JP2009245905A - Light guide plate and planar lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate which has a large and thin shape and has a high efficiency of using light and can emit light with little luminance unevenness in the vicinity of a light incident surface. <P>SOLUTION: The light guide plate includes a light emitting surface of rectangular shape, two light incident surfaces which include respectively two long sides opposed to of the light emitting surface and are arranged at the positions mutually opposed to, two symmetrical slopes of which the distance from the light emitting surface respectively becomes far as they go to the center of the light emitting surface from these two light incident surfaces, and a jointing part to joint these two slopes, and contains diffusion particles to propagate the light inside. At least one of the light emitting surface and the slopes has a large number of groove-shape or point-like recesses formed only in the outer edge region being the light incident surface side region including a tangent line with the light incident surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light guide plate in which light emitted from a light source is incident and propagates, scatters and exits from a light exit surface, and a planar illumination device that illuminates the interior and the exterior having the light guide plate and the light source, Alternatively, the present invention relates to a planar illumination device used as a backlight for illuminating a liquid crystal panel of a liquid crystal display device or a backlight for an advertisement panel, an advertising tower, a signboard, or the like.

  In the liquid crystal display device, a backlight unit that irradiates light from the back side of the liquid crystal display panel and illuminates the liquid crystal display panel is used. The backlight unit is configured by using components such as a light guide plate that diffuses light emitted from a light source for illumination and irradiates the liquid crystal display panel, a prism sheet that diffuses light emitted from the light guide plate, and a diffusion sheet. .

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. In this system, a plurality of cold-cathode tubes, which are light sources, are arranged on the back surface of the liquid crystal display 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, the direct type backlight unit needs a thickness of about 30 m in the vertical direction with respect to the liquid crystal display panel, and it is difficult to make it thinner.

Here, as a backlight unit that can be reduced in thickness, light emitted from a light source for illumination and guided incident light is guided in a predetermined direction and emitted from a light emitting surface that is different from the surface on which the light is incident. There is a backlight unit using a light guide plate.
As such a backlight unit using a light guide plate, a backlight unit using a light guide plate in which scattering particles for scattering light in a transparent resin are mixed (for example, see Patent Documents 1 to 4). Proposed.

For example, Patent Document 1 includes a light-scattering light guide having at least one light incident region and at least one light extraction surface region, and light source means for performing light incidence from the light incident surface region, and the light The light-scattering light-guide light source device is characterized in that the light-scattering light guide has a region that tends to decrease in thickness as the distance from the light incident surface increases.
Patent Document 2 includes a light scattering light guide, a prism sheet disposed on the light extraction surface side of the light scattering light guide, and a reflector disposed on the back side of the light scattering light guide. A surface light source device is described. Further, Patent Document 3 discloses a liquid crystal including a light emission direction correcting element made of a plate-like optical material having a light incident surface having repetitive undulations in a prism array and a light emission surface provided with light diffusibility. A display is described, and Patent Document 4 describes a light source device that includes a light scattering light guide provided with scattering ability therein, and a light supply unit that supplies light from an end surface of the light scattering light guide. Has been.

  Further, as the light guide plate, in addition to the above, the thickness of the intermediate portion is larger than the thickness of the end portion on the incident side and the end portion on the opposite side, and the thickness increases as the distance from the light incident portion increases. A light guide plate having a reflective surface inclined in a direction, and a light guide plate having such a shape that the distance between the front surface portion and the back surface portion is minimized at the incident portion, and the thickness is maximized at the maximum separation distance from the incident portion. Has been proposed (see, for example, cited references 5 to 8).

JP 07-36037 A JP 08-248233 A Japanese Patent Application Laid-Open No. 08-271739 JP-A-11-153963 JP 2003-90919 A JP 2004-171948 A JP 2005-108676 A JP 2005-302322 A

  However, a thin tandem backlight unit that uses a light guide plate that decreases in thickness as it moves away from the light source can be realized. There was a problem that it was inferior to the direct type. In addition, when using a light guide plate having a shape that accommodates a cold cathode tube in a groove formed in the light guide plate, the thickness can be reduced as the distance from the cold cathode tube increases, but when the thickness of the light guide plate is reduced, There is a problem in that the luminance directly above the cold cathode tube disposed in the groove is increased, and the luminance unevenness of the light exit surface becomes remarkable. In addition, these types of light guide plates are complicated in shape, which increases processing costs, and is used for backlights of liquid crystal televisions having a large size, for example, a screen size of 37 inches or more, particularly 50 inches or more. When the light guide plate is used, there is a problem that the cost becomes high.

In addition, Patent Documents 5 to 8 propose light guide plates that increase in thickness as they move away from the light incident surface in order to stabilize manufacturing and suppress luminance (light quantity) unevenness using multiple reflection. The light guide plate is a transparent body, and the light incident from the light source passes through to the end portion in the opposite direction as it is. Therefore, it is necessary to provide a prism or a dot pattern on the lower surface.
In addition, there is a method of disposing a reflecting member at the end opposite to the light incident surface and causing the incident light to be multiple-reflected and emitted from the light exit surface, but in order to increase the size, it is necessary to make the light guide plate thicker , It becomes heavy and the cost is high. There is also a problem that the light source is reflected, resulting in uneven brightness.

On the other hand, in the sidelight system using a flat light guide plate, minute scattering particles are dispersed inside in order to efficiently emit incident light from the light exit surface. In such a flat light guide plate, if the scattering fine particles are uniformly dispersed and the screen is enlarged, if the scattering fine particle concentration is 0.30 wt%, the light use efficiency of 83% can be ensured, but the solid line in FIG. As shown in the illuminance distribution shown in FIG. 1, there is a problem that the central portion becomes dark and uneven in brightness, that is, uneven in brightness, and is visually recognized.
In order to flatten the luminance unevenness, it is necessary to decrease the concentration of the scattering fine particles to increase the light leaked from the tip, resulting in a decrease in utilization efficiency and a decrease in luminance. For example, if the scattering particle concentration is 0.10 wt% under the same conditions, the luminance unevenness can be greatly reduced as shown by the dotted line in FIG. 17, but the luminance is reduced and the light utilization efficiency is also reduced to 43%. There was a problem.
Furthermore, the brightness distribution on the light exit surface required for large displays such as large liquid crystal televisions is a so-called medium-high distribution, for example, a bell-shaped distribution near the center of the screen compared to the periphery. . However, a flat-shaped light guide plate in which scattered fine particles are dispersed can obtain a flat brightness distribution by reducing the concentration of the scattered fine particles, but there is a problem that a medium-high brightness distribution cannot be realized. It was.

  For thin backlights, it is also considered to use a light guide plate that increases in thickness as it moves away from the light source, as opposed to a tandem light guide plate. However, there is no disclosure about obtaining a light distribution near the center of the screen required for large-screen flat-screen LCD TVs compared to the periphery, so-called medium-high brightness distribution. There was a problem that wasn't done.

  In addition, in order to increase the size of the light guide plate that disperses the scattering particles in the interior while reducing the thickness, the arrangement density (particle concentration) of the scattering particles is lowered to make the light reach farther. There is a need to. If the arrangement density of the scattering particles is made low in this way, the scattering particles in the vicinity of the light incident surface also become low in density, so that the degree of light diffusion is reduced and uneven brightness tends to occur in the vicinity of the light incident surface. There is also a problem of becoming.

  The object of the present invention is a screen required for a large-sized thin liquid crystal television, which has a large and thin shape, can emit light with high light utilization efficiency, and has little luminance unevenness in the vicinity of the incident surface. It is an object of the present invention to provide a planar lighting device that can obtain a brighter distribution in the vicinity of the central portion than that of the peripheral portion, that is, a so-called medium-high or bell-shaped brightness distribution, and that has little or no failure.

  In order to solve the above-mentioned problems, the present invention provides a rectangular light exit surface, two light incident surfaces each including two opposing long sides of the light exit surface, and disposed at positions facing each other. Two symmetric inclined surfaces whose distances from the light exit surface become farther from each light incident surface toward the center of the light exit surface, and a joint that joins the two inclined surfaces, and propagates to the inside. A light guide plate including scattering particles that scatter light, wherein at least one of the light exit surface and the inclined surface is only in an outer end region that is a region on the light incident surface side including a tangent to the light incident surface. The present invention provides a light guide plate in which a large number of groove-shaped or dot-shaped concave portions are formed.

Here, it is preferable that the outer end region has a length from a side in contact with the light incident surface to an end on the joint portion side of 5 mm or more and 20 mm or less.
In addition, it is preferable that the light exit surface and the inclined surface have a smooth shape in a region other than the region where the concave portion is formed.
Moreover, it is preferable that the said recessed part has a triangular cross section.
Moreover, it is preferable that the said recessed part is a groove | channel shape extended in the direction parallel to the direction which goes to the said junction part from the said light-incidence surface.
Moreover, it is preferable that the said recessed part is a spherical-shaped recessed part.

Furthermore, it is preferable that the joining portion has a curved shape.
The light guide plate has a light guide length between the two light incident surfaces of 480 mm or more and 500 mm or less, a particle size of the scattering particles of 4.0 μm or more and 12.0 μm or less, and a concentration of the scattering particles of 0.02 wt% or more and 0.22 wt% or less, and the particle diameter and concentration of the scattering particles are set such that the particle diameter (μm) of the scattering particles is a horizontal axis, and the particle concentration (wt%) of the scattering particles is ) On the vertical axis, 6 points (4.0, 0.02), (4.0, 0.085), (7.0, 0.03), (7.0, 0.12) , (12.0, 0.06) and (12.0, 0.22), and the ratio of the light incident from the two light incident surfaces is emitted from the light emitting surface. The utilization efficiency of light is 55% or more, and the brightness of light emitted from the vicinity of the light incident surface of the light emitting surface is That the middle-high ratio of brightness distribution of the light exit plane indicating a ratio of brightness of light emitted from a central portion of the light exit surface is greater than 0%, preferably not more than 25%.
The light guide plate has a light guide length between the two light incident surfaces of 515 mm to 620 mm, a particle size of the scattering particles of 4.0 μm to 12.0 μm, and a concentration of the scattering particles. Is not less than 0.015 wt% and not more than 0.16 wt%, and the particle diameter and concentration of the scattering particles are such that the particle diameter (μm) of the scattering particles is the horizontal axis, and the particle concentration (wt %) On the vertical axis, 6 points (4.0, 0.015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09) ), (12.0, 0.035) and (12.0, 0.16).

In the light guide plate, a light guide length between the two light incident surfaces is 625 mm or more and 770 mm or less, a particle diameter of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is Is 0.01 wt% or more and 0.12 wt% or less, and the particle diameter and concentration of the scattering particles are set such that the particle diameter (μm) of the scattering particles is a horizontal axis, and the particle concentration (wt%) of the scattering particles is ) On the vertical axis, 6 points (4.0, 0.01), (4.0, 0.05), (7.0, 0.01), (7.0, 0.06) , (12.0, 0.02) and (12.0, 0.12) are also preferable.
The light guide plate has a light guide length between the two light incident surfaces of 785 mm or more and 830 mm or less, a particle size of the scattering particles of 4.0 μm or more and 12.0 μm or less, and a concentration of the scattering particles. Is not less than 0.008 wt% and not more than 0.08 wt%, and the particle diameter and concentration of the scattering particles are set such that the particle diameter (μm) of the scattering particles is a horizontal axis, and the particle concentration (wt%) of the scattering particles is ) On the vertical axis, 6 points (4.0, 0.008), (4.0, 0.03), (7.0, 0.009), (7.0, 0.04) , (12.0, 0.02) and (12.0, 0.08).

  The light guide plate has a thickness of the light incident surface that is the thinnest is 0.5 mm or more and 3.0 mm or less, and a thickness of the center of the bent portion that is the thickest is 1.0 mm or more and 6 mm. 0.04 mm or less, the radius of curvature of the curved portion is 6,000 mm or more and 45,000 mm or less, and the taper of the inclined surface with respect to a line parallel to the light exit surface is 0.1 ° or more and 0.8 °. The following is preferable.

The light guide plate has a scattering cross section of the scattering particles of Φ, a density of the scattering particles of N _p , a correction coefficient of K _C , and a length from the light incident surface to the end surface in the light incident direction of L. It is also preferable to satisfy the inequality 1.1 ≦ Φ · N _p · L · K _C ≦ 8.2 and 0.005 ≦ K _C ≦ 0.1.

  According to another aspect of the present invention, there is provided the light guide plate according to any one of the above, a pair of light sources that are arranged to face each of the pair of light incident surfaces, and that make light incident on each of the pair of light incident surfaces. A planar lighting device is provided.

According to the present invention, by forming a groove-like or dot-like concave portion only in the outer end region which is a region on the light incident surface side (that is, near the light incident surface) of the light exit surface and / or the inclined surface, Of the light incident on the light guide plate, the light emitted from the light emitting surface and / or the inclined surface can be reflected and diffused in the vicinity of the incident surface, and the light is excessively emitted in the vicinity of the light incident surface. The occurrence of uneven brightness in the vicinity of the light incident surface can be suppressed, and a lighter distribution in the vicinity of the center than in the periphery, that is, a so-called medium-high or bell-shaped brightness distribution can be obtained. Further, since the light emitted in the vicinity of the light incident surface can be guided to the center side of the light guide plate, the light use efficiency can be increased.
In addition, according to the present invention, light having a thin shape, high light use efficiency, and less luminance unevenness can be emitted, and the vicinity of the center portion of the screen required for a large-screen thin liquid crystal television is provided. It is possible to obtain a bright distribution compared to the peripheral portion, that is, a so-called medium-high or bell-shaped brightness distribution. Further, it is possible to prevent the light source and the light guide plate from being damaged and the positional relationship from being shifted, and it is possible to obtain a light guide plate that is less likely to break down and that is less likely to cause uneven brightness.

A light guide plate and a planar lighting device according to the present invention will be described below in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a perspective view schematically showing a liquid crystal display device having the planar illumination device of the present invention using the light guide plate of the present invention, and FIG. 2 is a cross-sectional view taken along line II-II of the liquid crystal display device shown in FIG. FIG. 3 is an enlarged view of the vicinity of the light source unit of the planar illumination device (hereinafter also referred to as “backlight unit”) shown in FIG. 3A is a partially omitted plan view showing the light guide plate of the planar illumination device shown in FIG. 2 and the light sources arranged on the two sides thereof, and FIG. 3B is a cross-sectional view taken along line BB of FIG. It is line sectional drawing.

  As shown in FIG. 1, the liquid crystal display device 10 includes a backlight unit 20, a liquid crystal display panel 12 disposed on the light emission surface side of the backlight unit 20, and a drive unit 14 that drives the liquid crystal display panel 12. Have In FIG. 1, a part of the liquid crystal display panel 12 is not shown in order to show the configuration of the planar lighting device.

The liquid crystal display panel 12 is arranged in advance in a specific direction, and a liquid crystal cell that changes the arrangement of molecules by applying an electric field and switches between transmission and non-transmission of light using a change in refractive index. The liquid crystal cell layer is regularly arranged, and the color filter is disposed on the display surface side of the liquid crystal cell layer (the surface on the side where light incident on the liquid crystal cell is emitted).
The liquid crystal display panel 12 selectively applies an electric field to each liquid crystal cell of the liquid crystal cell layer to change the molecular arrangement, changes the refractive index generated in the liquid crystal cell, and switches between transmission and non-transmission of light, By selecting light that passes through the color filter 80, characters, figures, images, and the like are displayed on the surface of the liquid crystal display panel 12.

  The drive unit 14 applies a voltage to the transparent electrode in the liquid crystal display panel 12, changes the direction of the liquid crystal molecules in the liquid crystal cell, and controls the transmittance of light transmitted through the liquid crystal display panel 12. That is, as described above, the drive unit 14 controls whether or not light is transmitted through the filters of each color at each position by the liquid crystal cell of the liquid crystal display panel 12. In this way, an image or the like is displayed on the liquid crystal display panel 12 by switching whether to transmit the light that passes through the filter according to the position.

  The backlight unit 20 is an illuminating device that irradiates light from the back surface of the liquid crystal display panel 12 to the entire surface of the liquid crystal display panel 12, and has a light emission surface 24 a having substantially the same shape as the image display surface of the liquid crystal display panel 12.

The backlight unit 20 according to the present invention includes two light sources 28, a light guide plate 30, an optical member unit 32, and a reflection plate 34, as shown in FIGS. 1, 2, 3A, and 3B. The lighting device main body 24 has a lower housing 42, an upper housing 44, a reinforcing member 46, and a supporting member 48.
Further, as shown in FIG. 1, a power storage unit 49 that stores a plurality of power supplies for supplying power to the light source 28 is attached to the back side of the lower housing 42 (see FIG. 2) of the housing 26.
Hereinafter, each component which comprises the backlight unit 20 is demonstrated.

The illuminating device body 24 includes a light source 28 that emits light, a light guide plate 30 that emits light emitted from the light source 28 as planar light, and an optical axis distance and an optical axis vertical distance between the light guide plate 30 and the light source 28. Is kept constant, the optical member unit 32 that scatters and diffuses the light emitted from the light guide plate 30 to make the light more uniform, and the light leaked from the light guide plate 30 is reflected. And a reflection plate 34 that is incident again on the light guide plate.
Here, the optical axis distance between the light guide plate 30 and the light source 28 is a distance between the light emitting surface of the light source 28 and the light incident surfaces (30d, 30e) of the light guide plate 30 as shown in FIG. c. The optical axis vertical distance between the light guide plate 30 and the light source 28 refers to the distance between the respective optical axes in the thickness direction of the light guide plate 30 and the light source 28.

First, the light source 28 will be described.
4A is a schematic perspective view showing a schematic configuration of the light source 28 of the planar illumination device 20 shown in FIGS. 1 and 2, and FIG. 4B shows the light source 28 shown in FIG. It is a schematic perspective view which expands and shows only one LED chip (light emitting diode) 50 which comprises.
As illustrated in FIG. 4A, the light source 28 includes a plurality of LED chips 50 and a light source support portion 52.

The LED chip 50 is a chip (pseudo white LED chip) in which a fluorescent material is applied to the surface of a light emitting diode that emits blue light. The LED chip 50 has a light emitting surface 58 having a predetermined area, and emits white light from the light emitting surface 58. .
That is, when the blue light emitted from the surface of the light emitting diode of the LED chip 50 passes through the fluorescent material, the fluorescent material is excited to emit fluorescence. As the fluorescent material, if a fluorescent material that emits fluorescence that is complementary to the blue light emitted from the light emitting diode is selected, the blue light emitted from the light emitting diode transmits through the fluorescent material, thereby The emitted blue light and the complementary color emitted from the fluorescent material are mixed to generate white light, and this white light is emitted from the LED chip 50.

  Here, the LED chip 50 is exemplified by a chip in which a YAG (yttrium / aluminum / garnet) fluorescent material is applied to the surface of a GaN-based light-emitting diode, InGaN-based light-emitting diode, or the like.

The light source support portion 52 is a plate-like member that is disposed so as to face the light incident surface (30 d, 30 e) whose one surface is the thinnest side end surface of the light guide plate 30.
The light source support 52 supports the plurality of LED chips 50 on a side surface that is a surface facing the light incident surface (30d, 30e) of the light guide plate 30 with a predetermined distance therebetween. Specifically, the plurality of LED chips 50 constituting the light source 28 are arranged along the longitudinal direction of the first light incident surface 30d or the second light incident surface 30e of the light guide plate 30 to be described later, in other words, the light emitting surface 30a. Are arranged in an array parallel to the line where the first light incident surface 30d intersects or parallel to the line where the light exit surface 30a and the second light incident surface 30e intersect, and are fixed on the light source support 52. ing.
The light source support 52 is made of a metal having good thermal conductivity such as copper or aluminum, and also has a function as a heat sink that absorbs heat generated from the LED chip 50 and dissipates it to the outside. The light source support portion may be provided with fins that can increase the surface area and enhance the heat dissipation effect, or may be provided with a heat pipe that transfers heat to the heat dissipation member.

Here, as shown in FIG. 4B, the light emitting surface 58 of the LED chip 50 of this embodiment has a rectangular shape whose length in the direction orthogonal to the arrangement direction is shorter than the length of the LED chip 50 in the arrangement direction. That is, the light guide plate 30 has a rectangular shape with a short side in the thickness direction of the light guide plate 30 (to be described later) (direction perpendicular to the light exit surface 30a). In other words, the light emitting surface 58 has a shape in which b> a, where a is the length perpendicular to the light exit surface 30a of the light guide plate 30 and b is the length in the arrangement direction. Also, q> b, where q is the LED chip 50 adjacent to the LED chip 50. Thus, the relationship between the length a of the light emitting surface 58 of the LED chip 50 in the direction perpendicular to the light exit surface 30a of the light guide plate 30, the length b in the arrangement direction, and the arrangement interval q of the LED chips 50 is q> b. It is preferable to satisfy> a.
By making the light emitting surface 58 rectangular, a thin light source can be obtained while maintaining a large light output. By reducing the thickness of the light source, the planar illumination device can be reduced in thickness. In addition, the number of LED chips can be reduced.

  In addition, since the LED chip 50 can make a light source thinner, it is preferable that the light guide plate 30 has a rectangular shape having a short side in the thickness direction. However, the present invention is not limited to this, and a square shape, a circular shape, LED chips having various shapes such as a polygonal shape and an elliptical shape can be used.

In the present embodiment, since the device can be made thinner and more appropriately mixed, each LED chip 50 is arranged in the longitudinal direction of the first light incident surface 30d or the second light incident surface 30e of the light guide plate 30 described later. However, the present invention is not limited to this, and the arrangement relationship is not particularly limited, and is arranged in a direction orthogonal to the longitudinal direction of the first light incident surface 30d or the second light incident surface 30e. Also good.
In the present embodiment, the LED chips 50 are arranged in a single row to form a single layer structure. However, the present invention is not limited to this, and a plurality of LED arrays having a configuration in which a plurality of LED chips 50 are arranged on an array support are provided. A multi-layered LED array having a configuration of individual and stacked layers can also be used as a light source. Even when LED arrays are stacked in this manner, more LED arrays can be stacked by making the LED chip 50 rectangular and thinning the LED array. In this way, a larger amount of light can be output by stacking multiple LED arrays, that is, by increasing the filling rate of the LED array (each LED chip of the LED chip). Moreover, it is preferable that arrangement | positioning space | intervals also satisfy | fill the said formula similarly to the above-mentioned each LED chip of the LED array of the layer adjacent to each LED chip of an LED array. That is, in the LED array, it is preferable that each LED chip of the LED chip and each LED chip of the LED chip of the LED array in the adjacent layer are separated from each other by a predetermined distance.

Next, the light guide plate 30 will be described.
FIG. 5 is a schematic perspective view showing the shape of the light guide plate 30. 6A is a cross-sectional view showing the shape of the light guide plate 30, FIG. 6B is a partially enlarged cross-sectional view of the light guide plate 30 shown in FIG. 6A, and FIG. FIG. 7B is a partially enlarged view in which a part of the outer end region 60 of the light exit surface 30a of the light guide plate 30 is enlarged, and FIG. 7B is a cross-sectional view taken along the line VIIB-VIIB in FIG.
As shown in FIGS. 5 and 6, the light guide plate 30 has a substantially rectangular flat light emission surface 30 a and two ends formed substantially perpendicular to the light emission surface 30 a at both ends of the light emission surface 30 a. Two light incident surfaces (first light incident surface 30d and second light incident surface 30e) and opposite to the light exit surface 30a, that is, on the back side of the light guide plate, the first light incident surface 30d and the second light Parallel to the incident surface 30e, symmetrical with respect to a bisector α (see FIGS. 1 and 3) that bisects the light exit surface 30a, and tilted at a predetermined angle with respect to the light exit surface 30a. Two inclined surfaces (first inclined surface 30b and second inclined surface 30c) and both ends of the light emitting surface 30a where the light incident surface is not formed (perpendicular to the line of intersection of the light emitting surface 30a and the light incident surface) Two side surfaces (first side surface 30) formed substantially perpendicular to the light exit surface 30a. And a the second side surface 30 g). A curved portion 30h having a radius of curvature R is formed at a joint portion between the two inclined surfaces (the first inclined surface 30b and the second inclined surface 30c).

Note that the two light incident surfaces 30d and 30e are located opposite to the opposite long sides of the substantially rectangular light exit surface 30a, and the two light incident surfaces 30d are arranged from the light sources 28 disposed opposite to each other. And 30e propagate in the light guide plate 30 parallel to the opposing short sides of the substantially rectangular light exit surface 30a.
The first inclined surface (first inclined back surface) 30b and the second inclined surface (second inclined back surface) 30c are axisymmetric with respect to the bisector α and are inclined symmetrically with respect to the light exit surface 30a. . The curved portion 30h is also curved in line symmetry with respect to the bisector α. The light guide plate 30 has a thickness that increases from the first light incident surface 30d and the second light incident surface 30e toward the center, and a portion corresponding to the bisector α in the center, that is, the center of the curved portion 30h. The portion is thickest (tmax), and the two light incident surfaces (first light incident surface 30d and second light incident surface 30e) at both ends are thinnest (tmin).
That is, the cross-sectional shape of the light guide plate 30 is line symmetric with respect to the central axis passing through the bisector α.

Here, as shown in FIG. 5, the light guide plate 30 includes an outer end region 60 of the light exit surface 30 that is a fixed distance range from the first light incident surface 30d, an outer end region 62 of the first inclined surface 30b, and a second one. A large number of groove-shaped recesses 68 are formed in the outer end region 64 of the light emitting surface 30 and the outer end region 66 of the second inclined surface 30c, which are regions within a certain distance range from the light incident surface 30e.
Here, the outer end region includes a tangent line between the light incident surface and the light exit surface or the inclined surface, and is a region within a predetermined distance Lc from the tangent line. Further, in the optical axis direction (the direction from the first light incident surface toward the bisector α), the inside of the light guide plate corresponding to the portion where the light exit surface or the inclined surface becomes the outer end region is a mixing zone.
In addition, the outer end region 60 and the outer end region 62 have the same position at the end on the light guide plate center (bisector α) side in the optical axis direction. Further, both the outer end region 64 and the outer end region 66 have the same end portion on the light guide plate center (bisector α) side in the optical axis direction (direction from the second light incident surface toward the bisector α). It becomes. In this embodiment, the region other than the outer end region of the light exit surface or the inclined surface is a flat surface.

Next, the recessed part formed in each of the outer end regions 60, 62, 64, 66 will be described.
Since the recesses formed in the outer end regions 60, 62, 64, 66 have the same shape in any outer end region, the following description will be made using the recesses 68 of the outer end region 60.
As shown in FIGS. 7A and 7B, the recess 68 extends in the optical axis direction of the light guide plate (that is, extends in the direction from the tangent to the light incident surface toward the bisector). The cross-sectional shape cut by a plane parallel to the one light incident surface 30b is formed on the light emitting surface 30a so as to be a semicircle.
A large number of recesses 68 are formed in the outer end region 60 and are formed in parallel with the adjacent recesses 68. In other words, as shown in FIG. 7B, the outer end region 60 is formed so that the semicircular cross sections of the plurality of recesses 68 are arranged in a cross section cut along a plane parallel to the first light incident surface 30b. .
The outer end regions 60, 62, 64, 66 are formed with a large number of such recesses, and light that is incident on the light guide plate and reaches each outer end region is scattered toward the light guide plate by the recesses. , Reflected.

  Here, in the present invention, the light guide length L through which the light propagates between the first light incident surface 30d and the second light incident surface 30e has a liquid crystal panel 4 having a screen size of 37 inches (37 ″) or more. Since the target is the liquid crystal panel 4 having a screen size of 480 mm or more and a maximum screen size of 65 inches (65 ″) or more, it needs to be 830 mm or less. More specifically, for a screen size of 37 inches (37 ″), the light guide length L is not less than 480 mm and not more than 500 mm, resulting in screen sizes of 42 inches (42 ″) and 46 inches (46 ″). On the other hand, the light guide length L is not less than 515 mm and not more than 620 mm, and for screen sizes of 52 inches (52 ") and 57 inches (57"), the light guide length L is not less than 625 mm and not more than 770 mm. For a screen size of 65 inches (65 ″), the light guide length L is preferably 785 mm or more and 830 mm or less.

Further, the minimum thickness tmin of the light incident surfaces 30d and 30e where the light guide plate 30 has the smallest thickness is preferably 0.5 mm or more and 3.0 mm or less.
The reason is that if the minimum thickness is too small, the light incident surfaces 30d and 30e become too small, light incidence from the light source 28 decreases, and light with sufficient luminance cannot be emitted from the light emitting surface 30a. However, if the minimum thickness is too large, the maximum thickness becomes too thick, and the weight is too heavy to be suitable as an optical member such as a liquid crystal display device. It is because it does not satisfy more than%.
The maximum thickness tmax at the center of the curved portion 30h where the light guide plate 30 is thickest is preferably 1.0 mm or more and 6.0 mm or less.
The reason is that if the maximum thickness is too thick, the weight is too heavy to be suitable as an optical member such as a liquid crystal display device, and light penetrates and transmits, so that the light utilization efficiency does not satisfy 55% or more. If the maximum thickness is too thin, the radius of curvature R of the central curved portion 30h is too large to be suitable for molding, and as in the case of a flat plate, at a particle concentration that achieves a medium-high luminance distribution, This is because the light-use efficiency does not satisfy 55% or more, and conversely, a medium-high distribution cannot be realized at a particle concentration at which the light-use efficiency is 55% or more.

Therefore, the taper of the inclined surfaces 30b and 30c, that is, the taper angle (inclination angle) is preferably 0.1 ° or more and 0.8 ° or less.
The reason is that if the taper is too large, the maximum thickness will be larger than necessary, and the distribution will be too medium and high, and if the taper is too small, the minimum thickness will be small. Similarly to the case where the radius is too large, the curvature radius R (hereinafter also referred to as “center radius R”) of the curved portion 30h is too large to be suitable for molding, and a medium-high distribution is obtained at a particle concentration at which light utilization efficiency is 55% or more. This is because the light utilization efficiency does not satisfy 55% or more at a particle concentration that achieves a medium-high luminance distribution, as in the case of a flat plate.
As a result, the curvature radius R of the curved portion 30h is preferably 6,000 mm or more and 45,000 mm or less.
As shown in FIGS. 6A and 6B, when the taper angle of the inclined surfaces 30b and 30c is θ, L _R = 2R sin θ and the maximum thickness tmax = tmin − [(L _R / 2 ) Tan θ + R cos θ−R], and taper angle θ = tan ⁻¹ [(tmax−tmin) / (L / 2)].

In the present invention, the shape of the light guide plate 30 is made such that the thickness increases from the first light incident surface 30d and the second light incident surface 30e toward the center (hereinafter referred to as an inverted wedge shape). In this case, the incident light is easily propagated deeper, the in-plane uniformity is improved while maintaining the light use efficiency, and a so-called bell-shaped luminance distribution is obtained. That is, by adopting such a shape, the distribution in which the center becomes dark in the above-described conventional flat light guide plate can be made uniform or medium-high, so-called bell-shaped distribution.
In addition, by smoothly joining the central joint portions of the inclined surfaces 30b and 30c as the curved portion 30h, the band unevenness that can be formed in the central joint portion can be a uniform or medium-high so-called bell-shaped distribution.

In the light guide plate 30 shown in FIGS. 2A and 2B, the light incident from the first light incident surface 30d and the second light incident surface 30e is scattered fine particles contained in the light guide plate 30 (details will be described later). The light passes through the light guide plate 30 and is reflected directly or after being reflected by the first inclined surface 30b and the second inclined surface 30c, and then is emitted from the light exit surface 30a.
In addition, the light that has reached the light incident surface 30a, the first inclined surface 30b, and the second inclined surface 30c in the outer end region is basically the recesses of the light incident surface 30a, the first inclined surface 30b, and the second inclined surface 30c. The light is scattered and reflected toward the bisector side of the light incident surface (that is, as it advances toward the center of the light guide plate).
In addition, a part of light may leak from the first inclined surface 30b and the second inclined surface 30c (regions other than the outer end region thereof), but the leaked light is emitted from the first inclined surface 30b of the light guide plate 30 and The light is reflected by a reflection sheet (not shown) disposed so as to cover the second inclined surface 30 c and enters the light guide plate 30 again.

As described above, a large number of recesses are formed in the outer end region corresponding to the vicinity of the light incident surface (mixing zone) of the light guide plate, and the light that has reached the first inclined surface 30b and the second inclined surface 30c by the recesses is formed. By reflecting and scattering, light can be prevented from being emitted from the light guide plate in the vicinity of the light incident surface, and the light incident on the light guide plate can be delivered further. As a result, the incident light is easily emitted (particularly when the concentration of scattering particles described later is lowered and light is easily emitted), and the light emission near the light incident surface can be suppressed. It is possible to prevent the luminance from becoming excessively high in the vicinity, suppress the loss of light near the light incident surface, and increase the light use efficiency.
In addition, since the light can be efficiently delivered to the center of the light guide plate, a medium-high luminance distribution can be obtained.

  The light guide plate 30 is formed by kneading and dispersing minute scattering particles for scattering light in a transparent resin. Examples of the transparent resin material used for the light guide plate 30 include PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, or COP (cycloolefin polymer). An optically transparent resin such as As the scattering particles kneaded and dispersed in the light guide plate 30, Tospearl, silicone, silica, zirconia, dielectric polymer, or the like can be used. By including such scattering particles in the light guide plate 30, it is possible to emit illumination light that is uniform and has less luminance unevenness from the light exit surface.

Here, the particle diameter of the scattering fine particles dispersed in the light guide plate 30 of the present invention needs to be 4.0 μm or more and 12.0 μm or less. The reason is that high scattering efficiency can be obtained, the forward scattering property is large, the wavelength dependency is small, and color unevenness can be selected.
In addition, it is preferable to consider the following points in addition to the wavelength dependency in selecting the optimum particle size of the scattering fine particles to be dispersed in the light guide plate 30 of the present invention.
First, in the scattered light intensity distribution (angular distribution) by a single particle, it is necessary to satisfy the condition that the light scattered in the forward 0 to 5 ° is 90% or more. This is because the reverse wedge-shaped light guide plate 30 of the present invention has a light incident angle of at least 240 mm from the first light incident surface 30d and the second light incident surface 30e on the side surface of the light guide plate 30 when light is incident on one side. This is because it is necessary to guide a distance of at least 480 mm or more from the surface, and if the light scattered at 0 to 5 ° forward is less than 90%, the light cannot be guided to the back of the light guide plate 30.

For this reason, when the particle diameter of the scattering fine particles is smaller than 4.0 μm, that is, when the particle diameter is smaller than 4.0 μm, the scattering becomes isotropic, so the above condition cannot be satisfied. When an acrylic resin is selected as the base material and a silicone resin is selected as the particles, the particle size of the silicone resin scattering fine particles is more preferably 4.5 μm or more.
On the other hand, if the particle size of the scattering fine particles is larger than 12.0 μm, that is, if it exceeds 12.0 μm, the forward scattering property of the particles becomes too strong, so that the mean free path in the system increases and the number of scattering decreases. For this reason, luminance unevenness (firefly unevenness) between the light sources (LEDs) appears in the vicinity of the incident end, and thus the upper limit value is limited to 12.0 μm.
The reason is that if the particle concentration is too high, it becomes a phenomenon similar to that of a flat plate, so that a medium-high luminance distribution cannot be realized. If the particle concentration is too low, light penetrates and passes through. This is because the utilization efficiency does not satisfy 55% or more.

Thus, by selecting an optimum particle size (combination of particle refractive index and base material refractive index) included in the limited range of the particle size of the scattering fine particles of the present invention, it is possible to obtain outgoing light with no wavelength unevenness. Can do.
In the above-described example, scattering particles having a single particle size are used. However, the present invention is not limited to this, and a mixture of scattering particles having a plurality of particle sizes may be used.

Moreover, since the light guide length of the light guide plate 30 of the present invention is 480 mm to 830 mm, the concentration of the scattering particles needs to be 0.008 wt% or more and 0.22 wt% or less.
Specifically, when the light guide length L is 480 mm ≦ L ≦ 500 mm, the concentration of the scattering particles needs to be 0.02 wt% or more and 0.22 wt% or less.
In addition, when the light guide length of the light guide plate is L = 480 mm corresponding to a screen size of 37 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.02 wt% or more and 0.085 wt%. The content is more preferably as follows, and most preferably 0.047 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.03 wt% or more and 0.12 wt% or less, and most preferably 0.065 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.06 wt% or more and 0.22 wt% or less, and most preferably 0.122 wt%. .

Further, when the light guide length L is 515 mm ≦ L ≦ 620 mm, the concentration of the scattering particles is preferably 0.015 wt% or more and 0.16 wt% or less.
In addition, when the light guide length of the light guide plate is L = 560 mm corresponding to a screen size of 42 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.015 wt% or more and 0.065 wt%. More preferably, it is more preferably 0.035 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.02 wt% or more and 0.09 wt% or less, and most preferably 0.048 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.04 wt% or more and 0.16 wt% or less, and most preferably 0.09 wt%.

  In addition, when the light guide length of the light guide plate is L = 590 mm corresponding to a screen size of 46 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.015 wt% or more and 0.060 wt%. More preferably, it is more preferably 0.031 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.02 wt% or more and 0.08 wt% or less, and most preferably 0.043 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.035 wt% or more and 0.15 wt% or less, and most preferably 0.081 wt%.

When the light guide length L is 625 mm ≦ L ≦ 770 mm, the concentration of the scattering particles is preferably 0.01 wt% or more and 0.12 wt% or less.
When the light guide length of the light guide plate is L = 660 mm corresponding to a screen size of 52 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.010 wt% or more and 0.050 wt% or less. Is more preferable, and 0.025 wt% is most preferable. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.015 wt% or more and 0.060 wt% or less, and most preferably 0.034 wt%. Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.030 wt% or more and 0.120 wt% or less, and most preferably 0.064 wt%.

  Furthermore, when the light guide length of the light guide plate is L = 730 mm corresponding to a screen size of 57 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.010 wt% or more and 0.040 wt% or less. Is more preferable, and 0.021 wt% is most preferable. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.010 wt% or more and 0.050 wt% or less, and most preferably 0.028 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is preferably 0.020 wt% or more and 0.100 wt% or less, and most preferably 0.053 wt%.

When the light guide length L is 785 mm ≦ L ≦ 830 mm, it is preferable that the concentration of the scattering particles is 0.006 wt% or more and 0.08 wt% or less.
Further, when the light guide length of the light guide plate is L = 830 mm corresponding to a screen size of 65 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.008 wt% or more and 0.030 wt% or less. More preferably, it is most preferable to set it as 0.016 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.009 wt% or more and 0.040 wt% or less, and most preferably 0.022 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.020 wt% or more and 0.080 wt% or less, and most preferably 0.041 wt%. .

From the above, in the present invention, the particle size and concentration of the scattering particles dispersed in the light guide plate 30 need to satisfy a predetermined relationship in accordance with the light guide length between the two light incident surfaces 30d and 30e of the light guide plate 30. I understand that there is.
Therefore, in the present invention, when the light guide length of the light guide plate 30 is 480 mm or more and 500 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less. The concentration needs to be 0.02 wt% or more and 0.22 wt% or less, and as shown in the graph of FIG. 8A, the particle diameter (μm) of the scattering particles is taken as the horizontal axis, When the particle concentration (wt%) is the vertical axis, the particle size and concentration of the scattering particles are 6 points (4.0, 0.02), (4.0, 0.085), (7.0, 0). .03), (7.0, 0.12), (12.0, 0.06) and (12.0, 0.22).
When the light guide length of the light guide plate 30 is 515 mm or more and 620 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0.00. Scattering is 015 wt% or more and 0.16 wt% or less, and the particle diameter (μm) is on the horizontal axis and the particle concentration (wt%) is on the vertical axis as shown in the graph of FIG. The particle size and concentration of the particles are 6 points (4.0, 0.015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09), It must be within the region enclosed by (12.0, 0.035) and (12.0, 0.16).

When the light guide length of the light guide plate 30 is 625 mm or more and 770 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0.00. When the particle size (μm) is on the horizontal axis and the particle concentration (wt%) is on the vertical axis as shown in the graph of FIG. Particle size and concentration of 6 points (4.0, 0.01), (4.0, 0.05), (7.0, 0.01), (7.0, 0.06), ( 12.0, 0.02) and (12.0, 0.12).
When the light guide length of the light guide plate 30 is 785 mm or more and 830 mm or less, as described above, the particle diameter of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0.00. Scattering is 008 wt% or more and 0.08 wt% or less, and the particle diameter (μm) is the horizontal axis and the particle concentration (wt%) is the vertical axis as shown in the graph of FIG. The particle size and concentration of the particles are 6 points (4.0, 0.008), (4.0, 0.03), (7.0, 0.009), (7.0, 0.04), It must be within the area surrounded by (12.0, 0.02) and (12.0, 0.08).

  The reason why the particle size and concentration of the scattering particles need to be within the region surrounded by the six points in the graphs shown in FIGS. 8 (A), (B), FIG. 9 (A) and (B) If the particle concentration is too high, it becomes the same as a flat plate when the particle concentration is too high, and a medium-high luminance distribution cannot be realized. If the particle concentration is too low, light penetrates and passes through, so that the light utilization efficiency 55 If the particle size is too small, the light utilization efficiency is improved, but a medium-high luminance distribution cannot be realized, and if the particle size is too large, a medium-high luminance distribution can be realized. However, the light utilization efficiency is low.

Thus, by selecting the optimum particle concentration included in the limited range of the particle concentration of the scattering fine particles of the present invention, it is possible to emit light with higher light utilization efficiency compared to the case where it is dispersed in a flat light guide plate. it can. In the present invention, light utilization efficiency of at least 55% or more, that is, exceeding 70% can be achieved.
From the above, since an optimum combination of particle diameter and particle concentration can be selected, the light emitted from the LED light source can be emitted uniformly with a mixing length of about 10 mm by selecting these combinations.

The light guide plate 30 of the present invention in which the scattering fine particles are dispersed in the inside needs to have a light utilization efficiency of 55% or more indicating the ratio of the light incident from the two light incident surfaces being emitted from the light emitting surface. There is. The reason for this is that if the light utilization efficiency is less than 55%, a light source with a higher output is required to obtain the required luminance. However, if a light source with a higher output is used, the light source becomes hot and power consumption is increased. This is because the warpage and elongation of the light guide plate 30 increase, and the required brightness distribution, that is, the so-called medium-high or bell-shaped brightness distribution cannot be obtained.
Further, the medium to altitude degree of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, is greater than 0%. It must be 25% or less. The reason for this is that the vicinity of the center of the screen required for a large-screen thin LCD TV is brighter than the periphery, that is, a so-called medium-high or bell-shaped brightness distribution.
Such a light guide plate 30 can be manufactured using an extrusion molding method or an injection molding method.

Here, the light guide plate 30 includes a first light incident surface 30d, a second light incident surface 30e, a light exit surface 30a, which are light incident surfaces, a first inclined surface 30b, and a second inclined surface 30c, which are light reflecting surfaces. It is preferable that the surface roughness Ra of at least one of the surfaces is smaller than 380 nm, that is, Ra <380 nm.
By making the surface roughness Ra of the first light incident surface 30d and the second light incident surface 30e to be light incident surfaces smaller than 380 nm, diffuse reflection on the surface of the light guide plate can be ignored, that is, the surface of the light guide plate Diffuse reflection can be prevented, and the incident efficiency can be improved.
Further, by making the surface roughness Ra of the light exit surface 30a smaller than 380 nm, the diffuse reflection transmission on the light guide plate surface can be ignored, that is, the diffuse reflection transmission on the light guide plate surface can be prevented, Light can be transmitted to the back by total reflection.
Furthermore, by making the surface roughness Ra of the first inclined surface 30b and the second inclined surface 30c to be light reflecting surfaces smaller than 380 nm, diffuse reflection can be ignored, that is, diffuse reflection on the light reflecting surface is reduced. It is possible to prevent the total reflection component from being transmitted further.

The light guide plate of the present invention is basically configured as described above, but can be designed as follows. In the following design method, a case where the light guide plate is not formed with various holes for connecting to the upper housing 42 and the lower housing 44 of the housing 26 will be described. Since the light is formed only on the part, the light emitted from the light exit surface is basically the same.
FIG. 10 is a flowchart showing an example of the light guide plate designing method of the present invention.
First, as shown in FIG. 10, in step S10, from the screen size of the liquid crystal display device to which the backlight unit using the light guide plate of the present invention is applied, the short side length of the screen size is about 10 mm as the mixing zone length. To determine the light guide length.
Next, in step S12, the maximum thickness tmax of the light guide plate is determined from the screen size.
In step S14, the base material resin used for the light guide plate and the particle conditions of the scattering fine particles to be added are determined.

  Subsequently, in step S16, the particle concentration at which the light use efficiency E [%] is 55% or more is determined in the flat-plate-shaped scattered fine particle dispersion light guide plate (scattering light guide plate) having the determined light guide length. Here, E = Iout / Iin × 100 [%], and Iout and Iin represent incident and outgoing light beams [lm], respectively. The particle concentration is determined by simulation. If there is a difference between the actual measurement value of the light utilization efficiency E and the simulation value, it is necessary to determine the design value of the particle concentration in consideration of the difference. There is. If there is this difference, it is preferable to obtain in advance the difference between the actual measured value and the simulation value of the light utilization efficiency E.

  Next, in step S18, the design value of the particle concentration is fixed, the taper angle θ or the maximum thickness tmax of the inclined surface shape (reverse wedge shape) of the light guide plate of the present invention is changed, and the light exit surface of the light guide plate is changed. The brightness distribution is obtained, and it is determined whether or not the intermediate altitude is within a predetermined range, and the taper angle θ is determined. At this time, the radius of curvature R of the central curved portion is determined according to the light guide length and combined with the taper. Here, the intermediate altitude degree D is represented by 0 <D ≦ 25 and D = [(Lcen−Ledg) / Lcen] × 100 [%]. Here, the medium altitude degree D means the medium altitude degree (the degree at which the central portion becomes high) of the luminance distribution, and Lcen and Ledg represent the luminance at the central portion and the luminance at the screen end side (near the incident portion), respectively. The taper angle θ is determined by simulation. If there is a difference between the measured value of the particle concentration and the simulation value, the luminance distribution is grasped in consideration of the difference, and the intermediate altitude D It is necessary to determine the taper angle θ. When there is this difference, it is preferable to obtain the difference between the actually measured value of the particle concentration and the simulation value in advance.

Subsequently, in step S20, the incident portion thickness (minimum thickness) tmin is determined from the relationship between the maximum thickness tmax of the light guide plate and the taper (taper angle θ) and the radius of curvature R of the central curved portion. An LED chip having a light emitting part with a thickness less than the incident part thickness tmin is selected.
Thus, the light guide plate of the present invention can be designed.
The relationship between the particle concentration [wt%], the light utilization efficiency [%] and the intermediate altitude [%] in the case of a light guide plate with a screen size of 37 inches, a maximum thickness of 3.5 mm, and a light guide length of 480 mm As shown in FIG.
As is clear from the figure, in the range of the particle concentration from 0.05 wt% to 0.2 wt%, the light utilization efficiency exceeds 70%, but the particle concentration ranges from 0.05 wt% to 0.07 wt%, and It can be seen that in the range of 0.19 wt% to 0.2 wt%, the intermediate altitude is minus, that is, the luminance distribution is low in the central portion. For example, it is understood that if a medium to high degree of 10% or more is required, the particle concentration needs to be designed in the range of 0.08 wt% to 0.16 wt%.

  When the screen sizes designed in this way are 37 inches, 42 inches, 46 inches, 52 inches, 57 inches, and 65 inches, the light guide plate has a light guide length [mm], a maximum thickness [mm], and a particle concentration [wt%]. ], Taper, radius of curvature R [mm] of the central curved portion, light utilization efficiency [%] and intermediate altitude [%] are shown in Table 1. The following light guide plates are light guide plates (that is, light guide plates having a smooth surface) in which no recess is formed in any of the outer end regions of the light exit surface and the inclined surface. When formed, the same tendency can be obtained by the same design method. Moreover, since the light loss in the vicinity of the light incident surface can be suppressed by forming the concave portion, the light utilization efficiency can be further increased.

In any case, the light guide plate satisfies the preferable limitation range of the present invention, so that even a large screen has a thin shape, high light utilization efficiency, and emits light with less unevenness in luminance. In addition, a bright distribution in the vicinity of the center of the screen, which is required for a large-screen thin liquid crystal television, compared to the peripheral portion, that is, a so-called medium-high or bell-shaped brightness distribution can be obtained.
The light guide plate of the present invention is basically configured as described above.

Next, the optical member unit 32 will be described.
The optical member unit 32 converts the illumination light emitted from the light exit surface 30a of the light guide plate 30 into light with no uneven brightness, and emits the illumination light without uneven brightness from the light exit surface 24a of the illumination device body 24. As shown in FIG. 2, a diffusion sheet 32a that diffuses illumination light emitted from the light exit surface 30a of the light guide plate 30 to reduce luminance unevenness, and a tangent line between the light incident surface and the light exit surface It has a prism sheet 32b on which parallel microprism arrays are formed, and a diffusion sheet 32c that diffuses illumination light emitted from the prism sheet 32b to reduce luminance unevenness.

  As the diffusion sheets 32a and 32c and the prism sheet 32b, those disclosed in [0028] to [0033] of Japanese Patent Application Laid-Open No. 2005-23497 related to the applicant's application can be applied.

In the present embodiment, the optical member unit is constituted by the two diffusion sheets 32a and 32c and the prism sheet 32b disposed between the two diffusion sheets. However, the arrangement order and arrangement of the prism sheets and the diffusion sheets are not limited. The number is not particularly limited, and is also not particularly limited as a prism sheet or a diffusion sheet, as long as the luminance unevenness of the illumination light emitted from the light exit surface 30a of the light guide plate 30 can be further reduced, Various optical members can be used.
For example, as the optical member, in addition to or in place of the above-described diffusion sheet and prism sheet, a transmittance adjusting member in which a large number of transmittance adjusting bodies made of a diffusive reflector are arranged in accordance with luminance unevenness can also be used.

Next, the reflecting plate 34 of the lighting device main body will be described.
The reflection plate 34 is provided to reflect light leaking from the first inclined surface 30b and the second inclined surface 30c of the light guide plate 30 and to make it incident on the light guide plate 30 again, thereby improving the light utilization efficiency. be able to. The reflection plate 34 has a shape corresponding to the first inclined surface 30b and the second inclined surface 30c of the light guide plate 30, and is formed so as to cover the first inclined surface 30b and the second inclined surface 30c. In the present embodiment, as shown in FIG. 2, the first inclined surface 30b and the second inclined surface 30c of the light guide plate 30 are formed in a triangular cross section, and the reflecting plate 34 is also formed in a shape that complements this. ing.

  The reflecting plate 34 may be formed of any material as long as it can reflect light leaking from the inclined surface of the light guide plate 30. For example, the reflecting plate 34 is stretched after kneading a filler in PET, PP (polypropylene), or the like. Resin sheet with increased reflectivity by forming voids, a sheet with a mirror surface formed by vapor deposition of aluminum on the surface of a transparent or white resin sheet, a resin sheet carrying a metal foil or metal foil such as aluminum, or sufficient on the surface It can be formed of a thin metal plate having excellent reflectivity.

The upper guide reflection plate 36 is disposed between the light guide plate 30 and the diffusion sheet 32a, that is, on the light emission surface 30a side of the light guide plate 30, and the end of the light emission surface 30a of the light guide plate 30 and the light emission surface 30a (first light incident). The end portion on the surface 30d side and the end portion on the second light incident surface 30e side) are disposed so as to cover each other. In other words, the upper guide reflection plate 36 is disposed so as to cover from a part of the light exit surface 30a of the light guide plate 30 to a part of the light source support part 52 of the light source 28 in a direction parallel to the optical axis direction. . That is, the two upper guide reflectors 36 are disposed at both ends of the light guide plate 30, respectively.
Thus, by arranging the upper guide reflection plate 36, it is possible to prevent the light emitted from the light source 28 from leaking to the light exit surface 30 side without entering the light guide plate 30.
Thereby, the light emitted from each LED chip of the LED chip 50 of the light source 28 can be efficiently incident on the first light incident surface 30d and the second light incident surface 30e of the light guide plate 30, and the light utilization efficiency is improved. Can be made.

The lower guide reflection plate 38 is disposed on the side opposite to the light exit surface 30a side of the light guide plate 30, that is, on the first inclined surface 30b and the second inclined surface 30c side so as to cover a part of the light source 28. . The end of the lower guide reflector 38 on the center side of the light guide plate is connected to the reflector 34.
By providing the lower guide reflection plate 38, the light emitted from the light source 28 can be prevented from leaking to the first inclined surface 30b and the second inclined surface 30c side of the light guide plate 30 without entering the light guide plate 30. .
Thereby, the light emitted from each LED chip of the LED chip 50 of the light source 28 can be efficiently incident on the first light incident surface 30d and the second light incident surface 30e of the light guide plate 30, and the light utilization efficiency is improved. Can be made.
Here, as the upper guide reflector 36 and the lower guide reflector 38, various materials used for the reflector 34 described above can be used.
In the present embodiment, the reflecting plate 34 and the lower guiding reflecting plate 38 are connected. However, the present invention is not limited to this, and each may be a separate member.

Here, the upper guide reflector 36 and the lower guide reflector 38 reflect the light emitted from the light source 28 toward the first light incident surface 30d or the second light incident surface 30e, and the light emitted from the light source 28 is reflected. The shape and width are not particularly limited as long as the light can be incident on the first light incident surface 30d and the second light incident surface 30e and the light incident on the light guide plate 30 can be guided to the center side of the light guide plate 30.
In the present embodiment, the upper guide reflector 36 is disposed between the light guide plate 30 and the diffusion sheet 32a. However, the position of the upper guide reflector 36 is not limited to this, and constitutes the optical member unit 32. You may arrange | position between sheet-like members, and may arrange | position between the optical member unit 32 and the upper housing | casing 44. FIG.

Next, the housing 26 will be described.
As shown in FIG. 2, the housing 26 accommodates and supports the illuminating device main body 24 and is sandwiched between the light emitting surface 24 a side and the first inclined surface 30 b and the second inclined surface 30 c side of the light guide plate 30. The lower housing 42, the upper housing 44, the folding member 46, and the support member 48 are provided.

  The lower housing 42 has a shape having an open top surface and a bottom surface portion and side surfaces provided on four sides of the bottom surface portion and perpendicular to the bottom surface portion. That is, it is a substantially rectangular parallelepiped box shape with one surface open. As shown in FIG. 2, the lower housing 42 supports the illuminating device main body 24 housed from above with a bottom surface portion and a side surface portion, and a surface other than the light exit surface 24 a of the illuminating device main body 24, that is, the illuminating device main body. 24 covers the surface (back surface) and the side surface opposite to the light exit surface 24a.

The upper housing 44 has a rectangular parallelepiped box shape in which a rectangular opening smaller than the rectangular light emitting surface 24a of the lighting device body 24 serving as an opening is formed on the upper surface, and the lower surface is opened.
As shown in FIG. 2, the upper housing 44 includes the lighting device main body 24 and the lower housing 42 in which the lighting device main body 24 and the lower housing 42 are housed from above the planar lighting device main body 24 and the lower housing 42. The other side surface portion 22b is also placed so as to cover it.

The folding member 46 has a concave (U-shaped) shape whose cross-sectional shape is always the same. That is, it is a rod-like member having a U-shaped cross section perpendicular to the extending direction.
As shown in FIG. 2, the folding member 46 is inserted between the side surface of the lower housing 42 and the side surface of the upper housing 44, and the outer surface of one U-shaped parallel part is the bottom surface of the lower housing 42. It is connected to the side surface portion 22 b and the outer side surface of the other parallel portion is connected to the side surface of the upper housing 44.
Here, as a method for joining the lower housing 42 and the folding member 46, and a method for joining the folding member 46 and the upper housing 44, various known methods such as a method using bolts and nuts, a method using an adhesive, and the like. Can be used.

Thus, by arranging the folding member 46 between the lower housing 42 and the upper housing 44, the rigidity of the housing 26 can be increased, and the light guide plate can be prevented from warping. Thus, for example, light can be emitted efficiently with little or no luminance unevenness, but even when a light guide plate that is likely to warp is used, the warp can be corrected more reliably, or the light guide plate can be warped. Can be prevented more reliably, and light with no or uneven brightness can be emitted from the light exit surface.
In addition, various materials, such as a metal and resin, can be used for the upper housing | casing of a housing | casing, a lower housing | casing, and a folding member. In addition, as a material, it is preferable to use a lightweight and high-strength material.
In the present embodiment, the folding member is a separate member, but it may be formed integrally with the upper housing or the lower housing. Moreover, it is good also as a structure which does not provide a folding | turning member.

The support member 48 has a shape with the same cross-sectional shape perpendicular to the extending direction. That is, it is a rod-like member having the same cross-sectional shape perpendicular to the extending direction.
As shown in FIG. 2, the support member 48 is between the reflection plate 34 and the lower housing 42, more specifically, the end of the first inclined surface 30 b of the light guide plate 30 on the first light incident surface 30 d side. The light guide plate 30 and the reflection plate 34 are fixed to and supported by the lower housing 42.
The light guide plate 30 and the reflection plate 34 can be brought into close contact with each other by supporting the reflection plate 34 with the support member 48. Further, the light guide plate 30 and the reflection plate 34 can be fixed at predetermined positions of the lower housing 42.

In this embodiment, the support member is provided as an independent member. However, the present invention is not limited to this, and the support member may be formed integrally with the lower housing 42 or the reflection plate 34. In other words, a protrusion may be formed on a part of the lower casing 42 and used as a support member, or a protrusion may be formed on a part of the reflector and the protrusion may be used as a support member. .
Further, the arrangement position is not particularly limited, and it can be arranged at an arbitrary position between the reflector and the lower housing, but in order to stably hold the light guide plate, In the present embodiment, it is preferable to dispose near the first light incident surface 30d and near the second light incident surface 30e.

Further, the shape of the support member 48 is not particularly limited, and can be various shapes, and can be made of various materials. For example, a plurality of support members may be provided and arranged at predetermined intervals.
In addition, the support member has a shape that fills the entire space formed by the reflector and the lower housing, that is, the surface on the reflector side is shaped along the reflector, and the surface on the lower housing side is the lower housing. It is good also as a shape along. As described above, when the entire surface of the reflection plate is supported by the support member, it is possible to reliably prevent the light guide plate and the reflection plate from separating, and to prevent uneven brightness from being generated by the light reflected from the reflection plate. be able to.

The planar lighting device 20 is basically configured as described above.
The planar lighting device 20 emits light from the LED chips 50 of the light source 28 disposed at both ends of the light guide plate 30.
The light emitted from the light source unit 50 enters the light incident surface (the first light incident surface 30d and the second light incident surface 30e) of the light guide plate 30. Light incident from each surface passes through the light guide plate 30 while being scattered by the scatterers included in the light guide plate 30, and directly or after being reflected by the first inclined surface 30b and the second inclined surface 30c. The light exits from the light exit surface 30a. At this time, part of the light leaking from the first inclined surface 30 b and the second inclined surface 30 c is reflected by the reflecting plate 34 and enters the light guide plate 30 again.
In this way, the light emitted from the light exit surface 30 a of the light guide plate 30 passes through the optical member 32 and is emitted from the light exit surface 24 a of the illumination device body 24 to illuminate the liquid crystal display panel 12.
The liquid crystal display panel 12 displays characters, figures, images, and the like on the surface of the liquid crystal display panel 12 by controlling the light transmittance according to the position by the drive unit 14.

As described above, by using the light guide plate of the present invention, it is possible to suppress the loss of light in the vicinity of the light incident surface, and to make the light incident on the light guide plate reach farther. Light can be emitted. Further, since light emitted from the light source can be emitted with high utilization efficiency, light with high luminance can be emitted efficiently.
As a result, light that has a brighter distribution in the vicinity of the center of the screen required for large-screen flat-screen LCD TVs than the surroundings, that is, a so-called medium-high or bell-shaped brightness, and high brightness (or high illuminance). Can be emitted from the light exit surface 24 a of the illuminating device body 24.
Thereby, the liquid crystal display device 10 can be suitably used for a liquid crystal television or the like.

Further, the length in the optical axis direction of the outer end region (the distance from the light incident surface of the light incident portion to the boundary surface) Lc is preferably as follows. The length in the optical axis direction of the outer end region is the length in the optical axis direction of the region where the recess is formed.
When the length of the outer end region in the optical axis direction satisfies the above range, light leakage near the light incident surface can be prevented more reliably.
Further, the length Lc of the outer end region is a side connected to the light incident surface of the light emitting surface 30a of the light guide plate 30 so as not to affect the luminance distribution of the light emitted from the light emitting surface 30a. It is preferable to make it shorter than the width of the edge (frame) of the upper housing 44 that is placed so as to cover it.

  Further, the length Lc of the outer end region in the optical axis direction is defined as Lr when the length of the upper guide reflector (reflecting member on the light exit surface 30a side) 36 in the light incident direction is Lr. Is preferably Le, and the relationship of Lnpi <Lr <Le is preferably satisfied. By making the length Lc of the outer end region in the optical axis direction shorter than the width of the edge of the upper casing 44 and further the length Lr of the upper guide reflector 36, the center of the light guide plate from the light incident surface is obtained. It is possible to prevent the difference in the concentration of scattered particles between the light incident part and the main part from being recognized.

Moreover, it is preferable that the recessed part formed in an outer end area | region sets the length of the transversal direction (direction orthogonal to the extending direction in this embodiment) in the surface of a light emission surface or an inclined surface to 5 mm or more and 20 mm or less. . By making the recess have the above size, light can be appropriately reflected and scattered.
Moreover, it is preferable that the space | interval of a recessed part and the adjacent recessed part shall be below the light emission part dimension of the arrangement direction of an LED array. By setting the interval between the recesses in the above range, light can be appropriately reflected and scattered.

Here, in the present embodiment, the recess is formed in a groove shape, the cross-section is a semicircular shape, and the recesses are spaced apart from each other by a predetermined distance. However, the present invention is not limited to this.
12A to 12D are partial cross-sectional views showing other examples of the recesses, respectively.
As shown in FIG. 12A, the recesses 68a may have a triangular cross section, and the plurality of recesses 68a may be formed without any gaps, that is, with the recesses 68a in contact with the adjacent recesses 68. That is, the outer end region may have a jagged cross section.
Thus, light can be reflected and scattered suitably even if the cross section of the recess is triangular. Moreover, even if it arrange | positions a recessed part without a clearance gap, light can be reflected and scattered suitably.
Further, as shown in FIG. 12B, the recesses 68b may be formed so that the cross section has a triangular shape, and the intervals between the adjacent recesses 68b are separated by a predetermined interval.
In this way, even when the recesses are separated from each other by a predetermined distance, the light can be reflected and scattered suitably. Note that the angle of each vertex of the triangle of the cross section is not particularly limited, and is not limited to an isosceles triangle, and may be a triangle of various shapes.
Further, as shown in FIG. 12C, the recesses 68c may have an oval cross section, and the adjacent recesses 68b may be formed at a predetermined interval.
Thus, it is not limited to a circle or a triangle, and even an ellipse can suitably reflect and scatter light.
Furthermore, as shown in FIG. 12D, the recess 68d may have a cross-sectional shape having a sine curve (π / 2 to 5π / 2), and the plurality of recesses 68d may be formed without gaps. That is, the recess 68d may be formed in an arrangement in which the outer end region has a continuous sine curve.
Even when the concave portion has the shape described above, it is possible to suitably reflect and scatter light.
Further, the shape of the recess is not limited to the above shape, and may be various shapes capable of scattering and reflecting light when a flat surface such as a polygon is used.

  In this embodiment, the concave portion has a groove shape extending in the optical axis direction. However, the direction of the groove (extending direction of the concave portion) is not particularly limited, and is formed parallel to the light incident surfaces 30d and 30e. Alternatively, it may be inclined at an arbitrary angle. Alternatively, they can be formed so as to cross each other. And when it forms so that it may mutually cross | intersect, it will become a shape substantially the same as the case where the recessed part mentioned later is provided on a point, and will have a substantially the same effect.

In the above embodiment, the recess has a groove shape extending in one direction, but the recess may have a point shape.
13A is a partially enlarged view in which a part of the outer end region of the light exit surface of the light guide plate of another example is enlarged, and FIG. 13B is a line XIIIB-XIIIB in FIG. 13A. It is sectional drawing.

As shown in FIGS. 13A and 13B, in the outer end region 60a, a large number of recesses 70 are arranged on a staggered pattern with a predetermined spacing therebetween.
As shown in FIG. 13B, the concave portion 70 has a quadrangular pyramid shape with a triangular cross section and a quadrangular virtual bottom surface (light emission surface 30a).
In this way, the light reaching the outer end region 60a can be favorably reflected and scattered by forming a large number of dot-like recesses instead of the groove-like recesses, and the light loss near the light incident surface can be reduced. It is possible to reduce the luminance distribution of the light emitted from the light exit surface, and to make it high.
In addition, also when a recessed part is made into dot shape, it can be set as various shapes, and can be set as various shapes, such as spherical shape, a cone shape, a polygonal pyramid, a cylinder, and a prism.
Moreover, it is preferable to form one recessed part with the magnitude | size below the length of the transversal direction in the case of the groove | channel shape mentioned above, and it is preferable to make an arrangement | positioning space | interval into the arrangement | positioning space | interval similar to the above-mentioned recessed parts.

In the light guide plate 30, the outer end region 60 of the light exit surface 30, the outer end region 62 of the first inclined surface 30b, and the second light incident surface 30e, which are within a certain distance from the first light incident surface 30d. A large number of recesses are formed in each of the outer end region 64 of the light exit surface 30 and the outer end region 66 of the second inclined surface 30c, which are regions of the range, but the present invention is not limited to this, and the light exit surface And may be formed only on one of the inclined surfaces. That is, the outer end region in which a large number of recesses are formed may be provided only on one of the light exit surface and the inclined surface.
By forming a large number of concave portions on both the light exit surface and the inclined surface, the loss of light near the light incident surface can be reduced, but only one of the light exit surface and the inclined surface can be reduced. Further, even by forming a large number of recesses, it is possible to further reduce the light loss near the light incident surface.
Here, in the case where a large number of recesses are formed only in the outer end region of one surface, a large number of recesses are formed in the outer end region of the light exit surface (an outer end region in which a ridge recess is formed is provided). Is preferred. By providing the outer end region in which the concave portion is formed on the light emitting surface, the light emitted from the light emitting surface in the vicinity of the light incident surface can be more reliably reduced.
In order to target the luminance distribution of light emitted from the light exit surface, recesses are formed on both the first light incident surface side and the second light incident surface side of the light exit surface and / or the inclined surface. Although it is preferable to provide an outer end region, it may be provided only on one of the first light incident surface side and the second light incident surface side.
The outer end region on the first light incident surface side and the outer end region on the second light incident surface side are preferably symmetric, but they are asymmetrical, for example, different in length in the optical axis direction. The shape of the gaps between the recesses may be different.

In addition, the light guide plate 30 has a particle concentration of scattering particles in a mixing zone that is a certain distance range from the first light incident surface 30d or a certain distance range from the second light incident surface 30e as Npi, and other scattering particle particles. When the concentration is Np, it is preferable that Npi> Np.
By making the particle concentration satisfy Npi> Np, the light incident surface is more preferably maintained while maintaining the illuminance distribution (luminance distribution) of the light emitted from the light emitting surface in a bell-shaped (medium-high distribution) state. The occurrence of uneven brightness in the vicinity can be further suppressed. As described above, since the medium-high shape can be easily maintained, the light guide plate can be enlarged, and the planar lighting device can be enlarged. In addition, when giving dispersion | distribution to a scattering particle density | concentration, light utilization efficiency can be made more than fixed by making average particle density | concentration satisfy | fill each suitable range. More preferably, the particle concentration in each region satisfies the above range.

  Moreover, it is preferable that the density | concentration Npi of a scattering particle satisfy | fills 0.003 wt% <Npi <0.25 wt%. By setting the concentration Npi within the above range, it is possible to reduce the decrease in light utilization efficiency due to the scattering particles.

  Here, since this embodiment can efficiently emit light having higher luminance from the light exit surface, the side where the light incident surface 30a of the light guide plate 30 intersects the light incident surface becomes a long side and intersects the side surface. However, the present invention is not limited to this, and the light emission surface may be a square shape, the light incident surface side may be a short side, and the side surface side may be a long side.

  In this embodiment, the light source 28 is disposed only on the light incident surfaces 30d and 30e. However, the present invention is not limited to this, and the light source 28 disposed opposite to the light incident surfaces 30d and 30e is a main light source. Alternatively, a secondary light source may be provided to face the first side surface 30g and the second side surface 30f, and the first side surface 30g and the second side surface 30f may be the third light incident surface and the fourth light incident surface, respectively. By doing in this way, the brightness | luminance of the light inject | emitted from a light-projection surface can be made higher.

Moreover, you may produce a light-guide plate by mixing a plasticizer in said transparent resin.
Thus, by producing a light guide plate with a material in which a transparent material and a plasticizer are mixed, the light guide plate can be made flexible, that is, a flexible light guide plate. It can be deformed into a shape. Therefore, the surface of the light guide plate can be formed into various curved surfaces.
By making the light guide plate flexible in this way, for example, when using a light guide plate or a planar lighting device using the light guide plate as a display plate for illumination, the wall having a curvature is also used. It becomes possible to mount the light guide plate, and the light guide plate can be used for more types, a wider range of electric decoration, POP (POP advertisement), and the like.

Here, as the plasticizer, phthalate ester, specifically, dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), di-2-ethylhexyl phthalate (DOP (DEHP)) ), Di-normal octyl phthalate (DnOP), diisononyl phthalate (DINP), dinonyl phthalate (DNP), diisodecyl phthalate (DIDP), phthalic acid mixed ester (C _{6 to} C ₁₁ ) (610P, 711P, etc.) And butylbenzyl phthalate (BBP). In addition to phthalate esters, dioctyl adipate (DOA), diisononyl adipate (DINA), di-normal alkyl adipate (C6, _{8, 10} ) (610A), dialkyl adipate (C7, ₉ ) ( 79A), dioctyl azelate (DOZ), dibutyl sebacate (DBS), dioctyl sebacate (DOS), tricresyl phosphate (TCP), tributyl acetylcitrate (ATBC), epoxidized soybean oil (ESBO), trimellitic acid Examples include trioctyl (TOTM), polyester, and chlorinated paraffin.

  The planar lighting device according to the present invention has been described in detail above. However, the present invention is not limited to the above embodiment, and various improvements and modifications are made without departing from the gist of the present invention. May be.

For example, as a light source LED chip, a YAG fluorescent material is applied to the light emitting surface of a blue LED. However, the present invention is not limited to this, and a fluorescent material is arranged on the light emitting surface of another single color LED such as a red LED or a green LED. You may use the LED chip of the structure which carried out.
Moreover, as a light source, an LED unit having a configuration in which three types of LEDs, a red LED, a green LED, and a blue LED, are combined can be used. In this case, white light can be obtained by mixing the light emitted from the three types of LEDs.
Furthermore, an LD (semiconductor laser) chip can be used as the light source instead of the LED chip.

Further, a mixing unit made of a material having a refractive index close to that of the light guide plate 30 may be disposed between the light guide plate 30 and the light source 28. Further, a part of the light incident surface and / or side surface of the light guide plate may be formed of a material having a smaller refractive index than other portions.
By reducing the refractive index of the portion where the light emitted from the light source is incident, the light emitted from the light source can be made incident more efficiently and the light utilization efficiency can be further increased. .

  Further, for example, a plurality of light guide plates may be arranged in parallel at the positions where the side surfaces of the light guide plates face each other, and one light emission surface may be formed by the plurality of light guide plates. In this case, it is good also as a structure which arrange | positions a sublight source only to the side surface of the side which is not adjacent to the other light-guide plate of the light-guide plate of both ends.

  Moreover, since light with a medium and high luminance distribution can be emitted from the light exit surface, the light guide plate preferably satisfies the various ranges described above, but it is also preferable to use a light guide plate in the following ranges.

The light guide plate has a scattering cross-sectional area of scattering particles contained in the light guide plate 30 as Φ, and the length from the light incident surface of the light guide plate to the position where the thickness in the direction orthogonal to the light exit surface is maximized in the light incident direction. In this embodiment, L _{G is} the length of half of the light incident direction of the light guide plate (the direction perpendicular to the first light incident surface 30d of the light guide plate 30; hereinafter also referred to as “optical axis direction”). When the density of scattering particles (number of particles per unit volume) contained in the optical plate 30 is N _p and the correction coefficient is K _C , the value of Φ · N _p · L _G · K _C is 1.1 or more. And a value of the correction coefficient K _C of 0.005 or more and 0.1 or less is satisfied. Since the light guide plate 30 includes scattering particles that satisfy such a relationship, the illumination light can be emitted from the light exit surface with uniform and less uneven brightness.

In general, the transmittance T when a parallel light beam is incident on an isotropic medium is expressed by the following formula (1) according to the Lambert-Beer rule.
T = I / I ₀ = exp (−ρ · x) (1)
Here, x is a distance, I ₀ is incident light intensity, I is outgoing light intensity, and ρ is an attenuation constant.

The attenuation constant ρ is expressed by the following equation (2) using the scattering cross-sectional area Φ of particles and the number of particles N _p per unit volume contained in the medium.
ρ = Φ · N _p (2)
Therefore, the length of the half of the optical axis direction of the light guide plate when the L _G, the light extraction efficiency E _out is given by the following equation (3). Here, half the length L _G of the optical axis of the light guide plate, the length from one of the light incident surface of the light guide plate 30 in a direction perpendicular to the light incident surface of the light guide plate 30 to the center of the light guide plate 30 .
Furthermore, the light extraction efficiency and are, with respect to the incident light, the fraction of light reaching the position spaced the length L _G in the optical axis direction from the light incident surface of the light guide plate, for example, the light guide plate 30 shown in FIG. 2 In this case, it is a ratio of light reaching the center of the light guide plate (a position having a half length in the optical axis direction of the light guide plate) with respect to light incident on the end face.
E _out ∝exp (−Φ · N _p · L _G ) (3)

Here the formula (3) applies to a space of limited size, to introduce a correction coefficient K _C for correcting the relationship between the expression (1). The compensation coefficient K _C is a dimensionless compensation coefficient empirically obtained where light optical medium of limited dimensions propagates. Then, the light extraction efficiency E _out is expressed by the following formula (4).
_{E out = exp (-Φ · N} p · L G · K C) ··· (4)

According to the equation (4), when the value of Φ · N _p · L _G · K _C is 3.5, the light extraction efficiency E _out is 3%, and Φ · N _p · L _G · K _C When the value of is 4.7, the light extraction efficiency E _out is 1%.
From this result, it can be seen that the light extraction efficiency E _out decreases as the value of Φ · N _p · L _G · K _C increases. Since light is scattered as it travels in the direction of the optical axis of the light guide plate, the light extraction efficiency E _out is considered to be low.

Therefore, it can be seen that the larger the value of Φ · N _p · L _G · K _C is, the more preferable property is for the light guide plate. In other words, by increasing the value of Φ · N _p · L _G · K _C , it is possible to reduce the light emitted from the surface facing the light incident surface and increase the light emitted from the light emission surface. it can. That is, increasing the value of _{Φ · N p · L G ·} K C, ( hereinafter also referred to "light use efficiency".) Percentage of the light emitted from light exit plane to the light incident on the incident surface of the high can do. Specifically, by setting 1.1 or the value of _{Φ · N p · L G ·} K C, the light use efficiency can be 50% or more.
Here, when the value of Φ · N _p · L _G · K _C is increased, the illuminance unevenness of the light emitted from the light exit surface 30a of the light guide plate 30 becomes significant, but Φ · N _p · L _G · K _C By making the value of 8.2 or less, the illuminance unevenness can be suppressed to a certain value (within an allowable range). Note that the illuminance and the luminance can be handled in substantially the same manner. Therefore, in the present invention, it is presumed that luminance and illuminance have the same tendency.
Thus, the value of _{Φ · N p · L G ·} K C of the light guide plate of the present invention preferably satisfies the relationship of 1.1 or more and 8.2 or less, 2.0 or more and 7.0 The following is more preferable. The value of _{Φ · N p · L G ·} K C is more preferably as long as 3.0 or more, most preferably, not less than 4.7.
The correction coefficient K _C is preferably 0.005 or more and 0.1 or less.

Hereinafter, the light guide plate will be described in more detail with specific examples. In the following specific examples, the luminance and the like were measured using an LED chip composed of one kind of LED chip as a light source, but an LED chip having a pseudo white LED chip and a blue LED chip may also be used. Basically the same trend.
First, the scattering cross section Φ, the particle density N _p , the length L _G of the light guide plate half in the optical axis direction, and the correction coefficient K _C are set to various values, and the values of Φ · N _p · L _G · K _C are different. About each light-guide plate, the light use efficiency was calculated | required by computer simulation, and also illumination intensity nonuniformity was evaluated. Here, the illuminance unevenness [%] is the maximum illuminance of light emitted through the light exit plane of the light guide plate and I _Max, a minimum illuminance and I _Min, Average illuminance when the I _Ave [(I _Max - I _Min ) / I _Ave ] × 100.
The measured results are shown in Table 2 below. In the determination of Table 2, the case where the light use efficiency is 50% or more and the illuminance unevenness is 150% or less is indicated as ◯, and the case where the light use efficiency is less than 50% or the illuminance unevenness is greater than 150% is indicated as x.
FIG. 14 shows the relationship between the value of Φ · N _p · L _G · K _C and the light utilization efficiency (the ratio of the light emitted from the light exit surface to the light incident on the light incident surface). Results are shown.

As shown in Table 2 and FIG. 14, by setting Φ · N _p · L _G · K _C to 1.1 or more, the light use efficiency is increased, specifically, the light use efficiency is set to 50% or more. It can be seen that by setting it to 8.2 or less, the illuminance unevenness can be reduced to 150% or less.
In addition, when Kc is set to 0.005 or more, the light use efficiency can be increased, and when it is set to 0.1 or less, the illuminance unevenness of light emitted from the light guide plate can be reduced. Recognize.

Then, the particle density N _p of the particles which kneaded or dispersed in the light guide plate creates various values of the light guide plate was measured illuminance distribution of light emitted from the respective positions of the light emitting surface of each light guide plate . In this exemplary embodiment, other conditions except for the particle density N _p, specifically, the scattering cross section [Phi, half the length of the optical axis direction of the light guide plate L _G, the correction coefficient K _C, the light guide plate The shape and the like were the same value. Accordingly, in the present _{embodiment, Φ · N p · L G} · K C changes in proportion to the particle density _{N p.}
FIG. 15 shows the result of measuring the illuminance distribution of the light emitted from the light exit surface for the light guide plates having various particle densities in this way. In FIG. 15, the vertical axis is the illuminance [lx], and the horizontal axis is the distance (light guide length) [mm] from one light incident surface of the light guide plate.

Furthermore, the illuminance unevenness when the maximum illuminance of the light emitted from the side wall of the light guide plate of the measured illuminance distribution is I _Max , the minimum illuminance is I _Min , and the average illuminance is I _Ave [(I _Max −I _Min ) / I _Ave ] × 100 [%] was calculated.
FIG. 16 shows the relationship between the calculated illuminance unevenness and the particle density. In FIG. 16, the vertical axis is illuminance unevenness [%], and the horizontal axis is particle density [pieces / m ³ ]. FIG. 16 also shows the relationship between light utilization efficiency and particle density, where the horizontal axis is similarly the particle density and the vertical axis is the light utilization efficiency [%].

As shown in FIGS. 15 and 16, when the particle density is increased, that is, Φ · N _p · L _G · K _C is increased, the light utilization efficiency is increased, but the illuminance unevenness is also increased. It can also be seen that when the particle density is lowered, that is, when Φ · N _p · L _G · K _C is reduced, the light utilization efficiency is reduced, but the illuminance unevenness is reduced.
Here, by the _{Φ · N p · L G ·} K C 1.1 or more 8.2 or less, the light use efficiency of 50% or more and illuminance unevenness of 150% or less. By setting the illuminance unevenness to 150% or less, the illuminance unevenness can be made inconspicuous.
_{That, Φ · N p · L G} · K C to be to less than 1.1 and not greater than 8.2 yields light use efficiency above a certain level, and illuminance unevenness also seen that it is possible to reduce.

  In addition, since the planar lighting device can be made larger and light with an appropriate luminance distribution (and / or illuminance distribution) can be emitted with high light use efficiency, a rectangular light guide plate for the planar lighting device can be used. A light exit surface, two light incident surfaces disposed at positions facing each other and including two opposing long sides of the light exit surface, respectively, from the two light entrance surfaces toward the center of the light exit surface, respectively It has two symmetrical inclined surfaces whose distance from the light exit surface is far away, a curved portion that joins these two inclined surfaces, and a shape and configuration including scattering particles that scatter light propagating therein. However, the present invention is not limited to this, and can be used for light guide plates having various shapes. For example, it can be used for a planar illumination device and a liquid crystal display device using a light guide plate in which scattering particles are not dispersed, and can also be used for a planar illumination device and a liquid crystal display device using a flat light guide plate.

Next, the light guide plate having a flat light exit surface of the planar illumination device shown in FIG. 2 will be described in detail based on examples. In the following examples, the luminance and the like were measured using an LED chip composed of one kind of LED chip as the light source, but an LED chip having a pseudo white LED chip and a blue LED chip may also be used. Basically the same trend.
Using the light source 28 and the light guide plate 30 configured as shown in FIGS. 2A and 2B, the light guide length [mm] of the light guide plate 30, its shape, that is, the maximum thickness [mm] and the minimum thickness [mm]. The incident light is incident from the two light incident surfaces 30d and 30e of the light guide plate 30 by changing the taper, the center radius R [mm], the particle diameter [μm] and the particle concentration [wt%] of the scattering fine particles dispersed in the light guide plate 30. The light utilization efficiency [%] indicating the ratio of the light emitted from the light emitting surface 30a to the emitted light and the luminance distribution of the light emitted from the light emitting surface 30a are obtained, and the peripheral portion of the light emitting surface 30a, that is, the light The medium altitude [%] of the luminance distribution of the light emitting surface 30a indicating the ratio of the luminance of the light emitted from the central portion of the light emitting surface 30a to the luminance of the light emitted from the vicinity of the incident surfaces 30d and 30e was obtained.

Example 1
As Example 1, the maximum thickness [mm], the minimum thickness [mm], and the particle diameter [μm] when the light guide length L [mm] of the light guide plate 30 corresponding to a screen size of 37 inches is L = 480 mm. When the particle concentration [wt%] is variously changed as shown in Tables 1 and 3, the taper, the center radius (curvature radius of curvature) R [mm], the light utilization efficiency [%], the intermediate altitude [%] Was determined. The results are shown in Tables 3 and 4.
Here, Table 3 shows Invention Examples 11 to 16 for Example 1, and Table 4 shows Measurement Examples 11 to 15 for Example 1.

As is apparent from Tables 3 and 4, in all of the inventive examples 11 to 16, the particle diameter [μm] and the particle concentration [wt%] satisfy the preferable limited range of the present invention, and the maximum Since the thickness [mm] and the minimum thickness [mm] also satisfy the preferable limited range of the present invention, the light use efficiency [%] is 61% or more and higher than 55%. ] Is also 19% to 23%, and satisfies the preferred limited range required by the present invention of more than 0% and 25% or less.
On the other hand, since the measurement example 11 has a particle concentration higher than the preferable limited range of the present invention, the phenomenon is similar to that of a flat plate, and thus a medium-high luminance distribution cannot be realized.

In the measurement example 12, both the maximum thickness [mm] and the minimum thickness [mm] are larger than the upper limit values of 6.0 mm and 3.0 mm, which are preferable limited ranges of the present invention, and light penetrates through. For this reason, the light utilization efficiency does not satisfy the limited range of 55% or more, and the weight is too heavy to be suitable as an optical member for a liquid crystal TV.
In measurement example 13, the taper angle is small and less than 0.1 ° from the preferred limited range of the present invention, the center radius R is large, and it is not suitable for molding, and the light utilization efficiency is 55% or more. Medium-high distribution cannot be realized with particle concentration.

Measurement Example 14 has a large central radius R, is not suitable for molding, is similar to a flat plate, and cannot achieve a light utilization efficiency of 55% or more at a particle concentration that achieves a medium-high luminance distribution.
Measurement Example 15 has a particle size smaller than the preferred limited range of the present invention and good light utilization efficiency, but cannot achieve a medium-high luminance distribution, and Measurement Example 16 has a particle size smaller than the preferred limited range of the present invention. Large, medium and high luminance distribution can be realized, but the light utilization efficiency is low.

(Example 2)
As Example 2, the maximum thickness [mm] and the minimum thickness [mm] when the light guide length L [mm] of the light guide plate 30 corresponding to the screen size of 42 inches and 46 inches is L = 560 mm and 590 mm, When the particle diameter [μm] and particle concentration [wt%] are variously changed as shown in Tables 5 and 6, taper, central radius (curvature radius of curvature) R [mm], light utilization efficiency [% ], Intermediate altitude [%] was determined. The results are shown in Tables 5 and 6.
Here, Table 5 shows Invention Examples 21 to 24 for Example 2, and Table 6 shows Measurement Examples 21 to 23 for Example 2.

As is apparent from Tables 5 and 6, all of the present invention examples 21 to 24 of Example 2 satisfy the preferred limited range of the present invention in terms of particle diameter [μm] and particle concentration [wt%]. In addition, since the maximum thickness [mm] and the minimum thickness [mm] also satisfy the preferred limited range of the present invention, the light utilization efficiency [%] is 59% to 61%, which is higher than 55%. The intermediate altitude [%] is also 14% to 15%, which satisfies the preferred limited range required by the present invention of more than 0% and 25% or less.
On the other hand, measurement examples 21 and 22 have a particle concentration higher than the preferred limited range of the present invention, and thus exhibit the same phenomenon as a flat plate, and thus cannot achieve a medium-high luminance distribution.
In measurement example 23, both the maximum thickness [mm] and the taper angle are larger than the upper limit values of 6.0 mm and 0.8 ° of the preferred limited range of the present invention, the taper is too large, and the maximum thickness Becomes unnecessarily large and the distribution becomes too high and higher than necessary, and the weight is too heavy to be suitable as an optical member for a liquid crystal TV.

(Example 3)
As Example 3, the maximum thickness [mm], the minimum thickness [mm] when the light guide length L [mm] of the light guide plate 30 corresponding to the screen size of 52 inches and 57 inches is L = 660 mm and 730 mm, When the particle diameter [μm] and particle concentration [wt%] are variously changed as shown in Table 7 and Table 8, taper, central portion (curved portion radius) R [mm], light utilization efficiency [%], medium The altitude [%] was determined. The results are shown in Table 7 and Table 8.
Here, Table 7 shows Invention Examples 31 to 32 for Example 3, and Table 8 shows Measurement Examples 31 to 35 for Example 3.

As is apparent from Tables 7 and 8, all of the inventive examples 31 to 32 of Example 3 satisfy the preferred limited range of the present invention in terms of particle diameter [μm] and particle concentration [wt%]. In addition, since the maximum thickness [mm] and the minimum thickness [mm] also satisfy the preferred limited range of the present invention, the light use efficiency [%] is 60% to 61%, which is higher than 55%. The intermediate altitude [%] is also 14% to 14.2%, which satisfies the preferred limited range required by the present invention of more than 0% and 25% or less.
On the other hand, since the measurement example 31 has a particle concentration higher than the preferred limited range of the present invention, and thus exhibits the same phenomenon as a flat plate, it cannot realize a medium-high luminance distribution.

In Measurement Example 32, since the particle concentration is lower than the preferable limited range of the present invention, light penetrates and passes through, and thus the light utilization efficiency does not satisfy 55% or more.
Further, in measurement example 33, the taper angle is larger than the upper limit value of 0.8 ° of the preferred limited range of the present invention, the taper is too large, and the distribution becomes excessively higher than necessary.
In measurement examples 34 and 35, the taper angle is smaller than 0.1 ° of the upper limit value of the preferred limited range of the present invention, the taper is too small, and the center radius R is too large, which is not suitable for molding. In Measurement Example 34, the medium-high distribution cannot be realized at a particle concentration at which the light utilization efficiency is 55% or more. In addition, measurement example 35 is the same as a flat plate, and the light use efficiency does not satisfy 55% or more at a particle concentration that achieves a medium-high luminance distribution.

Example 4
As Example 4, the maximum thickness [mm] and the minimum thickness [mm] when the light guide length L [mm] of the light guide plate 30 corresponding to the screen size of 52 inches and 57 inches is L = 660 mm and 730 mm, When the particle diameter [μm] and the particle concentration [wt%] are variously changed as shown in Table 9 and Table 10, taper, central radius (curvature radius of curvature) R [mm], light utilization efficiency [% ], Intermediate altitude [%] was determined. The results are shown in Table 9 and Table 10.
Here, Table 9 shows Invention Examples 41 to 44 for Example 4, and Table 10 shows Measurement Examples 41 to 45 for Example 4.

As is apparent from Tables 9 and 10, all of the inventive examples 41 to 44 of Example 4 satisfy the preferred limiting range of the present invention in terms of particle diameter [μm] and particle concentration [wt%]. Moreover, since the maximum thickness [mm] and the minimum thickness [mm] also satisfy the preferred limited range of the present invention, the light utilization efficiency [%] is 57% to 68%, which is higher than 55%. The intermediate altitude [%] is also 11% to 24%, which satisfies the preferred limited range required by the present invention of more than 0% and 25% or less.
On the other hand, in the measurement example 41, since the particle concentration is lower than the preferable limited range of the present invention, the light penetrates and penetrates, so that the light utilization efficiency does not satisfy 55% or more.

In the measurement example 42, both the maximum thickness [mm] and the minimum thickness [mm] are larger than the upper limit values 6.0 mm and 3.0 mm of the preferable limited range of the present invention. For this reason, the light utilization efficiency does not satisfy the limited range of 55% or more of 50%, and the weight is too heavy to be suitable as an optical member for a liquid crystal TV.
In measurement example 43, the maximum thickness [mm] is smaller than the lower limit value 1.0 mm of the preferred limited range of the present invention, and the central radius R is too large, exceeding the preferred limited range of the present invention. If the particle concentration is not suitable for molding and the light utilization efficiency is 55% or more, a medium-high distribution cannot be realized.
In measurement example 44, the particle diameter is smaller than the preferred limited range of the present invention and the light utilization efficiency is good, but a medium-high luminance distribution cannot be realized. In measurement example 45, the particle diameter is smaller than the preferred limited range of the present invention. Large, medium and high luminance distribution can be realized, but the light utilization efficiency is low.

From the above results, the present invention has an appropriate shape according to the range of the respective light guide lengths of the light guide plate, and the maximum thickness [mm] and the minimum thickness [ mm], taper, central radius R [mm], and the particle diameter [μm] and particle concentration [wt%] of the scattering particles to be dispersed satisfy the preferred limited range of the present invention, and the light utilization efficiency [%] is 55. % Or more, the intermediate altitude [%] is more than 0% and 25% or less.
On the other hand, in the measurement examples, even in the range of the light guide length of any of the examples, since any of the above requirements is outside the preferable limited range of the present invention, the light utilization efficiency [%] does not satisfy 55% or more. The intermediate altitude [%] does not satisfy more than 0% and does not satisfy 25% or less, and excellent properties cannot be exhibited.
From the above, the effect of the present invention is clear.

It is a schematic perspective view which shows one Embodiment of the liquid crystal display device using the light-guide plate and planar illumination apparatus of this invention. It is the II-II sectional view taken on the line of the liquid crystal display device shown in FIG. (A) is a partially omitted plan view showing a light source and a light guide plate of the planar illumination device shown in FIG. 2, and (B) is a cross-sectional view taken along line BB of (A). (A) is a perspective view which shows schematic structure of the light source of the planar illuminating device shown in FIG. 2, (B) expands and shows one pseudo white LED chip which comprises the light source shown to (A). It is a schematic perspective view. It is a schematic perspective view which shows the shape of the light-guide plate shown in FIG. (A) is a cross-sectional schematic diagram of the light guide plate shown in FIG. 2, and (B) is a partially enlarged cross-sectional view of the light guide plate shown in (A). (A) is the elements on larger scale which expanded a part of outer edge area | region of the light-projection surface of a light-guide plate, FIG. (B) is a VIIB-VIIB sectional view taken on the line of FIG. (A) And (B) is a graph which shows the relationship between the particle diameter and particle concentration [wt%] of the scattering fine particles disperse | distributed to the light-guide plate of this invention, respectively. (A) And (B) is a graph which shows the relationship between the particle diameter and particle concentration [wt%] of the scattering fine particles disperse | distributed to the light-guide plate of this invention, respectively. It is a flowchart which shows an example of the design method of the light-guide plate of this invention. It is a graph which shows the relationship between the particle | grain density | concentration [wt%] of the light-guide plate used for this invention, light utilization efficiency [%], and middle altitude degree [%]. (A)-(D) are partial sectional drawings which show another example of a recessed part, respectively. (A) is the elements on larger scale which expanded a part of outer edge area | region of the light-projection surface of the light guide plate of another example, FIG. (B) is the XIIIB-XIIIB sectional view taken on the line of FIG. . It is a diagram showing the results of measuring the relationship between _{Φ · N p · L G ·} K C and light use efficiency. It is a figure which shows the result of having measured the illumination intensity of the light inject | emitted from each light guide from which particle density differs, respectively. It is a figure which shows the relationship between light use efficiency, illumination intensity nonuniformity, and particle density. It is a graph which shows the illumination intensity distribution of the front direction of the conventional flat light-guide plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Liquid crystal display panel 14 Drive unit 20 Backlight unit 24 Illuminating device main body 24a, 30a Light emission surface 26 Case 28, 28a, 28b Light source 29 Sub light source 30 Light guide plate 30b 1st inclined surface 30c 2nd inclined surface 30d First light incident surface 30e Second light incident surface 30f First side surface (third light incident surface)
30g Second side (fourth light incident surface)
32 Optical member unit 32a Diffusion sheet 32b Prism sheet 32c Diffusion sheet 34 Reflector plate 36 Upper guide reflector 38 Lower guide reflector 42 Lower housing 44 Upper housing 46 Reinforcing member 49 Power supply housing 50 LED chip 52 Light source support 58 Light emission Plane α bisector

Claims (14)

A rectangular light exit surface, two light incident surfaces each including two opposing long sides of the light exit surface and disposed at positions facing each other, from these two light incident surfaces to the center of the light exit surface A light guide plate that includes two symmetrical inclined surfaces whose distances from the light exit surface become farther toward each other and a joining portion that joins the two inclined surfaces, and includes scattering particles that scatter light propagating therein. And
At least one of the light exit surface and the inclined surface has a large number of groove-like or dot-like recesses formed only in an outer end region that is a region on the light incident surface side including a tangent to the light incident surface. A light guide plate characterized by   2. The light guide plate according to claim 1, wherein the outer end region has a length from a side in contact with the light incident surface to an end on the joint portion side of 5 mm or more and 20 mm or less.   3. The light guide plate according to claim 1, wherein the light emission surface and the inclined surface have a smooth shape other than the region where the concave portion is formed.   The light guide plate according to claim 1, wherein the recess has a triangular cross section.   The light guide plate according to claim 1, wherein the concave portion has a groove shape extending in a direction parallel to a direction from the light incident surface toward the joint portion.   The light guide plate according to claim 1, wherein the concave portion is a spherical concave portion.   Furthermore, the said junction part is curved shape, The light-guide plate in any one of Claims 1-6. The light guide length between the two light incident surfaces is 480 mm or more and 500 mm or less,
The particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, the concentration of the scattering particles is 0.02 wt% or more and 0.22 wt% or less, and
The particle size and concentration of the scattering particles are 6 points (4.0, 0) in a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the scattering particles. .02), (4.0, 0.085), (7.0, 0.03), (7.0, 0.12), (12.0, 0.06) and (12.0,0 .22) within the area surrounded by
The utilization efficiency of light indicating the ratio of the light incident from the two light incident surfaces being emitted from the light exit surface is 55% or more,
The medium to altitude of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the center of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, exceeds 0%. The light guide plate according to claim 7, which is 25% or less. The light guide length between the two light incident surfaces is 515 mm or more and 620 mm or less,
The particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, the concentration of the scattering particles is 0.015 wt% or more and 0.16 wt% or less, and
The particle size and concentration of the scattering particles are 6 points (4.0, 0) in a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the scattering particles. .015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09), (12.0, 0.035) and (12.0,0 .16) within the area surrounded by
The utilization efficiency of light indicating the ratio of the light incident from the two light incident surfaces being emitted from the light exit surface is 55% or more,
The medium to altitude of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the center of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, exceeds 0%. The light guide plate according to claim 7, which is 25% or less. The light guide length between the two light incident surfaces is 625 mm or more and 770 mm or less,
The particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, the concentration of the scattering particles is 0.01 wt% or more and 0.12 wt% or less, and the particle size and concentration of the scattering particles are In the graph in which the horizontal axis represents the particle size (μm) of the scattering particles and the vertical axis represents the particle concentration (wt%) of the scattering particles, 6 points (4.0, 0.01), (4.0, 0 .05), (7.0, 0.01), (7.0, 0.06), (12.0, 0.02) and (12.0, 0.12) ,
The utilization efficiency of light indicating the ratio of the light incident from the two light incident surfaces being emitted from the light exit surface is 55% or more,
The medium to altitude of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the center of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, exceeds 0%. The light guide plate according to claim 7, which is 25% or less. A light guide plate including scattering particles that scatter light propagating therein,
The light guide length between the two light incident surfaces is 785 mm or more and 830 mm or less,
The particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, the concentration of the scattering particles is 0.008 wt% or more and 0.08 wt% or less, and the particle size and concentration of the scattering particles are: In the graph in which the horizontal axis represents the particle diameter (μm) of the scattering particles and the vertical axis represents the particle concentration (wt%) of the scattering particles, 6 points (4.0, 0.008), (4.0, 0 .03), (7.0, 0.009), (7.0, 0.04), (12.0, 0.02) and (12.0, 0.08) ,
The utilization efficiency of light indicating the ratio of the light incident from the two light incident surfaces being emitted from the light exit surface is 55% or more,
The medium to altitude of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the center of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, exceeds 0%. The light guide plate according to claim 7, which is 25% or less. The thickness of the light incident surface with the smallest thickness is 0.5 mm or more and 3.0 mm or less,
The thickness of the center of the curved portion where the thickness is the largest is 1.0 mm or more and 6.0 mm or less,
The radius of curvature of the curved portion is 6,000 mm or more and 45,000 mm or less,
The light guide plate according to any one of claims 8 to 11, wherein a taper of the inclined surface with respect to a line parallel to the light exit surface is not less than 0.1 ° and not more than 0.8 °. When the scattering cross section of the scattering particles is Φ, the density of the scattering particles is N _p , the correction coefficient is K _C , and the length from the light incident surface to the end surface in the light incident direction is L, the inequality 1 The light guide plate according to claim 1, wherein: 1 ≦ Φ · N _p · L · K _C ≦ 8.2 and 0.005 ≦ K _C ≦ 0.1 are satisfied. A light guide plate according to any one of claims 1 to 13,
A planar illumination device, comprising: a pair of light sources that are arranged to face each of the pair of light incident surfaces and that allow light to enter each of the pair of light incident surfaces.

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