JP2009093863A - Planar lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar lighting system capable of emitting light having little nonuniformity of luminance, and obtaining a convex or bell-shaped brightness distribution while having a thin shape and high light utilization efficiency. <P>SOLUTION: This planar lighting system has a light guide plate which has symmetrical two inclined backs formed so that their distances from a light emitting surface becomes more distant respectively as they go toward the center of the light emitting surface from two light entering surfaces, and a curved portion to join the two inclined backs, and includes scattered particles to scatter light spreading in its inside, and in which the length between the two light entering surfaces, the thickness of the light entering surfaces, the thickness of the center of the curved portion, and the radius of the curvature of the curved portion and the taper of the inclined backs are in prescribed ranges, the particle diameters and concentration of the scattered particles are in prescribed ranges, utilization efficiency of light is not less than 55%, and the convex degree of the luminance distribution of the light emitting surface is not less than 0 and not more than 25, and reflective sheets which are disposed on the inclined surfaces of the light guide plate, and in which mat processing is applied to the surfaces on the light guide plate side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a planar illumination device used for a liquid crystal display device or the like.

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

At present, a backlight unit of a large-sized liquid crystal television is mainly used in a so-called direct type in which a light guide plate is disposed immediately above a light source for illumination (see, for example, Patent Document 1). In this system, a plurality of cold-cathode tubes, which are light sources, are arranged on the back surface of the liquid crystal display panel, and a uniform light quantity distribution and necessary luminance are ensured with the inside as a white reflecting surface.
However, in order to make the light amount distribution uniform, the direct type backlight unit needs a thickness of about 30 mm in the vertical direction with respect to the liquid crystal display panel, and it is difficult to make it thinner.

  On the other hand, in a small liquid crystal monitor used in a computer or the like, a sidelight system using a flat light guide plate is used for miniaturization and thinning. In addition, a method using a light guide plate whose thickness decreases as the distance from the light source is reduced as a thin backlight unit, for example, a tandem method has been proposed (for example, refer to citations 2 to 4).

  Further, the light guide plate having a thickness of the intermediate portion larger than the thickness of the end portion on the incident side and the end portion on the opposite side, and a light guide plate having a reflective surface inclined in a direction in which the thickness increases as the distance from the light incident portion increases. In addition, a light guide plate having 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 (for example, cited) See references 5 to 8.)

Japanese Utility Model Publication No. 5-4133 JP-A-2-208631 JP-A-11-288611 JP 2001-312916 A JP 2003-90919 A JP 2004-171948 A JP 2005-108676 A JP 2005-302322 A

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

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

On the other hand, in the sidelight system using a flat light guide plate, minute scattering particles are dispersed inside in order to efficiently emit incident light from the light exit surface. In such a flat light guide plate, if the scattering fine particles are uniformly dispersed and the screen is enlarged, if the scattering fine particle concentration is 0.30 wt%, the light use efficiency of 83% can be ensured, but the solid line in FIG. As in the illuminance distribution indicated by, there is a problem that the central portion becomes dark and unevenness in brightness, that is, unevenness in brightness occurs and is visually recognized.
In order to flatten the luminance unevenness, it is necessary to decrease the concentration of the scattering fine particles and increase the light leaked from the tip, resulting in a problem that the utilization efficiency is lowered and the luminance is also lowered. For example, if the scattering particle concentration is 0.10 wt% under the same conditions, the luminance unevenness can be greatly reduced as shown by the dotted line in FIG. 12, but the luminance is reduced and the light utilization efficiency is also reduced to 43%. There was a problem.
Furthermore, the brightness distribution on the light exit surface required for large displays such as large liquid crystal televisions is a so-called medium-high distribution, for example, a bell-shaped distribution near the center of the screen compared to the periphery. . However, a flat-shaped light guide plate in which scattered fine particles are dispersed can obtain a flat brightness distribution by reducing the concentration of the scattered fine particles, but there is a problem that a medium-high brightness distribution cannot be realized. It was.

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

  The object of the present invention is to solve the above-mentioned problems of the prior art, have a thin shape, have high light utilization efficiency, and can emit light with little unevenness in luminance, and is required for a large-screen thin liquid crystal television. It is an object of the present invention to provide a planar illumination device that can obtain a distribution that is brighter in the vicinity of the center portion of the screen than the peripheral portion, that is, a so-called medium-high or bell-shaped brightness distribution.

  In order to solve the above-described problems, a first embodiment of the present invention includes a rectangular flat light emission surface and two long sides facing each other, and is disposed at positions facing each other. Two light incident surfaces, two symmetrical inclined back surfaces, each of which has a distance away from the light emitting surface as it goes from the two light incident surfaces toward the center of the light emitting surface, and these two inclined back surfaces And a scattering particle that scatters the light propagating inside thereof, the length between the two light incident surfaces is 480 mm or more and 830 mm or less, and the particle size of the scattering particle is 4.0 μm or more and 12.0 μm or less, the concentration of the scattering particles is 0.008 wt% or more and 0.25 wt% or less, and light incident from the two light incident surfaces is emitted from the light emitting surface. The efficiency of light usage A medium height of the luminance distribution of the light emitting surface, which is a ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface is 55% or more A light guide plate that is greater than 0% and less than or equal to 25%, two light sources respectively disposed facing the two light incident surfaces of the light guide plate, and an inclined back surface of the light guide plate. The present invention provides a planar illuminating device comprising a reflection sheet having a matte-treated surface on the light guide plate side.

  In order to solve the above problem, the second embodiment of the present invention includes a rectangular flat light emission surface and two long sides facing each other, and is disposed at positions facing each other. Two light incident surfaces that are formed, two symmetrical inclined back surfaces that are distanced from the light emission surface toward the center of the light emission surface from these two light incident surfaces, and these two inclinations, respectively. A scattering portion that scatters light propagating in the inside, and a length between the two light incident surfaces is not less than 480 mm and not more than 830 mm. The diameter is 4.0 μm or more and 12.0 μm or less, the concentration of the scattering particles is 0.008 wt% or more and 0.25 wt% or less, and light incident from the two light incident surfaces is the light emission Of light emitted from the surface Luminance distribution of the light emitting surface, the utilization efficiency is 55% or more, and indicates a ratio of the luminance of light emitted from the central portion of the light emitting surface to the luminance of light emitted from the vicinity of the light incident surface of the light emitting surface. A light guide plate with a medium altitude of over 0% and 25% or less, two light sources respectively disposed facing the two light incident surfaces of the light guide plate, and the inclined back side of the light guide plate A planar lighting device comprising: a reflective sheet disposed on the light guide plate; and a mat film having a matte surface disposed between the inclined back surface of the light guide plate and the reflective sheet. It is.

Here, the mat film preferably has a thickness Tf of 100 μm <Tf <250 μm.
Further, the mat film is a diffusion film, and preferably 40% <Hf <90% when Haze is Hf.
More preferably, 70% <Hf <90%.
Alternatively, the mat film is a transparent film whose surface is matted, and when haze is Hb, it is also preferably 10% <Hb <40%, and more preferably 10% <Hb <20%. .
The transparent film is preferably formed using at least one of polyethylene terephthalate, polycarbonate, acrylic, and cycloolefin polymer as a material.
Furthermore, the light guide plate has a thickness of the light incident surface that is the thinnest that is 0.5 mm or more and 3.0 mm or less, and a thickness of the center of the bent portion that is the thickest is 1.0 mm or more. 6.0 mm or less, the radius of curvature of the curved portion is 6,000 mm or more and 45,000 mm or less, and the taper of the inclined back surface is 0.1 ° or more and 0.8 ° or less. preferable.

The light guide plate has a light guide length between the two light incident surfaces of 480 mm to 500 mm, a particle size of the scattering particles of 4.0 μm to 12.0 μm, and a concentration of the scattering particles of 0.02 wt% or more and 0.22 wt% or less, and the particle size and concentration of the scattering particles are such that the particle size (μm) of the scattering particles is the horizontal axis, and the particle concentration (wt%) of the scattering particles. In the graph with the vertical axis, 6 points (4.0, 0.02), (4.0, 0.085), (7.0, 0.03), (7.0, 0.12), It is preferable to be in a region surrounded by (12.0, 0.06) and (12.0, 0.22).
The light guide plate has a light guide length between the two light incident surfaces of 515 mm to 620 mm, a particle size of the scattering particles of 4.0 μm to 12.0 μm, and a concentration of the scattering particles. Is not less than 0.015 wt% and not more than 0.16 wt%, and the particle diameter and concentration of the scattering particles are such that the particle diameter (μm) of the scattering particles is the horizontal axis, and the particle concentration (wt %) On the vertical axis, 6 points (4.0, 0.015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09) ), (12.0, 0.035) and (12.0, 0.16).
In the light guide plate, a light guide length between the two light incident surfaces is 625 mm or more and 770 mm or less, a particle diameter of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is Is 0.01 wt% or more and 0.12 wt% or less, and the particle diameter and concentration of the scattering particles are set such that the particle diameter (μm) of the scattering particles is a horizontal axis, and the particle concentration (wt%) of the scattering particles is ) On the vertical axis, 6 points (4.0, 0.01), (4.0, 0.05), (7.0, 0.01), (7.0, 0.06) , (12.0, 0.02) and (12.0, 0.12) are also preferable.
The light guide plate has a light guide length between the two light incident surfaces of 785 mm or more and 830 mm or less, a particle size of the scattering particles of 4.0 μm or more and 12.0 μm or less, and a concentration of the scattering particles. Is not less than 0.008 wt% and not more than 0.08 wt%, and the particle diameter and concentration of the scattering particles are set such that the particle diameter (μm) of the scattering particles is a horizontal axis, and the particle concentration (wt%) of the scattering particles is ) On the vertical axis, 6 points (4.0, 0.008), (4.0, 0.03), (7.0, 0.009), (7.0, 0.04) , (12.0, 0.02) and (12.0, 0.08).

  According to the present invention, it is a thin shape, has high light utilization efficiency, can emit light with little unevenness in brightness, and a central portion of the screen required for a large-screen thin liquid crystal television is a peripheral portion. Compared to the above, a bright distribution, that is, a so-called medium-high or bell-shaped brightness distribution can be obtained.

A light guide plate according to the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings.
FIG. 1A is a perspective view illustrating an outline of a liquid crystal display device using a backlight unit including a light guide plate according to the present invention, and FIG. 1B is a schematic cross-sectional view of the liquid crystal display device. 2A is a schematic plan view of the light guide plate and the light source according to the present invention, and FIG. 2B is a schematic cross-sectional view of the light guide plate of the present invention.
The liquid crystal display device 10 drives the backlight unit (also referred to as “planar illumination device”) 2, the liquid crystal display panel 4 disposed on the light emission surface side of the backlight unit 2, and the liquid crystal display panel 4. And a drive unit 6.

The liquid crystal display panel 4 applies a partial electric field to liquid crystal molecules arranged in a specific direction in advance to change the arrangement of the molecules, and uses the change in the refractive index generated in the liquid crystal cell to make a liquid crystal display. Characters, figures, images, etc. are displayed on the surface of the display panel 4.
The liquid crystal display panel 4 targeted by the light guide plate has a large screen size of 37 inches (37 ") or more, and is used for a large and thin liquid crystal television having such a large screen. Examples of the screen size of the liquid crystal display panel 4 include 37 inches (37 "), 42 inches (42"), 46 inches (46 "), 52 inches (52"), and 57 inches (57 "). Large screens such as 65 inches (65 ").
The drive unit 6 applies a voltage to the transparent electrode in the liquid crystal display panel 4 to change the direction of the liquid crystal molecules to control the transmittance of light transmitted through the liquid crystal display panel 4.

The backlight unit 2 is an illumination device that irradiates light from the back surface of the liquid crystal display panel 4 to the entire surface of the liquid crystal display panel 4, and has a light emission surface that has substantially the same shape as the image display surface of the liquid crystal display panel 4.
As shown in FIGS. 1A and 1B and FIGS. 2A and 2B, the backlight unit 2 includes two light sources 12, an optical member unit 14, a light guide plate 18 of the present invention, And a reflection sheet 22. Hereinafter, each component constituting the backlight unit 2 will be described.

First, the light source 12 will be described.
3A is a schematic perspective view showing a schematic configuration of the light source 12 of the backlight unit 2 shown in FIGS. 1 and 2, and FIG. 3B is a cross-sectional view of the light source 12 shown in FIG. FIG. 3C is a schematic perspective view showing only one LED (light emitting diode) chip 50 constituting the light source 12 shown in FIG.

As shown in FIG. 3A, the light source 12 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 surface 58 having a predetermined area, and emits white light from the light emitting surface 58.
That is, when the blue light emitted from the surface of the light emitting diode of the LED chip 50 passes through the fluorescent material, the fluorescent material fluoresces. Accordingly, when the blue light emitted from the LED chip 50 is transmitted, white light is generated and emitted by the blue light emitted from the light emitting diode and the light emitted by the fluorescent substance 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. 3B, 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 12 are arranged along the longitudinal direction of the first light incident surface 30d or the second light incident surface 30e of the light guide plate 18 to be described later, in other words, the light emitting surface 30a. Are arranged in an array parallel to the line where the first light incident surface 30d intersects or parallel to the line where the light emitting surface 30a and the second light incident surface 30e intersect, and are fixed on the array substrate 54. .

The array substrate 54 is a plate-like member that is disposed so as to face the light incident surface (30 d, 30 e) whose one surface is the thinnest side end surface of the light guide plate 18. The LED chip 50 is supported on the side surface of the array substrate 54 that is the surface facing the light incident surface (30d, 30e) of the light guide plate 18.
Here, the array substrate 54 of the present embodiment is formed of a metal having good thermal conductivity such as copper or aluminum, and also has a function as a heat sink that absorbs heat generated from the LED chip 50 and dissipates it to the outside. .

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

Here, as shown in FIG. 3C, the LED chip 50 of this embodiment has a rectangular shape in which the length in the direction orthogonal to the arrangement direction is shorter than the length in the arrangement direction of the LED chip 50, that is, described later. The light guide plate 18 has a rectangular shape with a short side in the thickness direction (direction perpendicular to the light exit surface 30a). In other words, the LED chip 50 has a shape in which b> a, where a is a length in the direction perpendicular to the light exit surface 30a of the light guide plate 18 and b is a length in the arrangement direction. Further, q> b, where q is the arrangement interval of the LED chips 50. Thus, the relationship between the length a in the direction perpendicular to the light exit surface 30a of the light guide plate 18 of the LED chip 50, the length b in the arrangement direction, and the arrangement interval q of the LED chips 50 satisfies q>b> a. It is preferable.
By making the LED chip 50 into a rectangular shape, a thin light source can be obtained while maintaining a large light output. By reducing the thickness of the light source, the planar illumination device can be reduced in thickness. In addition, the number of LED chips can be reduced.

  In addition, since the LED chip 50 can make a light source thinner, it is preferable that the light guide plate 18 has a rectangular shape having a short side in the thickness direction. However, the present invention is not limited to this, and a square shape, a circular shape, LED chips having various shapes such as a polygonal shape and an elliptical shape can be used.

  In this embodiment, the LED chips are arranged in a single row to form a single layer structure. However, the present invention is not limited to this, and a plurality of LED arrays having a plurality of LED chips 50 arranged on an array support are provided. A multilayer LED array having a laminated structure can also be used as a light source. Even when LED arrays are stacked in this manner, more LED arrays can be stacked by making the LED chip 50 rectangular and thinning the LED array. In this way, a larger amount of light can be output by stacking multilayer LED arrays and increasing the filling rate of the LED arrays (LED chips). In addition, the LED chip of the LED array in the layer adjacent to the LED chip of the LED array preferably has the arrangement interval satisfying the above formula as described above. In other words, the LED array is preferably laminated with the LED chip and the LED chip of the LED array in the adjacent layer separated by a predetermined distance.

Next, the light guide plate 18 will be described with reference to FIGS. 2 (A), 2 (B), 4 (A) and 4 (B).
As shown in FIGS. 2A, 2B, 4A, and 4B, the light guide plate 18 of the present invention has a substantially rectangular flat light emission surface 18a and the opposite of the light emission surface 18a. Located on the side, parallel to one side of the light exit surface 18a, symmetrical with respect to the bisector X that bisects the light exit surface 18a, and inclined at a predetermined angle with respect to the light exit surface 18a. Two inclined surfaces (a first inclined surface 18b and a second inclined surface 18c) having a predetermined taper, and two light incident surfaces that face the two LED arrays 24 and receive light from the LED arrays 24 ( A first light incident surface 18d and a second light incident surface 18e), and a curved portion 18f having a radius of curvature R formed at a joint portion between the first inclined surface 18b and the second inclined surface 18c of the two inclined surfaces. is doing.

Note that the two light incident surfaces 18d and 18e are located opposite to the opposing long sides of the substantially rectangular light exit surface 18a, and the two light incident surfaces 18d and 18d are arranged from the opposed LEDs 24. The light incident on 18e propagates in the light guide plate 18 parallel to the opposing short sides of the substantially rectangular light exit surface 18a.
The first inclined surface 18b and the second inclined surface 18c are axisymmetric with respect to the bisector X, and are inclined symmetrically with respect to the light exit surface 18a. The bending portion 18f is also curved symmetrically with respect to the bisector X. The light guide plate 18 is thicker from the first light incident surface 18d and the second light incident surface 18e toward the center, and the portion corresponding to the bisector X in the center, that is, the center of the curved portion 18f. The portion is thickest (tmax), and the two light incident surfaces (first light incident surface 18d and second light incident surface 18e) at both ends are thinnest (tmin).
That is, the cross-sectional shape of the light guide plate 18 is line symmetric with respect to the central axis passing through the bisector X.

  Here, in the present invention, the light guide length L through which the light propagates between the first light incident surface 18d and the second light incident surface 18e has a liquid crystal panel 4 having a screen size of 37 inches (37 ″) or more. Since the target is the liquid crystal panel 4 having a screen size of 480 mm or more and a maximum screen size of 65 inches (65 ″) or more, it needs to be 830 mm or less. More specifically, for a screen size of 37 inches (37 ″), the light guide length L is not less than 480 mm and not more than 500 mm, resulting in screen sizes of 42 inches (42 ″) and 46 inches (46 ″). On the other hand, the light guide length L is not less than 515 mm and not more than 620 mm, and for screen sizes of 52 inches (52 ") and 57 inches (57"), the light guide length L is not less than 625 mm and not more than 770 mm. For a screen size of 65 inches (65 ″), the light guide length L is preferably 785 mm or more and 830 mm or less.

Further, the minimum thickness tmin of the light incident surfaces 18d and 18e where the light guide plate 18 has the smallest thickness is preferably 0.5 mm or more and 3.0 mm or less.
The reason is that if the minimum thickness is too small, the light incident surfaces 18d and 18e become too small, light incidence from the light source 12 decreases, and light with sufficient luminance cannot be emitted from the light emitting surface 18a. However, if the minimum thickness is too large, the maximum thickness becomes too thick, and the weight is too heavy to be suitable as an optical member such as a liquid crystal display device. It is because it does not satisfy more than%.
Further, the maximum thickness tmax at the center of the curved portion 18f where the light guide plate 18 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 R of the central curved portion 18f is too large to be suitable for molding, and as in the case of a flat plate, the particle concentration that achieves a medium and high luminance distribution This is because the utilization efficiency does not satisfy 55% or more, and conversely, the medium-high distribution cannot be realized at a particle concentration at which the light utilization efficiency is 55% or more.

Therefore, the taper of the inclined back surfaces 18b and 18c, that is, the taper angle (inclination angle) is preferably 0.1 ° or more and 0.8 ° or less.
The reason is that if the taper is too large, the maximum thickness will be larger than necessary, and the distribution will be excessively high, and if the taper is too small, the minimum thickness will be small. As in the case of too much, the center radius R is too large to be suitable for molding, and the medium / high distribution cannot be realized at a particle concentration where the light utilization efficiency is 55% or more. This is because the light utilization efficiency does not satisfy 55% or more at the particle concentration that achieves the distribution.
As a result, the curvature radius R of the curved portion 18f is preferably 6,000 mm or more and 45,000 mm or less.
4A and 4B, when the taper angle of the inclined back surfaces 18b and 18c is θ, L _R = 2R sin θ, and the maximum thickness tmax = tmin − [(L _R / 2 ) Tan θ + R cos θ−R], and taper angle θ = tan ⁻¹ [(tmax−tmin) / (L / 2)].

In the present invention, the shape of the light guide plate 18 is made such that the thickness increases from the first light incident surface 18d and the second light incident surface 18e toward the center (hereinafter referred to as an inverted wedge shape). This makes it easier to propagate the incident light deeper, improves the in-plane uniformity while maintaining the light utilization efficiency, and obtains a so-called bell-shaped luminance distribution that is medium to high. That is, by adopting such a shape, the distribution in which the center becomes dark in the above-described conventional flat light guide plate can be made uniform or medium-high, so-called bell-shaped distribution.
Further, by smoothly joining the joint portions at the center of the inclined back surfaces 18b and 18c as the curved portion 18f, the band unevenness that can be formed at the center joint portion can be made uniform or medium-high so-called bell-shaped distribution.

  In the light guide plate 18 shown in FIGS. 2A and 2B, the light incident from the first light incident surface 18d and the second light incident surface 18e is scattered fine particles contained in the light guide plate 18 (details will be described later). The light passes through the inside of the light guide plate 18 and is reflected directly or after being reflected by the first inclined surface 18b and the second inclined surface 18c, and then is emitted from the light exit surface 18a. At this time, a part of light may leak from the first inclined surface 18b and the second inclined surface 18c, but the leaked light covers the first inclined surface 18b and the second inclined surface 18c of the light guide plate 18. Then, the light is reflected by a reflection sheet (not shown) arranged in this manner and again enters the light guide plate 18.

  The light guide plate 18 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 18 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 18, Tospearl, silicone, silica, zirconia, dielectric polymer, or the like can be used. By including such scattering particles in the light guide plate 18, 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 18 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, regarding the selection of the optimum particle size of the scattering fine particles to be dispersed in the light guide plate 18 of the present invention, it is preferable to consider the following points in addition to the viewpoint of wavelength dependency.
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 inverted wedge-shaped light guide plate 18 is at least a distance of 240 mm or more from the first light incident surface 18d and the second light incident surface 18e on the side surface of the light guide plate 18, and in the case of single-sided incidence, it is the lowest from the light incident surface. This is because it is necessary to guide a distance of 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 18.

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

As described above, 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, it is possible to obtain outgoing light without wavelength unevenness.
In the above-described example, scattering particles having a single particle diameter are used. However, the present invention is not limited to this, and scattering particles having a plurality of particle diameters may be mixed and used.

Moreover, since the light guide length of the light guide plate 18 of the present invention is 480 mm to 830 mm, the concentration of the scattering particles needs to be 0.008 wt% or more and 0.22 wt% or less.
Specifically, when the light guide length L is 480 mm ≦ L ≦ 500 mm, the concentration of the scattering particles needs to be 0.02 wt% or more and 0.22 wt% or less.
In addition, when the light guide length of the light guide plate is L = 480 mm corresponding to a screen size of 37 inches and the particle diameter of the scattering particles is 4.5 μm, the concentration of the scattering particles is 0.02 wt% or more and 0.085 wt%. The content is more preferably as follows, and most preferably 0.047 wt%. When the particle diameter of the scattering particles is 7.0 μm, the concentration of the scattering particles is more preferably 0.03 wt% or more and 0.12 wt% or less, and most preferably 0.065 wt%. . Furthermore, when the particle diameter of the scattering particles is 12.0 μm, the concentration of the scattering particles is more preferably 0.06 wt% or more and 0.22 wt% or less, and most preferably 0.122 wt%. .

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

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

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

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

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

From the above, in the present invention, the relationship between the particle size and concentration of the scattering particles dispersed in the light guide plate 18 satisfies a predetermined relationship according to the light guide length between the two light incident surfaces 18d and 18e of the light guide plate 18. It turns out that it is necessary to satisfy.
Therefore, in the present invention, when the light guide length of the light guide plate 18 is 480 mm or more and 500 mm or less, as described above, the particle diameter of the scattering particles is 4.0 μm or more and 12.0 μm or less. The concentration needs to be 0.02 wt% or more and 0.22 wt% or less, and as shown in the graph of FIG. 5A, the particle size (μm) of the scattering particles is taken as the horizontal axis, When the particle concentration (wt%) is the vertical axis, the particle size and concentration of the scattering particles are 6 points (4.0, 0.02), (4.0, 0.085), (7.0, 0). .03), (7.0, 0.12), (12.0, 0.06) and (12.0, 0.22).
Further, when the light guide length of the light guide plate 18 is 515 mm or more and 620 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0.00. Scattering is 015 wt% or more and 0.16 wt% or less, and 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, 0.015), (4.0, 0.065), (7.0, 0.02), (7.0, 0.09), It must be within the region enclosed by (12.0, 0.035) and (12.0, 0.16).

Further, when the light guide length of the light guide plate 18 is 625 mm or more and 770 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0.00. When the particle size (μm) is on the horizontal axis and the particle concentration (wt%) is on the vertical axis as shown in the graph of FIG. 6A, the scattering particles are 01 wt% or more and 0.12 wt% or less. Particle size and concentration of 6 points (4.0, 0.01), (4.0, 0.05), (7.0, 0.01), (7.0, 0.06), ( 12.0, 0.02) and (12.0, 0.12).
When the light guide length of the light guide plate 18 is 785 mm or more and 830 mm or less, as described above, the particle size of the scattering particles is 4.0 μm or more and 12.0 μm or less, and the concentration of the scattering particles is 0.00. Scattering is 008 wt% or more and 0.08 wt% or less, and the particle size (μm) is on the horizontal axis and the particle concentration (wt%) is on the vertical axis as shown in the graph of FIG. The particle size and concentration of the particles are 6 points (4.0, 0.008), (4.0, 0.03), (7.0, 0.009), (7.0, 0.04), It must be within the region enclosed by (12.0, 0.02) and (12.0, 0.08).

  The reason why the particle size and concentration of the scattering particles need to be within the region surrounded by the six points in the graphs shown in FIGS. 5 (A), (B), FIG. 6 (A) and (B) If the particle concentration is too high, it becomes the same as a flat plate when the particle concentration is too high, and a medium-high luminance distribution cannot be realized. If the particle concentration is too low, light penetrates and passes through, so that the light utilization efficiency 55 If the particle size is too small, the light utilization efficiency is improved, but a medium-high luminance distribution cannot be realized, and if the particle size is too large, a medium-high luminance distribution can be realized. However, the light utilization efficiency is low.

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

The light guide plate 18 of the present invention in which the scattering fine particles are dispersed in the inside needs to have a light utilization efficiency of 55% or more indicating the ratio of light incident from the two light incident surfaces to the light exit surface. There is. The reason for this is that if the light utilization efficiency is less than 55%, a light source with a higher output is required to obtain the required luminance. However, if a light source with a higher output is used, the light source becomes hot and power consumption is increased. This is because the warpage and elongation of the light guide plate 18 are increased, and a required brightness distribution, that is, a so-called medium-high or bell-shaped brightness distribution cannot be obtained.
Further, the medium to altitude degree of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, is greater than 0%. It must be 25% or less. The reason for this is that the vicinity of the center of the screen required for a large-screen thin LCD TV is brighter than the periphery, that is, a so-called medium-high or bell-shaped brightness distribution.
Such a light guide plate 18 can be manufactured using an extrusion molding method or an injection molding method.

Here, the light guide plate 18 includes a first light incident surface 18d, a second light incident surface 18e, a light exit surface 18a, which are light incident surfaces, a first inclined surface 18b, and a second inclined surface 18c, which are light reflecting surfaces. It is preferable that the surface roughness Ra of at least one of the surfaces is smaller than 380 nm, that is, Ra <380 nm.
By making the surface roughness Ra of the first light incident surface 18d and the second light incident surface 18e, which are the 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 18a smaller than 380 nm, the diffuse reflection transmission on the light guide plate surface can be ignored, that is, the diffuse reflection transmission on the light guide plate surface can be prevented, Light can be transmitted to the back by total reflection.
Furthermore, by making the surface roughness Ra of the first inclined surface 18b and the second inclined surface 18c to be light reflecting surfaces smaller than 380 nm, diffuse reflection can be ignored, that is, diffuse reflection on the light reflecting surface is reduced. It is possible to prevent the total reflection component from being transmitted further.

The light guide plate of the present invention is basically configured as described above, but can be designed as follows.
FIG. 7 is a flowchart showing an example of the light guide plate designing method of the present invention.
First, as shown in FIG. 7, in step S10, from the screen size of the liquid crystal display device to which the backlight unit using the light guide plate of the present invention is applied, the short side length of the screen size is about 10 mm as the mixing zone length. To determine the light guide length.
Next, in step S12, the maximum thickness tmax of the light guide plate is determined from the screen size.
In step S14, the base material resin used for the light guide plate and the particle conditions of the scattering fine particles to be added are determined.

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

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

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

When the screen sizes designed in this way are 37 inches, 42 inches, 46 inches, 52 inches, 57 inches, and 65 inches, the light guide plate has a light guide length [mm], a maximum thickness [mm], and a particle concentration [wt%]. ], Taper, central curved portion R [mm], light utilization efficiency [%] and intermediate altitude [%] are shown in Table 1.

Any of the light guide plates satisfies the limited range of the present invention, so that even a large screen has a thin shape, high light utilization efficiency, and emits light with little unevenness in luminance. Therefore, a light distribution near the center of the screen, which is required for a large-screen thin liquid crystal television, can be obtained, that is, a so-called medium-high or bell-shaped brightness distribution.
The light guide plate of the present invention is basically configured as described above.

  Here, the light source 12 and the light guide plate 18 have a distance of 0.2 mm or more between the light emitting surface of the light source 12, for example, the light emitting surface (front surface) of the LED and the light incident surfaces 18 d and 18 e of the light guide plate 18. It is preferable to dispose them. That is, it is preferable that the light emitting surface (LED surface) of the light source 12 and the light incident surface of the light guide plate 18 have a distance of 0.2 mm or more. The reason for this is that the distance between them is 0.2 mm or more, so that the light-emitting surface of the light source 12 (specifically, the surface of the LED) and the light-guide plate 18 even when the light-guide plate is stretched or warped due to temperature changes. Can be prevented from damaging the light source 12 (specifically, the phosphor on the surface of the LED). The upper limit of the distance between the two is not particularly limited, but if the distance is too wide, the amount of light from the light source 12 incident on the light incident surfaces 18d and 18e of the light guide plate 18 is reduced. Is preferably 0.5 mm or less.

The description of the backlight unit shown in FIGS. 1 and 2 will be continued.
Next, the optical member unit 14 will be described.
The optical member unit 14 is laminated in order of the diffusion film 15a, the first prism sheet 15b, the second prism sheet 15c, and the polarization separation film 15d in this order from the light exit surface 18a side of the light guide plate 18.

Next, the diffusion film 15a will be described.
As shown in FIG. 1, the diffusion film 15a is disposed between the light guide plate 18 and the first prism sheet 15b. The diffusion film 15a is formed by imparting light diffusibility to a film-like member. The film-like member is optically transparent such as PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, or COP (cycloolefin polymer). Can be formed into a material.
Although the manufacturing method of the diffusion film 15a is not particularly limited, for example, the surface of the film-like member is subjected to surface roughening by fine unevenness processing or polishing to impart diffusibility, or silica, titanium oxide that scatters light on the surface, It can be formed by coating a pigment such as zinc oxide or beads such as resin, glass or zirconia together with a binder, or kneading the pigment or beads in the transparent resin. In addition, it is possible to use a material having high reflectance and low light absorption, for example, using a metal such as Ag or Al.
In the present invention, as the diffusion film 15a, a mat type or coating type diffusion film can be used.

The diffusion film 15 a may be arranged at a predetermined distance from the light exit surface of the light guide plate 18, and the distance can be appropriately changed according to the light amount distribution from the light exit surface of the light guide plate 18.
Thus, by separating the diffusion film 15a from the light emission surface of the light guide plate 18 by a predetermined distance, the light emitted from the light emission surface of the light guide plate 18 is further mixed (mixed) between the light emission surface and the diffusion film 15a. ) Thereby, the brightness | luminance of the light which permeate | transmits the diffusion film 15a and illuminates the liquid crystal display panel 4 can be made further uniform.
As a method of separating the diffusion film 15a from the light exit surface of the light guide plate 18 by a predetermined distance, for example, a method of providing a spacer between the diffusion film 15a and the light guide plate 18 can be used.

  As shown in FIGS. 1A and 1B, the first prism sheet 15b is a transparent film-like sheet formed by arranging a plurality of prisms in parallel, and the light exit surface 18a of the light guide plate 18 is used. The brightness can be improved by increasing the condensing property of the light emitted from. In the present invention, as shown in the illustrated example, the first prism sheet 15b is arranged such that the prism row, that is, the apex of each prism 16a faces the light exit surface 18a of the light guide plate 18, that is, downward in the figure. Be placed. The prism has an apex angle of 90 °.

As shown in FIGS. 1A and 1B, the second prism sheet 15c is also a transparent film-like sheet formed by arranging a plurality of prisms in parallel, and the light exit surface 18a of the light guide plate 18 is used. The brightness can be improved by improving the condensing property of the light emitted from. In the present invention, as shown in the illustrated example, the second prism sheet 15c has a prism row, that is, the apex of each prism 16a is opposed to the light exit surface 18a of the light guide plate 18, that is, downward in the figure. Be placed. The prism has an apex angle of 60 °.
In the present invention, the first prism sheet 15b and the second prism sheet 15c are arranged such that the extending direction of the prism row is parallel to the light incident surfaces 18b and 18c of the light guide plate 18, as shown in the illustrated example. Is preferably arranged.

Next, the polarization separation film 15d will be described.
In the present embodiment, the polarization separation film 15d selectively transmits a predetermined polarization component, for example, a p-polarization component, out of the light emitted from the light exit surface of the light guide plate, and other polarization components, for example, Most of the s-polarized component can be reflected. The polarized light separating film 15d allows the reflected light to enter the light guide plate again and can be reused. Therefore, the light use efficiency can be improved and the luminance can be remarkably improved.
The polarized light separation film 15d is obtained, for example, by stretching a plate material obtained by kneading and dispersing needle-like particles in a transparent resin and orienting the needle-like particles in a predetermined direction.
Moreover, conventionally well-known various things can be used as the polarization separation film 15d.

Next, the reflection sheet 22 of the backlight unit will be described.
The reflection sheet 22 reflects the light leaking from the inclined surfaces 18c and 18d of the light guide plate 18 and makes it incident on the light guide plate 18 again, and can improve the light use efficiency. The reflection sheet 22 is formed by being bent at the center so as to cover the inclined surfaces 18c and 18d of the light guide plate 18, respectively.
The reflection sheet 22 may be formed of any material as long as it can reflect light leaking from the inclined surfaces 18c and 18d of the light guide plate 18, such as PET or PP (polypropylene). Resin sheet with increased reflectivity by forming voids by kneading and stretching the filler, sheet with mirror surface formed by aluminum vapor deposition on transparent or white resin sheet surface, metal foil such as aluminum or metal foil supported It can be formed of a resin sheet or a metal thin plate having sufficient reflectivity on the surface.

Further, the reflective sheet 22 is matted on the inclined surfaces 18c and 18d side of the light guide plate 18. Here, the matting treatment is a matting treatment on the sheet surface, and includes, for example, a method of applying resin beads to the sheet surface together with a binder, a method of forming a sanded surface by blasting, and the like.
By matting the surface of the reflection sheet 22 on the light guide plate 18 side, the contact state between the light guide plate 18 and the reflection sheet 22 can be made constant. As a result, the reflection sheet 22 partially adheres to the inclined surfaces 18c and 18d of the light guide plate 18, and the luminance unevenness caused by the contact state between the reflection sheet 22 and the inclined surfaces 18c and 18d of the light guide plate 18 becoming non-uniform. Can be prevented.
Thereby, uneven brightness can be further reduced, or light without uneven brightness can be emitted from the light exit surface of the planar illumination device.

  As mentioned above, although each component of the backlight unit 2 was demonstrated in detail, this invention is not limited to this.

For example, the surface of the reflective sheet of the backlight unit on the light guide plate side is matted, but the present invention is not limited to this. Instead of matting the surface of the reflective sheet on the light guide plate side, the light guide plate and the reflective surface are reflected. You may arrange | position the mat | matte film which carried out the mat | matte process of the surface at the side of a light-guide plate between sheets.
FIG. 9 shows a schematic cross-sectional view of the backlight unit 100 in which a mat film is disposed.

The backlight unit 100 includes a light source 12, an optical member unit 14, a light guide plate 18, a reflection sheet 102, and a mat film 104.
Here, the light source 12, the optical member unit 14, and the light guide plate 18 have the same functions as those of the light source, the optical member unit, and the light guide plate shown in FIG.

The reflection sheet 102 reflects light leaking from the inclined surfaces 18c and 18d of the light guide plate 18 and makes it incident on the light guide plate 18 again, and can improve the light use efficiency. The reflection sheet 22 is formed by being bent at the center so as to cover the inclined surfaces 18c and 18d of the light guide plate 18, respectively.
The reflection sheet 102 may be formed of any material as long as it can reflect light leaking from the inclined surfaces 18c and 18d of the light guide plate 18, such as PET or PP (polypropylene). Resin sheet with increased reflectivity by forming voids by kneading and stretching the filler, sheet with a mirror surface formed by vapor deposition of aluminum on the surface of a transparent or white resin sheet, metal foil such as aluminum, or metal foil It can be formed of a resin sheet or a metal thin plate having sufficient reflectivity on the surface.

  The mat film 104 is a transparent film in which the surface on the light guide plate 18 side has been subjected to mat processing, and is disposed between the light guide plate 18 and the reflection sheet 102. Here, the film manufactured using transparent materials, such as PET (polyethylene terephthalate), PC (polycarbonate), an acryl, and COP (cycloolefin polymer), can be used for a transparent film. Moreover, the haze Hb of the transparent film on which the mat treatment has been performed is 10% <Hb <40%.

As described above, even when the mat film subjected to the mat treatment is disposed between the light guide plate and the reflection sheet, it is possible to prevent unevenness in luminance due to local change of light reflected by the reflection film. Furthermore, the viewing angle characteristics of the backlight unit can be controlled by disposing the matte film.
In addition, as for the transparent film to which the mat process was performed, it is more preferable that haze Hb shall be 10% <Hb <20%.

In the present embodiment, a mat-treated transparent film is used as the mat film, but a diffusion film may be used instead of the transparent film. That is, a diffusion film that has been subjected to mat processing may be disposed between the light guide plate 18 and the reflection sheet 102.
Here, the various films described above can be used as the diffusion film, and the haze Hf is 40% <Hf <90%.
Here, the diffusing film and the matte-processed transparent film can be selectively used depending on the viewing angle characteristics required for the backlight unit or the diffusing reflection characteristics of the reflective film. Further, by adjusting the haze of each film within the above range, a desired viewing angle characteristic of the backlight unit can be obtained more suitably.

Further, the mat film preferably has a thickness Tf of 100 μm <Tf <250 μm.
By setting the thickness Tf to 100 μm or more and 250 μm or less, it is possible to fit the inclined surface of the light guide plate (that is, to make the light guide plate and the matte film contact more uniformly).

In the above embodiment, the LED chip of the light source is configured by applying the YAG fluorescent material to the light emitting surface of the blue LED that emits light of the blue wavelength. However, the present invention is not limited to this, and the red fluorescent light is applied to the blue LED. A configuration in which a substance and a green fluorescent substance are applied can also be used. Moreover, you may use the LED chip of the structure which apply | coated the fluorescent substance to the light emission surface of other single color LED, such as red LED which inject | emits the light of red wavelength, and green LED which inject | emits the light of green wavelength.
Furthermore, it is good also as a structure which apply | coated the blue fluorescent material, the red fluorescent material, and the green fluorescent material to the light emission surface of the infrared color LED which inject | emits the light of an infrared wavelength.
In addition, the method of arrange | positioning a fluorescent substance in the light emission surface of LED is not limited to application | coating, You may make it adhere | attach or arrange | position at predetermined intervals.
In addition, as an LED chip of the light source, an LED unit having a configuration in which three types of LEDs, a red LED, a green LED, and a blue LED, are combined can be used. In this case, white light can be obtained by mixing the light emitted from the three types of LEDs.
Further, a semiconductor laser (LD) can be used instead of the LED.

The LED chip with the YAG fluorescent material coated on the light emitting surface of the blue LED is a monochromatic LED, so there are few color variations due to temperature changes over time, and the luminous efficiency can be increased. Easy to mass-produce.
In addition, an LED chip having a configuration in which a red fluorescent material and a green fluorescent material are applied to a blue LED is a single-color LED, and therefore, there is little color variation due to temperature changes over time, and high color rendering properties. Since light can be emitted, color reproducibility can be improved.
In addition, the LED chip having a configuration in which a blue fluorescent material, a red fluorescent material, and a green fluorescent material are coated on the light emitting surface of an infrared LED that emits light of an infrared wavelength is a monochromatic LED. There are few color variations due to temperature changes over time, and color variations can be particularly reduced even when the temperature changes compared to the above-described configuration.
In addition, an LED chip using an LED unit configured by combining three types of LEDs, a red LED, a green LED, and a blue LED, can have very high color rendering.

Further, a transmittance adjusting member having a function of reducing luminance unevenness of light emitted from the light emitting surface may be disposed on the light emitting surface side of the backlight unit.
FIG. 10 is a schematic cross-sectional view of the planar illumination device 180 in which the transmittance adjusting member 182 is arranged.

The backlight unit 180 includes the light source 12, the optical member unit 181, the light guide plate 18, and the reflection sheet 22. The optical member unit 181 includes a diffusion film 15a, a first prism sheet 15b, and a transmittance adjusting member 182.
Here, the light source 12, the diffusion film 15a, the first prism sheet 15, the light guide plate 18, and the reflection sheet 22 are the light source, diffusion film, first prism sheet, light guide plate, and reflection sheet shown in FIG. Since it has the same function, its detailed description is omitted.

In the optical member unit 181, a transmittance adjusting member 182, a diffusion film 15 a, and a prism sheet 188 are sequentially laminated on the light exit surface 18 a of the light guide plate 18. Here, the diffusion film 15a has the same functional shape as the diffusion film 15a described above. The prism sheet 15b has the same functional shape as the prism sheet 15b described above, and the apex angle thereof faces the liquid crystal display panel, that is, the base is parallel to the light incident surface 18a of the light guide plate 18. A plurality of prisms are formed.
As described above, the transmittance adjusting member 182 is used to reduce the luminance unevenness of light emitted from the light guide plate, and the transparent film 184 and a large number of transmittance adjusting bodies disposed on the surface of the transparent film 184. 186.

  The transparent film 184 has a film shape and is made of PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, other acrylic resins, or COP. It is formed of an optically transparent member such as (cycloolefin polymer).

The transmittance adjusting body 186 is a dot of various sizes having a predetermined transmittance, and has a shape such as a quadrangle, a circle, or a hexagon, and has a predetermined pattern, for example, a dot size or a dot according to a position. Are formed on the entire surface of the transparent film 184 on the light guide plate unit 18 side by printing or the like.
The transmittance adjuster 186 may be a diffuse reflector, for example, a material such as silica, titanium oxide, zinc oxide or the like that scatters light or a resin or glass, zirconia or other beads coated with a binder, A surface roughening pattern by fine unevenness processing or polishing may be used on the surface. In addition, it is a material with high reflectance and low light absorption. For example, metals such as Ag and Al can be used.
As the transmittance adjusting body 186, a general white ink used in screen printing, offset printing, or the like can be used. For example, an ink in which titanium oxide, zinc oxide, zinc sulfate, barium sulfate, etc. are dispersed in an acrylic binder, a polyester binder, a vinyl chloride binder, etc., or an ink in which silica is mixed with titanium oxide to impart diffusibility. Can be used.

The transmittance adjusting member 186 arranges a number of transmittance adjusting bodies 186 in a predetermined pattern on the surface of the transparent film 184 on the light guide plate unit 18 side, so that the pattern density of the transmittance adjusting body 186 depends on the position on the surface. Has changed.
Here, the pattern density at an arbitrary position (x, y) of the transmittance adjusting member 182 is ρ (x, y), and the light emitting surface (liquid crystal display) of the backlight unit 180 when the transmittance adjusting member 182 is not provided. The relative luminance of the light emitted from an arbitrary position (x, y) on the panel 4 side surface is defined as F (x, y). At this time, the relationship between the pattern density ρ (x, y) of the transmittance adjusting member 182 and the relative luminance F (x, y) preferably satisfies the following formula.
ρ (x, y) = c {F (x, y) −F _min } / (F _max −F _min )
In the above formula, F _max is the maximum luminance of light emitted from the light emission surface of the diffusion film 15a of the backlight unit 180 when the transmittance adjusting member 182 is not provided, and F _min is the minimum luminance. Note that the relative luminance F (x, y) uses the maximum luminance F _max as a reference point (F _max = 1).
Here, c is the maximum density, and is preferably 0.5 ≦ c ≦ 1.

Further, when designing the density of the arrangement of the transmittance adjusting bodies according to the above formula, luminance unevenness may be visually recognized depending on the angle observed from other than the front direction. In order to improve this, it is preferable to add a “uniform density distribution (bias density ρb)” to the calculated density distribution. Thereby, luminance unevenness can be reduced and the angle dependency of the luminance unevenness can be eliminated or reduced.
Here, the bias density ρb is preferably 0.01 to 1.50 (1 to 150%). In addition, when the arrangement density exceeds 1 (100%), the transmittance adjusting body is arranged twice. That is, the transmittance adjusting body having the arrangement density of (ρb-1) is arranged on the entire surface of the transmittance adjusting body.
Here, the pattern density ρ (x, y) is an occupancy rate per unit area (1 mm ² ) of the transmittance adjusting body 186 existing at an arbitrary position (x, y), and ρ (x, y). When = 1, the transmittance adjusting body 186 is disposed on the entire surface within the unit area, and when ρ (x, y) = 0, it is not disposed at all within the unit area.

  By arranging the transmittance adjusting body 186 of the transmittance adjusting body member 182 so as to satisfy the pattern density ρ (x, y) of the above formula, the average luminance of the light emitted from the light emitting surface of the backlight unit 180 can be reduced. It is possible to suppress the decrease and reduce the luminance unevenness. Thus, by reducing the luminance unevenness by using the transmittance adjusting member 182, the diffusion film 15a does not need to sufficiently diffuse light. As a result, the diffusion film 15a can be made thinner, the use of the prism sheet can be stopped, or the number of prism sheets used can be reduced, providing a lighter and cheaper backlight unit. can do.

Further, the shape of the transmittance adjusting body may be any shape such as a quadrangle, a triangle, a hexagon, a circle, and an ellipse.
Further, when the linear light source and the uniaxially extending light guide plate as in the present embodiment are used for the backlight unit, the shape of the transmittance adjusting body is an elongated strip shape parallel to the axis of the linear light source. It is good.

  Here, in the said embodiment, although the transparent film was used as an optical member by which the transmittance | permeability adjustment body is arrange | positioned, this invention is not limited to this, The transmittance | permeability adjustment body is arrange | positioned to a diffusion film or a prism sheet. Also good. For example, instead of the transparent film, a transmittance adjusting body may be formed on the diffusion film 15a or the prism sheet 15b shown in FIG. As a result, the number of parts can be reduced, and the manufacturing cost can be reduced.

  As described above, the light guide plate 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 may be made without departing from the gist of the present invention. Good.

Moreover, the structure of an optical member unit is not limited to the above-mentioned structure, It can be set as various structures.
For example, as a combination of the optical member units, it is preferable to use an optical member unit having a configuration in which three diffusion films and a polarization separation film are laminated in order from the light exit surface side of the light guide plate.

  Further, in order from the light exit surface side of the light guide plate, a diffusion film and a prism extending in a direction parallel to the longitudinal direction of the light exit surface with an apex angle of 90 ° are parallel to the direction perpendicular to the longitudinal direction of the light exit surface. In addition, it is also preferable to use an optical member unit having a configuration in which a large number of prism sheets and polarization separation films are laminated so that the apex angle of the prism faces the side opposite to the light guide plate side.

  Further, in order from the light exit surface side of the light guide plate, the diffusion film and a prism extending in a direction parallel to the longitudinal direction of the light exit surface at an apex angle of 90 ° are perpendicular to the longitudinal direction of the light exit surface. An optical member having a structure in which a large number of prism sheets, another diffusion film, and a polarization separation film are laminated in parallel so that the apex angle of the prism faces the side opposite to the light guide plate side It is also preferable to use a unit.

  Further, in order from the light exit surface side of the light guide plate, prisms extending in a direction parallel to the longitudinal direction of the light exit surface with an apex angle of 60 ° are arranged in parallel in a direction orthogonal to the longitudinal direction of the light exit surface, and It is also preferable to use an optical member unit having a structure in which a large number of prism sheets, a diffusion film, and a polarization separation film are laminated so that the prism apex angle faces the light guide plate side.

  Further, in order from the light exit surface side of the light guide plate, a diffusion film and a prism extending in a direction parallel to the longitudinal direction of the light exit surface with an apex angle of 90 ° are perpendicular to the longitudinal direction of the light exit surface. A large number of first prism sheets formed in parallel so that the apex angle of the prism faces the side opposite to the light guide plate side, and the apex angle of 90 ° in a direction perpendicular to the longitudinal direction of the light exit surface A plurality of second prism sheets formed in such a manner that the extending prisms are arranged in parallel in a direction perpendicular to the longitudinal direction of the light exit surface and the apex angle of the prisms is opposed to the side opposite to the light guide plate side, and the like It is also preferable to use an optical member unit having a configuration in which the diffusion film and the polarization separation film are laminated.

Although not shown in the above embodiment, the backlight unit further includes a housing that houses and supports a light source, an optical member unit, a light guide plate, a reflection sheet, and the like. This housing has an opening formed on the light emission surface side, and emits light from this opening.
Here, the backlight unit is in a space formed between the reflection sheet 22 and the casing, that is, the surface of the reflection sheet 22 opposite to the light guide plate 18 side and the surface of the casing on the reflection sheet side. It is preferable to arrange a buffer member. Here, the buffer member is a member having rigidity lower than that of the light guide plate deformed along the shape of the light guide plate, such as a sponge.
By supporting the reflection sheet 22 and the first inclined surface 18b and the second inclined surface 18c side of the light guide plate 18 with the buffer member, the reflection sheet 22 can be brought into contact with the light guide plate 18 in a uniform state. 22 can be prevented from bending. Further, by using the support as a buffer member, the light guide plate and the reflection sheet can be brought into uniform contact with each other in a uniform state. As a result, only a part of the reflection sheet comes into contact, diffusely reflects the light, and more reliably prevents the light from being viewed as a bright portion of the light emitted from the light exit surface, and emits uniform light from the light exit surface. Can be made.
Here, FIGS. 11A to 11D are exploded cross-sectional views illustrating an example of a schematic configuration of a buffer member that supports the light guide plate and the reflection sheet, respectively.
For example, as illustrated in FIG. 11A, a rectangular buffer member 202 may be disposed between the reflection sheet 22 and the housing 200. Here, as the buffer member 202, the maximum stress acting on the light guide plate 18 from the buffer member 202 when assembled as a planar lighting device is a connecting portion between the first inclined surface and the second inclined surface in this embodiment. It is preferable to use a material having a stress acting on the surface of 5 [N / cm ² ] or less.
Further, as shown in FIG. 11B, a buffer member 212 composed of multilayer buffer materials 212 a, 212 b, and 212 c is disposed between the reflection sheet 22 and the housing 200, and according to the shape of the light guide plate 18. The thickness of the buffer member 212 may be different depending on the position. Thus, by changing the thickness of the buffer member 212 according to the position, the compression rate of the buffer member can be reduced, and the maximum stress acting on the light guide plate can be reduced. Thereby, the force which acts on a light guide plate can be made more uniform, and a light guide plate and a reflective sheet can be made to contact uniformly.
In addition, as shown in FIG. 11C, the buffer member 222 may have a shape along the inclined surface of the light guide plate 18. That is, the buffer member 222 has a shape in which the first inclined surface 222a and the second inclined surface 222b having the same inclination angle as the first inclined surface and the second inclined surface of the light guide plate 18 are formed on the surface on the light guide plate 18 side. .
Thus, the light guide plate and the reflection sheet can be brought into contact with each other in a uniform state by forming the buffer member along the inclined surface of the light guide plate.
Further, as shown in FIG. 11D, the buffer member 232 is shaped along the inclined surface of the light guide plate 18, and the inclined surface of the light guide plate 18 is disposed on the surface of the buffer member 232 opposite to the light guide plate 18 side. It is good also as a structure which provided the sheet-metal member 234 along the shape of this. Here, in this embodiment, the housing | casing 200 and the sheet metal 234 become a housing | casing.
By providing the sheet metal member 234 along the shape of the inclined surface of the light guide plate 18 on the surface opposite to the light guide plate 18 side of the buffer member 232, the compression rate of the buffer member can be made uniform, and the buffer member By supporting the reflection sheet via the light guide plate, the light guide plate and the reflection sheet can be brought into uniform contact.
Further, the housing 200 and the sheet metal member 234 may be integrated or separated.

Hereinafter, the light guide plate will be described in detail based on examples.
Using the light source 12 and the light guide plate 18 configured as shown in FIGS. 2A and 2B, the light guide length [mm] of the light guide plate 18, its shape, that is, the maximum thickness [mm] and the minimum thickness [mm]. The incident light is incident from the two light incident surfaces 18d and 18e of the light guide plate 18 by changing the taper, the center radius R [mm], the particle diameter [μm] of the scattering fine particles dispersed in the light guide plate 18 and the particle concentration [wt%]. The light utilization efficiency [%] indicating the ratio of the light emitted from the light emitting surface 18a to the emitted light and the luminance distribution of the light emitted from the light emitting surface 18a are obtained, and the peripheral portion of the light emitting surface 18a, that is, the light The medium altitude [%] of the luminance distribution of the light emitting surface 18a indicating the ratio of the luminance of the light emitted from the central portion of the light emitting surface 18a to the luminance of the light emitted from the vicinity of the incident surfaces 18d and 18e was obtained.

Example 1
As Example 1, the maximum thickness [mm], the minimum thickness [mm], and the particle diameter [μm] when the light guide length L [mm] of the light guide plate 18 corresponding to a screen size of 37 inches is L = 480 mm. When the particle concentration [wt%] is varied as shown in Tables 1 and 2, the taper, the central part (curved part radius) R [mm], the light utilization efficiency [%], and the intermediate altitude [%] Asked. The results are shown in Tables 2 and 3.
Here, Table 2 shows Invention Examples 11 to 16 for Example 1, and Table 3 shows Comparative Examples 11 to 15 for Example 1.

As is apparent from Tables 2 and 3, in all of Examples 11 to 16 of the present invention, the particle diameter [μm] and the particle concentration [wt%] satisfy the limited range of the present invention, and the maximum thickness Since [mm] and the minimum thickness [mm] also satisfy the limited range of the present invention, the light utilization efficiency [%] is 61% or higher and higher than 55%, and the intermediate altitude [%] is 19%. % To 23%, satisfying the limited range required by the present invention of more than 0% and 25% or less.
On the other hand, the comparative example 11 has a particle concentration higher than the limited range of the present invention, and thus exhibits the same phenomenon as a flat plate, and thus cannot achieve a medium-high luminance distribution.

In Comparative Example 12, both the maximum thickness [mm] and the minimum thickness [mm] are larger than the upper limit values of 6.0 mm and 3.0 mm of the limited range of the present invention, and light penetrates and is transmitted. In addition, the light utilization efficiency does not satisfy 50% or more of the limited range of 55% or more, and the weight is too heavy to be suitable as an optical member for a liquid crystal TV.
In Comparative Example 13, the taper angle is less than 0.1 °, the center radius R is large, the particle concentration is not suitable for molding, and the light utilization efficiency is 55% or more than the limited range of the present invention. Then, middle-high distribution cannot be realized.

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

(Example 2)
As Example 2, the maximum thickness [mm] and the minimum thickness [mm] when the light guide length L [mm] of the light guide plate 18 corresponding to the screen size of 42 inches and 46 inches is L = 560 mm and 590 mm, When the particle diameter [μm] and particle concentration [wt%] are variously changed as shown in Tables 4 and 5, taper, central part (curved part radius) R [mm], light utilization efficiency [%], medium Altitude [%] was determined. The results are shown in Tables 4 and 5.
Here, Table 4 shows Examples 21 to 24 of the present invention for Example 2, and Table 5 shows Comparative Examples 21 to 23 for Example 2.

As is apparent from Tables 4 and 5, in each of Invention Examples 21 to 24 of Example 2, the particle diameter [μm] and the particle concentration [wt%] satisfied the limited range of the present invention, and Since the maximum thickness [mm] and the minimum thickness [mm] also satisfy the limited range of the present invention, the light use efficiency [%] is 59% to 61%, which is higher than 55%, [%] Is also 14% to 15%, and satisfies the limited range required by the present invention of more than 0% and 25% or less.
On the other hand, Comparative Examples 21 and 22 have a particle concentration higher than the limited range of the present invention, and thus have the same phenomenon as a flat plate, and thus cannot achieve a medium-high luminance distribution.
In Comparative Example 23, both the maximum thickness [mm] and the taper angle are larger than the upper limit values of 6.0 mm and 0.8 ° of the limited range of the present invention, the taper is too large, and the maximum thickness is In addition to being unnecessarily large and having a medium-high distribution more than necessary, the weight is too heavy and it is not suitable as an optical member for a liquid crystal TV.

(Example 3)
As Example 3, the maximum thickness [mm], the minimum thickness [mm] when the light guide length L [mm] of the light guide plate 18 corresponding to the screen size of 52 inches and 57 inches is L = 660 mm and 730 mm, When the particle diameter [μm] and particle concentration [wt%] are variously changed as shown in Table 6 and Table 7, taper, central portion (curved portion radius) R [mm], light utilization efficiency [%], medium Altitude [%] was determined. The results are shown in Tables 6 and 7.
Here, Table 6 shows Invention Examples 31 to 32 for Example 3, and Table 7 shows Comparative Examples 31 to 35 for Example 3.

As is apparent from Tables 6 and 7, the inventive examples 31 to 32 of Example 3 all have a particle diameter [μm] and a particle concentration [wt%] satisfying the limited range of the present invention. Since the maximum thickness [mm] and the minimum thickness [mm] also satisfy the limited range of the present invention, the light use efficiency [%] is higher than 55%, both 60% and 61%. [%] Is also 14% to 14.2%, which satisfies the limited range required by the present invention of more than 0% and 25% or less.
On the other hand, since the comparative example 31 has a particle concentration higher than the limited range of the present invention, the phenomenon is similar to that of a flat plate, and thus a medium-high luminance distribution cannot be realized.

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

Example 4
As Example 4, the maximum thickness [mm] and the minimum thickness [mm] when the light guide length L [mm] of the light guide plate 18 corresponding to the screen size of 52 inches and 57 inches is L = 660 mm and 730 mm, When the particle diameter [μm] and particle concentration [wt%] are variously changed as shown in Table 8 and Table 9, taper, central part (curved part radius) R [mm], light utilization efficiency [%], medium Altitude [%] was determined. The results are shown in Table 8 and Table 9.
Here, Table 8 shows Examples 41 to 44 of the present invention for Example 4, and Table 9 shows Comparative Examples 41 to 45 for Example 4.

As is clear from Tables 8 and 9, all of the inventive examples 41 to 44 of Example 4 satisfy the limited range of the present invention in terms of the particle diameter [μm] and the particle concentration [wt%]. Since the maximum thickness [mm] and the minimum thickness [mm] also satisfy the limited range of the present invention, the light use efficiency [%] is 57% to 68%, which is higher than 55%. [%] Is also 11% to 24%, and satisfies the limited range required by the present invention of more than 0% and 25% or less.
On the other hand, in Comparative Example 41, since the particle concentration is lower than the limited range of the present invention, light penetrates and passes through, and thus the light utilization efficiency does not satisfy 55% or more.

In Comparative Example 42, both the maximum thickness [mm] and the minimum thickness [mm] are larger than the upper limit values of 6.0 mm and 3.0 mm of the limited range of the present invention, and light penetrates and passes through. For this reason, the light utilization efficiency does not satisfy the limited range of 55% or more, and the weight is too heavy to be suitable as an optical member for a liquid crystal TV.
In Comparative Example 43, the maximum thickness [mm] is smaller than the lower limit of 1.0 mm of the limited range of the present invention, the center radius R is too large, exceeds the limited range of the present invention, and is suitable for molding. In addition, a medium-high distribution cannot be realized at a particle concentration at which the light utilization efficiency is 55% or more.
Comparative Example 44 has a particle size smaller than the limited range of the present invention and good light utilization efficiency, but cannot achieve a medium-high luminance distribution, and Comparative Example 45 has a particle size larger than the limited range of the present invention and is medium-high. A luminance distribution can be realized, but the light utilization efficiency is low.

From the above results, in any of the examples, the present invention has an appropriate shape according to the range of the respective light guide lengths of the light guide plate, and the maximum thickness [mm] and the minimum thickness [ mm], taper, central radius R [mm], and the particle diameter [μm] and particle concentration [wt%] of the scattering particles to be dispersed satisfy the limited range of the present invention, and the light utilization efficiency [%] is 55% or more. The intermediate altitude [%] is more than 0% and 25% or less.
On the other hand, in the comparative example, even in the range of the light guide length of any of the examples, either of the above requirements is out of the limited range of the present invention, so that the light use efficiency [%] does not satisfy 55% or more. The degree of altitude [%] does not satisfy more than 0% and 25% or less, and excellent characteristics cannot be exhibited.

(A) is a perspective view which shows the outline of the liquid crystal display device using the backlight unit of this invention, (B) is a schematic sectional drawing of a liquid crystal display device. (A) is a schematic plan view of the light guide plate and the light source shown in FIG. 1, and FIG. 2 (B) is a schematic cross-sectional view of the light guide plate and the light source. (A) is a perspective view which shows schematic structure of the light source of the planar illuminating device shown in FIG.1 and FIG.2, (B) is sectional drawing of the light source shown to (A), (C) is It is a schematic perspective view which expands and shows one LED of the light source shown to (A). (A) is a cross-sectional schematic diagram of the light guide plate shown in FIG. 2, and (B) is a partially enlarged cross-sectional view of the light guide plate shown in (A). (A) And (B) is a graph which shows the relationship between the particle diameter and particle concentration [wt%] of the scattering fine particle disperse | distributed to a light-guide plate, 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 a light-guide plate, respectively. It is a flowchart which shows an example of the design method of a light-guide plate. It is a graph which shows the relationship between the particle | grain density | concentration [wt%] of a light-guide plate, light utilization efficiency [%], and middle altitude degree [%]. It is a schematic sectional drawing which shows another example of the backlight unit of this invention. It is a schematic sectional drawing which shows an example of the backlight unit which has a transmittance | permeability adjustment member. (A)-(D) is an exploded sectional view which shows an example of schematic structure of the buffer member and housing | casing which respectively support a light-guide plate and a reflective sheet. It is a graph which shows the illumination intensity distribution of the front direction of the conventional flat light-guide plate.

Explanation of symbols

2, 180 Backlight unit 4 Liquid crystal display panel 6 Drive unit 10 Liquid crystal display device 12 Light source 14 Optical member unit 15a Diffusion film 15b First prism sheet 15c Second prism sheet 15d Polarization separation film 18 Light guide plate 18a Light exit surface 18b First Inclined surface 18c Second inclined surface 18d First light incident surface 18e Second light incident surface 18f Bending portion 22 Reflecting sheet 50 LED chip 52 Light source support portion

Claims (7)

A rectangular flat light exit surface;
Two light incident surfaces each including two opposing long sides of the light exit surface and disposed at positions facing each other;
Two inclined back surfaces that are symmetrically spaced from the light exit surface as they go from the two light entrance surfaces toward the center of the light exit surface,
A curved portion joining these two inclined back surfaces,
Contains scattering particles that scatter light propagating inside it,
The length between the two light incident surfaces is 480 mm or more and 830 mm or less,
The scattering particles have a particle size of 4.0 μm or more and 12.0 μm or less,
The concentration of the scattering particles is 0.008 wt% or more and 0.25 wt% or less,
The utilization efficiency of light indicating the ratio of the light incident from the two light incident surfaces being emitted from the light exit surface is 55% or more,
The medium to altitude of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, exceeds 0%. A light guide plate that is 25% or less;
Two light sources respectively disposed facing the two light incident surfaces of the light guide plate;
A planar lighting device, comprising: a reflective sheet disposed in contact with the inclined rear surface of the light guide plate, wherein the surface on the light guide plate side is matted. A rectangular flat light exit surface;
Two light incident surfaces each including two opposing long sides of the light exit surface and disposed at positions facing each other;
Two inclined back surfaces that are symmetrically spaced from the light exit surface as they go from the two light entrance surfaces toward the center of the light exit surface,
A curved portion joining these two inclined back surfaces,
Contains scattering particles that scatter light propagating inside it,
The length between the two light incident surfaces is 480 mm or more and 830 mm or less,
The scattering particles have a particle size of 4.0 μm or more and 12.0 μm or less,
The concentration of the scattering particles is 0.008 wt% or more and 0.25 wt% or less,
The utilization efficiency of light indicating the ratio of the light incident from the two light incident surfaces being emitted from the light exit surface is 55% or more,
The medium to altitude of the luminance distribution of the light emitting surface, which indicates the ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance of the light emitted from the vicinity of the light incident surface of the light emitting surface, exceeds 0%. A light guide plate that is 25% or less;
Two light sources respectively disposed facing the two light incident surfaces of the light guide plate;
A reflective sheet disposed on the inclined back side of the light guide plate;
A planar lighting device, comprising: a matte film disposed between the inclined back surface of the light guide plate and the reflective sheet and having a matte surface.   The planar lighting device according to claim 2, wherein the mat film has a thickness Tf of 100 μm <Tf <250 μm.   4. The planar lighting device according to claim 2, wherein the mat film is a diffusion film, and assuming that haze is Hf, 40% <Hf <90%. 5.   4. The planar lighting device according to claim 2, wherein the mat film is a transparent film whose surface is matted, and where hb is Hb, 10% <Hb <40%.   The planar lighting device according to claim 5, wherein the transparent film is made of at least one of polyethylene terephthalate, polycarbonate, acrylic, and cycloolefin polymer. The light guide plate is
The thickness of the light incident surface with the smallest thickness is 0.5 mm or more and 3.0 mm or less,
The thickness of the center of the curved portion where the thickness is the largest is 1.0 mm or more and 6.0 mm or less,
The radius of curvature of the curved portion is 6,000 mm or more and 45,000 mm or less,
The planar illumination device according to any one of claims 1 to 5, wherein a taper of the inclined back surface is 0.1 ° or more and 0.8 ° or less.

Images