JP2010245005A - Surface light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source, thin, and having a high luminance, with uniform luminance distribution, and having no contrast difference. <P>SOLUTION: The surface light source 1 is composed of a light guide plate 4 having a cut-out portion 5 on the surface side and at least one non-surface light source 2 which is arranged right below the cut-out portion 5 on the rear side of the light guide plate 4. The cut-out portion 5 consists of a slope 5c inclined toward the center 5b from an edge portion 5a and the tilt angle α of the slopes 5c in the cut-out portion is an angle which total-reflects light emitted from the non-surface light source 2 and total-reflects the light total-reflected by the slope 5c on the surface of the light guide plate 4, while a light extraction structure 6 is installed on all faces on the front surface side and/or rear face side of the light guide plate 4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surface light source used as a backlight of a liquid crystal display or the like, and in particular, can increase the luminance by using a large amount of a non-surface light source, and can be non-surface even if a light guide plate and a non-surface light source are arranged in proximity. The present invention relates to a surface light source that does not cause a difference in brightness between a portion where a light source is disposed and an intermediate portion thereof.

  In recent years, liquid crystal display devices have been used in various fields, and various performances are required depending on the respective applications. In particular, in cellular phones, OA devices, personal computers, word processors, and the like, there are strong demands for weight reduction, thickness reduction, size reduction, large screen size, high definition, and power saving.

  In order to meet these demands, surface light sources used as backlights arranged behind liquid crystal cells and the like are also required to have higher brightness, uniform brightness (no unevenness), and thinner thickness. . In such a surface light source, in general, a large number of point light sources and line light sources (collectively referred to as non-surface light sources) are used, and the direction of the light emitted from the non-surface light source is appropriately changed so that one surface Used as a light source. As the method, a so-called direct type in which non-surface light sources are arranged in parallel and the light is homogenized by a diffuser plate or the like, or a non-surface light source is arranged at least at one end of the light guide plate and light introduced into the light guide plate is appropriately emitted An edge light type that obtains a surface light source by the above method can be used.

However, in the case of the direct type, when the diffuser plate and the non-surface light source are arranged close to each other, the portion where the non-surface light source is arranged is too bright, while the portion between them is too dark, making it difficult to obtain uniform light with a sharp contrast. . This disadvantage can be suppressed to some extent if the diffuser plate and the non-surface light source are remotely arranged, but if the diffuser plate and non-surface light source are separated to such an extent that no difference in brightness is observed, the backlight becomes too thick as a whole, and the recent thin Cannot meet the demands of computerization.
On the other hand, in the case of the edge light type, it is easy to meet the demand for uniform and thin light, but the location of the non-surface light source is limited to the end of the light guide plate and the number of light sources cannot be increased. In order to meet the demand for higher brightness, there is no choice but to use a high-luminance non-surface light source even if it is expensive.

  Therefore, a so-called hybrid type is also disclosed as a surface light source capable of obtaining high brightness by using a number of non-surface light sources that are thin, have no contrast, and are inexpensive. As such, for example, a plurality of linear or rod-shaped light sources arranged in parallel, a plurality of light guide plates arranged along both longitudinal sides of the light sources, and any one surface of the light guide plate A light diffusing / reflecting means provided on the side, a light diffusing means provided on the surface of the light guide plate opposite to the surface facing the light diffusing / reflecting means, and a half provided between the light source and the light diffusing means. An illuminating device having a transmission / reflection means, and an illuminating device in which the inclination angle of the light guide plate surface is devised has been proposed (for example, Patent Document 1). In this type of hybrid surface light source, the light source and the light diffusing unit are arranged close to each other, and a transflective unit is provided between the light source and the light diffusing unit, and the amount of transmitted light is adjusted to eliminate the difference in light and darkness. I am trying.

  However, even if such a transflective means is used, a difference in brightness occurs between the portion where the means is disposed and the portion where the means is not disposed. Therefore, the brightness difference of the surface light source cannot be sufficiently eliminated. Further, the transmittance of light transmitted through the means is constant regardless of the location, whereas the intensity of light irradiated from the non-surface light source to the shielding means is strong at the center and weak at the end, and is not constant. Therefore, there is a problem that the light passing through the means is not uniform.

JP 2002-75036 A

  In view of such circumstances, the present invention provides a surface light source that eliminates the above-described problems of the prior art and uses a large number of non-surface light sources, has high brightness, has little contrast, and is thin. With the goal.

The present invention has been made in order to achieve the above object, and claim 1 of the present invention is arranged such that a light guide plate having a cut portion on the front surface side and a back surface side of the light guide plate immediately below the cut portion. A surface light source comprising at least one non-surface light source, wherein the cut portion is a slope inclined from the edge toward the center thereof;
The inclination angle of the slope in the notch is the angle at which the light emitted from the non-surface light source is totally reflected and the light totally reflected at the slope is totally reflected at the surface of the light guide plate,
The surface light source is characterized in that a light extraction structure is provided on the front side and / or the back side of the light guide plate.

  A second aspect of the present invention includes the surface light source according to the first aspect, wherein the light extraction structure is a concave portion and / or a convex portion provided on the surface side of the light guide plate.

  A third aspect of the present invention includes the surface light source according to the first or second aspect, wherein the light extraction structure is a diffuse reflection layer provided on the back side of the light guide plate.

  According to a fourth aspect of the present invention, the non-surface light source is a line light source, and the cut portion has a shape obtained by cutting the surface side of the light guide plate into a wedge shape. The content is a light source.

  According to a fifth aspect of the present invention, the non-surface light source is a point light source, and the cut portion has a shape obtained by cutting the surface side of the light guide plate into a conical shape. The content is a surface light source.

  According to a sixth aspect of the present invention, the rounded portion is provided near the center of the cut portion, and the light diffusion plate is provided on the surface side of the light guide plate. The content is a surface light source.

  According to the surface light source of the present invention, since the non-surface light source can be disposed in the vicinity of the light guide plate, a thin surface light source can be obtained. In addition, since the light emitted from the non-surface light source is totally reflected once by the slope of the cut portion, even if the light guide plate and the non-surface light source are arranged close to each other, it does not cause a difference in brightness. In addition, light is diffused in the width direction of the light guide plate while being repeatedly reflected and refracted between the front and back surfaces of the light guide plate, and light in the light guide plate can be taken out by providing an entire light extraction structure. The luminance can be made more uniform by adjusting the density distribution of the light extraction structure. As the light extraction structure, a concave or convex portion provided on the front surface side of the light guide plate or a diffuse reflection layer provided on the back surface side of the light guide plate can be used.

  As the non-surface light source, either a point light source or a line light source can be used, but when the line light source is used, the cut portion is a wedge shape, and when the point light source is used, the cut portion is a conical shape. The light emitted from the light tends to be more uniform.

  As a structure for extracting light from the cut portion, if a rounded portion is provided near the center of the cut portion, a part of the light emitted from the non-surface light source passes through the rounded portion directly from the surface side of the light guide plate. Since it is emitted, the light is not attenuated and a high-luminance surface light source is obtained. Further, the structure is simple and the manufacturing cost can be reduced.

FIG. 1 is a schematic explanatory view of a surface light source according to the present invention. FIG. 2 is a schematic explanatory diagram of another surface light source according to the present invention. FIG. 3 is a schematic explanatory view showing a surface light source in which the shape of the cut portion is a wedge shape. FIG. 4 is a schematic explanatory view showing a surface light source in which the shape of the cut portion is a conical shape. FIG. 5 is a schematic explanatory view showing an optical path in a light guide plate having a prism sheet attached to the front side. FIG. 6 is a schematic explanatory view showing an optical path of light emitted from a light guide plate having a prism sheet attached to the surface side. FIG. 7 is a schematic explanatory view of a cut portion provided with a rounded portion near the center. FIG. 8 is a schematic explanatory view showing a light diffusing plate provided in the cut portion of FIG. FIG. 9 is a graph showing the luminance distribution of the surface light source according to the first embodiment. FIG. 10 is a graph showing the luminance distribution of the surface light source according to the second embodiment. FIG. 11 is a graph showing the luminance distribution of the surface light source according to Comparative Example 1. FIG. 12 is a graph showing the luminance distribution of the surface light source according to Comparative Example 2. FIG. 13 is a graph showing the luminance distribution of the surface light source according to Comparative Example 3. FIG. 14 is a graph showing the luminance distribution of the surface light source according to Comparative Example 4.

  If the surface light source 1 in the present invention is described based on FIG. 1 and FIG. 2, the light guide plate 4 having the cut portion 5 on the front surface side and the back surface side of the light guide plate 4 are disposed directly below the cut portion 5. It comprises at least one non-surface light source 2, and the cut portion 5 comprises an inclined surface 5 c inclined from the edge 5 a toward its center 5 b, and the inclination angle α of the inclined surface 5 c in the cut portion is from the non-surface light source 2. The angle is such that the emitted light is totally reflected and the light totally reflected by the inclined surface 5c is totally reflected by the surface of the light guide plate 4. A light extraction structure 6 is provided on the front side and / or the back side of the light guide plate 4. It is provided over the entire surface. In FIG. 1, the concave portion 6 a and the convex portion 6 b provided on the front surface side of the light guide plate 4 are used as the light extraction structure 6, and the irregular reflection layer 6 c provided on the back surface side of the light guide plate 4 in FIG. Has been.

The non-surface light source 2 used in the surface light source 1 of the present invention is not particularly limited, and examples include a commercially available line light source 2a such as a fluorescent lamp, an incandescent light bulb, and a point light source 2b such as an LED, but with a low voltage and a low current. An LED is preferable because it can be driven, has high brightness, and is excellent in responsiveness.
Further, the non-surface light source 2 used in the present invention is preferably provided with condensing means 3 for condensing the light emitted from the non-surface light source 2 to a cut portion 5 described later. A concave mirror provided on the back surface side of the surface light source 2 or a condensing lens structure provided on the front surface side of the non-surface light source 2 can be provided.
In the present invention, if the light emitted from the non-surface light source 2 is directly emitted from the surface side of the light guide plate 4, it is not preferable because that portion is felt bright and causes a difference in brightness. . Therefore, a blocking means (not shown) for blocking excess light may be provided so that the light emitted from the non-surface light source 2 does not directly enter the surface side of the light guide plate 4.

  The light guide plate 4 used in the surface light source 1 of the present invention has a substantially flat plate shape as a whole, but is provided with a cut portion 5 at an appropriate position. The material is not particularly limited, and any resin that is used as a normal light guide plate, such as PMMA (acrylic), PC (polycarbonate), and COP (cycloolefin polymer) can be preferably used.

The notch portion 5 provided on the surface side of the light guide plate 4 is composed of a slope 5c that slopes down from the edge portion 5a toward the center 5b. That is, the notch portion 5 goes from the surface of the light guide plate 4 to the deep portion. It is a shape that seems to have been cut so as to become narrower.
Specific examples of the shape of the cut portion 5 include a conical shape and a wedge shape. However, the shape is not limited to this, and any shape may be used as long as it has a slope 5c that slopes down from the edge portion 5a toward the center 5b. Shape may be sufficient.
In order to make the light emitted from the surface light source 1 more uniform, when the linear light source 2a is adopted as the non-surface light source 2, the cut portion 5 is preferably a wedge shape, and when the point light source 2b is adopted. The notch 5 is preferably conical.
Further, the arrangement of the cut portions 5 is not particularly limited, but it is preferable to provide the cut portions 5 as uniformly as possible. For example, when the cut portions 5 are wedge-shaped, they are preferably provided parallel to each other at regular intervals as shown in FIG. In the case of a mold, it is preferably provided in a lattice shape or a triangular lattice shape as shown in FIG.

In the present invention, the inclination angle α of the inclined surface 5 c in the cut portion 5 totally reflects the light emitted from the non-surface light source 2 and totally reflects the light totally reflected by the inclined surface 5 c on the surface of the light guide plate 4. The light emitted from the non-surface light source 2 disposed immediately below the cut portion 5 is totally reflected by the inclined surface 5c, and further repeatedly reflected or refracted between the front and back surfaces of the light guide plate 4. The emitted light is diffused in the width direction. This light is incident on the light extraction structure 6 provided on the entire surface of the light guide plate 4, for example, the concave portion 6 a or the convex portion 6 b provided on the front surface side of the light guide plate 4 or the irregular reflection layer 6 c provided on the back surface side. The optical path is changed and emitted from the light guide plate 4. Here, the light extraction structure 6 includes a structure used to extract light from a light guide plate in a conventional edge light type backlight.
In the present invention, the state in which the non-surface light source 2 is arranged immediately below the notch 5 is, for example, as shown in FIG. 3 or FIG. A state in which all the light emitted from the non-surface light source 2 is directly incident on the inclined surface 5c.

  When the concave portion 6a or the convex portion 6b is provided on the surface side, the shape and form of the concave portion 6a and the convex portion 6b are particularly limited as long as the light in the light guide plate 4 can be emitted from the concave portion 6a and the convex portion 6b. Not. When the interval between the cut portions 5 is sufficiently narrow with respect to the thickness of the light guide plate 4, for example, when the interval between the cut portions 5 is 10 times or less the thickness of the light guide plate 4, the distribution of the concave portions 6a or the convex portions 6b becomes uniform. However, it is preferable to reduce the distribution at a location where the amount of light in the light guide plate 4 is large and to increase the distribution at a location where the amount of light is small, since the luminance of the surface light source 1 becomes uniform as a whole. In addition, the slope 5c in a notch part is also contained in the surface side of the light-guide plate 4 here.

  The method for forming the concave portion 6a or the convex portion 6b is not particularly limited, but a sheet (prism sheet, lenticular lens sheet, fly-eye lens sheet, diffusion sheet, etc.) provided with a minute convex portion 6b is provided on the surface of the light guide plate 4. The concave portion 6a can be formed by pasting or rubbing the surface with grinding paper or the like. Moreover, when creating the light guide plate 4, the surface side may be pressed with a female mold for forming the concave portion 6a or the convex portion 6b. In addition, when a prism sheet or a lens sheet is attached to the surface of the light guide plate in order to provide the convex portion 6b, it is preferable to dispose a diffusion sheet thereon. The prism sheet, lens sheet, diffusion sheet and the like that can be used as the convex portion 6b in the present invention may be commercially available, specifically GTL5000 (trade name, prism sheet manufactured by Goyo Paper Industries Co., Ltd.), BS- 702 (trade name, diffusion sheet manufactured by Ewa Co., Ltd.) and the like.

In the present invention, the irregular reflection layer 6c can be provided on the back surface side of the light guide plate 4 in place of or together with the concave portion 6a or the convex portion 6b. The irregular reflection layer 6c is not particularly limited as long as the reflected light irradiated to the back surface is diffusely reflected as diffused light.For example, a method of depositing a metal thin film on the back surface that roughens the entire back surface, Examples include a method of applying a white pigment-containing acrylic resin such as Reicure-SL (trade name, manufactured by Jujo Chemical Co., Ltd.), and a method of attaching a diffuse reflection sheet such as Lumirror EL-60L (trade name, manufactured by Toray Industries, Inc.). .
Further, the irregular reflection layer 6c may be provided over substantially the entire back surface side, but the irregular reflection layer 6c is not provided or partially provided in a portion irradiated with stronger light, and is totally reflected on the front surface side. A part or all of the light may be further totally reflected and returned to the surface side. In this way, since the amount of light emitted from the surface side can be adjusted, the luminance of the surface light source 1 can be made uniform overall.
In addition, if the irregular reflection layer 6c is provided in the area between the non-surface light source 2 and the cut portion 5, the light irradiated from the non-surface light source 2 to the cut portion 5 is blocked. Can not be provided, but can also be provided if it is partial.

  However, when a lens sheet that does not have a surface parallel to the light guide plate on the surface side, such as the prism sheet 6d, is attached to the surface of the light guide plate 4, the light totally reflected by the inclined surface with the inclination angle α is the surface of the light guide plate. However, the total reflection does not always occur on the surface of the lens sheet. However, for example, as shown by the solid line arrow in FIG. 5, the emitted light is reincident on the adjacent lens structure, and the emitted light is returned to the back side of the light guide plate due to refraction at this time, which is further reflected on the back side. Any configuration in which light from the light source can be diffused in the width direction while reciprocating between the front surface side and the back surface side of the light guide plate 4 such as being reflected and returned to the front surface side is included in the scope of the present invention. In such a case, for example, as shown in FIG. 6, the light reflected by the interface on the surface of the prism sheet 6 d or the like (shown by a broken arrow) is emitted from the back side of the light guide plate 4, and further, the light guide plate 4. Is irregularly reflected by the irregular reflection layer 6 c disposed below, and this is emitted from the surface side of the light guide plate 4.

  In the present invention, since the light emitted from the non-surface light source 2 is totally reflected by the inclined surface 5c of the cut portion 5, if the light extraction structure 6 is not provided in the cut portion 5, only this portion becomes dark. The light extraction structure 6 may be the concave portion 6a, the convex portion 6b, or the irregular reflection layer 6c. However, if the concave portion 6a and the convex portion 6b are provided in a recessed portion such as the cut portion 5, it is difficult to adjust the distribution density. is there. Further, as described above, when the irregular reflection layer 6c is provided between the non-surface light source 2 and the cut portion 5, the light radiated from the non-surface light source 2 is blocked, so that the irregular reflection layer 6c cannot be provided in the entire region. . Although it is possible to partially provide the irregular reflection layer 6c in the region, it is not preferable because the surface light source 1 becomes darker by that amount.

In the present invention, as a structure for suitably extracting light from the cut portion 5, for example, as shown in FIG. 7, a round processing portion 6 e can be provided near the center of the cut portion 5. In this case, the light emitted from the non-surface light source 2 passes through the round processing portion 6e and is emitted to the front surface side of the light guide plate 4. Since the round processing portion 6e acts like a concave lens, It spreads over the entire cut portion 5.
However, since the light that has passed through the R processing section 6e has an emission angle different from that emitted from other portions, it cannot be used as it is as a backlight of a liquid crystal display device. For this reason, for example, as shown in FIG. 8, it is necessary to make the whole uniform by disposing the light diffusion plate 7 on the surface side of the light guide plate 4.
In addition, when providing the round process part 6e, since the quantity of the light radiate | emitted from the notch part 5 is substantially proportional to the area of the part in which the round process part 6e was provided, the magnitude | size of the round process part 6e is the surface light source 1 whole. May be provided so that the brightness is uniform.

  The surface light source 1 as described above is used in the same manner as a surface light source that has been conventionally used, that is, by disposing a diffusion sheet, a lens sheet, a liquid crystal element, etc. on the surface side, and so on. Can be suitably used.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited only to these Examples.

Example 1
An acrylic plate having a width of 210 mm, a length of 300 mm, and a thickness of 6 mm as a light guide plate, provided with wedge-shaped cut portions having a depth of 5 mm and an apex angle of 45 degrees at intervals of 40 mm, parallel to the length direction of the acrylic plate Was used.
As a convex portion for extracting light, a commercially available prism sheet (manufactured by Goyo Paper Industries Co., Ltd., trade name: GTL5000) is a 20 μm thick non-support paste (manufactured by Sekisui Chemical Co., Ltd., trade name: double tack tape # 5511). ) Was attached to the surface of the light guide plate (excluding the slope of the cut portion). The slopes of the cuts were scratched by rubbing lightly with No. 1200 grinding paper, and this was used as a recess for taking out light.
As the light source, six 2 mmφ cold cathode fluorescent lamps were used, placed at a position 2 mm directly below the notch of the light guide plate, and a commercially available reflector (trade name: Lumirror EL-, manufactured by Toray Industries, Inc.) at a position 5 mm below the light guide plate. 60L) to provide a surface light source.

Example 2
Five notches 5 in the light guide plate are provided at an interval of 36 mm, and five LED arrays (12V, 12 mA of 100 mA arranged in a straight line) are used as the light source. A surface light source was prepared in the same manner as in Example 1 except that the thickness was 4 mm immediately below the notch.

Comparative Examples 1 and 2
A surface light source was prepared in the same manner as in Examples 1 and 2 except that a recess for taking out light was not provided on the slope of the cut portion of the light guide plate.

Comparative Examples 3 and 4
A surface light source was prepared in the same manner as in Examples 1 and 2 except that an acrylic plate having a thickness of 5 mm was used instead of the light guide plate.

  The luminance distribution was measured for the above examples and comparative examples. The luminance distribution was digitized by photographing the surface light sources of the example and the comparative example with a CCD camera and analyzing the image, and represented in a graph. The results are shown in FIGS.

  As described above, the surface light source according to the present invention is provided with a cut portion on the surface of the light guide plate, totally reflects light from the light source on the slope, and transmits the light between the front surface side and the back surface side of the light guide plate. Light is emitted in a width direction while reciprocating by reflection and refraction, and light is emitted uniformly by a separately provided light extraction structure, so even if a non-surface light source and a light guide plate are arranged close to each other, it does not cause a difference in brightness Therefore, it is useful as a surface light source that is thin, has high brightness, and has almost no difference in brightness.

DESCRIPTION OF SYMBOLS 1 Surface light source 2 Non-surface light source 2a Line light source 2b Point light source 3 Condensing means 4 Light guide plate 5 Notch part 5a Edge part 5b Center 5c Slope 6 Light extraction structure 6a Concave part 6b Convex part 6c Diffuse reflection layer 6d Prism sheet 6e Earl process part 7 Light diffusion plate α Tilt angle

Claims (6)

A surface light source comprising a light guide plate having a cut portion on the front surface side, and at least one non-surface light source disposed immediately below the cut portion on the back surface side of the light guide plate,
The notch is a slope that slopes down from the edge toward its center,
The inclination angle of the slope in the notch is the angle at which the light emitted from the non-surface light source is totally reflected and the light totally reflected at the slope is totally reflected at the surface of the light guide plate,
A surface light source, wherein a light extraction structure is provided on a front surface side and / or a back surface side of a light guide plate.   The surface light source according to claim 1, wherein the light extraction structure is a concave portion and / or a convex portion provided on the surface side of the light guide plate.   The surface light source according to claim 1, wherein the light extraction structure is a diffuse reflection layer provided on a back surface side of the light guide plate.   4. The surface light source according to claim 1, wherein the non-surface light source is a line light source, and the cut portion has a shape obtained by cutting the surface side of the light guide plate into a wedge shape.   4. The surface light source according to claim 1, wherein the non-surface light source is a point light source, and the cut portion has a shape obtained by cutting the surface side of the light guide plate into a conical shape.   6. The surface light source according to claim 1, wherein a rounded portion is provided near the center of the cut portion, and a light diffusing plate is provided on the surface side of the light guide plate.

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