JP2010218841A - Light guide plate and planar lighting device using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate and a planar lighting device using the same, of a large and thin shape, with high light utilization efficiency, capable of irradiating light with little luminance unevenness, and yet, capable of maintaining a middle-high or hanging-bell shape brightness distribution, even with enlarged scatterer concentration. <P>SOLUTION: The light guide plate is provided with a rectangular light irradiation face, two light-incident faces arranged at opposed positions including two opposed longer sides of the light irradiation face, two symmetrical slanted faces each getting farther from the light irradiation face as they head for the center of the light irradiation face from the two light-incident faces, and a multiple bent part jointing these two slanted faces, and contains scattering particles scattering light propagated inside. The planar lighting device utilizes the above light guide plate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light guide plate used for a liquid crystal display device and the like and a planar illumination device using the same.

  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, and a prism sheet and a diffusion sheet that uniformize light emitted from the light guide plate. .

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 directly 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 mm 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 formed 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, Patent Documents 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, but the light utilization efficiency depends on the relative dimensions of the cold cathode tube and the reflector. 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.

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 production and suppress unevenness in luminance (light quantity) using multiple reflection. The light guide plate is a transparent body, and 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. With such a flat light guide plate, if the scattering fine particles are uniformly dispersed and the screen is enlarged, a light utilization efficiency of 83% can be ensured if the scattering fine particle concentration is 0.30 wt%. 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. 21, 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.

Furthermore, it is also considered to use an inverted wedge-shaped light guide plate that becomes thicker as it gets away from the light source, as opposed to a tandem light guide plate, for thin backlights. In order to improve the above, it is necessary to increase the taper angle in the vicinity of the light incident portion, which causes a problem that the thickness increases.
Similarly, when using an elliptical light guide plate that increases in thickness as it moves away from the light source, increasing the scatterer concentration can improve the light utilization efficiency compared to the inverted wedge shape, but the luminance distribution near the center. Remains the problem of lowering.

  The object of the present invention is to solve the above-mentioned problems of the prior art and to have a large and thin shape. When using a reverse wedge-shaped or elliptical light guide plate, even if the thickness is made thinner than before, the reverse wedge-shaped or The center of the screen required for large-screen flat-screen LCD TVs can emit light with higher light utilization efficiency and less luminance unevenness than using an elliptical shape, and even if the scatterer density is increased. It is an object of the present invention to provide a light guide plate capable of maintaining a bright distribution near the portion as compared with the peripheral portion, that is, a so-called medium-high or bell-shaped brightness distribution, and a planar lighting device using the same.

  In order to solve the above-described problems, a first aspect of the present invention is a light emitting surface having a rectangular shape, and two light incidents that are arranged at positions facing each other, including two opposing long sides of the light emitting surface. A plane, two symmetric inclined surfaces whose distances from the light exit surface become longer as they go from the two light incident surfaces toward the center of the light exit surface, and a multiple curved portion that joins the two inclined surfaces. The light guide plate is characterized by including scattering particles that scatter light propagating therein.

Here, in the multiple bending portion, between the two inclined surfaces, the inclination angle of the inclined surface monotonously decreases toward the central portion, and then monotonously increases, and the inclination angle is 0 degree at the central portion. It is preferable that
Further, in the multiple curved portion, the cross-sectional shape of the inclined portion of the inclined surface is a combination of a quadratic curve and a circle, an inclined straight line and a circle, an inclined straight line and a quadratic curve between the two inclined surfaces. It is preferably represented by either.
In addition, the multiple curved portion has a cross-sectional shape of the inclined portion of the inclined surface between the two inclined surfaces, a combination of a higher order curve and a circle, an inclined straight line and a circle, an inclined straight line and a higher order curve. It is preferably represented by either.

  In order to solve the above-mentioned problem, the second aspect of the present invention includes a rectangular light emission surface, two long sides of the light emission surface that are opposed to each other, and two positions that are arranged opposite to each other. Light-incident surfaces, two symmetrical inclined surfaces whose distances from the light-exiting surfaces increase as they go from the two light-incident surfaces toward the center of the light-exiting surface, and multiple curves that join these two inclined surfaces A light guide plate including scattering particles that scatter light propagating therein, a plate-like support having a length substantially the same as the longitudinal direction of the light incident surface, and the light of the support A plurality of light emitting elements arranged in a row on a surface facing the incident surface, and two light sources respectively disposed facing the two light incident surfaces of the light guide plate. The planar illumination device is provided.

Here, in the multiple bending portion provided in the light guide plate, the inclination angle of the inclined surface monotonously decreases toward the central portion and then increases monotonically between the two inclined surfaces, and is inclined at the central portion. It is preferable that the angle is 0 degree.
Further, in the multiple curved portion provided in the light guide plate, the cross-sectional shape of the inclined portion of the inclined surface between the two inclined surfaces is a quadratic curve and a circle, an inclined straight line and a circle, an inclined straight line and a secondary It is preferably represented by any combination of curves.
In addition, in the multiple curved portion provided in the light guide plate, the cross-sectional shape of the inclined portion of the inclined surface between the two inclined surfaces is a higher order curve and a circle, an inclined straight line and a circle, an inclined straight line and a higher order. It is preferably represented by any combination of curves.

  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 such that the particle diameter of the scattering particles is the horizontal axis, and the particle concentration of the scattering particles is the vertical axis. In the graph, 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) in the region surrounded by (12.0, 0.22), the light use efficiency indicating the ratio of the light incident from the two light incident surfaces being emitted from the light emitting surface is 55. % Of the light emitting surface with respect to the luminance of light emitted from the vicinity of the light incident surface of the light emitting surface. It is preferable that the medium to high degree of the luminance distribution of the light emitting surface showing the proportion of the luminance of the light emitted from the central portion of the light is more than 0% and 25% or less.

  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 0.015 wt% or more and 0.16 wt% or less, and the particle diameter and concentration of the scattering particles are the horizontal axis of the particle diameter of the scattering particles and the particle concentration of the scattering particles of the vertical axis. In the graph, 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) are also preferable.

  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 a graph in which the particle diameter of the scattering particles is on the horizontal axis and the particle concentration 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).

  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 0.008 wt% or more and 0.08 wt% or less, and the particle size and concentration of the scattering particles is a graph in which the particle size of the scattering particles is on the horizontal axis and the particle concentration 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 central thickness of the thickest curved portion is 1.0 mm or more. 6.0 mm or less, a radius of curvature of the multiple curved portion is 6,000 mm or more and 45,000 mm or less, and a taper of the inclined surface with respect to a line parallel to the light exit surface is 0.1 ° or more and 0.00. It is preferably 8 ° or less.

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.

  The light emitting element constituting the light source is preferably a light emitting diode, and the light emitting diode has a long side perpendicular to the light incident surface along the longitudinal direction of the light incident surface of the light guide plate. It is preferable that they are arranged in an inclined state with respect to the direction in which they are made.

Further, the inclination angle β of the light emitting diodes arranged in the inclined state is when the width of the light emitting diodes is wmm, the height is hmm, the arrangement pitch in the horizontal direction is p, and p / 2 = x. ,
x cosβ <w / 2 (p cosβ <w)
Is preferably satisfied.

Further, the minimum thickness tmin of the light incident surface of the light guide plate is a dimension s in the vertical direction (thickness direction of the light guide plate) in the inclined state of the light emitting diode.
s = √w ² + h ² cos (β−φ)
Larger is preferred.
Here, φ in the above formula is
φ = tan ⁻¹ (w / h)
Represents.

  According to the present invention, it is a thin shape, has high light utilization efficiency, and can emit light with less luminance unevenness. When using an inverted wedge-shaped or elliptical light guide plate, the thickness can be made higher than before. A light guide plate that can obtain a light distribution near the center of the screen, which is required for a large-screen thin-screen LCD television, compared to the periphery, that is, a so-called medium-high or bell-shaped brightness distribution, even if it is thinned. The planar lighting device to be used can be obtained.

It is a schematic perspective view which shows one Embodiment of the liquid crystal display device using the planar illuminating device which concerns on 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) is sectional drawing of the light source shown to (A), (C) is (A). It is a schematic perspective view which expands and shows one LED which comprises the light source shown in FIG. It is a model perspective view which shows the arrangement | positioning condition of the LED chip in a light source, (A) has shown the state arrange | positioned upright, and (B) has shown the state arrange | positioned inclined. It is explanatory drawing of the value which should take the permissible inclination | tilt angle (beta) at the time of arranging LED chip in the horizontal direction (state which put the long side in the perpendicular direction) in 1 row. It is a figure for demonstrating the minimum thickness of the light-incidence surface of the light-guide plate which accept | permits the state, when arrange | positioning LED chip inclined. 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) And (B) is a graph which shows the relationship between the particle diameter and particle concentration of the scattering fine particle disperse | distributed to the light-guide plate used for the planar illuminating device of this invention, respectively. (A) And (B) is a graph which shows the relationship between the particle diameter and particle concentration of the scattering fine particle disperse | distributed to the light-guide plate used for the planar illuminating device of this invention, respectively. It is a flowchart which shows an example of the design method of the light-guide plate used for the planar illuminating device of this invention. It is a graph which shows the relationship between the particle | grain density | concentration of the light-guide plate used for the planar illuminating device of this invention, light utilization efficiency, and a medium high degree. (A) is a partial omission plan view showing a light source and a light guide plate of another example of the planar illumination device of the present invention, and (B) is a cross-sectional view taken along line BB of (A). 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 sectional drawing of the planar illuminating device which concerns on other embodiment. It is sectional drawing of the planar illuminating device which concerns on other embodiment. It is a graph which shows the relationship between the distance in the light-incidence direction of a light-guide plate, and the relative illuminance corresponding to it. It is a graph which shows the illumination intensity distribution of the front direction of the conventional flat light-guide plate.

The planar lighting device according to the present invention will be described below in detail based on preferred embodiments shown in the accompanying drawings.
In the following description, a two-sided incidence type planar illumination device that makes light from a light source incident on two sides of a light guide plate is a representative example, but it goes without saying that the present invention is not limited to this. That is.
FIG. 1 is a perspective view showing an outline of a liquid crystal display device including a planar illumination device according to 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. 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 applies a partial electric field to liquid crystal molecules arranged in a specific direction in advance to change the arrangement of the molecules, and uses the change in the refractive index generated in the liquid crystal cell to make a liquid crystal display. Characters, figures, images, etc. are displayed on the surface of the 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, and controls the transmittance of light transmitted through the liquid crystal display panel 12.

  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, a distance maintaining member 33, and an optical member unit 32, as shown in FIGS. 1, 2, 3A, and 3B. The lighting device main body 24 having the reflection plate 34 and the lower housing 42, the upper housing 44, the reinforcing member 46, and the housing 26 having the sliding mechanism 48. In the illustrated example, a heat sink 64 and a heat pipe 66 are further provided between the reflecting plate 34 and the lower housing 42.
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 illumination 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 maintained 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 reflecting 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. Say. 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 is a diagram of the light source 28 shown in FIG. FIG. 4C is a schematic perspective view showing only one LED (light emitting diode) chip 50 constituting the light source 28 shown in FIG.
As shown 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 in which a fluorescent material is coated on the surface of a light emitting diode that emits blue light. The LED chip 50 has a light emitting unit 51 having a predetermined area, and emits white light from a light emitting surface 58 of the light emitting unit 51.
Specifically, the LED chip 50 has a characteristic that a fluorescent material applied to the surface of the light emitting diode fluoresces when blue light emitted from the light emitting diode is transmitted. For this reason, the LED chip 50 emits blue light from the light emitting diode, so that the fluorescent material through which the blue light is transmitted also emits light. White light is generated and emitted by the light emitted by being fluorescent.
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.

  As illustrated in FIG. 4B, the light source support portion 52 includes an array substrate 54 and a plurality of fins 56. The plurality of LED chips 50 described above are arranged on the array substrate 54 in a line at a predetermined interval. 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 emitting surface 30a and the second light incident surface 30e intersect, and are fixed on the array substrate 54. .

The array substrate 54 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 LED chip 50 is supported on the side surface of the array substrate 54 which is the surface facing the light incident surface (30d, 30e) of the light guide plate 30.
Here, the array substrate 54 of the present embodiment is formed 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. .

Each of the plurality of fins 56 is a plate-like member made of a metal having good thermal conductivity such as copper or aluminum, and is adjacent to the surface of the array substrate 54 opposite to the surface on which the LED chip 50 is disposed. The fins 56 are connected to each other at a predetermined distance.
By providing a plurality of fins 56 on the light source support 52, the surface area can be increased and the heat dissipation effect can be enhanced. Thereby, the cooling efficiency of LED chip 50 can be improved.
In this embodiment, the array substrate 54 of the light source support 52 is used as a heat sink. However, when cooling of the LED chip is not necessary, a plate-like member that does not have a heat dissipation function is used as the array substrate instead of the heat sink. Also good.

Here, as shown in FIG. 4C, the light emitting surface 58 of the light emitting portion 51 of the LED chip 50 of the present embodiment is longer in the direction perpendicular to the arrangement direction than the length in the arrangement direction of the LED chip 50. Has a short rectangular shape, that is, a rectangular shape having a short side in the thickness direction of the light guide plate 30 to be described later (a 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. Further, q> b, where q is the arrangement interval of the LED chips 50. Thus, the relationship between the length a of the light emitting surface 58 of the light emitting portion 51 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 as follows. Q>b> a is preferably satisfied.
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, 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 manner, a larger amount of light can be output by stacking multiple LED arrays, that is, by increasing the filling rate of the LED array (LED chip). In addition, the LED chip of the LED array in the layer adjacent to the LED chip of the LED array preferably has the arrangement interval satisfying the above formula as described above. In other words, the LED array is preferably laminated with the LED chip and the LED chip of the LED array in the adjacent layer separated by a predetermined distance.

In addition, as will be described below with reference to FIG. 5, even when the LED chips 50 are arranged in a line, the dimension in the height direction of the light exit surface (that is, the thickness direction of the light guide plate 30). It is possible to reduce the thickness of the light guide plate 30 by, for example, about 30%.
FIG. 5A illustrates a case where LED chips 50 having a rectangular cross-sectional shape are arranged in a horizontal row in a vertically long direction (that is, a state in which the LED chip 50 is oriented in the vertical direction). B) illustrates the case where the same LED chip 50 is inclined 45 degrees from the above state and arranged in the same horizontal row.

In this example, the thickness of the light guide plate 30 is changed without changing (decreasing) the arrangement density of the LED chips 50 by arranging the LED chips 50 so as to be inclined as shown in FIG. For example, the thickness can be reduced by about 30%.
Here, the tilt angle when the LED chip 50 is tilted is not particularly limited, and is appropriately set according to the shape and dimensions of the LED chip chip 50 and the target thickness reduction amount of the light guide plate 30. be able to.

FIG. 6 shows that the adjacent LED chips 50 do not come into contact (contact) when the LED chips 50 are arranged in a horizontal row in a vertically long direction (a state in which the long side is oriented in the vertical direction). It is explanatory drawing of the value which allowable inclination | tilt angle (beta) should take in order to do.
When the width of the LED chip 50 arranged in this direction is wmm, the height is hmm, the arrangement pitch in the horizontal direction is p, and p / 2 = x, the inclination angle β of the LED chip 50 is
x cosβ <w / 2 (p cosβ <w)
Need to be satisfied.

FIG. 7 is a diagram for explaining the minimum thickness tmin of the light incident surfaces 30d and 30e of the light guide plate 30 that allows the LED chip 50 to be inclined when the LED chip 50 is disposed as described above. .
Since the dimension s in the vertical direction (thickness direction of the light guide plate 30) in the inclined state of the LED chip 50 is a dimension defined by the following equation, the LED chip 50 is arranged and used as shown in FIG. The minimum thickness tmin of the light incident surfaces 30d and 30e of the light guide plate 30 is preferably larger than the dimension s.

s = √w ² + h ² cos (β−φ)
Here, φ in the above equation is
φ = tan ⁻¹ (w / h)
Represents.

Next, the light guide plate 30 will be described.
FIG. 8 is a schematic perspective view showing the shape of the light guide plate 30. 9A is a cross-sectional view showing the shape of the light guide plate 30, and FIG. 9B is a partially enlarged cross-sectional view of the light guide plate 30 shown in FIG. 9A.
As shown in FIGS. 8 and 9, the light guide plate 30 has a substantially rectangular flat light emission surface 30 a and 2 formed at both ends of the light emission surface 30 a substantially perpendicular to 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 multiple curved portion 30h described in detail below is formed at a joint portion between the two inclined surfaces (first inclined surface 30b and second inclined surface 30c).

Note that the two light incident surfaces 30d and 30e are positioned opposite to the opposing long sides of the light emitting surface 30a having a substantially rectangular shape, and the two light incident surfaces 30d are disposed 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 30b and the second inclined surface 30c are axisymmetric with respect to the bisector α, and are inclined symmetrically with respect to the light exit surface 30a. The multiple bending portion 30h is also curved symmetrically with respect to the bisector α. The light guide plate 30 is thicker from the first light incident surface 30d and the second light incident surface 30e toward the center, and the portion corresponding to the bisector α in the center, that is, the multiple curved portion 30h. It is thickest at the center (tmax) and thinnest (tmin) at the two light incident surfaces (first light incident surface 30d and second light incident surface 30e) at both ends.
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, 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 multiple 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 and it is not suitable as an optical member such as a liquid crystal display device, and light penetrates and penetrates, so that the light utilization efficiency does not satisfy 55% or more. If the maximum thickness is too thin, the curvature radii R1 and R2 of the central multi-curved portion 30h are too large to be suitable for molding, and particles that achieve a medium and high luminance distribution as in the case of a flat plate. This is because the light utilization efficiency does not satisfy 55% or more in the concentration, and conversely, the medium-high distribution cannot be realized at the particle concentration where the light utilization efficiency is 55% or more.

Therefore, the taper of the inclined back 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 it is too large, the radii of curvature R1 and R2 (hereinafter collectively referred to as “central radius R”) of the multiple curved portion 30h described later are too large to be suitable for molding, and the light utilization efficiency is 55% or more. This is because a medium-high distribution cannot be realized at a particle concentration that achieves the above, and conversely, 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 central radius R of the multiple curved portion 30h is preferably not less than 6,000 mm and not more than 45,000 mm.
9A and 9B, when the taper angle of the inclined back 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 light guide plate 30 is shaped so as to increase in thickness 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). This makes it easier to propagate the incident light deeper, improves the in-plane uniformity while maintaining the light utilization efficiency, and obtains a so-called bell-shaped luminance distribution that is medium to high. 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.
Further, by smoothly joining the central joint portion of the inclined back surfaces 30b and 30c as the multiple curved portion 30h, the thickness of the light guide plate 30 is reduced, and the unevenness of the band formed in the central joint portion is made uniform. The so-called bell-shaped distribution can be obtained.

Here, details of the multiple bending portion 30h will be described.
In the example shown in FIG. 9B, the multiple curved portion 30h includes curved surfaces (cylindrical surfaces) 30x and 30y having a radius of curvature R2 connected to the inclined rear surfaces 30b and 30c, and curved surfaces (cylindrical surfaces) 30x and 30y. The curved surface (curved surface (cylindrical surface) having a radius of curvature R1 opposite to 30x and 30y) 30z is formed between the two surfaces.
In addition, it is preferable that the junction part (contact point) of the said curved surfaces 30x, 30y, and 30z is made into the point with which a differential coefficient corresponds.

Here, it is preferable to set R1 = R2 for the above-described curvature radii R1, R2, and for example, when the light guide length L (see FIG. 9) is 480 mm ≦ L ≦ 500 mm, Although it is good to set it as R1 = R2 = 10000mm, it is not specifically limited to this.
Regarding this, a specific configuration example will be described later in Examples including the scatterer concentration, so please refer to it.
Moreover, in the said embodiment, although the example which comprised the multiple curved part 30h connected to the inclination back surfaces 30b and 30c by three cylindrical surfaces was shown, as a curved surface to combine, secondary curved surfaces (cross section other than a cylindrical surface) were shown. It is also possible to use an ellipse, a parabola, a hyperbola, or a higher-order curved surface.

In addition, as shown also in the said embodiment, when connecting three curved surfaces, it cannot be overemphasized that it is preferable to make the curvature of the curved surface of both the outer sides the same.
Furthermore, as much as possible, it is also preferable to make the curvatures coincide between curved surfaces connected in a curved shape in opposite directions from the viewpoint of simplifying the manufacturing process.

Returning to FIG. 3, the operation of the light guide plate 30 will be described.
In the light guide plate 30 shown in FIGS. 3A and 3B, 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 emitted from the light exit surface 30a. At this time, some light may leak from the first inclined surface 30b and the second inclined surface 30c, but the leaked light covers the first inclined surface 30b and the second inclined surface 30c of the light guide plate 30. Then, the light is reflected by a reflection sheet (not shown) and is again incident on the light guide plate 30.

  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 size of the scattering fine particles dispersed in the light guide plate 30 used in the planar illumination device 20 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 used in the planar lighting device 20 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 light guide plate 30 used in the planar illumination device 20 of the present invention having an inverted wedge shape has a distance 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, at one side. In the case of incident light, it is necessary to guide light at least a distance of 480 mm or more from the light incident surface. If less than 90% of light scatters 0 to 5 ° forward, light is guided to the back of the light guide plate 30. It is not possible.

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, so that 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 diameter are used. However, the present invention is not limited to this, and a mixture of scattering particles having a plurality of particle diameters may be used.

Moreover, since the light guide length of the light guide plate 30 used in the planar lighting device 20 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 must satisfy a predetermined relationship according to 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 diameter 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 in FIG. On 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. When the particle diameter is 015 wt% or more and 0.16 wt% or less and the particle diameter is the horizontal axis and the particle concentration is the vertical axis as shown in the graph of FIG. , 6 points (4.0, 0.015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09), (12.0, 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 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. When the particle diameter is on the horizontal axis and the particle concentration is on the vertical axis as in the graph shown in FIG. , 6 points (4.0, 0.01), (4.0, 0.05), (7.0, 0.01), (7.0, 0.06), (12.0, 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 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 is 008 wt% or more and 0.08 wt% or less and the particle diameter is the horizontal axis and the particle concentration is the vertical axis as shown in the graph of FIG. , 6 points (4.0, 0.008), (4.0, 0.03), (7.0, 0.009), (7.0, 0.04), (12.0, 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. 10 (A), (B), FIG. 11 (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 used in the planar illumination device 20 according to the present invention in which the scattering fine particles are dispersed is used in the light utilization efficiency indicating the ratio of light incident from the two light incident surfaces. Needs to be 55% or more. 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 become large, and a required brightness distribution, that is, a 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 used in the planar illumination device 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. 12 is a flowchart showing an example of a method for designing a light guide plate used in the planar illumination device of the present invention.
First, as shown in FIG. 12, in step S10, the screen size of the liquid crystal display device to which the backlight unit using the light guide plate used in the planar lighting device of the present invention is applied is mixed to the short side length of the screen size. The light guide length is determined by adding about 10 mm as the zone 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 utilization efficiency E is 55% or more is determined in the flat-plate-shaped scattered fine particle dispersed 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, and the taper angle θ or the maximum thickness tmax of the inclined rear surface shape (reverse wedge shape) of the light guide plate used in the planar illumination device of the present invention is changed. The brightness distribution of the light exit surface of the light plate 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 center radius R of the multiple 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 curvature radii R1, R2 of the central multiple curved portion. Then, an LED having a light emitting portion less than the determined incident portion thickness tmin is selected.
In this way, the light guide plate used for the planar illumination device of the present invention can be designed.
FIG. 13 shows the relationship between the particle concentration, the light utilization efficiency, and the intermediate altitude when the screen size is 37 inches, the maximum thickness is 3.5 mm, and the light guide length is 480 mm.
As is clear from FIG. 13, in the range where the particle concentration is 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 level is negative, 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 length of the light guide plate, the maximum thickness, the particle concentration, the taper, and the central multiple curve portion Table 1 shows the center radius R, the light utilization efficiency, and the intermediate altitude.

In any case, the light guide plate satisfies the preferred limitation range of the present invention, so that even a large screen has a thin shape, high light utilization efficiency, and emits light with little unevenness in luminance. In addition, a bright distribution in the vicinity of the center of the screen required for a large-screen thin liquid crystal television, compared to the periphery, that is, a so-called medium-high or bell-shaped brightness distribution can be obtained.
The light guide plate used in the planar illumination device 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 illumination light with more uniform 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 30 b and the second inclined surface 30 c of the light guide plate 30 are formed in a triangular cross section, so that 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 array substrate 54 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.
As described above, 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 emitting surface 30 side without entering the light guide plate 30.
Thereby, the light emitted from 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 can be improved. .

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 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 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 can be improved. .
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 lighting device main body 24, and is sandwiched from the light emission surface 24a side and the first inclined surface 30b and second inclined surface 30c 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 also a surface other than the light emitting surface 24 a of the illuminating device main body 24, that is, the illuminating device. The 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 emission 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 using a light guide plate that is likely to warp, the warp can be corrected more reliably, or the light guide plate can be warped. It is possible to more reliably prevent the occurrence of light, and to emit light from the light exit surface with no or reduced brightness unevenness.
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 | turning 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, an end portion 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. Furthermore, 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 basically has the above-described configuration.
In the planar lighting device 20, light emitted from the light sources 28 disposed at both ends of the light guide plate 30 is incident on the light incident surfaces (the first light incident surface 30 d and the second light incident surface 30 e) 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.

  Further, by providing the spacing maintaining member 33 on the light incident surface (first light incident surface 30d or second light incident surface 30e) side of the light source support 50 of the light source 30, as described above, the LED chip ( The light emitting surface of the light emitting part) and the light guide plate can be prevented from contacting each other, the LED chip and the light guide plate can be prevented from being damaged, and the distance between the light incident surface and the light emitting surface can be kept constant. it can. Damage to the LED chip and the light guide plate can prevent uneven brightness and failure of the planar lighting device. In addition, since the distance between the light incident surface and the light emitting surface can be maintained constant, light emitted from the light emitting surface can be incident on the light guide plate under certain conditions, and uneven brightness can occur even when the distance changes. Can be prevented. Moreover, high light utilization efficiency can be maintained.

  Moreover, it is preferable to produce the space | interval maintenance member 33 with the transparent material which permeate | transmits light. By making the interval maintaining member transparent, it is possible to prevent the interval maintaining member from absorbing the light emitted from the light source or the light that has been emitted from the light guide plate and re-entered the light guide plate, thereby increasing the light utilization efficiency. can do.

  In the above 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 incident surfaces 30d and 30e are as shown in FIGS. The main light source 28 is the light source 28 disposed opposite to the first side surface 30f and the second side surface 30g. The auxiliary light source 29 is provided opposite to the first side surface 30f and the second side surface 30g. And it is good also as a 4th light-incidence surface. By doing in this way, the brightness | luminance of the light inject | emitted from a light-projection surface can be made higher.

The sub light source 29 basically has the same configuration as that of the main light source 28 described above in the first embodiment except for the arrangement position with respect to the light guide plate 30 and the arrangement density of the LED chips.
The two sub light sources 29 are respectively arranged to face the first sub incident surface 30 h and the second sub incident surface 30 i of the light guide plate 30. Specifically, the sub-light source 29 configured by the plurality of LED chips 50 and the light source support portion 52 is disposed to face the first side surface 30 h, and the sub-light source configured by the plurality of LED chips 50 and the light source support portion 52. 29 is arranged to face the second side face 30i.

Here, the interval maintaining members 33 are also arranged on the light source support portions 52 of the two sub light sources 29, and the interval maintaining members 33 are in contact with the opposing side surfaces.
Similarly to the interval support member disposed on the light source support portion 52 of the main light source 28, the interval maintaining member 33 disposed on the light source support portion 52 of the sub light source 29 also faces the LED chip 50 of the sub light source 29. The side surface of the light guide plate is in contact with the LED chip and the light guide plate is prevented from being damaged, and the distance between the light emitting surface and the side surface is kept constant.

As described above, the sub-light source 29 is disposed at a position facing the first sub-incident surface 30h and the second sub-incident surface 30i of the light guide plate 30 and light is incident also from the side surface side of the light guide plate 30. Light with higher luminance can be emitted from the light emission surface 30a, and the amount of light can be increased. Accordingly, a large amount of illumination light can be emitted from the light exit surface, the light exit surface can be enlarged, and a large screen can be realized in the liquid crystal display device.
Moreover, the occurrence of a failure due to a failure of the sub light source or the like can be prevented by disposing the interval maintaining member 33 on the light source support portion 52 of the sub light source.

In addition, you may produce a light-guide plate by mixing a plasticizer in the above-mentioned 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 spirit of the present invention. May be.

In addition, for example, the LED chip of the light source has a configuration in which a YAG fluorescent material is applied to the light emitting surface of a blue LED. However, the present invention is not limited to this. You may use the LED chip of the structure which has arrange | positioned.
Moreover, the LED unit of the structure which combined three types of LED of red LED, green LED, and blue LED as a light source can also be used. In this case, white light can be obtained by mixing light emitted from the three types of LEDs.
Further, a semiconductor laser (LD) can be used instead of the LED.

Further, a confusion portion 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 (the light source 28 and / or the sub light source 29). 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 making the refractive index of the portion where the light emitted from the light source is incident smaller than the other portions, the light emitted from the light source can be 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 the relationship of the correction coefficient K _C being 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, it is possible to emit illumination light that is uniform and has less luminance unevenness from the light exit surface.

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 the ratio of the light reaching the center of the light guide plate (the position that is half the length of the light guide plate in the optical axis direction) relative to the 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 is understood 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, by increasing the value of _{Φ · N p · L G ·} K C, ( hereinafter also referred to as "light use efficiency".) Ratio of light emitted through the 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.
From the above, it is preferable that the value of Φ · N _p · L _G · K _C of the light guide plate used in the planar illumination device of the present invention satisfies the relationship of 1.1 or more and 8.2 or less. More preferably, it is 0 or more and 7.0 or less. 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.
First, the scattering cross section Φ, particle density N _p , half length L _G of the light guide plate in the optical axis direction, and 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 uneven illuminance is [(I _Max −I _Min ) when the maximum illuminance of light emitted from the light exit surface of the light guide plate is I _Max , the minimum illuminance is I _Min , and the average illuminance is I _Ave. / 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.
Further, in FIG. 15 was measured the relationship between _{Φ · N p · L G ·} K C values and light use efficiency (ratio of light emitted through the light exit surface for light incident on the light incident surface) Results are shown.

As shown in Table 2 and FIG. 15, 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. 16 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. 16, the vertical axis is illuminance [lx], and the horizontal axis is the distance (light guide length) [mm] from one light incident surface of the light guide plate.

Further, the maximum illuminance of light emitted from the sidewalls of the illuminance distribution of the light guide plate was measured as _{I Max,} a minimum illuminance and I _Min, illuminance unevenness when the average illuminance was _{I Ave [(I Max -I Min} ) / I _Ave ] × 100 [%] was calculated.
FIG. 17 shows the relationship between the calculated illuminance unevenness and the particle density. In FIG. 17, the vertical axis represents illuminance unevenness and the horizontal axis represents particle density. FIG. 17 also shows the relationship between light utilization efficiency and particle density, where the horizontal axis is the particle density and the vertical axis is the light utilization efficiency.

As shown in FIGS. 16 and 17, when the particle density is increased, that is, Φ · N _p · L _G · K _C is increased, the light use 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 less than 1.1 and not greater than 8.2, the light use efficiency of 50% or more, and the 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.

Hereinafter, 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 embodiment, 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.
Using the light source 28 and the light guide plate 30 configured as shown in FIGS. 3A and 3B, the light guide length of the light guide plate 30, its shape, that is, the maximum thickness, the minimum thickness, the taper, the center radius R, the guide Use of light indicating the ratio of the light emitted from the light exit surface 30a to the light incident from the two light incident surfaces 30d and 30e of the light guide plate 30 by changing the particle diameter and particle concentration of the scattering fine particles dispersed in the light plate 30 The efficiency 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, from the central portion of the light emitting surface 30a with respect to the luminance of the light emitted from the vicinity of the light incident surfaces 30d and 30e. The middle to high level of the luminance distribution of the light exit surface 30a indicating the ratio of the luminance of the emitted light was obtained.

Example 1
As Example 1, the taper when variously changing the maximum thickness, the minimum thickness, the particle diameter, and the particle concentration when the light guide length L of the light guide plate 30 corresponding to a screen size of 37 inches is L = 480 mm, The central radius (the radius of curvature of the multiple curved portion) R, the light utilization efficiency, and the intermediate altitude were obtained. 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 Reference Measurement Examples 11 to 16 for Example 1.

  As is clear from Tables 3 and 4, in each of the inventive examples 11 to 16, the particle diameter and the particle concentration satisfy the preferred limiting range of the present invention, and the maximum thickness and the minimum thickness are Since the preferable limited range of the present invention is satisfied, the light utilization efficiency is 61% or more and higher than 55%, and the intermediate altitude is 19% to 23%, more than 0% and 25% or less. It satisfies the preferred range of limitation required by the invention.

On the other hand, since the measurement example 11 has a particle concentration higher than the preferred 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 measurement example 12, both the maximum thickness and the minimum thickness are larger than the upper limit values of 6.0 mm and 3.0 mm, which are the preferred limited ranges of the present invention, and light penetrates and is transmitted. Not only does efficiency not satisfy the limited range of 55% or more, and the weight is too heavy, making it unsuitable 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.

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

(Example 2)
As Example 2, the maximum thickness, the minimum thickness, the particle diameter, and the particle concentration when the light guide length L of the light guide plate 30 corresponding to the screen size of 42 inches and 46 inches is L = 560 mm and 590 mm are shown in Table 5 and As shown in Table 6, the taper, the central radius (the radius of curvature of the multiple curved portion) R, the light utilization efficiency, and the intermediate altitude were obtained when various changes were made. 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 Reference Measurement Examples 21 to 23 for Example 2.

  As is apparent from Tables 5 and 6, the inventive examples 21 to 24 of Example 2 all satisfy the preferred limiting range of the present invention in terms of particle diameter and particle concentration, and the maximum thickness and Since the minimum thickness also satisfies the preferred limited range of the present invention, the light utilization efficiency is 59% to 61%, which is higher than 55%, and the intermediate altitude is 14% to 15%, more than 0%. 25% or less of the preferred limiting range required by the present invention.

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 and the taper angle are larger than the upper limit values of 6.0 mm and 0.8 ° of the preferable limited range of the present invention, the taper is too large, and the maximum thickness is necessary. Not only does it become larger and the distribution becomes higher than necessary, but the weight is too heavy, making it unsuitable as an optical member for a liquid crystal TV.

Example 3
As Example 3, the maximum thickness, the minimum thickness, the particle diameter, and the particle concentration when the light guide length L of the light guide plate 30 corresponding to the screen size of 52 inches and 57 inches is L = 660 mm and 730 mm are shown in Table 7 and As shown in Table 8, the taper, the central radius (the radius of curvature of the multiple curved portion) R, the light utilization efficiency, and the intermediate altitude were obtained when various changes were made. The results are shown in Table 7 and Table 8.
Here, Table 7 shows Invention Examples 31 and 32 for Example 3, and Table 8 shows Reference Measurement Examples 31 to 35 for Example 3.

  As is apparent from Tables 7 and 8, the inventive examples 31 and 32 of Example 3 both satisfy the preferred limiting range of the present invention in terms of the particle diameter and particle concentration, and the maximum thickness and Since the minimum thickness also satisfies the preferred limited range of the present invention, the light utilization efficiency is higher than 60% to 61% and 55%, and the intermediate altitude is 14% to 14.2%. It satisfies the preferable limited range required by the present invention of more than 25% and 25% or less.

On the other hand, since the measurement example 31 has a particle concentration higher than the preferable limited range of the present invention, and thus exhibits the same phenomenon as a flat plate, a medium-high luminance distribution cannot be realized.
Further, in Measurement Example 32, the particle concentration is lower than the preferred limited range of the present invention, and thus light penetrates and passes, so that 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, the minimum thickness, the particle diameter, and the particle concentration when the light guide length L of the light guide plate 30 corresponding to the screen size of 52 inches and 57 inches is L = 660 mm and 730 mm are shown in Table 9 and As shown in Table 10, the taper, the central radius (the radius of curvature of the multiple curved portion) R, the light utilization efficiency, and the intermediate altitude were obtained when various changes were made. The results are shown in Table 9 and Table 10.
Here, Table 9 shows Examples 41-44 of the present invention for Example 4, and Table 10 shows Reference Measurement Examples 41-45 for Example 4.

  As is apparent from Tables 9 and 10, all of the inventive examples 41 to 44 of Example 4 have a particle diameter and a particle concentration that satisfy the preferred limiting range of the present invention, and the maximum thickness and Since the minimum thickness also satisfies the preferred limited range of the present invention, the light utilization efficiency is 57% to 68%, which is higher than 55%, and the intermediate altitude is 11% to 24%, more than 0%. 25% or less of the preferred limiting range required by the present invention.

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 use efficiency does not satisfy 55% or more.
Further, in the measurement example 42, the maximum thickness and the minimum thickness are both larger than the upper limit values 6.0 mm and 3.0 mm of the preferable limited range of the present invention, and the light penetrates and penetrates. Not only does the light utilization efficiency not exceed 50%, which is 55% or more of the limited range, but the weight becomes too heavy and is not suitable as an optical member for a liquid crystal TV.

Further, in measurement example 43, the maximum thickness is smaller than 1.0 mm which is the lower limit value of the preferred limited range of the present invention, the center radius R is too large, and exceeds the preferred limited range of the present invention. If the particle concentration is not suitable and the light utilization efficiency is 55% or more, the 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, and 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, in any of the embodiments, the present invention has an appropriate shape according to the range of the respective light guide lengths of the light guide plate, the maximum thickness, the minimum thickness, the taper, and the center. The part radius R and the particle diameter and particle concentration of the scattering particles to be dispersed satisfy the preferred limited range of the present invention, the light utilization efficiency is 55% or more, the intermediate altitude is more than 0%, and 25% or less. It can be seen that it has characteristics.
On the other hand, in the measurement examples, even in the range of the light guide length in any of the examples, either of the above requirements is out of the preferred limited range of the present invention, so that the light utilization efficiency does not satisfy 55% or more. The total content exceeds 0% and does not satisfy 25% or less, and excellent properties cannot be exhibited.

Next, a light guide plate of a planar lighting device according to another embodiment will be described.
The light guide plate of the planar lighting device shown in the present embodiment is a large light guide plate, which has a large expansion and contraction due to ambient temperature and humidity, and copes with problems caused by repeated expansion and contraction of 5 mm or more in a size of about 50 inches. Is to do. As a problem caused by the above-described expansion and contraction, in the worst case, the expanded and contracted light guide plate pushes up the liquid crystal panel, and pool-shaped unevenness occurs in the light emitted from the liquid crystal display device.

In order to avoid the above problem, the light guide plate of the planar illumination device shown in the present embodiment employs a light guide plate support mechanism that absorbs expansion and contraction of the light guide plate.
Specifically, as shown in FIG. 18 as an example, one incident surface side of the light guide plate 30A is fixedly supported as a fixed end 74, and the other incident surface side is moved using a sliding mechanism 70. (Sliding) It is configured to be supported.

  That is, on one incident surface side of the light guide plate 30A, the light source 28 is fixed to the fixed end 74 with a pin, and the fixed end 74 is fixed between the upper casing 44 and the lower casing 42. On the other incident surface side, the light source 28 is fixed to the sliding mechanism 70 (70a to 70d) with a pin. Since the sliding mechanism 70 is slidably supported between the upper housing 44 and the lower housing 42, one end of the light guide plate 30A is fixed but the other end moves (slides). This makes it possible to absorb the shrinkage.

In addition, about each component in FIG. 18, the detailed description shall be abbreviate | omitted by attaching | subjecting the same code | symbol to the same component as what was shown previously in FIG.
Also in the light guide plate 30A shown in FIG. 18, a multiple curved portion 30h is formed at the center of the lower surface, thereby reducing the thickness of the light guide plate 30 and creating uneven strips at the central joint. It is possible to obtain a uniform and so-called bell-shaped distribution that is medium to high.

Next, a light guide plate of a planar lighting device according to still another embodiment will be described.
As shown in FIG. 19, the light guide plate 30 </ b> B according to the present embodiment has a basic cross-sectional shape in which the lower surface is mainly an ellipse.
In the light guide plate 30 </ b> B according to the present embodiment, the multiple curved portion 30 h as described above is adopted in a part (lowermost part) of the elliptical shape on the lower surface.

Here, again, with respect to the components in FIG. 19, the same components as those shown in FIG.
Also in the light guide plate 30A shown in FIG. 18, a multiple curved portion 30h is formed in the central portion of the lower surface, thereby reducing the thickness of the light guide plate 30 and making the band unevenness formed in the central joint portion uniform. Moreover, it is possible to obtain a so-called bell-shaped distribution that is medium to high.

In the following, an example for explaining the effect of having the multiple curved portion 30h formed in the center portion of the lower surface including the inverted wedge-shaped light guide plate 30 shown in the above embodiment will be shown.
Table 11 stipulates the shape configuration of the multiple curved portions (or some monotonous curved portions), the radius of curvature of the curved portions, the maximum thickness, the taper angle, the particle concentration, etc. in the light guide plate based on various shapes. In this case, the light utilization efficiency is shown. Here, the light utilization efficiency is indicated by a relative value based on the case defined in item number 1.

  Item No. 1 relates to an example of an inverted wedge-shaped light guide plate, Item No. 2 to Item No. 4 are curvature radii R1, R1 of the multiple bending portion 30h in the light guide plate according to the embodiment shown in FIG. All of R2 are examples of 10,000 mm, and these three are different in particle concentration. Item No. 5 shows an example in which the curvature radii R1 and R2 of the multiple bending portion 30h are 10,000 mm in the light guide plate (having an elliptical reflection surface) according to the embodiment shown in FIG.

  As is apparent from Table 11, the results corresponding to the conditions of item numbers 3 to 6 are all improved in terms of the light utilization efficiency as compared with the results corresponding to the condition of item number 1 as the reference. Is recognized, and shows the effect of making the curved portion of the light guide plate according to the present invention into the multiple curved portion 30h.

FIG. 20 shows a relationship between the distance in the vertical direction (light incident direction) of a 32-inch light guide plate and the corresponding relative illuminance, which is a new example different from the conditions shown in Table 11 above. Indicates.
Table 12 shows the characteristics of the light guide plate shown in FIG.
As shown in Table 12, the item number A corresponds to the condition corresponding to the condition of the item number 1 in Table 11, that is, the inverted wedge-shaped light guide plate in which the curved portion is not a multiple configuration, and the item number B is the same Although it is an inverted wedge-shaped light guide plate, the curved portion has a multiple configuration, and items Nos. C to E correspond to an elliptical light guide plate having a multiple curved portion.

The curve A of the graph shown in FIG. 20 is shown as a reference in order to show the characteristics of the light guide plate according to the present invention, and the curves B to E positioned above this are all related to the present invention. This corresponds to a curved portion in the light guide plate that is a multiple curved portion 30h.
As is apparent from FIG. 20, the curved portion of the light guide plate is a multiple curved portion 30h, and the curvature radii R1, R2 and the like thereof are set within a predetermined range, so that the result is similar to the result in the above-described embodiment. In addition, the thickness of the light guide plate 30 can be reduced, the band unevenness formed in the central joint can be made uniform, and a so-called bell-shaped distribution can be achieved.

  As described above, the present invention has a thin shape, high light utilization efficiency, can emit light with little unevenness in brightness, and has a thickness when using an inverted wedge-shaped or elliptical light guide plate. Even if it is thinner than before, it is possible to obtain a light distribution near the center of the screen, which is required for thin LCD TVs with a large screen, compared to the periphery, that is, a so-called medium-high or bell-shaped brightness distribution. It has great industrial applicability that a light plate and a planar lighting device using the same can be realized.

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 Light source 29 Sub light source 30 Light guide plate 30b 1st inclined surface 30c 2nd inclined surface 30d 1st light Incident surface 30e Second light incident surface 30f First side surface (third light incident surface)
30g Second side (fourth light incident surface)
30h Multiple curved portions 30x, 30y, 30z Curved surface 32 Optical member unit 32a Diffusion sheet 32b Prism sheet 32c Diffusion sheet 33 Spacing member 34 Reflector 36 Upper guide reflector 38 Lower guide reflector 42 Lower housing 44 Upper housing 46 Reinforcement Member 49 Power supply storage unit 50 LED chip 51 Light emitting unit 52 Light source support unit 54 Array substrate 56 Fin 58 Light emitting surface 70 Sliding mechanism 70a, 70d Sliding member fixing member 70b Upper sliding member 70c Lower sliding member 74 Fixed end α 2 etc. Branch line

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 Two symmetrical inclined surfaces whose distance from the light exit surface becomes farther toward each other, a multiple curved portion joining these two inclined surfaces, and scattering particles that scatter light propagating therein Characteristic light guide plate.   In the multiple curved portion, between the two inclined surfaces, the inclination angle of the inclined surface monotonously decreases toward the central portion, then increases monotonically, and becomes an inclination angle of 0 degree at the central portion. The light guide plate according to claim 1.   In the multiple curved portion, between the two inclined surfaces, a cross-sectional shape of the inclined portion of the inclined surface is any one of a combination of a quadratic curve and a circle, an inclined straight line and a circle, and an inclined straight line and a quadratic curve. The light guide plate according to claim 1 represented by:   In the multiple curved portion, between the two inclined surfaces, the cross-sectional shape of the inclined portion of the inclined surface is any one of a combination of a higher order curve and a circle, an inclined straight line and a circle, and an inclined straight line and a higher order curve. The light-guide plate of Claim 2 represented by these. 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 Two symmetrical inclined surfaces each having a distance away from the light exit surface as it goes toward each other, and the multiple curved portions according to any one of claims 1 to 4 that join the two inclined surfaces are propagated therein. A light guide plate containing scattering particles that scatter light
Each includes a plate-like support having a length substantially the same as the longitudinal direction of the light incident surface, and a plurality of light emitting elements arranged in a row on the surface of the support that faces the light incident surface. And a two-light source arranged opposite to the two light incident surfaces of the light guide plate. The light guide plate is
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, 0.02) in a graph with the particle size (μm) of the scattering particles as the horizontal axis and the particle concentration of the scattering particles as the vertical axis. (4.0, 0.085), (7.0, 0.03), (7.0, 0.12), (12.0, 0.06) and (12.0, 0.22) In the enclosed area,
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 planar illumination device according to claim 5, which is 25% or less. The light guide plate is
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 with the particle size (μm) of the scattering particles as the horizontal axis and the particle concentration (wt%) of the scattering particles as the vertical axis. .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%. 25% or less, The planar illumination device according to claim 5 or 6. The light guide plate is
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 6 points (4.0, 0.01), (4.0, 0.05), (7. 7) in a graph in which the horizontal axis represents the particle diameter of the scattering particles and the vertical axis represents the particle concentration of the scattering particles. 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 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, exceeds 0%. 25% or less, The planar illuminating device in any one of Claims 5-7. The light guide plate is
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: 6 points (4.0, 0.008), (4.0, 0.03), (7. 7) in a graph in which the horizontal axis represents the particle diameter of the scattering particles and the vertical axis represents the particle concentration of the scattering particles. 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 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, exceeds 0%. 25% or less, The planar illuminating device in any one of Claims 5-8. The light guide plate is
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 multiple curved portion where the thickness is the thickest is 1.0 mm or more and 6.0 mm or less,
The radius of curvature of the multiple curved portion is 6,000 mm or more and 45,000 mm or less,
The planar illumination device according to any one of claims 5 to 9, wherein a taper of the inclined surface with respect to a line parallel to the light emitting surface is not less than 0.1 ° and not more than 0.8 °. In the light guide plate, 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. 11. The planar illumination device according to claim 5, wherein the inequality 1.1 ≦ Φ · N _p · L · K _C ≦ 8.2 and 0.005 ≦ K _C ≦ 0.1 is satisfied. .   The light emitting element constituting the light source is a light emitting diode, and the light emitting diode is inclined with respect to a direction perpendicular to the light incident surface along the longitudinal direction of the light incident surface of the light guide plate. The planar illumination device according to any one of claims 5 to 11, wherein the planar illumination device is arranged in a state. The inclination angle β of the light emitting diodes arranged in the inclined state is set such that the width of the light emitting diodes is wmm, the height is hmm, the arrangement pitch in the lateral direction is p, and p / 2 = x.
x cosβ <w / 2 (p cosβ <w)
The planar lighting device according to claim 12, wherein: The minimum thickness tmin of the light incident surface of the light guide plate is a dimension s in the vertical direction (thickness direction of the light guide plate) in the inclined state of the light emitting diode.
s = √w ² + h ² cos (β−φ)
The planar lighting device of claim 13, which is larger.
Here, φ in the above formula is
φ = tan ⁻¹ (w / h)
Represents.

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