WO2005121638A1

WO2005121638A1 - Light guide plate, planar lighting apparatus using the light guide plate, and liquid crystal display

Info

Publication number: WO2005121638A1
Application number: PCT/JP2005/010359
Authority: WO
Inventors: Motohiko Matsushita
Original assignee: Fuji Photo Film Co., Ltd.
Priority date: 2004-06-08
Filing date: 2005-06-06
Publication date: 2005-12-22

Abstract

A light guide plate, a planar lighting apparatus using the light guide plate, and a liquid crystal display. In the light guide plate, at least two light guide plate units having rectangular light outgoing surfaces and rear surfaces opposed to the light outgoing surfaces are connected to each other with the light outgoing surfaces placed on a same plane. Where the length of the longest side of a rectangular total light outgoing surface obtained by connecting the light outgoing surfaces of the light guide plate units to each other is LD (mm), a surface area difference between the light outgoing surfaces and the rear surfaces of the light guide plate units per unit length is α, the value of y is 3 or smaller, and K and b are coefficients, the moisture content w (mass%) of a transparent resin forming the light guide plate units meets the requirement of the following expression (1). Thus, the deformation of the light guide plate can be suppressed even under high humidity environment.

Description

Specification

Light guide plate, planar lighting device and liquid crystal display device using the same

Technical field

The present invention relates to a transparent light guide plate that diffuses light incident from a rod-shaped light source in the plane direction and emits uniform illumination light with a light exit surface force even in a high humidity environment, and a planar illumination using the same. The present invention relates to a device and a liquid crystal display device.

Background art

[0002] A backlight unit that illuminates a liquid crystal panel (LCD) with light from the rear side thereof to illuminate the liquid crystal panel is used in the liquid crystal display device. The backlight unit includes components such as a light source for illumination, a light guide plate for diffusing the emitted light and illuminating the liquid crystal panel, a prism sheet for uniformizing the light emitted from the light guide plate, and a diffusion sheet. It is configured using

In recent years, thinning and low power consumption of liquid crystal display devices have been demanded, and light guide plates of various shapes have been proposed in order to realize them (Japanese Patent Application Laid-Open Nos. 9-304623 and 8-62426). Reference, JP-A-10-133027 and JP-A-5-249320).

FIG. 27 is an exploded perspective view showing a surface light source device having a light guide plate disclosed in Japanese Patent Application Laid-Open No. 9 304623.

In the surface light source device (backlight unit) shown in the figure, after a fluorescent lamp 202 is embedded in a light guide plate 200, a reflection sheet 204 is disposed on the back of the light guide plate 200, and a transmitted light amount correction sheet is provided on an emission surface of the light guide plate 200. It is formed by laminating 206, light diffusion plate 208, and prism sheet 210.

[0004] The light guide plate 200 has a substantially rectangular shape, and is formed using a resin into which fine particles that diffuse illumination light are dispersed and mixed. In addition, the upper surface of the light guide plate 200 is flat, and is allocated to the emission surface. Further, a U-shaped groove 200a having a cross section for embedding the fluorescent lamp 202 is formed on the back surface (the surface opposite to the emission surface) of the light guide plate 200, and the emission surface of the light guide plate 200 is formed just above the fluorescent lamp 202. Avoid the light intensity correction surface 200b that promotes the emission of illumination light. The

As described above, Japanese Patent Application Laid-Open No. 9-304623 discloses that a light guide plate 200 is formed by mixing fine particles, and a light amount correction surface formed on a part or all of an emission surface except a portion right above the fluorescent lamp 202. It is described that by promoting the emission of the illumination light by 200b, the overall thickness can be reduced and unnatural luminance unevenness of the emitted light can be reduced.

[0005] Also, Japanese Patent Application Laid-Open No. 8-62426 discloses that a liquid crystal display device can be reduced in size and weight without reducing the irradiation amount of a knock light, and can be reduced in thickness and cost and power consumption can be reduced. In order to obtain the backlight of the liquid crystal display device, a rectangular irradiation surface, and a groove having a rectangular cross section for inserting a light source, which is cut out in the center of the short side in parallel with the long side, and sandwiches this groove There is disclosed a light guide plate having a back surface formed so that the plate thickness is gradually reduced in the direction of both side surfaces of the long side.

[0006] Also, Japanese Patent Application Laid-Open No. Hei 10-133027 discloses that a light source is arranged in order to obtain a bright backlight unit that can make the frame of a liquid crystal display device narrower and thinner, and has good light use efficiency. A light guide (light guide plate) having a parabolic shape in which the cross section parallel to the width direction of the concave portion is parallel to the depth direction is disclosed.

[0007] Further, Japanese Patent Application Laid-Open No. 5-249320 discloses that in order to keep the in-plane brightness of the display panel uniform and to provide high-luminance illumination, the light is sequentially refracted on a C-shaped high reflection layer. There is disclosed a light guide plate in which a plurality of plate-shaped optical waveguide layers are stacked so as to increase the efficiency, and the light diffusion layer is brightened by light emitted from each light emitting end face. Here, the concave portion for arranging the light source has a triangular shape.

The light guide plates disclosed in JP-A-9 304623, JP-A-8-62426, JP-A-10-133027 and JP-A-5-249320 disclose a liquid crystal display device that is thinner, smaller and lighter. In order to reduce the power consumption, reduce the cost, etc., one or more grooves are provided in the center of each of the grooves, and the rod-shaped light sources are housed in the grooves. Preferably, the groove force is also formed so that the plate thickness becomes gradually thinner toward the end face, thereby achieving a reduction in thickness.

Patent Document 1: Japanese Patent Application Laid-Open No. 9 304623

Patent Document 2: JP-A-8-62426 Patent Document 3: JP-A-10-133027

Patent Document 4: JP-A-5-249320

Disclosure of the invention

Problems to be solved by the invention

[0009] In the above-mentioned JP-A-9 304623, JP-A-8-62426, JP-A-10-133027 and JP-A-5-249320, the light guide plate in a high humidity environment is disclosed. No deformation is taken into account. For example, the light guide plate is assembled with a cold cathode tube and shipped to the market as a knock light unit. In this case, in the inspection process of the knock light unit, for example, the temperature is maintained at a high humidity of 60 ° C. and a relative humidity of 95% for a predetermined time. Under such a high humidity environment, there is a problem that the light guide plate is deformed into a concave or convex shape regardless of whether the light source is turned off or turned on.

[0010] There is a problem that the deformation of the light guide plate due to moisture absorption in such a high-humidity environment causes luminance unevenness and has a bad effect when a knock light unit is formed. In addition, the apparent thickness of the backlight unit is increased by the deformation, which hinders miniaturization. Furthermore, when the knock light unit is applied to a liquid crystal display device, the liquid crystal display panel, which is arranged at a distance of several millimeters, is pushed above the surface of the knock light unit, resulting in display unevenness. I will.

Hereinafter, a detailed description will be given with reference to FIGS. 28A and 28B.

Here, FIG. 28A is a schematic diagram for explaining a deformation when the knock light unit is turned off in a high humidity environment, and FIG. 28B is a schematic diagram for explaining a deformation when the backlight unit is turned on.

[0012] As shown in FIGS. 28A and 28B, the light guide plate 220 has a shape cut out in a rectangular shape from a top angle of a substantially pentagonal side view to a bottom side in a side view. The plan view of the bottom side of the light guide plate 220 has a substantially rectangular shape. In the light guide plate 220, the cut-out portion becomes the parallel groove 222 in a side view, and the bottom of the parallel groove 222 is a plane. In addition, the surface on the bottom side of the substantially pentagonal side view is the front surface 220a, and the two inclined surfaces form the rear surface 220b. A cold cathode tube 224 is disposed in the parallel groove 222 as a light source. The light guide plate 220 shown in FIGS. 28A and 28B has a larger surface area on the front surface 220a than on the back surface 220b. [0013] In a high humidity environment, when the light is turned off, as shown in Fig. 28A, the surface area of the front surface 220a is larger than the surface area of the rear surface 220b! Moment Mo acts. Due to the bending moment Mo, as shown in the light guide plate 230, both ends are deformed toward the surface 220a. In this case, the opening of the parallel groove 222 is further opened, and the light incident on the parallel groove 222 leaks the opening force and cannot be used effectively. As a result, the average brightness of the knock light unit decreases.

In addition, it is known that the expansion that causes the deformation of the backlight unit is caused not only by water absorption but also by heat. However, in the use environment of the knock light unit, the expansion due to heat is extremely small compared to the expansion due to water absorption. For this reason, expansion due to water absorption is treated as a cause of deformation.

[0014] On the other hand, in a high humidity environment, during lighting, as shown in FIG. 28B, the heat of the cold cathode tube 224 causes the moisture absorption of the rear surface 220b to be smaller than the moisture absorption of the front surface 220a. Therefore, a bending moment Mf acts from the front surface 220a to the rear surface 220b. Due to this bending moment M, as shown in the light guide plate 230, both ends are deformed toward the back surface 220b. As a result, the surface 220a is curved, causing uneven brightness.

[0015] In the light guide plate 200 disclosed in Japanese Patent Application Laid-Open No. 9-304623, the light emission correction surface such as a rough surface or a microprism surface is avoided so as not to be directly above the light source (fluorescent lamp) 202. Forming 200b to promote the emission of illumination light incident at an angle greater than the critical angle with respect to the emission surface, but as shown in Fig. 29, the light guide plate without the light intensity correction surface indicated by the dotted line Since the luminance N2 of the illumination light from the light guide plate 200 having the light amount correction surface 200b indicated by the solid line shown by the dotted line has a small effect on the luminance N1 of the illumination light, the luminance improvement effect by the light amount correction surface 200b is small. There is a problem in that the efficiency of use of the light source light is large and the light source efficiency is low. Since the light source light is insufficiently diffused, uniform and high-intensity light cannot be emitted from the emission surface.

[0016] In the light guide plate 200 disclosed in Japanese Patent Application Laid-Open No. 9-304623, a light source (fluorescent lamp) 202 is embedded in a groove 200a having a circular cross section, and as shown in FIG. Since the luminance peak due to the light remains as it is, in order to use it as a surface light source device, the transmitted light amount correction sheet 206, the light diffusion plate 208, and the prism It is necessary to remove unnatural luminance unevenness on the light exit surface by using a light guide 210 or the like, and there is a problem that the cost of the device increases.

[0017] Further, in the backlight of the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. H8-62426, components on the electronic circuit board are arranged in gaps created by tilting the back surface of the light guide plate, thereby reducing costs. Thus, the size and weight of the liquid crystal display device can be reduced and the thickness of the liquid crystal display device can be reduced, but the unevenness of the illumination light emitted from the emission surface of the light guide plate is not considered at all.

[0018] Further, in the backlight unit of the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 10-133027, the cross-sectional shape of the groove-shaped recess provided in the light guide (light guide plate) is made parabolic, so that the light guide is formed. Light is incident on the light guide where the diffusion of light in the light body is almost uniform, and it is said that the efficiency of light utilization can be improved. One V, all at all! /.

Further, the light guide plate disclosed in Japanese Patent Application Laid-Open No. 5-249320 has a complicated structure in which a plurality of plate-like optical waveguide plates are stacked, so that the brightness attenuation is reduced and uniform brightness is reduced as compared with the related art. It has the problem that the manufacturing cost is high.

[0020] An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a thin, lightweight, even, less uneven, and brighter illumination from a light exit surface even in a high humidity environment. An object of the present invention is to provide a light guide plate capable of emitting bright light, a planar illumination device and a liquid crystal display device using the light guide plate.

[0021] Another object of the present invention is to provide a light guide plate capable of providing a light emitting surface of a larger size.

Another object of the present invention is to be thin and lightweight, to be able to be manufactured at lower cost, to emit more uniform, less uneven, and higher-intensity illumination light, An object of the present invention is to provide a planar lighting device which can be used as a lighting surface of a size or can be applied to a liquid crystal display device such as a wall-mounted television.

Another object of the present invention is to provide a thin, lightweight, low-cost manufacturing, more uniform, less uneven, and higher-luminance display, and a large-size display. It is an object of the present invention to provide a liquid crystal display device which can be a display screen or a wall-mounted type such as a wall-mounted television.

Means for solving the problem

[0022] In order to achieve the above object, the present inventors set at least two light guide plate units each having a rectangular light exit surface and a back surface facing the light exit surface, and made the light exit surfaces coplanar. We conducted intensive experimental research on the light guide plate formed by connection.

As a result, the length of the longest side of the rectangular total light emitting surface obtained by connecting the light emitting surfaces of the light guide plate unit is L (mm), and the light output per unit length of the light guide plate unit is determined.

D

The difference in surface area between the reflecting surface and the back surface is a, the deformation amount is y (mm), when the coefficient K and b, the coefficient ^{K = 3. 3 X 10 _4 (} lZ (mm X mass ^_0/0)) , the coefficient ^{b = l. 9 X 10 _2} ( mass ^_0/0). At this time, the water absorption w (mass%) of the transparent resin constituting the light guide plate unit satisfies the following expression (1), whereby the deformation of the light guide plate can be suppressed even in a high humidity environment. I found that.

[0023] Further, in order to achieve the other objects, a thin and light-weight, more uniform, less uneven and higher-brightness illumination light can be emitted from the light emission surface, and a larger-sized illumination light can be emitted. In order to realize a light guide plate that can be used as a light emitting surface, the present inventors have conducted intensive experimental research and found that a rectangular light emitting surface, a thick portion parallel to one side thereof, A thin end formed parallel to both sides of the thick part, and a thin part that is thinner toward the thin ends on both sides of the thick part, and a slanted back part that forms a slanted back, and parallel to the thick part By forming a transparent light guide plate having a parallel groove for accommodating a rod-like light source formed in the above, it is possible to make the light guide plate thinner and lighter. By connecting, it is possible to make the light emitting surface large-sized, and if such a light guide plate is used, In the first part of the light emitting surface corresponding to the parallel groove, a peak of illuminance or brightness is formed by the emission light of the rod-shaped light source housed in the parallel groove, thereby causing illumination unevenness or uneven brightness. The peak of illuminance or luminance can be reduced by narrowing the cross-sectional shape of the parallel groove toward the front end portion facing the light emission surface, and the illuminance or brightness can be reduced by sharpening the top of the front end portion. Or a peak in the opposite direction (minus side) of the luminance, and the peak in the opposite direction (minus side) of the illuminance or luminance blunts the sharpness at the top of the tip of the parallel groove, ie, The inventors of the present invention have found that it can be reduced by chamfering or rounding, and that the degree of reduction in the illuminance or luminance peak depends on the degree to which the tip of the parallel groove is made thinner.

That is, in the first embodiment of the present invention, at least two light guide plate units each having a rectangular light emitting surface and a back surface opposed to the light emitting surface are connected by making the light emitting surfaces coplanar. A light guide plate, wherein the length of the longest side of the total light exit surface of the rectangular shape obtained by connecting the light exit surfaces of the light guide plate unit is L (mm);

D

When the surface area difference between the light exit surface and the rear surface per unit length of the unit is _α, and κ and b are coefficients, the water absorption w of the transparent resin constituting the light guide plate unit w (mass ^_0/0), (are those satisfying 1), the value of y is 3 or less, K = 3. 3 Χ 10 " 4 (1 / (mm X wt%) following formula), b = 1. 9 a light guide plate, wherein X 10_ is ² (wt%).

[0025] [number 1]

w≤ ~ b '' '(1)

Κ α L _D

[0026] In the present invention, the light guide plate unit is formed so as to have a rectangular light exit surface, a thick portion parallel to one side thereof and located substantially at the center of the light exit surface, and parallel to the thick portion. A thin end portion, a parallel groove formed substantially in the center of the thick portion and parallel to the one side, for storing a rod-shaped light source, and axes of the rod-shaped light source on both sides of the parallel groove. The thickness is symmetrical with respect to a plane perpendicular to the light emitting surface, and the thickness becomes thinner toward the thin end portions on both sides in a direction perpendicular to the one side, thereby forming an inclined back surface. The thin end portions of adjacent light guide plate units are connected, and the light exit surfaces of the connected light guide plate units are arranged on the same plane. Light guide adjoining from a plane passing through the center of the rod-shaped light source and perpendicular to the light emitting surface The distance to the end face of the thin end, which is the joint with the plate unit, is L (mm), the maximum thickness of the thick part is Dmax (mm), and the minimum thickness of the thin end is Dmin (mm). The distance between the bottom of the parallel groove and the light emitting surface is δ (mm), and a line passing through the center of the rod-shaped light source and perpendicular to the light emitting surface and one side wall in the cross-sectional shape of the parallel groove Is 0 (°), the surface area difference α can be expressed by the following equation (2). [0027] [Equation 2]

"ヽ

Dmax— d, f _τ Uma — 0 1, „ _π ., ₂

+ L-ten (umax—JJmin) — L

― Cos β \ l tan6), _r ,

a =

L

[0028] In the present invention, the value of y is preferably 1 or less.

[0029] Further, a second aspect of the present invention provides the light guide plate of the first aspect of the present invention, a rod-shaped light source housed in the parallel groove of the light guide plate, and the light guide plate so as to cover the parallel groove. A reflector provided behind the rod-shaped light source, a reflection sheet attached to the inclined rear surface of the inclined rear portion on both sides of the thick portion of the light guide plate, and disposed on the total light emitting surface of the light guide plate. A spread illuminating device having a diffusion sheet.

In the present invention, it is preferable that a prism sheet is further provided between the total light emitting surface of the light guide plate and the diffusion sheet or above the diffusion sheet.

[0031] A third aspect of the present invention is a knock light unit that also has the power of the planar lighting device according to the second aspect of the present invention, and a liquid crystal display arranged on the light emitting surface side of the backlight unit. An object of the present invention is to provide a liquid crystal display device comprising a panel, and a drive kit for driving the backlight unit and the liquid crystal display panel.

The invention's effect

According to the light guide plate of the present invention, for a light guide plate unit having a rectangular light exit surface and a back surface opposed to the light exit surface, at least two of the light guide plate units and the light exit surface are on the same plane. The length of the longest side is L (mm) of the rectangular total light emitting surface obtained by connecting the light emitting surfaces of the light guide plate unit, and the unit length of the light guide plate unit is

D

The difference in surface area between the light emitting surface and the back surface per the o, when the coefficient K and b, the coefficient ^{K = 3. 3 X 10 _4 (} lZ (mm X mass ^_0/0)), the coefficient b = l. is a 9 X 10 ^_2 (mass ^_0/0). At this time, the water absorption w (mass%) of the transparent resin constituting the light guide plate unit satisfies the following equation (1), thereby suppressing deformation of the light guide plate even in a high humidity environment. be able to. Thereby, even in a high humidity environment, it is possible to suppress luminance unevenness on the light emitting surface and prevent a decrease in average luminance on the light emitting surface. However, the value of y is 3 or less. [0033] [Equation 3]

w≤ ^ b

Κ α L _D … (1)

[0034] Further, according to the light guide plate of the present invention, the light guide plate can be made thinner and lighter, and more uniform, less uneven and higher brightness illumination light is emitted from the light emitting surface. be able to. Further, according to the light guide plate of the present invention, the light guide plate unit includes, for example, a rectangular light exit surface, a thick portion parallel to one side thereof and located at a substantially central portion of the light exit surface, and a thick portion. Light emission including a thin-walled end formed in parallel, a parallel groove formed substantially in the center of the thick-walled part in parallel with the one side, for accommodating a rod-shaped light source, and axes of the rod-shaped light source on both sides of the parallel groove. It is symmetrical with respect to a plane perpendicular to the surface, and is composed of a slanted back part that forms a slanted back surface by making the thickness thinner by applying force to the thin ends on both sides in the direction perpendicular to one side. What can be done. By connecting the thin ends of the light guide plate unit to each other, the size of the total light exit surface of the light guide plate can be made larger.

According to the spread illuminating apparatus of the present invention, the use of the light guide plate of the present invention can suppress deformation of the light guide plate even in a high humidity environment. Even in this case, it is possible to suppress luminance unevenness on the light emitting surface and prevent a decrease in average luminance on the light emitting surface.

Further, according to the spread illuminating apparatus of the present invention, by using the light guide plate of the present invention, it is thin and lightweight, can be manufactured at lower cost, and is more uniform, less uneven, and has higher brightness. The present invention can provide a planar illumination device which can emit a large amount of illumination light, can have a large illumination surface, and can be applied to a liquid crystal display device such as a wall-mounted television.

According to the liquid crystal display device of the present invention, the use of the planar lighting device of the present invention can suppress the deformation of the light guide plate even in a high humidity environment. However, part of the knock light unit does not come into contact with the liquid crystal display panel. Thereby, display unevenness does not occur. Furthermore, it is possible to suppress luminance unevenness and prevent a decrease in average luminance on the light emitting surface.

Further, according to the liquid crystal display device of the present invention, by using the planar illumination device of the present invention, the liquid crystal display device can be manufactured to be thinner and lighter, can be manufactured at a lower cost, and have a more uniform and less uneven power. Thus, a display with higher brightness can be performed, the display screen can be made larger, and a wall-mounted television or the like can be used.

Brief Description of Drawings

FIG. 1A is a schematic view showing a liquid crystal display device according to an embodiment of the present invention using a planar lighting device according to an embodiment of the present invention having a light guide plate according to the embodiment of the present invention as a backlight unit. FIG. 1B is a schematic partial cross-sectional perspective view taken along line AA of FIG. 1A.

FIG. 2 is a schematic perspective view showing a light guide plate according to an example of the present invention.

FIG. 3A to FIG. 3C are schematic perspective views showing modifications of the light guide plate.

FIG. 4 is a schematic side view showing a main part of a backlight unit according to an embodiment of the present invention.

FIG. 5 is a schematic perspective view illustrating the size of each part of the light guide plate unit of the present invention.

FIG. 6A and FIG. 6B are schematic side views illustrating a method for measuring the amount of warpage.

FIG. 7 is a graph showing the relationship between the amount of warpage and the length of the side of the light guide plate, with the vertical axis representing the amount of warpage and the horizontal axis representing the length of the second side.

FIG. 8 is a graph showing the relationship between the amount of warpage and the length of the side of the light guide plate, with the amount of warpage taken along the vertical axis and the length of the first side taken along the horizontal axis.

[FIG. 9] FIG. 9 is a graph showing the relationship between the amount of warpage and the water absorption by taking the amount of warpage on the vertical axis and the water absorption on the horizontal axis.

FIG. 10 is a graph showing the relationship between the amount of deformation and the water absorption by taking the amount of deformation on the vertical axis and the length of one side on the horizontal axis.

FIG. 11A is a schematic side view showing a light guide plate unit in which a prism sheet is disposed between a reflection sheet and an inclined surface of the light guide plate unit, and FIG. FIG. 11C is a schematic plan view of the light exit surface side force, and FIG. 11C is a cross-sectional view taken along line BB of FIG. 11B.

FIG. 12 is a schematic side view showing the light guide plate unit when the cross-sectional shape perpendicular to the length direction of the parallel groove is hyperbolic. FIG. 13 is a schematic side view showing a light guide plate unit when the cross-sectional shape perpendicular to the length direction of the parallel groove is elliptical.

[FIG. 14] FIG. 14 shows two arc curves in which the cross-sectional shape perpendicular to the length direction of the parallel groove is symmetrical with respect to the center line passing through the center of the parallel groove and perpendicular to the light exit surface of the light guide plate unit. FIG. 3 is a schematic side view showing a light guide plate unit partially formed.

FIG. 15 shows one of two parabolas whose cross section perpendicular to the length direction of the parallel groove is symmetric with respect to a center line passing through the center of the parallel groove and perpendicular to the light exit surface of the light guide plate unit. FIG. 4 is a schematic side view showing a light guide plate unit in which a partial force is formed.

[FIG. 16] FIG. 16 is a schematic side view showing a light guide plate unit in which a cross-sectional shape perpendicular to the length direction of the parallel groove is formed with two convex curved forces directed toward the center of the parallel groove. .

[FIG. 17] FIG. 17 shows a light guide plate unit in which a cross-sectional shape perpendicular to the length direction of the parallel groove is formed into a curved force that combines a convex curve and a concave curve toward the center of the parallel groove. It is a typical side view shown.

FIG. 18 is a plan view showing a light guide plate unit in which a halftone dot pattern is formed on a light emitting surface.

FIG. 19 is a graph showing the illuminance distribution of light emitted from the light exit surface of the light guide plate when the cross-sectional shape of the parallel groove of the light guide plate is changed to various shapes.

FIG. 20 is a graph showing the illuminance distribution of light emitted from the light exit surface of the light guide plate when the deepest part of the parallel groove is flattened and the length of the flat part is changed to various values. It is.

[FIG. 21] FIGS. 21A to 21D are schematic diagrams showing light guide plate units when the flat portions at the deepest portions of the parallel grooves are 1.5 mm, 1. Omm, 0.5 mm, and 0.25 mm, respectively. FIG.

[FIG. 22] FIG. 22 shows that the shape of the deepest portion of the parallel groove is a curved surface having a radius of curvature R, and the light exit surface force of the light guide plate when the radius of curvature of the curved surface is changed to various values. It is a graph which shows illuminance distribution.

[FIG. 23] FIGS. 23A to 23D show light guide plate units when the radii of curvature at the apexes of parallel grooves having a triangular cross section are 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm, respectively. It is a typical side view shown. FIG. 24 is a schematic side view showing another example of the light guide plate of the present invention.

FIG. 25 is a schematic side view showing a configuration example in which a reflection plate is arranged on the side surface of the light guide plate of the present invention.

FIG. 26A is a schematic perspective view showing a light guide plate according to another embodiment of the present invention, and FIG. 26B is a side view showing a light guide plate according to another embodiment of the present invention.

FIG. 27 is an exploded perspective view showing a surface light source device having a light guide plate disclosed in Japanese Patent Application Laid-Open No. 9-304623.

[FIG. 28] FIG. 28A is a schematic diagram illustrating a deformation when the backlight unit is turned off in a high humidity environment, and FIG. 28B is a schematic diagram illustrating a deformation when the backlight unit is turned on.

[FIG. 29] FIG. 29 is a graph showing a luminance distribution on an emission surface of a light guide plate of the surface light source device of FIG. 27.

Explanation of symbols

2 Knock light unit

4 LCD panel

6 Drive unit

10 Liquid crystal display

12 Bar light source

14 Diffusion sheet

16, 17, 21 prism sheet

18 Light guide plate

18a Total light exit surface

19, 50, 60, 70, 80, 100 Light guide plate cut

19a, 52 Light emission surface

19b Thick part

19c Thin end

19d slope

19e Inclined back 19f parallel groove

19g side wall

20 Reflector

22 Reflective sheet

24 Reflector

54a, 54b Arc curve

56 intersection

64a, 64b parabola

72a, 72b, 82a, 82b, 84a, 84b Curve

V halftone dot pattern

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the light guide plate of the present invention, a planar illumination device and a liquid crystal display device using the same will be described.

This will be described in detail based on preferred embodiments shown in the accompanying drawings.

FIG. 1A is a schematic view showing a liquid crystal display device according to an embodiment of the present invention using a planar lighting device according to an embodiment of the present invention having a light guide plate according to an embodiment of the present invention as a backlight unit. FIG. 1B is a side view, and FIG. 1B is a schematic partial cross-sectional perspective view taken along line AA of FIG. 1A.

As shown in FIGS. 1A and 1B, the liquid crystal display device 10 basically includes a knock light unit 2, a liquid crystal display panel 4 arranged on the light emission surface side of the backlight unit 2, and And a drive unit 6 for driving. Knock light unit 2 and liquid crystal display panel 4 are arranged with an interval (clearance) g. This interval g is generally about lmm.

[0042] The backlight unit 2 is a planar lighting device for irradiating the entire surface of the liquid crystal display panel 4 with uniform light from behind the liquid crystal display panel 4, and is substantially the same as the image display surface of the liquid crystal display panel 4. Light emitting surface (light emitting surface).

As shown in FIG. 1A, the knock light unit 2 basically includes a plurality of rod-like light sources 12, a diffusion sheet 14, two prism sheets 16 and 17, and a plurality of light guide plate units 19. A light guide plate 18, a reflector 20 provided on the lower surface of each light guide plate unit 19, And a reflection sheet 22 provided for each of the shape light sources 12.

The rod-shaped light source 12 is, for example, a small-diameter rod-shaped cold-cathode tube, and is used to illuminate the liquid crystal display panel 4. As shown in FIG. 1A, the rod-shaped light source 12 is disposed in a parallel groove 19f formed in the light guide plate unit 19, and is connected to the drive unit 6 via wiring (not shown). Here, a cold cathode tube is used as the rod-shaped light source 12, but the present invention is not limited to this, and any rod-shaped light source may be used. As the rod-shaped light source 12, for example, a normal fluorescent tube (hot cathode tube) or an LED (light emitting diode) can also be used.

The diffusion sheet 14 is for diffusing and equalizing the light emitted from the light exit surface 19a of the light guide plate unit 19, for example, PET (polyethylene terephthalate), PP (polypropylene), PC (Polycarbonate), PMMA (Polymethinolemethacrylate), Benzinolemethacrylate, MS (methacrylstyrene) resin, or other acrylic resins, or optical such as COP (cycloolefin polymer) It is formed by imparting light diffusivity to a flat member made of transparent resin. Although the method is not particularly limited, for example, a surface roughened by fine unevenness or polishing (hereinafter referred to as a “sand rubbing surface” ") To impart diffusivity, or a material such as silica, titanium oxide or zinc oxide, or a material that scatters light such as beads such as resin, glass or zirconia together with a binder together with a binder. Or by kneading the above-mentioned pigments or beads that scatter light into the transparent resin. In the present invention, as the diffusion sheet 14, a mat type or coating type diffusion sheet can be used.

In the present invention, as the diffusion sheet 14, it is also preferable to use a film-like member having a thickness of 500 μm or less, which is made of the above-mentioned material and has light diffusing properties.

The diffusion sheet 14 is preferably disposed at a predetermined distance from the light exit surface 19 a of the light guide plate unit 19, and the distance is preferably equal to the light amount distribution from the light exit surface 19 a of the light guide plate unit 19. Can be changed as appropriate. By separating the diffusion sheet 14 from the light exit surface 19a of the light guide plate unit 19 by a predetermined distance in this manner, light exiting from the light exit surface 19a of the light guide plate unit 19 can be transmitted between the light exit surface 19a and the diffusion sheet 14. Is further mixed (mixed). As a result, the illuminance of light passing through the diffusion sheet 14 and illuminating the liquid crystal display panel 4 is further increased. It can be made uniform. As a method of separating the diffusion sheet 14 from the light emitting surface 19a of the light guide plate unit 19 by a predetermined distance, for example, a method of providing a spacer between the diffusion sheet 14 and the light guide plate 18 can be used.

In particular, when the thickness of the knock light unit 2 may be slightly increased, the light emission of the light guide plate unit 19 corresponding to the parallel groove 19 f depends on the cross-sectional shape of the parallel groove 19 f of the light guide plate unit 19. It is not necessary to sufficiently reduce the peak value of the illuminance on the surface 19a, and the light is emitted from the diffusion sheet 14 by providing a gap between the diffusion sheet 14 and the light exit surface 19a of the light guide plate unit 19. The illumination distribution of the illumination light may be uniform. Further, there is a limit in improving the cross-sectional shape of the parallel groove 19f of the light guide plate unit 19 (the tapering of the tip of the parallel groove), and the illuminance of the light exit surface 19a of the light guide plate unit 19 corresponding to the parallel groove 19f is limited. Even when the peak value cannot be reduced completely or cannot be reduced sufficiently, a gap is provided between the diffusion sheet 14 and the light exit surface 19a of the light guide plate unit 19, and the illumination light emitted from the diffusion sheet 14 is The illuminance distribution may be uniform.

The prism sheets 16 and 17 are transparent sheets formed by arranging a plurality of prisms in parallel. The prism sheets 16 and 17 enhance the light-collecting property of light emitted from the light exit surface 19 a of the light guide plate unit 19. Brightness can be improved. One of the prism sheets 16 and 17 is arranged such that the direction in which the prism rows extend is parallel to the parallel groove 19f of the light guide plate unit 19, and the other is arranged so as to be vertical. That is, the prism sheets 16 and 17 are arranged such that the directions in which the prism rows extend are perpendicular to each other. The prism sheet 16 is arranged such that the apex angle of the prism faces the light exit surface 19a of the light guide plate unit 19. Here, the arrangement order of the prism sheets 16 and 17 is such that a prism sheet 16 having a prism extending in a direction parallel to the parallel groove of the light guide plate is arranged immediately above the light guide plate, and on the prism sheet 16, A prism sheet having a prism extending in a direction perpendicular to the parallel groove 19f of the light guide plate unit 19 may be provided, or vice versa.

In addition, the prism sheets 16 and 17 are provided with a force provided between the total light exit surface 18a of the light guide plate 18 (see FIG. 2) and the diffusion sheet 14. The present invention is not limited to this. These prism sheets 16 and 17 may be arranged above the diffusion sheet 14.

Although the prism sheet is used in the illustrated example, a prism sheet is used instead of the prism sheet. A sheet in which optical elements similar to the above are regularly arranged may be used. Further, a sheet regularly provided with an element having a lens effect, for example, an optical element such as a lenticular lens, a concave lens, a convex lens, or a pyramid type can be used instead of the prism sheet.

As shown in FIG. 1B, the light guide plate unit 19 includes a rectangular light exit surface 19a, a thick portion 19b parallel to one side thereof, and a thick portion 19b parallel to the one side on both sides of the thick portion 19b. A thin end portion 19c to be formed, an inclined back surface portion 19e whose thickness is reduced toward the thin end portions 19c on both sides in a direction perpendicular to the one side from the thick portion 19b, and an inclined back surface portion 19e to form an inclined surface 19d; The thick portion 19b has a parallel groove 19f formed in parallel with the one side to accommodate the rod-shaped light source 12. In other words, the light guide plate unit 19 is a flat plate having a light emitting surface 19a having a rectangular external shape, and is formed of a transparent resin. The light guide plate unit 19 has one surface (light emission surface 19a) that is flat, and the other surface (inclined back surface 19e) has one side so that the plate thickness becomes thinner toward one side. It is inclined with respect to the plane. Here, a force curved surface in which the inclined surface 19d is formed as a flat surface may be used.

Here, as shown in FIG. 2, the light guide plate 18 is formed by connecting the light guide plate units 19, and the respective light exit surfaces 19a of the connected light guide plate units 19 are gathered to form the total light. It becomes the emission surface 18a. This total light emitting surface 18a also has a rectangular shape. The length of the first side 18b of the total emission surface 18a is | 8, and the length of the second side 18c is γ. In the present invention, the length of the longest side (hereinafter, referred to as a long side) of the first side 18b and the second side 18c is represented by L.

D

In the present embodiment, the length β of the first side 18b is the same as the length of the light guide plate unit 19 in the connection direction. The length γ of the second side 18c is the same as the length in the direction in which the parallel groove 19f (see FIG. 1B) of the light guide plate unit 19 extends.

[0051] The light guide plate 18 may be deformed in three different forms as shown in Figs. 3A to 3C. 3A to 3C, the light guide plate 18 is schematically illustrated.

First, as shown in FIG. 3A, the first side 18b of the light guide plate 18 is deformed. Next, as shown in FIG. 3B, the second side 18c of the light guide plate 18 is deformed. Further, as shown in FIG. 3C, the first side 18b and the second side 18c of the light guide plate 18 are deformed. The modification shown in FIGS. 3A to 3C depends on the shape of the light guide plate 18 without depending on the length β of the first side 18b and the length γ of the second side 18c. Even if the amount of deformation is small, if the length of the side is long, the amount of deformation will be amplified. Therefore, as a result, the amount of warpage on the side having a longer side is the amount of deformation of the light guide plate 18.

It is known that the deformation of the light guide plate 18 is caused not only by water absorption but also by heat. However, in the use environment of the light guide plate of the present invention, expansion due to heat is extremely small as compared with expansion due to water absorption. Therefore, in the present invention, expansion due to water absorption is treated as a cause of deformation.

Here, FIG. 4 is a schematic side view showing a main part of the knock light unit according to the embodiment of the present invention.

Further, as shown in FIG. 4, the light guide plate unit 19 has, for example, a shape symmetrical with respect to a center line X passing through the center of the parallel groove 18f and perpendicular to the light emitting surface 19a of the light guide plate unit 19. The light guide plate 18 is formed by connecting at least two, that is, a plurality of the light guide plate units 19 with the thin portion of each light guide plate unit 19 as a joint. In the backlight unit 2 shown in FIG. 1A, for example, five light guide plate units 19 are connected.

In this light guide plate unit 19, as shown in FIG. 4, when the distance from the center line X to the thin end 19c is L, the length of the light guide plate unit 19 in the lateral direction is C (= 2L). It is. That is, the width of the light guide plate unit 19 is C, and the width C is a repeating unit in the backlight unit 2.

In the present invention, the thickness of the thick portion 19b of the light guide plate unit 19 is Dmax, and the thickness of the thin end portion 19c is Dmin.

A parallel groove 19f for accommodating the rod-shaped light source 12 extends in the longitudinal direction (one side direction) on the surface of the thick portion 19b of the light guide plate unit 19 opposite to the light emitting surface 19a. It is formed as That is, the parallel groove 19f is formed in a direction parallel to the longitudinal direction of the light emitting surface 19a.

The parallel groove 19f has a triangular shape such that two side walls 19g intersect on the center line X to form a bottom 98 in a cross-sectional shape perpendicular to the length direction of the parallel groove 19f (hereinafter, simply referred to as a cross-sectional shape of the parallel groove). It is formed in a shape. The distance between the bottom 98 on the center line X and the light exit surface 19a is δ (mm). In the present invention, the form of the bottom 98 of the parallel groove 19f is not particularly limited. The bottom 98 may, for example, intersect at a point and have substantially no width in the transverse direction, or may have a width in the transverse direction.

The depth of the parallel groove 19f is preferably determined so that part of the rod-shaped light source 12 does not protrude from the lower surface of the light guide plate unit 19, or the size of the rod-shaped light source 12 or the mechanical length of the light guide plate unit 19. It is preferable to determine in consideration of the target strength and the change with time.

The present inventor conducted intensive experimental research to solve the above-described problems as described above. As a result, the water absorption w (mass%) of the transparent resin constituting the light guide plate unit 19 in the light guide plate 18 was determined. ) And the shape of the light guide plate unit. Hereinafter, the relationship between the water absorption w (mass%) of the transparent resin constituting the light guide plate unit 19 and the shape of the light guide plate unit will be described in detail.

Here, FIG. 5 is a schematic perspective view illustrating the size of each part of the light guide plate unit of the present invention. In FIG. 5, only the light guide plate unit 19 is shown, and other components are omitted.

As shown in FIG. 5, the length of the light guide plate unit 19 of the present invention in the longitudinal direction is L.

W

The The angle between the average plane (not shown) of the side wall 19g and the center line X is Θ.

In the present invention, the average plane is a direction in which the rod-shaped light source 12 extends, passing through a bottom 98 where two side walls 19g of the parallel groove 12 intersect on the center line X and a point where the thickness Dmax of the thick part 19b becomes the maximum value. It is a plane parallel to. That is, the light guide plate unit shown in FIGS.

In 19, the side wall 19g is an average plane.

The present inventor first examined the influence of the length of the side on the deformation (the amount of warpage) in the light guide plate 18 shown in FIG.

The warpage was measured using a surface plate P as shown in Figs. 6A and 6B.

. In this case, in FIGS. 6A and 6B, for simplicity of explanation, the explanation is made using the light guide plate 19 instead of the light guide plate.

In the method for measuring the amount of warpage in the present invention, a light guide plate exposed to a high-temperature and high-humidity environment is placed on a surface plate with the light-emitting surface side and the opposite side facing each other, and The change from the original height of the four corners on the front and back was measured. Of these measured values, the maximum value was taken as the amount of warpage.

First, with respect to the light guide plate 18 shown in FIG. 2, a plurality of light guide plates were manufactured in which the length β of the first side 18b was 330 mm and the length γ of the second side 18c was changed. The light guide plate is formed by connecting a plurality of light guide plate units of the same type. In this light guide plate unit, the cross-sectional shape of the parallel groove is triangular, and the size of each part is Dmax = 5 mm, Dmin = δ = 1.5 mm, L = 15 mm, and Θ = 30 °.

Each of the produced light guide plates was left for 100 hours in a high humidity environment (temperature 60 ° C, relative humidity 95%), and the amount of warpage was examined.

The transparent榭脂used for the light guide plate unit, PMMA (Mitsubishi Rayon Co., Ltd., water absorption = 0.3 mass ^_0/0), PC (Mitsubishi Engineering Plastics Co., Ltd., water absorption = 0.15 mass ^_0/0 ) And ZEONOR (registered trademark, manufactured by Zeon Corporation, water absorption ≤ 0.01 mass%).

The result is shown in FIG. As shown in FIG. 7, the amount of warpage increases as the length of the second side increases.

[0059] Further, with respect to the light guide plate 18 shown in Fig. 2, a plurality of light guide plates were manufactured in which the length γ of the second side 18c was 500 mm and the length of the first side 18b was changed. The light guide plate is formed by connecting a plurality of light guide plate units of the same type. In this light guide plate unit, the cross-sectional shape of the parallel groove is triangular, and the size of each part is Dmax = 5 mm, Dmin = δ = 1.5 mm, L = 15 mm, and Θ = 30 °.

The transparent resin used for the light guide plate unit is the same as that shown in FIG. 7, and is of three types: PMMA, PC and ZEONOR (registered trademark).

The result is shown in FIG. As shown in FIG. 8, the amount of warpage increases as the length of the first side increases.

[0060] In the light guide plate as described above, the longer the length of the side, the larger the amount of warpage. For this reason, the inventor of the present application considers the amount of deformation of the long side of the light guide plate by considering the amount of warpage. It has been found that the water absorption rate can be defined according to the requirement.

Next, the relationship between the water absorption and the surface area difference α will be described based on the light guide plate 18 and the light guide plate unit 19 shown in FIG. 4 and FIG.

Here, assuming that the length of the side wall 19g shown in FIG. 5 is の長, the length E of the side wall 19g is expressed by the following equation (3). When the length of the slope 19d is S, the length S of the slope 19d is represented by the following equation (4).

[0062] [Equation 4]

E = ^DmaX — ⁶ ^,, .. (3)

cos Θ

[0063] [Equation 5]

S = iL- ^DmaX ~ ⁰ l + (Dmax-Dmin) ² ^... (4)

When the angle of the side wall 19g in the parallel groove 19f is Θ, the surface area difference between the light exit surface 19a per unit length (L = 1) in the longitudinal direction and the surface opposite to the light exit surface 19a is calculated. α

W

In this case, the surface area difference a is represented by the following equation (2).

[0065] [Equation 6]

_{Dmax- d, If T umax- o]} , "π., 2

+ L- tens (Umax—JJmin) — L

― Cos β \ l tan6), _r ,

a =

L

Next, using various materials having different water absorption rates, the cross-sectional shape of the parallel groove is triangular, and the size of each part is Dmax = 5 mm, Dmin = δ = 1.5 mm, L = A light guide plate unit with 15 mm and θ = 30 ° was fabricated. A plurality of light guide plates of the same type were connected to produce a light guide plate having a size of 500 mm × 500 mm.

The light guide plate was left in a high humidity environment (temperature: 60 ° C., relative humidity: 95%) for 100 hours, and the amount of warpage was examined. The transparent resin used for the light guide plate unit was PMMA (Mitsubishi Rayon Co., Ltd., water absorption = 0.3% by mass), MS resin (Nippon Nippon Chemical Co., Ltd., water absorption ratio = 0.15% by mass) , PC (Mitsubishi engineering plastics Co., Ltd., water absorption = 0. 15 mass ^_0/0), and ZEON oR (registered trademark, manufactured by Nippon Zeon Co., Ltd., water absorption ≤ 0. 01 wt%) is a four.

[0067] The amount of warpage is measured using a surface plate P as shown in Figs. 6A and 6B as described above. In this case, the light guide plate (light guide plate unit) exposed to high temperature and high humidity environment Then, the light-emitting surface side and the opposite side were placed on a surface plate, respectively, and the change from the original height of the four corners on the front and back of the light guide plate was measured. Of these measured values, the maximum value was taken as the amount of warpage. The results are shown in FIG.

FIG. 9 is a graph showing the relationship between the amount of warpage and the water absorption by plotting the amount of warpage on the vertical axis and the water absorption on the horizontal axis.

[0068] The water absorption in the present invention was measured based on the method specified in JIS K7209-2000. In the present invention, after the light guide plate unit to be measured was immersed in water at a temperature of 23 ° C. for 24 hours, the mass was measured, and the mass was calculated from the mass increase ratio with respect to the mass before immersion.

As a result obtained from FIG. 9, it was confirmed that the warpage amount ε (mm) and the water absorption w (mass%) had a relationship represented by the following equation (5). Note that k and b in the following equation (5) are coefficients. k = 83 (mmZ mass ⁰ / o), a b = l.9X 10 ^_2 (mass ^_0/0). Α is defined by the above equation (2).

[Mathematical formula 7] a = k a (w + b) ··· (5)

[0070] Next, using each material, the size was 90mm X 90mm (L = 90mm (= L)), 170mm

D W

XI 70mm (L = 170mm (= L)), 240mm X 240mm (L = 240mm (= L)), 3

D W D W

30mm X 330mm (L = 330mm (= L;)), and 500mm X 500mm (L = 500m

D W D

m (= L)). Note that the cross section of the parallel groove is

W

Triangle shape, Dmax = 5mm, Dmin = δ = 1.5mm, L = 15mm, Θ = 30

°.

Each light guide plate was left in a high humidity environment (temperature 60 ° C, relative humidity 95%) for 100 hours, and the amount of deformation of each light guide plate was examined. As shown in FIGS. 6A and 6B, the measuring method of the amount of deformation uses the platen P in the same manner as the amount of warpage. Figure 10 shows the measurement results of the amount of deformation. Here, FIG. 10 is a graph showing the relationship between the amount of deformation and the water absorption by taking the amount of deformation on the vertical axis and the length of one side on the horizontal axis.

As shown in Fig. 10, the relationship between the amount of deformation (y) and the length of one side (L) is approximated by a quadratic function.

W

Can. Therefore, in the above equation (5), k = K XL ² and L is replaced with L Then, when the warpage amount ε is replaced by the deformation amount y, the deformation amount y can be expressed as shown in the following equation (6). K in the following formula (6) is a coefficient, and K = 3.3 × 10 ″ ⁴ (l / (mmX mass%)).

[0071] [Equation 8] y = K a (w + b) XL _D ² · · · (6)

By transforming the above equation (6), the following equation (1) is obtained.

[0073] [Equation 9]

w≤ ^ (1)

K a L _D …

[0074] As shown in the above equation (1), y is a deformation amount. In the present invention, it is possible to calculate the water absorption when the amount of deformation is set to a predetermined value. By adjusting the water absorption based on the equation (1), the amount of deformation of the light guide plate unit can be suppressed.

The value of y is 3 or less, and more preferably, the value of y is 1 or less. Generally, the distance (clearance) g (see FIG. 1) between the liquid crystal display panel 4 and the backlight unit 2 is about lmm. For this reason, by setting the value of y to 1 or less and selecting a transparent resin having water absorbability that satisfies Equation (1), the amount of deformation of the knock light unit 2 can be reduced to 1 mm or less. Thus, it is possible to prevent external force from being applied to the liquid crystal display panel 4.

In the present invention, when the light guide plate unit 19 satisfies the above formula (1), for example, even in a high humidity environment where the temperature is 60 ° C. and the relative humidity is 95%, The amount of deformation of the knit 19 can be, for example, 1 mm or less. As a result, it is possible to suppress the occurrence of uneven brightness and a decrease in average brightness. Further, even when the present invention is applied to a backlight unit (planar lighting device), it is possible to suppress the occurrence of uneven brightness and a decrease in average brightness. Further, when applied to a liquid crystal display device, it is possible to suppress the occurrence of display unevenness, the occurrence of luminance unevenness, and the decrease in average luminance.

On the other hand, in the present invention, when the light guide plate unit 19 does not satisfy the above mathematical expression (1), in a high humidity environment (temperature 60 ° C., relative humidity 95%), the light guide plate unit 19 The amount may exceed lmm. At this time, when the opening force S of the parallel groove 19f of the light guide plate unit 19 is further expanded, the light from the rod-shaped light source 12 is effectively applied to the light guide plate unit 19. It cannot be made incident. As a result, the average luminance decreases. In addition, since the light exit surface 19a is not flat due to the deformation, luminance unevenness also occurs. Further, the thickness of the light guide plate unit 19 increases due to the deformation.

Also, when applied to a knock light unit (planar lighting device), brightness unevenness similarly occurs, and the average brightness also decreases. Further, when applied to a liquid crystal display device, display unevenness and brightness unevenness occur, and in addition, the average brightness also decreases.

For this reason, in the present invention, the water absorption w (mass%) of the transparent resin constituting the light guide plate unit 19 satisfies the above equation (1).

[0077] In the present invention, the thickness Dmax of the thick portion 19b is preferably 10 mm or less in order to reduce the weight of the light guide plate unit 19.

Further, the parallel groove 19f of the light guide plate unit 19 may be formed in a direction perpendicular to the longitudinal direction of the light guide plate unit 19, but the light utilization efficiency from the rod-shaped light source 12 housed in the parallel groove 19f may be provided. It is preferable to form it in the longitudinal direction in order to increase the length.

In the present invention, the amount of deformation can be limited by selecting a transparent resin that satisfies the above formula (1) according to the shape and size of the light guide plate unit. However, in the present invention, in order to suppress the amount of deformation, for example, a thin film for adjusting the water absorption may be formed on the surface of the light guide plate unit. Thus, by forming the thin film for adjusting the water absorption, the amount of deformation of the light guide plate unit can be further controlled.

This thin film is preferably transparent, for example, SiO, SiO or Al O is deposited

2 2 3

It is formed from this.

In the present invention, as shown in FIG. 11A, a prism sheet 21 may be further provided between the reflection sheet 22 and the inclined surface 19d on the opposite side of the light exit surface 19a of the light guide plate unit 19. preferable.

Here, FIG. 11A is a schematic side view showing a light guide plate unit in which a prism sheet is disposed between the reflection sheet and the inclined surface of the light guide plate unit, and FIG. FIG. 11C is a schematic plan view also showing the exit surface side force, and FIG. 11C is a cross-sectional view taken along line BB of FIG. 11B. Note that, in FIGS. 11A and 11B, the reference numerals given in FIG. 5 are omitted. The prism sheet 21 provided between the reflection sheet 22 and the inclined surface 19d of the light guide plate unit 19 is arranged such that the direction in which the prism 21a extends is perpendicular to the parallel groove 19f of the light guide plate unit 19. In addition, it is preferable that the prism 21a be disposed so that the apex angle 21b of the prism 21a faces the inclined surface 19b of the light guide plate unit 19.

In the present invention, an optical element having a lens effect that can be obtained by using an optical element having the same effect as the force prism sheet using the prism sheet 21, for example, a lenticular lens, a concave lens, a convex lens, or A sheet in which optical elements such as a pyramid are regularly arranged may be provided.

In the illustrated example, the prism sheets 16 and 17 and more preferably the prism sheet 21 are used. However, when the illuminance on the light exit surface 19a by the parallel grooves 19f of the light guide plate unit 19 is made more uniform. In addition, the prism sheet 21 is of course unnecessary, and one or both of the prism sheets 16 and 17 may not be used. The installation cost can be reduced by reducing the number of expensive prism sheets used or by omitting the use of prism sheets.

In the present embodiment, the reflector 20 is provided so as to close the opening of the parallel groove 19f extending in the longitudinal direction of the light guide plate unit 19, and has a substantially rectangular shape. The reflector 20 reflects, out of the light emitted from the rod-shaped light source 12, the light that also leaks the surface force on the side opposite to the light emitting surface 19 a, and transmits the light from the side wall 19 g of the parallel groove 19 f of the light guide plate unit 19. Can be incident.

In the present embodiment, the reflection sheet 22 reflects the light leaking from the inclined surface 19d (back surface) of the light guide plate unit 19 and makes the light enter the light guide plate unit 19 again. The light use efficiency of the light source 12 can be improved. The reflection sheet 22 is provided so as to cover the inclined surface 19d of the light guide plate unit 19.

The reflection sheet 22 may be made of any material as long as it can reflect light leaking from the inclined surface 19d (back surface) of the light guide plate unit 19, for example, PET or PP. (Polypropylene), etc. kneaded with fillers and then stretched to form voids to increase the reflectivity by forming voids, a transparent or white resin sheet with a mirror surface formed by aluminum deposition, etc., aluminum, etc. Metal foil, resin sheet carrying metal foil, Can be formed of a thin metal plate having sufficient reflectivity on the surface. Further, the reflector 20 can be formed of, for example, the same material as the above-mentioned reflective sheet 22, that is, a resin sheet, a metal foil or a metal plate having a surface with sufficient reflectivity.

[0085] In the light guide plate unit 19 having the structure shown in Fig. 1B, of the light emitted from the rod-shaped light source 12 disposed in the parallel groove 19f, the light guide plate unit 19 extends from the side wall 19g forming the parallel groove 19f. Is reflected by the inclined surface 19d of the light guide plate unit 19, and then exits from the light exit surface 19a. At this time, part of the light leaks from the lower surface of the light guide plate unit 19, and the leaked light is reflected by the reflection sheet 22 formed on the inclined surface 19b side of the light guide plate unit 19, and is returned again. The light enters the unit 19 and exits from the light exit surface 19a. Thus, uniform light is emitted from the light exit surface 19a of the light guide plate unit 19.

[0086] The light guide plate unit 19 is manufactured by, for example, a method of molding a heated raw resin by extrusion molding or injection molding, or a casting polymerization method of polymerizing and polymerizing monomers, oligomers and the like in a mold. be able to. As a material of the light guide plate unit 19, for example, PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), MS resin, benzyl methacrylate, isopropyl methacrylate (abbreviation: IBXMA, water absorption rate 0) . 02 mass ^_0/0) or Torishikurode force - Rume Tatari rate (abbreviation: TCDMA, water absorption 0.023% by weight) other acrylic containing such side chains bulky alicyclic Atari rates such榭脂, or COP (A cycloresin polymer, for example, ZEONOR (registered trademark, manufactured by Nippon Zeon Co., Ltd.)). Among them, COP, IBXMA, TCDMA, etc., which have a small water absorption, can be preferably used in the present invention. In addition, since the COP, IBXMA, or TCDMA has a high glass transition temperature of other polymers, the light guide plate produced by these is also preferable in that it can be used in a higher temperature environment.

In the present invention, fine particles for scattering light may be mixed in the transparent resin, whereby the light emitting efficiency of the light from the light emitting surface 19a can be further increased.

As shown in FIG. 4, the parallel groove 19f of the light guide plate unit 19 is formed such that the cross-sectional shape of the parallel groove 19f is triangular. In the present invention, a light guide plate unit is configured. The cross-sectional shape of the parallel groove is not particularly limited as long as the water absorption w (mass%) of the transparent resin to be satisfied satisfies the expression (1). In the application of the above formula (1), the cross-sectional shape of the parallel groove is not particularly limited, and the surface area difference α and the long side length L

D

Can be applied regardless of the cross-sectional shape.

For example, in the present invention, the cross-sectional shape of the parallel groove 19f is symmetric with respect to the center line of the light guide plate 19f passing through the deepest portion or the center of the parallel groove 19f and perpendicular to the light emitting surface, and A shape that becomes thinner toward the surface 19a may be used.

In the present invention, for example, as shown in FIGS. 12 and 13, the cross-sectional shapes of the parallel grooves 19h and 19j can be hyperbolic or elliptical. Furthermore, the cross-sectional shape of the parallel groove of the light guide plate unit 19 may be a catenary line.

Here, FIG. 12 is a schematic side view showing a light guide plate unit when the cross-sectional shape perpendicular to the length direction of the parallel groove is a hyperbola, and FIG. 13 is a cross-sectional shape perpendicular to the length direction of the parallel groove. It is a typical side view which shows the light-guide plate unit when is elliptical. In the light guide plate unit 19 shown in FIGS. 12 and 13, the same components as those in the light guide plate unit 19 shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. .

Further, in the present invention, in addition to the cross-sectional shapes of the parallel grooves 19h and 19j shown in FIGS. 12 and 13, the cross-sectional shape of the parallel groove is the deepest part of the parallel groove (the side wall 19g forming the parallel groove). (The connecting part of the head) can be formed into a point. In other words, the two cross-sectional shapes of the tip portions of the parallel grooves are symmetric with respect to a center line perpendicular to the light exit surface of the light guide plate unit, passing through the center of the parallel grooves and having one sharp intersection point intersecting with each other. Alternatively, it can be formed from a part of a straight line. In the present invention, even if the cross-sectional shape of the parallel groove of the light guide plate unit is any of the shapes described above, it is possible to emit light with a uniform light exit surface force of the light guide plate unit.

FIG. 14 is a cross-sectional view of the cross-sectional shape of the leading end of the parallel groove. The cross-sectional shape has a sharp point of intersection with the center of the parallel groove and is perpendicular to the light exit surface of the light guide plate unit. FIG. 9 is a schematic side view showing a light guide plate unit in which a partial force of two nominal curves is also formed. In the light guide plate unit 50 shown in FIG. 14, the same components as those in the light guide plate unit 19 shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. The light guide plate unit 50 shown in FIG. 14 is a case where two curves 54a and 54b symmetric with respect to a center line X perpendicular to the light exit surface 52 of the light guide plate unit 50 through the center of the parallel groove 19k are arcs. . In this case, as shown in FIG. 14, the center position of the arc 54a corresponding to one side wall 19g forming the parallel groove 19k is different from the center position of the arc 54b corresponding to the other side wall 19g. Is done. As a result, the portion 56 where the arc-shaped side walls 19g intersect has a pointed shape as shown in FIG.

[0091] Fig. 15 shows two parabolas whose cross sections perpendicular to the length direction of the parallel groove are symmetrical with respect to a center line passing through the center of the parallel groove and perpendicular to the light exit surface of the light guide plate unit. FIG. 9 is a schematic side view showing another example of the light guide plate unit partially formed. In the light guide plate unit 60 shown in FIG. 15, the same components as those in the light guide plate unit 19 shown in FIG. 13 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The light guide plate unit 60 shown in FIG. 15 is a case where two curves 64a and 64b symmetric with respect to a center line X perpendicular to the light exit surface 60a of the light guide plate unit 60 through the center of the parallel groove 19m are parabolic. . In FIG. 15, the side wall 19g of the parallel groove 19m is formed such that the focus of the parabola 64a corresponding to one side wall 19g of the parallel groove 19m and the focus of the parabola 64b corresponding to the other side wall 19g are different from each other. .

As shown in FIG. 15, when the cross-sectional shape of the tip portion of the parallel groove is formed by two curves 64a and 64b intersecting at the intersection 64, a curve 64a corresponding to one side wall 19g of the parallel groove 19m The angle 7? Between the tangent at the intersection (cusp) 66 and the tangent at the intersection 66 of the curve 64b corresponding to the other side wall 19g is preferably 90 ° or less, more preferably 60 ° or less. .

[0093] In Fig. 4 and Figs. 12 to 15, the curves forming the side walls 19g of the parallel grooves 19f, 19h, 19j, 19k, 19m in the cross-sectional shape of the parallel grooves 19f, 19h, 19j, 19k, 19m. Force showing an example of a light guide plate unit concave toward the center of the force parallel groove The present invention is not limited to these.

Also, in the light guide plate units 19, 50, and 60 shown in FIGS. 12 to 15, the angle 0 (not shown) is the same as that shown in FIG. At this time, the average plane is a hyperbolic shape or an ellipse constituting the parallel grooves 19h and 19j in the case of the parallel grooves 19h and 19j (see FIGS. 12 and 13). This is a plane parallel to the direction in which the rod-shaped light source 12 extends, passing through a bottom (not shown) where the side wall 19g of the shape intersects on the center line X and a point where the thickness Dmax of the thick part 19b has the maximum value.

In the case of the parallel groove 19k (see Fig. 14), it passes through the portion 56 where the arc-shaped side walls constituting the parallel groove 19k intersect on the center line X and the point where the thickness Dmax of the thick portion 19b becomes the maximum value. , A plane parallel to the direction in which the rod-shaped light source 12 extends.

In the case of the parallel groove 19m (see FIG. 15), the intersection point 66 of the curve 64a corresponding to one side wall 19g and the curve 64b corresponding to the other side wall 19g constituting the parallel groove 19m, and the thickness of the thick portion 19b This is a plane parallel to the direction in which the rod-shaped light source 12 extends, passing through the point at which Dmax has the maximum value.

Parallel grooves 19f, 19h, 19j, 19k, 19m force S Even with such a shape, it goes without saying that the same effect can be obtained if the above expression (1) is satisfied.

[0094] Here, Fig. 16 is a schematic side view showing a light guide plate unit in which a cross-sectional shape perpendicular to the length direction of the parallel groove is also formed with two curved forces that are convex toward the center of the parallel groove. It is. FIG. 17 is a schematic side view showing a light guide plate unit in which a cross-sectional shape perpendicular to the length direction of the parallel groove has a curved force formed by combining a convex curve and a concave curve toward the center of the parallel groove. FIG. In the light guide plate units 70 and 80 shown in FIGS. 16 and 17, the same components as those in the light guide plate unit 19 shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0095] The light guide plate unit 70 shown in Fig. 16 is an example of the light guide plate unit 70 in which two curves 72a and 72b that are convex toward the center of the parallel groove 19p are also formed.

Further, in the light guide plate unit 80 shown in FIG. 17, the cross-sectional shape of the parallel groove 19q is formed such that the convex curves 82a and 82b and the concave curves 84a and 84b are combined toward the center of the parallel groove 19q. This is an example of the light guide plate unit 80.

The light guide plates 70 and 80 having the parallel grooves 19p and 19q having the cross-sectional shapes as shown in FIGS. 16 and 17 also emit light with sufficient light emission surface power while suppressing generation of bright lines. be able to.

Note that the light guide plate units 70 and 80 shown in FIGS. 16 and 17 also have an angle of 0 (not shown). ) Are the same as those shown in FIG. At this time, in the case of the parallel groove 19p, the average plane is the bottom (not shown) where the two convex curves 72a and 72b constituting the parallel groove 19p intersect on the center line X, and the thickness Dmax of the thick portion 19b. Is a plane parallel to the direction in which the rod-shaped light source 12 extends, passing through the point at which the maximum value is obtained.

Further, in the case of the parallel groove 19q, a bottom (not shown) where a curve obtained by combining the convex curves 82a and 82b and the concave curves 84a and 84b constituting the parallel groove 19q intersect on the center line X, and a thick portion This is a plane parallel to the direction in which the rod-shaped light source 12 extends, passing through the point where the thickness Dmax of 19b has the maximum value.

Even if the parallel grooves 19p and 19q have such a shape, it goes without saying that the same effect can be obtained if the above expression (1) is satisfied.

[0096] As described above, in the present invention, in the cross-sectional shape of the parallel groove of the light guide plate unit, the portion corresponding to the parallel groove is convex or concave toward the center of the parallel groove. Or a linear shape, or a combination thereof. These curves may be any part of a curve such as an ellipse, a parabola, or a hyperbola that is convex or concave toward the center of the parallel groove, which is not limited to the arc in the illustrated example.

Further, in the present invention, if the cross-sectional shape of the tip portion of the parallel groove is tapered as described later, the curve constituting the parallel groove will have a convex, concave, circular, It is preferable that the curve be a part of a curve such as an ellipse, a parabola, or a hyperbola, and it is particularly preferable that the curve be a curve that can be approximated by a 10-order function.

In the light guide plate unit 19, which is a component of the light guide plate of the present invention, as shown in FIG. Dot pattern such that the density of the dots gradually decreases as you move in the vertical direction.

V may be formed on the light emitting surface 19a of the light guide plate unit 19 by, for example, printing. Such a halftone dot pattern V is formed on the light exit surface 19a of the light guide plate unit 19 such that the center line X of the halftone dot pattern V coincides with the position corresponding to the center line of the parallel groove of the light guide plate unit 19. By doing so, it is possible to suppress the generation of bright lines on the light exit surface 19a of the light guide plate unit 19 and to suppress the luminance unevenness. Instead of printing the halftone dot pattern V on the light guide plate unit 19, a thin sheet on which the halftone dot pattern is formed may be laminated on the light emitting surface. Halftone The shape can be an arbitrary shape such as a rectangle, a circle, and an ellipse, and the density of halftone dots can be appropriately selected according to the intensity or spread of the bright line. Instead of forming such a halftone pattern by printing, a portion corresponding to the halftone pattern may be roughened as a sand rubbing surface. Such a sand rubbing surface may be formed on the deepest portion or the side wall of the parallel groove of the light guide plate unit.

Next, when the cross-sectional shape of the parallel groove of the light guide plate is changed to various shapes, the illuminance distribution of light emitted from the light exit surface 19a of the light guide plate including one light guide plate unit 19 is examined. Was. First, as examples of the light guide plate unit of the light guide plate 18 of the present invention, the cross-sectional shape of the parallel groove 19f is triangular and hyperbolic as shown in FIGS. 1 and 12, respectively, and the cross-sectional shape is an example of the conventional light guide plate. Parabolic and semicircular (kamaboko) cases were investigated. FIG. 19 shows the relative illuminance distribution on the light exit side surface of the light guide plates. In FIG. 19, the vertical axis indicates the relative illuminance, and the horizontal axis indicates the distance from the center of the light guide plate unit (the center of the parallel groove).

[0099] Here, the relative illuminance was measured as follows.

First, a light source was incorporated in the light guide plate unit of the present invention, and light was made to enter the light guide plate unit and emitted from the light exit surface.

Next, in this state, the illuminometer is fixed to the XY stage, and the illuminometer is fixed to be perpendicular to the light emission surface of the light guide plate unit. Then, the illuminance is measured at the position of the light exit surface by the illuminometer to obtain illuminance information regarding the specific position of the light exit surface of the light guide plate.

Then, by moving the XY stage, the relationship between the position on the light emitting surface and the illuminance is determined, and the average value of the entire surface is calculated. The ratio of the illuminance at each position divided by the average value of the illuminance, respectively, is the relative illuminance at that position.

In addition, by measuring one axis perpendicular to the axial direction of the parallel groove and representing the value, it is possible to easily compare the cross-sectional shapes.

When measuring the relative luminance, a luminance meter may be used instead of the illuminometer, whereby the relative luminance distribution on the light emission side surface of the light guide plate can be obtained.

[0100] As shown in Fig. 19, when the cross-sectional shape of the parallel groove of the light guide plate unit is hyperbolic, the peak value of relative illuminance at the portion corresponding to the parallel groove is the output light of the inclined back surface force. Is less than or equal to 10 times the average value of the relative illuminance formed, indicating that the illuminance from the light emitting surface is substantially uniform.

On the other hand, in a conventional light guide plate unit in which the cross-sectional shape of a parallel groove is semicircular or parabolic, as shown in FIG. 19, the relative illuminance at the center of the parallel groove, that is, at the position immediately above the light source, Is high, and it can be seen that a bright line is generated. That is, in a conventional light guide plate having a parallel groove having a semicircular or parabolic cross section, the illuminance on the light irradiation surface is not uniform.

[0102] In a light guide plate in which the cross-sectional shape of the parallel groove is triangular, the relative illuminance at the center is low. When the cross-sectional shape of such a parallel groove is triangular, as shown below, the illuminance on the light exit surface is obtained by flattening the apex with a predetermined width or making it a curved surface with a relatively small radius of curvature. Can be made uniform.

[0103] Fig. 20 shows that, when the cross-sectional shape of the parallel groove of the light guide plate is triangular, the deepest part of the parallel groove (the vertex of the triangular parallel groove) is flattened, and the length of the flat part is varied. The light output surface force of the light guide plate when the value is changed. In FIG. 20, the vertical axis represents relative illuminance, and the horizontal axis represents the distance from the center of the parallel groove formed in the light guide plate. Here, in order to simplify the calculation, the diameter of the cold-cathode tube (light source) was set to 3 mm, and the lengths of the flat portions were set to 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm.

Figures 21A to 21D show that when the cross-sectional shape of the parallel groove 19f is triangular, the depth of the flat part 90 at the deepest part of the parallel groove 19f is 1.5mm, 1.Omm, 0.5mm, 0.25mm. The schematic side views showing the light plate cut are respectively shown.

In the light guide plate unit 19 shown in FIGS. 21A to 21D, the same components as those in the light guide plate unit 19 shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the light guide plate unit 19 shown in FIGS. 21A to 21D, the angle 0 (not shown) is the same as that shown in FIG. At this time, in the water absorption, the length of the flat portion 90 is sufficiently negligible. 21A to 21D, the average plane is the side wall 19g, and the angle Θ is the inclination of the side wall 19g with respect to the center line X. In this case, it is needless to say that the same effect can be obtained if the above equation (1) is satisfied. As shown in the graph of FIG. 20, it can be seen that the relative illuminance at the portion corresponding to the parallel groove 19f of the light guide plate unit changes according to the length of the flat portion 90. Here, in the present invention, the illuminance can be increased by lengthening the flat end portion 90 at the deepest portion of the parallel groove 19f. However, if the length is too long, an emission line may be formed. The thickness is preferably 20% or less of the diameter of the cold cathode tube (light source), more preferably 10% or less.

[0105] Fig. 22 shows that, in a light guide plate in which the cross-sectional shape of the parallel groove of the light guide plate is triangular, the shape of the deepest portion of the parallel groove is changed to a curved shape with a radius of curvature R, and the radius of curvature of the curved surface is changed to various values. 9 is a graph showing the illuminance distribution of light emitted from the light exit surface 19a of the light guide plate unit 19 when the light guide plate unit 19 is turned on.

Here, the radius of the cold-cathode tube (light source) was 3 mm, and the light guide plate units with the radii of curvature at the apexes of 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm were measured.

FIGS.23A to 23D are schematic diagrams showing light guide plate units in which the apex portion 92 has a radius of curvature of 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm when the cross-sectional shape of the parallel groove 19 f is a triangle. The side views are respectively shown.

In the light guide plate unit 19 shown in FIGS. 23A to 23D, the same components as those in the light guide plate unit 19 shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the light guide plate unit 19 shown in FIGS. 23A to 23D, the angle 0 (not shown) is the same as that shown in FIG. In terms of water absorption, the size of the peak portion 92 is sufficiently negligible. In the light guide plate unit 19 shown in FIGS.23A to 23D, the average plane is a rod-shaped light source 12 passing through a vertex portion 92 where the side wall 19g intersects on the center line X and a point where the thickness Dmax of the thick portion 19b becomes the maximum value. Is a plane parallel to the extending direction. In this case, it is needless to say that the same effect can be obtained if the above expression (1) is satisfied.

As shown in the graph of FIG. 22, the relative illuminance at the portion corresponding to the parallel groove 19f of the light guide plate unit 19 changes according to the radius of curvature of the vertex 92 of the parallel groove 19f, and the vertex 9 2 It can be seen that the relative illuminance on the light exit surface 19a of the light guide plate unit 19 is substantially uniform when the radius of curvature R of the light guide plate unit is 0.25 mm.

[0107] From the above, it can be seen that the shape of the tip portion of the parallel groove of the light guide plate unit largely depends on the illuminance of the light emitting surface force. That is, the shape of the parallel groove of the light guide plate is the shape shown in the present invention. It can be seen that the illuminance on the light exit surface 19a of the light guide plate unit 19 can be optimally adjusted and made uniform only by designing so that

On the surface of the light guide plate unit, the illuminance and the luminance can be handled in substantially the same manner. For this reason, from the relative illuminance graphs of FIG. 20 and FIG. 21, it is inferred that the present invention has the same tendency in luminance. Therefore, by designing the shape of the parallel grooves of the light guide plate so as to have the shape shown in the present invention, it is considered that the brightness on the light emitting surface 19a of the light guide plate unit 19 can be made uniform.

The cross-sectional shape of the top part (deepest part) of the tip of the parallel groove is not only a single point that is sharply symmetrical with respect to the center line of the parallel groove, but also has a chamfered flat shape or a rounded circular shape. Of course, it may be elliptical, parabolic, or hyperbolic. In addition to this, as described above, the peak (the deepest part) of the tip of the parallel groove may be a sand rubbing surface to reduce the illuminance or luminance peak value.

[0108] As described above, in the light guide plate of the present invention, the light guide plate with respect to the average value of the illuminance formed in the portion other than the parallel groove 19f on the light exit surface 19a of the light guide plate unit 19, ie, the portion corresponding to the inclined back surface 19d. The tip of the parallel groove 19f of the light guide plate unit 19 is tapered in accordance with the ratio of the peak value (peak value of illuminance) of the bright line formed in the portion corresponding to the parallel groove 19f on the light exit surface 19a of the light plate unit 19. Perform That is, the degree of tapering of the tip of the parallel groove 19f of the light guide plate unit 19 is controlled in accordance with the value of this ratio. The ratio is preferably 3 or less, more preferably 2 or less.

This ratio is determined by the thickness of the knock light unit 2 (the distance between the light exit surface 19a of the light guide plate unit 19 and the diffusion sheet 14) or the diffusion sheet used in the backlight unit 2. It is preferable to set according to the diffusion efficiency or the number of sheets of 14, the diffusion efficiency of the prism sheets 16, 17 and 21, or the number of sheets to be used. That is, when the thickness of the knock light unit 2 (the distance between the light exit surface 19a of the light guide plate unit 19 and the diffusion sheet 14) is somewhat thick or large, or when the diffusion sheet used in the backlight unit 2 is used. If the diffusion efficiency of 14 can be increased and the number of used sheets can be increased, or the diffusion efficiency of prism sheets 16, 17 and 21 can be increased and the number of used sheets can be increased, the light emitting surface 19a of the light guide plate unit 19 can be used. The emitted illumination light can be sufficiently diffused (mixing, etc.) Therefore, although the cost is high, the parallel groove 19f of the light exit surface 19a of the light guide plate unit 19 with respect to the average value of the illuminance of the second portion corresponding to the inclined back surface portion 19e on the light exit surface 19a of the light guide plate unit 19. The ratio of the peak value of the illuminance of the first portion corresponding to the ratio can be set to a relatively large value. However, if this is not the case, it is necessary to set the value of this ratio to a low value to reduce the cost.

On the other hand, in the present invention, the peak value of the illuminance of the first portion corresponding to the parallel groove 19f of the light exit surface 19a of the light guide plate unit 19 has an inclined rear surface portion 19e of the light exit surface 19a of the light guide plate unit 19. The tip shape of the parallel groove 19f of the light guide plate unit 19 is tapered so as to be three times or less, more preferably, two times or less the average value of the illuminance of the second portion corresponding to the following. Here, the peak value of the illuminance of the first portion of the light exit surface 19a of the light guide plate unit 19 is 3% of the average value of the illuminance of the second portion corresponding to the inclined back surface portion 19e of the light exit surface 19a of the light guide plate unit 19. The reason why the light guide plate unit 19 is not more than doubled is that the illuminance distribution of the illuminating light emitted from the light exit surface 19a of the light guide plate unit 19 is more uniform than before, and as a result, the light guide plate unit 19 It is possible to use a low-cost diffusion sheet 14 with low diffusion efficiency, which does not need to sufficiently diffuse (mixing, etc.) the illumination light emitted from the light exit surface 19a, and can reduce the number of sheets used. The use of expensive prism sheets 16, 17 and 21 themselves, or the use of low-cost prism sheets 16, 17 and 21 with low diffusion efficiency, or the number of sheets used To It is a force that can lath.

[0111] In the light guide plate of the present invention, in the cross-sectional shape of the parallel groove of the light guide plate unit, the leading end portion where the parallel groove is tapered has a perpendicular force (X) from the center of the rod-shaped light source to the light emitting surface. It is preferred that the angle force be within 90 ° on both sides, more preferably within 60 °. That is, in the present invention, in order to reduce the peak value of the illuminance of the first portion corresponding to the parallel groove on the light exit surface of the light guide plate unit, the portion where the parallel groove is tapered may be the entire parallel groove. However, if the peak value can be reduced, a predetermined tip portion may be used.

As described above, the light guide plate of the present invention, the backlight unit including the same, and the liquid crystal display device have been described in detail. However, the present invention is not limited to the above embodiments, and the present invention is not limited thereto. Of course, various improvements and changes may be made without departing from the gist of the invention.

For example, in the present invention, as shown in FIG. 24, a plurality of light guide plate units 94 and 96 are arranged in parallel so that the light exit surfaces 94a and 96a of the light guide plate units 94 and 96 all form the same plane. The light guide plate can be arranged to form a large light guide plate. When the light guide plate units 94 and 96 are arranged in parallel in this manner, the inclined surface 94d of one light guide plate unit 94 and the inclined surface 96d of the other light guide plate unit 96 connected to the light guide plate unit 94 do not cross each other. That is, the inclination angles of the inclined surfaces 94d and 96d of the light guide plate units 94 and 96 can be adjusted so that a smooth flat surface or a curved surface is formed at the connecting portion of the inclined surfaces. In the light guide plate shown in FIG. 24, the surfaces formed by the inclined surfaces 94d and 96d of the light guide plate units 94 and 96 are formed so as to have an arch shape. The light guide plate units 94 and 96 shown in FIG. 24 have basically the same configuration as the light guide plate unit 19 shown in FIG. 4, and a detailed description thereof will be omitted.

By using a light guide plate having such a large light emitting surface, a backlight unit having a large light irradiating surface can be obtained. Therefore, the present invention is applied to a liquid crystal display device having a large display screen. In particular, the present invention can be applied to a wall-mounted type liquid crystal display device such as a wall-mounted television.

[0114] As described above, the light guide plate according to the present invention is formed by connecting the thin portions of separately formed light guide plate units to form a large light guide plate by connecting a plurality of light guide plate units. . In addition to this, from the viewpoint of manufacturing efficiency, it is preferable to integrally mold as many light guide plate units as necessary to form a light guide plate corresponding to a required screen size.

Further, in the light guide plate of the present invention, as shown in FIG. 25, the reflector 24 may be arranged on the side surface of the outermost light guide plate unit 19. By arranging such a reflection plate 24 on the side surface, leakage of light from the side surface of the light guide plate unit 19 can be prevented, and the light use efficiency can be further enhanced. The reflection plate 24 can be formed using the same material as the reflection sheet or the reflector described above.

[0116] Further, in the light guide plate unit of the present invention, any of the light guide plate units has a shape symmetrical with respect to the center line, but the present invention is not limited to this. In the present invention May be asymmetrical with respect to the center line, as shown in FIGS. 26A and 26B.

FIG. 26A is a schematic perspective view showing a light guide plate according to another embodiment of the present invention, and FIG. 26B is a side view showing a light guide plate according to another embodiment of the present invention. In the light guide plate 100 shown in FIGS. 26A and 26B, the same components as those in the light guide plate 18 and the light guide plate unit 19 shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The light guide plate 100 of the present invention has a saw blade shape in a side view. The light guide plate 100 has a light exit surface 102a on the front surface side. Opposite to the light exit surface 102a, an inclined back surface 102e forming an inclined surface 102d is provided. The slope 102d is inclined so as to become narrower in one direction. Each slope 102d is connected by a vertical surface 102g. The rod-shaped light source 12 is provided in a region 102f where the inclined surface 102d and the vertical surface 102g are connected. The area surrounded by the light emitting surface 102a, one inclined surface 102d, and one vertical surface 102g is the light guide plate unit 102.

[0118] Also in the light guide plate 100 of the present embodiment, the water absorption of the transparent resin constituting the light guide plate unit 102 of the light guide plate 100 can be calculated by the above equation (1). Also in this case, the length of the longer side of the light guide plate 100 is L.

D

In the light guide plate 100 of the present embodiment, the vertical surface 102g is an average plane.

Further, in the light guide plate 100 of the present embodiment, it is preferable to use a light source having high directivity such as an LED array instead of the rod-shaped light source 12.

Industrial applicability

[0119] The light guide plate of the present invention is thin and lightweight, can suppress deformation even in a high-humidity environment, and can emit more uniform, less uneven, and higher-luminance light. it can . Therefore, it can be used for a light guide plate for a backlight used in a liquid crystal display device, particularly for a large light guide plate.

Further, the spread illuminating apparatus of the present invention is thin and lightweight, can suppress uneven brightness even in a high humidity environment, can prevent a decrease in average brightness, and can be manufactured at lower cost. Therefore, the surface illumination device of the present invention can be applied to a liquid crystal display device such as a liquid crystal monitor or a wall-mounted television.

Further, the liquid crystal display device of the present invention is thin and lightweight, and can be displayed even in a high humidity environment. The occurrence of uneven display can be prevented. The liquid crystal display device of the present invention can be used for a large-screen liquid crystal monitor, a large-screen wall-mounted television, and the like.

Claims

The scope of the claims

[1] A light guide plate, wherein at least two light guide plate units each having a rectangular light exit surface and a back surface facing the light exit surface are connected to each other with the light exit surfaces on the same plane. The length of the longest side of the rectangular total light emitting surface obtained by connecting the light emitting surfaces of the unit is L (mm), and the length per unit length of the light guide plate unit is

D

When the surface area difference between the light emitting surface and the back surface is α, and Κ and b are coefficients, the water absorption w (mass%) of the transparent resin constituting the light guide plate unit is represented by the following equation (1). is intended to satisfy, the value of y is 3 or less, that ^{K = 3. 3 X 10 _4 (} lZ (mm X mass ^_0/0)), which is b = l. 9 X 10 " 2 ( wt%) Characteristic light guide plate.

[Number 10]

w≤ ^-b '' '(1)

Κ α L _D

[2] The light guide plate unit has a rectangular light exit surface,

A thick portion parallel to one side thereof and located at a substantially central portion of the light emitting surface,

A thin end formed in parallel with the thick part,

A parallel groove formed substantially in the center of the thick portion and parallel to the one side for accommodating a rod-like light source, and including a shaft of the rod-like light source on both sides of the parallel groove and perpendicular to the light emitting surface. And a slanted back portion that forms a slanted back surface with the thinned portion facing the thin end portions on both sides in a direction orthogonal to the one side from the thick portion. Made of transparent resin,

The thin end portions of adjacent light guide plate units are connected, and the light emission surfaces of the connected light guide plate units are arranged on the same plane,

The distance from a plane passing through the center of the rod-shaped light source and perpendicular to the light emitting surface to an end surface of the thin end portion, which is a junction with an adjacent light guide plate unit, is L (mm), and the thickness of the thick portion is The maximum thickness is Dmax (mm), the minimum thickness of the thin end is Dmin (mm), the distance between the bottom of the parallel groove and the light emitting surface is δ (mm), and the center of the rod-shaped light source is When the angle between the line perpendicular to the light exit surface and the average plane of one side wall in the cross-sectional shape of the parallel groove is Θ (°), the surface area difference α is represented by the following equation (2). The light guide plate according to claim 1, wherein the light guide plate is represented by: [Number 11]

"ヽ

Dmax— d, f _τ Uma — 0 1, „ _π ., ₂

+ L-ten (umax—JJmin) — L

― Cos β \ l tan6), _r ,

a =

L

3. The light guide plate according to claim 1, wherein the value of y is 1 or less.

[4] The light guide plate according to any one of claims 1 to 3,

A rod-shaped light source housed in the parallel groove of the light guide plate;

A reflector provided behind the rod-shaped light source so as to close the parallel groove; and a reflection sheet attached to the inclined back surface of the inclined back surface on both sides of the thick portion of the light guide plate.

And a diffusion sheet disposed on the total light exit surface of the light guide plate.

[5] The surface according to claim 4, further comprising a prism sheet disposed between the total light exit surface of the light guide plate and the diffusion sheet or above the diffusion sheet. Lighting equipment.

[6] A backlight unit which also has the power of the planar lighting device according to claim 4 or 5,

A liquid crystal display device comprising: a liquid crystal display panel disposed on a light emitting surface side of the knock light unit; and a drive unit for driving the backlight unit and the liquid crystal display panel.