JP2006301518A - Light guide plate, surface lighting device using the same and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate which is thin and lightweight and can emit more uniform and higher luminous illumination light having high light utilizing efficiency and nearly free from unevenness from a light emission surface, to provide a surface lighting device and to provide a liquid crystal display device. <P>SOLUTION: The light guide plate has a plurality of transparent light guide plate units each constituted of a rectangular light emission surface, a thick part which is nearly parallel to one side thereof and positioned in a nearly center part thereof, a pair of thin end parts formed to be nearly parallel to the thick part, a parallel groove formed on the side opposite to the light emission side at a nearly center part of the thick part and housing a bar-shaped light source and an inclined back surface part whose thickness is made thin from the thick part toward the respective thin end parts and which forms an inclined back surface. The thin end parts of the adjacent light guide plate units are connected to each other and the light emission surfaces of the connected light guide plate units are disposed on the same flat surface. When the distance from a surface passing through the center of the bar-shaped light source and vertical to the light emission surface to a surface passing through the center of the bar shaped light source of the adjacent light guide plate unit and vertical to the light emission surface is defined as L and when the maximum thickness of the thick part is defined as D, the formula, D/L≤0.2, is satisfied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transparent 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, a planar illumination device using the same, and a liquid crystal display Relates to the device.

  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. The backlight unit uses a light source for illumination, a light guide plate that diffuses light emitted from the light source and irradiates the liquid crystal panel, and a component such as a prism sheet and a diffusion sheet that uniformizes the light emitted from the light guide plate. Composed.

  At present, a backlight unit of a large-sized liquid crystal television is mainly used in a so-called direct type in which a light guide plate is disposed immediately above a light source for illumination (see, for example, Patent Document 1). In this method, a plurality of cold-cathode tubes as light sources are arranged on the back surface of the liquid crystal panel, and a uniform light quantity distribution and necessary luminance are ensured with the inside as a white reflecting surface. 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 backlight unit, unevenness in the amount of light occurs when the thickness of the light guide plate is 10 mm or less. For this reason, there is a limit to reducing the thickness.
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. 36 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 avoiding the light source (fluorescent lamp) 102, and the light emission surface is formed on the light emission surface. On the other hand, as shown in FIG. 37, it is urged to emit illumination light that is incident at an angle greater than the critical angle, but as shown in FIG. 37, a solid line with respect to the luminance N1 of illumination light from a light guide plate that does not have a light quantity correction surface. The effect of improving the luminance N2 of the illumination light from the light guide plate 100 having the light amount correction surface 100b shown in FIG. 5 is little, so the luminance improvement effect by the light amount correction surface 100b is not great, and the light source light utilization efficiency is low. Since the diffusion of the light source light is insufficient, there is a problem that uniform and high-intensity light cannot be emitted from the emission surface.
In the light guide plate 100 disclosed in Patent Document 3, the light source (fluorescent lamp) 102 is embedded in the groove 100a having a circular cross-sectional shape, and the luminance peak due to the light source 102 remains as shown in FIG. In order to use as a surface light source device, it is necessary to remove the unnatural luminance unevenness on the exit surface by using the transmitted light amount correction sheet 106, the light diffusion plate 108, the prism sheet 110, etc. arranged on the exit side of the light guide plate. Therefore, there is a problem that the cost of the surface light source device increases.

Further, in the backlight of the liquid crystal display device disclosed in Patent Document 4, by disposing the components on the electronic circuit board in the gap generated by tilting the back surface of the light guide plate, the liquid crystal display is inexpensive and has low power consumption. Although the apparatus can be reduced in size, weight, and thickness, the unevenness of illumination light emitted from the exit surface of the light guide plate is not considered at all.
Further, in the backlight unit of the liquid crystal display device disclosed in Patent Document 5, the cross-sectional shape of the concave portion on the groove provided in the light guide (light guide plate) is a parabola, so that light diffusion in the light guide is substantially reduced. Although light is incident on the light guide to be uniform and the light use efficiency can be increased, the unevenness of light emitted from the light exit surface of the light guide is not considered at all.
In addition, the light guide plate disclosed in Patent Document 6 has a complicated structure in which a plurality of plate-like optical waveguide plates are stacked. Therefore, it is possible to obtain a uniform brightness with less attenuation of brightness than in the past. However, there is a problem that the manufacturing cost becomes high.

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

The 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. As an image display device used for various displays such as guidance display and advertisement display, or to provide a planar lighting device that can be applied to a liquid crystal display monitor used in a personal computer or the like Another object is to provide a surface light source device for general illumination, indoors or outdoors.
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 includes a rectangular light emitting surface, and a thick wall that is parallel to one side of the light emitting surface and located at a substantially central portion of the light emitting surface. A thin-walled end portion formed in parallel with the thick-walled portion, a parallel groove for accommodating a rod-shaped light source, formed substantially in the center of the thick-walled portion in parallel with the one side, and the parallel groove The axis of the rod-shaped light source is included on both sides and is symmetric with respect to a plane perpendicular to the light emitting surface, and the thickness increases from the thick part toward the thin end on both sides in a direction perpendicular to the one side. A plurality of transparent light guide plate units that are thin and formed with an inclined back surface portion that forms an inclined back surface, and the thin end portions of adjacent light guide plate units are connected to each other, and the light output surface of the connected light guide plate unit Are arranged on the same plane and pass through the center of the rod-shaped light source and are perpendicular to the light exit surface. When the distance from the center of the bar-shaped light source of the adjacent light guide plate unit to the surface perpendicular to the light emitting surface is L and the maximum thickness of the thick portion is D, the following equation is satisfied. A light guide plate characterized by the above is provided.
D / L ≦ 0.2

Here, the relationship between the distance L between the rod-shaped light sources and the light guide plate thickness D is D / L ≦ 0.16.
Is more preferable.

  In addition, in the cross-sectional shape of the parallel groove serving as the light incident portion of the light guide plate, it is preferable that the 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 exit 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 perpendicular to the rectangular light emitting surface including the axis of the rod-shaped light source, 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 front end portions of the parallel grooves has an illuminance (relative illuminance) or luminance (relative luminance) peak value 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 engraved on at least one of the rectangular light exit surface and the pair of inclined back surface portions.
In the cross-sectional shape of the parallel groove, it is preferable that the tip portion is a portion where an angle formed by the pair of contour lines is within 90 degrees.
In the cross-sectional shape of the parallel groove, it is preferable that the tip portion is 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 portion of the tip portion of the parallel groove is a shape connected with a straight line or a curve symmetrical 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-shaped light-projection surface.

In order to solve other problems in addition to the first problem, the second form of the first aspect of the present invention is to emit the rod-shaped light source and light incident from the rod-shaped light source from a light emitting surface. In a light guide plate unit having at least a substantially flat light guide plate, St represents the total area of the light emitting surface of the rod-shaped light source, St represents the diameter of the rod-shaped light source, and light incidence of the light emitting surface of the rod-shaped light source and the light guide plate. Let T be the distance to the surface
Provided is a light guide plate unit that satisfies the following expression when Sp is the area of the light emitting surface of the rod-shaped light source that satisfies T ≦ 2R.
Sp / St ≧ 0.5

In order to solve other problems in addition to the first problem, the third mode of the first aspect of the present invention is a light guide plate of any one of the first and second modes. A light guide plate comprising a plurality of light guide plate blocks as optical plate blocks, the thin end surfaces of which are connected to each other, is provided.
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 block the parallel grooves, a reflective sheet attached to the inclined back surface of the inclined back surface on both sides of the thick portion of the light guide plate, and the rectangular shape of the light guide plate The present invention provides a planar illumination device having a diffusion sheet disposed on a shaped light exit surface.

Here, the second aspect of the present invention is the above planar illumination device, further comprising a transmittance adjusting body unit disposed between the rectangular light emitting surface of the light guide plate and the diffusion sheet. It is preferable to have.
Moreover, it is preferable to have a prism sheet disposed between the rectangular light emitting surface of the light guide plate and the diffusion sheet.
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.

According to the first aspect of the present invention, the light guide plate can be reduced in thickness and weight, and from the light emission surface, the light utilization efficiency (light emission efficiency) is high, more uniform and less uneven, and more High-luminance illumination light can be emitted.
Further, according to the first form of the first aspect of the present invention, the light guide plate can be made thinner and lighter by defining the relationship between the distance L between the rod-shaped light sources and the maximum thickness D of the light guide plate, Light utilization efficiency can be increased. However, if the thickness is too thin so as to exceed 0.6R ≦ D, the light incident efficiency on the light guide plate is lowered, which is not preferable.
Further, according to the second form of the first aspect, by defining the area adjacent to the light guide plate, the incident efficiency of light incident on the light guide plate is increased, and the light use efficiency can be increased.
According to the preferred embodiment of the first aspect of the present invention, the peak of illuminance or luminance due to the light emitted from the rod-shaped light source housed in the parallel groove in the first portion of the light exit surface corresponding to the thickness parallel groove. Depending on the ratio of the value to the average value of the illuminance or luminance of the other part, the illuminance or luminance peak is reduced by narrowing the cross-sectional shape of the parallel groove toward the tip part toward the light exit surface. The illumination distribution or the luminance on the light exit surface can be made more uniform, the luminance distribution can be made more flat, and the inclination of the cross-sectional shape of the base end portion of the parallel groove is larger than the tip portion, for example, steeply By doing so, it is possible to improve the light utilization efficiency (light emission efficiency) and achieve high uniformity and high light emission efficiency required for the light emission surface.
Further, the cross-sectional shape of the parallel grooves is directed to the light exit surface so that the peak value of the illuminance or brightness of the first portion of the light exit surface is not more than three times the average value of the illuminance or brightness of the other portions. By narrowing toward the tip, the peak of illuminance or luminance can be reduced, and the illuminance or luminance on the light exit surface can be made uniform.

Moreover, in the light guide plate having a pair of inclined rear portions parallel to the light emission surface, the light utilization efficiency (light emission efficiency) can be further improved.
In addition, in the light guide plate in which a plurality of minute prisms are engraved on at least one of the rectangular light exit surface and the pair of inclined back surfaces, a prism sheet can be dispensed with when used as a backlight. The utilization efficiency of light as a backlight (light emission efficiency) can be improved, the structure of the backlight can be made compact, and the cost can be reduced.
Moreover, according to the 3rd form of the 1st aspect of this invention, the size of the light-projection surface of a light-guide plate is larger size by connecting the thin edge part of the light-guide plate of the said 1st form mutually. It can be.

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 As an image display device that can provide an illumination device, or can provide a planar illumination device that can be applied to a liquid crystal display monitor used in a personal computer or the like, or can be used for various displays such as a guidance display and an advertisement display It can be provided, or illumination can be provided as a surface light source device for general illumination purposes indoors and outdoors.
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 In addition, a liquid crystal display monitor used for a personal computer or the like 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 shows a schematic cross-sectional view of a planar lighting device 1 (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. The light guide plate unit 2 includes a cold cathode tube 12, a diffusion sheet 14, a diffusion plate 16, a prism sheet 17, a transmittance adjuster unit 181, a light guide plate 18, a reflector 20, and a reflection plate 22. .

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

  The backlight unit 2 is a planar illumination device for irradiating the entire surface of the liquid crystal display panel 4 with uniform light from behind the liquid crystal display panel 4. The backlight unit 2 is light having substantially the same size as the image display surface of the liquid crystal display panel 4. It has an emission surface (light emitting surface). As shown in FIG. 2, the backlight unit 2 basically includes a light source 12, a diffusion sheet 14, a diffusion plate 16, a prism sheet 17, a transmittance adjuster unit 181, a light guide plate 18, A reflector 20 and a reflector 22 are included.

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.
Further, the driving of the cooling fan provided on the back surface of the backlight unit may be controlled according to the temperature detected by providing the temperature sensor. When a cold cathode tube is used, it may be driven to detect the tube current of the light source and perform luminance modulation.

  In addition, for example, a field sequential system that uses R (red), G (green), and B (blue) light sources (for example, LED light sources) and sequentially turns these light sources on in accordance with the display on the liquid crystal display panel 4. Or may be driven by an intermittent lighting method in which light is emitted or turned off sequentially or simultaneously in accordance with the 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.

When a cold cathode tube is used as the light source, an inverter constituted by a winding transformer or an inverter constituted by a piezoelectric element can be used. From the viewpoint of durability and stability, an inverter composed of a piezoelectric element can be preferably used.
Also, one end of one cold cathode tube is driven by the inverter and the other end is connected to GND (one side driving), or both ends of the cold cathode tube are driven by a signal obtained by inverting the phase of the inverter (double side driving). ), Cold cathode tubes connected in series, two ends not connected are connected to an inverter and driven with a signal whose phase is inverted (pseudo U-tube double side drive), multiple cold cathode tubes with a single inverter A simultaneous lighting method for driving the light source, or a method combining these all can be used.

Note that the above-described constituent members constituting the backlight unit 2 may be integrated with each other by being disposed in the housing 280 and being fixed from the back side of the backlight unit 2 as shown in FIG. Good. As shown in FIG. 21, the housing 280 has a box-shaped structure with one surface open, and a rectangular opening is formed on the side where the light emission surface of the backlight unit is located.
Examples of such a housing 280 include a box-shaped structure formed of resin or metal, a frame of a skeleton structure formed of metal, and a box-shaped structure formed of a rigid resin other than metal. Examples include a case or a frame having a skeleton structure, a case having a rib formed of a metal and a strong resin, and extending in a direction perpendicular to the parallel groove of the light guide plate 18.
When the constituent members of the backlight unit 2 are incorporated into the housing 280 formed of resin, as shown in FIG. 21, a claw portion 281 that sandwiches the backlight unit is provided in the housing 280, and the claw portion 281 Further, the reflection sheet 22 of the backlight unit 2 or the like can be sandwiched.

  In addition, it is desirable to use a material that is as light and strong as possible in order to reduce the weight of the surface lighting device as such a housing 280. For example, a filler such as carbon fiber resin is mixed into the resin to obtain rigidity. A material having an increased resistance can also be preferably used.

Further, the weight of the light guide plate unit 2 is preferably 6 kg or less, more preferably 4 kg or less, per 1 m ² of the light emitting surface area.
Further, the thickness of the light guide plate unit 2 is preferably 20 mm or less, and more preferably 12 mm or less.

Although FIG. 21 shows a configuration in which the constituent members constituting the backlight unit 2 are arranged in the casing 280, the backlight unit and the liquid crystal display panel may be arranged in one casing. 22 to 24 show configuration examples of a housing that accommodates the backlight unit and the liquid crystal display panel. 22 is a schematic perspective view of a casing 290 in which a backlight unit (not shown) and the liquid crystal display panel 4 are accommodated. FIG. 23 is a casing 290 in which the backlight unit 2 and the liquid crystal display panel are accommodated. FIG. FIG. 24 is a schematic enlarged sectional view of both ends of the housing 290 shown in FIG.
The housing that houses the backlight unit and the liquid crystal display panel may be configured such that the backlight unit is housed in a dedicated housing and the backlight unit and the liquid crystal display panel housed in the backlight unit housing are housed. Alternatively, the backlight unit main body and the liquid crystal display panel may be fixedly accommodated without accommodating the backlight unit in the backlight unit housing.
Further, by replacing the light guide plate itself with the housing 280, the number of constituent members may be reduced or the weight may be reduced.

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), a semiconductor laser, or the like can be used. Or a light emitting diode is preferable.
A high color rendering type cold cathode tube or LED can also be preferably used.
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.
For example, a light guide using LEDs as shown in Japanese Patent Application No. 2004-200062 can be preferably used.
Moreover, LED as described in Unexamined-Japanese-Patent No. 2005-56653 can be used preferably.
Also, point light sources such as LEDs can be used in a line.
Also, a white LED that combines blue LED and yellow light-emitting phosphor, a white light that combines blue LED and green and red light-emitting phosphor, an ultraviolet light-emitting LED and blue, green, and red light-emitting phosphor A combination of these can be preferably used.

  Further, a plurality of bar-shaped light sources can be stored and used in the bar-shaped light source storage unit.

Further, as the light source, an aperture type lamp as shown in FIG. 25A may be used. In the present invention, an aperture type lamp is a member with high reflectivity provided in a portion excluding an angle at which light is desired to be emitted, that is, a member with high reflectivity is provided in a portion where light is not emitted, and light emitted from a predetermined angle is provided. A rod-shaped light source that increases the amount of light. FIG. 25C shows a sectional view of an aperture type lamp. In FIG. 25C, a region 320 is a light emitting region. The use efficiency of light can be further improved by using an aperture type lamp. In addition, it is not always necessary to provide a reflection sheet (reflector) disposed on the back side of the light source, the apparatus configuration can be further simplified, and uneven brightness due to an attachment error of the reflection sheet can be prevented.
Here, as the member having high reflectance, various materials such as metal and nonmetal can be used, and it is particularly preferable to use a nonmetal material. By using a non-metallic material as a member having high reflectance, leakage current can be reduced.

Further, when an aperture type lamp is used, it is preferable to provide positioning means at least at one place. As the positioning means, for example, as shown in FIG. 25B, a bent portion 322 is provided in the terminal portion of the lamp, a groove 326 is formed in the support member 324 that supports the lamp, and the groove 326 of the support member 324 is bent. There is a method of fixing the lamp by inserting the portion 322. Further, the angle of the bent portion 322 provided in the terminal portion of the lamp may be any angle as long as it can be defined with respect to the parallel groove of the light guide plate, as shown in the right diagram of FIG. Further, it is preferable that the bent portion 322 is provided so that the light emitting region 320 of the aperture type lamp is divided into two equal parts. In addition, the shape of the bent portion can be any shape as long as it can fix the arrangement position of the lamp and the arrangement direction of the highly reflective member with respect to the parallel groove and does not hinder the arrangement in the parallel groove. It may be in shape.
As described above, by providing the positioning means, it is possible to easily align the center of the opening of the light source and the center of the parallel groove of the light guide plate, and it is possible to efficiently make light incident on the light guide plate.

In the present invention, as shown in FIG. 26, when the light source is arranged in the parallel groove 18f of the light guide plate 18, the light source 12 and the parallel groove 18f formed in the light guide plate 18 are not in direct contact with each other. The light source 12 may be disposed in the parallel groove 18 of the light guide plate 18f by partially providing ribs 330 or the like in the parallel groove 18f of the light guide plate 18.
By adopting such a configuration, heat generated in the light source 12 is suppressed from being directly transmitted to the light guide plate 18, an excessive temperature rise of the light guide plate 18 is suppressed, and a cold cathode tube as a light source is partially provided. The cooling is avoided. For example, the rib 330 can have a convex shape with a width of 1 mm or less and a height of about 0.5 mm, and is partially provided in the center line direction of the parallel groove 18 f of the light guide plate. preferable.
Further, an opening may be provided on the side surface of the backlight unit corresponding to an extension line of the parallel groove of the light guide plate 18 in the center line direction, and the light source 12 may be exchanged through the opening. By doing so, it is possible to make it easy to replace the light source when the light source 12 is at the end of its life or failure, and not to separately provide a guide member for replacing the light source 12.

  In order to regulate the position of the light source 12 with respect to the reflection sheet 22, the reflection sheet 22 is formed of a rigid metal material or resin material, and the reflection sheet 22 and the light guide plate 18 including the light source 12 are integrated. It is preferable. At that time, as shown in FIGS. 27A to 27D, either one of the light guide plate 18 and the reflection sheet 22 is provided with a concave portion and the other provided with a convex portion, or is fixed by a screw. Alternatively, the light guide plate 18 and the reflection sheet 22 may be integrated.

It is known that when the reflective sheet 22 is formed of a metal material in order to ensure sufficient rigidity for reducing the thickness of the backlight unit, stray capacitance is generated depending on the combination of the metal material and the cold cathode tube. ing. On the other hand, stray capacitance can be reduced by providing an elongated hole in the portion of the reflective sheet that opposes the cold cathode tube.
It is also preferable to reduce the stray capacitance by increasing the distance from the cold cathode tube using a backlight frame having a shape as shown in FIG.

In FIG. 2, a diffusing plate 16 is for diffusing and making uniform 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 pigments such as silica, titanium oxide, and zinc oxide that scatter light on the surface, or beads such as resin, glass, zirconia, etc., together with a binder, or the above-mentioned pigments and beads that scatter light into the above resin It is formed by kneading a kind. 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 diffusing plate 16 is preferably disposed at a predetermined distance from the light exit surface 18a of the light guide plate 18, and the distance can be appropriately changed according to the light amount distribution from the light exit surface 18a of the light guide plate 18. Thus, by separating the diffusing plate 16 from the light emitting surface 18a of the light guide plate 18 by a predetermined distance, light emitted from the light emitting surface 18a of the light guiding plate 18 is further between the light emitting surface 18a and the diffusing plate 16. Mixed (mixed). Thereby, the brightness | luminance of the light which permeate | transmits the diffusion plate 16 and illuminates the liquid crystal display panel 4 can be made further uniform. As a method of separating the diffusion plate 16 from the light exit surface 18a of the light guide plate 18 by a predetermined distance, for example, a method of providing a spacer between the diffusion plate 16 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. It is not necessary to reduce the brightness sufficiently, and the brightness distribution of the illumination light emitted from the diffusion plate 16 is made uniform by partially reducing and providing a gap between the diffusion plate 16 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 plate 16 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 plate 16 uniform. Also good.
Moreover, the thickness of the diffusion plate 16 can be increased to make the luminance distribution uniform.

  The prism sheet 17 is a transparent sheet formed by arranging a plurality of prisms in parallel. The prism sheet 17 can improve the light collecting property of the light emitted from the light exit surface 18a of the light guide plate 18 to improve the luminance. . The prism sheet 17 is disposed so that the extending direction of the prism row is parallel to the parallel groove 18 f of the light guide plate 18.

  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 and 3B, a prism sheet 19 is also provided between the reflective sheet 22 and the inclined surface 18d opposite to the light exit surface 18a of the light guide plate 18. be able to. 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. It is the schematic plan view and schematic cross-sectional view which looked at the prism sheet 19 arrange | positioned between 18 d of inclined surfaces of the light-guide plate 18 from the light-guide plate side. The prism sheet 19 provided between the reflection sheet 22 and the inclined surface 18d of the light guide plate 18 is disposed so that the extending direction of the prism 19a is perpendicular to the parallel groove 18f of the light guide plate 18, and the prism 19a. It is preferable to arrange so that the apex angle of the light guide plate 18 faces the inclined surface 18 d of the light guide plate 18.

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

  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 addition, the reflectance of the reflection sheet can be distributed, and the emission pattern can be controlled to suppress the occurrence of luminance unevenness.

  Further, the backlight unit in the present invention is not limited to the configuration shown in FIGS. 2A and 2B, and for example, in order to improve the luminance of light emitted from the light guide plate 18, a reflective polarizing film Further, a brightness enhancement sheet such as a cholesteric polarizing film or a scattering polarizing film can be provided. Such a brightness enhancement sheet is preferably arranged between the light guide plate 18 and the liquid crystal display panel 4 (lower surface polarizing plate) in FIGS. 2A and 2B, and in particular, the liquid crystal display panel 4 (lower surface polarization). It is preferable to arrange on the light incident side surface of the plate.

In the present invention, an optical compensation film for widening the viewing angle can also 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.
Moreover, the surface treatment for the purpose of preventing reflection or an antireflective film can be used in combination.

  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, the prism sheet, and the brightness enhancement sheet 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, the diffusion plate 16, and the prism sheet 17 are disposed between the light guide plate 18 and the liquid crystal display panel 4 as described above. However, the configuration of these optical components is not limited to such a configuration example, and for example, the following configuration can be adopted. 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 brightness enhancement sheet 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 brightness enhancement sheet may 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 brightness enhancement sheet are arranged in this order on the light exit surface side of the light guide plate. You can also In this case, since a halftone dot is formed on the light exit surface of the light guide plate, a diffusion sheet without a halftone dot 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, and one brightness enhancement sheet are provided. It is also possible to adopt a configuration in which the are sequentially arranged. Further, a configuration may be adopted in which two diffusion sheets and one luminance enhancement sheet are sequentially arranged on the light exit surface side of the 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 components is small and the manufacturing cost can be reduced, a halftone dot is formed by printing on the light exit surface of the light guide plate, and the diffusion sheet and the brightness enhancement sheet 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.

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 slanted surface 18d, with a thickness decreasing toward the thin-walled end portions 18c on both sides in a direction perpendicular to the one side from the thick-walled 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 on the surface, and is formed of a transparent resin. One surface of the light guide plate 18 is flat to form a light emission surface 18a, and the other surface is formed so that the thickness of the light guide plate 18 decreases toward the one side from the thick portion 18b to both sides. The pair of inclined surfaces 18d are inclined with respect to one surface. Here, the inclined surface 18d is formed as a flat surface, but may be a curved surface.
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 utilization efficiency.

The light guide plate 18 can be manufactured using, for example, a method in which a heated raw material resin is molded by extrusion molding or injection molding, a casting polymerization method in which a monomer, an oligomer, or the like is polymerized in a mold. Examples of the material of the light guide plate 18 include acrylic resins such as PMMA (polymethyl methacrylate), PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, and MS resin. Other acrylic resins or transparent resins such as COP (cycloolefin polymer) can be used. The transparent resin may be mixed with fine particles for scattering light, whereby the light emission efficiency from the light exit surface 18a can be further increased. When fine particles for scattering light are mixed into the transparent resin, the fine particles may be isotropic or anisotropic.
Moreover, the scatterer-containing material used in Japanese Patent Application No. 2005-093997 can also be preferably used.

  It is also possible to adjust the color tone of the emitted light by mixing a color tone correction agent into the light guide plate. In addition, a color correction filter may be provided to correct the color tone of light incident on the liquid crystal display panel, instead of mixing the color tone correction agent into the light guide plate. Furthermore, a light guide plate mixed with a color correction agent and a color correction filter for correcting the color tone can be used in combination.

  Further, nano-sized phosphors as described in JP-A Nos. 2004-292282 and 2005-68326 can be used by mixing them in the light guide plate material. By using a light source having an excitation wavelength of a nano-sized phosphor, light can be emitted uniformly within the light guide.

Here, it is preferable to use a material that easily transmits blue for the transparent member used for the light guide plate. For example, when the light source is a rod-shaped light source such as a cold cathode tube, the color temperature of the light emission surface of the liquid crystal display panel is lower than the color temperature of the light source due to the spectral characteristics of the transmissive member. For this reason, it is necessary to set the color temperature of the light source higher in advance. However, if the color temperature of the light source is set high, the luminance efficiency may decrease. By using a material that easily transmits blue for the transparent member used for the light guide plate, the color temperature of the light source and the color temperature of the liquid crystal display surface can be made equal. As a result, high-luminance light emitted from the light source can be emitted from the liquid crystal display panel without lowering the color temperature. As a result, the power consumption can be further reduced, the light source can have a longer life, and the number of light sources and the number of inverters can be reduced to reduce the cost.
Moreover, you may apply | coat a static elimination material or a electrically conductive material to the light-projection surface side of a light-guide plate. Thereby, dust can be made difficult to accumulate inside the backlight due to static electricity.

The light guide plate 18 has a distance L shown in FIG. 39 and a maximum thickness of the thick portion D, where D / L ≦ 0.2, but D / L ≦ 0.16. preferable.
Further, 0.6R ≦ D is preferable, and R ≦ D is more preferable.
Further, the distance from the center line of the rod-shaped light source 12 to the light guide plate light exit surface is preferably 5 mm or less, and more preferably 3.5 mm or less.

As shown in FIG. 40, the total area of the light emitting surface of the rod-shaped light source is St, the diameter of the rod-shaped light source is R, and the distance from the light emitting surface of the rod-shaped light source to the light incident surface of the light guide plate. T
When the area of the light emitting surface of the rod-shaped light source satisfying T ≦ 2R is represented by Sp, it is desirable to satisfy Sp / St ≧ 0.5, and it is more desirable to satisfy Sp / St ≧ 0.7.

このように、本発明の範囲内だと、輝度が非常に高いことがわかる。
また、厚みをあまり下げすぎると試料４，５のようにむしろ効率が下がることが判る。 Table 1 shows the results when the thickness D of the light guide plate, the distance L of the light source, and the adjacent distance between the light source and the light guide plate are changed, and Table 2 shows the results when Sp / St is changed.

Thus, it can be seen that the luminance is very high within the scope of the present invention.
It can also be seen that if the thickness is reduced too much, the efficiency rather decreases as in Samples 4 and 5.

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.

  Here, the cross-sectional shape of the parallel groove 18f is a home base shape in which the tip portion forms a triangle and the base end portion forms a rectangle. However, the present invention is not limited to this, and the tip portion is inclined. Any shape may be used as long as the inclination of the base end portion connected to the tip end portion is steeper than the inclination of the tip 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. 4 (a), the pair of tip surfaces 40 of the parallel grooves 18f have a hyperbolic shape, and as shown in FIG. 4 (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. 4 (c), the cross-sectional shape of the pair of tip surfaces 50 of the parallel grooves has a sharp intersection with each other, and the center is perpendicular to the light exit surface of the light guide plate through the center of the parallel grooves 18f. 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. 4 (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. 4C, 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 portion 52 where the arc-shaped side walls intersect each other has a sharp shape as shown in FIG.

  Also, in FIG. 4D, the cross-sectional shape of the pair of tip 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. 4D 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. 4 (d), a pair of front end 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. 4D, 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 FIGS. 1 to 4 (d), in the cross-sectional shape of the parallel groove, an example of a light guide plate in which a curve forming a pair of front end surfaces of the parallel groove is concave toward the center of the parallel groove is shown. FIGS. 5A and 5B show another embodiment of the light guide plate of the present invention different from FIG. FIG. 5A 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. 5 (b), the cross-sectional shape of the pair of tip surfaces 63 of the parallel groove 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. 5A and 5B can also emit light with sufficient luminance from the light exit surface while suppressing the generation of bright lines.

  In FIG. 1 to FIG. 5B, 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 base 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 18h. Remote it may be formed by a line segment (hypotenuse) having a slope of acute predetermined angle. 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 be used. As shown in FIG. 6B, 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 °.

  In addition, in the light guide plate shown in FIG. 1 to FIG. 6B, 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. 7, 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. 8, 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). For example, the halftone dot pattern 92 having a low value may be formed on the light exit surface 18a of the light guide plate 18 by printing as the transmittance adjusting unit 181. 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.
In addition, designing the transmittance adjusting unit 181 in accordance with the method of Japanese Patent Application No. 2004-258340 can be preferably used in the sense of efficiently suppressing luminance unevenness.
In order to suppress color unevenness, it is also preferable to form a halftone dot pattern using ink that has been adjusted to the color of the light source.
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, the number of sheets used, etc. of the prism sheets 16, 17 and 19. That is, when the thickness of the backlight unit 2 (the distance between the light exit surface 18 a of the light guide plate 18 and the diffusion sheet 14) can be increased to a certain extent (or larger), or the diffusion sheet 14 used in the backlight unit 2. When the diffusion efficiency is high and the number of used sheets can be increased, or when the diffusion efficiency of the prism sheets 16, 17 and 19 is high and the number of used sheets can be increased, the illumination light emitted from the light exit surface 18a of the light guide plate 18 can be increased. Diffusion (mixing, etc.) can be performed sufficiently, so that the cost is high. However, the second light emission surface 18a of the light guide plate 18 with respect to the average value of the luminance of the second portion of the light output surface 18a of the light guide plate 18 can be obtained. The ratio of the luminance peak values of one portion can be set large to some extent. However, if this is not the case, the cost can be reduced, but the value of this ratio needs to be set small.

  On the other hand, 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 ( Mixing, etc.) does not need to be performed sufficiently, and a low-cost diffusion sheet 14 having a low diffusion efficiency can be used, the number of sheets used can be reduced, and expensive prism sheets 16, 17 and 19 can be used. This is because the use of the prism sheets 16, 17 and 19 with low diffusion efficiency can be used or the number of sheets used can be reduced.

  In the 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.
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. 9A, the cross-sectional shape of the tip surface 18h is perpendicular to the light exit surface 18a and has a predetermined angle with respect to a line passing through the center of the light source 12. It is formed by a line segment having an inclination (the hypotenuse), and the cross-sectional shape of the base end surface 18i is formed by a line segment that is in contact with the tip surface 18h and the parallel surface 18g and is perpendicular to the light exit surface 18a, and the top portion has a curved surface shape. It is formed. Further, the parallel surface 18g is an intersection of a line obtained by extending the line segment of the front end surface 18h of the parallel groove 18 and a line parallel to the light emitting surface and passing through the lower end of the light guide plate, and a pair of base end surfaces of the parallel groove It is provided between the lower end of.
Here, the light guide plate 18 shown in FIG. 9A has a diameter of the light source 12 of 3 mm, an inclination angle of the front end surface 18h with respect to a line perpendicular to the light exit surface 18a and passing through the center of the light source 12, and 30 degrees. The top curved surface 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 grooves 18f shown in FIG. Here, in the light guide plate 18 shown in FIG. 9B, the cross-sectional shape of the side surface 74 of the parallel groove 18f, that is, the pair of distal end surfaces and the pair of proximal end surfaces is a shape formed by only the oblique sides. Except for this, it has the same shape as the light guide plate shown in FIG.

FIG. 10 (a) shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. 9 (a) and the light guide plate shown in FIG. 9 (b). In FIG. 10A, 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. 9A 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. 9B is indicated by a dotted line.

As can be seen from FIG. 10 (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. 9 (a) is the brightness on the light exit surface of the light guide plate shown in FIG. 9 (b). Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 9A can emit light with reduced brightness unevenness, compared to the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the output efficiency of the light guide plate having the shape shown in FIG. 9A is 65.9%, and the light guide plate having the shape shown in FIG. The emission efficiency of was 59.7%. Moreover, the incident efficiency of the light guide plate having the shape shown in FIG. 9A was 84.0%, and the incident efficiency of the light guide plate having the shape shown in FIG. 9B was 95.5%. As described above, the light guide plate shown in FIG. 9A can have higher emission efficiency and incidence efficiency than the light guide plate shown in FIG. 9B.

As another example of the light guide plate of the present invention, as shown in FIG. 9C, a pair of base end surfaces 70 of parallel grooves is 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. 9A 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. 10B shows a luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 10B, 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. 9C 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. 9B is shown by a dotted line for comparison.

As can be seen from FIG. 10 (b), 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. 9 (c) is the brightness on the light exit surface of the light guide plate shown in FIG. 9 (b). Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 9C can emit light with reduced luminance unevenness more than that of the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the output efficiency of the light guide plate having the shape shown in FIG. 9C was 61.9%. In this way, the light guide plate shown in FIG. 9C can have higher emission efficiency than the light guide plate shown in FIG. 9B.

As still another example of the light guide plate of the present invention, as shown in FIG. 9 (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. 9 (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 a light guide plate having the same shape as the light guide plate in FIG.
FIG. 10C shows a luminance distribution on the light emitting side surface of the light guide plate shown in FIG. In FIG. 10C, 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. 9D 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. 9B is indicated by a dotted line for comparison.

As can be seen from FIG. 10 (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. 9 (d) is the brightness on the light exit surface of the light guide plate shown in FIG. 9 (b). Is substantially the same as the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 9 (d) can emit light with reduced luminance unevenness equivalent to the light guide plate shown in FIG. 9 (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 having the shape shown in FIG. 9D was 61.5%. As described above, the light guide plate shown in FIG. 9D can have the emission efficiency higher than that of the light guide plate shown in FIG.

As still another example of the light guide plate of the present invention, the cross-sectional shape of the pair of base end faces 72 of the parallel groove 18f shown in FIG. 9 (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. 10D shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 10D, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents 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. 9 (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. 9 (b) is shown by a dotted line for comparison.

As can be seen from FIG. 10 (d), 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. 9 (e) is the brightness on the light exit surface of the light guide plate shown in FIG. 9 (b). Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 9 (e) can emit light with less uneven brightness than the light guide plate shown in FIG. 9 (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. 9E was 70.9%. Thus, the light guide plate shown in FIG. 9 (e) can have higher emission efficiency than the light guide plate shown in FIG. 9 (b).

  As described above, from FIGS. 10A to 10D, 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 luminance unevenness as compared with the prior art. 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. 11 (a) to 11 (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. 11A is not provided with 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. Further, the light guide plate shown in FIGS. 11B and 11C also does not have a parallel surface, changes the inclination angle of the inclined surface 80, and the pair of base end surfaces 70 or 18i ′ of the parallel groove 18f and the inclined surface. Except for being directly connected to 80, it has the same shape as the light guide plate shown in FIG. 9C and FIG. 9D, respectively.

FIGS. 12A to 12C show the luminance distributions on the light emitting side surfaces of the light guide plates shown in FIGS. 11A to 11C, respectively. 12A to 12C, the vertical axis represents luminance [cd / m ² ], and the horizontal axis represents the distance [mm] from the light guide plate center (the central portion of the parallel groove). 12 (a) to 12 (c) show the luminance distribution on the light exit surface of the light guide plate shown in FIGS. 11 (a) to 11 (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. 12 (a) to 12 (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. 9 (b). Moreover, as a result of calculating the emission efficiency of the light guide plate from the calculated luminance distribution, the emission efficiency of the light guide plate shown in FIG. 11A is 61.5%, and the emission efficiency of the light guide plate shown in FIG. The light emission efficiency of the light guide plate shown in FIG. 11C 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.9 (b).
As described above, from FIGS. 12A to 12C, the parallel grooves of the light guide plate are formed in the shape of the present invention, so that the shape of the parallel grooves is 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 luminance distribution of the light emitted from the light exit surface of the light guide plate in which the cross-sectional shape of the pair of front end surfaces of the parallel grooves of the light guide plate shown in FIGS. 13 (a) to 13 (d) is a hyperbolic shape is examined. It was.
Here, the light guide plate 18 shown in FIG. 13A is the same as the light guide plate shown in FIG. 9A 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. 13B is a figure except that one of the side surfaces 78 of the parallel grooves 18f, that is, the cross-sectional shapes of the front end surface and the base end surface are each formed by one hyperbola. The shape is the same as that of the light guide plate shown in FIG.

FIG. 14 (a) shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. 13 (a) and the light guide plate shown in FIG. 13 (b). In FIG. 14A, 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. 13A 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. 13B is indicated by a dotted line.

As can be seen from FIG. 14 (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. 13 (a) is the brightness on the light exit surface of the light guide plate shown in FIG. 13 (b). Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 13A can emit light with reduced luminance unevenness more than that of the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the light emission efficiency of the light guide plate from the calculated luminance distribution, the light output efficiency of the light guide plate having the shape shown in FIG. 13A 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. 13A 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 faces 76 of the parallel grooves 18f 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. 14B shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 14B, 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. 13C 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. 13B is indicated by a dotted line for comparison.

As can be seen from FIG. 14B, the difference between the maximum value and the minimum value on the light exit surface of the light guide plate shown in FIG. 13C, 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. 13C 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. 13C was 59.1%. As described above, the light guide plate shown in FIG. 13C 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. 13D, the cross-sectional shape of a pair of base end faces of the parallel grooves is a concave curve toward the center of the parallel grooves. Then, the luminance distribution of the light emitted from the light exit surface was examined for the light guide plate having the same shape as the light guide plate in FIG.
FIG. 14C shows the luminance distribution on the light exit side surface of the light guide plate shown in FIG. In FIG. 14C, 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. 13D 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. 13B is shown by a dotted line for comparison.

As can be seen from FIG. 14 (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. 13 (d) is the brightness on the light exit surface of the light guide plate shown in FIG. 13 (b). Is smaller than the difference between the maximum and minimum values. That is, the light guide plate shown in FIG. 13D can emit light with reduced luminance unevenness more than that of the light guide plate shown in FIG. That is, the luminance on the light exit surface can be made more uniform.
Moreover, as a result of calculating the emission efficiency of the light guide plate from the measured luminance distribution, the emission efficiency of the light guide plate having the shape shown in FIG. 13 (d) was 67.8%. Thus, the light guide plate shown in FIG. 13 (d) can have higher emission efficiency than the light guide plate shown in FIG. 13 (b).
As described above, from FIGS. 14A to 14D, the parallel grooves of the light guide plate have the shape of the present invention, so that the shape of the parallel grooves can be a hyperbola shape that can reduce unevenness in luminance as compared with the prior art. 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, as shown in FIGS. 15 (a) and 15 (b), a pair of base end surfaces and inclined surfaces of the parallel grooves are directly connected to each other, and 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. 15A is not provided with a parallel surface, except that the inclined angle of the inclined surface is changed and the pair of base end surfaces and the inclined surface of the parallel groove are directly connected to each other. The shape is the same as that of the light guide plate shown in FIG. Further, the light guide plate shown in FIG. 15 (b) also does not provide a parallel surface, except that the inclined angle of the inclined surface is changed and the pair of base end surfaces of the parallel groove and the inclined surface are directly connected, respectively. The shape is the same as that of the light guide plate shown in FIG.

FIGS. 16A and 16B show the luminance distributions on the light exit side surfaces of the light guide plate shown in FIGS. 15A and 15B, respectively. 16A and 16B, 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. 16 (a) and 16 (b) show the luminance distribution on the light exit surface of the light guide plate shown in FIGS. 15 (a) and 15 (b) with a solid line, and FIG. 13 (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 of the light guide plates shown in FIGS. 16A and 16B, the luminance unevenness can be equal to or less than that of 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. 15A 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 radiation | emission efficiency rather than the light-guide plate shown in FIG.13 (b).
As described above, according to FIGS. 16A and 16B, the parallel groove of the light guide plate has the shape of the present invention, and the shape of the parallel groove has a hyperbolic 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.

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 so that all the light exit surfaces 18a of the light guide plate 18 form the same plane, as shown in FIG. In addition, a tangential line at the contact point between the inclined surface 18d of one light guide plate 18 and the inclined surface 18d 'of the other light guide plate 18' connected thereto is not crossed, that is, a smooth flat surface at the connecting portion of the inclined surfaces. Alternatively, the inclination angle of the inclined surface 18d of the light guide plate 18 can be adjusted so that a curved surface is formed. In the light guide plate shown in FIG. 17, the surfaces formed by the inclined surfaces 18 d and 18 d ′ 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. Is preferably shaped so as to make the luminance distribution 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-projection 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 arrange the halftone dot sheet 350 on which the halftone dots to be formed are covered so as to cover the light emission surfaces of the connected light guide plates 18. Such a halftone dot sheet 350 can have various sizes according to the number of light guide plates 18 to be connected. The halftone dots of the halftone dot sheet 18 are generated as bright lines on the light emitting surface of the light guide plate 18. Placed in position.
As the material of such a halftone dot sheet 350, 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 may be used from the viewpoint of suppressing the influence of thermal change. preferable. 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 positioned, for example, a positioning hole is formed in a region not used as a light emitting region on the light emitting surface of the light guide plate and a halftone dot sheet corresponding to the position. It is preferable. 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. In the case where a plurality of light guide plates 18 are arranged, as shown in FIG. 18B, 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.

  Further, as shown in FIGS. 29A and 29B, a reflection plate 362 made of the same material as that of the reflection sheet 22 and the reflector described above is disposed on the side surface in the longitudinal direction of the light source 12 of the light guide plate 18. Also good. Thereby, the emission efficiency can be further improved, and furthermore, the luminance unevenness at the end of the light guide plate 18 in the longitudinal direction of the light source 12 can be reduced.

  Further, when the luminance distribution of the light source is not flat in the longitudinal direction of the light source, there is a method of adjusting the shape of the parallel grooves of the light guide plate, particularly the angle of the tip portion, according to the position in the longitudinal direction of the light source. For example, in the case where the luminance of the light source increases in the longitudinal direction of the light source as it goes from the end toward the center, as shown in FIGS. It is good also as a shape where the angle of the front-end | tip part of the parallel groove 18f of the light-guide plate 18 becomes large toward the center part (refer FIG.30 (c)) from an edge part (refer FIG.30 (b) and FIG.30 (d)). .

  On the other hand, the luminance distribution of the light source is not flat in the direction parallel to the light exit surface of the light guide plate and orthogonal to the longitudinal direction of the light source, or the brightness distribution of light emitted from the light exit surface of the light guide plate is not flat. In such a case, the arrangement interval of the plurality of light sources may be changed, that is, the width of each light guide plate may be adjusted according to the arrangement position. For example, when the brightness increases in the direction parallel to the light exit surface and perpendicular to the longitudinal direction of the light source, from the end to the center of the light guide plate, as shown in the lower diagram of FIG. It is good also as a shape where the space | interval of arrangement | positioning of the light source 12 becomes narrow, so that it leaves | separates from the center of the light-guide plate 18 in the direction parallel to the light-projection surface 18a of the light plate 18, and orthogonal to the longitudinal direction of the light source 12.

  Further, the light emission surface of the light guide plate is a curved surface shape having a curved cross-sectional shape on a surface orthogonal to the longitudinal direction of the light source, and is parallel to the light emission surface and orthogonal to the longitudinal direction of the light source. The luminance distribution or the luminance distribution of light emitted from the light exit surface of the light guide plate may be flattened. For example, when the luminance increases in the direction parallel to the light exit surface and perpendicular to the longitudinal direction of the light source, from the end to the center of the light guide plate, the light guide plate 18 is used as the light source as shown in FIG. In the direction parallel to the light emission surface of the light guide plate 18 and perpendicular to the longitudinal direction of the light source, the light guide plate is formed as an r-shaped curved surface having a cross-sectional shape that is convex toward the light source 12 side. It is good also as a shape where the distance of the light source arrange | positioned at each light-guide plate and the liquid crystal display panel 4 leaves | separates as it goes to the center part from the edge part.

Further, when the luminance distribution in the vicinity of the end portion in the longitudinal direction of the light source is different from the other portions, the end portion 402 of the light guide plate 18 in the longitudinal direction of the light source 12 is connected to the light guide plate 18 as shown in FIG. It is good also as a shape which has the inclination of a predetermined angle from the direction perpendicular | vertical with respect to the light emission surface. Further, the case where the luminance distribution in the vicinity of the end portion of the light guide plate in the direction parallel to the light emission surface and orthogonal to the longitudinal direction of the light source is different from the other portions is also shown in FIGS. 33 (b) and 33 (c). As described above, the end portion of the light guide plate that is parallel to the light emission surface and orthogonal to the longitudinal direction of the light source may have a shape having an inclination of a predetermined angle from a direction perpendicular to the light emission surface of the light guide plate. .
Thus, uniform light can be emitted from the light exit surface by adjusting the shape of the light guide plate according to the light source.

  Further, when the thickness of the backlight can be increased, the light exit surface of the light guide plate 18 is a gently curved surface having a longitudinal cross-sectional shape of the light source 12 as shown in FIG. A rib 412 having a minute height extending in a direction orthogonal to the longitudinal direction of the light source 12 may be provided on the light exit surface of the light guide plate 19 as shown in FIG. Thereby, the bending of the light guide plate in the direction orthogonal to the longitudinal direction of the light source can be prevented. Further, the rib 412 also functions as a spacer that forms a predetermined gap between the light guide plate 18 and a sheet-like member that constitutes a backlight unit such as a diffusion sheet, and further increases the illuminance of light that illuminates the liquid crystal display panel. It can be made uniform.

Further, as shown in FIG. 35, the position of the light source is regulated or temporarily fixed by attaching a reflection sheet to the inclined surface of the light guide plate 18 and extending the reflection sheet to the parallel grooves of the light guide plate. May be.
By restricting the position of the light source, the position of the light source with respect to the light guide plate becomes constant, and luminance unevenness can be reduced. Moreover, the assembly property of the backlight unit can be improved by temporarily fixing the light source.

  As shown in FIG. 35, when a cold cathode tube is used as a light source, an elastic member that holds the cold cathode tube, for example, a transparent O-ring, may be provided at the end of the cold cathode tube. By providing such an elastic member, the elastic member acts as a buffer, so when the cold cathode tube is placed in the parallel groove of the light guide plate, the cold cathode tube collides with the parallel groove and the cold cathode tube is damaged. Can be prevented. Further, by fixing the elastic member to the cold cathode tube, handling in the assembly and manufacturing process is improved.

  In addition, by holding the end of the cold cathode tube in the longitudinal direction with a sponge or the like and closing the side surface in the longitudinal direction of the parallel groove of the light guide plate, dust can enter the parallel groove of the light guide plate from the outside. It is also possible to prevent the cold cathode tube from being partially cooled.

In the embodiment shown in FIGS. 1 to 3, the prism sheet is disposed on the light exit surface side of the light guide plate and / or between the inclined surface of the light guide plate and the reflection sheet, but the present invention is not limited to this. First, a prism whose groove is parallel to the axis of the rod-shaped light source directly on the surface of the light guide plate excluding the side surfaces (a pair of front end surfaces and a pair of base end surfaces) of the parallel grooves, for example, the light exit surface and / or the inclined surface. It may be engraved.
For example, the prism 25 may be directly formed on the inclined surface 18d of the light guide plate 18 as shown in FIGS. 19A and 19B, and the prism 26 is formed on the light exit surface 18a of the light guide plate 18 as shown in FIG. And the prism 25 may be formed on the inclined surface 18d.
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 contour line 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 slope of the base end face with respect to the slope of the front end face such as a triangle as shown in FIG. 9B and a hyperbola as shown in FIG. In the case of using a light guide plate having a shape that is not sharp and a shape in which the tip shape on the light emitting 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 formed on the inclined surface preferably has an apex angle θ _p1 of 100 ° ≦ θ _p1 ≦ 140 °. The prism formed on the light exit surface preferably has an apex angle θ _p2 of 40 ° ≦ θ _p2 ≦ 70 °. By setting the apex angle θ _p1 and apex angle θ _p2 of the prism to be formed within the above ranges, the emission efficiency as the planar illumination device can be improved more suitably.

The usage of the planar light source device of the present invention is not limited to a backlight unit for a liquid crystal display device for a large television.
For example, it can be preferably used as a backlight unit of an image display device used for various displays such as guidance display and advertisement display.
Moreover, illumination can be preferably used indoors and outdoors as a surface light source device for general illumination purposes.
It is also preferable to emit light other than white, such as blue, green, and red, and use it for indirect illumination or the like.

The shape of the light exit surface of the backlight unit of the present invention is not limited to a square, and for example, a circular shape, a triangular shape, or an arbitrary shape can be selected.
Further, the light guide plate of the present invention can be curved into a cylindrical shape and used as, for example, a cylindrical planar light source.

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 and schematic cross-sectional view which looked at the arrange | positioned prism sheet from the light-guide plate side. (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 bases of the parallel groove End face break Shape is a schematic cross-sectional view of parallel grooves around the concave of the light guide plate formed with a curve toward the center of the parallel groove. (A)-(d) are the luminance distribution of the light radiate | emitted from the light-projection surface of the light-guide plate shown to Fig.9 (a), FIG.9 (c), FIG.9 (d), and FIG.9 (e), respectively. It is a graph which shows. (A)-(c) is a schematic block diagram of the parallel groove periphery of a light-guide plate when not providing the parallel surface of the light-guide plate shown to Fig.9 (a), FIG.9 (c), and FIG.9 (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.11 (a), FIG.11 (b), and FIG.11 (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.13 (a), FIG.13 (c), and FIG.13 (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.13 (a) and FIG.13 (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.15 (a) and FIG.15 (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. It is a schematic sectional drawing which shows a mode that the prism is formed in the inclined surface and light-projection surface of a light-guide plate. It is a schematic block diagram of the housing | casing which accommodates a backlight unit. It is a typical perspective view of the housing | casing in which the backlight unit and the liquid crystal display panel were accommodated. It is typical sectional drawing of the housing | casing in which the backlight unit and the liquid crystal display panel were accommodated. It is a typical expanded sectional view of the both ends of the housing | casing shown in FIG. (A) is a schematic sectional drawing which shows an example of the light source used for the backlight unit of this invention, (b) is a schematic perspective view which shows an example of the positioning means of a light source, (c) is (a) It is a schematic sectional drawing of the light source shown to (b). It is a schematic diagram of the light-guide plate in which the rib for preventing a light source and a parallel groove from contacting a parallel groove directly was formed. (A) And (b) is the top view and side view which respectively showed typically the structure which integrated the reflecting sheet and the light-guide plate containing a light source, (c) is C of (a). It is a -C line arrow view, (d) is a DD line arrow view of (a). It is a figure for demonstrating the structure which integrated the reflection sheet and the light-guide plate containing a light source. It is a schematic diagram which shows a mode that the halftone dot sheet | seat in which the halftone dot was formed was arrange | positioned so that the light emission surface of the connected several light-guide plate might be covered. (A) is a structural example which has arrange | positioned the reflecting plate in the longitudinal direction side surface of the light source of the light-guide plate of this invention, (b) is sectional drawing of (a). (A) is a schematic perspective view which shows another example of the light-guide plate of this invention, (b) is BB sectional drawing of (a), (c) is C of (a). It is -C sectional view, (d) is the DD sectional view taken on the line (a). It is a schematic sectional drawing which shows another example of the light-guide plate which connected two or more light-guide plates from which width differs. It is a schematic sectional drawing which shows an example of the light-guide plate whose light-projection surface has r shape. (A) is a schematic sectional drawing which shows an example of the shape where the edge part of the light-guide plate in the longitudinal direction of a light source has inclination, (b) is parallel to a light-projection surface, and orthogonal to the longitudinal direction of a light source. It is a schematic perspective view which shows an example of the shape where the edge part of the light-guide plate of a direction has an inclination, (c) is CC sectional view taken on the line of (b). (A) is a schematic perspective view which shows an example of the light-curved light-guide plate of the gently curved surface shape where the longitudinal cross-sectional shape of the light source of a light emission surface becomes a curve, (b) is a longitudinal direction of a light source in light emission surface shape. It is a schematic perspective view which shows an example of the light-guide plate which has the rib of the minute height extended in the direction orthogonal to a direction. It is the schematic perspective view which looked at the backlight unit from the back side. 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. It is a schematic perspective view of a backlight frame. It is a schematic sectional drawing which shows the cross-sectional shape perpendicular | vertical to the length direction of a pair of front end surface of the parallel groove | channel of the light guide plate of this invention. It is a schematic sectional drawing of the parallel groove periphery which demonstrated Sp using the cross-sectional shape perpendicular | vertical to the length direction of a pair of front end surface of the parallel groove | channel of the light guide plate of this invention.

Explanation of symbols

2 Backlight unit 4 Liquid crystal display panel 6 Drive unit 10 Liquid crystal display device 12 Light source 14 Diffusion sheet 16 Diffusion plate 17, 19 Prism sheet 18 Light guide plate 18a, 52 Light exit surface 18b Thick portion 18c Thin end portion 18d Inclined surface 18e, 80 Inclined back surface portion 18f Parallel groove 18g Parallel surfaces 18h, 18h ', 40 One pair of tip surfaces 18i, 18i', 70, 72, 76 One pair of base end surfaces 181 Transmittance adjusting body unit 20 Reflector 22 Reflective sheet 24 Reflector 25, 26 Prism 54a, 54b Arc curve 56 Intersection 64a, 64b Parabola 72a, 72b, 82a, 82b, 84a, 84b Curve 74, 78 Side surface 92 Halftone dot pattern

Claims (22)

A rectangular light exit surface;
A thick wall portion parallel to the one side and positioned at a substantially central portion of the light emitting surface;
A thin end formed in parallel to the thick portion;
A parallel groove for accommodating a rod-shaped light source, which is formed in parallel with the one side at the approximate center of the thick part;
The axis of the rod-shaped light source is included on both sides of the parallel groove and is symmetric with respect to a plane perpendicular to the light emitting surface, and is directed from the thick portion to the thin end portions on both sides in a direction perpendicular to the one side. A plurality of transparent light guide plate units composed of an inclined back surface portion that forms an inclined back surface.
The thin end portions of the adjacent light guide plate units are connected, and the light output surfaces of the connected light guide plate units are arranged on the same plane,
The distance from the surface perpendicular to the light exit surface passing through the center of the rod light source to the surface perpendicular to the light exit surface passing through the center of the bar light source of the adjacent light guide plate unit is L, and the thickness A light guide plate satisfying the following formula, where D is the maximum thickness of the meat part.
D / L ≦ 0.2 The light guide plate according to claim 1, wherein when the diameter of the rod-shaped light source is R, the maximum thickness D of the thick portion satisfies the following formula.
0.6R ≦ D In a light guide plate unit having at least a rod-shaped light source and a substantially flat light guide plate that emits light incident from the rod-shaped light source from a light emitting surface, St represents the total area of the light emitting surface of the rod-shaped light source, and the diameter of the rod-shaped light source R, and T is the distance from the light emitting surface of the rod-shaped light source to the light incident surface of the light guide plate,
A light guide plate unit satisfying the following formula, where Sp is the area of the light emitting surface of the rod-shaped light source that satisfies T ≦ 2R.
Sp / St ≧ 0.5   The light guide plate unit according to claim 3, wherein a plurality of light guide plate units are connected.   The light guide plate unit according to claim 4, comprising the light guide plate according to claim 1. 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 5, wherein the base end side of the parallel groove has 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 claim 6, wherein the light guide plate is configured by a pair of contour lines whose intervals become narrower toward the surface. The pair of inclined back surface portions are symmetric with respect to a plane that includes an axis of the rod-shaped light source and is perpendicular to the rectangular light exit surface;
A pair of contour lines of the parallel grooves in the cross-sectional shape in the orthogonal direction is symmetric with respect to a center line perpendicular to the rectangular light exit surface of the parallel grooves,
The front end portion of the parallel groove is spaced from the center line perpendicular to the rectangular light exit surface of the parallel groove toward the rectangular light exit surface in the cross-sectional shape of the parallel groove in the orthogonal direction. The light guide plate according to claim 7, wherein becomes narrower symmetrically.   In the pair of contour lines at the tip portions of the parallel grooves, the peak value of illuminance or luminance of the first portion of the rectangular light exit surface is not more than three times the average value of illuminance or luminance of the second portion. The light guide plate according to claim 8, wherein the interval becomes narrow.   10. The light guide plate according to claim 1, wherein each of the pair of inclined rear surface portions has a portion parallel to the rectangular light exit surface in the vicinity of the parallel groove. 11.   The 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 that intersects each other. The light guide plate according to any one of 10.   A pair of contour lines of at least the tip portion of the parallel grooves, or the two curves that form a pair of contour lines of the parallel grooves are circles or ellipses that are convex or concave toward the center of the parallel grooves. The light guide plate according to claim 11, which is a part of a parabola or a hyperbola.   The light guide plate according to any one of claims 1 and 6 to 11, wherein a cross-sectional shape of at least the tip portion of the parallel groove or a cross-sectional shape of the parallel groove is a triangle.   The cross-sectional shape of the top of the tip portion of the parallel groove is a shape connected to each other by a straight line or a curve symmetric with respect to the center line before the two symmetrical straight lines or curves intersect. The light guide plate according to any one of the above.   The light guide plate according to claim 14, wherein a 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.   15. 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. The light guide plate described in 1.   The light guide plate according to any one of claims 1 and 6 to 10, wherein at least one pair of contour lines of at least the tip portion of the parallel groove is an ellipse or a part of a hyperbola.   The light guide plate according to any one of claims 1 to 17, wherein 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 a connection portion. A light guide plate according to any one of claims 1 to 18,
A rod-shaped light source housed in the parallel groove of the light guide plate;
A reflector provided behind the bar light source so as to close the parallel grooves;
A reflective sheet attached to the inclined back surface of the inclined back surface on both sides of the thick portion of the light guide plate;
A planar illumination device comprising: a diffusion sheet disposed on the rectangular light exit surface of the light guide plate.   The planar illumination device according to claim 19, further comprising a transmittance adjuster unit disposed between the rectangular light exit surface of the light guide plate and the diffusion sheet.   21. The planar lighting device according to claim 19, further comprising a prism sheet disposed between the rectangular light emitting surface of the light guide plate and the diffusion sheet. A backlight unit comprising the planar illumination device according to any one of claims 19 to 21,
A liquid crystal display device comprising: a liquid crystal display panel disposed on a light emission surface side of the backlight unit; and the drive unit for driving the backlight unit and the liquid crystal display panel.

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