JP2013008639A - Light guide plate and surface lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate having a high light utilization efficiency and can emit light having little luminous irregularities and can obtain a bright convex distribution in the vicinity of a central part of a screen as compared with a peripheral part, and provide a surface lighting device.SOLUTION: The light guide plate includes two layers comprising a first layer and a second layer which are superimposed in an almost vertical direction to a light emission surface and have different particle concentrations of diffusion particles. The second layer has a cross-sectional shape having at least a part in which the thickness in an almost vertical direction to the light emission surface is continuously increased up to the maximum in a direction as it goes apart from a light incident surface, and the diffusion particles are dispersed so that a synthetic scattering cross-sectional area S in a direction of the two layers in a position along a direction almost parallel with the light emission surface may be continuously and monotonously increased as it goes apart from the light incident surface, and the maximum value Sand the minimum value Sof the synthetic scattering cross-sectional area S shall satisfy 1.25≤S≤2.2, and moreover 0.90≤S≤1.6.

Description

  The present invention relates to a light guide plate having a two-layer structure in which a diffusing material such as diffusing fine particles for emitting planar illumination light is dispersed, a backlight of a liquid crystal display (liquid crystal display device) or an advertising display, and a surface for environmental illumination The present invention relates to a planar illumination device that emits planar illumination light used as a light source or the like.

As the liquid crystal display device, a planar illumination device (backlight unit) that irradiates light from the back side of the liquid crystal display panel and illuminates the liquid crystal display panel is used. The backlight unit is configured by using components such as a light guide plate that diffuses light emitted from a light source for illumination and irradiates the liquid crystal display panel, a prism sheet that diffuses light emitted from the light guide plate, and a diffusion sheet. .
In addition, in backlights for advertising displays and surface light sources for environmental illumination, in order to illuminate the display panel or illuminate the environment in a planar form, the light emitted from the illumination light source is diffused to produce planar illumination. A light guide plate for emitting light is used.

  Currently, there is a need to reduce the thickness of large LCD TVs, large advertising displays, and large surface light sources for environmental lighting, and the backlight unit also has a light guide plate directly above the light source for illumination. Rather than using the direct type, a plate-shaped light guide plate in which scattering particles for scattering light are mixed into a transparent resin is used. A light source for illumination is placed on the side of the light guide plate, and light enters from the side. Therefore, a method of emitting light from the surface has been demanded.

  For example, Patent Document 1 discloses a plate-like light scattering light guide element including at least two light scattering light guide block regions having complementary shapes, and at least one light that can be incident from the side thereof. Light scattering means, and when the scattering ability of each light scattering light guide block area is represented by an effective scattering irradiation parameter value, at least one of the effective scattering irradiation parameter values is any other effective scattering irradiation parameter. The average value of the effective scattering irradiation parameter on the cross section in the thickness direction of the plate-like light scattering light guide element is relatively small at a portion relatively close to the light incident means, and is not relative to the light incident means. A relatively large light-scattering light-guiding light source device has been proposed in a far part.

  Patent Document 2 discloses a plate-like body in which at least one non-scattering light guiding region and at least one scattering light guiding region in which particles having different refractive indexes are uniformly dispersed in the same material are overlapped. In the surface light source device, the light source lamp is mounted on the end face, and the distribution state of both emission from the main surface is controlled by locally adjusting the particle concentration by the thickness of both regions. A surface light source device is proposed in which the scattering light guide region is a convex light guide block and the non-scattering light guide region is a concave light guide block corresponding to the convex light guide block. .

  Further, Patent Document 3 is a light guide plate composed of two layers, and an inclination inclined in a direction approaching the light exit surface as the boundary surface between the first layer and the second layer goes from the end toward the center of the light guide plate. A light guide plate (a cross-sectional shape is, for example, an isosceles triangle) that is a surface is disclosed.

Japanese Patent No. 3215218 (Japanese Patent Laid-Open No. 06-324330) Japanese Patent No. 4127897 (Japanese Patent Laid-Open No. 11-345512) JP 2009-117357 A

By the way, the light-scattering light guide device proposed in Patent Document 1 is composed of two to three light-scattering light-guiding body block regions having different light-scattering capacities, each of which has a plate-like light-scattering light-guiding element. The light-scattering light guide block region having high light scattering ability is configured to be thick at the far part, but it is intended to obtain a uniform and bright light exit surface, and plate-like light scattering It has not been considered to adjust the shape of the light scattering light guide block region of the light guide element in order to optimize the emitted light amount distribution required for the backlight unit of the liquid crystal display device.
Also in the surface light source device described in Patent Document 2, the light guide is composed of a scattering light guide region and a non-scattering light guide region in order to increase the light emission luminance from the light emission surface (main surface) and the uniformity thereof. However, it has not been considered to adjust the shape of the scattering light guide region in order to optimize the distribution of the emitted light quantity required for the backlight unit of the liquid crystal display device described above.

  In addition, the large light guide plate greatly expands and contracts due to ambient temperature and humidity, and repeats expansion and contraction of 5 mm or more for a size of about 50 inches. Therefore, as in the light guide plate (a plate-like light scattering light guide element or light guide) disclosed in Patent Documents 1 and 2, it is not known whether the plate is flat or the light exit surface side or the reflection surface side is warped. When warped to the light emitting surface side, the stretched light guide plate pushes up the liquid crystal panel, and pool-like unevenness occurs in the light emitted from the liquid crystal display device. In order to avoid this, it is conceivable to increase the distance between the liquid crystal panel and the backlight unit in advance, but there is a problem that it is impossible to make the liquid crystal display device thin.

  The light guide plate described in Patent Document 3 is certainly a light guide plate composed of two layers having different particle concentrations. As a result, the light guide plate composed of two layers having different scattering powers as in Patent Document 1, As the boundary surface between the layer and the second layer is directed from the end toward the center of the light guide plate, the cross-sectional shape inclined in the direction approaching the light output surface is a substantially isosceles triangle, but the shape of the second layer It was not taken into account to adjust the light intensity to optimize the amount of emitted light.

In addition, when the backlight unit is thin and large, it is necessary to reduce the particle concentration of the scattering particles in order to guide the light to the depth of the light guide plate, but if the particle concentration of the scattering particles is low, the light incident surface Since the incident light is not sufficiently diffused in the vicinity, bright lines (dark lines, unevenness) due to the arrangement interval of the light sources may be visually recognized in the outgoing light emitted from the vicinity of the light incident surface.
On the other hand, if the particle concentration of the scattering particles is high in the region near the light incident surface, the light incident from the light incident surface is reflected in the region near the light incident surface and emitted from the light incident surface as return light, or There is a risk that light emitted from a region near the light incident surface that is covered and not used increases.

  An object of the present invention is to solve the above-mentioned problems of the prior art, has a large and thin shape, can emit light with high light utilization efficiency and little luminance unevenness, and is required for a large-screen thin liquid crystal television. The distribution near the center of the screen is brighter than the surrounding area, that is, the so-called medium-high or bell-shaped brightness distribution, that is, the luminance distribution of the light emitted from the light exit surface is the periphery of the incident part, etc. Another object of the present invention is to provide a light guide plate capable of obtaining a bell-shaped distribution (hereinafter referred to as “medium-high distribution”) higher than the luminance of the portion and a planar illumination device using the same.

In order to solve the above-described problems, a light guide plate of the present invention is provided with a rectangular light exit surface and light that travels in a direction substantially parallel to the light exit surface and is provided on the edge side of the light exit surface. A light guide plate having at least one light incident surface and a back surface opposite to the light output surface, in which diffusion particles are dispersed, wherein the light guide plate is substantially perpendicular to the light output surface. Two layers having different particle concentrations of the diffusing particles, which overlap each other, and these two layers are located at least on the first layer located on the light emitting surface side and on the back side, A second layer in contact with the first layer, and the second layer has a thickness in a direction substantially perpendicular to the light emitting surface in a direction substantially parallel to the light emitting surface, and the thickness is A cross-sectional shape having at least a portion that continuously increases in the direction away from the light incident surface and has a maximum is formed. The combined scattering cross section S in a direction substantially perpendicular to the light exit surface of the two layers at a position along a direction substantially parallel to the light exit surface is continuously and monotonously increased as the distance from the light entrance surface increases. The diffusion particles are dispersed, and the maximum value S _max and the minimum value S _min of the combined scattering cross section S satisfy the following formula (1).
1.25 ≦ S _max ≦ 2.2
0.90 ≦ S _min ≦ 1.6 (1)
Here, the second layer has a cross section in which the thickness in a direction substantially perpendicular to the light emitting surface in a direction substantially parallel to the light emitting surface has at least one minimum value and at least one maximum value. The shape is preferably formed.

The at least one light incident surface is preferably two light incident surfaces provided on two opposite sides of the light emitting surface.
The cross-sectional shape of the second layer preferably includes three arcs or four arcs, and has the minimum value on each side of the two light incident surfaces, and the two light beams It is preferable that the maximum value is at the approximate center between the incident surfaces, and an arc forming the minimum value is provided on each side of the two light incident surfaces, and the approximate center between the two light incident surfaces is provided. It is preferable to have an arc that forms the maximum value.
Moreover, it is preferable that the thickness of the second layer is the thickest in the approximate center of the light emitting surface.

Further, the at least one light incident surface is one light incident surface provided on one end side of the light emitting surface, and the cross-sectional shape of the second layer is that of the one light incident surface. It is preferable to have the minimum value on the side and to have the maximum value on the other end side of the light emitting surface.
The cross-sectional shape of the second layer has an arc that forms the minimum value on the one light incident surface side, and an arc that forms the maximum value on the other end side of the light emitting surface. It is preferable to have.

The light traveling length of light traveling in a direction substantially parallel to the light exit surface from the one light incident surface to the center or the other end is 500 mm or more and 615 mm or less, and the particle size of the diffusing particles Is not less than 4.5 μm and not more than 12.0 μm, and the concentration of the diffusing particles dispersed in the second layer is not less than 0.10 wt% and not more than 1.04 wt%, and is dispersed in the second layer The particle size and concentration of the diffusing particles are 6 points (4.5, 0. 10), (4.5, 0.30), (7.0, 0.14), (7.0, 0.39), (12.0, 0.38) and (12.0, 1. 04).
The concentration of the diffusion particles dispersed in the first layer is 0.00 wt% or more and 0.101 wt% or less, and the particle size and concentration of the diffusion particles dispersed in the first layer are the scattering particles. In the graph in which the horizontal axis is the particle diameter (μm) of the particle and the vertical axis is the particle concentration (wt%) of the diffusion particles, 5 points (4.5, 0.00), (4.5, 0.016) , (7.0, 0.022), (12.0, 0.00) and (12.0, 0.101).

The light traveling length of light traveling in a direction substantially parallel to the light exit surface from the one light incident surface to the center or the other end is 700 mm or more and 850 mm or less, and the particle size of the diffusing particles Is not less than 4.5 μm and not more than 12.0 μm, and the concentration of the diffusion particles dispersed in the second layer is not less than 0.07 wt% and not more than 0.74 wt%, and is dispersed in the second layer. The particle size and concentration of the diffusing particles are 6 points (4.5, 0. 07), (4.5, 0.21), (7.0, 0.10), (7.0, 0.28), (12.0, 0.27) and (12.0, 0.0. 74).
Further, the concentration of the diffusion particles dispersed in the first layer is 0.00 wt% or more and 0.072 wt% or less, and the particle size and concentration of the diffusion particles dispersed in the first layer are the scattering particles. In a graph in which the horizontal axis is the particle size (μm) of the particle and the vertical axis is the particle concentration (wt%) of the diffusing particles, 5 points (4.5, 0.00), (4.5, 0.011) , (7.0, 0.016), (12.0, 0.00) and (12.0, 0.072).

Further, the light use efficiency indicating the ratio of the light incident from the at least one light incident surface being emitted from the light exit surface is 70% or more, and the light emitted from the vicinity of the peripheral portion of the light exit surface The middle portion of the luminance distribution of the light emitting surface indicating the ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance is more than 0% and 45% or less, and the central portion of the light emitting surface It is preferable that the luminance distribution is convex.
Moreover, it is preferable that the said back surface is a plane parallel to the said light-projection surface.

  In order to solve the above problems, the planar illumination device of the present invention houses the light guide plate, a light source disposed to face the light incident surface of the light guide plate, the light guide plate and the light source, A housing having an opening smaller than the light exit surface is provided on the light exit surface side of the light guide plate.

According to the present invention, a large, thin shape, high light utilization efficiency, light with little luminance unevenness can be emitted, and the central portion of the screen required for a large-screen thin liquid crystal television A brightness distribution that is brighter than that of the peripheral portion, that is, a so-called medium-high or bell-shaped brightness distribution having a medium-high brightness can be obtained. In particular, according to the present invention, a medium-high luminance distribution can be simultaneously realized at a high efficiency (for example, 70% or more) that cannot be achieved by a conventional flat light guide plate.
In addition, according to the present invention, a method for designing the cross-sectional shape of the two-layer flat light guide plate is also included. By designing based on this method, the cross-sectional shape of the second layer (lower layer) on the back side is determined. In this case, it is possible to freely select the condition of the diffusing particles to be dispersed inside, and the degree of freedom in design can be improved.

It is a schematic perspective view which shows one Embodiment of a liquid crystal display device provided with the planar illuminating device using the light-guide plate 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 the III-III arrow directional view of the planar illuminating device shown in FIG. 2, (B) is BB sectional drawing of (A). (A) is a perspective view which shows schematic structure of the light source of the planar illuminating device shown to FIG.1 and FIG.2, (B) is a schematic perspective view which expands and shows one LED of the light source shown to (A). FIG. It is a schematic perspective view which shows the shape of the light-guide plate shown in FIG. FIG. 6 is a cross-sectional view taken along the line VI-VI for explaining the layer structure of the light guide plate shown in FIG. 5. (A) And (B) is a graph which shows the relationship between the particle diameter [micrometer] and particle concentration [wt%] of the scattering particle | grains disperse | distributed to the upper layer and lower layer of an example of the light-guide plate of this invention, respectively. (A) And (B) is a graph which shows the relationship between the particle diameter [micrometer] and particle concentration [wt%] of the scattering particle disperse | distributed to the upper layer and lower layer of the other example of the light-guide plate of this invention, respectively. It is a flowchart which shows an example of the design method of the light-guide plate of this invention. It is a graph which shows three examples of the cross-sectional shape of the 2nd layer (lower layer) of the light-guide plate designed with the design method of the light-guide plate shown in FIG. It is a graph which shows the synthetic | combination scattering cross section per unit length with respect to the light guide position about five design examples of the light guide plate designed with the design method of the light guide plate shown in FIG. It is a graph which shows the relative illumination intensity of the emitted light with respect to the light guide position about five design examples of the light-guide plate used as the synthetic | combination scattering cross section shown in FIG. It is a graph which shows the utilization efficiency of incident light with respect to the particle | grain density | concentration of the 2nd layer (lower layer) of the light-guide plate designed with the design method of the light-guide plate shown in FIG. (A)-(D) are schematic sectional drawings which show another example of the light-guide plate which concerns on this invention. (A)-(D) are schematic sectional drawings which show another example of the light-guide plate which concerns on this invention. It is a schematic sectional drawing which shows another example of the planar illuminating device which concerns on this invention. (A)-(E) are schematic sectional drawings which show another example of the light-guide plate which concerns on this invention.

Hereinafter, a planar illumination device using a light guide plate according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a perspective view schematically showing a liquid crystal display device including a planar illumination device using a light guide plate according to the present invention, and FIG. 2 is a cross-sectional view taken along the line II-II of the liquid crystal display device shown in FIG. is there.
3A is a view taken along the line III-III of the planar illumination device (hereinafter also referred to as “backlight unit”) shown in FIG. 2, and FIG. It is a BB sectional view taken on the line.

  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. In FIG. 1, a part of the liquid crystal display panel 12 is not shown in order to show the configuration of the backlight unit.

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 liquid crystal display panel 12 targeted by the light guide plate of the present invention has a large screen size of 37 inches (37 ") or more, and is used for a large and thin liquid crystal television having such a large screen. As the screen size of the liquid crystal display panel 12, for example, 40 inches (40 "), 42 inches (42"), 46 inches (46 "), 52 inches (52"), 55 inches ( 55 ") and 65 inches (65").
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 illumination 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 in this embodiment includes two light sources 28, a light guide plate 30 and an optical member unit 32 according to the present invention, as shown in FIGS. 1, 2, 3A, and 3B. And a housing 26 having a lower housing 42, an upper housing 44, a folding member 46, and a support member 48. 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 of the housing 26.
Hereinafter, each component which comprises the backlight unit 20 is demonstrated.

  The illuminating device body 24 includes a light source 28 that emits light, a light guide plate 30 that emits light emitted from the light source 28 as planar light, and a light that is emitted from the light guide plate 30 by scattering or diffusing the light. And an optical member unit 32 having light without unevenness.

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 backlight unit 20 shown in FIGS. 1 and 2, and FIG. 4B is one of the light sources 28 shown in FIG. It is a schematic perspective view which expands and shows only one LED chip.
As shown in FIG. 4A, the light source 28 includes a plurality of light emitting diode chips (hereinafter referred to as “LED chips”) 50 and a light source support portion 52.

The LED chip 50 is a chip in which a fluorescent material is applied to the surface of a light emitting diode that emits blue light. The LED chip 50 has a light emitting surface 58 having a predetermined area, and emits white light from the light emitting surface 58.
That is, when the blue light emitted from the surface of the light emitting diode of the LED chip 50 passes through the fluorescent material, the fluorescent material fluoresces. Accordingly, white light is generated and emitted from the LED chip 50 by the blue light emitted from the light emitting diode and the light emitted by the fluorescent substance 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.

The light source support portion 52 is a plate-like member that is disposed so that one surface thereof faces the light incident surface (30c, 30d) of the light guide plate 30.
The light source support 52 supports the plurality of LED chips 50 on a side surface that is a surface facing the light incident surface (30c, 30d) of the light guide plate 30 with a predetermined distance therebetween. Specifically, the plurality of LED chips 50 constituting the light source 28 are arranged along the longitudinal direction of the first light incident surface 30c or the second light incident surface 30d of the light guide plate 30, which will 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 30c intersects, or parallel to the line where the light emitting surface 30a and the second light incident surface 30d intersect, and are fixed on the light source support 52. ing.

  The light source support 52 is made of a metal having good thermal conductivity such as copper or aluminum, and also has a function as a heat sink that absorbs heat generated from the LED chip 50 and dissipates it to the outside. The light source support 52 may be provided with fins that can increase the surface area and increase the heat dissipation effect, or may be provided with a heat pipe that transfers heat to the heat dissipation member.

Here, as shown in FIG. 4B, the LED chip 50 of the present embodiment has a rectangular shape whose length in the direction orthogonal to the arrangement direction is shorter than the length of the LED chip 50 in the arrangement direction, that is, described later. The light guide plate 30 has a rectangular shape in which the thickness direction (the direction perpendicular to the light emitting surface 30a) is a short side. In other words, the LED chip 50 has a shape in which b> a when the length in the direction perpendicular to the light emitting surface 30a of the light guide plate 30 is a and the length in the arrangement direction is b. Further, q> b, where q is the arrangement interval of the LED chips 50. Thus, the relationship among the length a in the direction perpendicular to the light emitting surface 30a of the light guide plate 30 of the LED chip 50, the length b in the arrangement direction, and the arrangement interval q of the LED chips 50 satisfies q>b> a. It is preferable.
By making the LED chip 50 into a rectangular shape, a thin light source can be obtained while maintaining a large light output. By making the light source 28 thinner, the backlight unit can be made thinner. In addition, the number of LED chips can be reduced.

In addition, since the LED chip 50 can make the light source 28 thinner, it is preferable that the LED chip 50 has a rectangular shape having a short side in the thickness direction of the light guide plate 30. However, the present invention is not limited to this, and the square shape and the circular shape are not limited thereto. LED chips having various shapes such as a shape, a polygonal shape, and an elliptical shape can be used.
In this embodiment, the LED chips 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 plurality of LED chips 50 arranged on an array support are provided. A multilayer LED array having a laminated structure can also be used as a light source. Even when LED arrays are stacked in this manner, more LED arrays can be stacked by making the LED chip 50 rectangular and thinning the LED array. In this way, a larger amount of light can be output by stacking multilayer LED arrays and increasing the filling rate of the LED arrays (LED chips). 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.

Next, the light guide plate 30 according to the present invention will be described with reference to FIGS. 2, 3 </ b> A, 3 </ b> B, 5, and 6.
As shown in FIGS. 5A and 5B, the light guide plate 30 is a transparent flat plate that forms a rectangular parallelepiped with a small thickness, and is a light emitting surface 30a that is a flat surface having a substantially rectangular shape, for example, a rectangular shape. And a rear surface 30b that is a flat plane substantially the same shape as the light emitting surface 30a, on the opposite side of the light emitting surface 30a, that is, on the back side of the light guide plate 30, and the long side of the light emitting surface 30a. Both end surfaces have two light incident surfaces (a first light incident surface 30c and a second light incident surface 30d) formed substantially perpendicular to the light emitting surface 30a.

The two light sources 28 described above are arranged on the first light incident surface 30c and the second light incident surface 30d of the light guide plate 30 so as to face each other. Here, in the present embodiment, the length of the light emitting surface 58 of the LED chip 50 of the light source 28 and the lengths of the first light incident surface 30c and the second light incident surface 30d are substantially the same in the direction substantially perpendicular to the light emitting surface 30a. The same length is preferred.
Thus, in the backlight unit 20 of the present embodiment, the two light sources 28 are disposed so as to sandwich the light guide plate 30. That is, the light guide plate 30 is disposed between the two light sources 28 that are disposed to face each other with a predetermined distance therebetween.

  Accordingly, the two light incident surfaces 30c and 30d are located opposite to the opposite long sides of the light emitting surface 30a, and the two light incident surfaces 30c and 30c are disposed from the two light sources 28 disposed opposite to each other. The light respectively incident on 30d is directed toward the central portion of the light exit surface 30a (the bisector of the short side facing it) and is substantially parallel to the light exit surface 30a and diffused particles in the light guide plate 30 (details will be described later). The light propagates through the light guide plate 30 and is emitted from the light exit surface 30a.

  Here, in the present invention, the light guide length L through which the light propagates between the first light incident surface 30c and the second light incident surface 30d is 37 inches (37 ") or 40 inches (40"). Since the liquid crystal panel 12 of a size or larger is targeted, it is necessary to be 500 mm or larger, and the liquid crystal panel 12 having a screen size of 65 inches (65 ″) at the maximum is targeted, so that it is preferably 850 mm or smaller. For 40 inch (40 ″), for example, 37 inch (37 ″), 40 inch (40 ″), 42 inch (42 ″) and 46 inch (46 ″) 46 screen sizes. The length L is 500 mm or more and 615 mm or less, for example, 540 mm with a screen size of 40 inches (40 ″), and around 55 inches (55 ″), for example, 52 inches (52 ″), 55 inches ( 5 against the screen size ") and 65 inch (65"), light guiding length L is more than 700mm, 850 mm or less, for example, is good is 700mm in screen size of 52 inch (52 ").

  Here, the light guide plate 30 has dispersed therein diffused particles that scatter and diffuse light incident from the light incident surfaces 30c and 30d, but overlap each other in a direction substantially perpendicular to the light emitting surface 30a. It is formed in a two-layer structure that is divided into two layers having different particle concentrations of diffusion particles, that is, a first layer 60 on the light emitting surface 30a side and a second layer 62 on the back surface 30b side. Assuming that the boundary between the first layer 60 and the second layer 62 is a boundary surface z, the first light incident surface 30c and the second light incident surface 30d are respectively the first layer 60 side and the second layer 62 at the boundary surface z. The first layer 60 is a layer on the light emitting surface 30a side, is a cross-sectional area surrounded by the light emitting surface 30a and the boundary surface z, and the second layer 62 is It is a layer on the back surface 30b side with respect to one layer 60, and is a cross-sectional area surrounded by the boundary surface z and the back surface 30b.

  Further, the boundary surface z between the first layer 60 and the second layer 62 has a light emitting surface 30a in a direction substantially parallel to the light emitting surface 30a when viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 30c. The thickness of the second layer 62 in a direction substantially perpendicular to the maximum becomes a maximum (maximum in the illustrated example) at the central portion (that is, on the bisector α) of the light emitting surface 30a. It continuously changes so as to become thinner toward the incident surface 30c and the second light incident surface 30d, and becomes minimum (minimum in the illustrated example) before the first light incident surface 30c and the second light incident surface 30d. From these minimums, the thickness gradually changes toward the first light incident surface 30c and the second light incident surface 30d, respectively.

Specifically, as shown in FIG. 6, the cross-sectional shape of the boundary surface z, which is perpendicular to the longitudinal direction of the light incident surface 30c, is a curve that is convex toward the light emitting surface 30a at the center of the light emitting surface 30a. , Preferably one arc R1 (curvature radius R1) and two concave curves, preferably two arcs R2 (curvature radius) connected smoothly to this convex curve and connected to the light incident surfaces 30c, 30d respectively. R2).
Note that the uneven curve is not limited to a circular arc, and may be a part of a quadratic curve such as an ellipse, a parabola, or a hyperbola, or a part of a cubic or higher order curve, a trigonometric function, or another curve. May be. In addition, a straight line portion may be included in a connection portion between the convex curve and the concave curve, or in a connection portion between the concave curve and the light incident surfaces 30c and 30d.

Therefore, in the light guide plate 30 shown in FIG. 6, the cross-sectional shape of the boundary surface z in the cross section, that is, the cross-sectional shape of the second layer 62, is one arc R1 having a radius of curvature R1 and two arcs R2 having a radius of curvature R2. And three arcs. Therefore, the thickness of the second layer 62 is composed of three extreme values: one maximum value at the central portion of the light emitting surface 30a and two minimum values on the light incident surfaces 30c and 30d sides.
In the present specification, the unevenness of the curve is referred to toward the light emitting surface 30a, and the light emitting surface 30a side may be referred to as the upper side, and the back surface 30b side may be referred to as the lower side.

As described above, the light guide plate 30 of the present invention is formed by kneading and dispersing diffusion particles (hereinafter referred to as scattering particles) for scattering and diffusing light in a transparent resin as a base material. It is.
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 scattering particles to be kneaded and dispersed in the light guide plate 30, fine particles such as Tospearl, silicone, silica, zirconia, and dielectric polymer can be used.

  In the light guide plate 30 according to the present invention, the scattering particles are dispersed at different particle concentrations in the first layer 60 and the second layer 62, but are substantially parallel to the light exit surface 30a from the light incident surfaces 30c and 30d, respectively. The combined scattering cross sections S per unit length in the direction substantially perpendicular to the light exit surface 30a of the first layer 60 and the second layer 62 at the light guide position along the direction are respectively from the light incident surfaces 30c and 30d. It is necessary to be distributed so as to have at least a portion that increases continuously and monotonously as the light guide position (length or distance) increases. That is, in the light guide plate 30, the combined scattering cross section S per unit length continuously increases monotonically from the minimum value or the minimum value according to the light guide distance from the light incident surfaces 30c and 30d, or the maximum value or It is necessary to have a portion that reaches the maximum value.

The maximum value S _max and the minimum value S _min of the combined scattering cross section S per unit length must satisfy the following formula (1).
1.25 ≦ S _max ≦ 2.2
0.90 ≦ S _min ≦ 1.6 (1)
Here, in the light guide plate of the present invention, the maximum value S _max and the minimum value S _min of the combined scattering cross section S per unit length are large and thin by satisfying the following formula (1). However, it is possible to emit light with high light utilization efficiency and little unevenness in brightness, and a light distribution near the center of the screen, which is required for large-screen thin LCD TVs, compared to the periphery, so-called medium-high or bell A medium-high distribution of brightness can be obtained.

Here, the combined scattering cross section S [mm ² ] per unit length can be calculated from the following formulas (2), (3), and (4) as follows.

Where σx (σ [mm ² ]) is the combined scattering cross section at each light guide position x of the light guide plate 30, Δx is the unit length, a is the particle size of the scattering particles, T is the thickness of the light guide plate 30, t _x1 and t _x2 (t _xi , i = 1, 2) are the thicknesses of the first layer (upper layer) 60 and the second layer (lower layer) 60 at the light guide position x, and N ₁ and N ₂ (N _i , i = 1, 2) is the number of cross-sectional particles of the first layer 60 and the second layer 62 at each light guide position x, and C _i [wt%] (i = 1, 2) is the particles of the first layer 60 and the second layer 62. concentrations, d _p and d _m is the density of the scattering particles and the base material. Qsca1 and Qsca2 [mm ² ] (Qscai, i = 1, 2) are scattering efficiency of the scattering particles dispersed in the first layer 60 and the second layer 62, and the scattering particle condition (scattering particles and mother particles). Based on the Mie theory from the refractive index and wavelength of the material.

In the present invention, the combined scattering cross section S of the first layer 60 and the second layer 62 at the light guide position increases continuously and monotonously as the distance from the light incident surfaces 30c and 30d increases (the light guide position increases). It is necessary to satisfy the scattering particle dispersion condition of the present invention in which the scattering particles are dispersed and the maximum value S _max and the minimum value S _{min of} the combined scattering cross section S satisfy the above formula (1).
By the way, in the present invention, the particle concentration of the scattering particles dispersed in the first layer 60 and the second layer 62 may be any as long as this particle dispersion condition is satisfied. When the particle concentration of the scattering particles is Npo and the particle concentration of the scattering particles of the second layer 62 is Npr, the relationship between Npo and Npr is preferably 0 ≦ Npo <Npr. That is, the light guide plate 30 preferably has a higher particle concentration of scattering particles in the second layer on the back surface 30b side than in the first layer 60 on the light exit surface 30a side. In the present invention, the particle concentration Npo of the scattering particles of the first layer 60 is 0, that is, the first layer 60 may be a layer made of only a base material transparent resin in which scattering particles are not dispersed.

As described above, in the light guide plate 30 of the present embodiment, one maximum value (in which the thickness of the second layer 62 having a higher particle concentration of scattering particles than that of the first layer 60 is increased at the center of the emission surface 30a ( By continuously changing so as to have a maximum value that is the thickest in the illustrated example) and two local minimum values that are thin in the vicinity of the light incident surfaces 30c and 30d (the minimum value that is the thinnest in the illustrated example), The combined scattering cross section of the scattering particles is changed so as to have a maximum value (maximum value) at the center of the exit surface 30a and a minimum value (minimum value) near each of the light incident surfaces 30c and 30d. .
As a result, in the light guide plate 30 of the present embodiment, the scattering particles with different particle concentrations so that the maximum value S _max and the minimum value S _min of the above-described combined scattering cross section S satisfy the above formula (1). The first layer 60 and the second layer 62 can be formed, and even when the shape is large and thin, light use efficiency is high, for example, 70% or more, and light with less unevenness in brightness is emitted. It is possible to obtain a medium-high distribution in which the vicinity of the central portion is brighter than the peripheral portion, for example, a medium-high distribution of more than 0% and 45% or less, preferably 10% or more and 45% or less.

In addition, when adjusting the shape of the boundary surface z, the luminance distribution (scattering particle concentration distribution) can be arbitrarily set within the range satisfying the scattering particle dispersion condition of the present invention, thereby maximizing the efficiency. Can be improved.
In addition, if the particle concentration of the first layer 60 on the light emitting surface 30a side is lowered, the amount of scattered particles as a whole can be reduced, and the cost can be reduced.

Here, the light guide plate 30 in the illustrated example is divided into the first layer 60 and the second layer 62 at the boundary surface z, but the first layer 60 and the second layer 62 differ only in the particle concentration. The same scattering particles are dispersed in the same transparent resin, and are structurally integrated. That is, when the light guide plate 30 is divided on the basis of the boundary surface z, the particle concentration in each region is different, but the boundary surface z is a virtual line, and the first layer 60 and the second layer 62 are integrated. It has become.
Such a light guide plate 30 can be manufactured using an extrusion molding method or an injection molding method.

  In the light guide plate 30, the light emitted from the light source 28 and incident from the first light incident surface 30 c and the second light incident surface 30 d is included in the first layer 60 and the second layer 62 of the light guide plate 30. While being scattered by the scattering particles (scattering body), the light travels through and passes through the light guide plate 30 substantially parallel to the light exit surface 30a, and is emitted directly from the light exit surface 30a or once leaked from the back surface 30b. The light is reflected by a reflecting plate 34 (details will be described later) disposed on the back surface 30b side of the light 30 and enters the light guide plate 30 again, and then is emitted from the light emitting surface 30a.

Here, a preferable example of scattering particles dispersed in the first layer 60 and the second layer 62 of the light guide plate 30 will be described.
Here, the particle size of the scattering particles dispersed in the first layer 60 and the second layer 62 of the light guide plate 30 of the present invention is not particularly limited, but the particle size of the scattering particles dispersed in the second layer 62 is It is preferably 4.5 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, regarding the selection of the optimum particle size of the scattering particles to be dispersed in the first layer 60 and the second layer 62 of the light guide plate 30 of the present invention, it is preferable to consider the following points in addition to the viewpoint of wavelength dependence. .
First, in the scattered light intensity distribution (angular distribution) by a single particle, it is preferable to satisfy the condition that the light scattered in the forward 0 to 5 ° is 90% or more. This is because, for example, when the light guide plate 30 according to the present invention corresponds to a screen size of 40 inches, it is at least a distance of 250 mm or more from the light incident surface 30c and the second light incident surface 30d on the side surface of the light guide plate 30 and is incident on one side. This is because it is necessary to guide a distance of at least 500 mm from the light incident surface.

For this reason, if the particle diameter of the scattering particles dispersed in the second layer 62 is smaller than 4.5 μm, that is, less than 4.5 μm, the scattering becomes isotropic, so that the above condition cannot be satisfied. is there. As a result, an acrylic resin can be selected as the base material, and a silicone resin can be selected as the scattering particles.
On the other hand, if the particle size of the scattering particles dispersed in the second layer 62 is larger than 12.0 μm, that is, if it exceeds 12.0 μm, the forward scattering property of the scattering particles becomes too strong, so that the mean free path in the system is large. Thus, since the number of scattering times decreases, luminance unevenness (firefly unevenness) between the light sources (LEDs) 28 appears near the incident end, and therefore the upper limit value is preferably limited to 12.0 μm.
The reason is that if the particle concentration is too high, the medium-high distribution cannot be realized. If the particle concentration is too low, light penetrates and penetrates, so that the light utilization efficiency does not satisfy 70% or more. It is.

As described above, in the present invention, by selecting an optimum particle size (combination of the scattering particle refractive index and the base material refractive index) included in the limited range of the particle diameter of the scattering particles, the outgoing light without wavelength unevenness can be obtained. Obtainable.
In the above-described example, scattering particles having a single particle size are used. However, the present invention is not limited to this, and scattering particles having a plurality of particle sizes may be mixed and used.
In the present invention, as in the example described above, it is preferable to use the same scattering particles having the same particle diameter as the scattering particles dispersed in the first layer 60 and the second layer 62 of the light guide plate 30. The present invention is not limited to this, and different scattering particles may be used as long as the scattering particle dispersion conditions of the present invention described above can be satisfied.

  Further, as described above, the particle concentration of the scattering particles is preferably different between the first layer 60 and the second layer 62 of the light guide plate 30, but the light guide length of the light guide plate 30 of the present invention is 500 mm to 850 mm. In the case of the first layer 60, it is preferably 0.000 wt% or more and 0.101 wt% or less, and in the second layer 62, 0.07 wt% or more and 1.04 wt% or less is preferable.

  For example, when the light guide length L is 500 mm ≦ L ≦ 615 mm, in the first layer 60, the particle diameter is 4.5 μm or more and 12.0 μm or less, and the particle concentration is 0.000 wt% or more, 0.101 wt%. The second layer 62 preferably has a particle diameter of 4.5 μm or more and 12.0 μm or less, and a particle concentration of 0.10 wt% or more and 1.04 wt% or less.

Specifically, in the first layer 60, when the particle diameter is 4.5 μm, the particle concentration is preferably 0.000 wt% or more and 0.016 wt% or less, and when the particle diameter is 7.0 μm, The concentration is preferably 0.000 wt% or more and 0.022 wt% or less. When the particle diameter is 12.0 μm, the particle concentration is preferably 0.000 wt% or more and 0.101 wt% or less.
That is, in the first layer (upper layer) 60, as shown in the graph of FIG. 7A, the particle size (μm) of the scattering particles is on the horizontal axis, and the particle concentration (wt%) of the scattering particles is on the vertical axis. When the particle size and particle concentration of the scattering particles are 5 points (4.5, 0.00), (4.5, 0.016), (7.0, 0.022), (12.0, 0) .00) and (12.0, 0.101).

In the second layer 62, when the particle diameter is 4.5 μm, the particle concentration is preferably 0.10 wt% or more and 0.30 wt% or less, and when the particle diameter is 7.0 μm, the particle concentration is 0. .14 wt% or more and 0.39 wt% or less is preferable, and when the particle diameter is 12.0 μm, the particle concentration is preferably 0.38 wt% or more and 1.04 wt% or less.
That is, in the second layer (lower layer) 62, as shown in the graph of FIG. 7B, the particle size (μm) of the scattering particles is on the horizontal axis, and the particle concentration (wt%) of the scattering particles is on the vertical axis. When the particle size and particle concentration of the scattering particles are 6 points (4.5, 0.10), (4.5, 0.30), (7.0, 0.14), (7.0, 0) .39), (12.0, 0.38) and (12.0, 1.04).

  On the other hand, for example, when the light guide length L is 700 mm ≦ L ≦ 850 mm, in the first layer 60, the particle diameter is 4.5 μm or more and 12.0 μm or less, the particle concentration is 0.000 wt% or more, and 0.0. The second layer 62 may have a particle diameter of 4.5 μm or more and 12.0 μm or less, and a particle concentration of 0.07 wt% or more and 0.74 wt% or less.

Specifically, in the first layer 60, when the particle diameter is 4.5 μm, the particle concentration is preferably 0.000 wt% or more and 0.011 wt% or less, and when the particle diameter is 7.0 μm, The concentration is preferably 0.000 wt% or more and 0.016 wt% or less, and when the particle diameter is 12.0 μm, the particle concentration is preferably 0.000 wt% or more and 0.072 wt% or less.
That is, in the first layer (upper layer) 60, as shown in the graph of FIG. 8A, the particle size (μm) of the scattering particles is on the horizontal axis, and the particle concentration (wt%) of the scattering particles is on the vertical axis. When the particle size and concentration of the scattering particles are 5 points (4.5, 0.00), (4.5, 0.011), (7.0, 0.016), (12.0, 0.00). 00) and (12.0, 0.072).

In the second layer 62, when the particle diameter is 4.5 μm, the particle concentration is preferably 0.07 wt% or more and 0.21 wt% or less, and when the particle diameter is 7.0 μm, the particle concentration is 0. .10 wt% or more and 0.28 wt% or less is preferable, and when the particle diameter is 12.0 μm, the particle concentration is preferably 0.27 wt% or more and 0.74 wt% or less.
That is, in the second layer (lower layer) 62, as shown in the graph of FIG. 8B, the particle size (μm) of the scattering particles is on the horizontal axis, and the particle concentration (wt%) of the scattering particles is on the vertical axis. When the particle size and particle concentration of the scattering particles are 6 points (4.5, 0.07), (4.5, 0.21), (7.0, 0.10), (7.0, 0) .28), (12.0, 0.27) and (12.0, 0.74).

  As described above, in the light guide plate 30 of the present invention, the particle size and particle concentration of the scattering particles in the first layer 60 and the second layer 62 are as shown in FIGS. 7 (A) and 7 (B) and FIG. 8 (A). And the reason why it is necessary to be within the region surrounded by the points 5 and 6 of the graph shown in (B) is that if the particle concentration is too high outside this region, it is more than 0% and less than 45% If the particle concentration is too low, the light penetrates and passes through, so that the light utilization efficiency of 70% or more is not satisfied. Although the utilization efficiency is improved, a medium-high luminance distribution cannot be realized, and if the particle size is too large, a medium-high luminance distribution can be realized, but the light utilization efficiency is low.

When the first layer 60 and the second layer 62 of the light guide plate 30 satisfy the above relationship, the light guide plate 30 does not scatter incident light so much in the first layer 60 having a low particle concentration. The light can be guided to the back (center), and as it approaches the center of the light guide plate, light can be scattered by the second layer 62 having a high particle concentration, and the amount of light emitted from the light exit surface 30a can be increased. . That is, it is possible to make the illuminance distribution medium to high at a suitable ratio while further improving the light utilization efficiency.
Here, the particle concentration [wt%] is the ratio of the weight of the scattering particles to the weight of the base material.

Further, the thickness of the light guide plate of the present invention is not particularly limited, and may be several mm, for example, about 4 mm as in the case of a conventional printed light guide plate. Since the light guide plate does not cause a problem such as a dot pattern being recognized even if it is thin, it may have a thickness of 1 mm to 3 mm, preferably about 2 mm, or may be a film having a thickness of 1 mm or less. A so-called light guide sheet may be used.
In addition, as a method for producing a film-shaped light guide plate in which scattering particles having different particle concentrations are kneaded and dispersed in the two layers of the present invention, a base film containing scattering particles as a first layer is formed by an extrusion molding method or the like. After applying the monomer resin liquid (transparent resin liquid) in which the scattering particles are dispersed on the prepared base film, the monomer resin liquid is cured by irradiating with ultraviolet rays or visible light, thereby obtaining a desired In addition to a method of producing a second layer having a particle concentration to form a film-shaped light guide plate, there are a two-layer extrusion molding method and the like.
Even when the light guide plate is a film-like light guide sheet having a thickness of 1 mm or less, by making it a two-layer light guide plate, it is possible to increase the illuminance distribution at a suitable ratio while increasing the light utilization efficiency. it can.

  The thinner the light guide plate is, the lighter the light guide plate is, and there is an advantage that the material cost can be reduced. However, if the thickness is too small, the light incident surface becomes smaller, the size of the light source becomes smaller, and the amount of light is less. Therefore, light incidence from the light source is reduced, and light with sufficient luminance cannot be emitted from the light emission surface. On the other hand, if the thickness is too large, the weight is too heavy to be suitable as an optical member such as a liquid crystal display device, and if the diffusing particles are dispersed at a particle concentration that achieves a medium-high luminance distribution, light penetrates through the periphery. If the diffusion particles are dispersed at a particle concentration that increases the light utilization efficiency, the medium-high luminance distribution cannot be realized. Therefore, what is necessary is just to select the kind (size) of a light source, and the thickness of a light-guide plate according to the use application of a light-guide plate. For a light guide plate of about 2 mm for TV use, a 3 × 1.4 mm LED having a light emitting portion width in the thickness direction of the light guide plate of about 1 to 1.1 mm may be used as a light source because of its required performance. In addition, there is no such restriction in an illumination application that can be used as indirect illumination even with a small amount of light, so that an LED of about 0.1 to 0.5 mm that is used for a mobile phone can be used. Therefore, a film-shaped light guide sheet having a thickness of 0.1 mm to 1 mm is also possible.

In addition, the thickness and shape of the first layer 60 and the second layer 62 of the light guide plate 30 of the present invention, for example, the arcs R1 and R2, are dispersed in the first layer 60 and the second layer 62. The thickness should satisfy the above-described scattering particle dispersion condition of the present invention including the above formula (1), but is not particularly limited as long as the scattering particle dispersion condition is satisfied. However, the thickness and shape of the first layer 60 and the second layer 62 are determined depending on the ease of manufacturing, for example, restrictions such as an extrusion apparatus that simultaneously melt-extrudes two layers and a line speed for melt-extrusion. do it.
For example, in the case of the light guide plate 30 of about 2 mm, the maximum thickness of the second layer 62 is up to about 1.5 mm, more preferably 0.2 mm to 1.3 mm, and most preferably 0.35 mm to 0.8 mm. The minimum thickness of the second layer 62 is up to about 0 mm, more preferably 0.05 mm to 0.25 mm, and most preferably 0.1 mm to 0.15 mm. For example, when the thickness of the light guide plate 30 is 0.1 mm to 5 mm, the maximum thickness and the minimum thickness of the second layer 62 may be set to the same ratio as in the case of the light guide plate 30 of about 2 mm. That is, the ratio of the maximum thickness of the second layer 62 to the thickness of the light guide plate 30 is up to about 75%, more preferably 5% to 65%, and most preferably 17.5% to 40%. The ratio of the minimum thickness of the second layer 62 is up to about 0%, more preferably 2.5% to 12.5%, and most preferably 5% to 7.5%.

In addition, the shape of the second layer 62, that is, the uneven curves, for example, the arcs R1 and R2, may be determined according to the size of the light guide plate 30, the maximum thickness and the minimum thickness of the second layer 62, and the like.
For example, in the light guide plate 30 of about 2 mm, when the light guide length L is 500 mm ≦ L ≦ 615 mm, the radius of curvature R1 of the convex arc R1 that is the maximum thickness of the second layer 62 described above is 2500 mm ≦ R1. ≦ 250,000 mm, the radius of curvature R2 of the concave arc R2 that is the minimum thickness of the second layer 62 described above is preferably 2500 mm ≦ R2 ≦ 230000 mm, and when the light guide length L is 700 mm ≦ L ≦ 850 mm The curvature radius R1 of the convex arc R1 is preferably 5000 mm ≦ R1 ≦ 490000 mm, and the curvature radius R2 of the concave arc R2 is preferably 5000 mm ≦ R2 ≦ 450,000 mm. In addition, what is necessary is just to change the said range according to the difference, when the thickness of the light-guide plate 30 differs from 2 mm.

The light guide plate of the present invention is basically configured as described above, but can be designed as follows.
FIG. 9 is a flowchart showing an example of the light guide plate designing method of the present invention.
Below, the 1st layer (henceforth upper layer) 60 and 2nd layer which are used for the backlight unit 20 of the liquid crystal display device 10 shown in FIG.1 and FIG.2 and are shown in FIG.2, FIG.3, FIG.5 and FIG. A case where a two-layer light guide plate 30 made of (hereinafter also referred to as a lower layer) is designed will be described as a representative example.
First, as shown in FIG. 9, in step S10, from the screen size (effective screen area of the light emitting surface 30a) of the liquid crystal display device 10 to which the backlight unit 20 using the light guide plate 30 of the present invention is applied, the screen is changed. The light guide length L is determined by adding 10 to 30 mm as the width of the so-called frame as the length (including the mixing zone length) of the portion covered with the upper casing 44 to the short side length of the size. Strictly speaking, the light guide length L is determined in consideration of the installation position of the light source 28 (distance between the light emitting surface of the LED and the light incident surfaces 30c and 30d of the light guide plate 30).

Next, in step S12, the thickness of the light guide plate 30 is determined from the use of the liquid crystal display device 10 and the screen size.
In step S14, the cross-sectional shape (the cross-sectional shape perpendicular to the screen and parallel to the short side of the screen size) of the lower layer 62 of the light guide plate 30 is determined. Specifically, the lower layer maximum thickness and the lower layer minimum thickness (upper layer maximum thickness) are determined according to the thickness of the light guide plate 30, and based on them, the maximum value of the lower layer thickness (lower layer maximum thickness) ) And two concave arcs R2 constituting the minimum value of the lower layer thickness (lower layer minimum thickness) are determined. As a result, the cross-sectional shape of the upper layer 60 of the light guide plate 30 is also automatically determined.
For example, when the light guide length L of the light guide plate 30 is 540 mm and the thickness is 2 mm, as the cross-sectional shape of the lower layer 62, three lower layer cross sections A, B, and C indicated by solid lines, dotted lines, and one-dot chain lines in FIG. Can be determined.
Table 1 shows the lower layer maximum thickness, the lower layer minimum thickness, the convex arc R1 that constitutes the maximum value, and the concave arc R2 that constitutes the minimum value.

Next, in step S16, based on the determined sectional shapes of the lower layer 62 and the upper layer 60, the combined scattering cross section S per unit length at the light guide position x is obtained from the above formulas (2) to (4). The diffusion particle dispersion conditions are determined so that the obtained combined scattering cross section S satisfies the above formula (1). For example, specifically, as the diffusion particle dispersion conditions, the base resin of the light guide plate 30, the material and particle size of the diffusion particles, the particle concentrations of the upper layer 60 and the lower layer 62, and the like are determined.
In the present invention, when the cross-sectional shape of the lower layer 62 is different, for example, even in the case of the lower layer cross sections A to C shown in FIG. The combined scattering cross section distribution can be made.

  For example, when the light guide length L of the light guide plate 30 is 540 mm, the thickness is 2 mm, and the cross-sectional shape of the lower layer 62 of the light guide plate is the lower layer cross section B shown in FIG. The synthetic scattering cross-section distributions of the five design examples 1 to 5 shown can be obtained from the above formulas (2) to (4). The upper layer particle concentrations of the five design examples 1 to 5 are 0.005 wt%, and the lower layer particle concentrations of the design examples 1 to 5 are 0.165 wt%, 0.220 wt%, 0.265 wt%, and 0.09 wt% and 0.30 wt%.

In addition, as a dispersion | distribution condition of scattering particle | grains, scattering particle | grains shall be disperse | distributing uniformly also in the upper layer 60 and the lower layer 62. A specific dispersion state is a state in which scattering particles are kneaded and stirred in a molten base resin pellet. In such a light guide plate 30, resin in which scattered particles are dispersed at different particle concentrations is extruded from a two-layer extrusion apparatus at the same time by extrusion molding, laminated immediately before extrusion (die part), and sandwiched between rolls. To be molded. That is, since the scattering particles are sufficiently kneaded and stirred in the base resin, the scattering particles are dispersed at substantially equal distances, and the Mie theory can be applied.
From the graph of FIG. 11 showing the distribution of the combined scattering cross sections S of the five design examples 1 to 5 obtained in this way, design examples 1 to 3 satisfy the above formula (1), and design examples 4 to 5 It can be seen that the above formula (1) is not satisfied.

Subsequently, in step S18, the light guide plate 30 thus designed is subjected to (a) use efficiency of incident light, (b) medium to high altitude of luminance distribution of light emitted from the light emission surface 30a, and (c) light emission surface. Optical evaluation is performed on the three items of the uneven shape at the center of 30a, and it is examined whether or not the set values of these three items are satisfied.
For example, as a result of optical evaluation of five design examples 1 to 5 of the light guide plate having the combined scattering cross section distribution shown in FIG. 11, a graph showing the relative illuminance of the emitted light with respect to the light guide position shown in FIG. 12 can be obtained. . As can be seen from FIG. 12, in any of the design examples 1 to 5, the luminance distribution of the emitted light from the light exit surface 30a exhibits a medium-high distribution, and the design examples 1 to 3 satisfying the above formula (1) Although it becomes a luminance distribution, the design examples 4-5 which do not satisfy said Formula (1) do not become a desired luminance distribution.
That is, in the design examples 1 to 3 that satisfy the above formula (1), (a) utilization efficiency, (b) middle altitude degree, and (c) uneven shape at the center are respectively set values (a) 70. %, (B) more than 0% and less than 45%, and (c) the convex value of the three items are satisfied.

In contrast, the maximum value S _max and a minimum value S _min of the composite scattering cross section S is lower than the lower limit of the above formula (1), design example 4 that does not satisfy the above formula (1), as shown in FIG. 12 , (A) utilization efficiency, and (b) medium-to-high degree satisfy the specified values, respectively, but the uneven shape at the center of (c) has a concave luminance distribution at the center. The brightness is lowered, and the vicinity of the center is visually recognized as band unevenness.
Further, the design example 5 in which the maximum value _Smax of the combined scattering cross section S is higher than the upper limit value of the above formula (1) and does not satisfy the above formula (1) is shown in FIG. Although the concavo-convex shape is a convex shape, the luminance distribution in the central part becomes a medium-high distribution more than necessary, so that the vicinity of the central part is visually recognized as band unevenness, and the middle altitude of (b) satisfies the set value. No longer. Further, in Design Example 5, even when the setting value for the intermediate altitude of (b) is satisfied, if the utilization efficiency of (a) is less than 70%, the utilization efficiency is insufficient, and the light emitting surface 30a (light emitting surface) ) Cannot be used because the overall brightness is insufficient.

FIG. 13 shows the evaluation results for the two items of (a) utilization efficiency and (b) medium to high degree for the many light guide plates 30 thus designed.
FIG. 13 is a graph showing incident light utilization efficiency [%] and outgoing light medium altitude [%] with respect to the particle concentration [wt%] of the second layer (lower layer) for a number of designed light guide plates. .
An example of a method for determining the particle concentration of the lower layer 62 will be described with reference to FIG.
First, parameters other than the particle concentration of the lower layer 62 are set as follows.

Next, the particle concentration range of the scattering particles of the lower layer 62 can be determined by the following procedure.
First, from the graph of FIG. 13, to determine the extent of particle concentration x ₁ comprising (a) and the utilization efficiency of the incident light is 70% or more. As a result, x ₁ ≧ 0.08 [wt%] can be obtained as the particle concentration range.
Then, from the graph of FIG. 13, it determines the range of particle concentrations _{x 2} comprising (b) and the middle-high ratio is less than 0% and 45%. As a result, x ₂ ≧ 0.165 [wt%] can be obtained as the particle concentration range.
Subsequently, (c) the range of the particle concentration x _{3 in} which the uneven shape at the center of the luminance distribution is not concave is determined. As a result, x ₃ ≦ 0.285 [wt%] can be obtained as the particle concentration range.
From the particle concentration ranges x ₁ , x ₂ , and x ₃ thus obtained, the applicable particle concentration range of the lower layer 62 can be determined as 0.165 ≦ x ≦ 0.285 [wt%].

Thus, the light guide plate in which conditions such as the cross-sectional shapes of the first layer (upper layer) 60 and the second layer (lower layer) 62 and the particle concentration of the scattering particles dispersed therein are determined can be used for the scattering particle dispersion conditions of the present invention. Because it satisfies the limited range, even a large screen has a thin shape, high light utilization efficiency, and can emit light with little unevenness in luminance, which is required for a large-screen thin LCD TV It is possible to obtain a lighter distribution in the vicinity of the center of the screen than the peripheral part, that is, a so-called medium-high or bell-shaped brightness distribution.
The light guide plate of the present invention is basically configured as described above.

  Here, the light source 28 and the light guide plate 30 have an interval of 0.2 mm or more between the light emitting surface of the light source 28, for example, the light emitting surface (front surface) of the LED and the light incident surfaces 30 c and 30 d of the light guide plate 30. It is preferable to dispose them. That is, it is preferable that the light emitting surface (LED surface) of the light source 28 and the light incident surface of the light guide plate 30 have a distance of 0.2 mm or more. The reason for this is that the distance between them is 0.2 mm or more, so that the light-emitting surface of the light source 28 (specifically, the surface of the LED) and the light-guide plate even when the light-guide plate 30 is stretched or warped due to temperature changes. It is possible to prevent the light source 28 (specifically, the phosphor on the surface of the LED) from being damaged. The upper limit of the distance between the two is not particularly limited, but if the distance is too wide, the amount of light from the light source 28 incident on the light incident surfaces 30c and 30d of the light guide plate 30 is reduced. Is preferably 0.5 mm or less.

The description of the backlight unit shown in FIGS. 1 and 2 will be continued.
Next, 32 that can be preferably used in the present invention will be described.
The optical member unit 32 is for making the illumination light emitted from the light emission surface 30a of the light guide plate 30 light with more uneven brightness and illuminance, and emitting it from the light emission surface 24a of the illumination device body 24. As shown in FIG. 2, the diffusion sheet 32a that diffuses the illumination light emitted from the light emitting surface 30a of the light guide plate 30 to reduce luminance unevenness and illuminance unevenness, and the light incident surfaces 30c and 30d and the light emitting surface 30a. It has a prism sheet 32b on which microprism rows parallel to the tangent line are formed, and a diffusion sheet 32c that diffuses illumination light emitted from the prism sheet 32b to reduce luminance unevenness and illuminance unevenness.

  The diffusion sheets 32a and 32c and the prism sheet 32b are not particularly limited, and a known diffusion sheet or prism sheet can be used. For example, Japanese Patent Application Laid-Open No. 2005-23497 related to the application of the present applicant [ The ones disclosed in [0028] to [0033] can be applied.

In this embodiment, the optical member unit is composed of 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, and the brightness unevenness and the illumination unevenness of the illumination light emitted from the light exit surface 30a of the light guide plate 30 can be further reduced. If there are, various optical members can be used.
For example, as an optical member, in addition to or instead 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 diffuse reflector are arranged in accordance with luminance unevenness and illuminance unevenness is also used. You can also. Further, the optical member unit may have a two-layer configuration using one prism sheet and one diffusion sheet, or using only two diffusion sheets.

Next, the reflecting plate 34 of the lighting device body 24 will be described.
The reflection plate 34 is provided to reflect the light leaking from the back surface 30b of the light guide plate 30 and make it incident on the light guide plate 30 again, and can improve the light use efficiency. The reflection plate 34 has a shape corresponding to the back surface 30b of the light guide plate 30 and is formed so as to cover the back surface 30b. In the present embodiment, as shown in FIG. 2, the back surface 30 b of the light guide plate 30 is flat, that is, the cross section is formed in a linear shape. Therefore, the reflecting plate 34 is also formed in a shape complementary to this.

  The reflection plate 34 may be formed of any material as long as it can reflect light leaking from the back surface 30b of the light guide plate 30. For example, the reflection plate 34 may be stretched after a filler is kneaded into 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 at the end of the light emission surface 30a of the light source 28 and the light guide plate 30 (first light incident). The end portion on the surface 30c side and the end portion on the second light incident surface 30d side) are disposed so as to cover each other. In other words, the upper guide reflection plate 36 is arranged so as to cover a part of the light emitting surface 30a of the light guide plate 30 to a part of the light source support part 52 of the light source 28 in a direction parallel to the optical axis direction. . That is, the two upper guide reflectors 36 are disposed at both ends of the light guide plate 30, respectively.
Thus, by arranging the upper guide reflection plate 36, it is possible to prevent the light emitted from the light source 28 from leaking to the light emitting surface 30 a side without entering the light guide plate 30.
Thereby, the light emitted from the light source 28 can be efficiently incident on the first light incident surface 30c and the second light incident surface 30d of the light guide plate 30, and the light utilization efficiency can be improved.

The lower guide reflection plate 38 is disposed on the back surface 30 b side of the light guide plate 30 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 30 is connected to the reflector 34.
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.
By providing the lower guide reflection plate 38, it is possible to prevent light emitted from the light source 28 from entering the light guide plate 30 and leaking to the back surface 30 b side of the light guide plate 30.
Thereby, the light emitted from the light source 28 can be efficiently incident on the first light incident surface 30c and the second light incident surface 30d of the light guide plate 30, and the light utilization efficiency can be improved.
In addition, in this embodiment, although the reflecting plate 34 and the lower induction | guidance | derivation reflecting plate 38 were connected, it is not limited to this, Each is good also as 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 30c or the second light incident surface 30d, 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 30c and the second light incident surface 30d 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 and fixed from the light emitting surface 24 a side and the back surface 30 b side of the light guide plate 30. It has a body 42, an upper housing 44, a folding member 46, and a support member 48.

  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 a surface (back surface) and a side surface opposite to the light emitting surface 24a.

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

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, 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 30 can be prevented from warping. As a result, for example, there is no unevenness in brightness and unevenness in illuminance, or a small amount of light can be emitted efficiently, but even when a light guide plate that is likely to warp is used, the warp can be corrected more reliably or guided. It is possible to more reliably prevent the optical plate from being warped, and light with reduced or reduced brightness and illuminance unevenness can be emitted from the light exit surface.
In addition, various materials, such as a metal and resin, can be used for the upper housing | casing of a housing | casing, a lower housing | casing, and a folding member. In addition, as a material, it is preferable to use a lightweight and high-strength material.
In the present embodiment, the folding member is a separate member, but it may be formed integrally with the upper housing or the lower housing. Moreover, it is good also as a structure which does not provide a folding | turning member.

The support member 48 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 formed between the reflecting plate 34 and the lower housing 42, more specifically, the end of the rear surface 30 b of the light guide plate 30 on the first light incident surface 30 c side and the second end. The light guide plate 30 and the reflection plate 34 are fixed to and supported by the lower housing 42 and disposed between the reflection plate 34 and the lower housing 42 at a position corresponding to the end on the light incident surface 30d side.
The light guide plate 30 and the reflection plate 34 can be brought into close contact with each other by supporting the reflection plate 34 with the support member 48. Further, the light guide plate 30 and the reflection plate 34 can be fixed at predetermined positions of the lower housing 42.

In this embodiment, the support member is provided as an independent member. However, the present invention is not limited to this, and the support member may be formed integrally with the lower housing 42 or the reflection plate 34. That is, even if a protrusion is formed on a part of the lower housing 42 and this protrusion is used as a support member, a protrusion is formed on a part of the reflector 34 and this protrusion is used as a support member. Good.
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 30c and near the second light incident surface 30d.

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 uneven brightness and illuminance are caused by the light reflected from the reflection plate. Can be prevented.

The backlight unit 20 is basically configured as described above.
In the backlight unit 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 c and the second light incident surface 30 d) 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 is reflected directly or by the back surface 30b, and then exits from the light exit surface 30a. At this time, part of the light leaking from the back surface is reflected by the reflecting plate 34 and enters the light guide plate 30 again.
In this way, the light emitted from the light emitting surface 30 a of the light guide plate 30 passes through the optical member 32 and is emitted from the light emitting surface 24 a of the illuminating 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.

  In the light guide plate 30 shown in FIG. 2, FIG. 3, FIG. 5 and FIG. 6, the second layer 62 is composed of three arcs R1, R2, R2 in the cross section. Without being limited, the above scattering particle dispersion condition is satisfied, and the thickness in the direction substantially perpendicular to the light exit surface changes in a direction substantially parallel to the light exit surface, and the thickness continues in a direction away from the light entrance surface. As long as it has a cross-sectional shape having at least a maximum portion, it may have any shape, and may have any cross-sectional shape.

  For example, as in the light guide plate 31a shown in FIG. 14A, the cross-sectional shape of the boundary surface z in the cross section is such that the thickness of the second layer 62 is the central portion of the light emitting surface 30a (that is, the bisector α). A linear portion L1 parallel to the light emitting surface 30a and having a maximum (maximum) in the vicinity of the first light incident surface 30c. The thickness of the second layer 62 is connected to the linear portion L1 from the linear portion L1. And two curves convex toward the light exit surface 30a (two arcs R3 having a radius of curvature R3), which continuously change so as to become thinner toward the second light incident surface 30d, and the two convex shapes Each of the second layers 62 has a minimum thickness before the first light incident surface 30c and the second light incident surface 30d, and the first light incident surface 30c and the second light input surface 30c are respectively connected to the curved lines smoothly. The thickness of the second layer 62 increases toward the light incident surface 30d. Continuously changes to the light incident surface 30c as, (two arcs R4 radius of curvature R4) two concave curves which are connected to 30d and may be composed of four arcs having.

For example, as in the light guide plate 31b shown in FIG. 14B, the cross-sectional shape of the boundary surface z in the above cross section is such that the thickness of the second layer 62 is the central portion of the light emitting surface 30a (that is, the bisector α). The first convex curve (for example, the arc R5 having a radius of curvature R5) having a local maximum (maximum) in the vicinity, and the first convex curve smoothly connected to the back surface 30b and the light respectively. A so-called kamaboko having three arcs having two second convex curves (for example, two arcs R6 having different radii of curvature R6) connected to the connection parts (corner parts) with the incident surfaces 30c and 30d. It may be a shape.
In this example as well, a straight line portion is included in the connection portion between the first convex curve and the second convex curve and the connection portion between the second convex curve and the corner portion of the connection portion. Also good. Further, the second convex curve may be connected to the connection portion with the light incident surfaces 30c and 30d instead of the corner portion, or connected to the back surface 30b in the vicinity of the light incident surfaces 30c and 30d. Also good.

For example, as in the light guide plate 31c shown in FIG. 14C, the cross-sectional shape of the boundary surface z in the cross section has a maximum (maximum) thickness of the second layer 62 at the center of the light emitting surface 30a. A straight line portion L2 parallel to the light emission surface 30a and the second layer 62 connected to the straight line portion L2 are thinner from the straight line portion L2 toward the first light incident surface 30c and the second light incident surface 30d, respectively. It consists of two circular arcs (kamaboko shape) having two convex curves (for example, two circular arcs R7 having a radius of curvature R7) connected continuously to the light incident surfaces 30c and 30d. There may be.
In this example as well, a straight line portion may be included in the connection portion between the convex curve and the light incident surfaces 30c and 30d. Further, the convex curve may be connected to a connection portion between the back surface 30b and the light incident surfaces 30c and 30d, and not the light incident surfaces 30c and 30d but the back surface 30b in the vicinity of the light incident surfaces 30c and 30d. It may be connected.

For example, as in the light guide plate 31d shown in FIG. 14D, the cross-sectional shape of the boundary surface z in the cross-section is such that the thickness of the second layer 62 is the central portion of the light emitting surface 30a (that is, the bisector α). Top) One convexity connected to the light incident surfaces 30c and 30d by maximizing (maximum) in the vicinity and continuously changing so as to become thinner toward the first light incident surface 30c and the second light incident surface 30d, respectively. (For example, two circular arcs R8 having a radius of curvature R8) may be a single circular arc (kamaboko shape).
In this example as well, a straight line portion may be included in the connection portion between the convex curve and the light incident surfaces 30c and 30d. Further, the convex curve may be connected to a connection portion between the back surface 30b and the light incident surfaces 30c and 30d, and not the light incident surfaces 30c and 30d but the back surface 30b in the vicinity of the light incident surfaces 30c and 30d. It may be connected.

  By the way, in the light emitting surface 30a of the light guide plate 30 shown in FIGS. 2 and 6, the region corresponding to the opening 44a of the upper housing 44 is an effective region (effective screen area E) of the light emitting surface 30a. This is a region contributing to the emission of light as the light unit 20. On the other hand, the regions near the light incident surfaces 30c and 30d of the light guide plate 30 (light emitting surface 30a) are arranged outside the opening 44a of the upper housing 44, that is, in the frame portion forming the opening 44a. Therefore, this is a so-called mixing zone M for diffusing the light incident from the light incident surfaces 30c and 30d, although it does not contribute to the emission of light as the backlight unit 20.

  Therefore, as in the light guide plate 31e shown in FIG. 15A, the cross-sectional shape of the boundary surface z when viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 30a is excluded from the mixing zone M of the light emitting surface 30a. In the effective screen area E, it is formed in the same manner as the light guide plate 30 shown in FIGS. 2 and 6, that is, the thickness of the second layer 62 is set so that the first maximum value is taken at the central portion of the light emitting surface 30a. A convex curve (arc R1) is formed, and subsequently the second layer 62 is continuously changed so that the thickness thereof is reduced, and a concave curve is taken so as to take local minimum values in the vicinity of the light incident surfaces 30c and 30d, respectively. (Arc R2) is formed, and further thickened in the vicinity of the first light incident surface 30c and the second light incident surface 30d. In the mixing zone M on both sides, unlike the light guide plate 30, the second maximum value is obtained. After that, it changes continuously so that it becomes thinner again, and a concave curve (for example, an arc 9) may be formed of. In the light guide plate 31e, the thickness of the second layer 62 takes the second maximum value at the inner end of each mixing zone M, which is the position of the opening 44a of the upper housing 44, and the outer side of each mixing zone M. At the end, the boundary surface z coincides with the corners between the back surface 30b and the light incident surfaces 30c and 30d, and the thickness of the second layer 62 becomes zero.

  Thus, in the light guide plate 31e, the thickness of the second layer having a higher particle concentration of scattering particles than that of the first layer 60 is set to the first maximum value that is the thickest in the central portion of the light guide plate 31e, and the light incidence. The composite scattering cross-section s of the scattering particles is changed to each mixing zone by continuously changing it so as to have the second maximum value once thickened at the inner end of each mixing zone M in the vicinity of each of the surfaces 30c and 30d. It has a second maximum value at the inner end of M, and changes so as to have a first maximum value larger than the second maximum value at the center of the light exit surface 30a (effective screen area E). ing.

  As a result, in the light guide plate 31e, even if the light guide plate 31e is a large and thin light guide plate by setting the thickness of the second layer (synthetic scattering cross section s) to the first maximum value that is maximum in the central portion. The light incident from the light incident surfaces 30c and 30d can be delivered to a position farther from the light incident surfaces 30c and 30d, and the luminance distribution of the light emitted from the light emitting surface 30a (effective screen area E) is a medium-high luminance distribution. And arranging the second maximum value of the thickness of the second layer (synthetic scattering cross section s) in the vicinity of the light incident surfaces 30c and 30d (inner end of the mixing zone M), Light incident from the light incident surfaces 30c and 30d is sufficiently diffused in the mixing zone M, and the emission light emitted from the effective screen area E in the vicinity of the mixing zone M is a bright line (dark line) caused by the arrangement interval of the light sources 28, etc. , Unevenness) It can be prevented from being certified.

Further, in the light guide plate 31e, in the mixing zone M, the thickness of the second layer having a high particle concentration is set to be thinner than the first maximum value, so that the incident light is reduced by reducing the particle concentration. , The return light scattered by the scattering particles and emitted from the light incident surface, and the output light from the region near the light incident surface that is not used because it is covered by the housing (mixing zone M), The utilization efficiency of the light emitted from the effective screen area E of the light emission surface 30a can be improved.
Further, in the light guide plate 31e, the position where the second maximum thickness of the second layer is disposed on the inner end side of the mixing zone M, the mixing zone M is covered with the casing and is not used. The emitted light can be reduced, and the utilization efficiency of the light emitted from the effective screen area E of the light emitting surface 30a can be improved.

In the light guide plate 31e, the position of the second maximum value of the thickness of the second layer is arranged at the inner end of the mixing zone M (the position of the boundary of the opening 44a of the upper housing 44). However, the position of the second maximum value of the thickness of the second layer is within the effective screen area E (inside the opening 44a) as long as the position of the second maximum value is in the vicinity of the inner end of the mixing zone M. May be arranged at a position in the mixing zone M.
Further, in the light guide plate 31e, the boundary surface z is a curved surface (arc) that is concave downward in the mixing zone M, that is, in the region from the position of the second maximum value to the light incident surfaces 30c and 30d. Although it was set as the shape connected to the edge part (the corner | angular part of the light-incidence surfaces 30c and 30d and the back surface 30b) of 30c and 30d at the back surface 30b side, this invention is not limited to this.

  The light guide plates 31f, 31g, and 31h shown in FIGS. 15B to 15D are the thicknesses of the first layer 60 and the second layer 62 in the mixing zone M in the light guide plate 31e shown in FIG. Since the configuration is the same except that the shape of the boundary surface z from the light incident surfaces 30c and 30d to the position of the second maximum value is changed, the same portions are denoted by the same reference numerals and the following description is different. Do the site mainly.

Similarly, the light guide plate 31f shown in FIG. 15B includes a first layer 60 and a second layer 62 having a particle concentration higher than that of the first layer 60. The first layer in the mixing zone M is the same as the first layer 60. The boundary surface z between 60 and the second layer 62 is connected to the position of the second maximum value, is a curved surface (for example, arc R10) convex toward the light exit surface 30a, and the light incident surfaces 30c and 30d The shape is connected to the corner with the back surface 30b.
In the light guide plates 31e and 31f shown in FIGS. 15A and 15B, the boundary surface z is in the mixing zone M, which is a region from the position of the second maximum value to the light incident surfaces 30c and 30d. Although the concave and convex curved surfaces are respectively formed toward the light emitting surface 30a, the present invention is not limited to this, and may be a flat surface or an uneven surface.

The light guide plate 31g shown in FIG. 15C is different from the light guide plate 31f shown in FIG. 15B in that the second maximum value of the boundary surface z between the first layer 60 and the second layer 62 in the mixing zone M. The terminal portion from the position toward the light incident surfaces 30c and 30d is connected to the back surface 30b at the approximate center of the mixing zone M. Here, the position at which the terminal portion of the boundary surface z is connected to the back surface 30 b may not be substantially in the center as long as it is within the mixing zone M.
In the light guide plate 31g shown in FIG. 15C, the shape of the boundary surface z in the mixing zone M is a curved surface (for example, an arc R11) that is convex toward the light exit surface 30a. However, the present invention is not limited to this, and may be a concave curved surface, a flat surface, or an uneven surface.

  The light guide plate 31h shown in FIG. 15D is different from any of the light guide plates 31e to 31g shown in FIGS. 15A to 15C, and the boundary surface z between the first layer 60 and the second layer 62 is the first. In the mixing zone M, the position of the maximum value of 2 is eliminated, and only the first layer 60 is included. That is, the boundary surface z has a plane parallel to the light incident surfaces 30c and 30d through the position of the second maximum value, and the terminal end of the boundary surface z is on the back surface 30b at the inner end of the kissing zone M. The shape to be connected.

  Like the light guide plates 31e to 31h shown in FIGS. 15A to 15D, the shape of the boundary surface z is changed from the position of the first maximum value of the thickness of the second layer 62 toward the light incident surfaces 30c and 30d. By forming the second layer 62 so as to reduce the thickness, the particle concentration in the region (mixing zone M) from the position of the second maximum value to the light incident surface side 30c, 30d is changed to the second maximum value. The particle concentration is lower than that of the incident light to reduce the return light emitted from the light incident surface and the light emitted from the region (mixing zone M) near the light incident surface that is covered with the housing and is not used. The utilization efficiency of the light emitted from the effective area (effective screen area E) of the emission surface can be improved.

Moreover, in the example mentioned above, although the light-projection surface 30a was made into the plane, it is not limited to this, A light-projection surface is good also as a concave surface. By making the light exit surface concave, the light guide plate can be prevented from warping toward the light exit surface when the light guide plate expands and contracts due to heat or moisture, and the light guide plate contacts the liquid crystal display device 12. Can be prevented.
In the above-described example, the back surface 30b is a flat surface. However, the present invention is not limited to this, and the back surface may be a concave surface, that is, a surface inclined in a direction in which the thickness decreases as the distance from the light incident surface increases. Alternatively, it may be a convex surface, that is, a surface inclined in a direction in which the thickness increases as the distance from the light incident surface increases.

Here, in the said embodiment, although it was the both-sides incidence which has arrange | positioned two light sources on the two light-incidence surfaces of a light-guide plate, it is not limited to this, Only one light source is one light-incidence surface of a light-guide plate. It is good also as the one-sided incident arrange | positioned. By reducing the number of light sources, the number of parts can be reduced and the cost can be reduced.
In the case of single-sided incidence, a light guide plate having an asymmetric shape of the boundary surface z may be used. For example, the shape of the second layer has one light incident surface, and the thickness of the second layer of the light guide plate is maximized at a position farther from the light incident surface than the bisector of the light output surface. An asymmetrical light guide plate may be used.

  FIG. 16 is a schematic cross-sectional view showing a part of a backlight unit using another example of the light guide plate of the present invention. The backlight unit 70 shown in FIG. 16 has the single-sided incident light guide plate 80 instead of the light guide plate 30 shown in FIG. Since it has the same configuration as the backlight unit 20 except that it has the same configuration as the unit 20, the same components are denoted by the same reference numerals, detailed description thereof will be omitted, and different components will be described below. The explanation is mainly given.

The backlight unit 70 shown in FIG. 16 includes a light guide plate 80 and a light source 28 for making light incident on the light guide plate 80.
The light guide plate 80 has a light emitting surface 80a formed of a rectangular flat plane, and a back surface 80b that is located on the opposite side of the light emitting surface 80a, that is, on the back side, and is a flat plane having substantially the same shape as the light emitting surface 80a. A light incident surface 80c that is formed substantially perpendicular to the light exit surface 80a on one end surface on the long side of the light exit surface 80a and the light source 28 is opposed to, and a light incident surface 30c. Side surface 80d located on the opposite side, that is, the back side. The light emitting surface 80a, the back surface 80b, and the light incident surface 80c of the light guide plate 80 correspond to the light emitting surface 30a, the back surface 30b, and the first light incident surface 30c of the light guide plate 30 shown in FIG. The light source 28 is not disposed to face the side surface 80d of the light plate 80, and is different from the second light incident surface 30d of the light guide plate 30.

The light guide plate 80 is a two-layer flat light guide plate, and is formed by a first layer 82 on the light emitting surface 80a side and a second layer 82 on the back surface 80b side.
The boundary surface z between the first layer 82 and the second layer 84 is once seen from the light incident surface 80c toward the side surface 80d when viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 80c. , The second layer 84 is changed to be thicker, and the second layer 84 is continuously changed to be thinner again. That is, the boundary surface z is a curved surface (for example, arc R12) that is concave toward the light exit surface 80a on the light incident surface 80c side, and a curved surface that is convex toward the light exit surface 80a (for example, arc R12) on the side surface 80d side. , Arc R13). That is, the thickness of the second layer 84 is a curve that changes so as to have a minimum value on the light incident surface 80c side and a maximum value on the side surface 80d side.

Needless to say, the light guide plate 80 in the illustrated example also needs to satisfy the above-described scattering particle dispersion condition of the present invention, similarly to the light guide plate 30 shown in FIG. In other words, in the light guide plate 80, the scattering particles are dispersed at different particle concentrations in the first layer 82 and the second layer 84, but each extends from the light incident surface 30c in a direction substantially parallel to the light emitting surface 30a. The combined scattering cross section S of the first layer 82 and the second layer 84 at the light guide position in the direction substantially perpendicular to the light exit surface 30a continuously and monotonously increases as the light guide distance increases from the light incident surface 30c. For example, from a minimum value or a minimum value to a maximum value or a maximum value continuously increasing monotonously according to the light guide distance from the light incident surfaces 30c and 30d, and the combined scattering cross section S The maximum value S _max and the minimum value S _min of the lens must satisfy the above formula (1).

In the illustrated light guide plate 80, when the concave and convex curved surfaces of the boundary surface z are curves expressed by arcs in a cross section perpendicular to the longitudinal direction of the light incident surface, the concave shape The radius of curvature R12 of the arc R12 is preferably 2500 mm ≦ R12 ≦ 450,000 mm, and the radius of curvature R13 of the convex arc 13 is preferably 2500 mm ≦ R13 ≦ 490000 mm. By setting the arcs R12 and R13 in the above range, it is possible to make the illuminance distribution of the light more suitably medium-high.
The concave and convex curved surfaces forming the boundary surface z of the light guide plate 80 are not limited to arcs in a cross section perpendicular to the longitudinal direction of the light incident surface 80c, but are quadratic curves such as an ellipse, a parabola, and a hyperbola. Of course, it may be a part of the above, a higher-order curve of 3rd order or higher, a curve represented by a polynomial, or a curve combining these.

Thus, in the case of single-sided incidence using only one light source, the shape of the boundary surface z is set at a position close to the light incident surface, the thickness of the second layer is minimized, and at a position far from the light incident surface. By setting the asymmetric shape so that the thickness of the second layer is maximized, the light emitted from the light source and incident from the light incident surface can be guided to the back of the light guide plate. The illuminance distribution of the light emitted from the light can be made medium to high, and the light utilization efficiency can be improved.
In addition, since the light incident surface can be made larger than the flat light guide plate having the same average thickness, the light incident efficiency can be increased and the light guide plate can be lightened.

In the light guide plate 80 used in the present invention, the cross-sectional shape of the second layer 62 is not limited to the one formed by the two arcs R12 and 13, and any shape can be used as long as the scattering particle dispersion condition is satisfied. But it ’s okay.
For example, when the boundary surface z between the first layer 82 and the second layer 84 is viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 80c as in the light guide plate 81a shown in FIG. After changing from the incident surface 80c toward the side surface 80d so that the second layer 84 becomes thinner, the second layer 84 changes to become thicker, and then the thickness of the second layer 84 becomes constant. It may change continuously. That is, the boundary surface z is a curved surface that is concave toward the light exit surface 80a (for example, the cross-section arc R14) on the light incident surface 80c side, and a curved surface that is convex toward the light exit surface 80a at the center of the light guide plate. (For example, a cross-section arc R15), and may be a plane parallel to the light exit surface 80a (for example, a cross-section straight line L3) from the apex of the convex curved surface to the side surface 80d side.

  In the illustrated light guide plate 81a, when the concave and convex curved surfaces of the boundary surface z are curves expressed by arcs in a cross section perpendicular to the longitudinal direction of the light incident surface, the concave shape The radius of curvature R14 of the arc R14 is preferably 2500 mm ≦ R14 ≦ 450,000 mm, and the radius of curvature R15 of the convex arc R15 is preferably 2500 mm ≦ R15 ≦ 490000 mm. By setting R14 and R15 in the above range, the illuminance distribution of light can be more suitably made medium to high.

Moreover, like the light guide plates 81b to 81e shown in FIGS. 17B to 17E, the shape of the boundary surface z between the first layer 82 and the second layer 84 in the mixing zone M near the light incident surface 30c is The light guide plates 31e to 31h shown in FIGS. 15A to 15D may be changed in the same manner.
The light guide plates 81b to 81d shown in FIGS. 17B to 17D are the light guide plate 80 shown in FIG. 16, and the light guide plate 81ed shown in FIG. 17E is the light guide plate shown in FIG. Since it has the same structure except 81a and the shape of the boundary surface z in the mixing zone M in the vicinity of the light incident surface 30c, the same components are denoted by the same reference numerals, and detailed description thereof will be given. Is omitted, and the following description will mainly focus on the different components.

In the light guide plate 81b shown in FIG. 17B, similarly to the light guide plate 31f shown in FIG. 15B, the cross-sectional shape of the boundary surface z in the mixing zone M in the vicinity of the light incident surface 30c is changed to a convex curve (for example, , Arc R16), and a maximum value of the thickness of the second layer 84 is provided at the inner end of the mixing zone M.
In the light guide plate 81c shown in FIG. 17C, as in the case of the light guide plate 31g shown in FIG. 15C, the sectional shape of the boundary surface z in the mixing zone M in the vicinity of the light incident surface 30c is changed to a convex curve (for example, Arc R17), the end of the boundary surface z is connected to the substantially central back surface 80b of the mixing zone M, and the maximum value of the thickness of the second layer 84 is provided at the inner end of the mixing zone M. Yes.

In the light guide plate 81d shown in FIG. 17D, as in the case of the light guide plate 31h shown in FIG. 15D, the second layer 84 is not provided in the mixing zone M near the light incident surface 30c, and the mixing zone M is not provided. The cross-sectional shape of the boundary surface z at the inner end portion of M is a plane that is substantially parallel to the light incident surface 30c, the end portion thereof is connected to the back surface 80b, and the thickness of the second layer 84 at the inner end portion of the mixing zone M. The maximum value is set.
In the light guide plate 81e shown in FIG. 17E, similarly to the light guide plate 31f shown in FIG. 15B, the cross-sectional shape of the boundary surface z in the mixing zone M near the light incident surface 30c is changed to a convex curve (for example, , Arc R18), and a maximum value of the thickness of the second layer 84 is provided at the inner end of the mixing zone M.
In the above-described example, the sectional shape of the boundary surface z in the mixing zone M may be changed to a convex curve, and a concave curve, a plane, or a combination thereof may be used.

In addition, the backlight unit using the light guide plate of the present invention is not limited to the above-described various embodiments. In addition to the two light sources, one or both of the side surfaces on the short side of the light emission surface of the light guide plate are also provided. You may arrange | position a light source facing. Increasing the number of light sources can increase the intensity of light emitted by the device.
In the above-described embodiment, the first layer 60 is disposed on the light emitting surface 30a side, and the second layer 62 is disposed on the back surface 30b side. However, the present invention is not limited to this and is disposed in reverse. You may do it. That is, the first layer may be located on the back side, and the second layer may be located on the light emitting surface side.
Furthermore, in the embodiment described above, light is emitted only from the light emitting surface 30a, but the present invention is not limited to this, and light is emitted not only from the light emitting surface but also from the back side, that is, from both sides. May be.
In addition, the light guide plate of the present invention is composed of two layers having different particle concentrations of scattering particles, but is not limited thereto, and has a configuration of three or more layers having different particle concentrations of scattering particles. Also good.

  The light guide plate according to the present invention and the planar lighting device using the same have been described in detail with reference to various embodiments. However, the present invention is not limited to the above embodiments, and the gist of the present invention. It goes without saying that various improvements and changes may be made without departing from the scope of the present invention.

Hereinafter, the light guide plate according to the present invention will be specifically described with reference to examples.
As an example, a two-layer flat light guide plate 30 having a boundary surface z as shown in FIGS. 2, 3, 5, and 6 is emitted from the light exit surface 30 a of the light guide plate 30 by computer simulation. The illuminance distribution and the luminance distribution of the emitted light are obtained, (a) the utilization efficiency of the light incident from the light incident surfaces 30c and 30d of the light guide plate 30, and (b) the medium altitude of the luminance distribution of the emitted light from the light emitting surface 30a. And (c) the uneven shape of the central portion of the light exit surface 30a is obtained, optical evaluation is performed on these three items, and the set value (a) of each of these three items is 70% or more, and (b) 0%. It was determined whether or not the super 45% or less and (c) the convex shape were satisfied.
In the simulation, the transparent resin material of the light guide plate 30 was modeled as PMMA, and the scattering particle material was modeled as silicone. This is the same for all the following embodiments.

[Example 1]
As Example 1, a light guide plate 30 having a light guide length of 540 mm corresponding to a screen size of 40 inches was used. Specifically, the thickness of the light guide plate 30 is set to 2.0 mm, and the thickness of the second layer 62 at the position where the thickness of the second layer 62 is the thickest at the bisector α, that is, the position of the maximum value. The thickness is 0.80 mm, the thickness of the second layer 62 is the thinnest minimum thickness, the thickness of the second layer 62 at the position of the minimum value is 0.15 mm, and from the first maximum value to the light incident surface A light guide plate with a distance of 20 mm was used. The scattering particles to be kneaded and dispersed in the light guide plate are three types having a particle size of 4.5 μm, 7.0 μm, and 12 μm, and the particle concentration of the first layer 60 is determined according to the light guide plate design method of the present invention shown in FIG. Were set according to the particle diameter of the scattering particles, and then the particle concentration of the second layer 62 was determined according to this to design and manufacture a plurality of types of light guide plates.
The combined scattering cross-section S at the light guide position of the obtained multiple types of light guide plates 30 was determined using the above formulas (2) to (4).
The obtained results are shown in Tables 3 to 5.

Tables 3 and 4 above show Examples 1 to 16 of the present invention in which the maximum value S _max and the minimum value S _min of the combined scattering cross section S satisfy the above formula (1), and Table 5 shows the combined scattering section. Comparative examples 1 to 9 in which the maximum value S _max and the minimum value S _{min of the} area S do not satisfy the above formula (1) are shown.
For Invention Examples 1-16 and Comparative Examples 1-9 shown in Tables 3-5, the above (a) light utilization efficiency, (b) middle altitude, and (c) uneven shape at the center are obtained, and these These three items were optically evaluated, and it was determined whether or not the set values (a) of these three items (a) were 70% or more, (b) more than 0% and 45% or less, and (c) the convex shape was satisfied. .
Here, in the determination, (a) light utilization efficiency is sufficiently high as 75% or more, (b) middle altitude is most preferably about 30% or more, and (c) central part luminance distribution is When it does not become a concave shape, it is marked as ◎, (a) the light use efficiency is as high as 70% or more, (b) the medium-high state is about 0% to 30%, and (c) the central portion has a concave shape. If not, ○, and if not satisfying the above (a) to (c), ×, particularly not preferred among those not satisfying (a) to (c) (c) Central part luminance distribution When the shape was significantly concave and (b) the middle height was small, it was marked as xx.
The above results are also shown in Tables 3-5.

As is clear from the results of Tables 3 to 5, all of the inventive examples 1 to 16 in which the combined scattering cross-section S satisfies the scattering particle dispersion condition of the present invention (a) the light utilization efficiency is 70%. As described above, (b) the middle height of the luminance distribution is more than 0% and 45% or less, and (c) the shape of the central portion of the luminance distribution is a convex shape, satisfying the specified values of these three items, ◎, or In Examples 1 to 9 of the present invention in which the composite scattering cross section S satisfies the scattering particle dispersion condition of the present invention, at least one of the above three items is out of the specified value. , X, or xx.
From the results of Example 1 described above, the effect of the present invention is clear.

[Example 2]
As Example 2, a plurality of types of light guide plates were designed and manufactured in the same manner as Example 1 except that the light guide plate 30 having a light guide length of 700 mm corresponding to a screen size of 52 inches was used.
The composite scattering cross-section S at the light guide position of the obtained multiple types of light guide plates 30 was obtained using the above formulas (2) to (4) in the same manner as in Example 1.
The obtained results are shown in Tables 6 to 8.

Tables 6 and 7 above show Examples 21 to 36 of the present invention in which the maximum value S _max and the minimum value S _min of the combined scattering cross section S satisfy the above formula (1), and Table 8 shows the combined scattering section. Comparative examples 21 to 29 in which the maximum value S _max and the minimum value S _{min of the} area S do not satisfy the above formula (1) are shown.
Inventive Examples 21 to 36 and Comparative Examples 21 to 29 shown in Tables 6 to 8 are optically evaluated for the above three items in the same manner as in Example 1 and satisfy the set values of these three items. It was determined whether or not to do.
The above results are also shown in Tables 6-8.

As is apparent from the results of Tables 6 to 8, all of the inventive examples 21 to 36 in which the combined scattering cross section S satisfies the scattering particle dispersion conditions of the present invention (a) the light utilization efficiency is 70%. As described above, (b) the middle height of the luminance distribution is more than 0% and 45% or less, and (c) the shape of the central portion of the luminance distribution is a convex shape, satisfying the specified values of these three items, ◎, or In the present invention examples 21 to 29, in which the composite scattering cross section S satisfies the scattering particle dispersion condition of the present invention, at least one of the above three items deviates from the specified value. , X, or xx.
From the results of Example 2 above, the effect of the present invention is clear.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Liquid crystal display panel 14 Drive unit 20, 70 Backlight unit (planar illumination device)
24 Illuminating device body 24a, 30a, 80a Light exit surface 26 Case 28 Light source 30, 31a, 31b, 31c, 31d, 31e, 31f, 31g, 31h, 80, 81a, 81b, 81c, 81d, 81e Light guide plate 30b, 80b Back surface 30c, 30d, 80c Light incident surface 32 Optical member unit 32a, 32c Diffusing sheet 32b Prism sheet 34 Reflecting plate 36 Upper guiding reflecting plate 38 Lower guiding reflecting plate 42 Lower housing 44 Upper housing 44a Opening portion 46 Folding member 48 Support member 49 Power supply storage unit 50 LED chip 52 Light source support unit 58 Light emitting surface 60, 82 First layer 62, 84 Second layer 80d Side surface α2 bisector z Boundary surface

Claims (18)

The light emitting surface having a rectangular shape, at least one light incident surface that is provided on the edge side of the light emitting surface and that enters light traveling in a direction substantially parallel to the light emitting surface, and the light emitting surface A light guide plate having a back surface on the opposite side, in which diffusion particles are dispersed,
The light guide plate has two layers that overlap in a direction substantially perpendicular to the light emitting surface and have different particle concentrations of the diffusing particles, and these two layers are one of the light emitting surface side and the back surface side. A first layer located on the other side of the light emitting surface side and the back side, and a second layer in contact with the first layer,
The second layer has a thickness that changes in a direction substantially parallel to the light exit surface in a direction substantially parallel to the light exit surface, and the thickness continuously increases in a direction away from the light entrance surface. A cross-sectional shape having at least a maximum portion is formed,
The combined scattering cross section S of the two layers in a direction substantially perpendicular to the light exit surface at a position along a direction substantially parallel to the light exit surface is continuously and monotonously increased as the distance from the light entrance surface increases. The diffusing particles are dispersed,
The maximum value S _max and the minimum value S _min of the combined scattering cross section S satisfy the following formula (1).
1.25 ≦ S _max ≦ 2.2
0.90 ≦ S _min ≦ 1.6 (1)   The second layer has a cross-sectional shape in which the thickness in a direction substantially parallel to the light emitting surface is substantially perpendicular to the light emitting surface, and has at least one minimum value and at least one maximum value. The light guide plate according to claim 1.   The light guide plate according to claim 1, wherein the at least one light incident surface is two light incident surfaces provided on two opposite sides of the light emitting surface.   The light guide plate according to claim 3, wherein the cross-sectional shape of the second layer includes three arcs or four arcs.   The cross-sectional shape of the second layer has the local minimum value on each side of the two light incident surfaces, and the local maximum value in the approximate center between the two light incident surfaces. The light guide plate described.   The cross-sectional shape of the second layer has an arc that forms the minimum value on each side of the two light incident surfaces, and an arc that forms the maximum value at a substantially center between the two light incident surfaces. The light guide plate according to any one of claims 3 to 5.   The light guide plate according to any one of claims 3 to 6, wherein the thickness of the second layer is the thickest at the approximate center of the light emitting surface. The at least one light incident surface is one light incident surface provided on one end side of the light emitting surface;
3. The cross-sectional shape of the second layer has the minimum value on the one light incident surface side and the maximum value on the other end side of the light emitting surface. Light guide plate.   The cross-sectional shape of the second layer has an arc that forms the minimum value on the one light incident surface side, and an arc that forms the maximum value on the other side of the light emitting surface. The light guide plate according to claim 8. The light guide length from the one light incident surface to the center or the other end of the light traveling in a direction substantially parallel to the light emitting surface is 500 mm or more and 615 mm or less,
The diffusion particle has a particle size of 4.5 μm or more and 12.0 μm or less,
The concentration of the diffusing particles dispersed in the second layer is 0.10 wt% or more and 1.04 wt% or less,
The particle size and concentration of the diffusing particles dispersed in the second layer is a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the diffusing particles. Points (4.5, 0.10), (4.5, 0.30), (7.0, 0.14), (7.0, 0.39), (12.0, 0.38) The light guide plate according to claim 1, wherein the light guide plate is in a region surrounded by (12.0, 1.04). The concentration of the diffusing particles dispersed in the first layer is 0.00wt% or more and 0.101wt% or less,
The particle size and concentration of the diffusing particles dispersed in the first layer are 5 in a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the diffusing particles. Points (4.5, 0.00), (4.5, 0.016), (7.0, 0.022), (12.0, 0.00) and (12.0, 0.101) The light guide plate according to claim 10, wherein the light guide plate is in a region surrounded by. The light guide length from the one light incident surface to the center or the other end of light traveling in a direction substantially parallel to the light exit surface is 700 mm or more and 850 mm or less,
The diffusion particle has a particle size of 4.5 μm or more and 12.0 μm or less,
The concentration of the diffusing particles dispersed in the second layer is 0.07 wt% or more and 0.74 wt% or less,
The particle size and concentration of the diffusing particles dispersed in the second layer is a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the diffusing particles. Points (4.5, 0.07), (4.5, 0.21), (7.0, 0.10), (7.0, 0.28), (12.0, 0.27) And the light-guide plate of any one of Claims 1-9 which exists in the area | region enclosed by (12.0, 0.74). The concentration of the diffusion particles dispersed in the first layer is 0.00 wt% or more and 0.072 wt% or less,
The particle size and concentration of the diffusing particles dispersed in the first layer are 5 in a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the diffusing particles. Points (4.5, 0.00), (4.5, 0.011), (7.0, 0.016), (12.0, 0.00) and (12.0, 0.072) The light guide plate according to claim 12, wherein the light guide plate is in a region surrounded by. The light utilization efficiency indicating the ratio of the light incident from the at least one light incident surface being emitted from the light exit surface is 70% or more,
The medium to altitude of the luminance distribution of the light emitting surface indicating 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 peripheral portion of the light emitting surface is more than 0%, 45% or less,
The light guide plate according to any one of claims 1 to 13, wherein a luminance distribution in the central portion of the light emitting surface is convex.   The light guide plate according to claim 1, wherein the back surface is a plane parallel to the light emitting surface.   The light guide plate according to claim 1, wherein the first layer is located on the light emitting surface side, and the second layer is located on the back side.   The light guide plate according to claim 1, wherein the first layer is located on the back surface side, and the second layer is located on the light emitting surface side. The light guide plate according to any one of claims 1 to 17,
A light source disposed facing the light incident surface of the light guide plate;
A planar lighting device comprising: a housing that houses the light guide plate and the light source and has an opening smaller than the light exit surface on the light exit surface side of the light guide plate.