JP3298979B2 - Substrate for surface light source device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display (L).
The present invention relates to a light guide substrate used for a surface light source device disposed on the back surface of a liquid crystal display and illuminating the liquid crystal display.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays have excellent characteristics such as thinness, light weight, and low power consumption, and there are great expectations for use in various products as flat displays which can sufficiently exhibit these characteristics. Has been sent. However, the liquid crystal has a problem that it cannot emit light by itself, that is, it does not emit light in comparison with a CRT (Cathod Ray Tube) widely used for industrial and consumer purposes. In order to cope with this problem, a backlight type liquid crystal display in which a backlight device as a surface light source is disposed on the back of a liquid crystal has been developed.

A backlight device of this type is desired to be thin and lightweight, and it is a necessary condition that brightness is uniform over the entire area of the screen from the viewpoint of image quality.

[0004] Various techniques have already been proposed as a technique for improving the uniformity of luminance in a backlight device.

For example, in a backlight device described in Japanese Patent Application Laid-Open No. 57-13478, a milky white light scatterer is provided above a linear light source, and the layer thickness at the center of the milky white light scatterer is increased. In addition, the thickness is reduced toward the end so as to eliminate uneven illumination, and furthermore, it is possible to reduce the thickness and size. Further, Japanese Patent Application Laid-Open No. 60-26039 describes a backlight device using a meandering cold-cathode tube lamp. Also, JP-A-61-21998
No. 0 describes a backlight device utilizing an ultraviolet lamp and a phosphor coating layer disposed around the ultraviolet lamp. Japanese Patent Application Laid-Open No. Sho 62-10621 describes a backlight device in which a light source is incorporated in a light guide plate. Japanese Patent Application Laid-Open No. 62-127717 discloses a backlight device in which concave and convex lenses are arranged on upper and lower surfaces of a plurality of light sources. Also, JP-A-63-
Japanese Patent Laid-Open No. 125975 describes a backlight device using a U-shaped lamp. The publications listed above have been proposed for the purpose of eliminating luminance unevenness and achieving uniform luminance.

[0006]

However, the above-mentioned prior art has the following problems. That is, 1) disposing a light source on the lower surface of the light scatterer increases the thickness of the entire backlight device, so that the liquid crystal display becomes bulky. 2) When a plurality of lamps are provided in order to make the luminance uniform, However, the larger the area, the greater the number of lamps required and the higher the cost. 3) When a meandering lamp is used, a large-area lamp lacks mass productivity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a surface light source device which is thin, lightweight, and can maintain uniformity of luminance even in a large area.

[0008]

According to a first aspect of the present invention, there is provided a substrate for a surface light source device , comprising: an incident surface on which light from a light source is incident; A diffuse reflection surface having a diffuse reflection layer that diffusely reflects incident light;
A substantially transparent substrate having an emission surface for emitting incident light irregularly reflected on the irregular reflection layer surface, wherein the incident surface has a cutout having a stepped shape at both ends thereof,
The irregular reflection layer is provided over the entire surface of the substrate such that the degree of irregular reflection on the irregular reflection surface increases as the distance from the incident surface increases , and a region connected to a region including the cutout portion of the irregular reflection surface as an end. Is characterized in that the degree of irregular reflection is increased.

[0009]

In the above arrangement, the radiated light from the light source enters the inside of the substrate from the incident surface, and proceeds while repeating reflection due to the difference in optical density at the interface between the substrate and air. If the incident light enters the irregular reflection layer during this traveling, the incident light enters the irregular reflection layer, and the incident light is irregularly reflected and becomes a critical angle or less at the interface between the emission surface of the substrate and air, and is outside the substrate. Is radiated. The degree of irregular reflection of the irregular reflection layer changes in the vertical direction of the incident surface, and even if there is a portion on the incident surface where the amount of incident light is small, light can be emitted with uniform luminance from the exit surface.

Here, the light diffuse reflection layer covers the entire substrate.
In this case, the pattern is such that the degree of diffuse reflection increases as the distance from the light source increases, and the pattern of the degree of diffuse reflection increases in a region connected to a region including the cutout portion as an end, so that light from the light source is transmitted to the entire transparent substrate. Radiated out uniformly in the area.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the backlight device according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a plan view of the backlight device of this embodiment as viewed from the back side (the surface opposite to the light emitting surface). In FIG. 1, reference numeral 1 denotes a transparent substrate, which is formed of a thin plate having a good light transmittance so as to propagate light incident from an end face. As the material, a transparent plate made of an inorganic or synthetic resin, such as a glass plate, an acrylic resin plate, or a polycarbonate resin plate, is used. Reference numeral 2 denotes a light source, which is disposed on one side edge of the four peripheral portions of the transparent substrate 1. As the light source 2, a fluorescent lamp is generally widely used, but a cold-cathode tube having a small tube diameter is also applicable. Such a cold cathode ray tube is advantageous in utilization because it promotes a reduction in the thickness of the entire backlight device and suppresses the influence of temperature on a liquid crystal display (LCD) panel. In addition, various light sources such as an aperture-type lamp can be used as the light source 2.

Reference numeral 3 denotes a diffusely reflecting layer, which is provided on the back side of the transparent substrate 1 and diffusely reflects the radiated light from the light source 2 to emit the radiated light from the front surface of the transparent substrate 1. The light diffuse reflection layer 3 is arranged so that the occupancy of the light diffuse reflection layer 3 per unit area of the transparent substrate 1 changes based on the distance from the light source 2. In this example, the light diffuse reflection layer 3 has a dot shape, and the dot diameter changes based on the distance from the light source 2. That is, the dot diameter of the light diffuse reflection layer 3 increases as the distance from the light source 2 increases.

Further, when forming the light diffuse reflection layer 3 on the back surface of the transparent substrate 1, the dot diameter of the light reflection layer 3 at the left and right ends is formed larger than the dot diameter at the center. Here, the dot diameters of the light reflection layers 3 on both the left and right sides are 1.
It has a diameter of from 0.5 to 5 times, preferably from 1.1 to 2.5 times. The diameter of the dot at the center of the light irregular reflection layer 3 is 1 to 3.
000μ, preferably 10 to 1000μ.

The light scattering layer 3 uses, as reflective fine particles, a volatile curable or ultraviolet curable white ink containing titanium oxide or a colored ink of a desired color.
As a method of forming the light diffuse reflection layer 3 on the back surface of the transparent substrate 1, it can be formed by using screen printing, offset printing, or other known techniques.

[0016] Incidentally, the light from the light source 2 is may be rather is incident directly on the end face 1a and 1c are formed by cutting the left and right ends of the end surface of the light source 2 side of the transparent substrate 1. Yo
I, the end face 1a, the notches form a 1c, it is possible to incorporate the necessary members to attach the transparent substrate 1 and the light source 2. Also, the end surfaces 1a, 1 of the transparent substrate 1
Light from the light source 2 is directly incident on the end faces other than c (that is, the end face 1b).

FIG. 2 is a side sectional view of the present backlight device. In the figure, reference numeral 4 denotes a light diffusion layer, which diffuses and emits light emitted from the transparent substrate 1. Reference numeral 5 denotes an envelope in which the backlight device is incorporated. Reference numerals 6 and 7 are reflectors for improving illumination efficiency.

FIG. 3 is a diagram showing an example of a change in the dot diameter of the light irregular reflection layer 3 in the region of the end face to which the light emitted from the light source 2 can be directly incident and in the region of the end surface of the notch . As shown in the figure, the diffusely reflecting layer 3 is formed so that the dot diameter gradually increases from near the end face of the notch to the side end. In FIG. 3, the light diffusely reflecting layer 3a
Dot diameter <light diffuse reflection layer 3b dot diameter <light diffuse reflection layer 3
The dot diameter of c <the dot diameter of the light diffuse reflection layer 3d.

The operation of the backlight device having the above configuration will be described. First, radiation light from the light source 2 enters from one end surface of the transparent substrate 1. The radiated light from the light source 2 entering the transparent substrate 1 travels while repeating reflection depending on the incident angle due to the difference in optical density at the interface between the transparent substrate 1 and air. In the course of this progress, when the radiated light from the light source 2 enters the light diffuse reflection layer 3, it is irregularly reflected by the titanium oxide contained therein. The light that has been irregularly reflected has a critical angle or less with respect to the interface between the surface of the transparent substrate 1 and the air, and is emitted from the surface of the transparent substrate 1 to the outside. Light emitted from the transparent substrate 1 to the outside is further diffused by passing through the light diffusion layer 4 on the surface of the transparent substrate 1, and then emitted to the outside.

Here, the light diffuse reflection layer 3 is arranged so that the occupancy per unit area of the transparent substrate 1 increases as the distance from the light source 2 increases. It is arranged to increase. For this reason, the diffused reflection layer 3 emits less diffused light in the vicinity of the light source 2 having a large amount of light, and the diffused reflection of the diffused reflection layer 3 is large in places where the amount of light is small (at a distance from the light source 2 and on both sides). Become. For this reason, it is possible to obtain a uniform amount of diffused light over the front surface from the vicinity of the light source 2 to a position separated from the light source 2 and both ends.

FIG. 4 is a diagram showing a luminance distribution when the light diffuse reflection layer is uniformly provided on the transparent substrate 1. As shown in the figure, the brightness decreases toward the both ends. In this embodiment, in order to compensate for this decrease in luminance, the occupancy of the light diffusely reflecting layer is increased at both end portions.

Here, in the transparent substrate 1, it is considered that the loss of the light amount from both end surfaces is large. That is, the light is lost by being radiated to the outside from both ends.
In the present embodiment, the amount of light that is to escape from the end face is irregularly reflected on dots existing near the end face. In addition, the dot diameter near the end face is made larger than the dot existing at the center of the transparent substrate to increase the light diffuse reflectance. As a result, a backlight device which is excellent in uniformity of luminance, thin and lightweight, which has been difficult with conventional technology, and which can obtain excellent uniformity of luminance even if the area is increased, is provided. obtain.

The backlight device of the present embodiment as described above can be provided behind a liquid crystal display (LCD) to realize a thin, easy-to-view screen without luminance unevenness. Contribute greatly to improvement. Furthermore, it goes without saying that it can be used as other various backlight devices.

As described above, according to the present embodiment,
In order to achieve the above object, in a light guide plate on which illumination light is incident from the end face of the transparent substrate, the dot diameter of the end face portion that cannot enter the light in the structure where the illumination light cannot enter directly from the end face is a dot perpendicular to the optical axis. By controlling the pattern, a surface light source having uniform luminance can be obtained. That is, the end face brightness can be improved without lowering the center brightness, and the entire brightness distribution can be made uniform.

The method of changing the area occupied by the light diffuse reflection layer 3 is not limited to this example. For example, the dot density is changed by changing the dot pitch of the light reflection layer 3 having the same size. You may change it. Furthermore,
The shape of the light irregular reflection layer 3 is not limited to a dot, and a line may be used, and the thickness of the line and the interval between the lines may be changed.

In FIG. 1, the transparent substrate 1 has the end faces 1a,
Although the shape has 1c, the shape of the transparent substrate may be a simple square shape. At this time, for example, as shown in FIG. 5, when the end face of the transparent substrate 1 on the light incident side becomes larger than the light source 2, both side portions (10a, 10a) of the transparent substrate
The incident light amount of b) decreases. Even in such a case, it is possible to maintain uniform luminance by applying the present invention. Therefore, even when the transparent substrate is larger than the rod-shaped light source, it is possible to maintain uniform luminance, and it is possible to easily cope with a large screen.

[0027]

As described above, according to the surface light source device substrate of the present invention, it is possible to maintain the uniformity of luminance even when the substrate is thin, lightweight, and large in area.

[0028]

[Brief description of the drawings]

FIG. 1 is a plan view of a backlight device according to the present embodiment as viewed from a back side.

FIG. 2 is a side sectional view of the backlight device of the present embodiment.

FIG. 3 is a diagram illustrating an example of a change in dot diameter of a light diffuse reflection layer in a region of an end face to which light emitted from a light source can be directly incident and a region of both sides where light can not be directly incident.

FIG. 4 is a diagram illustrating a luminance distribution when a light diffuse reflection layer is uniformly provided on a transparent substrate.

FIG. 5 is a diagram illustrating a backlight device using a rectangular transparent substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light source 3 Diffuse reflection layer 4 Light diffusion layer

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigekuni Dewa 2-5-2-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Yuka Co., Ltd. (56) References JP-A-6-186432 (JP, A) Hei 4-40268 (JP, U) Japanese Utility Model Hei 4-61302 (JP, U) Japanese Utility Model Hei 5-33131 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02F 1 / 13357 G09F 9/00 336

Claims (4)

(57) [Claims] An incident surface on which light from a light source is incident, a diffuse reflection surface substantially orthogonal to the incident surface and having a diffuse reflection layer for irregularly reflecting incident light from the incident surface, and an incident light diffusely reflected on the diffuse reflection layer surface a substantially transparent substrate having an exit surface for emitting light, the incident plane is switching exhibiting stepped shape at its opposite ends
Ri-away portion has the irregular reflection layer over the entire surface of the substrate, with the degree of diffuse reflection in the irregular reflection surface is provided so as to be stronger as the distance from the incident surface, the notch of the random reflection surface A substrate for a surface light source device , wherein the degree of irregular reflection is increased in a region connected to a region including an end . 2. The method according to claim 1, wherein the irregular reflection layer is disposed on the substrate in a dot shape, and a degree of the irregular reflection by the irregular reflection layer is adjusted by changing a dot density on the substrate. 2. The substrate for a surface light source device according to 1. 3. The irregular reflection layer is arranged on the substrate in a dot shape, and a degree of the irregular reflection by the irregular reflection layer is adjusted by changing a dot diameter on the substrate. 2. The substrate for a surface light source device according to 1. 4. The irregular reflection layer includes a central region of the incident surface.
In the direction parallel to the incident surface in the region including
Along, the degree of irregular reflection is provided to be uniform
The surface light source according to claim 1, wherein the surface light source has an area.
Equipment substrate.