JPH08271890A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To make the luminance of an illuminator uniform all over the surface by arranging a light shielding layer in the central area of a long light source opposed to a light transmission plate. CONSTITUTION: The rectangular light transmission plate 4 is provided with a light reflector 7 being a low foaming film made of white polyester on its one main surface, and a sheet-like light diffusing plate 6 made of PET or polycarbonate on the other main surface. Furthermore, a fluorescent lamp 5 is disposed along one end face of the minor axis of the plate 4 as the long light source, and provided with a reflector 8 being a reflecting member, which has a reflection surface 8a vapor-deposited with silver and whose cross section is formed to be curved in the longitudinal direction of the lamp 5, on the outer periphery of the lamp 5. A light reflecting layer 12 is arranged in the central area of the lamp 5 opposed to the end face of the plate 4. The layer 12 is formed in such a shape that emitted quantity therefrom to the plate U becomes larger and larger from a center part to both ends. Thus, the unevenness of luminance distribution over the longitudinal direction of the lamp 5 is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device of a time division system or an active matrix system employs a backlight system in order to improve its visibility. As an example of this system, a one-lamp type edge light system has been proposed in response to the demands for thinning, weight reduction, and low power consumption (Japanese Patent Laid-Open No. H06-6).
-67025).

FIG. 5 shows an example of a liquid crystal display device 2 in which the above-mentioned one-lamp type edge light type thin lighting device 1 is mounted. A rectangular light guide plate 4 is arranged on a liquid crystal panel 3, and a light guide plate 4 is provided.
The fluorescent lamp 5 is arranged on the end face of the. Further, a diffusion plate 6 is provided on one main surface of the light guide plate 4, and a light reflection plate 7 and a light source reflection plate 8 are provided on the main surface of the light guide plate 4 so as to cover the other main surface and the fluorescent lamp 5, respectively. In addition, a reflection pattern 9 of white ink is printed in dots on the other main surface of the light guide plate 4.

FIG. 6 shows the pattern shape of the dot-shaped reflection pattern 9 in the lighting device 1. The size of each dot is increased as the distance from the fluorescent lamp 5 increases so that the reflectivity thereof is increased. It complements the light attenuation over distance.

According to the above liquid crystal display device 2, the irradiation light of the fluorescent lamp 5 directly projects the light guide plate 4, or a part of the irradiation light is reflected by the light source reflection plate 8 and the reflected light is also reflected. The light guided to the light guide plate 4 and introduced into the light guide plate 4 illuminates the liquid crystal panel 3 through the diffusion plate 6 while being reflected by the dot-shaped reflection pattern 9 and the light reflection plate 7. .

[0006]

However, the liquid crystal display device 2 having the above-mentioned configuration has a problem that the brightness of the illumination device 1 becomes non-uniform over the effective display area of the liquid crystal panel 3, which is a problem. This will be described with reference to FIG.

This figure shows the longitudinal direction of the fluorescent lamp 5 (part A-
(Between the parts B), and the illuminance at the ends is smaller than that at the center. Therefore, the lighting device 1
The luminance tends to be low in the vicinity of the end portion of the fluorescent lamp 5 in the effective light emitting area of 1., which makes the luminance of the lighting device 1 non-uniform, and as a result, the luminance of the effective display area of the liquid crystal panel 3. Also, there is a problem that the uniformity cannot be obtained as required.

Therefore, an object of the present invention is to provide a high-performance liquid crystal display device in which the brightness of an edge-light type illuminating device is made uniform and the brightness uniformity of the effective display area of the liquid crystal panel is achieved. is there.

[0009]

In the liquid crystal display device of the present invention, a light reflecting plate is provided on one main surface of the light guide plate, and a liquid crystal panel is provided on the other main surface side via a light diffusing plate, A long light source is provided on the end surface of the light guide plate, a reflecting member is provided along the longitudinal direction of the long light source, and light is shielded in the central region of the surface of the long light source facing the light guide plate. It is characterized by arranging layers.

[0010]

In the liquid crystal display device of the present invention, since the end portion of the elongated light source has a lower brightness than the central portion thereof, the light shielding layer is arranged in the central region facing the light guide plate of the elongated light source, It is possible to adjust the amount of light incident on the central portion of the light guide plate by the pattern shape of the light-shielding layer, which can correct the uneven brightness distribution in the longitudinal direction of the elongated light source, and the brightness of the lighting device becomes uniform over the surface, As a result, the luminance of the effective display area of the liquid crystal panel becomes a desired degree of uniformity.

[0011]

EXAMPLE FIG. 1 is a sectional view of a liquid crystal display device 10 of this example, and FIGS. 2 and 3 show a light reflecting layer as the light shielding layer provided on an elongated light source. The liquid crystal display device 2 of FIG.
The same reference numerals are given to the same portions as.

Reference numeral 11 denotes a one-lamp type edge light type illuminating device. According to the illuminating device 11, one main surface of a rectangular light guide plate 4 made of polymethylmethacrylate (PMMA) having a thickness of 4 mm is provided on the Toray Corporation. ) Is provided with a light-reflecting plate 7 of a low-foaming film made of white polyester and PE on the other main surface.
A sheet-like light diffusing plate 6 made of T or polycarbonate (PC) is provided, and a fluorescent lamp 5 (cold cathode type with a tube diameter of 3.8 mm or A hot cathode fluorescent lamp) is provided, and the reflector plate 8 is the above-mentioned reflecting member having a silver vapor-deposited reflecting surface 8a having a cross-sectional shape curved along the longitudinal direction of the fluorescent lamp 5 on the outer periphery of the fluorescent lamp 5. Is provided.

Further, as shown in FIG. 6, a reflection pattern 9 containing glass beads formed by adding titanium oxide is formed by printing on one main surface of the light guide plate 4 and distributed in a high density. By this, the brightness was adjusted so as to enhance the surface.

In this embodiment, a prism sheet (BEF100, trade name, manufactured by Sumitomo 3M Co., Ltd., not shown) is interposed between the light diffusion plate 6 and the liquid crystal panel 3 to further increase the brightness. There is.

A light reflecting layer 12 is arranged in the central region of the fluorescent lamp 5 which faces the end surface of the light guide plate 4. 2 shows a dot-shaped light reflecting layer 12a, and FIG. 3 shows a linear light reflecting layer 12b. Any light reflection layer 12
a and 12b also reduce the amount of light emitted from the central portion of the fluorescent lamp 5 to the light guide plate 4, and the light guide plate 4 from both ends thereof.
In order to make the amount of light emitted to the center part uniform, the amount of light emitted to the light guide plate 4 gradually increases from the center part to both ends.

Thus, according to the illuminating device 11 having the above-mentioned structure, since the illustrated light reflecting layers 12a and 12b are arranged, it is possible to correct the uneven luminance distribution in the longitudinal direction of the fluorescent lamp 5 and the luminance of the illuminating device 11. Becomes uniform over the surface.

When measuring the brightness of the lighting device 11 having the above-described structure, the present inventor designates nine parts on the surface as shown in the plan view of the lighting device 11 of FIG. When the brightness of each site was measured, the results shown in Table 1 were obtained. In the table, Example (1) and Example (2) are cases where the light reflecting layer 12a and the light reflecting layer 12b are provided, respectively. In addition, the luminance was similarly measured for the conventional lighting device 1 shown in FIG. Then, the ratio between the minimum luminance and the maximum luminance in each example was obtained. The unit of the numerical value of each luminance is cd / m ² .

[0018]

[Table 1]

As is clear from the results shown in Table 1, the uniformity of Example (1) is 93.6%, and the uniformity of Example (2) is 93.2%. The degree was 87.2%.

The present invention is not limited to the above embodiments, and various modifications and improvements may be made without departing from the scope of the present invention. For example, in the above embodiment, the light source is arranged along the one end face of the minor axis of the light guide plate, but the light source may be arranged along one end face of the major axis of the light guide plate. Further, in the above-described embodiment, the one-lamp type edge light type lighting device is used, but a similar effect can be obtained by the two-lamp type edge light type lighting device.

Alternatively, a light absorbing layer may be provided instead of the light reflecting layer as the light shielding layer. There is a black layer as the light absorbing layer. Further, in disposing the light shielding layer on the surface of the fluorescent lamp 5, a light shielding layer may be provided on a transparent sheet such as cellophane or plastic, and such a transparent sheet may be wound around the surface of the fluorescent lamp 5.

[0022]

As described above, according to the present invention, the light-shielding layer is arranged in the central region facing the light guide plate of the elongated light source so as to correct the uneven luminance distribution in the longitudinal direction of the elongated light source. As a result, the brightness of the illuminating device can be made uniform over the surface, whereby a liquid crystal display device can be provided in which the brightness of the effective display area of the liquid crystal panel has a desired degree of uniformity.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a liquid crystal display device of an example.

FIG. 2 is a perspective view of a main part of a light guide plate that constitutes the liquid crystal display device of the embodiment.

FIG. 3 is a perspective view of a main part of a light guide plate included in the liquid crystal display device according to the embodiment.

FIG. 4 is an explanatory diagram showing a luminance measurement portion of the illumination device.

FIG. 5 is a schematic cross-sectional view of a conventional liquid crystal display device.

FIG. 6 is a state diagram of a dot-shaped reflection pattern in a conventional liquid crystal display device.

FIG. 7 is an illuminance distribution chart of a fluorescent lamp.

[Explanation of symbols]

 3 Liquid crystal panel 4 Light guide plate 5 Fluorescent lamp 6 Light diffusing plate 7 Light reflecting plate 8 Reflecting plate 12, 12a, 12b Light reflecting layer 11 Lighting device

Claims (1)

[Claims] 1. A light reflecting plate is provided on one main surface of the light guide plate, a liquid crystal panel is provided on the other main surface side through a light diffusing plate, and a long light source is provided on an end face of the light guide plate. A liquid crystal display device in which a reflecting member is provided along the longitudinal direction of the elongated light source, wherein a light shielding layer is arranged in a central region of a surface of the elongated light source facing the light guide plate. Display device.