JP2010092683A - Light guide plate and planar illumination device equipped with this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large, thin and light-weight light guide plate capable of enhancing a whole efficiency and realizing a medium-high luminance distribution (illuminance distribution). <P>SOLUTION: A light reflection face (first light reflection faces 30b, 30c) of the light guide plate 30 having a light emitting face 30a and light incident faces 30d, 30e is formed by parts A1, A2 of an ellipse near the light incident faces 30d, 30e, slanted straight lines A3, A4 are connected with these, and these straight lines A3, A4 are connected with a part of a circle A5. A taper angle θ of the light reflection face is larger than the slanted face since it is the parts A1, A2 of the ellipse near the light incident faces 30d, 30e, and the same θ can be larger than the ellipse at subsequent straight lines A3, A4 and at a part of an arc near a central part. With this, the reflected light can be brought inward and the whole efficiency can be enhanced and moreover a medium-high luminance distribution can be realized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light guide plate whose thickness increases from two light incident surfaces facing each other toward the center of a light exit surface, and a planar illumination device including the same.

  As the liquid crystal display device, a planar illumination device (hereinafter also referred to as “backlight unit”) that irradiates light from the back side of the liquid crystal display panel and illuminates the liquid crystal display panel is used. The backlight unit is configured by using components such as a light guide plate that diffuses light emitted from a light source for illumination and irradiates the liquid crystal display panel, and a prism sheet and a diffusion sheet that uniformize light emitted from the light guide plate. .

At present, a backlight unit of a large-sized liquid crystal television is mainly used in a so-called direct type in which a light source for illumination is arranged on the back surface of a liquid crystal display panel. In this system, a plurality of cold-cathode tubes, which are light sources, are arranged on the back surface of the liquid crystal display panel, and a uniform light quantity distribution and necessary luminance are ensured with the inside as a white reflecting surface.
However, in order to make the light amount distribution uniform, the direct type backlight unit needs a thickness of about 30 mm in the vertical direction with respect to the liquid crystal display panel, and it is difficult to reduce the thickness below this.

On the other hand, as a backlight unit that can be thinned, it is emitted from a light emitting surface that is emitted from a light source for illumination, guides incident light in a predetermined direction, and is different from the surface on which the light is incident. There is a backlight unit using a light guide plate.
As such a backlight unit using a light guide plate, a backlight unit using a light guide plate in which scattering particles for scattering light in a transparent resin are mixed has been proposed.

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

As the light guide plate, in addition to the above, the thickness of the intermediate portion is larger than the thickness of the end portion on the incident side and the end portion on the opposite side, and as the distance from the light incident portion (light incident surface) increases. A light guide plate having a reflective surface inclined in the direction of increasing thickness, and a shape in which the distance between the front surface portion and the back surface portion is minimized at the incident portion, and the thickness is maximized at the maximum separation distance from the incident portion. Various types of reverse wedge type light guide plates such as a light guide plate having a shape have been proposed (see, for example, cited references 5 to 8).
Here, a large-screen thin-screen LCD TV, which is the main use of the backlight unit, requires a lighter distribution in the vicinity of the center of the screen than in the periphery, that is, a so-called medium-high or bell-shaped brightness distribution. The That is, with respect to the luminance of light on the light emitting surface, the luminance of light emitted from the vicinity of the light incident surface (a position closer to the center by L / 10 from the light incident surface when the light guide length of the light guide plate is L). When the ratio of the luminance of light emitted from the central portion is a medium to high ratio [%], a high medium to high ratio is required for a large-screen thin liquid crystal television.

20 and 21 show the simulation results of the luminance distribution (illuminance distribution) for one type of light guide plate among various types of reverse wedge light guide plates. Here, the reverse wedge-shaped light guide plate used has a pair of side surfaces facing each other as a light incident surface, and the thickness a is minimum (thinnest) at these light incident surfaces, and at the center of the two light incident surfaces. The thickness (a + b) is maximized (thickest). The back surface (light reflecting surface) is composed of two flat (flat) inclined surfaces. That is, the back surface is an inclined surface inclined downward from the lower end of each light incident surface toward the center. That is, assuming that the light emission surface is a flat surface, the inclination angle (taper angle θ) formed by the inclined surface with respect to the light emission surface is constant. Hereinafter, the light guide plate having this shape is referred to as an “inclined light guide plate” as appropriate.
In these drawings, the horizontal axis indicates the distance [mm] to the other light incident surface (end) with the position of one light incident surface (end) as 0. In addition, the vertical axis represents luminance (illuminance). As a whole, the luminance distribution (illuminance distribution) from one light incident surface to the other light incident surface is shown. 20 and 21, the inclined light guide plate is shown as a reference, and is shown by a thin dotted line in FIG. 20 and a thick dotted line in FIG. 21. In both cases, the thickness of the end portion serving as the light incident surface is 2 [mm], and the thickness at the center is 3.6 [mm], indicating the same luminance distribution.
From these figures, it can be seen that in the light guide plate having an inclined surface, the luminance distribution is relatively gentle, and it is difficult to obtain a luminance distribution with a high medium / high ratio. The reason for this is that since the taper angle in the vicinity of the light incident surface on the inclined surface is small, the light reflected in this vicinity does not easily reach the back (center).

Japanese Patent Laid-Open No. 7-36037 JP-A-8-248233 JP-A-8-271739 JP-A-11-153963 JP 2003-90919 A JP 2004-171948 A JP 2005-108676 A JP 2005-302322 A

Therefore, in order to obtain a light guide plate with a high medium / high ratio, a simulation is performed on a light guide plate (hereinafter referred to as an “elliptical light guide plate” as appropriate) having a back surface (light reflecting surface) formed of an ellipse among inverted wedge light guide plates. went. The results are shown in FIGS.
In FIG. 20, the thickness of the light incident surface (end) is 2 [mm], the major axis of the ellipse coincides with the line segment connecting the lower ends of the two light incident surfaces, and the length of the major axis is the light guide length L. And the length of half of the short axis is 1.6 [mm] (= 3.6 [mm] −2.0 [mm]). As for the ellipse, the results are shown in which the particle concentrations of light scattering particles (described later) are 0.1, 0.1125, 0.125, and 0.15 [wt%], respectively.

As a result, in the elliptical light guide plate, the luminance distribution as a whole is increased and the overall efficiency is higher than that of the inclined light guide plate. There is a problem of becoming.
In FIG. 21, the shape of the ellipse is the same as in FIG. 20, and the thickness is 3 [mm] (= 5 [mm] −2 [mm]) thicker than this, that is, as a whole The light guide plate was 3 [mm] thick. However, the particle concentration may be different from that of FIG.

As is clear from FIG. 21, in the elliptical light guide plate, when the thickness is increased, there is a problem that the overall efficiency is lowered in addition to a decrease in luminance at the center.
The cause of the result shown in FIG. 21 is that in the elliptical light guide plate, the elliptical taper angle is steep in the vicinity of the light incident surface (end), so the light reflected in this vicinity is On the other hand, the taper angle tends to decrease rapidly after passing through this steep portion, so that the light reflected at this portion does not easily reach the back. As a result, although the overall efficiency is higher than that of the light guide plate having the inclined surface, the medium / high ratio is lowered. Furthermore, as the thickness increases, the overall efficiency also decreases.

  The object of the present invention is to solve the problems based on the above prior art, and in the light guide plate, in particular, in a large, thin and light light guide plate, the overall efficiency is prevented from being lowered and a medium-high luminance distribution (illuminance distribution) is obtained. An object of the present invention is to provide a light guide plate that can be realized, and a planar illumination device including the same.

  In order to solve the above-mentioned problem, a first aspect of the present invention is formed in a substantially plate shape by a surface, a back surface, and four side surfaces, has a rectangular light emission surface on the surface, and reflects light on the back surface. A light guide plate having a light incident surface on each of two opposing side surfaces of the four side surfaces, the light reflecting surface including scattering particles that scatter light propagating therein, The cross section orthogonal to the longitudinal direction of the two light incident surfaces is formed symmetrically with respect to the perpendicular bisector of the light emitting surface and is convex toward the direction away from the light emitting surface And the distance from the light exit surface increases as it approaches the vertical bisector from the two light incident surfaces, and the line is a back side end of the two light incident surfaces. Smoothly connected to each of the sections and toward the vertical bisector And a part of two quadratic curves with a small inclination angle with respect to the light exit surface, two straight lines smoothly connected to a part of the quadratic curve, and a center on the perpendicular bisector And a light guide plate characterized by being represented by a part of a circle smoothly connected to the two straight lines.

Here, it is preferable that the two light incident surfaces are orthogonal to the light exit surface.
The quadratic curve is preferably an ellipse.
Further, the ellipse is preferably an ellipse whose major axis coincides with a line segment connecting the back side end of one light incident surface and the back side end of the other light incident surface. .

The scattering particles have a scattering cross section of the scattering particles of Φ, a density of the scattering particles of N _p , a correction coefficient of K _C , and a length from the two light incident surfaces to the perpendicular bisector. When L _G , the following inequality 1.1 ≦ Φ · N _p · L _G · K _C ≦ 8.2
0.005 ≦ K _C ≦ 0.1
It is preferable to satisfy

  Next, in order to solve the above-described problem, the second aspect of the present invention includes a light guide plate according to the first aspect, a first light source disposed to face one of the light incident surfaces of the light guide plate, and the light guide. A second light source disposed opposite to the other light incident surface of the light plate, wherein the first light source and the second light source emit at least one LED chip that emits blue light from the light emitting surface; and A phosphor coating part that is disposed between the light emitting surface and the light guide plate, converts blue light emitted from the light emitting surface into white light, and emits blue light emitted from the light emitting surface as blue light. And a fluorescent member having a blue light transmitting portion to be emitted.

  According to the present invention, the shape of the reflection surface of the light guide plate is configured such that the vicinity of the light incident surface is constituted by a part of an ellipse, a straight line is connected thereto, and the vicinity of the center is constituted by a part of a circle, thereby allowing light incidence The taper angle is increased in the vicinity of the surface, the taper angle is constant in the straight line portion, and further, the taper angle drop can be suppressed in the vicinity of the central portion as compared with the ellipse, so that the light incident from the light incident surface can be reduced. It can be reflected effectively on the reflecting surface and reach the back. As a result, overall efficiency can be improved and a medium-high luminance distribution can be realized.

A planar illumination device and a light guide plate according to the present invention will be described below in detail based on preferred embodiments shown in the accompanying drawings.
In the following description, a two-sided incidence type planar illumination device that makes light from a light source incident on two sides of a light guide plate is a representative example, but it goes without saying that the present invention is not limited to this. That is.
FIG. 1 is a perspective view showing an outline of a liquid crystal display device including a planar illumination device according to the present invention, and FIG. 2 is a cross-sectional view taken along line II-II of the liquid crystal display device shown in FIG. 3A is a partially omitted plan view showing a light guide plate and light sources arranged on two sides of the planar illumination device (hereinafter also referred to as “backlight unit”) shown in FIG. FIG. 3B is a cross-sectional view taken along line BB in FIG.

  As shown in FIG. 1, the liquid crystal display device 10 includes a backlight unit 20, a liquid crystal display panel 12 disposed on the light emission surface 24 a side of the backlight unit 20, and a drive unit 14 that drives the liquid crystal display panel 12. And have. 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 20.

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 utilizes the change in the refractive index generated in the liquid crystal cell. Characters, figures, images, etc. are displayed on the surface of the liquid crystal display panel 12.
The drive unit 14 applies a voltage to the transparent electrode in the liquid crystal display panel 12, changes the direction of the liquid crystal molecules, and controls the transmittance of light transmitted through the liquid crystal display panel 12.

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

As shown in FIGS. 1, 2, 3A, and 3B, the backlight unit (planar illumination device) 20 according to the present invention includes two light sources 28, a light guide plate 30, and a distance maintaining unit. A luminaire main body 24 having a member 31, an optical member unit 32, and a reflecting plate 34, a casing having a lower casing 42, an upper casing 44, a reinforcing member (folding member) 46, and a supporting member (sliding mechanism) 48. 26.
Further, as shown in FIG. 1, a power storage unit 49 that stores a plurality of power supplies for supplying power to the light source 28 is attached to the back side of the lower housing 42 (see FIG. 2) of the housing 26.
Hereinafter, each component which comprises the backlight unit 20 is demonstrated.

The illuminating device main 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, an optical axis distance between the light guide plate 30 and the light source 28, and an optical axis vertical. An interval maintaining member 31 that keeps the distance constant, an optical member unit 32 that scatters and diffuses light emitted from the light guide plate 30 to make the light more uniform, and reflects light leaked from the light guide plate 30 And a reflecting plate 34 to be incident on the light guide plate 30 again.
Here, as shown in FIG. 3B, the optical axis distance between the light guide plate 30 and the light source 28 is the light emitting surface 58 of one light source 28 (first light source 28) and the first light of the light guide plate 30. The distance c between the incident surface 30d and the distance c between the light emitting surface 58 of the other light source 28 (second light source 28) and the second light incident surface 30e of the light guide plate 30 are referred to. The optical axis vertical distance between the light guide plate 30 and the light source 28 refers to the distance between the respective optical axes in the thickness direction of the light guide plate 30 of the light guide plate 30 and the light source 28.

First, the light source 28 will be described.
4A is a schematic perspective view showing a schematic configuration of the light source 28 of the backlight unit 20 shown in FIGS. 1 and 2, and FIG. 4B is a cross-sectional view of the light source 28 shown in FIG. 4A. FIG. 4C is a schematic perspective view showing only one LED (light emitting diode) chip 50 constituting the light source 28 shown in FIG.
As shown in FIG. 4A, the light source 28 includes a plurality of LED chips 50 and a light source support portion 52.

The LED chip 50 is a chip in which a fluorescent material is coated on the surface of a light emitting diode that emits blue light. The LED chip 50 has a light emitting unit 51 having a predetermined area, and emits white light from a light emitting surface 58 of the light emitting unit 51.
Specifically, the LED chip 50 has a characteristic that the fluorescent material applied to the surface of the light emitting diode fluoresces when blue light emitted from the light emitting diode is transmitted. For this reason, the LED chip 50 emits blue light from the light emitting diode, so that the fluorescent material through which the blue light is transmitted also emits light. White light is generated and emitted by the light emitted by being fluorescent.
Here, the LED chip 50 is exemplified by a chip in which a YAG (yttrium / aluminum / garnet) fluorescent material is applied to the surface of a GaN-based light-emitting diode, InGaN-based light-emitting diode, or the like.

  As illustrated in FIG. 4B, the light source support portion 52 includes an array substrate 54 and a plurality of fins 56. The plurality of LED chips 50 described above are arranged on the array substrate 54 in a line at a predetermined interval. Specifically, the plurality of LED chips 50 constituting the light source 28 include a first light incident surface 30d and a second light incident surface 30e of the light guide plate 30 (to be described later). When there is no need to distinguish the incident surface 30e, it is simply referred to as the “light incident surface”), in other words, parallel to the line where the light exit surface 30a and the first light incident surface 30d intersect. Alternatively, the light emitting surface 30a and the second light incident surface 30e are arranged in an array parallel to a line intersecting the second light incident surface 30e and fixed on the array substrate 54.

The array substrate 54 is a plate-like member disposed so as to face the first light incident surface 30d and the second light incident surface 30e, one surface of which is the thinnest side end surface of the light guide plate 30. The LED chip 50 is supported on the side surface of the array substrate 54 which is the surface facing the first light incident surface 30d and the second light incident surface 30e of the light guide plate 30.
Here, the array substrate 54 of the present embodiment is formed of a metal having good thermal conductivity such as copper or aluminum, and also has a function as a heat sink that absorbs heat generated from the LED chip 50 and dissipates it to the outside. .

Each of the plurality of fins 56 is a plate-like member made of a metal having good thermal conductivity such as copper or aluminum, and is adjacent to the surface of the array substrate 54 opposite to the surface on which the LED chip 50 is disposed. The fins 56 are connected to each other at a predetermined distance.
By providing a plurality of fins 56 on the light source support 52, the surface area can be increased and the heat dissipation effect can be enhanced. Thereby, the cooling efficiency of LED chip 50 can be improved.
In the present embodiment, the array substrate 54 of the light source support 52 is used as a heat sink. However, when the LED chip 50 is not required to be cooled, a plate-like member having no heat dissipation function is used as the array substrate instead of the heat sink. May be.

Here, as shown in FIG. 4C, the light emitting surface 58 of the light emitting portion 51 of the LED chip 50 of the present embodiment is longer in the direction perpendicular to the arrangement direction than the length in the arrangement direction of the LED chip 50. Has a short rectangular shape, that is, a rectangular shape having a short side in the thickness direction of the light guide plate 30 to be described later (a direction perpendicular to the light exit surface 30a). In other words, the light emitting surface 58 has a shape such that b1> a1 when the length in the direction perpendicular to the light emitting surface 30a of the light guide plate 30 is a1 and the length in the arrangement direction is b1. Further, q> b1 when the arrangement interval of the LED chips 50 is q. Thus, the relationship between the length a1 of the light emitting surface 58 of the light emitting section 51 of the LED chip 50 in the direction perpendicular to the light emitting surface 30a of the light guide plate 30, the length b1 in the arrangement direction, and the arrangement interval q of the LED chips 50 is as follows. Q>b1> a1 is preferably satisfied.
By making the light emitting surface 58 rectangular, it is possible to make the light source 28 thin while maintaining a large light output. By reducing the thickness of the light source 28, the planar illumination device can be reduced in thickness. In addition, the number of LED chips 50 can be reduced.

  In addition, since the LED chip 50 can make the light source 58 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 a square shape or a circular shape is preferable. LED chips having various shapes such as a polygonal shape and an elliptical shape can be used.

  In the present embodiment, the LED chips 50 are arranged in a single row to form a single layer structure. However, the present invention is not limited to this, and a plurality of LED arrays having a configuration in which a plurality of LED chips 50 are arranged on an array support are provided. A multi-layered LED array having a configuration in which the light sources are stacked can also be used as the light source 58. Even when LED arrays are stacked in this manner, more LED arrays can be stacked by making the LED chip 50 rectangular and thinning the LED array. In this manner, a larger amount of light can be output by stacking multiple LED arrays, that is, by increasing the filling rate of the LED array (LED chip). Further, the LED chip 50 of the LED array of the layer adjacent to the LED chip 50 of the LED array preferably has the arrangement interval satisfying the above formula as described above. That is, in the LED array, it is preferable that the LED chip 50 and the LED chip 50 of the LED array in the adjacent layer are stacked with a predetermined distance therebetween.

Next, the light guide plate 30 will be described.
FIG. 5 is a schematic perspective view showing the shape of the light guide plate 30. However, in the figure, a part of the bisector α direction described later is omitted. 6A is a cross-sectional view taken along the line VI-VI of the light guide plate 30 shown in FIG. 5, and FIGS. 6B, 6C, and 6D show the light guide plate 30 shown in FIG. FIG.

As shown in FIG. 5, the light guide plate 30 is formed in a substantially plate shape, and has six surfaces, that is, a front surface (upward surface in FIG. 5) and a back surface (downward surface in FIG. 5) and 4. And has two sides.
A rectangular (rectangular) and planar (flat) light exit surface 30a is formed on the surface. The light emission surface 30a has four sides, that is, a pair (two) of long sides m facing each other, and a pair (two) of short sides n orthogonal to each other and facing each other. Yes. Here, a straight line connecting the midpoints of the two short sides n, that is, a straight line that is at an equal distance from the two long sides n and is parallel to these long sides n, is a bisector α of the light exit surface 30a. In addition, if a plane passing through the bisector α and orthogonal to the light exit surface 30a is a plane H, the light guide plate 30 is formed so as to be symmetrical with respect to the plane H as a whole.

A light reflecting surface 30h facing the light emitting surface 30a is formed on the back surface. The light reflecting surface 30h is divided into a first light reflecting surface 30b and a second light reflecting surface 30c by the above-described plane H, and the first light reflecting surface 30b and the second light reflecting surface 30c It is symmetrical as a reference.
The light reflecting surface 30h has a curved surface as described later, whereas the light emitting surface 30a described above is formed in a flat shape, and the distance from the light emitting surface 30a as a whole. , The portion corresponding to the long side m is the smallest, and the portion corresponding to the plane H is the largest. That is, the light guide plate 30 is the thinnest at a position corresponding to each long side m (thickness tmin), gradually increases away from the long side m and approaches the plane H, and at a position corresponding to the plane H. It is the thickest (thickness tmax). The light reflecting surface 30h (the first light reflecting surface 30b and the second light reflecting surface 30c) will be described in detail later.

  Of the four side surfaces 30d, 30e, 30f, and 30g, the two side surfaces 30d and 30e facing each other are side surfaces including the long side m of the light emitting surface 30a, and extend long in a band shape along the long side m. Exist. The two side surfaces 30d and 30e are both orthogonal to the light exit surface 30a and are arranged in parallel to each other. Of the two side surfaces 30d and 30e, the side surface 30d on the first light reflecting surface 30b side is the first light incident surface (hereinafter referred to as “first light incident surface 30d”), and the side surface 30e on the second light reflecting surface 30c side. Is a second light incident surface (hereinafter referred to as “second light incident surface 30e”). The first light incident surface 30d and the second light incident surface 30e are disposed so that the first light source 28 and the second light source 28 disposed along the longitudinal direction face each other, and emitted from these light sources 28. Light is incident.

  The remaining two side surfaces 30f and 30g are side surfaces including the short side n of the light exit surface 30a, and extend along the short side n. The two side surfaces 30f and 30g are both orthogonal to the light emitting surface 30a and the two light incident surfaces, and are arranged in parallel to each other. The side surfaces 30f and 30g are different in shape from the side surface on which the light incident surface is formed as described above, and the side (ridge line) corresponding to the light reflecting surface 30h is formed following the light reflecting surface 30h. ing. In the light guide plate 30 of the present embodiment, the shapes of the side surfaces 30f and 30g are the same as the shape of the cross section S perpendicular to the bisector α (or the long side m) in the light guide plate 30. Further, the cross-sectional shape is the same at an arbitrary position along the bisector α. The direction of the cross section S substantially matches the traveling direction (propagation direction) of light emitted from the light source 28 and incident on the light incident surface.

Subsequently, the shape of the light guide plate 30 in the direction along the light propagation path, that is, the shape of the cross section S of the light guide plate 30 perpendicular to the bisector α, particularly the first light reflecting surface 30b and the second light. The shape of the reflective surface 30c will be described in detail.
Here, for comparison, the light guide plate 30A in which the first light reflection surface 33b and the second light reflection surface 33c are formed in a planar shape will be described with reference to FIG. A light guide plate 30B in which the entire light reflecting surface is formed by a part of an ellipse will be described with reference to FIG. 11 and 12 are diagrams corresponding to FIG. 6, that is, diagrams showing a cross section S of the light guide plates 30A and 30B orthogonal to the bisector α. In these light guide plates 30A and 30B, the light exit surface 30a, the first light incident surface 30d, and the second light incident surface 30e are the same as the light guide plate 30 shown in FIG.

  As shown in FIG. 11, the light reflecting surface 33h of the light guide plate 30A includes two planar inclined surfaces, that is, a first light reflecting surface 33b and a second light reflecting surface 33c. Here, the lower ends of the first light incident surface 30d and the second light incident surface 30e are edge edges (back side end portions) 30i and 30j, respectively, and a center line β that is a perpendicular bisector of the light emitting surface 30a. When the intersection of the light reflecting surface 33h is a point 30k, the first light reflecting surface 33b appears as a line segment connecting the edge 30i and the point 30k. Similarly, the second light reflecting surface 33c appears as a line segment connecting the end edge 30j and the point 30k. Here, the inclination angle of the first light reflection surface 33b and the second light reflection surface 33c with respect to the light exit surface 30a is a taper angle θ (where θ> 0 °). Similar to the light guide plate 30 shown in FIG. 6A, the light guide plate 30A has a cross section S that is axisymmetric with respect to the center line β, and the first light incident surface 30d and the second light have a thickness. It is the minimum (tmin) at the reflecting surface 30e and the maximum (tmax) at the center (center line β).

  As shown in FIG. 12, in the light guide plate 30B, the light incident surface 35h is formed by a part of an ellipse. Here, if the major axis of the ellipse is k1, the major axis k1 coincides with the line segment connecting the two end edges 30i and 30j. The center C1 of the ellipse is a point where the major axis k1 and the center line β intersect. The short axis k2 coincides with the center line β. Here, let b be the half length of the minor axis k2. As will be described later, the length b is appropriately changed as a parameter for determining the shape of the ellipse within a range not exceeding the point 30k at which the distance from the light exit surface 30a is maximum. The light reflecting surface 35h shown in FIG. 12 has a shape obtained by cutting out the lower half of the ellipse, and is formed symmetrically with respect to the center line β. In this light reflecting surface 35h, the angle formed by the tangent of the ellipse and the light emitting surface 30a corresponds to the taper angle θ described above, and this taper angle θ is determined by two light incident surfaces (the first light incident surface 30d and the first light incident surface 30d). The maximum is 90 degrees at the two light incident surfaces 30e), and decreases as the distance from the two light incident surfaces approaches the center line β, and becomes 0 degrees at the center line β.

In the light guide plate 30A shown in FIG. 11, as pointed out in the prior art, the taper angle θ is constant, and particularly when the size of the light guide plate 30A is large (the light guide length L is long), the taper angle. θ decreases. For this reason, the light incident from the light incident surface and reflected in the vicinity of the light incident surface of the light reflecting surface 33h does not reach the vicinity of the center of the light guide plate 30A. For this reason, it is difficult to realize medium and high luminance distributions. In order to solve this problem, it is conceivable to increase the taper angle θ. However, in this case, there is a problem that the thickness of the light guide plate 30A is increased.
On the other hand, the light guide plate 30B shown in FIG. 12 has a large taper angle θ in the vicinity of the light incident surface of the light reflecting surface 35h, so that the light reflected in this vicinity can effectively reach the vicinity of the center. Can do. However, due to the nature of the ellipse, the taper angle θ is abruptly reduced slightly toward the center from the light incident surface. For this reason, there has been a problem that light cannot be effectively delivered to the vicinity of the center.

Therefore, in the present embodiment, the above-described problem is solved by configuring the light reflecting surface 30h by combining a part of an ellipse, a straight line, and a part of a circle.
6A, in the cross section S of the light guide plate 30, the light exit surface 30a is represented by a horizontal straight line, and the first light entrance surface 30d is one edge of the light exit surface 30a (same figure). The second light incident surface 30e is represented by a straight line that hangs vertically from the other edge (right end in the figure) of the light exit surface 30a. The first light incident surface 30d and the second light incident surface 30e have the same length and are parallel to each other. Here, the light guide plate 30 shown in FIG. 6A is also half the length of the ellipse center C1, the long axis k1, the short axis k2, and the short axis k2, similarly to the light guide plate 30B described in FIG. Let b be the size. Also, the thickness of the light guide plate 30 shown in the figure is the minimum (tmin) at the two light incident surfaces, and the maximum (tmax) at the center (center line β).

  The shape of the light reflecting surface 30h appearing in the cross section S of the light guide plate 30 shown in FIG. 6A is a part A1 of an ellipse as a quadratic curve connected to the edge 30i on the first light incident surface 30d side, A portion A2 of an ellipse as a quadratic curve connected to the edge 30j on the second light incident surface 30e side, straight lines A3 and A4 respectively connected to the portions A1 and A2 of these ellipses, and these straight lines A3 and A3 A part of the circle (arc) A5 connected between A4 and A5 is combined. As described above, since the first reflecting surface 30b and the second reflecting surface 30c are symmetric with respect to the plane H (and thus with respect to the center line β), a part of the ellipse A1 that is a part of each. And the straight line part A2 of the ellipse are objects with respect to the center line β, the straight lines A3 and A4 are objects with respect to the center line β, and the arc part A5 is symmetrical with respect to the center line β. is there.

  The above ellipse is an ellipse having the center C1 as the center and the length of the major axis k1 equal to the light guide length L. For the minor axis k2, the shape of the ellipse is changed by variously changing the half length b within the range of b <tmax−tmin. Since the ellipse parts A1 and A2 are formed symmetrically with respect to the center line β and have the same shape, the ellipse part A2 will be mainly described below. A part A2 of the ellipse has an outer edge (an edge far from the center line β) smoothly connected to the edge 30j of the second light incident surface 30e. That is, the tangent at the outer edge of the part A2 of the ellipse coincides with the second light incident surface 30e. This prevents the occurrence of band unevenness due to the fact that the connection is not smooth. In the part A2 of this ellipse, the taper angle θ (equal to the differential coefficient) with respect to the light exit surface 30a is 90 degrees on the second light incident surface 30e, and decreases with distance from the center (center line β). A part A2 of this ellipse is smoothly connected to the outer end of the straight line A4 at a connection point T1 at the inner end. Here, “smoothly connected” means that the taper angle θ of the straight line A4 coincides with the angle of the tangent of the part A2 of the ellipse at the connection point T1.

  The straight line A4 is inclined so that the end on the second light incident surface 30d side is close to the light exit surface 30a and conversely the center line β side is farther away, and the taper angle θ (inclination angle) is It is constant. Regarding the taper angle θ, for example, when the first light reflection surface 33b and the second light reflection surface 33c are planar like the light guide plate 30A shown in FIG. 11, the taper angles of these light reflection surfaces 30h. θ can be set. An end of a part A5 of a circle described below is connected to the end of the straight line A4 on the center line β side.

  As shown in FIG. 6D, the center C3 of the circle is located on the center line β and above the part A5 of the circle. Therefore, the taper angle θ of the part aA5 of the circle with respect to the light exit surface 30a is 0 at the center (center line β), and increases as it approaches the second light incident surface 30e. For this reason, a point at which the taper angle θ coincides with the straight line A4 is defined as a connection point T2. At the connection point T2, the differential coefficients of the straight line A4 and the part A5 of the circle coincide with each other, and the two are smoothly connected. This prevents the occurrence of band unevenness due to the fact that the connection is not smooth. The position of the connection point T2 between the straight line A4 and the part A5 of the circle can be changed by changing the radius R of the circle. For example, as the radius R of the circle decreases, the connection point T2 approaches the center line β. Conversely, as the radius R of the circle increases, the connection point T2 moves away from the center line β and the second light incident Approaches the surface 30e.

  Here, in the present invention, the light guide length L through which the light propagates between the first light incident surface 30d and the second light incident surface 30e is 22 inches (22 ") or more of the liquid crystal display panel 12 having a screen size or more. Is intended for the liquid crystal display panel 12 having a screen size of 280 mm or more and a maximum screen size of 65 inches (65 ″) or more, and therefore needs to be 830 mm or less. More specifically, the light guide length L is 280 mm or more and 320 mm or less for a screen size of 22 inches (22 ″), and the light guide length for a screen size of 37 inches (37 ″). L is not less than 480 mm and not more than 500 mm. For screen sizes of 42 inches (42 ″) and 46 inches (46 ″), the light guide length L is not less than 515 mm and not more than 620 mm, and 52 inches (52 ”) And 57 inch (57 ″) screen sizes, the light guide length L is not less than 625 mm and not more than 770 mm, and for 65 inch (65 ″) screen sizes, the light guide length L is 785 mm or more and 830 mm or less.

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

  In the present invention, the light guide plate 30 is shaped so as to increase in thickness from the two light incident surfaces toward the center (hereinafter referred to as an inverted wedge shape), thereby making the incident light deeper. It is easy to propagate, improves the in-plane uniformity while maintaining the light use efficiency, and obtains a so-called bell-shaped luminance distribution having a medium to high height. That is, by adopting such a shape, the above-described light reflecting surface has a planar inclined surface (see FIG. 11) light guide plate 30A (hereinafter referred to as “an inclined surface light guide plate”), or light reflection. Compared to an elliptical surface (see FIG. 12) (hereinafter, referred to as an “elliptical light guide plate” as appropriate), the so-called bell-shaped distribution can be achieved with high efficiency and medium to high.

  In the light guide plate 30 shown in FIGS. 3A and 3B, light incident from two light incident surfaces (the first light incident surface 30 d and the second light incident surface 30 e) is included in the light guide plate 30. The light exit surface passes through the inside of the light guide plate 30 and is reflected directly or directly by the light reflecting surface 30h (the first reflecting surface 30b and the second reflecting surface 30c) while being scattered by the scattering fine particles (details will be described later). Inject from 30a. At this time, a part of the light may leak from the light reflecting surface 30h, but the leaked light is reflected by a reflecting sheet (not shown) arranged so as to cover the light reflecting surface 30h of the light guide plate 30. Then, it enters the light guide plate 30 again.

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

Here, the particle diameter of the scattering fine particles dispersed in the light guide plate 30 used in the backlight unit 20 of the present invention needs to be 4.0 μm or more and 12.0 μm or less. The reason is that high scattering efficiency can be obtained, the forward scattering property is large, the wavelength dependency is small, and color unevenness can be selected.
In addition, it is preferable to consider the following points in addition to the wavelength dependency in selecting the optimum particle size of the scattering fine particles to be dispersed in the light guide plate 30 used in the backlight unit 20 of the present invention.
First, in the scattered light intensity distribution (angular distribution) by a single particle, it is necessary to satisfy the condition that the light scattered in the forward 0 to 5 ° is 90% or more. This is because the light guide plate 30 used in the backlight unit 20 of the present invention having an inverted wedge shape is at least a distance of 240 mm or more from the two light incident surfaces on the side surface of the light guide plate 30. This is because it is necessary to guide a distance of at least 480 mm or more, and if less than 90% of the light scattered in the forward 0 to 5 ° is less than 90%, the light cannot be guided to the back of the light guide plate 30.

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

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

Moreover, since the light guide length L of the light guide plate 30 used in the backlight unit 20 of the present invention is 280 to 830 mm, the concentration of the scattering particles needs to be 0.008 wt% or more and 0.76 wt% or less.
Specifically, when the light guide length L is 280 mm ≦ L ≦ 320 mm, the concentration of the scattering particles needs to be 0.02 wt% or more and 0.22 wt% or less.
When the light guide length of the light guide plate is L = 280 mm corresponding to a screen size of 22 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.1 wt% or more and 0.32 wt%. More preferably, it is more preferably 0.14 wt%. When the particle size of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.14 wt% or more and 0.5 wt% or less, and most preferably 0.21 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.25 wt% or more and 0.76 wt% or less, and most preferably 0.35 wt%. .
When the light guide length L is 480 mm ≦ L ≦ 500 mm, the concentration of the scattering particles needs to be 0.02 wt% or more and 0.22 wt% or less.
Further, when the light guide length L of the light guide plate 30 is L = 480 mm corresponding to a screen size of 37 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.02 wt% or more, 0.0. The content is more preferably 085 wt% or less, and most preferably 0.047 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.03 wt% or more and 0.12 wt% or less, and most preferably 0.065 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.06 wt% or more and 0.22 wt% or less, and most preferably 0.122 wt%. .

Further, when the light guide length L is 515 mm ≦ L ≦ 620 mm, the concentration of the scattering particles is preferably 0.015 wt% or more and 0.16 wt% or less.
In addition, when the light guide length L of the light guide plate 30 is L = 560 mm corresponding to a screen size of 42 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.015 wt% or more, 0.0. It is more preferably 065 wt% or less, and most preferably 0.035 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.02 wt% or more and 0.09 wt% or less, and most preferably 0.048 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.04 wt% or more and 0.16 wt% or less, and most preferably 0.09 wt%.

  Further, when the light guide length L of the light guide plate 30 is L = 590 mm corresponding to a screen size of 46 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.015 wt% or more, 0.0. More preferably, it is 060 wt% or less, and most preferably 0.031 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.02 wt% or more and 0.08 wt% or less, and most preferably 0.043 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.035 wt% or more and 0.15 wt% or less, and most preferably 0.081 wt%.

When the light guide length L is 625 mm ≦ L ≦ 770 mm, the concentration of the scattering particles is preferably 0.01 wt% or more and 0.12 wt% or less.
When the light guide length L of the light guide plate 30 is L = 660 mm corresponding to a screen size of 52 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.010 wt% or more and 0.050 wt%. % Or less is more preferable, and 0.025 wt% is most preferable. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.015 wt% or more and 0.060 wt% or less, and most preferably 0.034 wt%. Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.030 wt% or more and 0.120 wt% or less, and most preferably 0.064 wt%.

  Further, when the light guide length of the light guide plate 30 is L = 730 mm corresponding to a screen size of 57 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.010 wt% or more and 0.040 wt%. More preferably, it is more preferably 0.021 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.010 wt% or more and 0.050 wt% or less, and most preferably 0.028 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is preferably 0.020 wt% or more and 0.100 wt% or less, and most preferably 0.053 wt%.

When the light guide length L is 785 mm ≦ L ≦ 830 mm, it is preferable that the concentration of the scattering particles is 0.006 wt% or more and 0.08 wt% or less.
Furthermore, when the light guide length of the light guide plate 30 is L = 830 mm corresponding to a screen size of 65 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.008 wt% or more and 0.030 wt%. The content is more preferably as follows, and most preferably 0.016 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.009 wt% or more and 0.040 wt% or less, and most preferably 0.022 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.020 wt% or more and 0.080 wt% or less, and most preferably 0.041 wt%. .

From the above, in the present invention, the particle size and concentration of the scattering particles dispersed in the light guide plate 30 need to satisfy a predetermined relationship according to the light guide length L between the two light incident surfaces of the light guide plate 30. I understand that.
Therefore, in the present invention, when the light guide length of the light guide plate 30 is 280 mm or more and 320 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less. The concentration needs to be 0.1 wt% or more and 0.76 wt% or less, and as shown in the graph of FIG. 7, the particle diameter (μm) of the scattering particles is taken as the horizontal axis, and the particle concentration ( wt%) is the vertical axis, the particle size and concentration of the scattering particles are 6 points (4.0, 0.1), (4.0, 0.32), (7.0, 0.14). , (7.0, 0.5), (12.0, 0.25) and (12.0, 0.76).

In the present invention, when the light guide length L of the light guide plate 30 is not less than 480 mm and not more than 500 mm, the particle diameter of the scattering particles is not less than 4.0 μm and not more than 12.0 μm as described above. The concentration of the particles should be 0.02 wt% or more and 0.22 wt% or less, and as shown in the graph of FIG. 8A, the particle diameter (μm) of the scattering particles is taken as the horizontal axis, and the scattering particles The vertical axis is the particle concentration (wt%), and the particle size and concentration of the scattering particles are 6 points (4.0, 0.02), (4.0, 0.085), (7.0, 0.03), (7.0, 0.12), (12.0, 0.06), and (12.0, 0.22).
When the light guide length L of the light guide plate 30 is 515 mm or more and 620 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0. .015 wt% or more and 0.16 wt% or less, and when the particle diameter (μm) is on the horizontal axis and the particle concentration (wt%) is on the vertical axis as shown in the graph of FIG. The particle size and concentration of the scattering particles are 6 points (4.0, 0.015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09). , (12.0, 0.035) and (12.0, 0.16).

When the light guide length L of the light guide plate 30 is 625 mm or more and 770 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0. .01 wt% or more and 0.12 wt% or less, and when the particle diameter (μm) is on the horizontal axis and the particle concentration (wt%) is on the vertical axis as shown in the graph of FIG. The particle size and concentration of the particles are 6 points (4.0, 0.01), (4.0, 0.05), (7.0, 0.01), (7.0, 0.06), It must be within the region enclosed by (12.0, 0.02) and (12.0, 0.12).
When the light guide length L of the light guide plate 30 is 785 mm or more and 830 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0. 0.008 wt% or more and 0.08 wt% or less, and when the particle diameter (μm) is the horizontal axis and the particle concentration (wt%) is the vertical axis as shown in the graph of FIG. The particle size and concentration of the scattering particles are 6 points (4.0, 0.008), (4.0, 0.03), (7.0, 0.009), (7.0, 0.04). , (12.0, 0.02) and (12.0, 0.08).

  The reason why the particle size and concentration of the scattering particles need to be within the region surrounded by the six points in the graphs shown in FIG. 7, FIG. 8 (A) and (B), FIG. 9 (A) and (B). Outside this region, if the particle concentration is too high, it becomes the same as a flat plate, and a medium-high luminance distribution cannot be realized. On the other hand, if the particle concentration is too low, the light penetrates and passes through, so the light utilization efficiency of 55% or more is not satisfied. If the particle size is too small, the light utilization efficiency is improved, This is because a medium-high luminance distribution cannot be realized, while if the particle size is too large, a medium-high luminance distribution can be realized, but the light utilization efficiency is low.

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

The light guide plate 30 used in the backlight unit (planar illumination device) 20 of the present invention in which scattered fine particles are dispersed inside has two light incident surfaces (a first light incident surface 30d and a second light incident surface 30e). ), The light use efficiency indicating the ratio of the light emitted from the light exit surface 30a needs to be 55% or more. The reason for this is that if the light utilization efficiency is less than 55%, a light source with a higher output is required to obtain the required luminance. However, if a light source with a higher output is used, the light source becomes hot and power consumption is increased. This is because the warpage and elongation of the light guide plate 30 become large, and a required brightness distribution, that is, a so-called medium-high or bell-shaped brightness distribution cannot be obtained.
Further, the medium to altitude degree of the luminance distribution of the light emitting surface indicating the ratio of the luminance of the light emitted from the central portion of the light emitting surface 30a to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface 30a is 0%. It must be greater than 25%. The reason for this is that the vicinity of the center of the screen required for a large-screen thin LCD TV is brighter than the periphery, that is, a so-called medium-high or bell-shaped brightness distribution.
Such a light guide plate 30 can be manufactured using an extrusion molding method or an injection molding method.

Here, the light guide plate 30 includes a first light incident surface 30d and a second light incident surface 30e serving as a light incident surface, a light exit surface 30a, and a first reflecting surface 30b and a second reflecting surface serving as a light reflecting surface 30h. The surface roughness Ra of at least one surface of 30c is preferably smaller than 380 nm, that is, Ra <380 nm.
By making the surface roughness Ra of the first light incident surface 30d and the second light incident surface 30e to be light incident surfaces smaller than 380 nm, the diffuse reflection on the surface of the light guide plate can be ignored, that is, the surface of the light guide plate Diffuse reflection can be prevented, and the incident efficiency can be improved.

Further, by making the surface roughness Ra of the light exit surface 30a smaller than 380 nm, the diffuse reflection transmission on the light guide plate surface can be ignored, that is, the diffuse reflection transmission on the light guide plate surface can be prevented, Light can be transmitted to the back by total reflection.
Furthermore, by making the surface roughness Ra of the first reflecting surface 30b and the second reflecting surface 30c to be the light reflecting surface 30h smaller than 380 nm, diffuse reflection can be ignored, that is, diffusion on the light reflecting surface 30h. Reflection can be prevented, and the total reflection component can be transmitted further.

Next, the interval maintaining member 31 will be described.
Here, FIG. 10 (A) is a front view showing a schematic configuration of the periphery of the interval maintaining member 31 of the backlight unit 20 shown in FIG. 2, and FIG. 10 (B) is a cross-sectional view of FIG. It is B line sectional drawing.
The interval maintaining member 31 is fixed to a region where the LED chips 50 on the two light incident surface sides of the light guide plate 30 of the light source support portion 52 (more precisely, the array substrate 54 of the light source support portion 52) are not disposed. The tip of the light guide plate 30 side protrudes from the light emitting surface 58 of the light emitting portion 51 of the LED chip 50 toward the light incident surface side of the light guide plate 30 facing the light guide plate 30. In the interval maintaining member 31, the tip of the portion of the light guide plate 30 that protrudes toward the facing light incident surface is in contact with the facing light incident surface of the light guide plate 30.
In addition, the interval maintaining member 31 of the present embodiment is disposed on the surface on the light source support portion 52 so as to cover three sides of the outer periphery of the LED chip 50 excluding the surface on the back side of the light guide plate 30. Has been.

The gap maintaining member 31 is made of a material having high heat resistance and a shock absorbing property (that is, cushioning property) such that a portion in contact with the light guide plate does not damage the light guide plate 30, for example, silicon rubber. ing. In addition, the material used for manufacturing the interval maintaining member 31 has a shock absorption property, but is also a material having such a rigidity that the substantial shape does not change even when an external force is applied.
By producing the gap maintaining member 31 with the above material, the light guide plate 30 can be prevented from being damaged even when the light guide plate 30 expands and contracts and the light guide plate 30 and the gap maintaining member 31 are rubbed. Even when heated by heat, denaturation and deformation can be prevented.
In addition, the fixing method of the space | interval maintenance member 31 to the light source support part 52 is not specifically limited, Although various fixing methods can be used, the space | interval maintenance member 31 and the light source support part 52 are couple | bonded chemically or mechanically. By doing so, it is preferable to fix the interval maintaining member 31 to the light source support portion 52.
Here, as a chemical bonding method, a method of bonding the light guide plate 30 and the light guide plate 30 with an adhesive or silicone adhesive similar to the light guide plate material, which is an adhesive that does not cause a chemical change, is exemplified. Examples of the coupling method include a method of fixing with screws.

By providing the interval maintaining member 31, even when the light guide plate 30 expands and contracts (particularly when the light guide plate 30 expands), the light emitting surface 58 of the light emitting unit 51 of the light source 28 and the light incident surface facing the light guide plate 30 are opposed to each other. The distance can be constant. As a result, the light incident surface of the light guide plate 30 and the light emitting surface 58 of the light emitting portion 52 of the LED chip 50 of the light source 28 come into contact with each other, so that the LED chip 50 breaks down or the LED chip 50 is displaced. It is possible to prevent occurrence or damage to the light incident surface of the light guide plate 30.
Further, by providing the interval maintaining member 31 in the outer periphery of the LED chip 50 of the light source support portion 52, that is, in the region where the LED chip 50 is not disposed, it is possible to more reliably prevent external force from acting on the LED chip 50, and the LED It can prevent more reliably that the chip | tip 50 is damaged.
In addition, since the distance between the light emitting surface 58 and the light incident surface can be made constant, the light emitted from the light emitting surface 58 is guided in the same positional relationship even when the light guide plate 30 expands and contracts or when vibration occurs in the apparatus. The light can be incident on the optical plate 30. Thereby, even if the light guide plate 30 expands and contracts, light without unevenness in brightness can be emitted from the light exit surface 30a.

  The spacing maintaining member 31 has a distance c (see FIG. 3B) between the light emitting surface 58 of the light emitting portion 51 of the LED chip 50 and the light incident surface facing the light guide plate 30 of 0.1 mm or more and 0.5 mm. The following is preferable. By making the distance c 0.1 mm or more and 0.5 mm or less, the use efficiency of the light emitted from the LED chip 50 can be increased, the light can be used efficiently, and the brightness of the light emission surface 30a can be increased. High light can be emitted.

Next, the optical member unit 32 will be described with reference to FIG.
The optical member unit 32 converts the illumination light emitted from the light exit surface 30a of the light guide plate 30 into light having no uneven brightness, and emits the illumination light without uneven brightness from the light exit surface 24a of the illumination device body 24. A diffusion sheet 32a for diffusing illumination light emitted from the light exit surface 30a of the light guide plate 30 to reduce luminance unevenness, and a microprism array parallel to a tangent line between the light incident surface and the light exit surface 30a Are formed, and a diffusion sheet 32c that diffuses illumination light emitted from the prism sheet 32b to reduce luminance unevenness.

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

In the present embodiment, the optical member unit 32 is composed of the two diffusion sheets 32a and 32c and the prism sheet 32b disposed between the two diffusion sheets 32a and 32c. The arrangement order and the number of the sheets 32a and 23c are not particularly limited, and the prism sheet 32b and the diffusion sheets 32a and 32c are not particularly limited, and the luminance of the illumination light emitted from the light emission surface 30a of the light guide plate 30 is not particularly limited. As long as unevenness can be further reduced, various optical members can be used.
For example, as the optical member unit 32, in addition to or instead of the above-described diffusion sheets 32a and 32c and the prism sheet 32b, a transmittance adjustment in which a large number of transmittance adjusting bodies made of a diffuse reflector are arranged in accordance with the luminance unevenness. Members can also be used.

Next, the reflecting plate 34 of the lighting device body 24 will be described.
The reflecting plate 34 is provided to reflect light leaking from the light reflecting surface 30h (the first reflecting surface 30b and the second reflecting surface 30c) of the light guide plate 30 and to make it incident on the light guide plate 30 again. The utilization efficiency can be improved. The reflection plate 34 has a shape corresponding to the light reflection surface 30h of the light guide plate 30 and is formed so as to cover the light reflection surface 30h. In the present embodiment, as shown in FIG. 6, the light reflecting surface 30h of the light guide plate 30 is formed by ellipse portions A1, A2, straight lines A3, A4, and a circle portion A5. It is formed in a shape following this.

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

The upper guide reflection plate 36 is disposed between the light guide plate 30 and the diffusion sheet 32a, that is, on the light emission surface 30a side of the light guide plate 30, and the end of the light emission surface 30a of the light guide plate 30 and the light emission surface 30a (first light incident). The end portion on the surface 30d side and the end portion on the second light incident surface 30e side) are disposed so as to cover each other. In other words, the upper guide reflection plate 36 is disposed so as to cover from a part of the light exit surface 30a of the light guide plate 30 to a part of the array substrate 54 of the light source 28 in a direction parallel to the optical axis direction. That is, the two upper guide reflectors 36 are disposed at both ends of the light guide plate 30, respectively.
As described above, by arranging the upper guide reflection plate 36, it is possible to prevent the light emitted from the light source 28 from leaking to the light emitting surface 30 side without entering the light guide plate 30.
Thereby, the light inject | emitted from the LED chip 50 of the light source 28 can be efficiently entered in the light-incidence surface of the light-guide plate 30, and light utilization efficiency can be improved.

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

Here, the upper guide reflection plate 36 and the lower guide reflection plate 38 can reflect the light emitted from the light source 28 to the light incident surface side, and allow the light emitted from the light source 28 to enter the light incident surface. The shape and width are not particularly limited as long as 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 emission surface 24 a side and the reflecting plate 34 side. It has an upper housing 44, a reinforcing member (folding member) 46, and a supporting member (sliding mechanism) 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 a surface other than the light exit surface 24 a of the illuminating device main body 24, i. 24 covers the surface (back surface) and side surfaces opposite to the light exit surface 24a.

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

The reinforcing 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 reinforcing member 46 is inserted between the side surface portion 42 a of the lower housing 42 and the side surface portion 44 a of the upper housing 44, and the outer surface of one U-shaped parallel portion is the lower portion. The side surface portion 42 a of the housing 42 is connected, and the outer side surface of the other parallel portion is connected to the side surface portion 44 a of the upper housing 44.
Here, as a method for joining the lower housing 42 and the reinforcing member 46, and a method for joining the reinforcing 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 reinforcing 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. Accordingly, for example, even when the light guide plate 30 that can emit light efficiently with little or no luminance unevenness and easily warps, the warpage can be corrected more reliably, or the light guide plate It is possible to more reliably prevent the warp 30 from occurring, and it is possible to emit light from the light exit surface 24a with no or uneven brightness.
Note that various materials such as metal and resin can be used for the upper housing 44, the lower housing 42, and the reinforcing member 46 of the housing 26. In addition, as a material, it is preferable to use a lightweight and high-strength material.
In this embodiment, the reinforcing member 46 is a separate member, but it may be formed integrally with the upper housing 44 or the lower housing 42. Further, the reinforcing member 46 may not be provided.

The support member 48 has a shape with the same cross-sectional shape perpendicular to the extending direction. That is, it is a rod-like member having the same cross-sectional shape perpendicular to the extending direction.
As shown in FIG. 2, the support member 48 is disposed between the reflection plate 34 and the lower housing 42, more specifically, the reflection plate 34 at a position corresponding to the end of the light guide plate 30 on the light incident surface side. It arrange | positions between the lower housing | casing 42, fixes the light-guide plate 30 and the reflecting plate 34 to the lower housing | casing 42, and supports it.
The light guide plate 30 and the reflection plate 34 can be brought into close contact with each other by supporting the reflection plate 34 with the support member 48. Furthermore, the light guide plate 30 and the reflection plate 34 can be fixed at predetermined positions of the lower housing 42.

In the present embodiment, the support member 48 is provided as an independent member. However, the present invention is not limited to this, and the support member 48 may be formed integrally with the lower housing 42 or the reflection plate 34. In other words, a protrusion may be formed on a part of the lower housing 42, and this protrusion may be used as the support member 48. Also, a protrusion may be formed on a part of the reflector 34, and this protrusion may be used as a support member. 48 may be used.
Further, the arrangement position is not particularly limited, and the arrangement position can be arranged at an arbitrary position between the reflection plate 34 and the lower housing 42, but in order to stably hold the light guide plate 30, the end of the light guide plate 30 is arranged. In the present embodiment, that is, in the present embodiment, it is preferable to dispose near the first light incident surface 30d and the second light incident surface 30e.

Further, the shape of the support member 48 is not particularly limited, and can be various shapes, and can be made of various materials. For example, a plurality of support members 48 may be provided and arranged at predetermined intervals.
Further, the support member 48 has a shape that fills the entire space formed by the reflecting plate 34 and the lower housing 42, that is, the reflecting plate side surface is shaped like the reflecting plate 34, and the lower housing side surface is It is good also as the shape which followed the lower housing | casing 42. FIG. As described above, when the entire surface of the reflection plate 34 is supported by the support member 48, it is possible to reliably prevent the light guide plate 30 and the reflection plate 34 from separating, and uneven brightness is caused by the light reflected from the reflection plate 34. It can be prevented from occurring.

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 d and the second light incident surface 30 e) of the light guide plate 30. Light incident from each surface passes through the light guide plate 30 while being scattered by the scatterers included in the light guide plate 30, and directly or after being reflected by the first reflecting surface 30b and the second reflecting surface 30c. The light exits from the light exit surface 30a. At this time, part of the light leaking from the first reflecting surface 30 b and the second reflecting surface 30 c is reflected by the reflecting plate 34 and enters the light guide plate 30 again.
In this way, the light emitted from the light emitting surface 30 a of the light guide plate 30 passes through the optical member unit 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.

  Further, by providing the spacing maintaining member 31 on the light incident surface side surface of the light source support portion 52 of the light source 28, the light emitting surface 58 of the light emitting portion 51 of the LED chip 50 and the light guide plate 30 are in contact as described above. This can prevent the LED chip 50 and the light guide plate 30 from being damaged, and can keep the distance between the light incident surface and the light emitting surface 58 constant. Damage to the LED chip 50 and the light guide plate 30 can prevent uneven brightness and failure of the backlight unit 20. In addition, since the distance between the light incident surface and the light emitting surface 58 can be maintained constant, the light emitted from the light emitting surface 58 can be incident on the light guide plate 30 under certain conditions, and uneven brightness occurs even when the distance changes. Can be prevented. Moreover, high light utilization efficiency can be maintained.

  Moreover, it is preferable to produce the space | interval maintenance member 31 with the transparent material which permeate | transmits light. By making the interval maintaining member 31 transparent, it is possible to prevent the interval maintaining member 31 from absorbing the light emitted from the light source 28 and the light once emitted from the light guide plate 30 and reentering the light guide plate 30. Light utilization efficiency can be increased.

Here, in the said embodiment, although the space | interval maintenance member 31 has been arrange | positioned so that the outer periphery 3 sides of LED chip 50 may be covered, it is not limited to this, It is fixed to a light source support part, Light emission of the light emission part 51 of LED chip 50 Various members that prevent the surface 58 from contacting the light incident surface of the light guide plate 30, do not damage the light incident surface of the light guide plate 30, and make the distance therebetween constant can be used.
Further, in the present embodiment, since light with higher luminance can be efficiently emitted from the light emitting surface 30a, the side where the light incident surface of the light guide plate 30 intersects the light emitting surface 30a becomes a long side, and the side surface However, the present invention is not limited to this, and the light emission surface 30a may be a square shape, the light incident surface side may be a short side, and the side surface side may be a long side.

Moreover, when producing the light guide plate 30, a light guide plate may be produced by mixing a plasticizer into the transparent resin.
Thus, by making the light guide plate 30 with a material in which a transparent material and a plasticizer are mixed, the light guide plate 30 can be made flexible, that is, a flexible light guide plate. It can be deformed into various shapes. Therefore, the surface of the light guide plate can be formed into various curved surfaces.
By making the light guide plate 30 flexible in this manner, for example, when the light guide plate 30 or the backlight unit 20 using the light guide plate 30 is used as a display plate related to illumination (illumination), it has a curvature. The light guide plate 30 can be mounted on a wall, and the light guide plate 30 can be used for more kinds, a wider range of use in electrical decoration, POP (POP advertisement), and the like.

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

  As described above, the backlight unit 20 according to the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications are made without departing from the gist of the present invention. May be.

In addition, for example, the LED chip 50 of the light source 28 has a configuration in which a YAG fluorescent material is applied to a light emitting surface of a blue LED, but is not limited thereto, and the light emitting surface of another single color LED such as a red LED or a green LED is used. You may use the LED chip of the structure which has arrange | positioned the fluorescent substance.
In addition, as the light source 28, an LED unit having a configuration in which three kinds of LEDs, a red LED, a green LED, and a blue LED, are combined can be used. In this case, white light can be obtained by mixing light emitted from the three types of LEDs.
Further, a semiconductor laser (LD) can be used instead of the LED.

Further, a confusion portion made of a material having a refractive index close to that of the light guide plate 30 may be disposed between the light guide plate 30 and the light source 28. Further, a part of the light incident surface and / or side surface of the light guide plate 20 may be formed of a material having a smaller refractive index than other portions.
By reducing the refractive index of the portion where the light emitted from the light source 28 is incident, the light emitted from the light source 28 can be made incident more efficiently and the light utilization efficiency can be increased. Can do.

  Further, for example, a plurality of light guide plates 30 may be arranged in parallel at a position where the side surfaces of the light guide plates 30 face each other, and one light emitting surface 30 a may be formed by the plurality of light guide plates 30. In this case, it is good also as a structure which arrange | positions a sublight source only to the side surface of the side which is not adjacent to the other light-guide plate 30 of the light-guide plate 30 of both ends.

  In addition, since light with a medium and high luminance distribution can be emitted from the light exit surface 30a, the light guide plate 30 preferably satisfies the various ranges described above, but the light guide plate 30 in the following ranges may also be used. preferable.

The light guide plate 30 has a scattering cross-sectional area of the scattering particles contained in the light guide plate 30 as Φ, and reaches a position where the thickness in the direction perpendicular to the light exit surface 30a is maximum from the light incident surface of the light guide plate 30 in the light incident direction. In this embodiment, the half length of the light incident direction of the light guide plate 30 (the direction perpendicular to the first light incident surface 30d of the light guide plate 30, hereinafter also referred to as “optical axis direction”). When L _G , the density of scattering particles contained in the light guide plate 30 (number of particles per unit volume) is N _p , and the correction coefficient is K _C , the value of Φ · N _p · L _G · K _C is 1. is 1 or more, and is 8.2 or less, further, the value of the correction coefficient _{K C} satisfies the relationship of 0.005 to 0.1. Since the light guide plate 30 includes scattering particles that satisfy such a relationship, the illumination light can be emitted from the light exit surface with uniform brightness and less unevenness in luminance.

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

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

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

According to the equation (4), when the value of Φ · N _p · L _G · K _C is 3.5, the light extraction efficiency E _out is 3%, and Φ · N _p · L _G · K _C When the value of is 4.7, the light extraction efficiency E _out is 1%.
From this result, it is understood that the light extraction efficiency E _out decreases as the value of Φ · N _p · L _G · K _C increases. Since light is scattered as it travels in the optical axis direction of the light guide plate 30, it is considered that the light extraction efficiency E _out decreases.

Therefore, it can be seen that the larger the value of Φ · N _p · L _G · K _C , the more preferable properties for the light guide plate 30. That is, by increasing the value of Φ · N _p · L _G · K _C , the light emitted from the surface facing the light incident surface is reduced, and the light emitted from the light emitting surface 30a is increased. Can do. That is, by increasing the value of _{Φ · N p · L G ·} K C, the ratio of light emitted through the light exit plane 30a to light incident on the incident surface (hereinafter referred to as "light use efficiency".) Can be high. Specifically, by setting 1.1 or the value of _{Φ · N p · L G ·} K C, the light use efficiency can be 50% or more.

Here, when the value of Φ · N _p · L _G · K _C is increased, the illuminance unevenness of the light emitted from the light exit surface 30a of the light guide plate 30 becomes significant, but Φ · N _p · L _G · K _C By making the value of 8.2 or less, the illuminance unevenness can be suppressed to a certain value (within an allowable range). Note that the illuminance and the luminance can be handled in substantially the same manner. Therefore, in the present invention, it is presumed that luminance and illuminance have the same tendency.
From the above, it is preferable that the values of Φ · N _p · L _G · K _C of the light guide plate 30 used in the backlight unit 20 of the present invention satisfy the relationship of 1.1 or more and 8.2 or less. More preferably, it is not less than 0.0 and not more than 7.0. The value of _{Φ · N p · L G ·} K C is more preferably as long as 3.0 or more, most preferably, not less than 4.7.
The correction coefficient K _C is preferably 0.005 or more and 0.1 or less.

Hereinafter, the light guide plate 30 shown in FIGS. 5 and 6 will be described in detail based on examples.
13, 14, and 15 are graphs showing changes in the taper angle (tilt angle) of the elliptical cross section of the light guide plate 30. These differ in the light guide length L of the light guide plate 30, and L = 480, 560, and 590 [mm] in this order.
13, 14, and 15, FIG. 13 shows changes in the taper angle (inclination angle) of the elliptical cross section of the light guide plate 30 with L = 480 [mm] (corresponding to 37 inches). On the horizontal axis, the position [mm] up to the end (see the second light incident surface 30e in FIG. 6) with respect to the center in the depth direction (center line β in FIG. 6A) on the light guide plate 30. Have taken. This is the same as the distance from the center line β. However, the range of 0 to 150 [mm] is omitted. On the other hand, the vertical axis represents the taper angle (deg).

  The ellipse in the figure is the ellipse described with reference to FIG. 6 (A) and FIG. That is, with the center C1 as the center, the length of the major axis k1 is L (L = 480 [mm] in the example shown in FIG. 13), and half of the length of the minor axis k2 is b. Here, the ellipse has a length b which is half of the short axis, and is 7 pieces every 0.1 [mm] between b = 1.0 [mm] and b = 1.6 [mm]. In the drawing, that is, b = 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6 are illustrated in this order from the bottom. In addition, in the drawing, the taper angle θ = 0.48 [deg] of the inclined surface (second light reflecting surface 30h1) when the 37-inch light guide plate 30 is manufactured in the shape shown in FIG. ing. In the figure, the taper angle of each ellipse is 90 degrees at the maximum on the light incident surface (the first light incident surface 30d and the second light incident surface 30e), and shows a steep taper angle in the vicinity of the light incident surface. The taper angle gradually decreases gradually after passing a steep portion toward the center. The position of the horizontal axis of the intersection of the upward-sloping curve indicating the taper angle of this ellipse and the horizontal straight line indicating the taper angle of the inclined surface is the difference between the taper angle of each ellipse and the taper angle of the inclined surface. The position where the magnitude relationship is reversed is shown. These intersections shift to the center side (left side in the figure) as b in the ellipse is larger (the shorter axis is longer). For example, an ellipse of b = 1.6 [mm] having the largest value of b intersects the inclined surface at the position indicated by the point P on the most central side, 188 [mm]. That is, the taper angle of the ellipse of b = 1.6 [mm] exceeds the taper angle of the inclined surface on the light incident surface side (right side in the figure) from this point P, and conversely, from this point P On the center side, it is less than the taper angle of the inclined surface. This means that at least on the light incident surface side than the point P, the ellipse is more effective in reaching incident light farther than the inclined surface.

FIG. 14 shows a change in the inclination angle of the elliptical cross section of the light guide plate 30 with L = 560 [mm] (for 42 inches). In the 42-inch type, as shown in FIG. 11, the taper angle when the light reflecting surface 33h is formed as an inclined surface is 0.42 [degrees]. Therefore, the ellipse when the value of b is changed and other conditions are the same as those of the light guide plate 30 in FIG.
FIG. 15 shows a change in the inclination angle of the elliptical cross section of the light guide plate 30 with L = 590 [mm] (corresponding to 46 inches). In the 42-inch type, as shown in FIG. 11, the taper angle when the light reflecting surface 33h is formed as an inclined surface is 0.42 [degrees]. Other conditions are the same as those of the light guide plate 30 of FIGS.

  From FIGS. 13 to 15, in any case of L = 480, 560, and 590, when the value of b in the ellipse is set to the above b = 1.0 to 1.6 [mm], As shown in FIG. 11, it can be seen that a region where the taper angle can be increased can be secured in the vicinity of the light incident surface as compared with the case where the light reflecting surface 33h is an inclined surface having a constant taper angle. For example, when viewing b = 1.6 [mm], the region on the light incident surface side (right side in the drawing) from each point P in FIGS. 13 to 15 has a larger taper angle than the inclined surface. It is an area. Further, when L is constant, it can be seen that the larger the value of b, the closer the point P is to the center.

  The taper angle of each ellipse is 90 degrees at the maximum on the light incident surface, and shows a steep taper angle in the vicinity of the light incident surface portion. After passing the steep part, the taper angle is gradually reduced gradually. And it becomes 0 degree at the center. On the other hand, although the taper angle varies depending on the diameter R of the circle, it tends to be 0 at the center and becomes larger as the distance from the center approaches the light incident surface. In this embodiment, a part A2 of the ellipse and a part A5 of the circle are connected by a straight line A4.

  The point at which the taper angle of the part A2 of the ellipse and the taper angle of the straight line A4 are the same, that is, the intersection of both is the point at which the part A2 of the ellipse and the straight line A4 are smoothly connected. For example, in FIG. 13, a part A2 of an ellipse with b = 1.6 [mm] and a straight line A4 with a taper angle θ = 0.48 [deg] are at a position indicated by a point P, 188 [mm]. Intersect. The distance from this point P to the light incident surface is 240-188 = 52 [mm] because the distance from the center to the light incident surface is 480/2 = 240 [mm] in the case of 37 inches. .

  In the illustrated example, a part A2 of an ellipse having a major axis length of 480 [mm] and a minor axis length b of b = 1.6 [mm] and a straight line A4 are 188 [m] from the center. mm], and intersects at a position of 52 [mm] from the light incident surface (end). That is, the part A2 of the ellipse and the straight line A4 are smoothly connected at this point P. The taper angle is larger on the light incident surface side than the point P on the part A2 of the ellipse than on the straight line A4. Conversely, on the center side of the point, it is larger than the part A2 of the ellipse. The straight line A4 is larger. That is, by smoothly connecting the part A2 of the ellipse and the straight line A4, the steep taper angle of the part A2 of the ellipse is used in the vicinity of the light incident surface, and the taper angle is larger than the ellipse on the center side. A straight line A4 can be used. This effect will be described later.

  2A and 2B, the light guide length L of the light guide plate 30 is 560 [mm] (corresponding to 42 inches), its shape, that is, the maximum thickness tmax [ mm], minimum thickness tmin (= a) [mm], half of the minor axis of the ellipse b [mm], radius R [mm] of the circle, and particle concentration [wt%] of the scattering fine particles dispersed in the light guide plate 30 I changed the simulation. The results are shown in FIGS. 20 to 22, and the results are summarized in FIG. As shown in FIG. 19, overall efficiency [%], overall efficiency comparison (1) [%], overall efficiency comparison (2) [%], medium / high rate count calculation [%], medium / high rate graph judgment, central area illumination Central part illuminance comparison (1) and central part illuminance comparison (2) were obtained.

Here, the comparison reference (1) is shown as a reference, and is “an inclined surface light guide plate” with tmin = a = 2 [mm], tmax = 3.59 [mm], and a particle concentration of 0.1 [wt%]. is there.
The comparison reference (2) is “ellipse light guide plate”, where a = 2 [mm], the length of the major axis of the ellipse = L = 560 [mm], and the half of the minor axis b = 1.6 [ mm] and a particle concentration of 0.1125 [wt%].
The overall efficiency indicates a ratio of light emitted from the light exit surface 30a to light incident from the two light incident surfaces (the first light incident surface 30d and the second light reflecting surface 30c) of the light guide plate 30.

Further, the medium-high rate D is represented by 0 <D ≦ 25 and D = {(Lcen−Ledg) / Lcen} × 100 [%]. Here, Lcen and Ledg represent the luminance at the central portion and the luminance at the screen end side (near the incident portion: a position closer to the center by L / 10 from the end portion), respectively.
The taper angle θ is determined by simulation. If there is a difference between the measured value of the particle concentration and the simulation value, the luminance distribution is grasped in consideration of the difference, and the intermediate altitude D It is necessary to determine the taper angle θ. When there is this difference, it is preferable to obtain the difference between the actually measured value of the particle concentration and the simulation value in advance.

Example 1
The conditions and results of Example 1 are shown in FIG. 17 and FIG. 16 in the third stage of the four upper and lower stages. In the first embodiment, the light guide length L [mm] of the light guide plate 30 corresponding to a screen size of 42 inches is L = 560 mm, the maximum thickness tmax = 4.02 [mm], and the minimum thickness tmin = a = 2 [ mm], half of the major axis of the ellipse b = 1.6 [mm], circle radius R = 20000 [mm], and particle concentration [wt%] were variously changed as shown. Then, overall efficiency, overall efficiency comparison (1), overall efficiency comparison (2), and medium-to-high rate numerical calculation were obtained. In addition, the judgment was made based on the medium-high rate graph, and the quality was indicated by good “◯” and no “x”. Moreover, center part illumination intensity, center part illumination intensity comparison (1), and center part illumination intensity comparison (2) were calculated | required. The comparison (1) is a percentage when the reference (comparison standard (1)) is 100%, and the comparison (2) is the percentage when the ellipse comparison standard (2) is 100%. . Hereinafter, the comparison reference (1) is appropriately referred to as “an inclined surface” or “an inclined surface light guide plate”. Further, the comparison standard (2) is appropriately referred to as “ellipse” or “elliptical light guide plate”. Further, the present invention is appropriately referred to as “ellipse + taper + circle” or “ellipse + taper + circle light guide plate”.

FIG. 18 shows the result of the same example as FIG. These differences are that, in FIG. 17, an “inclined surface” is shown as a comparison, whereas in FIG. 18, an “ellipse” is shown. That is, FIG. 17 illustrates the second stage and the third stage in FIG. 16, and FIG. 18 illustrates a part of the first stage and the third stage in FIG. .
As is apparent from the second and third stages of FIG. 17 and FIG. 16, the “ellipse + taper + circle” has an overall efficiency and a central portion at any particle concentration compared to the “inclined surface”. The illuminance is more than “inclined surface”. That is, the overall efficiency comparison (1) and the central illumination comparison (1) were 100% or more. The medium / high rate exceeded the “inclined surface” at 0.15 [wt%], but this is “x” in the medium / high rate graph judgment.
From the above results, it can be said that “ellipse + taper + circle” is superior to the “inclined surface” mainly in overall efficiency and central portion illumination.
Further, as is clear from a part of the first stage and the third stage of FIG. 18 and FIG. 16, the “ellipse + taper + circle” has a particle concentration of 0.1375 [wt%] compared to “ellipse”. ] In all items exceeded "Ellipse".
(Example 2)
The second embodiment will be described with reference to part of the first stage and the fourth stage in FIGS. 19 and 16. From these results, even when b is changed from 1.6 [mm] to 1.2 [mm] and R is changed from 20000 [mm] to 27500 [mm], the overall tendency is as in Example 1. In the case of “ellipse + taper + circle” except for the overall efficiency of the particle concentration of 0.1 [wt%], the overall efficiency and the central portion illuminance exceed the “ellipse” at any particle concentration. ing. In addition, the medium / high ratio is higher than “ellipse” in 0.125 and 0.15, but the medium / high ratio graph judgment is “x” in 0.15.
From FIG. 16 to FIG. 19, “ellipse + taper + circle” indicates “inclined surface” and “ellipse” in any of the overall efficiency, medium / high rate, and central illumination when the particle concentration is appropriately set. Can be exceeded.
From the above, the effect of the present invention is clear.
In the above description, the case where the ellipse parts A1 and A2 are used as the quadratic curve connected to the first light incident surface 30d and the second light incident surface 30e has been described as an example. However, it is possible to use a part of a parabola or a hyperbola having a differential coefficient (taper angle θ) similar to the parts A1 and A2 of these ellipses.

It is a schematic perspective view which shows one Embodiment of the liquid crystal display device using the planar illuminating device which concerns on this invention. It is the II-II sectional view taken on the line of the liquid crystal display device shown in FIG. (A) is a partially omitted plan view showing a light source and a light guide plate of the planar illumination device shown in FIG. 2, and (B) is a cross-sectional view taken along line BB of (A). (A) is a perspective view which shows schematic structure of the light source of the planar illuminating device shown in FIG. 2, (B) is sectional drawing of the light source shown to (A), (C) is (A). It is a schematic perspective view which expands and shows one LED which comprises the light source shown in FIG. It is a schematic perspective view which shows the shape of the light-guide plate shown in FIG. (A) is a cross-sectional schematic diagram of the light guide plate shown in FIG. 2, and (B), (C), and (D) are partial enlarged cross-sectional views of the light guide plate shown in (A). It is a graph which shows the relationship between the particle diameter and particle concentration [wt%] of the scattering fine particles disperse | distributed to the light-guide plate used for the planar illuminating device of this invention. (A) And (B) is a graph which shows the relationship between the particle diameter and particle concentration [wt%] of the scattering fine particle disperse | distributed to the light-guide plate used for the planar illuminating device of this invention, respectively. (A) And (B) is a graph which shows the relationship between the particle diameter and particle concentration [wt%] of the scattering fine particle disperse | distributed to the light-guide plate used for the planar illuminating device of this invention, respectively. (A) is a front view which shows schematic structure of the peripheral part of the space | interval maintenance member of the planar illuminating device shown in FIG. 2, (B) is BB sectional drawing of (A). It is a figure which shows typically the cross section of the direction orthogonal to a longitudinal direction of the light-guide plate whose light reflection surface is an inclined surface. It is a figure which shows typically the cross section of the direction orthogonal to a longitudinal direction of the light-guide plate whose light reflection surface is an elliptical cross section. It is a figure which shows the change of the taper angle (inclination angle) of the elliptical cross section in a 37-inch light-guide plate. It is a figure which shows the change of the taper angle (inclination angle) of the elliptical cross section in a 42-inch light-guide plate. It is a figure which shows the change of the taper angle (inclination angle) of the elliptical cross section in a 46-inch light-guide plate. It is a figure explaining the effect of the whole efficiency in this invention, a medium-high rate, and center part illumination intensity. The luminance distribution of “ellipse + taper + circle” and “inclined surface” when the particle concentration is changed at b = 1.6 [mm] and R = 20000 [mm] in Example 1 will be described. FIG. The figure explaining the luminance distribution of "ellipse + taper + circle" and "ellipse" when the particle concentration is changed with b = 1.6 [mm] and R = 20000 [mm] in Example 1. It is. FIG. 6 is a diagram for explaining the luminance distribution of “ellipse + taper + circle” and “ellipse” when the particle concentration is changed with b = 1.2 [mm] and R = 27500 [mm] in Example 2. It is. It is a figure explaining the luminance distribution of an "ellipse" and an inclined surface when the particle concentration is changed when the minimum thickness is 2 [mm]. It is a figure explaining the luminance distribution of an "ellipse" and an inclined surface when the particle concentration is changed when the minimum thickness is 5 [mm].

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Liquid crystal display panel 14 Drive unit 20 Backlight unit (planar illumination device)
24 Illuminating device body 24a Light exit surface 26 Housing 28 Light source (first light source, second light source)
30 light guide plate 30A light guide plate 30B light guide plate 30a light emitting surface 30b first light reflecting surface 30c second light reflecting surface 30d first light incident surface 30e second light incident surface 30f short side surface 30g short side surface 30h Light reflecting surface 30i edge (back side edge)
30j edge (back side edge)
30k point 31 interval maintaining member 32 optical member unit 32a diffusion sheet 32b prism sheet 32c diffusion sheet 33b first light reflecting surface 33c second light reflecting surface 33h light reflecting surface 34 reflecting plate 35b first light reflecting surface 35c second light reflecting surface 35h Light reflecting surface 36 Upper guide reflecting plate 38 Lower guide reflecting plate 42 Lower housing 42a Side surface 44 Upper housing 44a Side surface 46 Reinforcing member (folding member)
48 Support member (sliding mechanism)
49 Power storage 50 LED chip (light emitting diode)
51 Light emitting part 52 Light source support part 54 Array substrate 56 Fin 58 Light emitting surface A1, A2 Ellipse part A3, A4 Straight line A5 Circle part a Light incident surface width b Half length of ellipse major axis k1 Major axis k2 short axis m long side n short side L light guide length S cross section T1, T2 connection point α 2 bisector β center line (vertical bisector)
θ Taper angle (tilt angle)

Claims (6)

The front surface, the back surface, and the four side surfaces are formed in a substantially plate shape, the surface has a rectangular light emission surface, the back surface has a light reflection surface, and the four side surfaces face each other. A light guide plate having a light incident surface on each of two side surfaces,
Contains scattering particles that scatter light propagating inside it,
In the light reflecting surface, a cross section perpendicular to the longitudinal direction of the two light incident surfaces is formed symmetrically with respect to a perpendicular bisector of the light emitting surface, and in a direction away from the light emitting surface. And is formed with a line that increases in distance from the light exit surface as it approaches the vertical bisector from the two light incident surfaces,
Furthermore, the line is
A portion of two quadratic curves that are smoothly connected to the back side end portions of the two light incident surfaces and that have a smaller inclination angle with respect to the light exit surface toward the vertical bisector, and Represented by two straight lines that are each smoothly connected to a part of a quadratic curve, and a part of a circle that has a center on the perpendicular bisector and is smoothly connected to the two straight lines,
A light guide plate characterized by that. The two light incident surfaces are orthogonal to the light exit surface;
The light guide plate according to claim 1. The quadratic curve is an ellipse;
The light guide plate according to claim 1 or 2. The ellipse is an ellipse whose major axis coincides with a line segment connecting the back side end of one light incident surface and the back side end of the other light incident surface.
The light guide plate according to claim 3. The scattering particles have a scattering cross section of the scattering particles of Φ, a density of the scattering particles of N _p , a correction coefficient of K _C , and a length from the two light incident surfaces to the perpendicular bisector of L _G , The following inequality 1.1 ≦ Φ · N _p · L _G · K _C ≦ 8.2
0.005 ≦ K _C ≦ 0.1
Satisfy,
The light-guide plate of any one of Claims 1-4 characterized by the above-mentioned. The light guide plate according to any one of claims 1 to 5,
A first light source disposed opposite to the one light incident surface of the light guide plate, and a second light source disposed opposite to the other light incident surface of the light guide plate,
The first light source and the second light source are:
At least one LED chip emitting blue light from the light emitting surface;
A phosphor coating unit that is disposed between the light emitting surface of the LED chip and the light guide plate, converts blue light emitted from the light emitting surface into white light, and emits blue light emitted from the light emitting surface. A fluorescent member having a blue light transmitting portion that emits blue light as a blue light,
A planar illumination device characterized by that.

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