JP2013137927A - Sheet-like light guide plate, planar lighting device, and planar lighting unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-like light guide plate of large and thin size which has high light utilization efficiency, little luminance unevenness, and can uniformly emit light even in bening, and a planar lighting device using the same, and a planar lighting device for flexible planar illumination can be used by bending a light-emitting face in a concavo-convex shape.SOLUTION: The thin-size sheet-like light guide plate has a rectangular light-emission face, light-incident faces, and a rear face, with diffusion particles dispersed inside, and has two or more layers by way of a first layer and a second layer with different particle concentration. The second layer has a cross-sectional shape which has at least a part wherein a thickness becomes a maximum by continuously increasing in a direction away from the light-incident face, and the diffusion particles are dispersed so that a compound scattering cross-sectional area S in a thickness direction of the two or more layers may be continuously and monotonously increased as they are separated from the light-incident face, and the maximum value Sand the minimum value Sof the compound scattering cross-sectional area S satisfy A*k≤S≤B*k, and C*k≤S≤D*k ( a coefficient k is an inverse of a ratio to a reference light guide length, A, B, C and D are a constant determined by the light guide length).

Description

  The present invention relates to a sheet-like light guide plate having a thin, particularly ultra-thin, two-layer structure for flexible lighting, in which a diffusion material such as diffusion fine particles for emitting planar illumination light can be dispersed and bent into irregularities. In addition, a planar illumination device capable of emitting planar illumination light, used as a backlight of a liquid crystal display (liquid crystal display device) or an advertising display, a surface light source for environmental illumination, and the like, and a light emitting surface bent into an uneven shape The present invention relates to a planar lighting unit for flexible surface lighting that can be used.

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

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

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

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

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

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

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

  In addition, the large light guide plate greatly expands and contracts due to ambient temperature and humidity, and repeats expansion and contraction of 5 mm or more in the size of about 50 type (50 inches; diagonal length: 1270 mm). Therefore, as in the light guide plates (plate-like light scattering light guide elements and light guides) disclosed in Patent Documents 1 and 2, if the plate is a flat plate, it cannot be determined whether the light exit surface side or the reflection surface side is warped. However, when the light guide plate warps, the stretched light guide plate pushes up the liquid crystal panel, and pool-like unevenness occurs in the light emitted from the liquid crystal display device. In order to avoid this, it is conceivable to increase the distance between the liquid crystal panel and the backlight unit in advance, but there is a problem that it is impossible to make the liquid crystal display device thin.

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

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

In addition, in the case of a thin (particularly, 1.2 mm or less) sheet-like light guide plate, the conventional print light guide plate having a thickness of about 4 mm has a problem that the conventional print pattern size is visually recognized. ing. On the other hand, it is possible to cope with this by reducing the print pattern so that it is not visually recognized. However, in the case of a conventional screen printing plate, if the pattern is smaller than 0.3 mm, ink clogging occurs, and printing is performed. There is a problem that becomes difficult. On the other hand, according to the ink jet method, printing is possible in principle, but since the nozzle needs to be miniaturized, a problem that the manufacturing cost is very high can be easily predicted.
For this reason, in the conventional printed light guide plate, a thin sheet-like light guide plate of 1.2 mm or less has not been realized.

  An object of the present invention is to solve the above-mentioned problems of the prior art, has a large and thin shape, can emit light with high light utilization efficiency and little luminance unevenness, and is required for a large-screen thin liquid crystal television. In the brightness distribution of the emitted light, the distribution near the center of the screen is brighter than the peripheral part, that is, the so-called medium-high or bell-shaped brightness distribution, that is, the brightness distribution of the emitted light from the light exit surface. Thin (ultra-thin) that can obtain a bell-shaped distribution (hereinafter referred to as “medium-high distribution”) whose luminance is higher than that of the peripheral part such as the incident part, and that can emit light even when bent. ) Sheet-like light guide plate, a planar illumination device using the same, and a planar illumination unit for flexible surface illumination that can be used by bending the light emitting surface into irregularities.

In order to solve the above problems, a sheet-like light guide plate according to a first aspect of the present invention is provided on a rectangular light emitting surface and an end side of the light emitting surface, and is substantially parallel to the light emitting surface. A thin surface having a thickness of 1.2 mm or less, having at least one light incident surface on which light traveling in any direction is incident, and a back surface opposite to the light emitting surface, in which diffused particles are dispersed The light guide plate has two or more layers that overlap each other in a direction substantially perpendicular to the light exit surface, and each of the two or more layers includes one or more types. The diffusing particles are dispersed at different particle concentrations, and the two or more layers are at least a first layer located on the light emitting surface side and a back surface side and in contact with the first layer A second layer, and the second layer is substantially perpendicular to the light exit surface in a direction substantially parallel to the light exit surface. The thickness of the direction changes, and the cross-sectional shape has at least a portion where the thickness continuously increases in the direction away from the light incident surface and becomes a local maximum, along the direction substantially parallel to the light emitting surface The diffused particles are dispersed so that the combined scattering cross section S in the direction substantially perpendicular to the light emitting surface of the two layers at a position increases continuously and monotonously as the distance from the light incident surface increases. The maximum value S _max and the minimum value S _min of the area S satisfy the following formula (1).
A ・ k ≦ S _max ≦ B ・ k
C ・ k ≦ S _min ≦ D ・ k (1)
Here, the coefficient k is the reciprocal of the ratio of the screen size V or the light guide length L (mm) to the reference screen size V ₀ or the light guide length L ₀ (mm) (k = V ₀ / V = L ₀ / L), and A, B, C, and D are constants determined in the reference screen size V ₀ or the reference light guide length L ₀ .

Here, when the reference screen size V ₀ is a screen size of 20 type (20 inches; diagonal length: 508 mm), or when the reference light guide length L ₀ is 269.5 mm, the above formula ( 1), A = 0.833, B = 2.150, C = 0.672, D = 1.590 in the case of bilateral incidence, and A = 1.000, B = 1. 761, C = 0.500, and D = 0.645.
The second layer has a cross-sectional shape in which a thickness in a direction substantially perpendicular to the light emitting surface in a direction substantially parallel to the light emitting surface has at least one minimum value and at least one maximum value. It is preferable that
The at least one light incident surface is preferably two light incident surfaces provided on two opposite sides of the light emitting surface.
The cross-sectional shape of the second layer preferably includes three arcs or four arcs, and has the minimum value on each side of the two light incident surfaces, and the two light beams It is preferable that the maximum value is at the approximate center between the incident surfaces, and an arc forming the minimum value is provided on each side of the two light incident surfaces, and the approximate center between the two light incident surfaces is provided. It is preferable to have an arc that forms the maximum value.
Moreover, it is preferable that the thickness of the second layer is the thickest in the approximate center of the light emitting surface.

Further, the at least one light incident surface is one light incident surface provided on one end side of the light emitting surface, and the cross-sectional shape of the second layer is that of the one light incident surface. It is preferable to have the minimum value on the side and to have the maximum value on the other end side of the light emitting surface.
The cross-sectional shape of the second layer has an arc that forms the minimum value on the one light incident surface side, and an arc that forms the maximum value on the other end side of the light emitting surface. It is preferable to have.
The two or more layers preferably further include a third layer located on the back surface side and in contact with the second layer, and a boundary surface between the second layer and the third layer is The light exit surface is preferably substantially parallel to the light exit surface.

The light guide length of light traveling in a direction substantially parallel to the light emitting surface from the one light incident surface to the other light incident surface or to the other end is 260 mm (20 type (20 inches: Diagonal length: 508 mm)) to 1350 mm (100 type (100 inches; diagonal length: 2540 mm)) or less, and the particle size of the diffusion particles is 4.5 μm to 12.0 μm, The concentration of the diffusing particles dispersed in the two layers is 0.005 wt% or more and 4.438 wt% or less, and the particle size and concentration of the diffusing particles dispersed in the second layer are the particle size of the scattering particles ( In the graph in which the horizontal axis is μm) and the particle concentration (wt%) of the diffusing particles is the vertical axis, 6 points (4.5, 0.005), (4.5, 1.085), (7. 0,0.0006), (7.0,1.693), (12. Preferably in the surrounded by regions at 0.019) and (12.0,4.438). Specifically, in the case of double-sided incidence in which the light is incident from two light incident surfaces provided on two opposite sides of the light emitting surface, one side from the one light incident surface to the center The light guide lengths of the light are 130 mm (20 type) or more and 675 mm (100 type) or less, respectively, and the total light guide length of the light is 260 mm (20 type) or more and 1350 mm (100 type) or less. Or in the case of one side incidence where the light is incident from one light incident surface provided on one end side of the light emitting surface, the other end (of the light emitting surface of the light emitting surface). The light guide length to the other end side) is preferably 260 mm (20 type) or more and 1350 mm (100 type) or less.
The concentration of the diffusion particles dispersed in the first layer is 0.0004 wt% or more and 0.195 wt% or less, and the particle size and concentration of the diffusion particles dispersed in the first layer are the scattering particles. In the graph in which the horizontal axis is the particle diameter (μm) of the particle and the vertical axis is the particle concentration (wt%) of the diffusion particles, 6 points (4.5, 0.0004), (4.5, 0.048) , (7.0, 0.0006), (7.0, 0.074), (12.0, 0.0015) and (12.0, 0.195). .

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

  Moreover, in order to solve the said subject, the planar illuminating device which concerns on the 2nd aspect of this invention arrange | positions the sheet-like light-guide plate of the said 1st aspect, and the said light-incidence surface of the said light-guide plate facing. The light guide plate and the light source, and a housing having an opening smaller than the light exit surface on the light exit surface side of the light guide plate.

Moreover, in order to solve the said subject, the planar illumination unit which concerns on the 3rd aspect of this invention is the sheet-like light-guide plate of the said 1st aspect, and the said light-projection surface and the said back surface of this light-guide plate, respectively. A planar lighting unit including a plurality of structural members including the optical member, wherein the plurality of structural members configuring the entire planar lighting unit is represented by the following formula (3): It is characterized in that the deflection rigidity D [N · m] of the entire planar illumination unit is configured to satisfy the following formula (2).
D <1.3 (2)

Here, k is the number of types of materials of different materials of the plurality of constituent members constituting the planar lighting unit, N _k is the number of parts of the material k, E _k is the Young's modulus of the material k [N / m ² ], h _k is the thickness [mm] of the material k, and ν is the Poisson's ratio.

Here, it is preferable that the plurality of constituent members further include a housing that houses the light guide plate and the optical member.
Moreover, the material of the material of the light guide plate is acrylic, the material of the material of the parts constituting the housing is an aluminum alloy, and the thickness of the material of the housing is 0.5 mm or less. The thickness of the optical member is preferably 0.6 mm or less.

  Moreover, in order to solve the said subject, the planar illuminating device which concerns on the 4th aspect of this invention is the light incidence of the planar illuminating unit of the said 3rd aspect, and the said light-guide plate of this planar illuminating unit. And a light source disposed so as to face the surface.

ADVANTAGE OF THE INVENTION According to this invention, what is called a flexible planar illumination device and surface light source device which cannot be implement | achieved by the surface illumination unit using the conventional light-guide plate, and can light-emit even if it bends is realizable.
In addition, according to the present invention, the central portion of the screen required for a large-sized thin liquid crystal television has a large and thin shape and can emit light with high light utilization efficiency and little luminance unevenness. It is possible to obtain a brightness distribution whose brightness is brighter in the vicinity, that is, a so-called medium-high or bell-shaped brightness. In particular, according to the present invention, a medium-high luminance distribution can be simultaneously realized at a high efficiency (for example, 70% or more) that cannot be achieved by a conventional flat light guide plate.

Further, according to the present invention, the light guide plate and the casing component are made thin, in particular, an ultra-thin sheet, thereby simultaneously realizing super light weight.
In addition, according to the present invention, a method for designing the cross-sectional shape of the two-layer sheet-shaped light guide plate is also included. When it is determined, the condition of the diffusing particles to be dispersed inside can be freely selected, and the degree of freedom in design can be improved.

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

Below, the sheet-like light-guide plate which concerns on this invention, the planar illuminating device using the same, and the planar illuminating unit for flexible surface illumination are demonstrated in detail based on suitable embodiment shown to attached drawing.
FIG. 1 is a perspective view schematically showing a liquid crystal display device including a planar illumination device using the sheet-like light guide plate according to the first embodiment of the present invention, and FIG. 2 is a diagram of the liquid crystal display device shown in FIG. It is II-II sectional view taken on the line.
3A is a view taken along the line III-III of the planar illumination device (hereinafter also referred to as “backlight unit”) shown in FIG. 2, and FIG. It is a BB sectional view taken on the line.

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

The liquid crystal display panel 12 applies a partial electric field to liquid crystal molecules arranged in a specific direction in advance to change the arrangement of the molecules, and uses the change in the refractive index generated in the liquid crystal cell to make a liquid crystal display. Characters, figures, images, etc. are displayed on the surface of the display panel 12.
The liquid crystal display panel 12 targeted by the sheet-like light guide plate of the present invention is not particularly limited, but the screen size is 20 inches (20 inches (20 ″): diagonal length: 508 mm) or more, 100 It is a large screen of a type (100 inches (100 "); diagonal length: 2540 mm), and is preferably used for a thin liquid crystal television having a screen of such a size, more preferably 37 type ( 37 inches (37 ″); diagonal length: 940 mm) or more, and is used for large and thin LCD TVs having such a large screen. Large screen size of such a liquid crystal display panel 12 In addition, for example, 40 type (40 inch (40 "); diagonal length: 1016 mm), 42 type (42 inch (42"); diagonal length: 1067 mm), 46 type (46 inch (4 "); Diagonal length: 1168 mm), 52 type (52 inches (52"); diagonal length: 1321 mm), 55 types (55 inches (55 "); diagonal length: 1397 mm), 65 types (65 inches ( 65 ″); diagonal length: 1651 mm), 70 type (70 inch (70 ″); diagonal length: 1778 mm), 80 type (80 inch (80 ″); diagonal length: 2032 mm), 90 type (90 inch) (90 "); diagonal length: 2286 mm).
The drive unit 14 applies a voltage to the transparent electrode in the liquid crystal display panel 12, changes the direction of the liquid crystal molecules, and controls the transmittance of light transmitted through the liquid crystal display panel 12.

  The backlight unit 20 constitutes the planar illumination device according to the second and fourth aspects of the present invention, and is an illumination device that irradiates light from the back surface of the liquid crystal display panel 12 to the entire surface of the liquid crystal display panel 12. The liquid crystal display panel 12 has a light emission surface 24a having substantially the same shape as the image display surface.

  As shown in FIGS. 1, 2, 3A and 3B, the backlight unit 20 in the present embodiment includes two light sources 28 and a sheet-like light guide plate according to the present invention (hereinafter simply referred to as a guide). A lighting device main body 24 having an optical member unit 32, and a housing 26 having a lower housing 42, an upper housing 44, a folding member 46, and a support member 48. As shown in FIG. 1, a power storage unit 49 that stores a plurality of power supplies for supplying power to the light source 28 is attached to the back side of the lower housing 42 of the housing 26.

First, prior to the sheet-like light guide plate of the first aspect of the present invention, the planar illumination unit according to the third aspect of the present invention and the planar illumination apparatus of the fourth aspect of the present invention using the same will be described.
Here, the backlight unit 20 has a planar lighting unit according to the third aspect of the present invention for flexible planar lighting that can be used with the light-emitting surface bent into irregularities, and the fourth aspect of the present invention using the same. It also functions as a planar illumination device of the aspect.
The backlight unit 20 of the present embodiment has a sheet-like light guide plate 30 having a rectangular light emitting surface 30a, a back surface 30b, and light incident surfaces 30c and 30d, which will be described later, in which diffusing particles are dispersed. And optical members (the diffusion sheets 32a and 32c of the optical member unit 32, the prism sheet 32b, the reflecting plate 34, the upper and lower guide reflecting plates 36 and 38, which are respectively disposed on the light emitting surface 30a and the back surface 30b of the light guide plate 30. And a planar illumination unit according to the third aspect of the present invention comprising a plurality of constituent members including a light guide plate 30 and a housing 26 that accommodates these optical members, and the planar illumination unit The light guide plate 30 includes a light source 28 that is disposed to face the light incident surfaces 30 c and 30 d and is accommodated in the housing 26. In the following description, the backlight unit 20 also represents a planar illumination unit.

In the plurality of constituent members constituting the entire backlight unit 20, the deflection rigidity D [N · m] represented by the following formula (3) of the entire backlight unit 20 satisfies the following formula (2). Need to be configured.
D <1.3 (2)

Here, k is the number of types of materials of different materials constituting the backlight unit 20, N _k is the number of parts of the material k, and E _k is the Young's modulus of the material k [N / m ² ], H _k is the thickness [mm] of the material k, and ν is the Poisson's ratio.

The reason why the deflection rigidity D of the entire backlight unit 20 is limited to the above range is that when the deflection rigidity D satisfies the above range, a flexible planar lighting device that can be bent and emit light, a flexible surface light source device, and the like are realized. However, when the flexural rigidity D is 1.3 N / m ² or more as in a conventional surface illumination unit using a light guide plate, a flexible planar illumination device capable of emitting light by bending, a flexible surface light source device, etc. This is because it cannot be realized.
The lower limit value of the deflection rigidity D of the entire backlight unit 20 is not particularly limited and should be as low as possible. However, since there is a limit depending on the material used, it may be determined according to the material used. Although it is good, considering the feasibility of the planar lighting device composed of a light guide plate, a housing, a film, etc., it is preferably 0.2 N / m ² or more.
In the case of a dual emission type or a dual emission type without a housing, it is preferably 0.04 N / m ² or more.

In the 3rd aspect of this invention, it is preferable that the some structural member which comprises the whole backlight unit 20 satisfy | fills the following material conditions.
Here, as long as the material which comprises the light-guide plate 30 is an optically transparent resin material, what kind of thing may be sufficient as it. Thus, as a material of the material of the transparent resin used for the light guide plate 30, for example, PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), acrylic resin, PMMA (polymethyl methacrylate), benzyl methacrylate, MS A transparent resin such as a resin or COP (cycloolefin polymer) can be mentioned, and among these, an acrylic resin is preferable.
Moreover, it is preferable that the thickness of the material of the light-guide plate 30 is 1.2 mm or less. The reason for this is that if the above range is satisfied, even if it is bent and used, the material will continue to be used without being broken, and it will not be plastically deformed. The minimum curvature radius, for example, the stress when bent at R300 is less than the allowable stress (proportional limit), so that it is possible to realize a flexible planar lighting device that can be bent to emit light, but the material of the light guide plate 30 This is because if the thickness exceeds 1.2 mm, plastic deformation may occur at the curvature radius, and it becomes difficult to realize a flexible planar lighting device that can be bent and emit light.
The lower limit value of the material thickness of the light guide plate 30 is not particularly limited, and is preferably as thin as possible as long as the required performance as the light guide plate 30 can be satisfied. However, there is a limit to the material used. Therefore, it can be determined according to the material used, but if it is too thin, the strength will be insufficient, and even if it is possible in strength, it cannot be bent flexibly, and it may be bent or wrinkled. In view of feasibility, the thickness is preferably 0.3 mm or more.

In addition, the materials of the components constituting the casing 26, such as the lower casing 42, the upper casing 44, the folding member 46, and the support member 48, are the optical members and the reflecting plate 34 of the light guide plate 30 and the optical member unit 32. As long as the light guide plate 30 and the optical member can be accommodated and held in a bent state, that is, in a curved state, the optical member can be bent according to the bending of the optical member, etc. In addition, a metal such as an aluminum alloy, a magnesium alloy, a stainless steel sheet, and a phosphor bronze sheet, a resin containing a metal filler, and the like can be given. Of these, an aluminum alloy is preferable.
Moreover, it is preferable that the thickness of the material of the component which comprises a housing | casing is 0.5 mm or less. The reason for this is that if the above range is satisfied, even if it is bent and used, the material will continue to be used without being broken, and it will not be plastically deformed. The minimum curvature radius, for example, the stress when bent at R300 is less than the allowable stress (proportional limit), so that it is possible to realize a flexible planar lighting device and the like that can be bent and emit light. If the thickness is more than 0.5 mm, plastic deformation may occur at the radius of curvature, which makes it difficult to realize a flexible planar lighting device that can be bent to emit light.
When the allowable bending stress of the material is σa, the Young's modulus is E, and the radius of curvature is R, the upper limit value ta of the material thickness t must satisfy ta <t = 2Rσa / E.
In addition, the lower limit of the thickness of the material of the casing component is not particularly limited, and as long as the required performance as a flexible planar lighting unit can be satisfied, it is better to be as thin as possible. Since there is a limit, it may be determined according to the material used, but if it is too thin, the strength will be insufficient, and even if it is possible in strength, it can not be bent flexibly, it will be bent or wrinkled In view of the feasibility, it is preferably 0.3 mm or more.

Further, the optical members respectively disposed on the light emitting surface 30a and the back surface 30b of the light guide plate 30 are not particularly limited and are preferably a thin sheet, but any optical member that is usually used in a planar illumination unit may be used. Anything may be used. For example, the diffusion sheets 32a and 32c and the prism sheet 32b of the optical member unit 32 disposed on the light emitting surface 30a side used as an optical member, and the reflection plate 34 and the upper and lower guide reflection plates 36 and 38 disposed on the back surface 30b. Also, conventionally known ones such as a diffusion film and a reflection film which are usually used in a planar lighting device or the like may be used.
Here, it is preferable that the thickness of the material of each optical member used is 0.3 mm or more and 0.5 mm or less. The reason is the same as in the case of the material of the parts constituting the housing.
The backlight unit 20 constituting the planar illumination unit according to the third aspect of the present invention is basically configured as described above.

Hereinafter, each component which comprises the backlight unit 20 is demonstrated.
The illuminating device body 24 includes a light source 28 that emits light, a light guide plate 30 that emits light emitted from the light source 28 as planar light, and a light that is emitted from the light guide plate 30 by scattering or diffusing the light. And an optical member unit 32 having light without unevenness.

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

The LED chip 50 is a chip in which a fluorescent material is applied to the surface of a light emitting diode that emits blue light. The LED chip 50 has a light emitting surface 58 having a predetermined area, and emits white light from the light emitting surface 58.
That is, when the blue light emitted from the surface of the light emitting diode of the LED chip 50 passes through the fluorescent material, the fluorescent material fluoresces. Accordingly, white light is generated and emitted from the LED chip 50 by the blue light emitted from the light emitting diode and the light emitted by the fluorescent substance fluorescent.
Here, the LED chip 50 is exemplified by a chip in which a YAG (yttrium / aluminum / garnet) fluorescent material is applied to the surface of a GaN-based light-emitting diode, InGaN-based light-emitting diode, or the like.

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

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

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

In addition, since the LED chip 50 can make the light source 28 thinner, it is preferable that the LED chip 50 has a rectangular shape with a short side in the thickness direction of the light guide plate 30. LED chips having various shapes such as a shape, a polygonal shape, and an elliptical shape can be used.
In this embodiment, the LED chips are arranged in a single row to form a single layer structure. However, the present invention is not limited to this, and a plurality of LED arrays having a plurality of LED chips 50 arranged on an array support are provided. A multilayer LED array having a laminated structure can also be used as a light source. Even when LED arrays are stacked in this manner, more LED arrays can be stacked by making the LED chip 50 rectangular and thinning the LED array. In this way, a larger amount of light can be output by stacking multilayer LED arrays and increasing the filling rate of the LED arrays (LED chips). In addition, the LED chip of the LED array in the layer adjacent to the LED chip of the LED array preferably has the arrangement interval satisfying the above formula as described above. In other words, the LED array is preferably laminated with the LED chip and the LED chip of the LED array in the adjacent layer separated by a predetermined distance.

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

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

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

Here, in the present invention, the light guide length L through which the light between the first light incident surface 30c and the second light incident surface 30d propagates is intended for the liquid crystal panel 12 having a screen size of 20 inches (inch) or more. Therefore, it is necessary to be 260 mm or more, and since it is intended for the liquid crystal panel 12 having a screen size of a maximum of 100 inches (inch), it is preferably 1350 mm or less. For example, for a screen size of 20 inches (inch), the light guide length L is 260 mm to 270 mm, and is around 40 inches (inch), that is, 37 inches (inch), 40 inches (inch), 42 inches. For screen sizes of (inch) and 46 type (inch), the light guide length L is not less than 500 mm and not more than 630 mm. Specifically, the screen size of 40 type (inch) is 539 mm. In the vicinity of 55-inch (inch), ie, 52-inch (inch), 55-inch (inch) and 65-inch (inch) screen sizes, the light guide length L is 700 mm or more and 880 mm or less, Is 700 mm with a 52-inch (inch) screen size. For example, for a 100-inch (inch) screen size, the light guide length L is preferably 1250 mm to 1350 mm.
In the case of the both-side incident light guide plate 30 shown in FIGS. 3, 5, 6 and the like, the light incident on the first light incident surface 30c and the second light incident surface 30d is centered from the respective incident surfaces 30c and 30d. Therefore, the light guide length of the light incident from each of the incident surfaces 30c and 30d may be half the distance between the both incident surfaces 30c and 30d, but in the present invention, the light guide length L Represents the overall light guide length, and in the case of bilateral incidence, it is defined by the distance between the first light incidence surface 30c and the second light incidence surface 30d, and in the case of single side incidence as shown in FIG. Is defined as the distance between the light incident surface 80c and the side surface 80d.

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

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

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

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

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

In the light guide plate 30 according to the first aspect of the present invention, the scattering particles are dispersed at different particle concentrations in the first layer 60 and the second layer 62, but from the light incident surfaces 30c and 30d, respectively, the light exit surface. The combined scattering cross section S per unit length of the first layer 60 and the second layer 62 in the light guide position along the direction substantially parallel to 30a in the direction substantially perpendicular to the light exit surface 30a is the light incident surface. It is necessary to be distributed so as to have at least a portion that continuously and monotonously increases as the distance from 30c and 30d increases, that is, as the light guide position (length or distance) increases. That is, in the light guide plate 30, the combined scattering cross section S per unit length continuously increases monotonically from the minimum value or the minimum value according to the light guide distance from the light incident surfaces 30c and 30d, or the maximum value or It is necessary to have a portion that reaches the maximum value.
Although details will be described later, the first layer 82 and the second layer 84 of the light guide plate 80 incident on one side (one side) of the backlight unit 70 shown in FIG. This is the same as the first layer 60 and the second layer 62 of the optical plate 30. In the following description, the first layer 60 and the second layer 62 of the light guide plate 30 that are incident on both sides will be described as representative examples, and the same description will be omitted. The first layer 82 and the second layer 84 will also be described.

The maximum value S _max and the minimum value S _min of the combined scattering cross section S per unit length must satisfy the following formula (1).
A ・ k ≦ S _max ≦ B ・ k
C ・ k ≦ S _min ≦ D ・ k (1)
Here, the coefficient k is the reciprocal of the ratio of the screen size V or the light guide length L to the reference screen size V ₀ or the light guide length L ₀ (k = V ₀ / V = L ₀ / L), and A , B, C, and D are constants determined by the reference screen size V ₀ or the reference light guide length L ₀ .
Here, in the light guide plate of the present invention, the maximum value S _max and the minimum value S _min of the combined scattering cross section S per unit length have a large and thin shape by satisfying the above formula (1). However, it is possible to emit light with high light utilization efficiency and less unevenness in brightness, and a light distribution near the center of the screen, which is required for large-screen thin LCD TVs, compared to the periphery, so-called medium-high or bell A medium-high distribution of brightness can be obtained.

When the reference screen size V ₀ is a 20-inch (inch) screen size or when the reference light guide length L ₀ is 269.5 mm, constants A (mm ² ), B (mm ² ), The values of C (mm ² ) and D (mm ² ) are
In the case of double-sided incidence as shown in FIGS. 3, 5, 6, etc., A = 0.833 (mm ² ), B = 2.150 (mm ² ), C = 0.672 (mm ² ), D = 1.590 (mm ² )
On the other hand, in the case of one-side incidence as shown in FIG. 17 and the like described later, A = 1.000 (mm ² ), B = 1.761 (mm ² ), C = 0.500 (mm ² ), D = It is preferable that it is 0.645 (mm < ² >).

That is, in the case of such a both side incident, for example, screen size V is a reference picture size _{V 0} which 20-inch (inch), light guiding length L is the reference light guiding length _{L 0} of 269.5mm In the case, the above formula (1) is represented by the following formula (1a).
0.833 (mm ² ) ≦ S _max ≦ 2.150 (mm ² )
0.672 (mm ² ) ≦ S _min ≦ 1.590 (mm ² ) (1a)
For example, when the screen size V is 40 inches (inch) and the light guide length L is 539 mm, the above equation (1) is expressed by the following equation (1b).
0.417 (mm ² ) ≦ S _max ≦ 1.075 (mm ² )
0.336 (mm ² ) ≦ S _min ≦ 0.795 (mm ² ) (1b)
For example, when the screen size V is 46 type (inch) and the light guide length L is 620 mm, the above formula (1) is expressed by the following formula (1c).
0.362 (mm ² ) ≦ S _max ≦ 0.935 (mm ² )
0.292 (mm ² ) ≦ S _min ≦ 0.691 (mm ² ) (1c)
Further, for example, when the screen size V is 100 inches (inch) and the light guide length L is 1347.5 mm, the above equation (1) is expressed by the following equation (1d).
0.167 (mm ² ) ≦ S _max ≦ 0.430 (mm ² )
0.135 (mm ² ) ≦ S _min ≦ 0.318 (mm ² ) (1d)

From the above, in the case of both-side incidence, when the screen size V is in the range from 20 inches (inch) to 100 inches (inch), as shown in the graphs of FIGS. )) As the horizontal axis and the maximum value S _max and the minimum value S _min of the combined scattering cross section S as the vertical axis, the maximum value S _max (mm ² ) of the combined scattering cross section S is 4 points (20 , 0.833), (40, 0.417), (46, 0.362) and (100, 0.167) and four points (20, 2.150), (40, 1.075), (46, 0.935) and a region surrounded by a hyperbolic line segment passing through (100, 0.430), and the minimum value S _min (mm ^2), four points (20,0.672), (40,0.336), (46,0.29 ) And (100, 0.135) and a hyperbolic line segment and four points (20, 1.590), (40, 0.795), (46, 0.691) and (100, 0.318) It is preferable that it exists in the area | region enclosed with the hyperbolic line segment which passes through.

In the case of one-side incidence, for example, when the screen size V is a 20-inch (inch) reference screen size V ₀ and the light guide length L is a reference light guide length L ₀ of 269.5 mm. The above formula (1) is represented by the following formula.
In the case of such both-side incidence, for example, when the screen size V is a 20-inch (inch) reference screen size V ₀ and the light guide length L is a reference light guide length L ₀ of 269.5 mm. Is represented by the following formula (1e).
1.000 (mm ² ) ≦ S _max ≦ 1.761 (mm ² )
0.500 (mm ² ) ≦ S _min ≦ 0.645 (mm ² ) (1e)
For example, when the screen size V is 40 inches (inch) and the light guide length L is 539 mm, the above equation (1) is expressed by the following equation (1f).
0.500 (mm ² ) ≦ S _max ≦ 0.881 (mm ² )
0.250 (mm ² ) ≦ S _min ≦ 0.323 (mm ² ) (1f)
For example, when the screen size V is 46 type (inch) and the light guide length L is 620 mm, the above formula (1) is expressed by the following formula (1g).
0.435 (mm ² ) ≦ S _max ≦ 0.766 (mm ² )
0.217 (mm ² ) ≦ S _min ≦ 0.280 (mm ² ) (1 g)
For example, when the screen size V is 100 inches (inch) and the light guide length L is 1347.5 mm, the above formula (1) is expressed by the following formula (1h).
0.200 (mm ² ) ≦ S _max ≦ 0.352 (mm ² )
0.100 (mm ² ) ≦ S _min ≦ 0.128 (mm ² ) (1h)

From the above, in the case of single-sided incidence, when the screen size V is in the range from 20 inches (inch) to 100 inches (inch), as shown in the graphs of FIGS. )) As the horizontal axis and the maximum value S _max and the minimum value S _min of the combined scattering cross section S as the vertical axis, the maximum value S _max (mm ² ) of the combined scattering cross section S is 4 points (20 , 1.000), (40, 0.500), (46, 0.435) and (100, 0.200) and four points (20, 1.761), (40, 0.881), (46, 0.766), and preferably within a region surrounded by hyperbolic line segments passing through (100, 0.352), and the minimum value S _min (mm ^2), four points (20,0.500), (40,0.250), (46,0.21 ) And (100, 0.10) and a hyperbolic line segment and four points (20, 0.645), (40, 0.323), (46, 0.280) and (100, 0.128) It is preferable that it exists in the area | region enclosed with the hyperbolic line segment which passes through.

Here, the synthetic scattering cross section S [mm ² ] per unit length can be calculated from the following formulas (4), (5) and (6) as follows.

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

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

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

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

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

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

Here, a preferable example of scattering particles dispersed in the first layer 60 and the second layer 62 of the light guide plate 30 will be described.
Here, the particle size of the scattering particles dispersed in the first layer 60 and the second layer 62 of the light guide plate 30 of the present invention is not particularly limited, but the particle size of the scattering particles dispersed in the second layer 62 is It is preferably 4.5 μm or more and 12.0 μm or less. The reason is that high scattering efficiency can be obtained, the forward scattering property is large, the wavelength dependency is small, and color unevenness can be selected.
In addition, regarding the selection of the optimum particle size of the scattering particles to be dispersed in the first layer 60 and the second layer 62 of the light guide plate 30 of the present invention, it is preferable to consider the following points in addition to the viewpoint of wavelength dependence. .
First, in the scattered light intensity distribution (angular distribution) by a single particle, it is preferable to satisfy the condition that the light scattered in the forward 0 to 5 ° is 90% or more. This is because, for example, when the light guide plate 30 of the present invention corresponds to a screen size of 100 inches (inch), the distance from the light incident surface 30c and the second light incident surface 30d on the side surface of the light guide plate 30 is at least 675 mm or more. In the case of the one-side incident light guide plate 80 to be described later, it is necessary to guide a distance of at least 1350 mm or more from the light incident surface 80c (see FIG. 17).

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

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

  In addition, as described above, the particle concentration of the scattering particles is preferably different between the first layer 60 and the second layer 62 of the light guide plate 30, but the light guide length of the light guide plate 30 of the present invention is 260 mm to 1350 mm. In the case of the first layer 60, it is preferably 0.0004 wt% or more and 0.195 wt% or less, and in the second layer 62, it is preferably 0.001 wt% or more and 4.438 wt% or less.

  That is, when the light guide length L is 260 mm to 1350 mm, in the first layer 60, the particle diameter is 4.5 μm or more and 12.0 μm or less, and the particle concentration is 0.0004 wt% or more and 0.195 wt% or less. In the second layer 62, the particle diameter is preferably 4.5 μm or more and 12.0 μm or less, and the particle concentration is 0.001 wt% or more and 4.438 wt% or less.

Specifically, in the first layer 60, when the particle diameter is 4.5 μm, the particle concentration may be 0.0004 wt% or more and 0.048 wt% or less, and when the particle diameter is 7.0 μm, The concentration is preferably 0.0006 wt% or more and 0.075 wt% or less, and when the particle diameter is 12.0 μm, the particle concentration is preferably 0.0015 wt% or more and 0.195 wt% or less.
That is, in the first layer (upper layer) 60, as shown in the graph of FIG. The particle size and particle concentration of the particles are 6 points (4.5, 0.0004), (4.5, 0.048), (7.0, 0.0006), (7.0, 0.075). , (12.0, 0.0015) and (12.0, 0.195).
Similarly, in the case of the first layer (upper layer) 82 of the one-side incident light guide plate 80 shown in FIG.

In the second layer 62, when the particle diameter is 4.5 μm, the particle concentration is preferably 0.001 wt% or more and 1.085 wt% or less, more preferably 0.002 wt% or more and 0.580 wt%. Hereinafter, most preferably 0.022 wt% or more and 0.452 wt% or less, and when the particle diameter is 7.0 μm, the particle concentration is 0.001 wt% or more and 1.663 wt% or less. More preferably, it is 0.002 wt% or more and 0.707 wt% or less, and most preferably 0.027 wt% or more and 0.551 wt% or less. When the particle diameter is 12.0 μm, the particle concentration is It is preferably 0.002 wt% or more and 4.438 wt% or less, more preferably 0.008 wt% or more and 2.869 wt% or less, and most preferably 0.108 w. % Or more, is good for more than 2.235wt%.
That is, in the second layer (lower layer) 62, as shown in the graph in FIG. 10, when the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the scattering particles, The particle size and particle concentration of the particles are 6 points (4.5, 0.001), (4.5, 1.085), (7.0, 0.001), (7.0, 1.893). , (12.0, 0.002) and (12.0, 4.438).
In the case of the second layer (lower layer) 84 (see FIG. 17) of the one-side incident light guide plate 80, similarly, the particle diameter and particle concentration of the scattering particles are preferably in the above-mentioned region, more preferably When the particle diameter is 4.5 μm, the particle concentration is 0.001 wt% or more and 0.363 wt% or less, most preferably 0.010 wt% or more and 0.363 wt% or less, and the particle diameter is 7.0 μm, 0.001 wt% or more and 0.443 wt% or less, most preferably 0.012 wt% or more and 0.443 wt% or less, and when the particle size is 12.0 μm, 0.002 wt% or more and 1.797 wt% or less, most Preferably, it is good to set it as 0.049 wt% or more and 1.797 wt% or less.

  As described above, in the light guide plate 30 of the present invention, the particle size and the particle concentration of the scattering particles in the first layer 60 and the second layer 62 are the first layer 82 and the second layer 84 of the one-side incident light guide plate 80. Similarly, in the case of (see FIG. 17), the reason why it is necessary to be within the region surrounded by the six points in the graphs shown in FIG. 9 and FIG. This is because a medium-high luminance distribution of more than 0% and less than 45% cannot be realized, and when the particle concentration is too low, light penetrates through and does not satisfy the light utilization efficiency of 70% or more. 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, but the light utilization efficiency is low. is there.

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

Moreover, the thickness of the sheet-like light guide plate of the present invention needs to be 1.2 mm or less as described above. That is, the thickness of the sheet-like light guide plate of the present invention is such that a dot pattern that is not a problem with a light guide plate having a thickness of more than 1.2 mm, particularly a conventional printed light guide plate with a thickness of about 4 mm is recognized. Therefore, it may be a film-like light guide sheet.
In particular, in the present invention, a film-like light guide plate having a thickness of 1 mm or less, that is, a so-called light guide sheet is preferable.
In addition, as a method for producing a film-shaped light guide plate in which scattering particles having different particle concentrations are kneaded and dispersed in the two layers of the present invention, a base film containing scattering particles as a first layer is formed by an extrusion molding method or the like. After applying the monomer resin liquid (transparent resin liquid) in which the scattering particles are dispersed on the prepared base film, the monomer resin liquid is cured by irradiating with ultraviolet rays or visible light, thereby obtaining a desired In addition to a method of producing a second layer having a particle concentration to form a film-shaped light guide plate, there are a two-layer extrusion molding method and the like.
In particular, even when the light guide plate is a film-like light guide sheet having a thickness of 1 mm or less, by using a two-layer light guide plate, the illuminance distribution is increased to a medium-high ratio at a suitable ratio while improving the light utilization efficiency. be able to.

  The thinner the light guide plate is, the lighter the light guide plate is, and there is an advantage that the material cost can be reduced. However, if the thickness is too small, the light incident surface becomes smaller, the size of the light source becomes smaller, and the amount of light is less. Therefore, light incidence from the light source is reduced, and light with sufficient luminance cannot be emitted from the light emission surface. On the other hand, if the thickness is too large, the weight is too heavy to be suitable as an optical member such as a liquid crystal display device, and if the diffusing particles are dispersed at a particle concentration that achieves a medium-high luminance distribution, light penetrates through the periphery. If the diffusion particles are dispersed at a particle concentration that increases the light utilization efficiency, the medium-high luminance distribution cannot be realized. Therefore, what is necessary is just to select the kind (size) of a light source, and the thickness of a light-guide plate according to the use application of a light-guide plate. In the present invention, with a 1.2 mm light guide plate, if a 3 × 1.4 mm LED having a width of the light emitting portion in the light guide plate thickness direction of about 1 to 1.1 mm is used as a light source from the required performance. good. In addition, there is no such restriction in an illumination application that can be used as indirect illumination even with a small amount of light, so that an LED of about 0.1 to 0.5 mm that is used for a mobile phone can be used. Therefore, the film-like light guide sheet of the present invention having a thickness of 0.1 mm or more and 1 mm or less can be used.

In addition, the thickness and shape of the first layer 60 and the second layer 62 of the light guide plate 30 of the present invention, for example, the arcs R1 and R2, are dispersed in the first layer 60 and the second layer 62. The thickness should satisfy the above-described scattering particle dispersion condition of the present invention including the above formula (1), but is not particularly limited as long as the scattering particle dispersion condition is satisfied. However, the thickness and shape of the first layer 60 and the second layer 62 are determined depending on the ease of manufacturing, for example, restrictions such as an extrusion apparatus that simultaneously melt-extrudes two layers and a line speed for melt-extrusion. do it.
For example, in the case of the light guide plate 30, it is preferable that the maximum thickness of the second layer 62 is closer to the thickness of the light guide plate 30 in order to realize manufacturing stability and high efficiency. The ratio of the minimum thickness of the second layer 62 is more preferably 1/4 or less with respect to the maximum thickness, and about 1/10 is most preferable in consideration of manufacturing stability.

In addition, the shape of the second layer 62, that is, the uneven curves, for example, the arcs R1 and R2, may be determined according to the size of the light guide plate 30, the maximum thickness and the minimum thickness of the second layer 62, and the like.
For example, in the 1.2 mm light guide plate 30, when the light guide length L is 260 mm ≦ L ≦ 1350 mm, the radius of curvature R1 of the convex arc R1 that is the maximum thickness of the second layer 62 described above is 1417 mm ≦ The radius of curvature R2 of the concave arc R2 that is R1 ≦ 8443750 mm and the minimum thickness of the second layer 62 described above is preferably 3333 mm ≦ R2 ≦ 866667 mm. Here, when the light guide length L is 260 mm ≦ L ≦ 270 mm, the curvature radii R1 and R2 are more preferably 1417 mm ≦ R1 ≦ 35000 mm, 3333 mm ≦ R2 ≦ 33333 mm, and the light guide length L is 500 mm ≦ L. When ≦ 615 mm, it is more preferable that 5000 mm ≦ R1 ≦ 135000 mm, 13333 mm ≦ R2 ≦ 135000 mm, and when the light guide length L is 700 mm ≦ L ≦ 850 mm, 12991 mm ≦ R1 ≦ 356586 mm, 35556 mm ≦ R2 ≦ 366667 mm is more preferable, and when the light guide length L is 1250 mm ≦ L ≦ 1350 mm, it is more preferable that 307996 mm ≦ R1 ≦ 843750 mm and 81197 mm ≦ R2 ≦ 866667 mm.

In addition, what is necessary is just to change the said range according to the difference, when the thickness of the light-guide plate 30 differs from 1.2 mm.
For example, in the light guide plate 30 of 0.6 mm, when the light guide length L is 260 mm ≦ L ≦ 1350 mm, the above-mentioned radius of curvature R1 is 2833 mm ≦ R1 ≦ 1687500 mm, and the above-mentioned radius of curvature R2 is 6667 mm ≦ R2. It is preferable that ≦ 1733333 mm. That is, in the 0.6 mm light guide plate 30, both a preferable numerical range and a more preferable numerical range may be set to twice the numerical value in the case of 1.2 mm.
Further, in the 0.3 mm light guide plate 30, when the light guide length L is 260 mm ≦ L ≦ 1350 mm, the curvature radius R1 is 5667 mm ≦ R1 ≦ 3375000 mm, and the curvature radius R2 is 13333 mm ≦ R2. It is preferable that ≦ 3466667 mm. That is, in the 0.3 mm light guide plate 30, the preferable numerical range and the more preferable numerical range may be set to 4 times the numerical value in the case of 1.2 mm or twice the numerical value in the case of 0.6 mm. .
Furthermore, in the case of one-side (one side) incidence described later shown in FIG. 17, it may be four times that in the case of the above-described two-side (two sides) incidence shown in FIGS. For example, in the case of a plate thickness of 1.2 mm, when the light guide length L is 1040 mm ≦ L ≦ 5400 mm, the curvature radius R1 of the convex arc R1 that is the maximum thickness of the second layer 62 described above is It is preferable that the radius of curvature R2 of the concave arc R2 which is 5667 mm ≦ R1 ≦ 3375000 mm and the minimum thickness of the second layer 62 described above is 13333 mm ≦ R2 ≦ 3466667 mm.

The light guide plate of the present invention is basically configured as described above, but can be designed as follows.
FIG. 11 is a flowchart showing an example of the light guide plate designing method of the present invention.
Below, the 1st layer (henceforth upper layer) 60 and 2nd layer which are used for the backlight unit 20 of the liquid crystal display device 10 shown in FIG.1 and FIG.2 and are shown in FIG.2, FIG.3, FIG.5 and FIG. A case where a two-layer light guide plate 30 made of (hereinafter also referred to as a lower layer) is designed will be described as a representative example.
First, as shown in FIG. 11, in step S10, from the screen size (effective screen area of the light emitting surface 30a) of the liquid crystal display device 10 to which the backlight unit 20 using the light guide plate 30 of the present invention is applied, the screen is changed. The light guide length L is determined by adding 10 to 30 mm as the width of the so-called frame as the length (including the mixing zone length) of the portion covered with the upper casing 44 to the short side length of the size. Strictly speaking, the light guide length L is determined in consideration of the installation position of the light source 28 (distance between the light emitting surface of the LED and the light incident surfaces 30c and 30d of the light guide plate 30).

Next, in step S12, the backlight unit 20 is configured so that the deflection rigidity D of the entire backlight unit 20 satisfies the above formula (2) based on the application, screen size, and determined light guide length L. The material, thickness, and the number of members of the plurality of constituent members, that is, the material and thickness of the light guide plate 30, and the material and thickness of the constituent components of the housing 26 are determined.
That is, using the material and thickness of the light guide plate 30, the material and thickness of the components of the housing 26, and the material and thickness of the optical member used, the deflection rigidity D of the backlight unit 20 as a whole is expressed by the above equation. The material, thickness, and number of members of the constituent members, that is, the material and the thickness of the light guide plate 30 so that the flexural rigidity D obtained from (3) satisfies the flexural rigidity condition of the above formula (2), The combination of the material and thickness of the component parts of the housing 26 and the material and thickness of the optical member used is obtained. Thus, the material and thickness of the light guide plate 30 are determined.
Subsequently, in step S14, the cross-sectional shape (the cross-sectional shape perpendicular to the screen and parallel to the short side of the screen size) of the lower layer 62 of the light guide plate 30 is determined. Specifically, the lower layer maximum thickness and the lower layer minimum thickness (upper layer maximum thickness) are determined according to the thickness of the light guide plate 30, and based on them, the maximum value of the lower layer thickness (lower layer maximum thickness) ) And two concave arcs R2 constituting the minimum value of the lower layer thickness (lower layer minimum thickness) are determined. As a result, the cross-sectional shape of the upper layer 60 of the light guide plate 30 is also automatically determined.
For example, when the screen size of the light guide plate 30 is 40, the light guide length L is 540 mm, and the thickness is 1.0 mm, the cross-sectional shape of the lower layer 62 is shown by a solid line, a dotted line, and a one-dot chain line in FIG. Three lower layer cross sections A, B and C can be determined.
Table 1 shows the lower layer maximum thickness, the lower layer minimum thickness, the convex arc R1 that constitutes the maximum value, and the concave arc R2 that constitutes the minimum value.

Next, in step S16, based on the determined cross-sectional shapes of the lower layer 62 and the upper layer 60, the combined scattering cross section S per unit length at the light guide position x is obtained from the above formulas (4) to (6). The diffusion particle dispersion condition is determined so that the obtained combined scattering cross section S satisfies the above formula (1). As described above, in the case of a double-sided light guide plate having a screen size V of 40 inches (inch) and a light guide length L of 540 mm, the condition of the combined scattering cross section S is expressed by the above formula ( 1) is represented by the above formula (1b).
For example, specifically, as the diffusion particle dispersion condition, the base material resin of the light guide plate 30, the material and particle size of the diffusion particle, the particle concentration of the upper layer 60 and the lower layer 60, and the like are determined.
In the present invention, when the cross-sectional shape of the lower layer 62 is different, for example, even in the case of the lower layer cross sections A to C shown in FIG. The combined scattering cross section distribution can be made.

For example, when the light guide length L of the light guide plate 30 is 540 mm, the thickness is 1.0 mm, and the cross-sectional shape of the lower layer 62 of the light guide plate is the lower layer cross section B shown in FIG. 13 can be obtained from the above formulas (4) to (6). The upper layer particle concentrations of the five design examples 1 to 5 are 0.004 wt%, and the lower layer particle concentrations of the design examples 1 to 5 are 0.169 wt%, 0.208 wt%, and 0.096 wt%, respectively. 0.227 wt% and 0.267 wt%.
From the graph of FIG. 13 showing the distribution of the combined scattering cross sections S of the five design examples 1 to 5 thus obtained, the design examples 1 to 3 satisfy the above formula (1), that is, the above formula (1b). It can be seen that the design examples 4 to 5 do not satisfy the above formula (1), that is, the above formula (1b).

Subsequently, in step S18, the light guide plate 30 thus designed is subjected to (a) use efficiency of incident light, (b) medium to high altitude of luminance distribution of light emitted from the light emission surface 30a, and (c) light emission surface. Optical evaluation is performed on the three items of the uneven shape at the center of 30a, and it is examined whether or not the set values of these three items are satisfied.
For example, as a result of optical evaluation of five design examples 1 to 5 of the light guide plate having the combined scattering cross-section distribution shown in FIG. 13, the design examples 1 to 3 satisfying the above formula (1b) The luminance distribution of the emitted light from 30a is a desired medium-high luminance distribution, but Design Examples 4 to 5 that do not satisfy the above formula (1b) have a concave shape and do not have the desired medium-high luminance distribution.
That is, in Design Examples 1 to 3 that satisfy the above formula (1b), (a) the utilization efficiency is 77%, 77%, and 72%, respectively, (b) the intermediate altitude is 26%, 17%, and 39%, (C) All the concave and convex shapes in the central part are convex shapes, and the set values of (a) 70% or more of each set value, (b) more than 0% and less than 45%, and (c) convex values of three items are specified. Satisfied.

In contrast, design examples 4 and 5 in which the maximum value S _max and the minimum value S _{min of} the combined scattering cross section S are both higher than the lower limit value of the above equation (1b) and do not satisfy the above equation (1b) are ( a) Both usage efficiencies are as high as 78% and satisfy the specified value, but (c) the uneven shape in the central part has a concave luminance distribution in the central part, and (b) the intermediate altitude is less than 0%. For this reason, the brightness of the central portion is lowered, and the vicinity of the central portion is visually recognized as band unevenness.

FIG. 14 shows the evaluation results for two items of (a) utilization efficiency and (b) medium to high degree for a large number of light guide plates 30 designed in this way.
FIG. 14 is a graph showing incident light utilization efficiency [%] and outgoing light medium altitude [%] with respect to the particle concentration [wt%] of the second layer (lower layer) for a number of designed light guide plates. .
An example of a method for determining the particle concentration of the lower layer 62 will be described with reference to FIG.
First, parameters other than the particle concentration of the lower layer 62 are set as follows.

Next, the particle concentration range of the scattering particles of the lower layer 62 can be determined by the following procedure.
First, from the graph of FIG. 14, to determine the extent of particle concentration x ₁ comprising (a) and the utilization efficiency of the incident light is 70% or more. As a result, x ₁ ≧ 0.061 [wt%] can be obtained as the particle concentration range.
Next, from the graph of FIG. 14, the range of the particle concentration x _{2 in which} the intermediate altitude (b) is more than 0% and less than 45% is determined. As a result, x ₂ ≧ 0.208 [wt%] can be obtained as the particle concentration range.
Subsequently, (c) the range of the particle concentration x _{3 in} which the uneven shape at the center of the luminance distribution is not concave is determined. As a result, x ₃ ≦ 0.208 [wt%] can be obtained as the particle concentration range.
From the particle concentration ranges x ₁ , x ₂ , and x ₃ thus obtained, the applicable particle concentration range of the lower layer 62 can be determined as 0.061 ≦ x ≦ 0.208 [wt%].

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

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

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

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

In this embodiment, the optical member unit is composed of the two diffusion sheets 32a and 32c and the prism sheet 32b disposed between the two diffusion sheets. However, the arrangement order and arrangement of the prism sheets and the diffusion sheets are not limited. The number is not particularly limited, and is also not particularly limited as a prism sheet or a diffusion sheet, and the brightness unevenness and the illumination unevenness of the illumination light emitted from the light exit surface 30a of the light guide plate 30 can be further reduced. If there are, various optical members can be used.
For example, as an optical member, in addition to or instead of the above-described diffusion sheet and prism sheet, a transmittance adjusting member in which a large number of transmittance adjusting bodies made of a diffuse reflector are arranged in accordance with luminance unevenness and illuminance unevenness is also used. You can also. Further, the optical member unit may have a two-layer configuration using one prism sheet and one diffusion sheet, or using only two diffusion sheets.

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

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

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

The lower guide reflection plate 38 is disposed on the back surface 30 b side of the light guide plate 30 so as to cover a part of the light source 28. The end of the lower guide reflector 38 on the center side of the light guide plate 30 is connected to the reflector 34.
Here, as the upper guide reflector 36 and the lower guide reflector 38, various materials used for the reflector 34 described above can be used.
By providing the lower guide reflection plate 38, it is possible to prevent light emitted from the light source 28 from entering the light guide plate 30 and leaking to the back surface 30 b side of the light guide plate 30.
Thereby, the light emitted from the light source 28 can be efficiently incident on the first light incident surface 30c and the second light incident surface 30d of the light guide plate 30, and the light utilization efficiency can be improved.
In addition, in this embodiment, although the reflecting plate 34 and the lower induction | guidance | derivation reflecting plate 38 were connected, it is not limited to this, Each is good also as a separate member.

Here, the upper guide reflector 36 and the lower guide reflector 38 reflect the light emitted from the light source 28 toward the first light incident surface 30c or the second light incident surface 30d, and the light emitted from the light source 28 is reflected. The shape and width are not particularly limited as long as the light can be incident on the first light incident surface 30c and the second light incident surface 30d and the light incident on the light guide plate 30 can be guided to the center side of the light guide plate 30.
In the present embodiment, the upper guide reflector 36 is disposed between the light guide plate 30 and the diffusion sheet 32a. However, the position of the upper guide reflector 36 is not limited to this, and constitutes the optical member unit 32. You may arrange | position between sheet-like members, and may arrange | position between the optical member unit 32 and the upper housing | casing 44. FIG.
The reflector 34, the upper guide reflector 36, and the lower guide reflector 38 described above are used for efficiently emitting the light emitted from the light source 28 from the light exit surface 30a of the light guide plate 30. The optical member has a function of reflecting light outside the light guide plate 30 into the light guide plate 30.

Next, the housing 26 will be described.
As shown in FIG. 2, the housing 26 accommodates and supports the lighting device main body 24, and is sandwiched and fixed from the light emitting surface 24 a side and the back surface 30 b side of the light guide plate 30. It has a body 42, an upper housing 44, a folding member 46, and a support member 48.

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

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

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

Thus, by arranging the folding member 46 between the lower housing 42 and the upper housing 44, the rigidity of the housing 26 can be increased, and the light guide plate 30 can be prevented from warping. As a result, for example, there is no unevenness in brightness and unevenness in illuminance, or a small amount of light can be emitted efficiently, but even when a light guide plate that is likely to warp is used, the warp can be corrected more reliably or guided. It is possible to more reliably prevent the optical plate from being warped, and light with reduced or reduced brightness and illuminance unevenness can be emitted from the light exit surface.
In addition, various materials, such as a metal and resin, can be used for the upper housing | casing of a housing | casing, a lower housing | casing, and a folding member. In addition, as a material, it is preferable to use a lightweight and high-strength material.
In the present embodiment, the folding member is a separate member, but it may be formed integrally with the upper housing or the lower housing. Moreover, it is good also as a structure which does not provide a folding | turning member.

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

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

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

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

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

  For example, as in the light guide plate 31a shown in FIG. 15A, the cross-sectional shape of the boundary surface z in the cross section is such that the thickness of the second layer 62 is the central portion of the light emitting surface 30a (that is, the bisector α). A linear portion L1 parallel to the light emitting surface 30a and having a maximum (maximum) in the vicinity of the first light incident surface 30c. The thickness of the second layer 62 is connected to the linear portion L1 from the linear portion L1. And two curves convex toward the light exit surface 30a (two arcs R3 having a radius of curvature R3), which continuously change so as to become thinner toward the second light incident surface 30d, and the two convex shapes Each of the second layers 62 has a minimum thickness before the first light incident surface 30c and the second light incident surface 30d, and the first light incident surface 30c and the second light input surface 30c are respectively connected to the curved lines smoothly. The thickness of the second layer 62 increases toward the light incident surface 30d. Continuously changes to the light incident surface 30c as, (two arcs R4 radius of curvature R4) two concave curves which are connected to 30d and may be composed of four arcs having.

For example, as in the light guide plate 31b shown in FIG. 15B, the cross-sectional shape of the boundary surface z in the above cross section is such that the thickness of the second layer 62 is the central portion of the light emitting surface 30a (that is, the bisector α). The first convex curve (for example, the arc R5 having a radius of curvature R5) having a local maximum (maximum) in the vicinity, and the first convex curve smoothly connected to the back surface 30b and the light respectively. A so-called kamaboko having three arcs having two second convex curves (for example, two arcs R6 having different radii of curvature R6) connected to the connection parts (corner parts) with the incident surfaces 30c and 30d. It may be a shape.
In this example as well, a straight line portion is included in the connection portion between the first convex curve and the second convex curve and the connection portion between the second convex curve and the corner portion of the connection portion. Also good. Further, the second convex curve may be connected to the connection portion with the light incident surfaces 30c and 30d instead of the corner portion, or connected to the back surface 30b in the vicinity of the light incident surfaces 30c and 30d. Also good.

For example, as in the light guide plate 31c shown in FIG. 15C, the cross-sectional shape of the boundary surface z in the cross section has a maximum (maximum) thickness of the second layer 62 at the central portion of the light emitting surface 30a. A straight line portion L2 parallel to the light emission surface 30a and the second layer 62 connected to the straight line portion L2 are thinner from the straight line portion L2 toward the first light incident surface 30c and the second light incident surface 30d, respectively. It consists of two circular arcs (kamaboko shape) having two convex curves (for example, two circular arcs R7 having a radius of curvature R7) connected continuously to the light incident surfaces 30c and 30d. There may be.
In this example as well, a straight line portion may be included in the connection portion between the convex curve and the light incident surfaces 30c and 30d. Further, the convex curve may be connected to a connection portion between the back surface 30b and the light incident surfaces 30c and 30d, and not the light incident surfaces 30c and 30d but the back surface 30b in the vicinity of the light incident surfaces 30c and 30d. It may be connected.

For example, as in the light guide plate 31d shown in FIG. 15D, the cross-sectional shape of the boundary surface z in the cross-section is such that the thickness of the second layer 62 is the central portion of the light emitting surface 30a (that is, the bisector α Top) One convexity connected to the light incident surfaces 30c and 30d by maximizing (maximum) in the vicinity and continuously changing so as to become thinner toward the first light incident surface 30c and the second light incident surface 30d, respectively. (For example, two circular arcs R8 having a radius of curvature R8) may be a single circular arc (kamaboko shape).
In this example as well, a straight line portion may be included in the connection portion between the convex curve and the light incident surfaces 30c and 30d. Further, the convex curve may be connected to a connection portion between the back surface 30b and the light incident surfaces 30c and 30d, and not the light incident surfaces 30c and 30d but the back surface 30b in the vicinity of the light incident surfaces 30c and 30d. It may be connected.

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

  Therefore, like the light guide plate 31e shown in FIG. 16A, the cross-sectional shape of the boundary surface z when viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 30a is excluded from the mixing zone M of the light emitting surface 30a. In the effective screen area E, it is formed in the same manner as the light guide plate 30 shown in FIGS. 2 and 6, that is, the thickness of the second layer 62 is set so that the first maximum value is taken at the central portion of the light emitting surface 30a. A convex curve (arc R1) is formed, and subsequently the second layer 62 is continuously changed so that the thickness thereof is reduced, and a concave curve is taken so as to take local minimum values in the vicinity of the light incident surfaces 30c and 30d, respectively. (Arc R2) is formed, and further thickened in the vicinity of the first light incident surface 30c and the second light incident surface 30d. In the mixing zone M on both sides, unlike the light guide plate 30, the second maximum value is obtained. After that, it changes continuously so that it becomes thinner again, and a concave curve (for example, an arc 9) may be formed of. In the light guide plate 31e, the thickness of the second layer 62 takes the second maximum value at the inner end of each mixing zone M, which is the position of the opening 44a of the upper housing 44, and the outer side of each mixing zone M. At the end, the boundary surface z coincides with the corners between the back surface 30b and the light incident surfaces 30c and 30d, and the thickness of the second layer 62 becomes zero.

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

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

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

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

  The light guide plates 31f, 31g, and 31h shown in FIGS. 16B to 16D are the thicknesses of the first layer 60 and the second layer 62 in the mixing zone M in the light guide plate 31e shown in FIG. Since the configuration is the same except that the shape of the boundary surface z from the light incident surfaces 30c and 30d to the position of the second maximum value is changed, the same portions are denoted by the same reference numerals and the following description is different. Do the site mainly.

Similarly, the light guide plate 31f shown in FIG. 16B includes a first layer 60 and a second layer 62 having a particle concentration higher than that of the first layer 60. However, the first layer in the mixing zone M is the first layer 60. The boundary surface z between 60 and the second layer 62 is connected to the position of the second maximum value, is a curved surface (for example, arc R10) convex toward the light exit surface 30a, and the light incident surfaces 30c and 30d The shape is connected to the corner with the back surface 30b.
In the light guide plates 31e and 31f shown in FIGS. 16A and 16B, the boundary surface z is a mixing zone M that is a region from the position of the second maximum value to the light incident surfaces 30c and 30d. Although the concave and convex curved surfaces are respectively formed toward the light emitting surface 30a, the present invention is not limited to this, and may be a flat surface or an uneven surface.

Unlike the light guide plate 31f shown in FIG. 16B, the light guide plate 31g shown in FIG. 16C has a second maximum value of the boundary surface z between the first layer 60 and the second layer 62 in the mixing zone M. The terminal portion from the position toward the light incident surfaces 30c and 30d is connected to the back surface 30b at the approximate center of the mixing zone M. Here, the position at which the terminal portion of the boundary surface z is connected to the back surface 30 b may not be substantially in the center as long as it is within the mixing zone M.
In the light guide plate 31g shown in FIG. 16C, the shape of the boundary surface z in the mixing zone M is a curved surface (for example, arc R11) convex toward the light exit surface 30a. However, the present invention is not limited to this, and may be a concave curved surface, a flat surface, or an uneven surface.

  In the light guide plate 31h shown in FIG. 16D, unlike the light guide plates 31e to 31g shown in FIGS. 16A to 16C, the boundary surface z between the first layer 60 and the second layer 62 is the first. In the mixing zone M, the position of the maximum value of 2 is eliminated, and only the first layer 60 is included. That is, the boundary surface z has a plane parallel to the light incident surfaces 30c and 30d through the position of the second maximum value, and the terminal end of the boundary surface z is on the back surface 30b at the inner end of the kissing zone M. The shape to be connected.

  As in the light guide plates 31e to 31h shown in FIGS. 16A to 16D, the shape of the boundary surface z is changed from the position of the first maximum value of the thickness of the second layer 62 toward the light incident surfaces 30c and 30d. By forming the second layer 62 so as to reduce the thickness, the particle concentration in the region (mixing zone M) from the position of the second maximum value to the light incident surface side 30c, 30d is changed to the second maximum value. The particle concentration is lower than that of the incident light to reduce the return light emitted from the light incident surface and the light emitted from the region (mixing zone M) near the light incident surface that is covered with the housing and is not used. The utilization efficiency of the light emitted from the effective area (effective screen area E) of the emission surface can be improved.

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

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

  FIG. 17 is a schematic cross-sectional view showing a part of a backlight unit using another example of the light guide plate of the present invention. The backlight unit 70 shown in FIG. 17 has the one-side incident light guide plate 80 instead of the light guide plate 30 shown in FIG. Since it has the same configuration as the backlight unit 20 except that it has the same configuration as the unit 20, the same components are denoted by the same reference numerals, detailed description thereof will be omitted, and different components will be described below. The explanation is mainly given.

The backlight unit 70 shown in FIG. 17 includes a light guide plate 80 and a light source 28 for making light incident on the light guide plate 80.
The light guide plate 80 has a light emitting surface 80a formed of a rectangular flat plane, and a back surface 80b that is located on the opposite side of the light emitting surface 80a, that is, on the back side, and is a flat plane having substantially the same shape as the light emitting surface 80a. A light incident surface 80c that is formed substantially perpendicular to the light exit surface 80a on one end surface on the long side of the light exit surface 80a and the light source 28 is opposed to, and a light incident surface 30c. Side surface 80d located on the opposite side, that is, the back side. The light emitting surface 80a, the back surface 80b, and the light incident surface 80c of the light guide plate 80 correspond to the light emitting surface 30a, the back surface 30b, and the first light incident surface 30c of the light guide plate 30 shown in FIG. The light source 28 is not disposed to face the side surface 80d of the light plate 80, and is different from the second light incident surface 30d of the light guide plate 30.

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

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

In the illustrated light guide plate 80, when the concave and convex curved surfaces of the boundary surface z are curves expressed by arcs in a cross section perpendicular to the longitudinal direction of the light incident surface, the concave shape The curvature radius R12 of the arc R12 is preferably 10,000 mm ≦ R12 ≦ 1,800,000 mm, and the curvature radius R13 of the convex arc 13 is preferably 10,000 mm ≦ R13 ≦ 1,960,000 mm. . By setting the arcs R12 and R13 in the above range, it is possible to make the illuminance distribution of the light more suitably medium-high. Further, in the case of one-side (one side) incidence described later shown in FIG. 17, which will be described later, it may be four times the case of the above-described two-side (two side) incidence shown in FIGS.
Note that the concave and convex curved surfaces forming the boundary surface z of the light guide plate 80 are not limited to arcs in a cross section perpendicular to the longitudinal direction of the light incident surface 80c, but are quadratic curves such as ellipses, parabolas, and hyperbolic curves. Of course, it may be a part of the above, a higher-order curve of 3rd order or higher, a curve represented by a polynomial, or a curve combining these.

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

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

In the illustrated light guide plate 81a, when the concave and convex curved surfaces of the boundary surface z are curves expressed by arcs in a cross section perpendicular to the longitudinal direction of the light incident surface, the concave shape The radius of curvature R14 of the arc R14 is preferably 10,000 mm ≦ R14 ≦ 1,800,000 mm, and the radius of curvature R15 of the convex arc R15 is preferably 10,000 mm ≦ R15 ≦ 1,960,000 mm. . Further, in the case of one-side (one side) incidence described later shown in FIG. 17, which will be described later, it may be four times the case of the above-described two-side (two side) incidence shown in FIGS.
By setting R14 and R15 in the above range, the illuminance distribution of light can be more suitably made medium to high.

Further, like the light guide plates 81b to 81e shown in FIGS. 18B to 18E, the shape of the boundary surface z between the first layer 82 and the second layer 84 in the mixing zone M near the light incident surface 30c is The light guide plates 31e to 31h shown in FIGS. 16A to 16D may be changed in the same manner.
The light guide plates 81b to 81d shown in FIGS. 18B to 18D are the light guide plate 80 shown in FIG. 17, and the light guide plate 81ed shown in FIG. 18E is the light guide plate shown in FIG. Since it has the same structure except 81a and the shape of the boundary surface z in the mixing zone M in the vicinity of the light incident surface 30c, the same components are denoted by the same reference numerals, and detailed description thereof will be given. Is omitted, and the following description will mainly focus on the different components.

In the light guide plate 81b shown in FIG. 18B, similarly to the light guide plate 31f shown in FIG. 16B, the cross-sectional shape of the boundary surface z in the mixing zone M in the vicinity of the light incident surface 30c is changed to a convex curve (for example, , Arc R16), and a maximum value of the thickness of the second layer 84 is provided at the inner end of the mixing zone M.
In the light guide plate 81c shown in FIG. 18C, similarly to the light guide plate 31g shown in FIG. 16C, the cross-sectional shape of the boundary surface z in the mixing zone M near the light incident surface 30c is changed to a convex curve (for example, Arc R17), the end of the boundary surface z is connected to the substantially central back surface 80b of the mixing zone M, and the maximum value of the thickness of the second layer 84 is provided at the inner end of the mixing zone M. Yes.

In the light guide plate 81d shown in FIG. 18D, as in the case of the light guide plate 31h shown in FIG. The cross-sectional shape of the boundary surface z at the inner end portion of M is a plane that is substantially parallel to the light incident surface 30c, the end portion thereof is connected to the back surface 80b, and the thickness of the second layer 84 at the inner end portion of the mixing zone M. The maximum value is set.
In the light guide plate 81e shown in FIG. 18E, as in the case of the light guide plate 31f shown in FIG. 16B, the sectional shape of the boundary surface z in the mixing zone M near the light incident surface 30c is changed to a convex curve (for example, , Arc R18), and a maximum value of the thickness of the second layer 84 is provided at the inner end of the mixing zone M.
In the above-described example, the sectional shape of the boundary surface z in the mixing zone M may be changed to a convex curve, and a concave curve, a plane, or a combination thereof may be used.

In addition, the backlight unit using the light guide plate of the present invention is not limited to the above-described various embodiments. In addition to the two light sources, one or both of the side surfaces on the short side of the light emission surface of the light guide plate are also provided. You may arrange | position a light source facing. Increasing the number of light sources can increase the intensity of light emitted by the device.
Further, light may be emitted not only from the light emitting surface but also from the back side.
In addition, the light guide plate of the present invention is composed of two layers having different particle concentrations of scattering particles, but is not limited thereto, and has a configuration of three or more layers having different particle concentrations of scattering particles. Also good.

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

Hereinafter, the light guide plate according to the first aspect of the present invention and the planar illumination unit according to the third aspect will be specifically described by way of examples.
[Example I]
First, an example of the planar illumination unit according to the third aspect of the present invention will be described.
As the first embodiment, the backlight unit 20 as shown in FIGS. 1 and 2 is used, and the component material of the casing 26 is aluminum and the thickness is 0.3 mm as the constituent members. The material of the optical member unit 32 is acrylic resin, the thickness is 1.0 mm, the material of the reflection sheet used as the reflection plate 34 is PET, the thickness is 0.2 mm, the material of the diffusion sheet 32a of the optical member unit 32 is PET, The thickness is set to 0.2 mm, and the above-described equation (3) is used to calculate the deflection rigidity D of the backlight unit 20 as a whole by computer simulation, and it is determined whether or not the deflection rigidity condition of the above equation (2) is satisfied. did.
The value of the flexural rigidity D was 0.48, which satisfied the above formula (2), so the determination was good.
The results are shown in Table 3.

As Example 2-7 and Comparative Examples 1-4, the backlight unit 20 comprised with the structural member shown in Table 1 is carried out similarly to Example 1, and uses said Formula (3) by computer simulation, The deflection rigidity D of the entire backlight unit 20 was obtained, and it was determined whether or not the deflection rigidity condition of the above formula (2) was satisfied.
The obtained results are shown in Tables 3 and 4.

In Table 3 and Table 4 above, the determination when the value of the flexural rigidity D satisfies the above formula (2) is indicated as “Good”, and the value of the flexural rigidity D does not satisfy the above formula (2). Judgment was described as x as bad.
Here, Table 3 above shows Examples 1 to 7 in which the material of the component of the casing 26 and the material of the light guide plate 30 satisfy the above materials, and the deflection rigidity D of the entire backlight unit 20 is expressed by the above formula ( 2) is satisfied, and is determined to be good (good), but Table 4 above shows Comparative Examples 1 to 1 in which the material of the component of the casing 26 and the material of the light guide plate 30 do not satisfy the above-mentioned materials. In all cases, the flexural rigidity D does not satisfy the above formula (2) and is determined as x (defective).
From the results of Example I above, the effect of the present invention is clear.

Example II
Next, examples of the light guide plate according to the first aspect of the present invention will be described.
As Example II, by using a two-layer sheet-shaped light guide plate 30 having a boundary surface z as shown in FIGS. 2, 3, 5 and 6, both sides (two sides) incident light guide plate 30 was obtained by computer simulation. The illuminance distribution and the luminance distribution of the emitted light emitted from the 30 light emitting surfaces 30a are obtained, (a) the utilization efficiency of the light incident from the light incident surfaces 30c and 30d of the light guide plate 30, and (b) the light emitting surface 30a. And (c) the unevenness shape of the central portion of the light exit surface 30a is obtained, optical evaluation is performed for these three items, and the set values (a It was determined whether or not 70) or more, (b) more than 0% and 45% or less, and (c) a convex shape was satisfied.
In the simulation, the transparent resin material of the light guide plate 30 was modeled as PMMA, and the scattering particle material was modeled as silicone. This is the same for all the following embodiments.

In Example II, the screen size is 269.5 mm in light guide length corresponding to 20 inches (inch), 539 mm in light guide length corresponding to 40 inches (inch), and the light guide length 1347 corresponding to 100 inches (inch). A 5 mm light guide plate 30 was used. Specifically, the thicknesses of the light guide plates 30 of each screen size are all 1.0 mm, and the second layer 62 is thickest at the bisector α, that is, at the maximum value position. A light guide plate was used in which the thickness of the second layer 62 was 0.4 mm, the thickness of the second layer 62 was the smallest, and the thickness of the second layer 62 at the position of the minimum value was 0.075 mm. . In addition, the scattering particles to be kneaded and dispersed in the light guide plate are three types having a particle size of 4.5 μm, 7.0 μm, and 12 μm. According to the light guide plate design method of the present invention shown in FIG. The material and thickness of the optical plate 30 are determined, the cross-sectional shapes of the first layer 60 and the second layer 62 are determined, the particle concentration of the first layer 60 is set according to the particle size of the scattering particles, and then In response to this, a plurality of types of particle concentrations of the second layer 62 were determined, and a plurality of types of light guide plates were designed and manufactured.
The combined scattering cross section S at the light guide position of the obtained multiple types of light guide plates 30 was determined using the above formulas (4) to (6).
The obtained results are shown in Tables 5 to 13.

Tables 5 to 13 above show nine types of particle sizes of three types of scattering particles of 4.5 μm, 7.0 μm, and 12 μm and three types of screen sizes of 20 type, 40 type, and 100 type, respectively. It corresponds to the light guide plate 30 of the combination.
Tables 5, 8 and 11 all show the case of a light guide plate having a screen size of 20 and particle sizes of scattering particles of 4.5 μm, 7.0 μm and 12 μm, respectively. Examples 11 to 20, 41 to 50 and 71 to 80 in which the maximum value S _max and the minimum value S _{min of the} cross-sectional area S satisfy the above formula (1a), and the comparative example 11 that does not satisfy the above formula (1a). -13, 41-43 and 71-73 are shown.
Tables 6, 9 and 12 are for light guide plates having a screen size of 40 types and particle sizes of scattering particles of 4.5 μm, 7.0 μm and 12 μm, respectively. Examples 21 to 30, 51 to 60 and 81 to 90 in which the maximum value S _max and the minimum value S _{min of the} cross-sectional area S satisfy the above formula (1b), and Comparative Example 21 in which the above formula (1b) is not satisfied -23, 51-53 and 81-83.
Tables 7, 10 and 13 all show the case of a light guide plate having a screen size of 100 type and particle sizes of scattering particles of 4.5 μm, 7.0 μm and 12 μm, respectively. Examples 31 to 40, 61 to 70 and 91 to 100 in which the maximum value S _max and the minimum value S _{min of the} cross-sectional area S satisfy the above formula (1d), and Comparative Example 31 in which the above formula (1d) is not satisfied. -33, 61-63 and 91-93 are shown.

Examples 11 to 100 shown in Table 5 to Table 13, and Comparative Examples 11 to 13, 21 to 23, 31 to 33, 41 to 43, 51 to 53, 61 to 63, 71 to 73, 81 to 83, and 91 to 91 For 93, the above (a) light utilization efficiency, (b) medium altitude, and (c) the uneven shape at the center are obtained, and optical evaluation is performed for these three items, and the set values for each of these three items It was determined whether (a) 70% or more, (b) more than 0% and 45% or less, and (c) a convex shape was satisfied.
Here, in the determination, (a), (b), and (c) are all satisfied, and in particular, when (b) is in the range of 30 to 40%, “◎” is given. When b) was not in the range of 30 to 40%, it was marked as ◯, and when any one of (a), (b), and (c) was not satisfied, it was marked as x.
The above results are also shown in Tables 5 to 13.

As is clear from the results of Tables 5 to 13, all of Examples 11 to 100 in which the combined scattering cross section S satisfies the scattering particle dispersion condition of the present invention (a) the light utilization efficiency is 70% or more. , (B) The medium altitude of the luminance distribution is more than 0% and 45% or less, and (c) the shape of the central portion of the luminance distribution is a convex shape, satisfying the specified values of these three items, ◎ or ○ Comparative Examples 11-13, 21-23, 31-33, 41-43, 51-53, 61-63 whose composite scattering cross section S does not satisfy the scattering particle dispersion condition of the present invention. , 71-73, 81-83, and 91-93 are determined as x because at least one of the above three items deviates from the specified value.
From the results of Example II above, the effect of the present invention is clear.

Example III
Next, Example III of the light guide plate according to the first aspect of the present invention will be described.
As Example III, instead of the light guide plate 30 incident on both sides (two sides) shown in FIGS. 2, 3, 5 and 6, a light guide plate 80 on one side (one side) shown in FIG. Except for changing the shape, maximum thickness, and minimum thickness of the two layers 84, the screen sizes were 20 inches (inch), 40 inches (inch), and 100 inches (inch) in exactly the same manner as in Example II. A plurality of types of light guide plates 80 were designed and manufactured. Specifically, the thickness of the light guide plate 80 of each screen size is 1.0 mm, and the maximum thickness of the second layer 84 is the largest, that is, the thickness of the second layer 84 at the position of the maximum value. The thickness of the second layer 84 was set to 0.45 mm, and the thickness of the second layer 84 at the position where the thickness of the second layer 84 was the smallest and the minimum value was set to 0.055 mm.
A plurality of types of manufactured light guide plates 80 were optically evaluated in the same manner as in Example II.
The combined scattering cross section S at the light guide position of the obtained multiple types of light guide plates 80 was determined using the above formulas (4) to (6).
The obtained results are shown in Tables 14-22.

Tables 14 to 22 above show nine types of particle sizes of three kinds of scattering particles of 4.5 μm, 7.0 μm, and 12 μm and three types of screen sizes of 20 type, 40 type, and 100 type, respectively. It corresponds to the light guide plate 80 of the combination.
Tables 14, 17 and 20 are all cases of a light guide plate having a screen size of 20 and particle sizes of scattering particles of 4.5 μm, 7.0 μm and 12 μm, respectively. Examples 101 to 107, 131 to 137 and 161 to 167 in which the maximum value S _max and the minimum value S _{min of the} cross-sectional area S satisfy the above formula (1e), and the comparative example 101 that does not satisfy the above formula (1e). -102, 131-132 and 161-162.
Tables 15, 18 and 21 are for light guide plates having a screen size of 40 and particle sizes of scattering particles of 4.5 μm, 7.0 μm and 12 μm, respectively. Examples 111 to 117, 141 to 137, and 171 to 177 in which the maximum value S _max and the minimum value S _{min of the} cross-sectional area S satisfy the above formula (1f), and the comparative example 111 that does not satisfy the above formula (1f). ~ 112, 141-142 and 171-172.
Tables 16, 19 and 22 are the cases where the screen size is 100 type and the light guide plate has scattering particle sizes of 4.5 μm, 7.0 μm and 12 μm, respectively. Examples 121 to 127, 151 to 157 and 181 to 187 in which the maximum value S _max and the minimum value S _{min of the} cross-sectional area S satisfy the above formula (1h), and the comparative example 121 that does not satisfy the above formula (1h). ~ 122, 151-152 and 181-182.

Examples 101 to 107, 111 to 117, 121 to 127, 131 to 137, 141 to 147, 151 to 157, 161 to 167, 171 to 177, and 181 to 187 shown in Tables 14 to 22, and Comparative Examples 101 to 101 102, 111-112, 121-122, 131-132, 141-142, 151-152, 161-162, 171-172, and 181-182 were optically evaluated for the above three items in exactly the same manner as in Example II. Then, it was determined whether or not the set values of these three items were satisfied.
The above results are also shown in Tables 14 to 22.

As is clear from the results of Tables 14 to 22, Examples 101 to 107, 111 to 117, 121 to 127, 131 to 137, 141 to 147 in which the combined scattering cross section S satisfies the scattering particle dispersion conditions of the present invention. 151-157, 161-167, 171-177, and 181-187 all have (a) a light utilization efficiency of 70% or more, (b) a medium-to-high degree of luminance distribution of more than 0% to 45%, And (c) the shape of the central portion of the luminance distribution is a convex shape, satisfies the specified values of these three items, and is judged as ◎ or ○, but the combined scattering cross section S is Comparative Examples 101 to 102, 111 to 112, 121 to 122, 131 to 132, 141 to 142, 151 to 152, 161 to 162, 171 to 172, and 181 to 182 that do not satisfy the scattering particle dispersion condition, Serial at least one of the three items is deviated from a specified value, it is those determined in ×.
The effect of the present invention is clear from the results of Example III.

[Example IV]
Next, Example IV of the light guide plate according to the first aspect of the present invention will be described.
As Example IV, a plurality of types of light guide plates 30 were designed and manufactured in exactly the same manner as Example II, except that a light guide plate 30 having a light guide length of 620 mm corresponding to a 46-inch (inch) screen size was used. Specifically, the thickness of the light guide plate 30 is 1.0 mm, and the thickness of the second layer 62 at the position of the maximum value, that is, the thickness of the second layer 62 at the bisector α is the largest. The thickness was 0.37 mm, and the thickness of the second layer 62 at the position where the thickness of the second layer 62 was the smallest and the minimum value was 0.17 mm. A plurality of types of manufactured light guide plates were optically evaluated in the same manner as in Example II.
The combined scattering cross section S at the light guide position of the obtained multiple types of light guide plates 30 was determined using the above formulas (4) to (6).
The results obtained are shown in Table 23.

Table 23 above shows Examples 191 to 200 in which the maximum value S _max and the minimum value S _min of the combined scattering cross section S satisfy the above formula (1c) and the comparative examples 191 to 193 that do not satisfy the above formula (1c). Indicates.
For Examples 191 to 200 and Comparative Examples 191 to 193 shown in Table 23, optical evaluation was performed on the above three items, and it was determined whether or not each set value of these three items was satisfied.
The above results are also shown in Table 23.

As is clear from the results in Table 23, in all of Examples 191 to 200 in which the combined scattering cross section S satisfies the scattering particle dispersion condition of the present invention, (a) the light utilization efficiency is 70% or more, (b ) The medium altitude of the luminance distribution is more than 0% and 45% or less, and (c) The shape of the central part of the luminance distribution is convex, satisfying the specified values of these three items, and judged as ◎ or ○ However, in Comparative Examples 191 to 193 in which the combined scattering cross-section S does not satisfy the scattering particle dispersion condition of the present invention, at least one of the above three items deviates from the specified value, and is determined as x. Is.
The effects of the present invention are also apparent from the results of Example IV above.

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

Claims (21)

The light emitting surface having a rectangular shape, at least one light incident surface that is provided on the edge side of the light emitting surface and that enters light traveling in a direction substantially parallel to the light emitting surface, and the light emitting surface A thin sheet-like light guide plate having a thickness of 1.2 mm or less, having a back surface on the opposite side and having diffusion particles dispersed therein,
The light guide plate has two or more layers overlapped in a direction substantially perpendicular to the light exit surface,
In each of the two or more layers, one or more kinds of the diffusing particles are dispersed at different particle concentrations,
The two or more layers include at least a first layer located on the light emitting surface side and a second layer located on the back surface side and in contact with the first layer,
The second layer has a thickness that changes in a direction substantially parallel to the light exit surface in a direction substantially parallel to the light exit surface, and the thickness continuously increases in a direction away from the light entrance surface. A cross-sectional shape having at least a maximum portion is formed,
The combined scattering cross section S of the two layers in a direction substantially perpendicular to the light exit surface at a position along a direction substantially parallel to the light exit surface is continuously and monotonously increased as the distance from the light entrance surface increases. The diffusing particles are dispersed,
A maximum value S _max and a minimum value S _min of the combined scattering cross section S satisfy the following formula (1).
A ・ k ≦ S _max ≦ B ・ k
C ・ k ≦ S _min ≦ D ・ k (1)
Here, the coefficient k is the reciprocal of the ratio of the screen size V or the light guide length L (mm) to the reference screen size V ₀ or the light guide length L ₀ (mm) (k = V ₀ / V = L ₀ / L), and A, B, C, and D are constants determined in the reference screen size V ₀ or the reference light guide length L ₀ . When the reference screen size V ₀ is a screen size of 20 type (20 inches; diagonal length: 508 mm), in the above formula (1),
In the case of bilateral incidence, A = 0.833, B = 2.150, C = 0.672, D = 1.590,
2. The sheet-like light guide plate according to claim 1, wherein A = 1.000, B = 1.761, C = 0.500, and D = 0.645 in the case of one-side incidence.   The second layer has a cross-sectional shape in which the thickness in a direction substantially parallel to the light emitting surface is substantially perpendicular to the light emitting surface, and has at least one minimum value and at least one maximum value. The sheet-like light guide plate according to claim 1 or 2.   The sheet light guide plate according to any one of claims 1 to 3, wherein the at least one light incident surface is two light incident surfaces provided on two opposite sides of the light emitting surface.   The sheet-like light guide plate according to claim 4, wherein the cross-sectional shape of the second layer includes three arcs or four arcs.   The cross-sectional shape of the second layer has the local minimum value on each side of the two light incident surfaces, and the local maximum value in the approximate center between the two light incident surfaces. The sheet-like light guide plate as described.   The cross-sectional shape of the second layer has an arc that forms the minimum value on each side of the two light incident surfaces, and an arc that forms the maximum value at a substantially center between the two light incident surfaces. The sheet-like light guide plate according to any one of claims 4 to 6.   The sheet-like light guide plate according to any one of claims 1 to 7, wherein the thickness of the second layer is the thickest at substantially the center of the light emitting surface. The at least one light incident surface is one light incident surface provided on one end side of the light emitting surface;
The cross-sectional shape of the second layer has the minimum value on the one light incident surface side, and has the maximum value on the other end side of the light emitting surface. The sheet-like light guide plate according to Item 1.   The cross-sectional shape of the second layer has an arc that forms the minimum value on the one light incident surface side, and an arc that forms the maximum value on the other side of the light emitting surface. The sheet-like light guide plate according to claim 9.   The light guide plate according to claim 1, wherein the two or more layers further include a third layer located on the back side and in contact with the second layer.   The light guide plate according to claim 11, wherein a boundary surface between the second layer and the third layer is substantially parallel to the light emitting surface. The light guide length from the one light incident surface to the center or the other end of the light traveling in a direction substantially parallel to the light emitting surface is 260 mm or more and 1350 mm or less,
The diffusion particle has a particle size of 4.5 μm or more and 12.0 μm or less,
The concentration of the diffusing particles dispersed in the second layer is 0.001 wt% or more and 4.438 wt% or less;
The particle size and concentration of the diffusing particles dispersed in the second layer is a graph in which the horizontal axis is the particle size (μm) of the scattering particles and the vertical axis is the particle concentration (wt%) of the diffusing particles. Points (4.5,0.001), (4.5,1.085), (7.0,0.001), (7.0,1.693), (12.0,0.002) And the sheet-like light-guide plate of any one of Claims 1-12 which exists in the area | region enclosed by (12.0, 4.438). The concentration of the diffusing particles dispersed in the first layer is 0.0004 wt% or more and 0.195 wt% or less,
The particle size and concentration of the diffusing particles dispersed in the first layer is a graph in which the horizontal axis represents the particle size (μm) of the scattering particles and the vertical axis represents the particle concentration (wt%) of the diffusing particles. Points (4.5, 0.0004), (4.5, 0.048), (7.0, 0.0006), (7.0, 0.074), (12.0, 0.0015) And the sheet-like light-guide plate of Claim 13 which exists in the area | region enclosed by (12.0,0.195). The light utilization efficiency indicating the ratio of the light incident from the at least one light incident surface being emitted from the light exit surface is 70% or more,
The medium to altitude of the luminance distribution of the light emitting surface indicating the ratio of the luminance of the light emitted from the central portion of the light emitting surface to the luminance of the light emitted from the vicinity of the peripheral portion of the light emitting surface is more than 0%, 45% or less,
The sheet-like light guide plate according to any one of claims 1 to 14, wherein a luminance distribution at the central portion of the light emitting surface is convex.   The sheet-like light guide plate according to claim 1, wherein the back surface is a plane parallel to the light emitting surface. The sheet-like light guide plate according to any one of claims 1 to 16,
A light source disposed facing the light incident surface of the light guide plate;
A planar lighting device comprising: a housing that houses the light guide plate and the light source and has an opening smaller than the light exit surface on the light exit surface side of the light guide plate. The sheet-like light guide plate according to any one of claims 1 to 16,
A planar illumination unit composed of a plurality of constituent members including optical members respectively disposed on the light exit surface and the back surface of the light guide plate,
The plurality of constituent members constituting the entire planar lighting unit is such that the deflection rigidity D [N · m] of the entire planar lighting unit represented by the following formula (3) satisfies the following formula (2). A planar lighting unit characterized by being configured.
D <1.3 (2)
Here, k is the number of types of materials of different materials of the plurality of constituent members constituting the planar lighting unit, N _k is the number of parts of the material k, E _k is the Young's modulus of the material k [N / m ² ], h _k is the thickness [mm] of the material k, and ν is the Poisson's ratio.   The planar lighting unit according to claim 18, wherein the plurality of constituent members further include a housing that houses the light guide plate and the optical member.   The material of the material of the light guide plate is acrylic resin, the material of the material of the parts constituting the housing is an aluminum alloy, and the thickness of the material of the housing is 0.5 mm or less. The planar illumination unit according to claim 19, wherein the thickness of the optical member is 0.6 mm or less. The planar lighting unit according to any one of claims 18 to 20,
And a light source arranged to face the light incident surface of the light guide plate of the planar illumination unit.