JP4680883B2 - Light guide plate and planar illumination device using the same - Google Patents

Description

  The present invention relates to a transparent light guide plate that diffuses light from a linear light source in a plane direction and emits uniform illumination light from a light exit surface, and a planar illumination device using the transparent light guide plate.

A liquid crystal display device uses a backlight unit that irradiates light from the back side of a liquid crystal panel (LCD) to illuminate the liquid crystal panel. As a backlight unit, one using a light guide plate for converting light from a light source into planar light using a transparent resin flat plate is known. The backlight unit using the light guide plate is usually a light source for illumination, a light guide plate that diffuses light emitted from the light source to illuminate the liquid crystal panel, a prism sheet that uniformizes light emitted from the light guide plate, It is configured using parts such as a diffusion sheet.
In recent years, thinning of liquid crystal display devices and reduction in power consumption have been demanded, and light guide plates having various shapes have been proposed in order to realize them (for example, Patent Documents 1 to 3).

FIG. 15 is a schematic cross-sectional view of the surface light source device disclosed in Patent Document 1.
In the surface light source device (backlight unit) shown in the figure, after the fluorescent lamp 102 is embedded in the light guide plate 100, the reflection sheet 104 is disposed on the back surface of the light guide plate 100, and the transmitted light amount correction sheet is provided on the exit surface of the light guide plate 100. 106, a light diffusion plate 108, and a prism sheet 110 are laminated.
The light guide plate 100 has a substantially rectangular shape and is formed using a resin in which fine particles that diffuse illumination light are dispersed and mixed. In addition, the upper surface of the light guide plate 100 is flat and assigned to the exit surface. Further, a groove 100a having a U-shaped cross-section for embedding the fluorescent lamp 102 is formed on the back surface (surface opposite to the emission surface) of the light guide plate 100, and the emission surface of the light guide plate 100 is directly above the fluorescent lamp 102. Avoiding this, a light amount correction surface 100b that prompts emission of illumination light is formed.

  As described above, in Patent Document 1, the light guide plate 100 is formed by mixing fine particles, and the illumination light is corrected by the light amount correction surface 100b formed on a part or all of the emission surface except directly above the fluorescent lamp 102. It is described that by promoting the emission, the entire thickness can be reduced and unnatural luminance unevenness of the emitted light can be reduced.

Patent Document 2 discloses a backlight of a liquid crystal display device that can realize a reduction in size and weight of the liquid crystal display device and reduction in cost and power consumption without reducing the amount of backlight irradiation. For this purpose, a rectangular irradiation surface, a rectangular cross section grooved in parallel with the long side at the center of the short side, and a groove with a rectangular cross-section for inserting the light source, facing both sides of the long side across this groove A light guide plate having a back surface formed so that the plate thickness is gradually reduced is disclosed.
Further, in Patent Document 3, the frame of the liquid crystal display device can be narrowed and the thickness can be reduced, and in order to obtain a bright backlight unit with good light utilization efficiency, the width direction of the concave portion for arranging the light source is described. A light guide (light guide plate) is disclosed in which the parallel cross-sectional shape is a parabolic shape with the depth direction as the main axis.

However, in the planar illumination device using the light guide plate disclosed in Patent Documents 1 to 3, luminance unevenness occurs on the light emitting surface, and light utilization efficiency is poor, and uniform and high luminance light is emitted. There was a problem that the light could not be emitted from the surface.
Therefore, the present applicant, in Patent Document 4, a rectangular light emitting surface, a thick portion parallel to one side thereof and positioned at a substantially rectangular central portion, and a thin end portion formed in parallel to the thick portion. And a parallel groove for accommodating the rod-shaped light source is formed in the center of the thick portion in parallel with the one side, and includes the shaft of the rod-shaped light source on both sides of the parallel groove. An inclined back surface portion that is symmetric with respect to a plane perpendicular to the thick wall portion, the wall thickness decreases toward the thin wall end portions on both sides in a direction perpendicular to the one side from the thick wall portion, and forms an inclined back surface; And a peak value of illuminance or luminance formed by light emitted from a rod-shaped light source housed in the parallel groove in a first portion corresponding to the parallel groove on the rectangular light emitting surface. Of the emitted light in the second portion corresponding to the inclined back surface portion. In the cross-sectional shape of the parallel groove in the orthogonal direction according to the ratio to the average value of illuminance or luminance formed by the rectangular groove, the rectangular shape is perpendicular to the rectangular light exit surface of the parallel groove. A light guide plate is disclosed in which the end portions of the parallel grooves are thinned symmetrically toward the shaped light exit surface. The light guide plate having such a configuration is thin and lightweight, and has high light utilization efficiency (light emission efficiency) from the light emission surface, and can emit illumination light that is more uniform, less uneven, and has higher luminance. it can.

Japanese Patent Laid-Open No. 9-304623 JP-A-8-62426 JP 10-1333027 A Japanese Patent Laid-Open No. 2005-23497

  In a planar illumination device having a structure in which a linear light source is arranged in a groove formed on the back surface of the light guide plate, when the linear light source is turned on, the temperature on the lower surface side of the light guide plate is higher due to the heat generated by the linear light source. It becomes higher than the temperature on the side, and a temperature difference occurs between the upper surface side and the lower surface side of the light guide plate. For this reason, a difference in expansion amount due to thermal expansion occurs between the upper surface side and the lower surface side of the light guide plate, and stress is generated inside the light guide plate, causing warpage of the light guide plate. Such warpage of the light guide plate causes distortion on the light exit surface of the light guide plate, thereby causing uneven brightness in the illumination light of the planar illumination device or reducing the average brightness.

The present invention has been made to eliminate such inconveniences, and an object of the present invention is to provide a light guide plate in which the occurrence of warpage due to heat of a linear light source disposed in a groove is suppressed. is there.
Another object of the present invention is to prevent or suppress the occurrence of warpage of the light guide plate due to the heat of the linear light source arranged in the groove of the light guide plate, and to emit uniform illumination light with reduced luminance unevenness. An object of the present invention is to provide a planar lighting device that can be used.

In order to solve the above-described problem, a first aspect of the present invention is a light guide plate configured by integrally connecting a plurality of unit light guide plates formed of a transparent resin material, and the unit light guide plate includes: A flat rectangular light emitting surface, and a back surface in which a parallel groove parallel to one side of the light emitting surface is formed at a substantially center opposite to the light emitting surface, and a linear light source is disposed in the parallel groove. When the length of the light guide plate in the direction perpendicular to the parallel grooves is L ₀ [mm], the linear expansion coefficient of the resin material is k [/ ° C.], and the light guide plate is in a stable state after lighting. The surface temperature of the linear light source is Ts [° C.], the value of half of the cut area when the unit light guide plate is cut by a plane perpendicular to the parallel groove is S [mm ² ], and T = Ts−25 when the inequality ^{_{(L 0/280) 2 ·}} k (14T 2 + 710T) · (-0.65logS + .9) ≦ 10
A light guide plate that satisfies the requirements is provided.

  In the light guide plate according to the first aspect of the present invention, the back surface of the unit light guide plate is composed of a pair of symmetrical inclined surfaces with the parallel groove interposed therebetween, and the pair of inclined surfaces are formed from the parallel groove to the unit. It is preferable that the unit light guide plate is inclined so that the thickness gradually decreases toward the end of the light guide plate, and the pair of inclined surfaces are preferably formed of curved surfaces.

In order to solve the above-mentioned problem, a second aspect of the present invention is a flat rectangular light emitting surface, and a parallel groove parallel to one side of the light emitting surface at the substantially center opposite to the light emitting surface. A light guide plate configured by integrally connecting a plurality of unit light guide plates formed of a transparent resin material, and a linear light source disposed in a parallel groove of the light guide plate. When the length of the light guide plate in the direction perpendicular to the parallel grooves is L ₀ [mm], the linear expansion coefficient of the resin material of the unit light guide plate is k [/ ° C.], and the light guide plate is in a stable state after lighting. The surface temperature of the linear light source is Ts [° C.], the value of half of the cut area when the unit light guide plate is cut by a plane perpendicular to the parallel groove is S [mm ² ], and T = Ts−25 And when
^{_{(L 0/280) 2 ·}} k (14T 2 + 710T) · (-0.65logS + 1.9) ≦ 10
A planar lighting device that satisfies the above requirements is provided.

  2nd aspect of this invention WHEREIN: The back surface of the said unit light-guide plate is comprised from a pair of symmetrical inclined surface on both sides of the said parallel groove, and a pair of said inclined surface is the said unit light-guide plate from the said parallel groove. It is preferable that the unit light guide plate is inclined so as to gradually decrease toward the end, and the pair of inclined surfaces are preferably formed as curved surfaces.

  The light guide plate of this invention can suppress generation | occurrence | production of the curvature by the heat | fever of the linear light source arrange | positioned at the groove | channel on the back. Therefore, planar illumination light that is uniform and has almost no luminance unevenness can be emitted from the light exit surface.

  Further, the planar illumination device of the present invention prevents or suppresses the warpage of the light guide plate due to the heat of the linear light source disposed in the groove of the light guide plate, so that uniform illumination light with reduced luminance unevenness is obtained. Can be emitted.

Below, the light-guide plate according to this invention and the planar illuminating device using the same are demonstrated.
FIG. 1 is a schematic perspective view of an embodiment of the planar illumination device of the present invention as viewed from the light exit surface side. 2A, 2B, 2C, and 2D are a front view, a bottom view, a side view, and a rear view of the planar illumination device shown in FIG. 1, respectively. FIG. 3 is a partial cross-sectional view of an embodiment of the planar lighting device shown in FIG. In addition, in the following figures including these figures, in order to facilitate understanding, they are shown enlarged in the direction of the thickness of the planar lighting device.
As shown in FIG. 1 and FIGS. 2A to 2D, the planar illumination device 10 includes a plurality of linear light sources 12 and emits uniform light from a rectangular light exit surface 14 a. 14, a housing 16 in which the lighting device main body 14 is housed, a rectangular opening 16a is formed on the light emitting surface 14a side (surface side), and the housing 16 is opposite to the light emitting surface 14a. An inverter storage unit 20 that stores a plurality of inverter units 18 that are attached to the side (rear surface side) and that is used to light each of the plurality of linear light sources 12, and a plurality of inverter units 18 that are stored in the inverter storage unit 20 And a power source 38 (see FIG. 13) for lighting the plurality of linear light sources 12 respectively.

Here, the illuminating device main body 14 is for emitting uniform light from the rectangular light emitting surface 14a, and basically, as shown in FIGS. 3, 4 and 5A, A plurality of linear light sources 12 and a rectangular light exit surface 22a are formed on the side of the light exit surface 14a, and a plurality of parallel grooves 22b for accommodating the plurality of linear light sources 12 are formed on the back side thereof. The light guide plate 22 according to the present invention in which the thinnest portion 22c having the thinnest thickness from the light exit surface 22a side to the back side is formed between the grooves 22b, and the light exit surface 22a side of the light guide plate 22 is disposed on the light exit surface 22a side. An optical member unit 24 having a rectangular plane that forms the emission surface 14 a and a reflection member 26 disposed along the back surface 22 d of the light guide plate 22 are provided.
4 shows only the unit light guide plate 23 having one parallel groove 22b which is one unit constituting the light guide plate 22, but as shown in FIG. The illuminating device main body 14 is constituted by a light guide plate 22 including a plurality of unit light guide plates 23, and the optical member unit 24 arranged on the upper portion of the light guide plate 22 is also substantially the same as the light emitting surface 22 a of the light guide plate 22. Needless to say, it has a size (area).

The linear light source 12 is disposed in the plurality of parallel grooves 22 b of the light guide plate 22 and is connected to the inverter unit 18. The linear light source 12 used in the present invention is a linear, that is, a thin rod-shaped cold cathode tube (CCFL: see FIG. 13), and is used to illuminate a surface. Here, a cold cathode tube is used as the linear light source 12, but the present invention is not limited to this, and the linear light source 12 may be any rod-shaped light source (linear light source), In addition to the cold cathode fluorescent lamp (CCFL), for example, a normal fluorescent tube (hot cathode fluorescent tube; HCFL), an external electrode tube (EEFL), a light emitting diode (LED), a semiconductor laser, or the like can be used. When an LED is used as the linear light source 12, a cylindrical or prismatic transparent light guide having the same length as the parallel grooves 22b of the light guide plate 22 is used, and the upper surface of the light guide and An LED light source may be used in which an LED is disposed on the bottom surface, LED light is incident from the top and bottom surfaces of the light guide, and is emitted from the side surface of the light guide.
The inverter unit 18 and the power source 38 (see FIG. 13B) that turn on and off the plurality of linear light sources 12 will be described later.

Next, the light guide plate 22 according to the present invention will be described.
The light guide plate 22 includes a plurality of unit light guide plates 23 as shown in FIG.
The unit light guide plate 23 is formed of a transparent resin, and as shown in FIG. 5B, a rectangular individual light emitting surface 23a, a thick portion 23b parallel to one side thereof, and both sides of the thick portion 23b. A thin end portion 23c formed parallel to one side, and the thickness is reduced from the thick portion 23b toward the thin end portions 23c on both sides in a direction perpendicular to the one side, constituting the back surface 22d of the light guide plate 22; An inclined back surface portion 23e that forms a flat inclined surface 23d, in which only a part in the vicinity of the end portion is curved, and a parallel groove 22b that is formed parallel to one side of the thick portion 23b and that houses the light source 12. Have That is, the unit light guide plate 23 includes one parallel groove 22b, and has an individual light exit surface 23a having the same length as the light exit surface 14a of the light guide plate 22 in a direction parallel to the parallel groove 22b. .

In the light guide plate 22 according to the present invention, the length of the light guide plate 22 in the direction perpendicular to the parallel grooves 22b is L ₀ [mm], the linear expansion coefficient of the resin material constituting the light guide plate 22 is k [/ ° C.], lighting The surface temperature of the linear light source 12 when it becomes stable later is Ts [° C.], and the value of half of the cut area when the unit light guide plate is cut by a plane perpendicular to the parallel groove is S [mm ² ], When T = Ts−25, the following inequality (1),
^{_{(L 0/280) 2 ·}} k (14T 2 + 710T) · (-0.65logS + 1.9) ≦ 10 ··· (1)
It is configured to satisfy. This inequality (1) will be described in detail later.
In the present invention, as long as the inequality (1) is satisfied, the structure and material of the unit light guide plate 23 and the light guide plate 22 are described in [0036] to [0039] of Japanese Patent Application Laid-Open No. 2005-23497 related to the present applicant. It is possible to apply those disclosed in the above.

The parallel grooves 22b may have a triangular shape as shown in the figure, but any other shape that has an effect of uniforming the luminance such as two hyperbolic shapes, U-shapes, and parabolic shapes that intersect is also possible. However, what is disclosed in [0040] to [0058] of Japanese Patent Application Laid-Open No. 2005-23497 related to the applicant's application can be applied.
Further, the inclined surface 23d may be formed from a flat surface in which only a part near the end portion is formed as a curved surface, as shown in the drawing, or the entire surface may be formed as a curved surface. The entire surface having a constant inclination angle with respect to the light emitting surface 23a may be a flat plane, or may be composed of a plurality of planes whose inclination angle gradually changes. These curved surfaces and planes are parallel grooves 22b. Must be parallel.
The profile of the cross section of the parallel groove 22b and the inclined surface 23d perpendicular to the parallel groove 22b is not particularly limited, but the luminance uniformity of the illumination light emitted from the individual light emission surface 23a is high, and If there is little decrease in luminance, the present invention is not particularly limited, but the one disclosed in Japanese Patent Application No. 2004-325251 relating to the application of the present applicant can be applied.

The unit light guide plate 23 allows illumination light emitted from the linear light source 12 accommodated in the parallel groove 22b to enter and is inclined in a direction parallel to the individual light emitting surface 23a from the thick portion 23b toward the thin end portion 23c. The illumination light propagated in the back surface portion 23e and the illumination light reflected from the inclined surface 23d and the reflecting member 26 arranged along the inclined surface 23d that forms the back surface are uniformly distributed from the individual light emitting surface 23a. Is emitted as a simple illumination light.
Thus, uniform illumination light is emitted from the light emitting surface 22a of the light guide plate 22 to which the plurality of unit light guide plates 23 are connected.
As shown in FIG. 5A, the light guide plate 22 has a structure in which the unit light guide plates 23 adjacent to each other in the direction orthogonal to the parallel groove 22b are connected to each other by the thin end portions 23c. The connecting portion forms the thinnest portion 22 of the light guide plate 22. In this case, it goes without saying that the light emitting surfaces 23a of the plurality of unit light guide plates 23 are connected to one another, and the light guide plate 22 forms a uniform light emitting surface 22a.

  As shown in FIG. 5A, the light guide plate 22 may be a single light guide plate connector integrally formed with a plurality of unit light guide plates 23 connected, but cost reduction and yield are achieved. In consideration of the improvement of the above and the ease of manufacture, a plurality of integrally formed light guide plate assemblies of unit light guide plates 23 may be connected to form a large-sized light guide plate having a large area light output surface 22a. In this case, the light guide plate connector is connected to the thin end portions 23c of the unit light guide plates 23 of the adjacent light guide plate connectors, and is connected in a direction orthogonal to the parallel grooves 22b to increase the size and emit light. The surface 22a may be increased in area, or the end portions orthogonal to the thin-walled end portion 23c of the adjacent light guide plate connector are connected to each other, connected in a direction parallel to the parallel groove 22b, and increased in size to emit light. The surface 22a may be increased in area, or these may be performed simultaneously and connected in a direction parallel to and perpendicular to the parallel grooves 22b, and further increased in size to increase the area of the light exit surface 22a. At this time, it is needless to say that the uniform planar light emitting surfaces of the plurality of light guide plate connectors are connected to each other, and the light guide plate 22 forms a uniform planar light emitting surface 22a. Absent. In this case, the linear light source 12 is preferably a linear light source having the length of the parallel groove 22b of the light guide plate 22 to which the light guide plate connector is connected, and is disposed above the light guide plate 22. The optical member unit 24 preferably has substantially the same size (area) as the light exit surface 22 a of the light guide plate 22.

Here, as described above, in the light guide plate 22 according to the present invention, the length of the light guide plate 22 in the direction perpendicular to the parallel grooves 22b is L ₀ [mm], and the linear expansion coefficient of the resin material constituting the light guide plate 22 is K [/ ° C.], Ts [° C.] of the surface temperature of the linear light source 12 when it is in a stable state after lighting, and half the cutting area when the unit light guide plate is cut by a plane perpendicular to the parallel groove Is S [mm ² ] and T = Ts−25, the following inequality (1),
^{_{(L 0/280) 2 ·}} k (14T 2 + 710T) · (-0.65logS + 1.9) ≦ 10 ··· (1)
It is configured to satisfy. Thereby, even if the lower surface of the light guide plate becomes high temperature by turning on the linear light source for a long time, the light guide plate is hardly warped and always provides uniform and uniform illumination from the light emitting surface. Can be emitted. Hereinafter, the basis of the inequality (1) will be described in detail.

First, using the thermal structure analysis software, the amount of warpage of the light guide plate was calculated by changing the stable temperature of the linear light source and the linear expansion coefficient of the light guide plate. In the analysis of the amount of warpage, a light guide plate having a structure in which ten unit light guide plates each having the shape shown in FIG. Further, the diameter of the light source is 2.6 mm, and the dimensions of the unit light guide plate are the pitch of the unit light guide plates 18, that is, the width L of the unit light guide plate 22, as shown in FIG. The thickness D of the thickest portion 22b of the thickness 22 is set to 5.5 mm, the distance d ₁ between the tip portion of the parallel groove 22b and the light emitting surface 23a is set to 1.0 mm, and the end of the inclined back surface 23d is The thickness d ₂ of the surface where the thickness of the light guide plate unit becomes the thinnest when flat is 2.87 mm, the width G ₁ of the end of the parallel groove 22 b opposite to the light emitting surface 23 a is 5.2 mm, and adjacent The inclined rear surface of the joint portion with the unit light guide plate is formed into a planar shape, and the curvature radius R of the minimum thickness portion near the joint surface 23f is set to 15 mm. Further, the angle formed by the light exit surface 23a and the inclined back surface 23d was 15.76 degrees.
Further, the linear expansion coefficient of the light guide ^{plate, 3.00 × 10 -5 [/℃],6.00×10 -5} [/℃],7.00×10 -5 [/ ℃], and 1. 00 × 10 ⁻⁴ [/ ° C.], and the stable temperature of the linear light source was 60 ° C. and 90 ° C.
Here, the stable temperature is a temperature when the surface temperature of the light source becomes constant.
As shown in FIG. 6, the warpage amount of the light guide plate 22 is the lowest position of the light emitting surface 22 a in the thickness direction (vertical direction) of the light guide plate 22 when both ends of the light guide plate 22 are placed horizontally. A distance h from A to the highest position B was set. The amount of warpage of the light guide plate 22 was the amount of warpage when the linear light source 12 was turned on and the linear light source reached a stable temperature.

FIG. 7 shows the amounts of warpage of four types of light guide plates having different linear expansion coefficients when the temperature (stable temperature) when stabilized after the linear light source 12 is turned on is 60 ° C. and 90 ° C. The graph is shown. FIG. 8 is a graph showing changes in the amount of warp with respect to the stable temperature of four types of light guide plates having different linear expansion coefficients. From the graph of FIG. 7, it can be seen that the amount of warpage of the light guide plate is proportional to the linear expansion coefficient of the material constituting the light guide plate. Moreover, it can be seen from the graph of FIG. 8 that the amount of warpage of the light guide plate increases as the stable temperature of the light source becomes higher than the room temperature of 25 ° C.
Here, in the graph of the warpage amount with respect to the stable temperature Ts of the light guide plate having a linear expansion coefficient of 1.00 × 10 ⁻⁴ shown in FIG. 8, a graph in which coordinates are converted so that the room temperature (25 ° C.) is the origin is shown. 9 shows. FIG. 9 shows an approximate curve represented by the following fourth-order polynomial (2) and an approximate curve represented by the following second-order polynomial (3).
Y = 1.8 × 10 ⁻⁶ T ⁴ −1.8 × 10 ⁻⁴ T ³ + 6.1 × 10 ⁻³ T ² + 5.7 × 10 ⁻² T (2)
Y = 1.4 × 10 ⁻³ T ² + 7.1 × 10 ⁻² T (3)
From the above results, the warpage amount Y of the light guide plate is expressed by the following formula (4) using the linear expansion coefficient k and the temperature T (= stable temperature Ts−25).
Y = k (14T ² + 710T) (4)

Next, the relationship between the warpage amount Y and the half-pitch cross-sectional area S of the unit light guide plate was examined as follows. Here, the cross-sectional area S is a half value of the area of the cut surface when the unit light guide plate is cut by a plane perpendicular to the parallel grooves, and as shown in FIG. That is, it is an area of a region (a region indicated by oblique lines) from the center line M of the cut surface of the unit light guide plate 23 to the end surface 23f. First, a model of a light guide plate having a structure in which 20 unit light guide plates having a pitch of 14 [mm] are connected (20 stations) with a constant length 280 [mm] (= L ₀ ) of the entire light guide plate, A model of a light guide plate having a structure in which five (5) unit light guide plates having a pitch of 56 [mm] are connected was analyzed using thermal structure analysis software in the same manner as described above. In the analysis, only by changing the pitch of the unit light guide plates, that is, only by changing the number of unit light guide plates to be connected, the shape of the parallel grooves of the unit light guide plates is basically shown in FIG. The same shape as the light guide plate 23 shown in FIG. Then, when the linear expansion coefficient k of the light guide plate is 1 × 10 ⁻⁴ [/ ° C.] and the stable temperature is 60 ° C. and 90 ° C., the same analysis is performed to obtain the warpage amount of the light guide plate. It was. In FIG. 11, the graph of the curvature amount with respect to the cross-sectional area S of the half pitch of a unit light-guide plate is shown.

Furthermore, the pitch is 28 [mm] for a model of a light guide plate having a pitch of 14 [mm] (a light guide plate having a 20-unit structure) and a model of a light guide plate having a pitch of 56 [mm] (a light guide plate having a 5-unit structure). The ratio of the model of the light guide plate (light guide plate having a 10-unit structure) to the amount of warpage was obtained. FIG. 12 shows the ratio of the warpage amount to the half-pitch cross-sectional area S of the unit light guide plate.
As can be seen from the graph shown in FIG. 12, when the cross-sectional area S is halved, the warpage amount of the light guide plate is 1.2 times, and when the cross-sectional area is doubled, the warpage amount of the light guide plate is 1 / fold. 1.2 times. That is, it can be seen that the warpage amount Y of the light guide plate is expressed by the logarithm of the cross-sectional area S and a linear function.

From the above results, the warpage amount Y of the light guide plate is determined by calculating the length of the light guide plate 22 in the direction perpendicular to the parallel groove 22b as L ₀ [mm], the linear expansion coefficient k, and the temperature T (= stable temperature Ts-25). And the half-pitch cross-sectional area S of the unit light guide plate is expressed by the following equation. Analysis model of the light guide plate, since it has a length L ₀ of 280mm in a direction perpendicular to the parallel grooves, multiplication in equation (5), in order to normalize the model length, the coefficient (L _0/280) ² is doing.
_{Y = (L 0/280)} 2 · k (14T 2 + 710T) × (-0.65logS + 1.9) ··· (5)
Therefore, if a combination of the linear expansion coefficient k, the temperature T (= stable temperature Ts-25), and the half-pitch cross-sectional area S of the unit light guide plate is used so that Y becomes 10 mm or less, the Y is disposed in the parallel grooves. It is possible to obtain a light guide plate that hardly generates warpage due to the heat of the linear light source.
For example, if the linear light source to be used in the planar illumination device is determined, the stable temperature of the linear light source is measured, and the linear expansion coefficient k and the unit light guide plate are set so as to satisfy the inequality (1). By setting the range of the half-pitch cross-sectional area S and manufacturing the light guide plate so as to be included in the range, it is possible to obtain a light guide plate having almost no warp due to heat generated by the linear light source. Furthermore, in addition to the linear light source to be used, when the material that can be used for the light guide plate is limited, the shape of the light guide plate may be designed so that the cross-sectional area S satisfies the inequality (1). .
Table 1 below shows suitable resin materials for the light guide plate and their linear expansion coefficients.

  Among these materials, it is more preferable to use PMMA from the viewpoint of the above inequality (1), price, and transparency.

The light guide plate 22 according to the present invention has been described in detail above.
Next, the optical member unit will be described. The optical member unit 24 makes the uniform illumination light emitted from the light exit surface 22a of the light guide plate 22 more uniform, and emits the illumination light with further improved uniformity from the light exit surface 14a of the illumination device body 14. As shown in FIGS. 3 and 4, a microprism array parallel to the parallel grooves 22 b of the light guide plate 22 and forming the light output surface 14 a is formed, and illumination emitted from the light output surface 22 a of the light guide plate 22. A prism sheet 24a that improves light collection by improving light collection, a diffusion sheet 24b that diffuses and equalizes illumination light emitted from the light exit surface 22a of the light guide plate 22, and an exit from the light exit surface 22a of the light guide plate 22 Is used to reduce the luminance unevenness of the illumination light, and is arranged on the transparent film 25a and the surface according to the luminance unevenness, and a large number of transmittance adjusting bodies 25 made of a diffuse reflector. And a transmittance adjusting member 24c provided with.

The transmittance adjusting member 24c is preferably provided on the side of the light guide plate 22 close to the light emitting surface 22a. However, the arrangement order and the number of arrangement of the prism sheets 24a and the diffusion sheets 24b are not limited, and optical The prism sheet 24a, the diffusion sheet 24b, and the transmittance adjusting member 24c used in the member unit 24 are not limited to those described above, and the illumination light emitted from the light emitting surface 22a of the light guide plate 22 can be made more uniform. Any optical member may be used as long as it can be used. The prism sheet 24a may be disposed between the light guide plate 22 and the reflecting member 26 on the back surface 22d side, or a prism row may be formed on the back surface 22d of the light guide plate 22 itself.
Regarding optical members used in the optical member unit 24 including the prism sheet 24a, the diffusion sheet 24b, and the transmittance adjusting member 24c, paragraphs [0028] to [0033] of Japanese Patent Application Laid-Open No. 2005-23497 related to the applicant's application. What is disclosed in can be applied.

The reflecting member 26 used in the illuminating device main body 14 is disposed along the back surface 22 d of the light guide plate 22 and is for improving the utilization efficiency of the illumination light emitted from the linear light source 12. A reflective sheet 26a that is disposed along the back surface 22d of the light guide plate 22 excluding the parallel grooves 22b on the back side where the grooves 22b are formed, reflects light leaking from the back surface of the light guide plate 22 and reenters the light guide plate 22; The light guide plate 22 is arranged on the back surface of the linear light source 12 so as to block the parallel grooves 22b of the light guide plate 22 between the adjacent reflection sheets 26a. And a reflector 26b for making the reflected light incident from the side wall surface of 22b.
The illumination device body 14 is basically configured as described above.

  Next, the housing 16 for housing the lighting device main body 14 will be described. As shown in FIG. 3, the housing 16 accommodates and supports the lighting device main body 14, and is sandwiched and fixed from the light emitting surface 14 a side and the reflecting member 26 side, and the upper surface is opened. The light guide plate assembly 14 is housed and supported from above, and a lower housing 30 that covers the four side surfaces of the light guide plate assembly 14 and an opening 16a on the upper surface that is smaller than the rectangular light emitting surface 14a of the illuminating device body 14. A rectangular opening is formed, a lower surface is opened, and an upper housing 32 that covers the light guide plate assembly 14 and the lower housing 30 in which the light guide plate assembly 14 is housed, including its four side surfaces, from above. The concave (U-shaped) folding member 34 inserted between the side wall of the lower housing 30 and the side wall of the upper housing 32, and the back surface 22d of the light guide plate 22 are disposed at the bottom of the lower housing 30. A planar illumination device supported through a reflective member 26 And a light guide plate supporting member 36 also supports the whole body 14. Although not shown in FIG. 3, an inverter storage unit 20 (see FIG. 2) that stores a plurality of inverter units 18 is attached to the back side of the lower housing 30.

Here, as a method for joining the lower housing 30 and the folding member 34, and a method for joining the folding member 34 and the upper housing 32, various known methods such as a method using bolts and nuts, a method using an adhesive, and the like. Can be used.
The upper housing 32 is larger than the lower housing 30 and at least outer wall surfaces at both ends of the lower housing 30 parallel to the parallel grooves 22b of the light guide plate 22 of the illuminating device body 14 or the linear light source 12 housed therein. The folding member 34 needs to be disposed in each gap between the inner wall surface of the upper casing 32 and the upper casing 32 opposed to the lower casing 30 on the four side surfaces of the casing 16. It may be arranged between the side wall of the upper housing 32 and the side wall of the upper housing 32. Moreover, it is preferable to attach the reinforcement member which reinforces the recessed part of the concave folding member 34. FIG.
By arranging the folding member 34 in this manner, the rigidity of the housing 16 can be increased, and further, the strength of the housing 16 can be further increased by attaching a reinforcing member.

The light guide plate support 36 is formed of a resin such as polycarbonate. In the illustrated example, the light guide plate support 36 is a convex member having a shape obtained by inverting the shape of the back surface 22d of the thinnest portion 22c of the light guide plate 22. Although it arrange | positions at predetermined intervals for every thinnest part 22c of the light-guide plate 22 along the back surface 22d of the light-guide plate 22 at the bottom part of the lower housing | casing 30, this invention is not limited to this, A light-guide plate It may be a continuous member in which convex portions having a shape obtained by inverting the shape of the back surface 22d of 22 are provided at a predetermined interval.
Note that the casing 16 has a stopper such as an L-shaped bracket that joins the four corners thereof, or a rubber between the prism sheet 24a of the lighting device main body 14 and the peripheral portion of the opening 14a of the upper casing 30. There may be provided an elastic member made of an elastic material such as a protective member that protects the entire upper surface of the prism sheet 24a of the planar apparatus main body 14.
The housing 16 is basically configured as described above.

Next, driving devices for the plurality of linear light sources 12 housed in the parallel grooves 22b of the light guide plate 22 of the illuminating device body 14 will be described.
A drive device 37 shown in FIGS. 13A and 13B drives a linear light source 12 such as a plurality of CCFLs, that is, turns on and off, and drives the illumination of the planar illumination device 10. A plurality of inverter units 18 respectively connected to the linear light sources 12 such as a plurality of CCFLs, and a power source 38 to which the plurality of inverter units 18 are connected. FIG. 13B shows a block diagram of the drive unit 37 for lighting the linear light source 12 such as one CCFL in order to show the detailed configuration of the inverter unit 18.
The power source 38 is a DC power source that outputs a DC voltage, for example, a DC voltage of 24V DC. This DC voltage is supplied to each of the plurality of inverter units 18 connected to the power source 38.

  The inverter unit 18 is connected to the drive circuit 18a that generates a primary AC signal having a predetermined frequency of a predetermined voltage (for example, 650 Vp-p) from the DC voltage supplied from the power supply 38, and the linear light source 12, and is connected to the drive circuit. A transformer 18b that boosts the primary AC signal generated in 18a to a high-voltage secondary AC signal (for example, 6500 Vp-p, 1000 to 2400 Vrms) necessary for lighting the linear light source 12 such as CCFL; The tube current detection circuit 18c for detecting the tube current connected to the linear light source 12 such as CCFL and the tube current output from the tube current detection circuit 18c are fed back, and the drive circuit 18a receives the primary AC signal. A voltage-controlled oscillation circuit 18d that oscillates a clock (fundamental wave) having a predetermined frequency for generation according to the fed-back tube current; That.

In the present invention, by configuring the drive device 37 of the linear light source 12 in this way, the plurality of linear light sources 12 are lit simultaneously and uniformly efficiently, stably and safely, with uniform brightness. Can emit light.
In the present invention, the plurality of linear light sources 12 are turned on at the same time. However, only a part of them may be turned on by the inverter unit 18 or these may be switched.
The linear light source driving device and the planar illumination device are basically configured as described above.
Such a planar illumination device can be used as a planar illumination device that illuminates indoors or outdoors, or a planar illumination device that is used as a backlight of a liquid crystal display panel, an advertising panel, an advertising tower, a signboard, or the like.
In particular, since the light guide plate according to the present invention suppresses the occurrence of warping, when the planar lighting device according to the present invention including the light guide plate is used as a backlight of a liquid crystal display panel, the light guide plate warps. Due to the deformation of the planar lighting device, a part of the planar lighting device is not pressed against the liquid crystal display panel. Therefore, if the planar illumination device of the present invention is used for a backlight of a liquid crystal display panel, the occurrence of display unevenness due to deformation of the planar illumination device can be prevented or suppressed.

  Although the planar lighting device 10 of the above-described embodiment is provided with the inverter storage portion 20 on the back side of the housing 16 and stores a plurality of inverter units 18, the planar lighting device of the present invention is limited to this. 14, between the lower housing 30 and the upper housing 32 in the periphery of the opening 16 a of the housing 16 on the side orthogonal to the linear light source 12, as in the planar lighting device 11 shown in FIG. 14. A space may be provided to serve as the inverter storage unit 20, and a plurality of inverter units 18 may be stored. By doing so, the back surface of the planar illumination device 11, that is, the back surface of the housing 16 can be flattened, and attachment to a ceiling or a wall surface can be facilitated.

  As described above, the light guide plate and the planar lighting device of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various modifications and changes may be made without departing from the spirit of the present invention. Of course it is good.

It is the schematic perspective view seen from the light-projection surface side of one Embodiment of the planar illuminating device of this invention. (A), (b), (c), and (d) are the front view of the planar illuminating device shown in FIG. 1, the side view of a longitudinal direction, the side view of a transversal direction, and a rear view, respectively. It is a fragmentary sectional view of one Embodiment of the planar illuminating device shown in FIG. It is a schematic perspective view of the planar illuminating device main body corresponding to one unit light-guide plate used for the planar illuminating device shown in FIG. (A) is a schematic perspective view of the light-guide plate used for the planar illuminating device shown in FIG. 3, (b) shows the cross-sectional shape of one unit light-guide plate of the planar illuminating device main body shown in FIG. FIG. It is a schematic diagram for defining the curvature amount of a light-guide plate. It is a graph of the curvature amount of four types of light-guide plates from which the linear expansion coefficient differs when the stable temperature of a linear light source is 60 degreeC, and 90 degreeC. It is a graph which shows the change of the curvature amount with respect to stable temperature of four types of light-guide plates from which a linear expansion coefficient differs. FIG. 9 is a graph obtained by performing coordinate conversion so that room temperature (25 ° C.) is the origin in the graph of the warpage amount with respect to the stable temperature of the light guide plate having a linear expansion coefficient of 1.00 × 10 ⁻⁴ shown in FIG. 8. It is a schematic diagram for demonstrating the cross-sectional area of the half pitch of a unit light-guide plate. It is a graph of the curvature amount with respect to the cross-sectional area S of the half pitch of a unit light-guide plate. It is a graph which shows ratio of curvature amount with respect to cross-sectional area S of the half pitch of a unit light-guide plate. (A) is the wiring diagram of one Embodiment of the drive device of the linear light source used for the planar illuminating device shown in FIG. 2, (b) is the block of the drive device of the linear light source shown to (a). FIG. It is a schematic block diagram which shows other embodiment of the planar illuminating device of this invention. It is a disassembled perspective view of the surface light source device which has the conventional light-guide plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 11 Planar illuminating device 12 Linear light source 14 Illuminating device main body 14a Light emission surface 16 Case 16a Opening 18 Inverter unit 18a Drive circuit 18b Transformer 18c Tube current detection circuit 18d Voltage control oscillation circuit 20 Inverter accommodating part 22 Light guide plate 22a Light exit surface 22b Parallel groove 22c Thinnest portion 22d Back surface 23 Unit light guide plate 23a Individual light exit surface 23b Thick portion 23c Thin end portion 23d Inclined surface 23e Inclined back surface portion 24 Optical member unit 24a Prism sheet 24b Diffusion film 24c Transmittance adjustment Member 25a Transparent sheet 25b Transmittance adjusting body 26 Reflective member 26a Reflective film 26b Reflector 30 Lower housing 32 Upper housing 34 Folding member 36 Light guide plate support member 37 Drive device 38 Power supply

Claims (6)

A light guide plate configured by integrally connecting a plurality of unit light guide plates formed of a transparent resin material,
The unit light guide plate has a flat rectangular light exit surface, and a back surface in which a parallel groove parallel to one side of the light exit surface is formed at a substantially center opposite to the light exit surface,
A linear light source is disposed in the parallel groove and used.
The length of the light guide plate in the direction perpendicular to the parallel grooves is L ₀ [mm], the linear expansion coefficient of the resin material is k [/ ° C.], and the linear light source is in a stable state after being turned on. When the surface temperature is Ts [° C.], the value of half of the cut area when the unit light guide plate is cut by a plane perpendicular to the parallel groove is S [mm ² ], and T = Ts−25, the inequality ^{_{(L 0/280) 2 ·}} k (14T 2 + 710T) · (-0.65logS + 1.9) ≦ 10
Satisfying light guide plate.   The back surface of the unit light guide plate is composed of a pair of inclined surfaces that are symmetrical to each other with the parallel groove interposed therebetween, and the pair of inclined surfaces extends from the parallel groove toward the end of the unit light guide plate. The light guide plate according to claim 1, wherein the light guide plate is inclined so as to gradually decrease in thickness.   The light guide plate according to claim 2, wherein the pair of inclined surfaces are formed as curved surfaces. It has a flat rectangular light exit surface and a back surface in which a parallel groove parallel to one side of the light exit surface is formed at the approximate center opposite to the light exit surface, and is formed of a transparent resin material. A light guide plate configured by connecting a plurality of unit light guide plates integrally;
A linear light source disposed in a parallel groove of the light guide plate,
The length of the light guide plate in the direction perpendicular to the parallel grooves is L ₀ [mm], the coefficient of linear expansion of the resin material of the unit light guide plate is k [/ ° C.], and when the light guide plate is in a stable state after lighting. The surface temperature of the linear light source is Ts [° C.], the value of half of the cut area when the unit light guide plate is cut by a plane perpendicular to the parallel groove is S [mm ² ], and T = Ts−25. sometimes,
^{_{(L 0/280) 2 ·}} k (14T 2 + 710T) · (-0.65logS + 1.9) ≦ 10
A planar lighting device that satisfies the requirements.   The back surface of the unit light guide plate is composed of a pair of inclined surfaces that are symmetrical to each other with the parallel groove interposed therebetween, and the pair of inclined surfaces extends from the parallel groove toward the end of the unit light guide plate. The planar illumination device according to claim 4, wherein the surface illumination device is inclined so as to be gradually reduced.   The planar illumination device according to claim 5, wherein the pair of inclined surfaces are formed as curved surfaces.

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