JPH0961635A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of heat radiation from a long size light source. SOLUTION: On one main surface of a light guide plate 4 which has a fluorescent lamp 5 arranged on an end surface, a dotted print pattern and a light reflecting plate 7 are provided and on the other main surface side, a liquid crystal panel 3 is arranged across a light diffusion plate 6; and a reflecting plate 11 is arranged along the length of the fluorescent lamp 5 and given slits (a) and (b), and irradiation light from the fluorescent lamp 5 is entered into the light guide plate 4 while reflected by the reflecting plate 11, projecting from the other main surface, and projected on the effective display area of the liquid crystal panel 3.

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 In a time-division or active matrix liquid crystal display device, a backlight system is employed to improve the visibility. As an example of this method, a one-light type edge light method has been proposed in response to demands for thinner, lighter, and lower power consumption (see, for example, JP-A-6-67025).

FIG. 4 shows an example of a liquid crystal display device 2 equipped with this one-light type edge light type illumination device 1. A rectangular light guide plate 4 is provided on a liquid crystal panel 3, and the light guide plate 4 The fluorescent lamp 5 is arranged on one end face. Further, a light diffusing plate 6 is provided on the light guide plate 4, a light reflecting plate 7 is provided so as to cover the opposing main surface and the other end surface thereof, and a light source reflecting plate 8 is provided so as to cover the fluorescent lamp 5.

According to the liquid crystal display device 2, the irradiation light of the fluorescent lamp 5 is directly projected on the light guide plate 4, or a part of the irradiation light is reflected by the light source reflector 8, and the reflected light is also reflected. The light guided to the light guide plate 4 and then introduced into the light guide plate 4 irradiates the liquid crystal panel 3 through the light diffusion plate 6 while being reflected by the light reflection plate 7. In this configuration, the effective light emitting area of the illuminating device 1 is defined in correspondence with the effective display area of the liquid crystal panel 3, and normally, this effective light emitting area has substantially the same dimension as the effective display area.

[0005]

However, according to the liquid crystal display device 2 having the above structure, the temperature of the liquid crystal panel 3 in the vicinity thereof rises partially due to the heat generated by the fluorescent lamp 5,
As a result, temperature unevenness occurs in the plane of the liquid crystal panel 3,
There is a problem that a difference in threshold voltage is caused, and as a result, a color tone becomes uneven on a screen, and display quality is remarkably deteriorated.

Therefore, an object of the present invention is to provide a high-performance liquid crystal display which eliminates the influence of heat generation of the elongated light source in the edge light type illuminating device so that there is no threshold voltage difference in the plane of the liquid crystal panel. To provide a device.

[0007]

In the liquid crystal display device of the present invention, a light reflecting means is provided on one main surface of a light guide plate having an elongated light source on its end surface, and a light diffusing plate is provided on the other main surface side. A liquid crystal panel is arranged, a reflecting member is arranged along the longitudinal direction of the elongated light source, and a slit is provided in the reflecting member so that light emitted from the elongated light source is reflected by the reflecting member. It is characterized in that it is introduced into the liquid crystal panel, emitted from the other principal surface, and projected onto the liquid crystal panel.

[0008]

1 is a sectional view of a liquid crystal display device 9 of the present invention, and FIGS. 2 and 3 are front views of an illuminating device 10 as seen from an arrow A in FIG. FIG.
The same parts as those of the liquid crystal display device 2 shown in FIG.

Reference numeral 10 denotes a one-lamp type edge light type lighting device. According to this lighting device 10, the thickness is 4 mm.
The light guide plate 7 made of a low foaming film of white polyester manufactured by Toray Industries, Inc., which is a light reflection means, is provided on one main surface of the rectangular light guide plate 4 made of polymethylmethacrylate (PMMA), and PET is formed on the other main surface. Alternatively, a sheet-like light diffusing plate 6 made of polycarbonate (PC) is provided, and a fluorescent lamp 5 (cold-cathode type or hot-cathode type fluorescent lamp having a tube diameter of 3.8 mm) is provided along the minor axis one end face of the light guide plate 4. Is provided on the outer periphery of the fluorescent lamp 5 and is made of a polyethylene film having a curved transverse cross section along the longitudinal direction of the fluorescent lamp 5, and a reflective plate 11 having a reflective surface of silver vapor deposition or aluminum vapor deposition on this film. Is provided. The reflection plate 11 is fixed to the light guide plate 4 with an adhesive tape.

On one main surface of the light guide plate 4, a print pattern (not shown) containing glass beads formed by adding titanium oxide exhibiting a white or milky white color is provided as a means for adjusting the brightness in a planar manner. ) Are formed on almost the entire surface so as to be distributed in high density. In this print pattern, as the distance from the fluorescent lamp 5 increases, the density of the dot pattern increases. The light reflection plate 7 is provided below the light reflection plate 7. By combining such a dot-shaped print pattern and the light reflection plate 7, the brightness of the lighting device 10 is increased and the brightness uniformity is improved. It is increasing. Furthermore, a prism sheet (not shown) of Sumitomo 3M's product name BEF100 is interposed between the light diffusion plate 6 and the liquid crystal panel 3 to further increase the brightness.

According to the liquid crystal display device 9 described above, the irradiation light of the fluorescent lamp 5 irradiates the liquid crystal panel 3 through the light guide plate 4 and the light diffusion plate 6 with this structure. The effective display area of the liquid crystal panel 3 and the effective light emitting area of the illuminating device 10 are defined by substantially the same shape.

Further, as a characteristic part of the present invention, FIG. 2 and FIG.
As shown in FIG. 3, the reflector 11 is provided with the slit a or the slit b. The slit a is cut out in both the longitudinal directions, and the reflector 11 is substantially composed of two reflectors, or the both ends in the longitudinal direction are halfway. Good.
The slit b has a configuration in which a plurality of small slits are arranged, and the shape of each slit can be arbitrarily changed.

Thus, according to the illuminating device 10 having the above structure, since the reflecting plate 11 having the slits a and b is provided, the heat energy of the fluorescent lamp 5 is generated by the slits a and b.
The heat transmitted from the fluorescent lamp 5 to the effective display area of the liquid crystal panel 3 can be reduced by the heat radiation scattered and diffused through the liquid crystal panel 3, so that the temperature nonuniformity does not occur in the plane of the liquid crystal panel 3 and the threshold value is reduced. The voltage difference is reduced, and as a result, the display quality is improved.

[0014]

EXAMPLE The inventor of the present invention uses the illumination device 10 having the above-described configuration to arbitrarily determine nine measurement sites when measuring the optimum drive voltage related to the threshold voltage, and determines the maximum contrast of each site. When the optimum driving voltage, which is the indicated voltage, was measured, the results as shown in Table 1 were obtained. In the same table, the optimal driving voltage was similarly measured for the conventional lighting device 1 shown in FIG.

[0015]

[Table 1]

As is clear from the results shown in Table 1, in the examples, the voltage was 28.8 to 29.2V and the difference was 0.4V. In contrast, the conventional one is 28.2-29.2V.
And the difference was 1.0V.

As described above, it can be seen that in this embodiment, the temperature unevenness in the plane of the liquid crystal panel 3 is significantly reduced and the threshold voltage difference is also significantly reduced.

The present invention is not limited to the above embodiments, and various changes and improvements may be made without departing from the scope of the present invention. For example, in the above-described embodiment, the one-lamp type edge light type lighting device is used, but a similar effect can be obtained with a two-lamp type edge light type lighting device. Although the fluorescent lamps 5 are arranged along one short-axis end surface of the light guide plate 4, they may be arranged along one long-axis end surface.

[0019]

As described above, according to the liquid crystal display device of the present invention, the elongated light source is dissipated by providing slits in the reflecting member arranged along the longitudinal direction of the elongated light source. The heat transmitted from the long light source to the effective display area of the liquid crystal panel can be reduced, which prevents temperature unevenness in the liquid crystal panel surface and reduces the threshold voltage difference. We were able to provide a high-performance liquid crystal display device with no unevenness.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a front view of a long light source reflection member in a liquid crystal display device of the present invention.

FIG. 3 is a front view of another elongated light source reflection member in the liquid crystal display device of the present invention.

FIG. 4 is a schematic sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 3 Liquid crystal panel 4 Light guide plate 5 Fluorescent lamp 6 Light diffusing plate 7 Light reflecting plate 8, 11 Reflecting plate 9 Liquid crystal display device 10 Illuminating device a, b Slit

Claims (1)

[Claims] 1. A light reflecting means is provided on one main surface of a light guide plate having an elongated light source arranged on an end surface, and a liquid crystal panel is provided on the other main surface side via a light diffusing plate, wherein the elongated shape is formed. A reflection member is arranged along the longitudinal direction of the light source, and a slit is provided in the reflection member, and the irradiation light of the elongated light source is introduced into the light guide plate while being reflected by the reflection member, and emitted from the other main surface. A liquid crystal display device that is designed to project on a liquid crystal panel.