JP2001110220A - Planar lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar lighting device capable of preventing the lowering of a brightness at the end of a light conductor opposed to an electrode portion at the end of a light source if the light conductor consists of two light conducting portions different in light scattering performance. SOLUTION: A light conductor 2 has a brightness control portion 24 on a second light conducting portion 22 with high light scattering performance, arranged at a light conductor side portion 7 opposed to an electrode portion 4a at the end of a light source 4 and having a plate thickness increased as closer to a light conductor end face 2a and a light conductor side face 2b. Therefore, the plate thickness of the second light conducting portion 22 at the light conductor side portion 7 is increased for compensating the shortage of the quantity of light at the electrode portion 4a of the light source 4 so that scattering lines themselves inside the second light conducting portion 22 at the light conductor side portion 7 are increased to increase the quantity of light, whereby the brightness is improved without changing an emission angle at the light conductor side portion 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface illumination that scatters light incident on a light guide from a light source and emits illumination light from an output surface of the light guide, such as a backlight of an object such as a liquid crystal. The present invention relates to an apparatus, and more particularly, to prevention of a decrease in luminance at a light guide side portion facing an electrode portion at an end of a light source.

2. Description of the Related Art Conventionally, as a surface illumination device such as a backlight for a liquid crystal display, for example, as shown in FIG. 6 (a), a wedge-shaped light guide 30 and a cold cathode tube disposed on an end face 30a thereof are used. And a light guide 30 from the light source 4.
There is known a device that scatters light incident on a light guide and emits illumination light from an emission surface of the light guide 30. Although the amount of light in the light guide 30 decreases as the distance from the light source 4 increases, the wedge-shaped light guide 30 has a smaller angle from the light source by forming an angle on the exit surface or the reflection surface facing the exit surface. In accordance with the increase, the amount of light emitted forcibly is increased to compensate for the decrease in the amount of light, so that uniformity of luminance can be obtained.

However, the electrode portions 4a at both ends of the light source (cold cathode tube) 4 hardly emit light. For this reason, since the brightness of the light source 4 is insufficient with respect to both sides of the light guide 30 facing the electrode portion 4a, the brightness of the emission surface on the side is reduced, and the brightness of the emitted light becomes uneven. Therefore, in order to prevent the luminance unevenness from occurring, it is necessary to make the light source 4 protrude from the side surface 30b of the light guide 30. Since the protruding portion becomes a frame portion of the display screen, it is difficult to reduce the frame width of the display screen, and the device cannot be downsized.

[0004] As a device for reducing the uneven brightness,
(1) A light diffusion region is formed on a side surface and an incident surface (end surface) of a wedge-shaped plate-like member (light guide), and illumination light is diffusely reflected by the light diffusion region, so that the brightness of the side portion is reduced. A correction device is known (JP-A-9-258030).
issue). Also, (2) the back surface of the wedge-shaped plate member (light guide) is formed by a substantially flat surface and a curved surface, and the curved surface narrows the width of the incident surface (end surface) of the plate member as the distance from the light source increases. In addition, there is known a device that reduces the luminance unevenness at the side (Japanese Patent Laid-Open No. 10-308113).

[0005]

However, in the device (1) for forming a light diffusion region on the side surface and the end face of the wedge-shaped plate-like member, since the mat processing for forming fine unevenness on the end face is performed, the amount of incident light is increased. Decrease. In addition, although a countermeasure against luminance unevenness in which the amount of emitted light is corrected by attaching a diffusion sheet to a side portion is performed, the work of attaching a small diffusion sheet is complicated, and
An error in the attachment position is likely to occur.

On the other hand, in the device (2) for narrowing the width of the end face of the wedge-shaped plate member, the light output angle is greatly changed by the reflection surface on the side of the end face side to increase the amount of light emitted. Therefore, unlike the inclination of the long section of the wedge-shaped part other than the side part, the angle of incidence is greatly changed by being reflected at an angle opposite to the inclination angle and at the short part of the side part, so that this side part and other parts are different. Due to the difference in the emission angle of the wedge-shaped portion, the brightness varies depending on the viewing direction, and the uneven brightness may not be sufficiently reduced.

[0007] Further, instead of the light guide having a single wedge-shaped light guide as described above, a light guide formed by stacking two wedge-shaped light guides having different light scattering performances in a plate thickness direction. And Figure 6
As shown in (b), a light guide 50 having a prism-shaped mountain shape formed by combining two light guides 53 each having two wedge-shaped light guide portions 51 and 52, and an end face 50a thereof. There is also known a surface illuminating device or the like including a pair of light sources 4 and 4 arranged opposite to each other. In these cases, as above,
There is a problem of a decrease in the brightness of the side portion 57 of the light guide 50 facing the electrode portion 4a at the end of the light source 4, but no effective means has been found yet.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and in the case where the light guide comprises two light guides having different light scattering performances, the light guide side portion facing the electrode portion at the end of the light source. It is an object of the present invention to provide a surface lighting device capable of preventing a decrease in luminance of a surface.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found that a flat-plate-like light guide and a rod-like light source disposed opposite to an end face thereof are provided. A surface illumination device that scatters light incident on the light guide from the light source and emits illumination light from the emission surface of the light guide, wherein the light guide includes a first light guide and a first light guide. 2nd with high light scattering performance
The first light guide is formed such that the thickness thereof decreases as the distance from the light guide end surface increases, and the second light guide is formed by overlapping the light guide with the light guide. The main body portion is formed such that the plate thickness increases as the distance from the end surface of the light source increases, and the main body portion is disposed on the light guide side portion facing the electrode portion at the end portion of the light source, and faces the light guide end surface and the light guide side surface. It has been found that a device having a brightness adjusting portion with an increased plate thickness is useful, and the present invention has been completed.

According to the present invention, the light guide is disposed on the second light guide having high light scattering performance, on the side of the end of the light source opposite to the electrode portion, and the end face of the light guide and the light guide are provided. It has a brightness adjustment section whose thickness increases toward the side. Therefore,
The thickness of the second light guide portion on the side of the light guide is increased so as to compensate for the insufficient light amount in the electrode portion of the light source, and the scattered radiation itself inside the second light guide on the side of the light guide is increased. As a result, the amount of light is increased, so that the brightness can be improved without changing the emission angle at the side of the light guide.
Thus, unlike the conventional case (2), the emission angle is not changed at the side of the light guide, so that the emission direction is not shifted, so that uniformity of luminance is high and high luminance is obtained. Also,
As in the conventional method (1), a high luminance can be obtained without a decrease in the amount of incident light at the end of the light guide, and there is no need to attach a diffusion sheet. it can.

Further, as compared with a wedge-shaped light guide composed of a single light guide, a light guide combined with light guides having different light scattering performances as in the present invention provides a second light guide having a high light scattering performance. Can be increased. For example, in the case of a single wedge, light having an angle smaller than the critical angle appears and exits even on the light source side due to the reflection surface having a wedge-shaped slope. For this reason, if the light scattering performance is increased, the light source side becomes too bright and uniformity cannot be maintained, so that the scattering particle concentration is as low as 0.01 to 0.1 wt%. On the other hand, in the present invention, the scattering particle concentration of the second light guide can be as high as 0.2 to 0.5 wt%. This is because the light emitted from the inclined surface disappears as described above because the reflecting surface is not wedge-shaped, and the uniformity cannot be maintained unless the light scattering performance is increased. Is higher, the brightness adjusting section can increase the plate thickness to obtain high light scattering performance and prevent a reduction in brightness. That is, it is preferable to increase the scattering particle concentration as much as possible, reduce the thickness of the main body portion, and increase the thickness of the brightness adjustment section. Thereby, higher luminance can be obtained.

In the light guide according to the present invention, the first resin and the second resin having different scattering particle concentrations are sequentially injected into the first and second molds and laminated, and the first light guide portion and the It is preferable to form the second light guide section having high light scattering performance in a so-called two-color injection molding method in which the second light guide section is formed in a flat plate shape.

By the two-color injection molding, the brightness adjusting section 24 can be easily formed using the first and second molds. In addition, by using the same composition for the first resin and the second resin, it is easy to adhere at the interface during lamination. Further, if the materials have the same composition, the refractive index becomes the same, which is the same as the absence of the interface. Therefore, the reflection does not occur at the interface, and the brightness does not become uneven due to the reflection at the interface.

Preferably, the brightness adjusting section is provided continuously with the main body, is interposed between the first light guide and the main body of the second light guide, and is provided on an end face of the light guide. And on the side surface of the light guide, a triangular pyramid having a triangular side surface having the intersection line of both surfaces as a common side and a triangular bottom surface on the main body portion. Therefore, the brightness of the side of the light guide can be sufficiently improved by the small brightness adjustment unit.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a surface lighting device according to an embodiment of the present invention. The present device comprises a flat plate-shaped light guide 2,
And a pair of parallel light sources 4 disposed along the longitudinal direction so as to face the two end surfaces 2a, and scatter light incident on the light guide 2 from the light source 4 to form a light guide 4. The illumination light is emitted from the emission surface 5 of the light source. As the light source 4, for example, a cold cathode tube is used.

The light guide 2 is formed by stacking a first light guide 21 and a second light guide 22 having a higher light scattering performance in the thickness direction of the first light guide 21. It has a flat prismatic chevron shape. The first light guide section 21 is formed as a non-scattering area such that the plate thickness decreases as the distance from the light guide end face 2a increases. In this example, the two first light guide portions 21 and 21 are formed continuously and symmetrically. Therefore, the plate thickness decreases as the distance from the two end surfaces 2a increases, and the plate thickness becomes the smallest at the center thereof. It has an inverted chevron recess.

The second light guide portion 22 has a main body portion 23 formed so that the plate thickness increases as the distance from the end face 2a increases.
And a brightness adjuster 24 arranged on the light guide side 7 facing the electrode portion 4a at the end of the light source 4 and increasing in thickness toward the light guide end face 2a and the light guide side face 2b. ing. The main body portion 23 has, for example, a mountain-shaped convex portion in which the plate thickness increases as the distance from the two end surfaces 2a increases, and the plate thickness becomes the largest at the center. The light guide 2 is formed by overlapping the first light guide 21 and the second light guide 22 in the thickness direction.
Has a flat prism-shaped mountain-shaped second light guide section 22, and high luminance can be obtained by entering light from each end face 2 a.

FIG. 2 shows an example of the light guide side portion 7 facing the electrode portion 4a at the end of the light source 4. As shown in FIG. FIG. 2 (a), (b)
As shown in the figure, the brightness adjustment unit 24 is
Are interposed between the first light guide portion 21 and the main body portion 23 and intersect at the light guide end surface 2a and the light guide side surface 2b. Are formed in a triangular pyramid shape having a triangular side surface having a common side and a triangular bottom surface on the main body portion 23.

The brightness adjustment section 24 formed in the second light guide section 22 having high light scattering performance allows the electrode portion 4a of the light source 4 to be formed.
To compensate for the shortage of light amount with respect to the light guide side 7 due to
Since the thickness of the second light guide portion 22 in the light guide side portion 7 is increased and the amount of scattered radiation itself in the second light guide portion 22 in the light guide side portion 7 is increased, the amount of light is increased. The brightness can be improved at the body side portion 7 without changing the emission angle. With this configuration, the emission angle is not changed at the side of the wedge-shaped light guide unlike the related art (2), so that the emission direction is not shifted, so that the uniformity of the brightness is high and the high brightness is obtained. Further, unlike the conventional case (1), the incident light quantity does not decrease at the end of the wedge-shaped light guide, high luminance can be obtained, and there is no need to attach the diffusion sheet on the side, so that the light can be easily guided. It is possible to prevent a decrease in the brightness of the body side.

In this embodiment, the brightness adjusting unit 24
Is formed in a triangular pyramid shape, as shown in FIG. 2A, light is emitted from the light source 4 other than the electrode portion 4a.
Is obliquely incident on the light guide side 7, the amount of the oblique incident light is obtained as the distance from the light guide end face 2 a increases, so that a decrease in luminance is reduced, and a square (two-dot chain line) is formed on the main body portion 23. Rather, it is enough to form a triangular bottom surface.

The light guide 2 is formed by sequentially injecting and laminating a first resin and a second resin having different scattering particle concentrations into a first mold and a second mold, respectively.
1 and the second light guide portion 22 having higher light scattering performance are formed into a flat plate shape (two-color injection molding method). This 2
By the color injection molding method, the brightness adjusting section 24 can be easily formed using the first and second molds.

In this case, the first light guide section 21 is formed first in the first mold, and then the second light guide section 22 is formed in the second mold and laminated, so that there is a time lag between them. As shown in FIG. 5A, the light guide 2 injection-molded is
For example, a warp phenomenon in which the first light guide section 21 side is convex may occur.

For this reason, as shown in FIG. 5 (a), after injection molding, the light guide 2 is placed on a flat heat insulating plate 40 with the first light guide 21 facing upward, and (b) As described above, only the upper side is heated by the infrared heater 41. If left in this state, the light guide 2 becomes flat. At this point, the light guide 2 is detached from the infrared heater 41 and gradually cooled as shown in FIG. Thereby, the warpage of the light guide 2 is eliminated.

In this embodiment, the second light guide section 22
Is formed in the shape of a triangular pyramid on the main body part 23, but as shown in FIG. 3, the luminance adjustment part 34 is formed on the end face 2a on the main body part 23 of the second light guide 22. Side 2b
It has a triangle on the top and a quadrilateral on the other side.
It may be formed in a tetrahedral shape in which the plate thickness increases toward the side a and the side surface 2b.

In this embodiment, the light guide 2 is the second light guide.
Although the light guide section 22 has a prism-shaped mountain shape, the light guide portion 22 may have a polygonal pyramid shape such as a triangular pyramid or a quadrangular pyramid.
Further, instead of the chevron shape, two wedge-shaped light guide portions having different light scattering performances may be simply formed by overlapping in the plate thickness direction.

[0026]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. The first resin and the second resin having different light scattering performances were sequentially injected into the mold, respectively, and laminated to produce a flat plate-shaped light guide. As the first resin, Acrypet Grade VH (manufactured by Mitsubishi Rayon Co., Ltd.) was used. The second resin is Delpet grade 70FR (manufactured by Asahi Kasei Corporation) and Tospearl grade 145.
(Toshiba Silicone Co., Ltd., silicone particles having a diameter of 4.5 μm) were mixed at 0.3 wt%, and a pelletized material was used. As shown in FIG. 1, the light guide 2 has a prism-shaped chevron-shaped second light guide 22 and a triangular pyramid-shaped luminance adjuster 24. A pair of parallel light sources 4 was arranged along the longitudinal direction of the end face of the light guide 2. (For example, the light guide 2 is 15 inches in size, and the electrode portion 4a of the light source 4 is 8 mm.)
In the case of, as shown in FIG.
4 is formed on the main body portion 23 by two triangles formed on the end face 2a and the side face 2b with a height of 2 mm (the height of the corner where the end face 2a and the side face 2b intersect) and a length of 15 mm. It was formed in a triangular pyramid shape.

Using the above light guide 2, the relative luminance ratio was measured for each light guide distance. FIG. 4 shows the results. The horizontal axis indicates the light guide distance, that is, the distance (mm) from the end face 2a, and the vertical axis indicates the relative luminance ratio. Line 61 shows the case where the luminance adjustment unit according to the present invention is provided, and the relative luminance ratio of the side of the light guide is 64.0.
%. A line 62 indicates a case without a luminance adjustment unit as shown in FIG. 6B, and the relative luminance ratio of the light guide side is 51.1.
%. Therefore, by providing the brightness adjusting section according to the present invention, it is possible to prevent the brightness of the side of the light guide from lowering due to the electrode portion.
(Mm), and the size of the device could be reduced.

[0028]

As described above, according to the present invention, the light guide is disposed on the side of the second light guide having high light scattering performance, on the side opposite to the electrode at the end of the light source. It has a brightness adjusting section whose plate thickness increases toward the end surface of the light body and the side surface of the light guide. Accordingly, the plate thickness of the second light guide section on the light guide side is increased so as to compensate for the insufficient light quantity at the electrode portion of the light source, and the scattered radiation itself inside the second light guide section on the light guide side is reduced. Increasing the number increases the amount of light, so that the luminance can be improved without changing the emission angle at the side of the light guide.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a surface lighting device according to an embodiment of the present invention.

FIG. 2A is a perspective view showing a side portion of a light guide according to the present invention, and FIG. 2B is a side view thereof.

FIG. 3 is a perspective view showing a surface lighting device according to another embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a relative luminance ratio for each light guide distance of a light guide.

FIG. 5 is a side view showing a method for eliminating the warpage of the light guide in two-color injection molding.

FIG. 6A is a perspective view showing a conventional wedge-shaped surface lighting device, and FIG. 6B is a perspective view showing a conventional flat surface lighting device.

[Explanation of symbols]

2 light guide, 2a light guide end face, 2b light guide side face, 4
... Light source, 4a ... Light source electrode part, 5 ... Emission surface, 7 ... Light guide side, 21 ... First light guide, 22 ... Second light guide, 23 ...
Body part, 24... Brightness adjustment unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaya Morino 1-4-5 Kamimaezu, Naka-ku, Nagoya City, Aichi Prefecture Inside Hayashi Telemp Co., Ltd. (72) Inventor Hiroshi Nakayama 1-4-4 Kamimaezu, Naka-ku, Nagoya City, Aichi Prefecture No.5 Hayashi Telemp Co., Ltd. F term (reference) 2H038 AA52 AA55 BA06 2H091 FA23Z FA41Z FB02 LA16 LA18

Claims (2)

[Claims] 1. A light guide having a flat plate-like shape and a rod-like light source disposed opposite to an end face thereof to scatter light incident on the light guide from the light source and emit the light from the light guide. A surface illumination device that emits illumination light from the light guide, wherein the light guide is formed by stacking a first light guide and a second light guide having higher light scattering performance in a plate thickness direction; The first light guide section is formed such that the plate thickness decreases as the distance from the light guide end face increases, and the second light guide section increases in thickness as the distance from the light guide end face increases. A surface having a main body portion and a brightness adjustment portion arranged on a light guide side portion facing an electrode portion at an end portion of the light source and having a thickness increasing toward a light guide end surface and a light guide side surface. Lighting equipment. 2. The light guide according to claim 1, wherein the brightness adjustment section is provided continuously to the main body, and is interposed between the first light guide and the second light guide. A surface lighting device having a triangular pyramid shape having a triangular side surface on the end surface of the light body and on the side surface of the light guide, the intersection line of both surfaces being a common side, and having a triangular bottom surface on the main body portion.