or different characteristics, one polarization separating film, and It is also possible to adopt a configuration in which are sequentially arranged. Moreover, you may make it the structure which has arrange | positioned two diffusion sheets and one polarization separation film in order at the light-projection surface side of a light-guide plate. In this case, a halftone dot is not formed on the light exit surface of the light guide plate, but a halftone dot is formed on the surface of the diffusion sheet located on the side close to the light guide plate facing the light exit surface of the light guide plate by printing. It is preferable.
In the above configuration example, from the viewpoint that the number of parts is small and the manufacturing cost can be reduced, a halftone dot is formed on the light exit surface of the light guide plate by printing, and a diffusion sheet and a polarization separation film are formed on the light exit surface side of the light guide plate. A configuration in which these are arranged in this order is preferable.

Next, the shape of the parallel grooves of the light guide plate according to the present invention will be described in detail.
In the light guide plate shown in FIGS. 2 (a) and 2 (b), 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, and any shape may be used as long as the distal end portions intersect with each other and the inclination of the proximal end portion connected to the distal end portion is steeper than the inclination of the distal end 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. .

  In FIG. 1 to FIG. 14D, in the cross-sectional shape of the parallel groove, an example of a light guide plate in which a curve forming a pair of tip surfaces of the parallel groove is concave toward the center of the parallel groove is shown. FIGS. 15A and 15B show another embodiment of the light guide plate of the present invention different from FIG. 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 tip surfaces 63 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.

  Further, in FIGS. 1 to 15B, in the cross-sectional shape of the parallel groove, the pair of base end surfaces of the front end portion of the parallel groove are parallel to the light emitting surface 18a in contact with the front end surface 18h and the parallel surface 18g. Although it is a symmetrical vertical line segment, the cross-sectional shape of the parallel groove 18f is composed of a pair of contour lines that are narrowed toward the light exit surface 18a and intersect at the vertices. It has a part where the angle of inclination with respect to a line perpendicular to the exit surface changes, and the base end side (base end face) of the parallel groove far from the apex is sharper than the tip end (tip end face) near the apex. For example, when the cross-sectional shape of the pair of distal end surfaces of the parallel grooves is a triangle (see FIG. 2), the cross-section of the pair of proximal end surfaces 70 of the parallel grooves is shown in FIG. The angle between the shape and a line perpendicular to the light exit surface 18a and passing through the center of the light source is the tip surface 1 It may be formed by a line segment (hypotenuse) having a slope of acute predetermined angle than h. 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, It is preferable to have a smooth shape with R> 0.01 [mm]. 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 exit surface, but it is more preferable to form such prisms on both the inclined surface and the light exit surface. preferable.
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 °.

  Further, in the light guide plate shown in FIGS. 1 to 16 (b), a pair of parallel surfaces is provided between the pair of inclined surfaces and the pair of base end surfaces of the parallel grooves. The surface is not necessarily provided, and as shown in FIG. 17, a parallel surface may not be provided, and the inclined surface 80 and the base end surface 18 i of the parallel groove 18 f may be directly connected.

  In the light guide plate of the present invention, as shown in FIG. 18, the density of halftone dots is high at a certain center line X, and the density of halftone dots gradually increases from the center line X toward both sides (perpendicular to the center line). A halftone dot pattern 92 that lowers may be formed on the light exit surface 18a of the light guide plate 18 by, for example, printing. By forming such a halftone dot pattern 92 on the light exit surface 18a of the light guide plate 18 so that the center line X of the halftone dot pattern coincides with the position corresponding to the center line of the parallel groove of the light guide plate 18, The generation and unevenness of bright lines on the light exit surface 18a of the light guide plate 18 can be suppressed. Further, instead of printing the halftone dot pattern 92 on the light guide plate 18, a thin sheet on which the halftone dot pattern is formed may be laminated on the light emitting surface. 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. Further, instead of forming such a halftone dot pattern by printing, a portion corresponding to the halftone dot pattern may be roughened as a sand rubbing surface. Such a rubbing surface may be formed in the deepest part or side wall of the parallel groove of the light guide plate.

Here, since the luminance distribution of the light emitted from the light exit surface largely depends on the shape of the tip of the parallel groove of the light guide plate, the shape of the parallel groove of the light guide plate is changed to the shape shown in the present invention described above. By simply designing so that the luminance can be made uniform, the luminance on the light exit surface of the light guide plate can be optimally adjusted.
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 shape shown in the present invention.
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.

  As described above, in the light guide plate of the present invention, the light guide plate with respect to the average value of the brightness formed in the portion (second portion) corresponding to the inclined surface 18d other than the parallel grooves 18f in the light exit surface 18a of the light guide plate 18 is obtained. 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 is 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 of prism sheets 16 and 19 and the number of sheets used. 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 and 19 is high and the number of used sheets can be increased, diffusion of illumination light emitted from the light exit surface 18a of the light guide plate 18 ( The first portion of the light exit surface 18a of the light guide plate 18 with respect to the average value of the luminance of the second portion of the light exit surface 18a of the light guide plate 18 is high in cost. The ratio of the luminance peak values 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, in the light guide plate of the present invention, the peak luminance value of the first portion of the light exit surface 18a of the light guide plate 18 is 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. 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 ( It is possible to use a low-cost diffusion sheet 14 that does not have a very high diffusion efficiency, reduce the number of sheets used, and reduce the number of expensive prism sheets 16 and 19 themselves. This is because the use can be stopped, or low-cost prism sheets 16 and 19 having a very low diffusion efficiency can be used, or the number of sheets used can be reduced.

  In the light guide plate of the present invention, in the cross-sectional shape of the parallel groove 18 f of the light guide plate 18, the tip portion for tapering the parallel groove 18 f is perpendicular to the perpendicular (X) from the center of the rod-shaped light source 12 toward the light exit surface 18 a. It is preferable that the angle be a portion that is within 90 degrees on both sides, and more preferably a portion that is 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 surfaces) of the parallel groove far from the apex is more acute than the tip end side (a pair of front end surfaces) 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 the light emitted from the light exit surface of the light guide plate according to the cross-sectional shape of the parallel groove of the light guide plate, the light guide plate is not provided with a diffusing portion but only a transparent portion. The configuration.
First, as an example of the light guide plate according to the present invention, 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. 19A, 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 face 18i is formed by a line segment that is in contact with the tip end face 18h and the parallel face 18g and is perpendicular to the light exit surface 18a, and has a curved top. 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. 19A has a diameter of the light source 12 of 3 mm, an inclination angle of the tip end face 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 shape was R = 0.25 mm, and the joint between the distal end surface 18 h and the proximal end surface 18 i was R = 15 mm.
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 parallel groove 18f shown in FIG. Here, in the light guide plate 18 shown in FIG. 19B, the side surface 74 of the parallel groove 18f, that is, the pair of distal end surfaces and the pair of proximal end surfaces has a cross-sectional shape formed by only the oblique sides. Except for this, it has the same shape as the light guide plate shown in FIG.

FIG. 20 (a) shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. 19 (a) and the light guide plate shown in FIG. 19 (b). In FIG. 20A, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 19A 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. 19B is indicated by a dotted line.

As can be seen from FIG. 20 (a), the difference between the maximum value and the minimum value of the brightness on the light exit surface of the light guide plate shown in FIG. 19 (a) is the brightness on the light exit surface of the light guide plate shown in FIG. 19 (b). Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 19A 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.
Further, as a result of calculating the light 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. 19A 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. 19A was 84.0%, and the incident efficiency of the light guide plate having the shape shown in FIG. 19B was 95.5%. As described above, the light guide plate shown in FIG. 19A can have higher emission efficiency and incident efficiency than the light guide plate shown in FIG. 19B.

As another example of the light guide plate of the present invention, as shown in FIG. 19C, a pair of base end surfaces 70 of parallel grooves are half of the inclination of the front end surface 18h, that is, with respect to the light exit surface 18a. The light guide plate having the same shape as that of the light guide plate in FIG. 19A 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 luminance distribution of light emitted from the surface was examined.
FIG. 20B shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 20B, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 19C is indicated by a solid line, and for comparison, the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 19B is indicated by a dotted line.

As can be seen from FIG. 20B, the difference between the maximum value and the minimum value on the light exit surface of the light guide plate shown in FIG. 19C is the brightness on the light exit surface of the light guide plate shown in FIG. Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 19C 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.
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. 19C was 61.9%. In this way, the light guide plate shown in FIG. 19C can have higher emission efficiency than the light guide plate shown in FIG.

As still another example of the light guide plate of the present invention, as shown in FIG. 19 (d), the connecting portion between the front end face 18h ′ and the base end face 18i ′ of the parallel groove 18f is connected to the guide shown in FIG. 19 (a). Except for being provided closer to the parallel portion 18g than the light plate, the luminance distribution of light emitted from the light exit surface was examined for the light guide plate having the same shape as the light guide plate of FIG.
FIG. 20C shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 20C, the vertical axis represents the luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 19D 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. 19B is indicated by a dotted line for comparison.

As can be seen from FIG. 20C, the difference between the maximum value and the minimum value of the brightness on the light exit surface of the light guide plate shown in FIG. 19D is the brightness on the light exit surface of the light guide plate shown in FIG. It is almost the same as the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 19D can emit light with reduced luminance unevenness equivalent to the light guide plate shown in FIG.
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. 19D was 61.5%. Thus, the light guide plate shown in FIG. 19 (d) can have higher emission efficiency than the light guide plate shown in FIG. 19 (b).

As still another example of the light guide plate of the present invention, the cross-sectional shape of the pair of base end faces 72 of the parallel groove 18f shown in FIG. 19 (e) is a concave curve toward the center of the parallel groove 18f. Except for this, the luminance distribution of light emitted from the light exit surface of the light guide plate having the same shape as the light guide plate of FIG.
FIG. 20D shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 20D, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 19 (e) is shown by a solid line, and the brightness distribution on the light exit surface of the light guide plate having the shape shown in FIG. 19 (b) is shown by a dotted line for comparison.

As can be seen from FIG. 20D, the difference between the maximum value and the minimum value of the brightness on the light exit surface of the light guide plate shown in FIG. 19E is the brightness on the light exit surface of the light guide plate shown in FIG. Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 19 (e) can emit light with less uneven brightness than the light guide plate shown in FIG. 19 (b). 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 measured luminance distribution, the emission efficiency of the light guide plate having the shape shown in FIG. 19 (e) was 70.9%. As described above, the light guide plate shown in FIG. 19 (e) can have higher emission efficiency than the light guide plate shown in FIG. 19 (b).

  As described above, from FIG. 20A to FIG. 20D, the parallel grooves of the light guide plate have the shape of the present invention, so that the shape of the parallel grooves has a triangular shape that can reduce the luminance unevenness compared to the conventional case. It can be seen that the luminance unevenness equivalent to the case or even the luminance unevenness can be reduced and the emission efficiency can be improved.

Next, the base end face 18i of the parallel groove 18f shown in FIGS. 21 (a) to 21 (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 the parallel surfaces. The brightness distribution of the light was investigated.
Here, the light guide plate shown in FIG. 21A does not have a parallel surface, except that the inclination angle of the inclined surface 80 is changed and the base end surface 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 FIGS. 21 (b) and 21 (c) are not provided with a parallel surface, the inclined angle of the inclined surface 80 is changed, and the pair of base end surfaces 70 or 18i ′ of the parallel groove 18f and the inclined surface are provided. Except for being directly connected to 80, the shape is the same as that of the light guide plate shown in FIGS. 19 (c) and 19 (d).

FIGS. 22A to 22C show the luminance distributions on the light emitting side surfaces of the light guide plates shown in FIGS. 21A to 21C, respectively. 22A to 22C, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center of the light guide plate (the central portion of the parallel groove). 22 (a) to 22 (c) show the luminance distribution on the light exit surface of the light guide plate shown in FIGS. 21 (a) to 21 (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. 22 (a) to 22 (c), it can be seen that in any light guide plate, the luminance unevenness can be equal to or less than that of the light guide plate shown in FIG. 19 (b). 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 shown in FIG. 21A 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. 21C was 62.0% and 61.6%. Thereby, it turns out that any light-guide plate can improve radiation | emission efficiency rather than the light-guide plate shown in FIG.19 (b).
As described above, from FIG. 22A to FIG. 22C, the parallel grooves of the light guide plate have the shape of the present invention, so that the shape of the parallel grooves has a triangular shape that can reduce the luminance unevenness compared to the conventional case. It can be seen that the luminance unevenness equivalent to the case, or the luminance unevenness can be further reduced, and the emission efficiency can be improved.

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 tip surfaces of the parallel grooves of the light guide plate shown in FIGS. 23 (a) to 23 (d) is a hyperbolic shape is examined. It was.
Here, the light guide plate 18 shown in FIG. 23A is the same as the light guide plate shown in FIG. 19A 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. 23B is a figure except that one of the side surfaces 78 of the parallel grooves 18f, that is, the cross-sectional shape of the front end surface and the base end surface is formed by one hyperbola. The shape is the same as that of the light guide plate shown in FIG.

FIG. 24A shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. 23A and the light guide plate shown in FIG. In FIG. 24A, the vertical axis represents the luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 23A 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. 23B is indicated by a dotted line.

As can be seen from FIG. 24A, the difference between the maximum value and the minimum value of the brightness on the light exit surface of the light guide plate shown in FIG. 23A is the brightness on the light exit surface of the light guide plate shown in FIG. Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 23A 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.
Further, as a result of calculating the light 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. 23A 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. 23A can have higher emission efficiency than the light guide plate shown in FIG.

As another example of the light guide plate of the present invention, the cross-sectional shape of the pair of base end surfaces 76 of the parallel groove 18f is a hyperbola having a half inclination of the hyperbola of the front end surface 40 as shown in FIG. Except that there is a hyperbola that is perpendicular to the light exit surface 18a and a line that passes through the center of the light source and is smaller than the hyperbola of the tip surface 40, the light guide plate of FIG. The light intensity distribution of the light emitted from the light exit surface was examined for the light guide plate having the same shape as in FIG.
FIG. 24B shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 24B, the vertical axis represents the luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 23C 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. 23B is indicated by a dotted line for comparison.

As can be seen from FIG. 24B, the difference between the maximum value and the minimum value of the brightness on the light exit surface of the light guide plate shown in FIG. 23C, and the brightness on the light exit surface of the light guide plate shown in FIG. The difference between the maximum value and the minimum value is substantially the same. That is, the light guide plate shown in FIG. 23C 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 emission efficiency of the light guide plate having the shape shown in FIG. 23C was 59.1%. Thus, the light guide plate shown in FIG. 23C can have higher emission efficiency than the light guide plate shown in FIG.

As still another example of the light guide plate of the present invention, except that the cross-sectional shape of the pair of base end surfaces of the parallel grooves as shown in FIG. 23 (d) is a concave curve toward the center of the parallel grooves. Then, the luminance distribution of the light emitted from the light exit surface of the light guide plate having the same shape as the light guide plate of FIG.
FIG. 24C shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 24C, the vertical axis represents the luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center 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. 23 (d) 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. 23 (b) is indicated by a dotted line for comparison.

As can be seen from FIG. 24 (c), the difference between the maximum value and the minimum value of the brightness on the light exit surface of the light guide plate shown in FIG. 23 (d) is the brightness on the light exit surface of the light guide plate shown in FIG. Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 23 (d) can emit light with less uneven brightness than the light guide plate shown in FIG. 23 (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. 23D was 67.8%. In this way, the light guide plate shown in FIG. 23 (d) can have higher emission efficiency than the light guide plate shown in FIG. 23 (b).
As described above, from FIGS. 24A to 24D, the parallel groove of the light guide plate is formed in the shape of the present invention, so that the shape of the parallel groove is a hyperbola shape that can reduce luminance unevenness as compared with the conventional case. It can be seen that the luminance unevenness equivalent to the case, or the luminance unevenness can be further reduced, and the emission efficiency can be improved.

Next, as shown in FIGS. 25 (a) and 25 (b), 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. 25 (a) does not have a parallel surface, except that the inclination angle of the inclined surface is changed and the pair of base end surfaces of the parallel grooves 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. 25 (b) is also provided with no parallel surface, except that the inclined angle of the inclined surface is changed and the pair of base end surfaces of the parallel grooves 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.

FIGS. 26A and 26B show luminance distributions on the light exit side surfaces of the light guide plate shown in FIGS. 25A and 25B, respectively. 26A and 26B, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the center of the light guide plate (the central portion of the parallel groove). FIGS. 26 (a) and 26 (b) show the luminance distribution on the light exit surface of the light guide plate shown in FIGS. 25 (a) and 25 (b) with a solid line, and FIG. 23 (b) shows a 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. 26A and 26B, the luminance unevenness and 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 shown in FIG. 25A is 63.9%, and the emission efficiency of the light guide plate shown in FIG. 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.23 (b).
As described above, from FIGS. 26A and 26B, the parallel groove of the light guide plate has the shape of the present invention, so that the shape of the parallel groove has a hyperbola shape that can reduce the luminance unevenness as compared with the conventional case. It can be seen that the equivalent luminance unevenness or the luminance unevenness can be further reduced and the emission efficiency can be improved.

  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, it is possible to widen the range of transmittance depending on the ink type.
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.

  As described above, the light guide plate of the present invention, the planar illumination device including the light guide plate, and the liquid crystal display device have been described in detail. However, the present invention is not limited to the above-described embodiment, Of course, improvements and changes may be made.

For example, in the present invention, when a large-sized light guide plate is configured by arranging a plurality of light guide plates 18 in parallel so that all the light exit surfaces 18a of the light guide plate 18 form the same plane, as shown in FIG. In addition, the tangent 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 does not intersect, that is, a smooth flat surface at the connecting portion of these 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. 27, 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.

As described above, in order to form a large-sized light guide plate by connecting a plurality of light guide plates according to the present invention, the light guide plates of the present invention that are separately formed are arranged so that the thin portions are in contact with each other, or formed by joining. In order to improve the uniformity of the emitted light, it is preferable that the two or more light guide plates of the present invention are connected and formed integrally.
From the viewpoint of manufacturing efficiency, it is preferable to integrally form the number of the light guide plates of the present invention necessary for forming the light guide plate corresponding to the required screen size.

  Moreover, in the said embodiment, although it comprised so that the light emission surface of the light guide plate connected in multiple numbers may be flat, ie, it may become flush | planar, it does not necessarily comprise so that the light emission surface of each light guide plate may become flat. Alternatively, the entire light exit surface of the light guide plate may be configured to have the same curved surface, or a part of the light exit surface of the light guide plate may be configured to be a curved surface. May be. Or each light-guide plate can also be comprised so that the undulation of a fixed period may be formed in the whole surface of the light emission surface of a light-guide plate when two or more are connected. In addition, a sand rubbing surface, a large number of dimples or a large number of minute protrusions may be formed on the entire surface or a part of the light emission surface, or a large number of scatterers may be formed by printing. The generation of bright lines on the light exit surface of the light guide plate can also be suppressed by such a rubbing surface, dimples, protrusions, and scatterers.

In addition, as shown in FIG. 28, when a large-sized backlight unit is configured by connecting a plurality of light guide plates 18, the occurrence of uneven brightness on the light emission surface of the connected light guide plates 18 is suppressed. It is preferable to dispose one halftone dot sheet on which the halftone dots for forming are covered so as to cover the light emission surfaces of the plurality of connected light guide plates 18. Such a halftone dot sheet can be variously sized according to the number of light guide plates 18 to be connected. The halftone dots of the halftone dot sheet 18 are positions where bright lines are generated on the light exit surface of the light guide plate 18. Placed in.
As a material for such a halftone dot sheet, it is preferable to use the same material as that of the light guide plate 18 or a material having substantially the same coefficient of thermal expansion and high transmittance and diffusion effect from the viewpoint of suppressing the influence of heat change. . By configuring the halftone sheet using such a material, the position of the halftone dot of the halftone sheet is changed from the generation position of the bright line on the light exit surface of the light guide plate due to temperature and humidity changes accompanying the manufacturing environment and the use environment. The shift is suppressed, and a change in the illuminance distribution of the light emitted from the light exit surface of the light guide plate unit can be suppressed.

Further, the light guide plate may have a structure that is divided along the center line of the parallel groove for arranging the light source in the light guide plate 18 shown in FIG. When the light guide plate having such a structure is used, the light guide plates are connected to each other at a portion corresponding to the parallel groove 18f of the light guide plate 18 having the structure shown in FIG. It is preferable to arrange the halftone dot sheet so as to coincide with the portion having the highest halftone dot density in the dot sheet. Furthermore, when connecting a plurality of light guide plates, a part of the light guide plates is configured with a structure divided along the center line of the parallel grooves, and the other light guide plates are as shown in FIG. When configured in such a structure, it is preferable to form the halftone dot pattern of the halftone sheet so as to increase the density of the halftone dots at positions corresponding to the center lines of the parallel grooves of the light guide plate other than the connecting portion.
By forming such a halftone dot pattern, when a large-sized backlight unit is manufactured by connecting a plurality of light guide plates, generation of bright lines and unevenness at a connecting portion of the plurality of light guide plates can be suppressed. it can. Such a halftone dot sheet can be joined to the light guide plate by laminating an adhesive layer on the back surface.

  In addition, when arranging such a halftone sheet on the light exit surface of a plurality of connected light guide plates, the position of the halftone dot pattern formed on the halftone sheet corresponds to the center line of the parallel grooves of the light guide plate. In order to accurately and surely match the position to be moved, for example, an arbitrary position in a region not used as a light emitting region of the light emitting surface of the light guide plate and a position of the halftone sheet corresponding to the position are used for positioning. It is preferable to form a hole. By passing a fixing tool such as a pin through these positioning holes, the bright line generation position of the light guide plate and the halftone dot position of the halftone sheet can be accurately and reliably positioned. The formation position of the positioning hole is not particularly limited as long as it is an area that is not used as the light emission area, but the position corresponding to the center line of the parallel groove of the light guide plate due to the influence of temperature and humidity changes, etc. In order to reduce the deviation of the light guide plate, a hole is formed in the center of the light exit surface in the direction perpendicular to the center line of the parallel groove of the light guide plate on the end side in the length direction of the parallel groove of the light guide plate. Is preferred.

  Further, it is desirable that the halftone dot sheet is regulated in position with respect to the light guide plate in the vicinity of the center of the combined light guide plates, and the outer peripheral portion is fitted with a gap only by thickness.

  In the light guide plate of the present invention, the reflecting plate 24 may be arranged on the side surface of the light guide plate 18 as shown in FIG. When a plurality of light guide plates 18 are arranged, as shown in FIG. 28 (b), 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 FIG. 2, the prism sheet is disposed between the inclined surface of the light guide plate of the light guide plate and the reflective sheet. However, the present invention is not limited to this, and the side surfaces of the parallel grooves (a pair of tips) A prism whose groove is parallel to the axis of the rod-like light source may be directly engraved on the surface of the light guide plate excluding the surface and a pair of base end surfaces), for example, an inclined surface.
For example, the prism 25 may be formed directly on the inclined surface 18d of the light guide plate 18 as shown in FIGS. Further, a prism may be formed on the parallel surface 18g.
In this way, by forming the prism directly 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 same effect as when the prism sheet is disposed can be obtained. it can. Furthermore, since it is not necessary to provide a prism sheet, it is possible to eliminate light attenuation (decrease in luminance) caused by the gap formed by arranging the prism sheet. As a result, the light use efficiency as the planar illumination device, that is, the light emission efficiency can be made higher than when the prism sheet is disposed. Furthermore, since it is not necessary to provide a prism sheet, the apparatus can be further downsized (thinned).
Here, in this invention, the space | interval becomes narrow toward a light-projection surface, and it is comprised by a pair of outline which cross | intersects at a vertex, and each inclination angle changes with respect to a line perpendicular | vertical to a light-projection surface. A light guide plate having a shape with a sharper angle on the base end side (a pair of base end surfaces) of the parallel groove far from the apex than the front end side (a pair of front end surfaces) near the apex is used. However, the present invention is not limited to this, and the parallel groove has a steep inclination of the base end face with respect to the inclination of the front end face such as a triangle as shown in FIG. In the case of using a light guide plate having a shape that is not sharp or a shape in which the tip shape on the light exit surface side is only sharpened, the surface of the light guide plate excluding the side surfaces of the parallel grooves (one pair of tip surfaces and one pair of base end surfaces) is also used. By forming the prism, the same effect as described above can be obtained.

Here, the prism engraved on the inclined surface preferably has an apex angle θ _p1 of 70 ° ≦ θ _p1 ≦ 140 °. As described above, 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 improved more suitably.

30A to 30C show an example of a light guide plate in which prisms are engraved on inclined surfaces and parallel surfaces. 30A is a schematic diagram showing the parallel surface and the inclined surface of the light guide plate 18, and FIG. 30B is a schematic diagram showing the prism 27 engraved on the parallel surface 18g in an enlarged manner, FIG. FIG. 4C is a schematic diagram showing an enlarged view of the prism 25 engraved on the inclined surface 18d. In FIG. 30A, the concave and convex shapes of the prism 25 and the prism 27 are not shown, and the prism portion is also shown by a straight line.
As shown in FIG. 30A, the light guide plate 18 has a prism 25 engraved on the inclined surface 18d and a prism 27 engraved on the parallel surface 18g. As shown in FIG. 30 (b), the prism 27 engraved on the parallel surface 18g has an isosceles triangular shape having an apex angle of 82 degrees, and as shown in FIG. 30 (c), the inclined surface 18d. The prism 25 carved in the shape of an isosceles triangle having an apex angle of 120 degrees.
Thus, the emission efficiency can be improved by engraving the prism that satisfies the above range on the inclined surface. Further, the emission efficiency can be further improved by forming prisms on the parallel surfaces.

Here, in the above-described light guide plate, the prism 25 formed on the inclined surface 18d has a shape that is perpendicular to the bottom surface and symmetrical with respect to the surface passing through the apex, that is, the prism 25 formed on the inclined surface is the bottom surface. However, in the present invention, the prism formed on the inclined surface and the parallel surface has a shape with respect to the bottom surface. It is more preferable that the shape is asymmetric with respect to a plane perpendicular to and passing through the apex. In other words, in the shape that is asymmetric with respect to a plane that passes through the apex and does not have a prism and is perpendicular to the inclined back surface portion, that is, in the cross-sectional shape in the orthogonal direction, a contact with an adjacent prism is connected. A shape that is perpendicular to the ellipse and is asymmetric with respect to the line passing through the vertex, in other words, in the cross-sectional shape in the orthogonal direction, the length of the contour line connecting the vertex and the end on the parallel groove side And it is more preferable that the length of the contour line connecting the apex and the end on the thin end side is different.
Here, the bottom surface of the prism is a virtual surface that faces the apex angle of the prism, that is, a virtual surface that connects a contact point with an adjacent prism of the prism, that is, an end portion on the parallel groove side of the prism. Is a virtual surface connecting the end portion on the thin end side.

By making the shape of the prism formed on the inclined surface and the parallel surface asymmetric with respect to the surface perpendicular to the bottom surface and passing through the apex, the angular distribution characteristics of the light emitted from the light exit surface can be obtained. It can be made uniform, and the front luminance can be further improved.
Here, the angle distribution characteristic is a luminance distribution characteristic with respect to the viewing angle of the light emitted from the backlight unit, and the luminance distribution characteristic with respect to the viewing angle is suppressed by making the angle distribution characteristic at any point of the light guide plate uniform. can do.

In addition, the prism engraved on the inclined surface and the parallel surface has an angle (θ1) formed between the surface perpendicular to the bottom surface and passing through the apex and the surface on the parallel groove side of 0 ° or more and 70 ° or less, that is, 0 ≦ θ1 ≦ 70 °, and the angle (θ2) formed between the surface perpendicular to the bottom surface and passing through the apex and the surface on the thin end side is not less than 45 degrees and not more than 70 degrees, that is, 45 ° ≦ θ2 ≦ The angle is preferably 70 °. Further, θ1 is more preferably 30 degrees or more and 70 degrees or less, that is, 30 ° ≦ θ1 ≦ 70 °.
As an example, as shown in FIG. 30 (d), the prism 25 formed on the inclined surface 18d is perpendicular to the bottom surface (β line in FIG. 30 (d)) and passes through its apex (FIG. 30). (D) α-line) and the surface (hereinafter referred to as θ1) formed by the parallel groove side surface is 60 degrees, a plane perpendicular to the bottom surface (β line) and passing through the apex (α line) And an angle (hereinafter referred to as θ2) formed by the surface on the thin-walled end side is 55 degrees, or as shown in FIG. 30 (e), θ1 is 60 degrees, θ2 is 50 degrees, or FIG. As shown in f), there is a shape engraved with θ1 being 60 degrees and θ2 being 45 degrees.
In this way, by making the prism engraved on the inclined surface into a shape that satisfies the above range, the angle distribution characteristics of the light emitted from the light exit surface can be made uniform, and the front luminance can be improved. it can. Furthermore, .theta.1 and by a 30 ° ≦ θ1 ≦ 70 °, apex angle theta _p1 of the prism is 70 degrees or more, can be more favorably improved emission efficiency of the planar lighting device.
Here, in the above-described embodiment, all the prisms formed on the inclined surface have an asymmetric shape with respect to the surface perpendicular to the bottom surface and passing through the apex, but the present invention is not limited to this. Or, by making a part of the parallel surface asymmetric with respect to the surface perpendicular to the bottom surface and passing through the apex, the angle distribution characteristics of the light emitted from the light exit surface can be made uniform. And the front luminance can be improved.

Furthermore, as another example of the light guide plate in which prisms are engraved on the inclined surface and the parallel surface, the prism engraved on the inclined surface in FIG. 31 differs depending on the position of the inclined surface in the direction orthogonal to the parallel grooves. An example in which the shape is engraved is shown. Here, FIG. 31A is a schematic diagram showing a parallel surface and an inclined surface of the light guide plate 18.
In the light guide plate 18 shown in FIG. 31A, a prism 27 is engraved on the parallel surface 18g. In the light guide plate 18 shown in FIG. 31 (a), the A region and the B region from the portion in contact with the parallel surface 18g of the inclined surface 18d to the portion connected to the inclined surface of the adjacent light guide plate Different shapes of prisms are formed in the three regions of the C region. That is, the prism 25a is engraved in the A area on the parallel plane side, the prism 25b is engraved in the B area on the thinner end side than the A area, and the prism 25c is engraved in the C area on the thinner end side than the B area. It is installed.

The shapes of the prisms formed on the parallel plane, A region, B region, and C region of the light guide plate 18 are shown in FIGS. FIG. 31B is a schematic diagram of the prism 27 engraved on the parallel surface, and FIG. 31C is a schematic diagram of the prism 25a engraved in the area A of the inclined surface 18d. FIG. 31D is a schematic diagram of the prism 25b engraved in the B region of the inclined surface 18d, and FIG. 31E is a schematic diagram of the prism 25c engraved in the C region of the inclined surface 18d.
As shown in FIG. 31B, the prism 27 has an isosceles triangular shape with an apex angle of 82 degrees, that is, a symmetrical shape. Further, as shown in FIG. 31C, the prism 25a has a triangular shape with θ1 of 60 degrees and θ2 of 45 degrees, and the prism 25b has a triangular shape with θ1 of 60 degrees and θ2 of 40 degrees. The prism 25c has a triangular shape in which θ1 is 60 degrees and θ2 is 60 degrees.

FIG. 32 shows another example in which the prisms engraved on the inclined surface and the parallel surface are engraved with different shapes depending on the position of the inclined surface in the direction orthogonal to the parallel grooves.
As in the above example, an isosceles triangular prism 27 having an apex angle of 82 degrees is engraved on the parallel surface of the light guide plate. Further, A ′ region, B ′ region, C ′ region, D ′ region, E ′ from the portion of the inclined surface 18d in contact with the parallel surface 18g to the portion connected to the inclined surface of the adjacent light guide plate. In five areas, prisms 25a ′, 25b ′, 25c ′, 25d ′, and 25e ′ are engraved, respectively. Here, the prism 25a ′ is engraved in a triangular shape with θ1 being 60 degrees and θ2 is 55 degrees, and the prism 25b ′ is engraved with a triangular shape having θ1 being 60 degrees and θ2 being 50 degrees. 25c ′ is engraved in a triangular shape with θ1 of 60 degrees and θ2 of 60 degrees, and the prism 25d ′ is engraved with a triangular shape with θ1 of 60 degrees and θ2 of 50 degrees, and the prism 25e ′ is It is engraved in a triangular shape with θ1 being 60 degrees and θ2 being 60 degrees.

  Thus, by engraving differently shaped prisms according to the position of the inclined surface in the direction orthogonal to the parallel grooves, the angular distribution characteristics of the light emitted from the light exit surface can be made more uniform, The front luminance can be further improved.

The prism preferably has a base length of 0.1 mm or less in a direction perpendicular to the parallel grooves.
By setting the length of the base of the prism to 0.1 mm or less, the visibility of the prism structure can be almost ignored.
Here, the number, width, and ratio of the prism regions formed on the inclined surface and the parallel surface are not particularly limited, and can be any number, width, and ratio. In the above-described embodiment, the prism formed on the parallel surface is symmetric with respect to the surface perpendicular to the bottom surface and passing through the apex.
Also, as shown in FIGS. 31 and 32, the arrangement pattern of the prisms is not particularly limited, and it is needless to say that various arrangement patterns may be used as necessary. In this embodiment, the prisms to be engraved are divided for each region, but the present invention is not limited to this. For example, a triangular prism having θ1 of 60 degrees and θ2 of 50 degrees, and θ1 of 60 Alternatively, prisms having a triangular shape with an angle θ2 of 50 degrees may be alternately formed.

In addition, the prisms engraved on the inclined surfaces and the parallel surfaces are engraved on the pair of inclined surfaces and the parallel surfaces so as to be symmetric with respect to the center line perpendicular to the light exit surface through the center of the parallel groove. (Formation) is preferable.
The method for forming the prism is not particularly limited. The prism may be formed by cutting an inclined surface or may be provided with a prism. When the light guide plate is manufactured by extrusion molding or injection molding, the prism is You may make it produce the light-guide plate in which the prism was formed using the formed metal mold | die.

  Here, it is preferable to form a convex portion on the light exit surface 18 a of the light guide plate 18. As an example, a convex portion having a rounded upper portion that is obtained by cutting an ellipse in half is arranged at a boundary portion between adjacent light guide plates with a certain height and width in a direction parallel to the parallel groove. Here, the height of the convex portion is not particularly limited as long as the unevenness in luminance 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 is not particularly limited, and the cross-sectional shape of the convex portion may be, for example, a rectangle, a trapezoid, a semicircle, or a triangle. Moreover, the position of the convex part formed in the light emission surface 18a of the light-guide plate 18 is not specifically limited, It can provide in arbitrary positions. Further, the number of convex portions is not limited, and, for example, three or more convex portions can be formed for three light guide plates.

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.
Thus, the convex part formed in the light emission surface can be used as a spacer for ensuring a space between the optical member constituting the backlight unit and the light emission surface. That is, a film-like optical member such as a prism sheet or a diffusion sheet disposed on the light exit surface can be used as a spacer for separating the flat portion of the light exit surface by a predetermined distance. That is, unevenness in luminance can be reduced by forming a convex portion on the light exit surface.
Further, by providing the light guide plate integrally with the light guide plate, the manufacturing becomes easy as described above, and it is not necessary to adjust the alignment between the light guide plate and the convex portion during assembly.

It is a schematic structure sectional view at the time of arranging a plurality of light guide plates of the present invention in parallel. (A) And (b) is the schematic perspective view and schematic sectional drawing of a liquid crystal display device which respectively used the backlight unit which has the light-guide plate of this invention. (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 which looked at the arranged prism sheet from the light-guide plate side, (c) is a schematic cross-sectional view of a prism sheet. (A) is a schematic sectional drawing of the light-guide plate which has a diffusion layer of uniform thickness, (b) is a schematic block diagram of the light-guide plate which has a flat diffuser in the part directly above a parallel groove, c) is a schematic configuration diagram of a light guide plate having a curved diffusion portion directly above a parallel groove. It is a schematic sectional drawing which shows schematic structure of the backlight unit which has a light-guide plate provided with the spreading | diffusion part of uniform thickness. It is a graph which shows the thickness distribution of the adjusted diffusion part. The measurement result of the luminance of light emitted from the light exit surface of the light guide plate in which the shape of the diffuser has a distribution in thickness, and the light exit from the light exit surface of the light guide plate having a shape having a uniform thickness It is a graph which shows the measurement result of the luminance distribution of the light to be performed. It is a graph which shows the thickness distribution of the diffusion part which adjusted the thickness of the diffusion part twice. It is a graph which shows the measurement result of the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate of the shape which has a diffusion part which adjusted the thickness of the diffusion part twice. It is a graph which shows the measurement result of the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate which has a diffusion part which made the thickness of the whole diffusion part various. It is a schematic sectional drawing which shows schematic structure of the backlight unit using the light-guide plate of the other structural example according to this invention. It is a schematic sectional drawing which shows schematic structure of the backlight unit using the light-guide plate of the other structural example according to this invention. It is a schematic sectional drawing which shows schematic structure of the backlight unit using the light-guide plate of the other structural example according to this invention. (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 of this invention. It is an example of the halftone dot pattern formed in the light-projection surface side of a light-guide plate. (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 parallel grooves 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.19 (a), FIG.19 (c), FIG.19 (d), and FIG.19 (e), respectively. It is a graph which shows. (A)-(c) is a schematic block diagram around the parallel groove | channel of a light-guide plate when not providing the parallel surface of the light-guide plate shown in FIG.19 (a), FIG.19 (c) and FIG.19 (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.21 (a), FIG.21 (b), and FIG.21 (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.23 (a), FIG.23 (c), and FIG.23 (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.23 (a) and FIG.23 (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.25 (a) and FIG.25 (b), respectively. It is a schematic sectional drawing of another example when the light-guide plate of this invention 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 of this invention, (b) has arrange | positioned the reflecting plate in the side surface of the light-guide plate when the light-guide plate of this invention is arrange | positioned in parallel. It is a structural example. (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. (A) is a schematic diagram which shows the parallel surface and inclined surface of the light-guide plate 18, (b) is a schematic diagram which expands and shows the prism 27 carved in the parallel surface 18g, (c) is It is a schematic diagram which expands and shows the prism 25 engraved in the inclined surface 18d, (d)-(f) is a schematic diagram which shows another example of the prism 25 engraved in an inclined surface. (A) is a schematic diagram which shows the parallel surface and inclined surface of the light-guide plate 18, (b) is a schematic diagram which shows the prism 27 carved in the parallel surface, (c) is 18d of inclined surfaces. It is a schematic diagram which shows the prism 25a engraved in A area | region, (d) is a schematic diagram which shows the prism 25b engraved in B area | region of the inclined surface 18d, (e) is inclined surface 18d. It is a schematic diagram which shows the prism 25c engraved in C area | region. It is a schematic diagram which shows another example when the prism carved in the inclined surface of the light-guide plate is divided | segmented into plurality with respect to the orthogonal direction, and is carved with a different shape according to the position. 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.

Explanation of symbols

2, 200, 220, 240 Backlight unit 4 Liquid crystal display panel 6 Drive unit 10 Liquid crystal display device 12 Light source 14 Diffusion sheet 16, 19 Prism sheet 18, 202, 222, 242 Light guide plate 18a, 52 Light exit surface 18b Thick part 18c Thin end portion 18d Inclined surface 18e, 80 Inclined rear surface portion 18f Parallel groove 18g Parallel surface 18h, 18h ', 40 One pair of tip surfaces 18i, 18i', 70, 72, 76 One pair of base end surfaces 20 Reflectors 21, 204 224, 244 Transparent portion 22 Reflective sheet 23, 206, 226, 246 Diffusing portion 24 Reflector 25, 26 Prism 54a, 54b Arc curve 56 Intersection 64a, 64b Parabola 72a, 72b, 82a, 82b, 84a, 84b Curve 74, 78 Side 92 Halftone dot pattern 208, 230 Priz Unit 228, 248 Polarization separation unit

Claims (12)

A rectangular light exit surface;
A thick portion located substantially parallel to one side of the rectangular light exit surface and substantially at the center,
A pair of thin end portions formed substantially parallel to the thick portion;
A parallel groove for accommodating a rod-shaped light source, formed substantially in parallel with the one side on the opposite side of the rectangular light exit surface at the approximate center of the thick part,
The thickness decreases from the thick portion toward each of the pair of thin end portions on both sides in a direction substantially perpendicular to the one side, and a pair of inclined back surfaces are formed on both sides of the parallel groove, respectively. A transparent light guide plate having a pair of inclined back surfaces,
A light guide plate having a diffusion portion for diffusing light incident on at least a portion facing the parallel groove on the light emission surface side.   The light guide plate according to claim 1, wherein the diffusing portion is disposed on the entire surface of the light exit surface.   The light guide plate according to claim 1, wherein the diffusing portion has a shape in which a thickness in a direction perpendicular to the light emitting surface is different depending on a position on the light emitting surface. The arbitrary value of the light guide plate having the diffusion portion of the reference thickness tx, where dtx is an adjustment amount of the thickness in the direction perpendicular to the light emission surface with respect to the reference thickness tx at an arbitrary position x on the light emission surface of the diffusion portion. If the intensity of the light emitted from the position x is Ip (x), the target light intensity is I (target_ave), and the constant determined according to the material of the diffusion portion is A, the arbitrary position x The light guide plate according to any one of claims 1 to 3, wherein a thickness T (x) of the diffusing portion satisfies the following formula.
I (target_ave) / Ip (x) = Exp (−A · dt (x))
Tx = tx + dtx   5. The light guide plate according to claim 4, wherein A is a constant determined based on a scattering cross section and a particle density of particles mixed in the diffusion portion.   Furthermore, the light-guide plate in any one of Claims 1-5 which has a polarization separation part in the light-projection surface side.   Furthermore, the light-guide plate in any one of Claims 1-6 which have a prism part in the light-projection surface side. 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. The light guide plate according to any one of claims 1 to 7, wherein the base end side of the parallel groove is formed to have an acute angle.   In the cross-sectional shape of the parallel groove in the orthogonal direction, the front end portion of the parallel groove is emitted light from a rod-shaped light source housed in the parallel groove in a first portion corresponding to the parallel groove of the rectangular light emission surface. The rectangular light emission according to the ratio of the illuminance or luminance peak value formed by the illuminance or luminance average value formed by the emitted light in the second portion corresponding to the pair of inclined back surface portions. The light guide plate according to any one of claims 1 to 8, wherein the light guide plate is configured by a pair of contour lines whose intervals become narrower toward the surface. A light guide plate according to any one of claims 1 to 9,
A rod-shaped light source housed in the parallel groove of the light guide plate;
A reflector provided behind the rod-shaped light source so as to close the parallel grooves;
A planar illumination device comprising: a reflective sheet attached to the inclined back surface of the inclined back surface portion on both sides of the thick portion of the light guide plate.   Furthermore, the planar illuminating device of Claim 10 which has a diffusion sheet arrange | positioned at the said rectangular light emission surface shape of the said light-guide plate. The planar illumination device according to claim 10 or 11,
A liquid crystal display panel disposed on the light exit surface side of the planar illumination device;
A liquid crystal display device comprising a drive unit for driving the liquid crystal display panel.

Images