JP2710465B2 - Surface light source element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface light source element used in a surface light source device, and more particularly to a surface light source element such as a liquid crystal display element which can be suitably used as a back lighting unit.

BACKGROUND ART Conventionally, backlighting of a liquid crystal display device (backlight).
As a means, a structure is generally used in which a linear lamp is used as a light source, the light is placed at the focal point of a rotating parabolic reflector, and a milky white diffusion plate is placed above the lamp. In the device having this structure, improvement is achieved by adjusting the shape of the reflector and the diffusivity of the diffusion plate.

In addition, a device that combines a linear lamp and a light guide, simulates the shape of the light guide by approximating a point light source, and processes the light guide into an approximate curve shape so as to converge outgoing light in a certain direction. There is a device that changes the thickness of the light guide, a device that uses a lenticular whose prism angle is changed according to the distance from the light source, and a combination of these.

In recent years, surface light source elements have been used as liquid crystal display elements. However, when trying to improve display quality by using conventional surface light source elements, particularly for large displays of 10 to 12 inches, The thickness of the element portion alone is 20 to 30 mm, which cannot satisfy the demand for a thin surface light source element.

On the other hand, a plate-shaped transparent material such as an acrylic resin is used as a transparent light guide, and an edge light type surface light source device that receives light from an end of the transparent light guide and emits light from an upper surface or a lower surface of the light guide. Have been proposed. However, 10-
In the case of a large 12-inch liquid crystal display device, it was not always possible to perform a favorable display because the display became dark or uneven depending on the distance from the light source.

On the other hand, measures have been taken to reduce the thickness of the light guide according to the distance from the lamp, and to geometrically change the path of light, but precise processing is required. And there is an inconvenience in manufacturing cost. Moreover, the light use efficiency was low.

Recently, with respect to an edge light type surface light source element, Japanese Patent Application Laid-Open No. 1-245220 discloses that a light scattering substance is densely applied or adhered to a surface facing a light emitting surface of a light guide as the distance from the light incident portion increases, or A display method in which a light-scattering reflection surface is provided and a light-scattering substance is similarly applied or adhered to the surface is disclosed. In Japanese Patent Application Laid-Open No. 1-107406, fine spots (scattering substances) are provided on the transparent plate surface. There has been reported a surface illumination device capable of uniformly brightening the entire surface of a light diffusion plate by stacking a plurality of transparent plates having different spot patterns.

However, in these methods, generally, a light-impermeable inorganic substance (often a white pigment such as titanium oxide or barium sulfate) is used as a scattering substance,
When the light striking the scattering material is scattered, light loss such as light absorption occurs, and the luminance of the emitted light decreases.

Oe is a Japanese Utility Model Publication No. 61-171001, U.S. Pat.
In the publication, a light diffusion layer is provided on a light guide through a layer exhibiting properties intermediate between the light guide and the diffusion layer, and an emission light adjusting member is provided thereon to obtain uniform emission light. Reported diffuser.

Further, the present inventors also disclose in JP-A-1-244490 and JP-A-1-252933 that at least one of the light exit surface of the light guide and the opposite surface is a lens or a matte surface, An edge light type surface light source element in which an emission light adjusting member and a light diffusion plate having a light reflection pattern corresponding to the reciprocal of the emission light distribution on a surface are proposed.

Although the light diffusion device and the surface light source element using these emission light adjusting members show an excellent effect of improving the uniformity of the emitted light, the light reflected by the emission light adjusting member cannot be reused, and It has been found that the luminance of the image becomes low near the minimum value of the luminance before adjustment.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultra-thin surface light source element that has uniform brightness over the entire light emitting surface and can obtain high-luminance emitted light.

DISCLOSURE OF THE INVENTION The surface light source element of the present invention has at least one side end as a light incident surface, one surface orthogonal to this as a light emitting surface, and a light reflecting layer on the surface opposite to the light emitting surface. A transparent light guide (1), and a diffuser (2) for diffusing light from the light exit surface of the transparent light guide, wherein at least one of the light exit surface of the transparent light guide and its opposite surface A roughened portion having a directional emission function of emitting light incident from the light incident surface of the transparent light guide obliquely to the traveling direction of the light or a portion having a large number of lens units, and an optical plane And a control function of increasing the proportion of the smooth portion as approaching the light incident surface to make the luminance value of light emitted from the light emitting surface uniform over the entire light emitting surface. It is characterized by the following.

The amount of internal light incident on the light guide from the light incident surface decreases as the distance from the light incident surface decreases due to emission from the light exit surface, light absorption inside the light guide, and the like. Since the ratio of the smooth portion is increased as approaching the light incident surface, even if the transparent light guide is made thin, the incident light is emitted from the entire surface of the light emitting surface with a substantially uniform luminance value. Further, the light incident on the transparent light guide is not wasted and is used with high light use efficiency, so that high-intensity emitted light can be obtained without increasing the wattage of the light source. Therefore, according to the present invention, it is possible to provide an ultra-thin surface light source element that has uniform brightness over the entire light emitting surface and can obtain high-luminance emitted light.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are cross-sectional views each showing a configuration of a conventional surface light source element. FIG. 2 is a diagram showing changes in luminance values corresponding to the distances of various surface light sources from the light incident surface.

FIG. 3 is a partially cutaway perspective view of a backlight device incorporating a surface light source element according to one embodiment of the present invention, FIG. 4 is a partial cross-sectional view taken along line IV-IV of FIG. 3, and FIG. (A)-(e)
Is a schematic diagram showing an example of a planar pattern of a smooth portion, FIGS. 6 (a) to (c) are schematic sectional views illustrating various lens units, and FIGS. 7 and 8 are planes of the present invention. FIG. 9 is a partial sectional view showing a modification of the light source element, and FIG. 9 is a schematic side view showing a modification of the backlight device. FIG. 10 is a graph showing an area ratio distribution of a smooth portion of a pattern formed on a mold for producing a light guide used in the examples, and FIGS. 11 (a) and (b) are graphs showing the produced light guide. , FIG. 12 is a graph showing the measurement results of the luminance distribution of each surface light source element, FIG. 13 is a schematic view showing a method of measuring the directivity emission angle of the manufactured surface light source element, FIG. 7A and 7B are graphs showing measurement results of the directivity emission angle of the manufactured surface light source element.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the surface light source device of the present invention will be described in more detail.

First, the basic principle of the surface light source element of the present invention will be described. The refractive index n of light of the light guide with respect to air is approximately
n = 1.4 to 1.6, and the critical angle is about 45 degrees in an edge lighting shape in which the entrance surface 7 and the exit plane 6 of the light guide 1 are perpendicular to each other as shown in FIG. No light is emitted from the emission plane 6 in principle. In FIG. 1 (a), reference numeral 4 denotes a light source such as a fluorescent lamp, 5 denotes a reflector thereof, and 2 denotes a reflection surface formed on the opposite side of the emission plane 6 of the light guide 1.

Therefore, as shown in FIG. 1 (b), the emission plane 6 is generally made to be a plane 6a subjected to light scattering processing, and the reflection surface 2 is generally made to be a scattering reflection surface 9a.

The present inventors studied scattering processing of one or both of the light guide surface and the opposing surface in order to maximize the amount of light emitted from the light guide, and found that the surfaces were made as uniform as possible. A method of performing rough surface processing and a method of providing a large number of lens units for emitting light in a predetermined direction on those surfaces is a method of applying a scattering substance to one or both of a light guide surface and a facing surface thereof or during polymerization of an acrylic plate. It has been found that the method is more effective than a method in which a layer of a scattering material is formed on the surface.

On the other hand, a fluorescent lamp in which a silver-evaporated polyester film is wound as a reflector is placed on one end surface of the roughened surface light guide, and a white film is disposed as a reflector in close contact with the roughened surface to emit light. When the luminance was measured, the luminance of the emitted light was attenuated as the distance from the fluorescent lamp increased, and at a distance of 70 to 80 times the thickness of the light guide, 1 / l of the luminance value near the incident end.
About 10 This is shown by the line in FIG.

The present inventors have proposed, as described above, JP-A-1-244490 and JP-A-1-2529 in order to improve the nonuniformity.
In Japanese Patent Publication No. 33, it has been proposed to make the luminance uniform with a light-transmitting sheet for adjusting the emitted light. However, although the uniformity of the luminance of the emitted light is achieved by this method, the luminance value of the entire emitted light is 1/10 or less of the luminance value near the incident end.
The light energy dropped to about 1.5 / 10 was not efficiently used. This is shown by the line in FIG. This is because the emitted light adjusting translucent sheet only cuts out the emitted light, and reflects the light in the adjustment pattern and cannot reuse it.

In view of this, the present inventors have considered that, from such a viewpoint, in order to use the incident light as effectively as possible, the adjustment pattern of the light-transmitting sheet for adjusting the emission light, and Japanese Patent Application Laid-Open No. 1-245220 described above. Rather than performing light emission by applying a scattering substance densely as the distance from the light incident portion increases as in the publication, the present inventors disclosed in Japanese Unexamined Patent Publication No.
No. 17, JP-A-2-84618, JP-A-2-176629
In the transparent light guide as reported in Japanese Patent Application Publication No. H10-27139, the amount of outgoing light is adjusted using interface reflection with the least loss optically, and the brightness of the outgoing light surface is adjusted. An attempt was made to equalize the values.

That is, the surface light source element of the present invention is configured such that light incident from at least one of the light exit surface and the reflection surface of the transparent light guide from the light incident surface of the transparent light guide is oblique to the traveling direction of the light. Provide a rough surface or a large number of lens units having a directional emission function of emitting light to the surface, and provide a smooth portion on the rough surface or a surface having a large number of lens units, and make the ratio of the smooth portion closer to the light incident surface. And a control function to make the luminance value of light emitted from the light exit surface of the transparent light guide uniform over the entire light exit surface so that the overall luminance value of the exit light is near the incident end. It has been found that a surface light source element can be obtained which can be increased to about 3/10 of the luminance value and which exhibits a uniform luminance value over the entire light emitting surface. This is shown by the line in FIG.

EXAMPLES The surface light source device of the present invention will be specifically described by the following examples.

Surface Light Source Device FIG. 3 shows an embodiment of a backlight (backlight) device incorporating the surface light source device according to the present invention, and FIG. 4 shows one example of the IV-IV line of the device shown in FIG. FIG.

This device comprises a rectangular flat light guide 1, a film light diffuser 3 provided on the light exit surface 6 side to cover the surface, and an end side surface (light incident surface) of the light guide 1. 7) A light source 4 such as a fluorescent lamp provided in 7), and a reflector 5 which holds the light source 4 and reflects light to an incident surface by a reflection surface provided on an inner surface. Light guide 1
The light reflection layer 2 is provided on the side opposite to the light exit surface 6.

The feature of the surface light source element of the present invention is that light incident from at least one of the light exit surface and the opposite surface of the light guide 1 from the light incident surface 6 of the light guide 1 is oblique to the traveling direction. A rough surface or a large number of lens units having a directional emission function for emitting light is provided, and a smooth portion is provided on the rough surface or a surface having a large number of lens units. That is, a control function is provided for making the luminance value of light emitted from the light exit surface of the light guide 1 uniform over the entire light exit surface.

In this embodiment, a smooth portion 8 is provided on a roughened surface (opposite surface) 9 on the opposite side of the light exit surface 6, and the ratio of the smooth portion 8 is as shown by an arrow A in FIG. , Light incident surface 7
It is configured to increase as approaching.

The ratio of increasing the smooth portion of the light guide, the shape and pattern of the smooth portion, the material and shape of the light guide, the type of light source, the degree of processing of the light emitting / reflecting surface, and the like are appropriately selected, changed, and determined. can do.

FIGS. 5A to 5E show examples of the pattern of the smooth portion. In each of these examples, the ratio of the smooth portion 8 increases as approaching the light incident surface 7 as shown by the arrow A in FIG.

The diffuser 3 used in the present invention may be any material as long as it can diffuse the light from the light guide 1 in a non-directional manner. Light guide 1 of diffuser 3
In addition to the method of bonding only the end portion of the light guide with an adhesive or the like by forced contact by pressure bonding, the light guide can be simply placed. Further, the light guide 1 and the diffuser 3 may be closely adhered to each other, or may be laminated via a thin air layer.

In the present invention, the light guide 1 can be obtained from a transparent resin such as an acrylic resin, a polycarbonate resin, or a vinyl chloride resin, or a transparent inorganic material such as glass or quartz, and an acrylic resin having a large visible light transmittance is particularly preferable. . The method of forming the light guide 1 can be appropriately selected and changed.

The light source 4 in the present invention is not particularly limited, and is a continuous linear light source such as a fluorescent lamp, a filament lamp, a plurality of point light sources arranged along an incident surface, an optical transmitter that leaks light from a side surface, and a light source. A light source device or the like in which a light source provided on an end incident surface of an optical transmission body is combined can be used as a light source.

The reflection layer 2 of the surface light source element in the present invention can be formed by laminating a reflection film or the like obtained by depositing a metal (silver, aluminum, or the like) on a film. As this reflecting material, a material having a high reflectance is preferable.

In the present invention, the light guide 1 needs to have at least one of the light emitting surface 6 and the opposite surface roughened or formed with a large number of lens units for emitting light in a predetermined direction. In addition, it is necessary that the surface on which the surface is roughened or on which a large number of lens units are formed is provided so that a smooth portion increases as approaching the light incident surface.

In a preferred embodiment of the present invention, the surface of the smooth portion 8 of the light guide 1 is preferably an optical plane, and particularly preferably a mirror surface. This is because light incident on the optical plane at an angle of incidence equal to or greater than the critical reflection angle is reflected with little loss and does not become leaked light, so that light can be used effectively and the brightness of the entire light exit surface is reduced. This is because it can be improved.

The shape of the lens unit used in the present invention is not particularly limited. For example, a lens unit having the shape proposed by the present inventors in Japanese Patent Laid-Open No. 2-17 can be used. 6 (a) and 6 (b) illustrate lenses 20 having various lens shapes.

As the performance of the roughened surface used in the present invention, the haze value of the roughened portion is preferably about 30% or more, particularly preferably 50% or more.

The surface light source element of the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, the smoothed portion 8 is provided on the roughened reflecting surface 9 of the light emitting surface 6, but as shown in FIG. A portion 8 can be provided, and the area ratio of the smooth portion 8 can be increased as approaching the light incident surface 7 as shown by an arrow A in FIG.

Further, as shown in FIG. 8, a smooth portion can be provided on both the roughened surfaces of the light emitting surface 6 and the opposite surface 9, and as shown by an arrow A in FIG. It is also possible to adopt a configuration in which the area ratio of the smooth portion increases as approaching.

In the above embodiment, the light source 4 is provided only on one end side of the light guide 1. However, as shown in FIG.
May be arranged at both ends of the light guide 1.

Method for Adjusting Surface Light Source Element The surface light source element according to the present invention can be adjusted and manufactured by various methods.

For example, in the present invention, when providing a smooth portion on the roughened surface of the light guide or the surface having the lens unit, a method of providing a smooth portion on the roughened surface or the surface having the lens unit, A target light guide can be produced by using any method of providing a roughened portion or a lens unit on a smooth surface. For example, by a roughening treatment such as sand blasting or etching, a mold having a desired rough surface pattern or surface roughness or a mold having a specific lens unit and a smooth portion is prepared, and a resin is formed using these molds. By molding by injection or hot pressing, it is possible to obtain a light guide in which a predetermined smooth portion is provided on at least one of the roughened or unitary light emitting surface and the opposite surface. In particular, the injection molding method is excellent in terms of accuracy and molding speed, and is a preferred molding method.

The manufacture of the surface light source element can be performed by preparing members such as a light guide, a diffuser, and a reflective material and assembling them.

Detailed Example (Preparation of Light Guide Mold) Glass beads are sprayed on one side of a polished brass plate, and a plate having a uniformly roughened metal plate surface is prepared by a conventional homing method. (Mold-1) A gradation pattern is produced by CAD such that the distribution of the area ratio of the smooth portion is as shown in FIG. Mold-
A pattern is baked and developed on the surface of 1 by photolithography using a conventional photolithography method, and a portion to be left as a rough surface (the same portion as the rough portion 22 shown in FIG. 11 (a)) is protected by a film. Then, the remaining part is polished to an Emery # 800 fineness. Thereafter, the protective film is removed, and a mold having a predetermined smooth portion is manufactured (Mold-2).

Separately, the surface of the brass plate is buffed with Emery # 800 to produce a mirror-finished plate (die-3).

One surface is the same surface as the mold-2, and the other surface is the mold-3
A nesting mold for injection molding having the same surface as that described above is prepared (Mold-4).

(Production of light guide) A 150 mm × 250 mm acrylic resin plate having a thickness of 3 mm was molded into a mold-2.
It is sandwiched between the molds 3 and a replica is taken as usual by a hot press. Further, it is cut so as to have a size and a pattern position as shown in FIGS. 11 (a) and 11 (b), and the cut four sides are polished to a mirror surface by a conventional method (light guide).
1).

Reference numeral 22 in FIG. 11 (a) denotes a rough surface portion.
In FIG. 2B, the size of the light guide 1 is 225 m in height (B).
m, width (C) 132 mm, zone 0 width (D) 15 mm, effective width (E): width of zones 1 to 11) 205 mm, zone 12 width (F) 5
mm.

3mm thick acrylic resin plate 150mm by exactly the same process
× 250 mm is inserted between the mold-1 and the mold-3, a replica is taken by hot pressing, cut and polished to produce a light guide (light guide-2).

As a comparative example, a negative EP image in which ink is printed by screen printing on a portion corresponding to the rough surface of the mold 2 is prepared, and a printing plate for screen printing is prepared using the negative EP image. 3mm thick
Screen printing using a commercially available white ink (Seiko Advance VIC 120 White) on one side of an acrylic resin plate of 150 mm x 250 mm, then cut and polished in the same manner as Light Guide-1 and Light Guide-2 To produce a light guide for comparison (light guide-
3).

Using a 200-ton injection molding machine, a light guide was produced from acrylic resin pellets (Acrypet VH Mitsubishi Rayon Co., Ltd.) using a mold-4 at a cylinder temperature of 240 ° C. (light guide-4).

(Measurement of Haze Value of Light Guide-2) A 50 mm x 50 mm test piece was cut out from the rough surface portion of Light Guide-2, and the haze value was measured according to ASTM-D1003-61, and the haze value was determined by the following equation. Was.

Haze value = {(diffuse light transmittance) / (total light transmittance)} × 100
% As a result, the haze value of Light Guide-2 was 64.8.

(Assembly of surface light source element) Crystal white made of Sky Aluminum Co., Ltd. (one side white painted aluminum plate thickness 0.25mm) has ribs of 3mm and flat part of 132mm
Fold it up with the white side inside so that it becomes × 225 mm. However, one of the two short sides is a light-incident surface and has no rib. This is referred to as a light reflector. As a diffuser, a milky white polyethylene terephthalate film EK300W (0.075nn) manufactured by Somar Co., Ltd. is used after being cut into 132 mm x 225 mm. For the lamp case, a cylinder with an aperture with a white part of crystal white inside and an opening of 3 mm with an inner diameter of 6 mmφ is manufactured.

The light guide is placed so that the zero zone of FIG. 11 (b) comes to the short side of the light emitting body without the rib and the rough surface or the printed surface is close to the white surface, and the diffuser is further placed thereon. Is placed, and these three points are collectively inserted into the aperture of the lamp case. In this lamp case, KC130T4E74 manufactured by Matsushita Industrial Co., Ltd.
(4mmφ × 130mm) lamp is inserted to make a surface light source element. The lamp lighting inverter uses TDK Corporation's CXA-L10L and is lit by applying DC12V.

(Brightness measurement of surface light source element) The brightness meter uses BM-5 of Topcon Co., Ltd.
° Measure with a measurement circle of 10 to 15 mmφ. The measurement points are measured at the center of the zones 1 to 11 shown in FIG. All the surface light source elements are mounted vertically on a predetermined measuring table with the lamp facing upward and fixed, and after applying DC 12 V, the lamp is measured after a lamp aging time of 15 minutes or more. The measurement temperature was 23 ° C. ± 2 ° C.

(Luminance Measurement Results) The measurement results of the luminance are shown in Table 1 and FIG.

As is clear from Table 1 and FIG. 12, in the light guide 1 according to the present invention, emitted light having substantially uniform brightness is emitted from the entire light emitting surface, and light is emitted on the display surface with uniform brightness. Can be irradiated. In addition, since the light use efficiency is higher than that of the light guide-3, emitted light with high luminance was obtained even with the same light source.

Note that the surface light source element produced from the light guide-4 was also the light guide-1.
The same results as those of the surface light source element manufactured from the above were obtained.

(Measurement of directivity emission angle of light guide) A sample is placed on a measurement table so that lamp y is positioned on the left side, and the sample is rotated as shown in FIG. 13 to measure the luminance at a predetermined angle. I do.

The sample from which the diffuser was removed from the surface light source element using the light guide-1 was designated as 1-, and the sample on which the diffuser was mounted was designated as 1-.

The sample from which the diffuser was removed from the surface light source element using the light guide-3 was designated as 3-, and the sample on which the diffuser was mounted was designated as 3-.

The measurement point is fixed at the center of zone 6 in FIG. 11 in each case. The results are shown in FIGS. 14 (a) and (b).

INDUSTRIAL APPLICABILITY As described above, the surface light source element of the present invention provides a light-emitting surface of a transparent light guide and at least one of the opposite surface to light incident from a light incident surface of the transparent light guide. A roughened portion or a portion having a large number of lens units having a directional emission function of emitting light obliquely to the traveling direction of the light, and a smooth portion made of an optical plane are provided. By providing a control function to increase the luminance value of the light emitted from the light exit surface over the entire light exit surface by increasing the light exit surface as it approaches the light entrance surface, even if the transparent light guide is made thinner, The emitted light is emitted from the entire surface of the light emission surface with a substantially uniform luminance value. Further, since the transparent light guide has a high light use efficiency, emitted light with high luminance can be obtained without increasing the wattage of the light source.

Therefore, according to the present invention, it is possible to provide an ultra-thin surface light source element that has uniform brightness over the entire light emitting surface and can obtain high-luminance emitted light.

Claims (7)

(57) [Claims] A transparent light guide (1) having at least one side surface as a light incident side, one surface orthogonal to the side as a light emitting surface, and having a light reflecting layer on a surface opposite to the light emitting surface. And a diffuser (2) for diffusing light from the light exit surface of the transparent light guide.
Wherein at least one of the light exit surface and the opposite surface of the transparent light guide emits light incident from the light incident surface of the transparent light guide obliquely to the traveling direction of the light. It is composed of a roughened portion having a directional light emitting function and a smooth portion made of an optical plane, and the luminance value of light emitted from the light emitting surface by increasing the ratio of the smooth portion as approaching the light incident surface. A surface light source element characterized by having a control function of making the surface uniform over the entire light exit surface. 2. The surface light source device according to claim 1, wherein a transparent light guide obtained by injection molding is used as the transparent light guide. 3. The rough surface formed on the transparent light guide has a haze value of 30%.
2. The surface light source device according to claim 1, wherein: 4. The surface light source device according to claim 1, wherein the transparent light guide is made of an acrylic resin. 5. A transparent light guide (1) having at least one side surface as a light incident side, one surface orthogonal to the side as a light exit surface, and having a light reflection layer on a surface opposite to the light exit surface. And a diffuser (2) for diffusing light from the light exit surface of the transparent light guide.
Wherein at least one of the light exit surface and the opposite surface of the transparent light guide emits light incident from the light incident surface of the transparent light guide obliquely to the traveling direction of the light. A light having a plurality of lens units having a directional light emission function, and a smooth portion formed of an optical plane, the light emitted from the light emission surface by increasing the ratio of the smooth portion as approaching the light incident surface. A surface light source element having a control function of making the luminance value of the light emitting surface uniform over the entire light emitting surface. 6. The surface light source device according to claim 5, wherein a transparent light guide obtained by injection molding is used as the transparent light guide. 7. The surface light source device according to claim 5, wherein the transparent light guide is made of an acrylic resin.