WO2013011774A1 - Planar illumination device - Google Patents

Abstract

An objective of the present invention is to provide a planar illumination device which is large, has a thin shape, is flexible, and with which it is possible to emit light with high light usage efficiency and low brightness unevenness, as well as to prevent buckling of a diffusion sheet and obtain a luminosity distribution which is either uniform or convex. This planar illumination device comprises two or more layers with different particle concentrations which a light-guiding plate overlaps in a direction which is perpendicular to a light emission plane. In the direction which is perpendicular to a light entrance plane, the thicknesses of the two or more layers respectively change, the composite particle concentrations change, the light-guiding plate, a light source unit, the diffusion sheet, and a casing fit together on the light source unit side, and with the radius of curvature when the planar illumination device overall is curved designated R, then the bending stress P satisfies the formulae P > μ₀/tan(a/R), and P ≤ P_max.

Description

Surface lighting device

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

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

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

On the other hand, as a backlight unit that can be thinned, a light emitting surface that is a surface that is different from the surface on which light is emitted from a light source for illumination and incident from a side surface is guided in a predetermined direction. There is a sidelight type backlight unit that uses a plate-shaped light guide plate that emits light from a light source.
As such a backlight unit using a light guide plate, a backlight unit using a light guide plate in which scattering particles for scattering light in a transparent resin are mixed has been proposed. Here, in the sidelight-type backlight unit, when the backlight unit is enlarged, it becomes difficult to guide incident light to the back of the light guide plate, that is, to the center of the light guide plate. There has been a problem that the brightness of the emitted light at the central portion is lowered. Therefore, in the light guide plate mixed with scattering particles, in order to guide the incident light to the back of the light guide plate, it consists of two layers having different particle concentrations, and the particle concentration is higher as the distance from the light incident surface increases. It has been proposed to make the luminance distribution of the emitted light uniform or medium height by using a light guide plate in which the layer thickness is increased.

For example, Patent Document 1 has a rectangular light emission surface, a light incident surface including one side of the light emission surface, and a back surface that is the surface opposite to the light emission surface, and scattering particles are contained inside. It is a dispersed light guide plate, which is composed of a first layer on the light exit surface side and a second layer on the back surface side having a particle concentration different from that of the first layer, and the particle concentration of the scattering particles in the first layer is defined as Npo. Assuming that the particle concentration of the scattering particles in the second layer is Npr, a light guide plate in which the relationship between Npo and Npr satisfies Npo <Npr is described.
In Patent Document 2, a rod-like light source lamp is mounted on the end face of a light guide having a portion where the non-scattering light guide region and the scattering light guide region overlap, and the portion that does not face the light guide of the light source lamp A surface light source device is described in which the concentration of particles is locally adjusted with the thickness of both regions.

Also, if the light guide plate is made larger and thinner, the expansion and contraction and warpage due to the influence of temperature and humidity will increase, and the light guide plate and the light source and the liquid crystal panel may come into contact with each other and the parts may be damaged. Therefore, a planar illumination device having a mechanism in which the light guide plate and the light source can move integrally with respect to the housing according to the expansion and contraction of the light guide plate has been proposed.

For example, in Patent Document 3, two symmetrical inclined surfaces whose distances from the light emitting surface become longer from the two light incident surfaces toward the center of the light emitting surface, and a curved portion that joins the two inclined surfaces, respectively. And includes scattering particles that scatter light propagating therein, the length between the two light incident surfaces, the thickness of the light incident surface, the thickness of the center of the curved portion, the radius of curvature of the curved portion, and the inclined surface A light guide plate having a taper satisfying a predetermined range, a scattering particle size, a concentration, light utilization efficiency, and a medium to high degree of luminance distribution of the light exit surface satisfying the predetermined range, a light source, a housing, and a light source There is described a planar illumination device provided with a fixing means for fixing the distance between the light incident surface of the light guide plate to be constant and a sliding mechanism for sliding the fixing means with respect to the housing.

JP 2009-117357 A Japanese Patent Laid-Open No. 11-345512 JP 2009-117349 A

With the increase in size of liquid crystal display devices, backlight units are required to be larger and thinner and lighter. Furthermore, in addition to thinning, the backlight unit is flexible, that is, has flexibility, and the surface of the backlight unit is formed into various curved surfaces, so that it can be used as a flexible liquid crystal display or flexible. There is a demand for a planar lighting device that can also be used for electrical decoration and general lighting.

However, as in Patent Document 1 and Patent Document 2, the light guide plate is composed of two layers having different particle concentrations, and the thickness of the layer having the higher particle concentration increases as the distance from the light incident surface increases. Even if the backlight unit is made larger and thinner, or if it is a flexible backlight unit, the incident light can be sufficiently guided to the back of the light guide plate. Therefore, there is a possibility that the light emitted from the backlight unit cannot be made uniform.

In addition, when using a light guide plate in which scattering particles are kneaded and dispersed, at least one diffusion sheet is disposed on the light output surface of the light guide plate, and the light emitted from the light guide plate is transmitted in the front direction of the backlight unit. It is necessary to convert the angle.
Here, when a flexible backlight unit is used, even if the backlight unit is bent by using a mechanism that integrally holds the light guide plate and the light source, as in Patent Document 3, the light guide plate And the relative position of the light source can be prevented from shifting. However, in a flexible backlight unit, when the backlight unit is bent and then returned to a flat shape as shown in FIG. 11A, the light of the light guide plate is returned as shown in FIG. The diffusion sheet placed on the exit surface will buckle near the edge of the light exit of the housing, causing slack and wrinkles, and the light emitted from the backlight unit will have a non-uniform luminance distribution. Or the light utilization efficiency may be reduced.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to have a large and thin shape and a flexible planar lighting device that emits light with high light utilization efficiency and less unevenness in luminance. Another object of the present invention is to provide a planar lighting device that can prevent the buckling of the diffusion sheet and obtain a uniform or medium-high brightness distribution.

In order to solve the above-mentioned problems, the present invention provides a light emitting surface having a rectangular shape and a light incident surface that is provided on the edge side of the light emitting surface and that travels in a direction substantially parallel to the light emitting surface. A light guide plate having a thickness of 1.5 mm or less in a direction perpendicular to the light output surface, and a back surface provided on the opposite side of the light output surface and scattering particles dispersed therein A light source unit disposed facing the light incident surface, a diffusion sheet disposed facing the light output surface of the light guide plate, and a light output surface of the light guide plate containing the light guide plate, the light source unit, and the diffusion sheet The light guide plate has two or more layers having different particle concentrations of scattering particles, which overlap each other in a direction substantially perpendicular to the light exit surface, In the direction perpendicular to the light incident surface, the thickness of two or more layers is approximately perpendicular to the light exit surface. As a result, the synthetic particle concentration of the light guide plate is changed, and the light guide plate, the light source unit, the diffusion sheet, and the housing are engaged with each other on the light source unit side, and the entire planar illumination device is made light incident. When curved in a direction perpendicular to the surface, the radius of curvature is R [mm], the bending stress is P [N / mm ² ], the maximum static friction coefficient between the casing and the diffusion sheet is μ _0, and diffusion When the length of the sheet in the direction perpendicular to the light incident surface is a [mm], the thickness is h [mm], the Young's modulus of the material of the diffusion sheet is E [N / mm ² ], and the Poisson's ratio is ν. The planar lighting device is characterized in that the bending stress P satisfies P> μ ₀ / tan (a / R) and P ≦ P _max . Here, P _max = E · π ² / (6 (1-ν) ² ) · (h / a) ² .

Here, when the longitudinal width of the light incident surface of the diffusion sheet is b [mm], the thickness h, length a, width b, and radius of curvature R of the diffusion sheet are 0.25 <h ≦ It is preferable that 1.0 and 300 <R <10000 and 1.0 ≦ b / a <3.0 are satisfied.
Moreover, it is preferable to use a biaxially stretched polyethylene terephthalate resin substrate as the substrate of the diffusion sheet.
Here, when the thickness h [mm] of the diffusion sheet is 0.3 <h ≦ 1.0, two or more biaxially stretched polyethylene terephthalate resin substrates are bonded as the diffusion sheet substrate. It is preferable to use the composite base material.

Alternatively, it is preferable to use a base material formed by extrusion or cast polymerization using any one of acrylic resin, polystyrene resin, MS resin, and polycarbonate resin as the base material of the diffusion sheet.

Further, the two or more layers of the light guide plate are composed of two layers, a first layer on the light emitting surface side and a second layer on the back surface side having a higher particle concentration than the first layer, and the thickness of the second layer However, it is preferable that the thickness continuously changes so as to become thicker after becoming thinner as the distance from the light incident surface increases.

Alternatively, the two or more layers of the light guide plate are composed of two layers, a first layer on the light emitting surface side and a second layer on the back surface side having a higher particle concentration than the first layer, and the thickness of the second layer As the distance from the light incident surface increases, it is preferable that the thickness is once changed to be thicker and then continuously changed so as to become thicker again.

Further, it is preferable that the back surface of the light guide plate is a plane parallel to the light exit surface.

According to the present invention, it is a large and thin shape, and is a flexible planar illuminating device, which can emit light with high light use efficiency and little luminance unevenness, and is used in a curved manner. It is possible to prevent slack and wrinkles due to buckling of the diffusion sheet, and to obtain a uniform or medium-high brightness distribution.

It is a schematic perspective view which shows one Embodiment of a liquid crystal display device provided with the planar illuminating device which concerns on this invention. (A) is a schematic front view of the backlight unit of the liquid crystal display device shown in FIG. 1, (B) is a cross-sectional view taken along line II in (A), and (C) is a cross-sectional view taken along line II-II in (A). FIG. It is a schematic perspective view of the light-guide plate of the backlight unit shown in FIG. (A) is a schematic sectional drawing of the light-guide plate shown in FIG. 3, (B) and (C) are schematic sectional drawings showing another example of the light-guide plate used for the planar illuminating device of this invention. . (A) is the partial schematic perspective view of the light source unit of the planar illuminating device shown in FIG. 2, (B) is a schematic perspective view of a LED chip, (C) is a schematic front view of a light source. It is a figure which shows notionally the diffusion sheet used for the planar illuminating device shown in FIG. (A) is a schematic fragmentary sectional view of the diffusion sheet used for the planar illuminating device shown in FIG. 2, (B) is a schematic fragmentary sectional view of another example of a diffusion sheet. It is the schematic at the time of curving the planar illuminating device shown in FIG. It is a graph which shows the relationship between the dimension of a diffusion sheet, and coefficient (alpha). (A) And (B) is a graph which shows the relationship between the curvature radius R and the bending stress P. FIG. (A) And (B) is the schematic showing the planar illuminating device for demonstrating the subject of this invention.

The planar illumination device according to the present invention will be described in detail below based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 shows a schematic perspective view of an example of a liquid crystal display device using the planar illumination device of the present invention.
A liquid crystal display device 10 shown in FIG. 1 is a display device using a so-called liquid crystal display panel (liquid crystal display panel = LCD) 12 such as a liquid crystal television. Basically, the liquid crystal display panel 12 and the surface illumination device of the present invention are used. The backlight unit 20 and the drive unit 14 for driving the liquid crystal display panel 12 are included.
The backlight unit 20 is disposed on the back surface (opposite to the image display surface) of the liquid crystal display panel 12 with the light emission surface (light emission surface) facing the liquid crystal display panel 12. In the following description, for the sake of convenience, the extending direction of the short side of the liquid crystal display panel 12 (light guide plate 30 to be described later) is the vertical (UD) direction, the extending direction of the long side, that is, the direction orthogonal to the vertical direction. Is also referred to as the left-right (LR) direction.
In FIG. 1, a part of the liquid crystal display panel 12 is omitted in order to clearly show the configuration of the backlight unit 20.

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

The backlight unit 20 is an illuminating device that irradiates light from the back surface of the liquid crystal display panel 12 to the entire surface of the liquid crystal display panel 12, and has a light emission port 24 having substantially the same shape as the image display surface of the liquid crystal display panel 12.
As shown in FIGS. 1 and 2, the backlight unit 20 in the illustrated example includes a light source unit 28, a light guide plate 30, a diffusion sheet 32, and a housing 26.
2A is a diagram conceptually showing the front (display surface side of the liquid crystal display device 10) from which the upper housing 44 is removed from the backlight unit 20, and FIG. 2B is a diagram showing the backlight unit. FIG. 2A is a cross-sectional view taken along the line II of FIG. 20, and FIG.

The housing 26 accommodates / holds the light source unit 28, the light guide plate 30, the diffusion sheet 32, and the like at predetermined positions.
The housing 26 has a lower housing 42 and an upper housing 44.

The lower housing 42 is a rectangular parallelepiped housing whose one surface (maximum surface) is open, and accommodates / holds the light source unit 28, the light guide plate 30 having a rectangular light emitting surface, the diffusion sheet 32, and the like at predetermined positions. To do. The light guide plate 30 is accommodated in the lower housing 42 with the light emission surface 30a described later facing the open surface. In addition, a power storage unit 49 that stores a plurality of power supplies that supply power to the light source unit 28 is attached to the back side of the lower housing 42.

On the other hand, the upper housing 44 is a housing having the same shape as the lower housing in which the lower housing 42 is inserted like a so-called lid, and the light emitted from the light guide plate 30 is liquid crystal on the surface facing the open surface. A light exit 24 for irradiating the back surface of the display panel 12 is formed.
Here, the backlight unit of the present invention is a flexible backlight unit and can be curved. Therefore, the upper housing 44 and the lower housing 42 are formed of a material that can be elastically deformed so as to be a flexible backlight unit. As a material of the upper casing 44 and the lower casing, an aluminum alloy, a magnesium alloy, a carbon fiber sheet, a stainless steel sheet, a phosphor bronze sheet, a resin containing a metal filler, a carbon material-based sheet, or the like can be used.

FIG. 3 is a conceptual perspective view of the light guide plate 30.
As shown in FIG. 3, the light guide plate 30 is a flat plate-like member having a rectangular (rectangular) light exit surface 30a that can include the entire surface of the light exit port 32 and can be accommodated in the lower housing. The light emitting surface 30a, the back surface 30b that is the surface opposite to the light emitting surface 30a, and the light incident surface 30c and the side surface 30d that are set on the end surface on the long side of the light emitting surface, respectively.

In the illustrated example, light enters from the light incident surfaces 30c and 30d, propagates in the light guide plate 30 in the short side direction, emits light from the light emitting surface 30a, and emits light to the back surface of the liquid crystal display panel 12. Incident.
Here, in the present invention, in order to make the backlight unit thin and flexible, the thickness of the light guide plate 30 is 1.5 mm or less.

Further, the light guide plate 30 has dispersed therein fine scattering particles for scattering light.
Examples of the transparent resin material used for the light guide plate 30 include PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethyl methacrylate), benzyl methacrylate, MS resin, or COP (cycloolefin). And an optically transparent resin such as a polymer.
Examples of the scattering particles kneaded and dispersed in the light guide plate 30 include silicone particles such as Tospearl (registered trademark), particles made of silica, zirconia, dielectric polymer, and the like. By including such scattering particles in the light guide plate 30, it is possible to emit illumination light that is uniform and has less luminance unevenness from the light exit surface 30a.

Here, the particle size of the scattering particles dispersed in the light guide plate 30 used in the planar lighting device of the present invention is preferably 4.0 to 12.0 μm. By setting the particle diameter of the scattering particles in this range, it is preferable in that high scattering efficiency can be obtained, forward scattering properties are large and wavelength dependency is small, and color unevenness can be suitably suppressed.
The scattering particles to be used may have a single particle size or a mixture of scattering particles having a plurality of particle sizes.

Here, the light guide plate 30 is formed in a two-layer structure divided into 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 layer 60 is an area of a cross section surrounded by the light emitting surface 30a, the light incident surface 30c, the side surface 30d, and the boundary surface z. The second layer 62 is a layer adjacent to the back surface 30b side of the first layer, and is a cross-sectional region surrounded by the boundary surface z, the light incident surface 30c, the side surface 30d, and the back surface 30b.

When the particle concentration of the scattering particles in the first layer 60 is Npo and the particle concentration of the scattering particles in the second layer 62 is Npr, the relationship between Npo and Npr is Npo <Npr. That is, in the light guide plate 30, the particle concentration of the scattering particles is higher in the second layer on the back surface 30b side than on the first layer on the light emitting surface 30a side.
Here, the light guide plate 30 is divided into a first layer 60 and a second layer 62 at the boundary surface z, but the first layer 60 and the second layer 62 have the same transparent resin only in the particle concentration. The same scattering particles are dispersed to each other and are integrated in structure. 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.

When the boundary surface z between the first layer 60 and the second layer 62 is viewed in a cross section perpendicular to the longitudinal direction of the light incident surface, the second layer 62 becomes thinner from the light incident surface 30c toward the side surface 30d. Then, it continuously changes so as to become thicker, and continuously changes so as to become thinner again in the vicinity of the side surface 30d.
Specifically, the boundary surface z is a curved surface that is concave toward the light exit surface 30a on the light incident surface 30c side, and a curved surface that is convex toward the light exit surface 30a on the side surface 30d side.

Thus, the thickness of the second layer having a higher concentration of scattering particles than the first layer 60 is continuously changed so as to be once thinned near the light incident surface 30c and once thickened near the side surface 30d. By doing so, the concentration of the synthesized particles of the scattering particles is changed to be the smallest near the light incident surface 30c and the largest near the side surface 30d.
That is, the concentration profile of the synthetic particle concentration is a curve that changes so as to have a minimum value on the first light incident surface 30c side and a maximum value on the side surface 122d side.

In the present invention, the synthetic particle concentration means that light is incident on the light guide plate by using the amount of scattered particles added (synthesized) in a direction substantially perpendicular to the light emitting surface at a certain position in the direction perpendicular to the light incident surface. It is the concentration of scattering particles when it is regarded as a flat plate having a thickness of the surface. That is, at a certain position away from the light incident surface, when the light guide plate is regarded as a flat light guide plate having a thickness of the light incident surface and having one type of concentration, the scattering particles added in a direction substantially perpendicular to the light exit surface The quantity per unit volume or the weight percentage with respect to the base material.

Thus, the synthetic particle concentration of the light guide plate 30 continuously changes so as to increase after decreasing from the light incident surface 30c, and continuously so as to decrease again in the vicinity of the side surface 30d. By adopting the changing configuration, it is possible to guide the light incident from the light incident surface 30c to a farther position. Therefore, even when the light guide plate 30 (backlight unit 20) is thinned and enlarged, the backlight The luminance distribution of the emitted light from the unit 20 can be made uniform or medium-high, and the light utilization efficiency can be improved.

Further, by arranging the minimum value in the vicinity of the light incident surface 30c, the light incident from the light incident surfaces 30c and 30d is sufficiently diffused in the vicinity of the light incident surface, and the emitted light emitted from the vicinity of the light incident surface is It is possible to prevent the bright line (dark line, unevenness) caused by the arrangement interval of the light sources from being visually recognized.
Further, by adjusting the shape of the boundary surface z, the luminance distribution (scattering particle concentration distribution) can be arbitrarily set, and the efficiency can be improved to the maximum.
Further, since the particle concentration of the layer on the light exit surface side is lowered, the amount of scattered particles as a whole can be reduced, leading to cost reduction.

In the light guide plate 30 shown in FIG. 2, the light emitted from the light source unit 28 and incident from the light incident surface 30 c passes through the light guide plate 30 while being scattered by scatterers (scattered particles) included in the light guide plate 30. Then, it is emitted from the light exit surface 30a directly or after being reflected by the back surface 30b. At this time, a part of the light may leak from the back surface 30 b, but the leaked light is reflected by the reflecting plate disposed on the back surface 30 b side of the light guide plate 30 and enters the light guide plate 30 again.

Here, in the illustrated light guide plate 30, the boundary surface z is a concave curved surface on the light incident surface 30c side and a convex curved surface on the side surface 30d side, but the present invention is not limited to this.

The light guide plates 100 and 102 shown in FIGS. 4B and 4C have the same configuration except that the shape of the boundary surface z of the light guide plate 30 shown in FIG. The same reference numerals are attached, and the following description will mainly focus on different parts.

The boundary surface z of the light guide plate 100 shown in FIG. 4 (B) is temporarily second layer 62 from the light incident surface 30c toward the side surface 30d when viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 30c. , The thickness of the second layer 62 is changed to be thick, and then the thickness of the second layer 62 is continuously changed to be constant. That is, the boundary surface z is a curved surface that is concave toward the light emitting surface 30a on the light incident surface 30c side, and is a curved surface that is convex toward the light emitting surface 30a at the center of the light guide plate. On the side surface 30d side from the apex, the plane is parallel to the light emitting surface 30a.

As described above, the shape of the boundary surface z is such that the thickness of the second layer is minimized at a position close to the light incident surface, and the thickness of the second layer is maximized at a position far from the light incident surface. By using an asymmetric shape, 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, and the illuminance distribution of the light emitted from the light exit surface can be made to be medium to high And the light utilization efficiency can be improved.

The boundary surface z of the light guide plate 102 shown in FIG. 4C is thicker in the second layer 62 from the light incident surface 30c toward the side surface 30d when viewed in a cross section perpendicular to the longitudinal direction of the light incident surface 30c. Once changed so that the second layer 62 becomes thinner, the second layer 62 changes again so as to become thicker, and continuously changes so as to become thinner on the side surface 30d side. .
Specifically, the boundary surface z is connected to the side surface 30d side of the convex curved surface toward the light emitting surface 30a, a concave curved surface smoothly connected to the convex curved surface, and the concave curved surface, It consists of a concave curved surface connected to the end of the light incident surface 30c on the back surface 30b side. On the light incident surface 30c, the thickness of the second layer 62 is zero.
That is, the synthetic particle concentration (thickness of the second layer) of the scattering particles is larger than the first maximum value in the vicinity of the first light incident surface 30c and the first maximum value on the side surface 30d side from the central portion of the light guide plate. It is continuously changed so as to have the second maximum value.

Thus, the synthetic particle concentration (thickness of the second layer 62) of the light guide plate 102 has the first maximum value at a position close to the light incident surface 30c, and the first maximum value on the side surface 30d side from the central portion. By setting the concentration to have a second maximum value larger than the value, even a large and thin light guide plate can deliver light incident from the light incident surface to a position farther from the light incident surface. The luminance distribution can be a medium-high luminance distribution.
In addition, by arranging the first maximum value of the synthetic particle concentration in the vicinity of the light incident surface, the light incident from the light incident surface is sufficiently diffused in the vicinity of the light incident surface and is emitted from the vicinity of the light incident surface. It is possible to prevent bright lines (dark lines, unevenness) caused by the arrangement interval of the light sources from being visually recognized in the incident light.
In addition, by setting the region closer to the light incident surface than the position where the synthetic particle concentration becomes the first maximum value to the synthetic particle concentration lower than the first maximum value, the incident light is returned from the light incident surface. It is possible to reduce light and outgoing light from a region near the light incident surface that is covered with the casing and not used, and to improve the utilization efficiency of light emitted from an effective region of the light outgoing surface.

In the backlight unit 20 of the present invention, it is preferable to provide a reflection plate that reflects light toward the light guide plate 30 at a necessary portion, such as the back surface 30b serving as a light reflection surface, similarly to the known light guide plate. By providing the reflecting plate, the light utilization efficiency can be further improved.
As the reflection plate, all known ones used for the light guide plate can be used. For example, a void is formed by kneading and stretching a filler in, for example, PET or PP (polypropylene) to increase the reflectance. Resin sheet, transparent or white resin sheet surface with mirror surface formed by vapor deposition of aluminum, etc., aluminum or other metal foil or resin sheet carrying metal foil, or metal sheet with sufficient reflectivity on the surface Is possible.

Here, as will be described in detail later, the light emitting surface 30a of the light guide plate 30 is locked at both corners on the light incident surface 30c side and the center thereof by the light source unit 28 (its light source support portion 52) described later. In addition, holding members 84a to 84c (in FIG. 3, the holding member 84c at the center in the upper left and right direction is omitted) for locking the diffusion sheet 32 described later are fixed.
This will be described in detail later.
The method for fixing the holding members 84a to 84c to the light guide plate 30 is not particularly limited, and various known methods can be used depending on the formation material and shape of the light guide plate 30 and the holding member. A fixing method using an adhesive is preferable in that there is no need for perforation or the like and damage such as cracking of the light guide plate 30 can be prevented.

FIG. 5A shows a schematic perspective view of a part of the light source unit 28 (near the end in the left-right direction).
As shown in FIG. 5A, the light source unit 28 includes a plurality of LED chips (light emitting diodes) 50 and a light source support portion 52, and the LED chips 50 are arranged on the light source support portion 52. Have.

The LED chip 50 is a chip in which a fluorescent material is coated on the surface of a light emitting diode that emits blue light. The LED chip 50 has a light emitting surface 50a having a predetermined area, and emits white light from the light emitting surface 50a.
Specifically, the LED chip 50 has a characteristic that the fluorescent material applied to the surface of the light emitting diode fluoresces when blue light emitted from the light emitting diode is transmitted. For this reason, the LED chip 50 emits blue light from the light emitting diode, so that the fluorescent material through which the blue light is transmitted also emits light. White light is generated and emitted from the light emitted by the fluorescence.
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.

In the planar lighting device of the present invention, various light emitting devices other than the LED chip 50 can be used for the light source unit 28, and various light emitting devices according to the application of the planar lighting device are used. Is possible.
For example, in the case of the liquid crystal display device 10 as in the illustrated example, an LED unit having a configuration in which three types of LEDs, a red LED, a green LED, and a blue LED, are combined may be used. In addition, a semiconductor laser (LD) can be used instead of the LED.

The light source support portion 52 is a plate-like member that is disposed so that one surface thereof faces the light incident surface 30 c of the light guide plate 30.
The light source support portion 52 supports the plurality of LED chips 50 on a side surface that is a surface facing the light incident surface 30c of the light guide plate 30 in a state of being spaced apart from each other by a predetermined distance. Specifically, the plurality of LED chips 50 constituting the light source 28 are arranged in an array along the longitudinal direction of the light incident surface 30 c of the light guide plate 30 and are fixed on the light source support portion 52.
The light source support 52 is made of a metal having good thermal conductivity such as copper or aluminum, and also has a function as a heat sink that absorbs heat generated from the LED chip 50 and dissipates it to the outside. The light source support 52 may be provided with fins that can increase the surface area and increase the heat dissipation effect, or may be provided with a heat pipe that transfers heat to the heat dissipation member.

Here, as shown in FIG. 5B, 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. By making the LED chip 50 into a rectangular shape, a thin light source can be obtained while maintaining a large light output. By making the light source 28 thinner, the backlight unit can be made thinner. In addition, the number of LED chips can be reduced.

In addition, since the LED chip 50 can make the light source 28 thinner, it is preferable that the LED chip 50 has a rectangular shape having a short side in the thickness direction of the light guide plate 30. However, the present invention is not limited to this, and the square shape and the circular shape are not limited thereto. LED chips having various shapes such as a shape, a polygonal shape, and an elliptical shape can be used.

As schematically shown in FIG. 5C, the light source support portion 52 of the light source unit 28 penetrates the plate on the surface on which the LED chips 50 are arranged, and supports support pins 64a and 64b of the lower casing 42 described later. Long holes 70a and 70b for insertion and through holes 72 for insertion of the support pins 66 of the lower housing 42 are formed. Also, support pins 74a and 74b for supporting support members 84a and 84b of the light guide plate 30 described later are fixed near both ends in the left-right direction.
These will be described in detail later.

As shown in FIGS. 2B and 2C, a diffusion sheet 32 is disposed on the front surface of the light guide plate 30 (in front of the light exit surface 30a).
The diffusion sheet 32 diffuses the emitted light emitted from the light guide plate 30 to reduce luminance unevenness, and converts the emission angle of the emitted light to the front direction (direction perpendicular to the light emitting surface 30a).
Further, the diffusion sheet 32 is formed with long holes 90a and 90b and through holes 90c for inserting support pins 86a, 86b and 86c provided in support members 84a, 84b and 84c fixed to the light guide plate 30. (See FIG. 6A).

Here, when the thickness of the diffusion sheet 32 is h, the thickness h of the diffusion sheet preferably satisfies 0.25 mm <h ≦ 1.0 mm.
When the thickness h of the diffusion sheet is 0.25 mm or less, when the backlight unit 20 is bent, flattened or deformed, loosening and wrinkles are likely to occur, and the plastic deformation without wrinkles returning. Or, in extreme cases, it may be broken, resulting in a problem that the appearance quality is degraded.
On the other hand, if the thickness h of the diffusion sheet is thicker than 1.0 mm, the flexibility of the backlight unit 20 may be reduced, or the thickness of the light guide plate may be exceeded, resulting in an increase in the overall thickness of the illumination system. Therefore, it is necessary to increase the strength of the housing, which may cause a problem that the weight of the entire illumination system increases.
Therefore, by setting the thickness h of the diffusion sheet to 0.25 mm <h ≦ 1.0 mm, the backlight unit 20 can be bent, flattened or deformed without lowering the flexibility of the backlight unit 20. In this case, it is possible to prevent slack and wrinkles from occurring.

Moreover, as a material of the base material of the diffusion sheet 32, it is preferable to use biaxially stretched PET (polyethylene terephthalate) resin. By using a biaxially stretched PET resin as the base material of the diffusion sheet 32, it is possible to ensure mechanical strength and heat resistance. In addition, performance such as dimensional stability, chemical resistance, and optical characteristics is improved, so bending rigidity is increased, wrinkles are less likely to occur even with relatively thin films, and birefringence can be suppressed. It is preferable in that it is suitable.
When the biaxially stretched PET resin is used as the base material of the diffusion sheet 32, when the thickness h of the diffusion sheet is 0.25 mm <h ≦ 0.3 mm, a single base material PET It is preferable to use a resin.
On the other hand, when a biaxially stretched PET resin is used as the base material of the diffusion sheet 32, if the thickness h of the diffusion sheet is 0.3 mm <h ≦ 1.0 mm, two or three sheets are used. It is preferable to use a composite base material on which a base material made of PET resin is bonded.

An example when a composite base material is used as the base material of the diffusion sheet 32 is shown in FIGS.
A diffusion sheet 32 shown in FIG. 7A is obtained by laminating a first base material 110, a second base material 112, and a third base material 114 with an adhesive layer 116 interposed therebetween.

The first base 110 has a biaxially stretched PET resin as a base 120, a light diffusion layer 126 is formed on the surface of the base 120 on the side that becomes the surface of the diffusion sheet 32, and the other surface (second base). 112), an easy adhesion layer 122 is formed on the surface.

The light diffusion layer 126 is a layer for diffusing light, and is coated with pigments such as silica, titanium oxide, and zinc oxide, or beads such as resin, glass, and zirconia that scatter light together with a binder. It is formed by kneading the aforementioned pigments and beads that scatter light.

The easy-adhesion layer 122 is for improving the adhesiveness with other base materials, and by providing the easy-adhesion layer 122, peeling of the adhered base materials can be suppressed. As the easy adhesion layer 122, for example, those described in paragraphs [0016] to [0027] of JP-A-2009-199001 can be applied.
The easy-adhesion layer 122 is usually formed by applying a coating liquid composed of a binder, a curing agent, and a surfactant to one surface of the base 120. A slipping agent such as organic or inorganic fine particles or wax may be added to the easy adhesion layer 122 as necessary.
The binder used for the easy-adhesion layer 122 is not particularly limited as long as it can improve the adhesion to the base 120. From the viewpoint of easy adhesion, one of a polyester resin, a polyurethane resin, an acrylic resin, and a styrene-butadiene resin is used. It is preferred to use more than one. A water-soluble or water-dispersible binder is particularly preferable from the viewpoint of environmental load.
Further, for the purpose of adjusting the refractive index of the easy adhesion layer 122, metal oxide fine particles may be added to the easy adhesion layer 122. As the metal oxide fine particles, high refractive index metal oxides such as tin oxide, zirconium oxide, zinc oxide, titanium oxide, cerium oxide and niobium oxide are preferable.
The particle diameter of the metal oxide fine particles is preferably in the range of 1 nm to 50 nm, particularly preferably in the range of 2 nm to 40 nm. The addition amount of the metal oxide in the easy-adhesion layer 122 is preferably added in the range of 10 to 90 parts by mass in the easy-adhesion layer 122 in order to obtain a desired refractive index, and particularly 30 to 80 parts by mass. It is preferable to add in the range of parts.
The refractive index of the easy-adhesion layer 122 is preferably in the range of 1.56 to 1.64 for the purpose of reducing the interference color due to the reflection of the laminated film. If the refractive index is smaller than 1.56 or larger than 1.64, the effect of reducing the interference color is reduced.
The formation method of the easy-adhesion layer 122 is not particularly limited, and a known coating method can be appropriately selected according to the purpose. For example, a spin coater, a roll coater, a bar coater, a curtain coater and the like can be mentioned. In any method, after a solution containing a material for forming the easy-adhesion layer 122 is applied to a desired surface, the layer is formed by drying the solution. Here, the drying method is not particularly limited, and a commonly used method can be appropriately selected.
The thickness of the easy adhesion layer 122 is preferably 0.01 μm to 2 μm, and more preferably 0.01 μm to 1 μm. In addition, before forming the easy adhesion layer 122 on the base 120, the base 120 and the easy adhesion layer 122 are subjected to corona discharge treatment, glow discharge treatment, atmospheric pressure plasma treatment, UV-ozone treatment, flame treatment, and the like. Adhesion with can be improved.
In addition, it is preferable that the easily bonding layer 122 used for the diffusion sheet 32 has high transparency.

The second base material 112 has a biaxially-stretched PET resin as a base 120, and an easy adhesion layer 122 is formed on both surfaces of the base 120.

The third base material 114 has a biaxially stretched PET resin as a base 120, a hard coat layer 124 is formed on the surface of the base 120 on the side that becomes the surface of the diffusion sheet 32, and the other surface (second base material). 112), an easy adhesion layer 122 is formed on the surface.

The hard coat layer 124 is for preventing the surface of the diffusion sheet 32 from being scratched, and is a layer provided for improving scratch resistance. The thickness of the hard coat layer 124 is preferably 1 μm to 20 μm, and more preferably 1 μm to 10 μm.
As the material of the hard coat layer 124, moisture-heat curing using polyfunctional acrylic monomer and oligomer-containing material that can be cured by irradiation with ultraviolet rays, electron beams, etc., hydrolysis of alkoxysilane and dehydration condensation of silanol generated there. A type of silica-based hardcoat is included. The hard coat layer 124 used for the diffusion sheet 32 is preferably highly transparent.

The adhesive layer 116 is for bonding the substrates together. There are no particular limitations on the adhesive layer 116, such as acrylic, urethane, epoxy, and silicone, and materials that are usually used for adhesion can be appropriately selected and used according to the purpose. Specifically, as a laminate-based commercial product, for example, there is a two-component dry laminate material that can be used by adding an LCR-901 isocyanate-based curing agent to LIS805 urethane-based main ingredient manufactured by Toyo Ink. can give. Furthermore, as the laminate, materials suitable for the extrusion method and the hot melt method can be used as appropriate.
The refractive index of the adhesive layer 116 is preferably 1.5 to 1.67.
The thickness of the adhesive layer 116 is preferably 1 μm to 50 μm, and more preferably 1 μm to 15 μm, from the viewpoint of securely bonding without impairing light transmittance.

Here, the first substrate 110, the second substrate 112, and the third substrate 114 preferably each have a thickness in the range of 150 to 300 μm. Thus, when the thickness h of the diffusion sheet is 0.3 mm <h ≦ 1.0 mm, the mechanical strength is obtained by bonding and forming a plurality of substrates having a thickness of 150 to 300 μm. Is preferable in that wrinkles and twists are less likely to occur.

In the example shown in FIG. 7A, the light diffusion layer 126 is formed on the surface of the diffusion sheet 32. However, the present invention is not limited to this, and the light diffusion layer 126 is formed inside the diffusion sheet 32. It is good also as a structure formed.
For example, as in the diffusion sheet shown in FIG. 7B, the first base material 110 having the light diffusion layer 126 may be stacked and sandwiched between the two third base materials 114.

In the illustrated example, the light diffusion layer 126 or the hard coat layer 124 is formed on the surface on the surface side of the diffusion sheet. However, the present invention is not limited to this, and the surface on the surface side of the diffusion sheet is easily formed. The adhesive layer 122 may be formed. For example, the first base material 110, the second base material 112, and the second base material 112 may be stacked in this order, or the second base material 112, the first base material 110, and the second base material 122 may be stacked. You may laminate | stack in order.

Further, as the base material of the diffusion sheet 32, one of acrylic (PMMA) resin, polystyrene resin, MS resin (styrene-PMMA copolymer resin), and polycarbonate is used as a material and is molded by extrusion or cast polymerization. It is also preferable to use a base material that has been prepared. Use of a base material obtained by molding the above resin by extrusion or cast polymerization is preferable in that smoothness and surface properties can be improved even in a large size, and optical characteristics can be made uniform.

In the illustrated backlight unit 20, one diffusion sheet 32 is arranged. However, the present invention is not limited to this, and a plurality of diffusion sheets may be arranged. In addition to the sheet 32, various optical sheets used in the backlight unit, such as a prism sheet, may be arranged.

In the illustrated backlight unit 20, the light source unit 28 is locked to the lower housing 42, the light guide plate 30 is locked to the light source unit 28, and the diffusion sheet 32 is locked to the light guide plate 30. And held.
The configuration will be described below with reference to FIGS. 2, 3, and 6 (A).

On the inner wall surface on the back surface 30b side of the lower housing 42, a support pin 66 is erected at the center in the upper left and right (LR) direction. Further, at the same position in the vertical (UD) direction with respect to the support pin 66, the support pin 64a is spaced a predetermined distance from the support pin 66 in one of the left and right directions, and the support pin 64b is spaced the same distance in the other direction. Established.
Moreover, in the light source support part 52 of the light source unit 28, as described above, the light source support part 52 to which the LED chip 50 is fixed penetrates in the thickness direction of the light guide plate 30 and penetrates in the center part in the left-right direction. A hole 72a is formed, and a long hole 70a that extends from the through hole 72 in one direction in the left-right direction and extends in the left-right direction and penetrates the same is separated in the other direction by the same distance. Are formed respectively. Both the long holes 70a and 70b are formed so that the distance from the center of the through hole 72 to the center in the left-right direction is equal to the distance between the support pin 66 and the support pins 64a and 64b.

In the illustrated backlight unit 20, the support pin 66 of the lower housing 42 is in the through hole 72 of the light source unit 28, the support pin 64 a of the lower housing 42 is in the long hole 70 a of the light source unit 28 a, and the lower housing 70. The lower housing 42 supports the light source unit 28 at a predetermined position by inserting the support pins 64b into the long holes 70b of the light source unit 28a.

Further, in the light source support portion 52 of the light source unit 28, a support pin 74a is erected in the vicinity of one end portion in the left-right direction on the front end surface of the plate portion on which the LED chips 50 are arranged, and the other end portion. Support pins 74b are erected at the same vertical position in the vicinity. Further, a support pin 74c is erected at the same position in the vertical direction as the support pin 74a and the like, and at the center in the horizontal direction.
On the other hand, as described above, the holding members 84a and 84b are fixed to both corners of the light emitting surface 30a of the light guide plate 30 on the light incident surface side. A holding member 84c is fixed at the center in the left-right direction.
In the holding members 84a and 84b fixed to the left and right end portions on the light incident surface side of the light guide plate 30, elongated holes 88a and 88b, which are through holes extending in the left and right direction, are provided at the same position in the vertical direction, respectively. It is formed. Both the long holes 88a and 88b have a distance from the center in the left-right direction of the light guide plate 30 to the center in the left-right direction of itself (the long hole) and the through-hole 72 formed in the light source support portion 52. It is formed to be equal to the distance between the pin 74a and the support pin 74b.
The holding member 84c fixed to the upper center is formed with a through hole 88c at the same position in the vertical direction as the elongated hole 88a and the like, and at the center in the horizontal direction of the light guide plate 30.

In the illustrated backlight unit 20, the support pin 74c of the light source support portion 52 of the light source unit 28 is supported in the through hole 88c, the support pin 74a of the light source unit 28 is supported in the elongated hole 88a of the holding member 84a, and the light source unit 28 is supported. The pins 74b are inserted through the long holes 88b of the holding member 84b.
Accordingly, the light incident surface 30c of the light guide plate 30 and the LED chip 50 row of the light source unit 28 face each other, and the light guide plate 30 is supported by the light source unit 28 (its light source support portion 52). Here, the vertical positions of the support pins and the corresponding holding members are set so that the distance between the light source unit 28 (light emitting surface of the LED chip 50) and the light incident surface 30c is appropriate. Needless to say.

A support pin 86a is erected on the holding member 84a fixed to the light guide plate 30, a support pin 86b is erected on the holding member 84b, and a support pin 86c is erected on the holding member 84c at the center in the left-right direction.
Further, as shown in FIG. 6, a reinforcing member 92a and a reinforcing member 92b are fixed to one end in the left-right direction and the other end in the upper end of the diffusion sheet 32, respectively. A reinforcing member 92c is fixed at the center of the.
In the reinforcing members 92a and 92b, elongated holes 90a and 90b, which are through-holes extending in the left-right direction (also through the diffusion sheet 32), are formed at the same position in the up-down direction. Both of the long holes 90a and 90b have a distance from the center in the left-right direction of the light guide plate 30 to the center in the left-right direction of the light guide plate 30 and the support pin 86c of the holding member 84c of the light guide plate 30. It is formed to be equal to the distance between the support pin 86a of the member 84a and the support pin 86b of the holding member 84b. Further, a through hole 90c (same as above) is formed in the central reinforcing member 92c in the left-right direction at the same position in the vertical direction as the support pin 86a and the like, and in the center in the left-right direction.

In the illustrated backlight unit 20, the support pin 86c of the holding member 84c fixed to the light guide plate 30 is inserted into the through hole 90c of the reinforcing member 92c, and the support pin 86a of the holding member 84a is connected to the through hole 90a of the reinforcing member 92a. Then, the support pins 86b of the holding member 84b are inserted through the through holes 90b of the reinforcing member 92b.
Thereby, the diffusion sheet 32 is supported by the light guide plate 30.

As is clear from the above description, in the backlight unit 20, the light source unit 28 is supported by the lower housing 42, the light guide plate 30 is supported by the light source unit 28, and the diffusion sheet 32 is supported by the light guide plate 30. Thus, each component is installed at a predetermined position in the lower housing 42.

When a flexible backlight unit is configured, if the light guide plate, diffusion sheet, and housing are fixed on both ends of the light incident surface (light source unit) side and the opposite surface side, the backlight When the light unit 20 is bent or flattened and deformed, each member regulates the movement of other members, so that the light guide plate and the diffusion sheet are damaged or the flexibility is lowered. There is a risk of doing so.
On the other hand, the light source unit 28, the light guide plate 30, the diffusion film 32, and the housing 26 of the backlight unit 20 are respectively locked on the light source unit 28 side, and the other end side is made free. Even when the backlight unit 20 is deformed by bending or flattening it as the flexible backlight unit 20, the end opposite to the fixed end can be freely moved. Each member does not restrict the movement of other members, the light guide plate 30 and the diffusion sheet 32 are damaged, the flexibility of the backlight unit 20 is reduced, and the diffusion film is wrinkled or twisted. Can be prevented.

In the backlight unit 20, the light guide plate 30 and the diffusion sheet 32 expand and contract due to heat of the light source unit 28, moisture absorption due to the installation environment, and the like.
Since the expansion and contraction amounts of the diffusion sheet and the light guide plate are different due to the influence of heat and moisture absorption, the expansion and contraction of the diffusion sheet and the light guide plate affect each other when they are fixed at both ends. There is a possibility that the light plate is damaged or the flexibility is lowered.

In contrast, the backlight unit 20 of the present invention locks the light source unit 28, the light guide plate 30, the diffusion sheet 32, and the housing 26 of the backlight unit 20 on the light source unit 28 side, and the other end side. By adopting a free configuration, one end portion is configured to be freely movable, so that the light guide plate 30 and the diffusion sheet 32 do not affect each other even if the light guide plate 30 and the diffusion sheet 32 expand or contract. Damage and a decrease in flexibility can be prevented.

In the illustrated example, as a preferred mode, the light guide plate 30 is locked to the light source unit 28. With such a configuration, even when the backlight unit 20 is bent or flattened and deformed, or when the light guide plate 30 is expanded and contracted, the light incident surface 30c of the light guide plate 30 The distance of the light emitting surface 50a of the LED chip 50 can be kept constant, and the light incident efficiency can be kept.

In the illustrated example, the housing 26 and the light source unit 28, the light source unit 28 and the light guide plate 30, and the light guide plate 30 and the diffusion sheet 32 are respectively locked by forming pins and through holes (long holes). Although it was set as the structure, it is not limited to this, You may fix by a well-known means, respectively.

Moreover, in the backlight unit 20 of the example of illustration, as a preferable aspect, engagement with the light-guide plate 30 and the diffusion sheet 32 is performed with the long hole and support pin which are extended in the left-right direction. Thereby, not only the vertical direction but also the expansion and contraction of the light guide plate 30 and the diffusion sheet 32 in the left and right direction can be absorbed, and the distortion and warpage of the light guide plate 30 and the diffusion sheet 32 due to the expansion and contraction in the left and right direction are also suitable. Can be prevented.
In this regard, the same applies to the relationship between the housing 26 and the light source unit 28 and between the light source unit 28 and the light guide plate 30.

Here, in the illustrated example, as a preferred embodiment, a support pin 86c is erected at the center of the light guide plate 30 in the left-right direction, and further, at the center of the diffusion sheet 32 in the left-right direction, the support pin 86c is approximately the same size ( A through hole 90c that is large enough to allow insertion is formed, and the support pin 86c is inserted through the through hole 90c.
In this way, by fixing the center portion in the left-right direction in the left-right direction, the left-right expansion / contraction can be distributed to both sides, and the movement of the end due to the expansion / contraction can be halved. In addition, since the support pin 86c and the through hole 90c are provided, the diffusion sheet 32 can be positioned using this as a reference position.
This also applies to the relationship between the housing 26 and the light source unit 28 and between the light source unit 28 and the light guide plate 30.

In the illustrated example, a support pin is erected on the holding member of the light guide plate 30 and the light guide plate 30 and the diffusion sheet 32 are locked by forming a through hole in the diffusion sheet 32. However, the present invention is not limited to this, and conversely, a pin may be erected on the diffusion sheet 32 and a through hole may be formed in the light guide plate holding member (or the light guide plate itself). In addition, the support pins may be erected directly on the light guide plate 30 without providing the holding member.
This also applies to the relationship between the housing 26 and the light source unit 28, and the relationship between the light source unit 28 and the light guide plate 30.

The liquid crystal display device 10 basically has such a configuration.
In the backlight unit 20, the light emitted from the light source unit 28 disposed facing the light incident surface 30 c of the light guide plate 30 enters the light incident surface 30 c of the light guide plate 30. The light incident from the light incident surface 30c passes through the light guide plate 30 while being scattered by the scatterers included in the light guide plate 30, and is emitted directly or after being reflected by the back surface 30b. To do.
Thus, the light emitted from the light emitting surface 30 a of the light guide plate 30 passes through the diffusion sheet 32 and is emitted from the light emitting port 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.

Here, as described above, the backlight unit 20 of the present invention is formed flexibly, and can be deformed by being bent or flattened.

FIG. 8 shows a schematic diagram of a state in which the backlight unit 20 is curved. In FIG. 8, members other than the light guide plate 30, the diffusion sheet 32, the light source unit 28, and the casing 26 (members for locking the members to each other (support pins, holding members, reinforcing members)) and the like Is not shown.
The backlight unit 20 shown in FIG. 8 is curved with a radius of curvature R [mm] in a direction perpendicular to the light incident surface 30 c of the light guide plate 30.
Here, the bending stress of the diffusion sheet 32 when curved with a radius of curvature R [mm] is P [N / mm], and the length of the diffusion sheet 32 in the direction perpendicular to the light incident surface 30c is a [ mm], the longitudinal width of the light incident surface 30c is b [mm], the thickness is h [mm], the Young's modulus of the material of the diffusion sheet 32 is E [N / mm], and the Poisson's ratio is ν, The bending ω of the entire housing when bent is expressed by ω = R (1-cos (a / 2R)), and the bending stress P of the diffusion sheet 32 is P = (ω · E · h ² · b) / (Α · a ⁴ ).
Here, α is a coefficient obtained from the dimensions (thickness h, length a, width b) of the diffusion sheet 32. FIG. 9 shows the relationship between the coefficient α and the dimension of the diffusion sheet.

In order to return to the flat state so that the diffusion sheet 32 does not bend or wrinkle when the backlight unit 20 is returned to the flat state after being bent, the force to return to the casing 26 is required to return to the flat state. It is necessary to be larger than the friction force between them, and the force applied to the film by the friction force needs to be smaller than the force causing the film to bend. Accordingly, when the maximum static friction coefficient between the casing 26 (upper housing 44) and the diffusion sheet 32 is μ ₀ , the bending stress P of the diffusion sheet 32 needs to satisfy P> μ ₀ / tan (a / R). is there.

Further, when the amount of bending is large, that is, when the radius of curvature R is small, the stress at the time of bending increases, so that bending occurs. Therefore, the bending stress P of the diffusion sheet 32 needs to satisfy P ≦ P _max . Here, P _max is a stress that causes the diffusion sheet to bend, and is expressed by P _max = E · π ² / (6 (1-ν) ² ) · (h / a) ² .

Here, FIGS. 10A and 10B show the relationship between the radius of curvature R and the bending stress P. FIG.
FIG. 10A shows the case where the thickness h of the diffusion sheet 32 is 0.3 [mm], the length a is 500 [mm], the width b is 700 [mm], and P _max is It is about 0.08 [N / mm ² ].
FIG. 10B shows the case where the thickness h of the diffusion sheet 32 is 0.5 [mm], the length a is 500 [mm], the width b is 500 [mm], and P _max is It is about 0.26 [N / mm ² ].
As shown in FIGS. 10A and 10B, the smaller the radius of curvature R, the greater the stress at the time of bending, so that bending occurs.

As described above, when the backlight unit is bent and then returned to the flat state, the diffusion sheet causes a buckling phenomenon in the vicinity of the end of the light emission port of the housing as shown in FIG. As a result, slack and wrinkles may occur, and the light emitted from the backlight unit may have a non-uniform luminance distribution.

On the other hand, the maximum static friction coefficient μ ₀ , the thickness h and the length of the diffusion sheet 32 so that the bending stress P satisfies P> μ ₀ / tan (a / R) and P ≦ P _max. By setting a, width b, the Young's modulus E of the material of the diffusion sheet 32, and the Poisson's ratio ν, the buckling phenomenon is prevented even when the backlight unit is bent and then flattened. Since no slack or wrinkle occurs, it is possible to prevent the light emitted from the backlight unit from having a non-uniform luminance distribution or reducing the light utilization efficiency.

Here, the thickness h, the length a, the width b, and the curvature radius R of the diffusion sheet 32 are 0.25 <h ≦ 1.0, 300 <R <10000, and 1.0 ≦ b. It is preferable to satisfy /a<3.0.
When the thickness h, the length a, the width b, and the radius of curvature R of the diffusion sheet 32 satisfy the above ranges, the flexible back can be obtained in the aspect ratio (ratio between a and b) of the surface assumed as illumination. The film incorporated in the backlight unit used at the curvature radius R assumed as the light is preferable in that the film can function as a uniform curved light source without bending or peeling.

Hereinafter, specific examples of the present invention will be given and the backlight unit of the present invention will be described in detail.

[Example]
As Example 1, the backlight unit 20 shown in FIG. 2 was used, and after the backlight unit 20 was bent, the diffusion sheet was inspected for bending and wrinkling when it was returned to the flat state.
The diffusion sheet 32 used in Example 1 had a thickness h of 0.3 mm, a length a of 500 mm, a width b of 700 mm, and a bending radius of curvature R of 500 mm. At this time, the coefficient α is 0.077, the maximum stress P _max is 0.080 N / mm ² , and the bending stress P is 0.065 N / mm ² .
Using such a backlight unit 20, the backlight unit 20 was bent and then inspected for the presence / absence of wrinkles / wrinkles of the diffusion sheet 32 when it was returned to a flat state. The test was performed a plurality of times, and a case where no bending / wrinkling occurred was evaluated as “good”, and a case where bending / wrinkling occurred even once was evaluated as “poor”.
As a result, the evaluation was good.

Further, as Example 2, the diffusion sheet 32 was inspected for bending / wrinkle in the same manner as Example 1 except that the radius of curvature R was 750 mm.
As Example 3, the diffusion sheet 32 was inspected for bending and wrinkles in the same manner as in Example 1 except that the radius of curvature R was 1000 mm.
As Example 4, the diffusion sheet 32 was inspected for bending / wrinkle in the same manner as in Example 1 except that the width b of the diffusion sheet 32 was 500 mm and the radius of curvature R was 700 mm.
As Example 5, the diffusion sheet 32 was inspected for bending / wrinkle in the same manner as in Example 1 except that the width b of the diffusion sheet 32 was 900 mm and the curvature radius R was 350 mm.
As Example 6, the diffusion sheet 32 was inspected for bending / wrinkle in the same manner as in Example 1 except that the thickness h of the diffusion sheet 32 was 0.5 mm and the curvature radius R was 350 mm.
As Example 7, the diffusion sheet 32 was inspected for bending and wrinkling in the same manner as in Example 6 except that the thickness of the diffusion sheet 32 was 0.5 mm.
The evaluation results are shown in Table 1. As shown in Table 1, in all of Examples 2 to 7, the bending stress P was smaller than the maximum stress P _max , and no bending or wrinkle occurred. Therefore, evaluation was (circle).

Further, as Comparative Example 1, the diffusion sheet 32 was inspected for bending and wrinkling in the same manner as in Example 1 except that the thickness h of the diffusion sheet 32 was 0.2 mm.
As Comparative Example 2, the diffusion sheet 32 was inspected for bending and wrinkling in the same manner as in Comparative Example 1, except that the width b of the diffusion sheet 32 was 500 mm and the radius of curvature R was 700 mm.
As Comparative Example 3, the diffusion sheet 32 was inspected for bending and wrinkling in the same manner as in Comparative Example 1 except that the width b of the diffusion sheet 32 was 900 mm and the curvature radius R was 350 mm.
The evaluation results are shown in Table 2. As shown in Table 2, in each of Comparative Examples 1 to 3, the bending stress P was larger than the maximum stress P _max , and bending and wrinkling occurred. Therefore, evaluation was x.

The planar lighting device according to the present invention has been described in detail above. However, the present invention is not limited to the above embodiment, and various improvements and modifications are made without departing from the gist of the present invention. May be.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Liquid crystal display panel 14 Drive unit 20,200 Backlight unit (planar illumination device)
24 Light exit port 26, 208 Housing 28, 206 Light source unit 30, 100, 102, 204 Light guide plate 30a Light exit surface 30b Back surface 30c Light entrance surface 30d Side surface 32, 202 Diffusion sheet 42 Lower housing 44 Upper housing 49 Power supply Storage unit 50 LED chip 50a Light emitting surface 52 Light source support unit 60 First layer 62 Second layer 64a, 64b, 66, 74a, 74b, 74c, 86a, 86b, 86c Support pins 70a, 70b, 88a, 88b, 90a, 90b Long hole 72, 90c Through hole 84a, 84b, 84c Retaining member 92a, 92b, 92c Reinforcing member 110 First base material 112 Second base material 114 Third base material 116 Adhesive layer 120 Base 122 Easy adhesive layer 124 Hard coat layer 126 Light diffusion layer α bisector z interface

Claims (8)

1. A rectangular light exit surface, one light entrance surface that is provided on the edge side of the light exit surface and that enters light traveling in a direction substantially parallel to the light exit surface, and the light exit surface are opposite to each other A light guide plate having a back surface provided on the side and scattering particles dispersed therein, and having a thickness in a direction perpendicular to the light exit surface of 1.5 mm or less,
   A light source unit disposed to face the light incident surface of the light guide plate;
   A diffusion sheet disposed to face the light exit surface of the light guide plate; and
   A planar lighting device having a housing that houses the light guide plate, the light source unit, and the diffusion sheet and includes an opening corresponding to the light exit surface of the light guide plate,
   The light guide plate has two or more layers with different particle concentrations of the scattering particles overlapped in a direction substantially perpendicular to the light exit surface, and the two or more layers in the direction perpendicular to the light incident surface. The thickness of each layer in a direction substantially perpendicular to the light exit surface is changed, and the composite particle concentration of the light guide plate is changed,
   And the light guide plate, the light source unit, the diffusion sheet, and the housing are engaged with each other on the light source unit side,
   When the entire planar lighting device is curved in a direction perpendicular to the light incident surface, the radius of curvature is R [mm], the bending stress is P [N / mm ² ], and the casing and the diffusion sheet The maximum static friction coefficient is μ ₀ , the length of the diffusion sheet in the direction perpendicular to the light incident surface is a [mm], the thickness is h [mm], and the Young's modulus of the material of the diffusion sheet Is E [N / mm ² ] and Poisson's ratio is ν, the bending stress P is
   P> μ ₀ / tan (a / R) and P ≦ P _max
   Here, P _max = E · π ² / (6 (1-ν) ² ) · (h / a) ²
   A planar illumination device characterized by satisfying the above.
2. When the width of the light incident surface of the diffusion sheet in the longitudinal direction is b [mm], the thickness h, the length a, the width b, and the radius of curvature R of the diffusion sheet are:
   The planar lighting device according to claim 1, wherein 0.25 <h ≦ 1.0, 300 <R <10000, and 1.0 ≦ b / a <3.0 are satisfied.
3. The planar illumination device according to claim 1 or 2, wherein a biaxially stretched polyethylene terephthalate resin substrate is used as the substrate of the diffusion sheet.
4. When the thickness h [mm] of the diffusion sheet is 0.3 <h ≦ 1.0, two or more biaxially stretched polyethylene terephthalate resin base materials were bonded as the base material of the diffusion sheet. The planar lighting device according to claim 3, wherein a composite base material is used.
5. The planar illumination according to claim 1 or 2, wherein a base material molded by extrusion or cast polymerization using any one of acrylic resin, polystyrene resin, MS resin, and polycarbonate resin as a base material of the diffusion sheet is used. apparatus.
6. The two or more layers of the light guide plate are composed of two layers, a first layer on the light emitting surface side and a second layer on the back surface side having a particle concentration higher than that of the first layer. The planar illumination device according to any one of claims 1 to 5, wherein the thickness of the two layers is continuously changed so as to become thicker after becoming thinner as the distance from the light incident surface increases.
7. The two or more layers of the light guide plate are composed of two layers, a first layer on the light emitting surface side and a second layer on the back surface side having a particle concentration higher than that of the first layer. 6. The thickness of the two layers is continuously increased so as to become thicker again after becoming thicker and thinner after being separated from the light incident surface. Planar lighting device.
8. The planar illumination device according to any one of claims 1 to 7, wherein the back surface of the light guide plate is a plane parallel to the light exit surface.
   

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