JP2853968B2 - Surface light source device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device employed as a backlight source for a liquid crystal display, which is a display unit of a television receiver mounted on a vehicle or a portable computer.

[0002]

2. Description of the Related Art FIGS. 5 and 6 show an example of the structure of a conventional surface light source device of this type. First, a surface light source device 90 shown in FIG. 5 is formed of a transparent resin member such as an acrylic resin. Light introducing surface 9 which is one side of the flat light guide plate 91
A reflector 92 having a substantially U-shaped cross section and an inner surface formed with a reflective film 92a having a mirror surface is attached to 1a.

In the reflector 92, a fluorescent tube 93 such as a cold-cathode fluorescent lamp is disposed so as to face the light introduction surface in the axial direction. A sheet 94 is arranged to reflect light from the fluorescent tube 93 on the back side, and a diffusion sheet 95 is arranged on the front side, which is a light emitting surface, to transmit and diffuse the light from the fluorescent tube 93. The liquid crystal display 20 is illuminated from behind.

A surface light source device 80 shown in FIG. 6 employs a tapered light guide plate 81 in place of the above-mentioned flat light guide plate 91. The tapered light guide plate 81 has a light introducing surface on the rear side. The inclination is provided so that the plate thickness becomes thinner as the distance from 81a increases, thereby increasing the amount of reflected light reaching the front surface side and improving the illumination efficiency for the liquid crystal display 20. Except for the tapered light guide plate 81, the configuration is completely the same as the surface light source device 90 described above.

Accordingly, the surface light source device 80 is
On the other hand, brighter illumination can be performed on the liquid crystal display 20 with the same power consumption of the fluorescent tube 93, and the tapered light guide plate 81 reduces the weight and is suitable for portable equipment. At present, the surface light source device 80 is generally adopted as a backlight light source of the liquid crystal display 20.

[0006]

However, in the surface light source device 80 employing the above-described tapered light guide plate 81, the liquid crystal display device is certainly compared with the surface light source device 90 employing the flat light guide plate 91. However, when viewed from an oblique direction indicated by an arrow Z in FIG. 6, a stripe pattern that repeats light and dark appears on the surface of the diffusion sheet 95. There is a problem that the display quality is degraded by affecting the lighting effect of the display device 20, and solving this problem is an issue to be solved.

[0007]

According to the present invention, as a specific means for solving the above-mentioned conventional problems, a tapered light guide plate and a light introducing surface which is a predetermined side of the tapered light guide plate are provided. In a surface light source device comprising: a reflector having a reflection film formed on an inner surface thereof having a substantially U-shaped cross section, and a fluorescent tube disposed in the reflector so as to face the light introduction surface in the axial direction, When the parallel line from the light introduction surface of the light guide plate to the light introduction surface is moved to a position that intersects the central axis of the fluorescent tube, the reflection film in the range from the intersection with the reflector has at least one diffusion surface. The present invention solves the problem by providing a surface light source device characterized by the following.

[0008]

Next, the present invention will be described in detail based on an embodiment shown in the drawings. 1 is a surface light source device according to the present invention. The surface light source device 1 is attached to a tapered light guide plate 2 and a light introduction surface 2a which is one side of the tapered light guide plate 2. A reflector 3 having a substantially U-shaped cross section and a reflection film 4 formed on the inner surface side, a fluorescent tube 5 disposed in the reflector 3, and the tapered light guide plate 2
Of the related art (see FIG. 6), which comprises a reflection sheet 6 disposed on the back side of the liquid crystal panel and a diffusion sheet 7 disposed on the front side thereof, and illuminates the liquid crystal display 20 from the back side.
It is similar to that of

Here, in the present invention, a predetermined area of the reflection film 4 provided on the reflector 3 is defined as a diffusion surface 4a. At this time, the reflection film 4 is moved from the light introduction surface 2a to the light introduction surface 4a. The parallel line H to the center axis X of the fluorescent tube 5 is
Is provided over a range up to an intersection P with the reflector 3 when it is moved to a position where it intersects with the reflector 3.
At this time, the above-mentioned parallel line H intersects the reflector 3 at two places, but in the present invention, at least one side is the diffusion surface 4a.

FIG. 2 shows the result of a study conducted by the inventor to achieve the present invention. When the tapered light guide plate 2 is employed, the light emitting surface 2b is formed.
The resulting stripes of light and dark on the side is re-light from the fluorescent tubes 5
The light is reflected by the mirror-like reflective film 4 on the linear portion 3a of the reflector 3, and the reflected light enters the tapered light guide plate 2 from the light introduction surface 2a and is disposed on the back surface 2c side.
At the surface 2b side, the linear portion 3a
It has been found that the location (i.e., the angle) at which the light is internally reflected at the surface 2b side and the location at which the light exits from the surface 2b occur almost alternately.

Here, the linear portion 3a has a range from the light introducing surface 2a to the intersection P (see FIG. 1).
Therefore, by forming the reflective film 4 in this range as the diffusion surface 4a so as not to have a remarkable directionality with respect to the reflected light, it is possible to prevent the occurrence of the above-mentioned bright and dark stripes.

In this case, if both the linear portions 3a of the reflector 3 are made to be the diffusion surfaces 4a, it is possible to surely prevent the occurrence of bright and dark stripes, but on the other hand, the liquid crystal display 20 If there is no problem in practical use, only one side (in this embodiment, the surface 2b side of the tapered light guide plate 2) is connected to the diffusing surface 4.
a.

In the actual implementation, there are various fluctuation factors in the conditions such as the use of a fluorescent tube 5 having an outer diameter of 10 mm to 3 mm. Strictly speaking, only the linear portion 3a is diffused. There is a case where the light and dark stripes cannot be eliminated by using the surface 4a, or a case where the light and dark stripes can be eliminated without using the entire linear portion 3a as the diffusion surface 4a. Fine adjustment of the range of the diffusion surface 4a may be performed according to the above.

Next, a specific configuration for forming the diffusion surface 4a will be described. For example, when the reflector 3 is formed of a metal plate, the linear portion 3a
If a portion corresponding to the above is previously formed into a so-called satin surface having fine irregularities by sandblasting or the like, and then the reflection film 4 is formed by an appropriate means such as vacuum evaporation or electroplating of aluminum, a portion of the satin surface is thereby obtained. Is the diffusion surface 4
a.

When the reflector 3 is formed by molding a resin, a portion corresponding to the linear portion 3a is made matte with a mold at the time of molding, and thereafter processing such as vacuum deposition is performed in the same manner as described above. It is good. The reflector 3 has a portion overlapping the tapered light guide plate 2 in the straight portion 3a for locking, and the diffusion surface 4a
Can be extended to this part,
It has no special effect on the effect.

In this case, the amount of light transmitted through the diffusion sheet 7 in the above-described configuration, that is, the amount of light illuminating the liquid crystal display 20 is 1930 cd / m ^{2 according} to the results of trial production by the inventor. This is almost the same as 1950 cd / m ² of the conventional example, and therefore, the present invention can eliminate bright and dark stripes without substantially reducing the light amount.

FIG. 3 shows another embodiment of the present invention. In the previous embodiment, the diffusing surface 4a was formed directly on the reflection film 4 of the reflector 3, but in this embodiment,
The reflector 3 has only a mirror-like reflective film 4 formed on the entire surface as in the conventional example, and a member having a diffusive property is adhered to the surface of the reflective film 4 corresponding to the linear portion 3a. Then, the diffusion surface 4a is formed.

In addition, in this embodiment, the reflection sheet 6 formed of, for example, a white resin plate disposed on the back surface 2c side of the tapered light guide plate 2 is smaller than the reflection film 4 formed as a mirror surface by aluminum evaporation or the like. In general, the reflective sheet 6 is used because of its high diffusibility. According to this, the reflective sheet 6 is extended to reach the linear portion 3a on the back side of the reflector 3, and the reflective film 4 is extended by this extended portion. And the diffusion surface 4a is formed.

If the light and dark stripes are not sufficiently eliminated in the straight portion 3a on the back side as in the above embodiment,
As shown in FIG. 4, a reflection sheet 6 of the same member may be adhered to the linear portion 3a on the front side. With the above configuration, for example, by slightly changing the cutting dimension of the reflection sheet 6, the surface light source device currently mass-produced can be changed.
Without making any changes to the reflector 3 mold, etc.
Light and dark stripes can be eliminated.

[0020]

As described above, according to the present invention, the point of intersection with the reflector when it is moved from the light introduction surface of the reflector to a position where a parallel line with the light introduction surface intersects the center axis of the fluorescent tube. By using a surface light source device in which the reflection film in the range up to at least one side is a diffusion surface,
It is possible to eliminate the occurrence of bright and dark stripes peculiar to the tapered light guide plate without impairing the illumination efficiency when the tapered light guide plate is adopted. This is extremely effective in improving the display quality of the device.

Further, the diffusion surface is configured by extending a reflection sheet disposed on the back side of the tapered light guide plate to a predetermined position. This makes it possible to carry out the apparatus without making any change in the mold, process, etc. of the reflector of the apparatus, and makes it possible to carry out the above simply.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a surface light source device according to the present invention.

FIG. 2 is an explanatory diagram showing the causes of light and dark stripes.

FIG. 3 is a cross-sectional view showing a main part of another embodiment of the present invention.

FIG. 4 is a sectional view showing still another embodiment of the present invention in a main part.

FIG. 5 is a sectional view showing a conventional example.

FIG. 6 is a sectional view showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Surface light source device 2 ... Tapered light guide plate 2a ... Light introduction surface 2b ... Front surface 2c ... Back surface 3 ... Reflector 3a ... Linear part 4 ... Reflective film 4a ... Diffusion surface 5 ... Fluorescence Tube 6 Reflective sheet 7 Diffusion sheet 20 Liquid crystal display

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-269702 (JP, A) JP-A-6-281928 (JP, A) JP-A-7-36033 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G02B 6/00 331 G02F 1/1335 530

Claims (2)

(57) [Claims] 1. A tapered light guide plate, a reflector having a substantially U-shaped cross-section and a reflection film formed on an inner surface thereof, the reflector being fixed to a light introduction surface which is a predetermined side of the tapered light guide plate; A surface light source device comprising a fluorescent tube disposed axially opposite to the light introduction surface, wherein a parallel line from the light introduction surface of the tapered light guide plate to the light introduction surface is a central axis of the fluorescent tube. The reflective film in the range up to the point of intersection with the reflector when moved to a position where it intersects with the reflector has at least one side as a diffusion surface. 2. The light diffusing surface of the reflection film is formed by extending a reflection sheet disposed on the back side of the tapered light guide plate to a predetermined position. Surface light source device.