JP2000066201A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the illuminance of a liquid crystal layer by maintaining the constitution of a thin type without increasing the thickness of a light transmission plate and well maintaining light emission efficiency in the state of suppressing the increase in electric power consumption without increasing the supply current to fluorescent tubes when the device is provided with an edge type backlight. SOLUTION: The edge type backlight 10 constituted by disposing the plural fluorescent tubes 5 to a cylindrical form by paralleling their axes to each other is arranged at the side end of the light transmission plate 3 disposed on the rear surface side of a display section. The respective fluorescent tubes 5 are formed with reflection surface parts in part of the tube surfaces facing the central side of the cylinder constituted of the respective fluorescent tubes 5. The luminous fluxes emitted from the fluorescent tubes 5 are directly made incident on the light transmission plate 3 and besides, these luminous fluxes are reflected by the reflection surface parts and are made incident on the light transmission plate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a liquid crystal layer sandwiched between an electrode and a glass substrate and displaying an image.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device (LC) in which both surfaces of a liquid crystal layer are sandwiched between glass substrates on a front side and a rear side.
D) has been proposed.

[0003] Such a liquid crystal display device includes a first electrode group disposed on a first surface of a liquid crystal layer and a first electrode group disposed opposite to a second surface of the liquid crystal layer. There has been proposed a plasma addressed liquid crystal display (PALC) including a second scan electrode group having a plurality of plasma discharge channels formed in a direction orthogonal to the group.

Some of such liquid crystal display devices are provided with a backlight (illumination device) that illuminates the liquid crystal layer from the back side so that an image displayed on the liquid crystal layer can be easily viewed. As the backlight, a direct-type backlight in which a liquid crystal layer is provided on the back side to directly illuminate the liquid crystal layer, and a backlight provided in a side edge of the liquid crystal layer and provided in the back edge of the liquid crystal layer And an edge type backlight that illuminates the liquid crystal layer via a light guide plate disposed on the side.

In order to increase the luminous flux in the liquid crystal layer by increasing the emitted light flux in the edge type backlight, it is conceivable to increase the thickness of the light guide plate and arrange a plurality of fluorescent tubes in the thickness direction. It is also conceivable to increase the amount of current supplied per fluorescent tube.

[0006]

By the way, in a liquid crystal display device provided with the above-mentioned edge type backlight, if the illuminance of the liquid crystal layer is improved by increasing the thickness of the light guide plate, As a result, the overall thickness is increased and the weight is increased.

If the amount of current supplied per fluorescent tube is increased, the luminous efficiency of the fluorescent tube is reduced, and the emitted light flux does not increase as expected.

That is, as shown in FIG. 6, when the power (W) of the fluorescent tube is increased and the supplied current is increased, the luminance (nt) of the fluorescent tube increases, but as shown in FIG. The efficiency (nt / W) decreases as the supplied current increases. Also, when the supply current to the fluorescent tube is increased, the temperature of the fluorescent tube increases, and the mercury vapor pressure deviates from the optimum value, so that the luminous efficiency decreases. As shown in FIG. 8, the relationship between the temperature (° C.) and the mercury vapor pressure (mmHg) of the fluorescent tube and the luminous efficiency (%) is because there is an optimal mercury vapor pressure at which the luminous efficiency becomes the best. It is.

In view of the above, the present invention has been proposed in view of the above-mentioned circumstances, and in a liquid crystal display device having an edge type backlight, it is possible to increase the thickness of a light guide plate or increase the current supplied to a fluorescent tube. The present invention aims to provide a liquid crystal display device in which the illuminance of a liquid crystal layer is improved while suppressing an increase in power consumption by enabling a reduction in the device configuration and maintaining good luminous efficiency without performing Things.

[0010]

In order to solve the above-mentioned problems, a liquid crystal display device according to the present invention comprises a display section having a light guide plate disposed on the back side and a plurality of fluorescent tubes whose axes are parallel to each other. An edge-type backlight arranged in a cylindrical shape and arranged at least at a side end of the light guide plate, wherein each fluorescent tube constituting the edge-type backlight has a center of a cylinder formed by each fluorescent tube. A reflective surface is formed on a part of the tube surface facing the side. In this edge type backlight, the luminous flux emitted from the fluorescent tube is
In addition to directly entering the side end of the light guide plate, the light is reflected by the reflection surface and enters the side end of the light guide plate.

In the edge type backlight, it is possible to arrange a cooling pipe in a cylinder formed by each fluorescent tube, and further connect the cooling pipe to a heat sink.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the liquid crystal display device according to the present invention has a display unit 1, a light diffusion plate 2 disposed on the back side of the display unit 1, and a light diffusion plate 2 The light guide plate 3 is provided on the rear side, and the edge type backlight 10 is provided on both side ends of the light guide plate 3.

The display unit 1 has a thin flat plate shape having thin glass plates on the front and back sides and a liquid crystal layer sealed between these glass plates. For the liquid crystal layer,
A voltage based on the video signal is applied by the transparent electrode. The flat display device has an electronic circuit unit (not shown) that applies a voltage based on a video signal to the display unit 1 to display a video. Light diffusion plate 2 and light guide plate 3
Are formed of a transparent synthetic resin material in a flat plate shape.

The edge type backlight 10 includes a plurality of fluorescent tubes 5 arranged in a cylindrical shape with their axes parallel to each other. A cooling pipe 6 is provided in a cylinder formed by each of the fluorescent tubes 5 along a central axis of the cylinder. As shown in FIG. 2, each of the fluorescent tubes 5 is supported by a thermal contact member 9 in a state of good heat conduction with respect to the outer peripheral surface of the cooling pipe 6. The cooling pipe 6 is connected to a radiator plate (not shown) outside the device. That is, the heat generated by each fluorescent tube 5 is transmitted to the cooling pipe 6 via the thermal contact member 9, and is radiated outward from the radiator plate through the cooling pipe 6.

A cooling liquid flows through the cooling pipe 6. The cooling liquid is circulated by connecting the cooling pipe 6 to a heat radiating portion such as an external heat radiating plate. By the circulation of the liquid, each fluorescent tube 5 is maintained at the optimum temperature. Instead of such a so-called liquid cooling type, the cooling pipe 6 may be formed of a material having good heat conductivity.

As shown in FIG. 1, the edge type backlight 10 has a cylindrical reflector (reflection plate) 4 surrounding each fluorescent tube 5. The reflector 4 is formed in a cylindrical shape substantially coaxial with the cooling pipe 6. The reflector 4 has a slit corresponding to a side end of the light guide plate 3, and a light beam emitted from each fluorescent tube 5 enters the side end of the light guide plate 3 through the slit. It is possible.

As shown in FIG. 2, each of the fluorescent tubes 5 constituting the edge type backlight 10 has a reflecting surface 8 formed on a part of the tube surface of the fluorescent tube 5 facing the center of the cylinder. Have been. Such a reflective surface portion 8 can be manufactured by a technique for manufacturing a so-called aperture tube. The reflecting surface portion 8 may be formed on the inner surface of the tube of the fluorescent tube 5, or may be formed on the outer surface of the tube of the fluorescent tube 5, as shown in FIG. When the reflecting surface portion 8 is formed on the inner surface of the tube of the fluorescent tube 5, the phosphor 7 is applied to the inner surface of the reflecting surface portion 8 further.

The fluorescent material 7 in the fluorescent tube 5 is shown in FIG.
As shown in (1), a part of the portion that does not correspond to the reflection surface portion 8, that is, a part of the portion of each fluorescent tube 5 that is directed toward the outer periphery of the cylinder may be removed. In the portion where the phosphor 7 is removed as described above,
Since only the glass forming the tube is present, the light transmittance is high.

As described above, in the fluorescent tube 5 having the reflecting surface 8, the luminance of the tube surface at the opening, which is a portion without the reflecting surface 8, is higher than when the reflecting surface 8 is not provided. This is because the light to be emitted from the fluorescent material 7 on the opposite side of the opening or to be emitted to the outside of the fluorescent tube 5 through the fluorescent material 7 on the opposite side of the opening is reflected by the reflective surface 8. This is because they are concentrated on the opening side. As shown in FIG. 4, the tube surface luminance at this opening is 2.5 times or more of the tube surface luminance when the reflecting surface 8 is not provided with the same tube diameter and tube current when the opening is 60 °. 3 times.

As a general characteristic of the fluorescent tube, as shown in FIG. 5, from the relationship between the power supplied to the fluorescent tube and the luminous efficiency, the smaller the diameter of the fluorescent tube, the higher the surface brightness. Also, the lower the supply current per fluorescent tube, the more
The luminous efficiency is improved. As described above, since there is an optimal mercury vapor pressure in terms of luminous efficiency, if the temperature change of the fluorescent tube increases, a deviation from the optimal value occurs, and the luminous efficiency decreases.

For these reasons, it is better to use a plurality of thin tube diameter fluorescent tubes and to suppress the supply current per tube than to supply a large current to one large tube diameter fluorescent tube. The luminous efficiency is good. It is also important to release heat from the fluorescent tube to the outside and maintain the temperature of the fluorescent tube at an optimum value.

The edge type backlight 10 in the liquid crystal display device according to the present invention comprises a plurality of fluorescent tubes 5 arranged in a cylindrical shape, and a cooling pipe 6 disposed in a cylinder formed by the fluorescent tubes 5. The above conditions are satisfied.

That is, the edge type backlight 10
In designing the light guide plate 3, the light guide plate 3 can be treated as one thick fluorescent tube having a diameter of a cylinder formed by a plurality of fluorescent tubes 5. However, the tube surface brightness of the plurality of fluorescent tubes 5 is higher than that of a single thick fluorescent tube under the condition that the input power is the same, due to the increase in brightness due to the smaller tube diameter and the reflection of the reflecting surface 8. Due to the increase in luminance, the luminance becomes about 1.5 to 3 times.

In the edge type backlight 10, as described above, the cooling pipe 6
Each fluorescent tube 5 is maintained at an optimum temperature.

[0026]

As described above, the liquid crystal display device according to the present invention includes the edge type backlight, and can efficiently use the light beam emitted from the edge type backlight. Even if the edge type backlight is configured as a large one and the total amount of emitted light is increased, a decrease in luminous efficiency due to heat generation does not cause a problem.

That is, according to the present invention, in a liquid crystal display device having an edge-type backlight, it is possible to reduce the thickness of the device structure without increasing the thickness of the light guide plate or increasing the current supplied to the fluorescent tube. An object of the present invention is to provide a liquid crystal display device in which the illuminance of a liquid crystal layer is improved while maintaining high luminous efficiency and suppressing an increase in power consumption.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an overall configuration of a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view showing a backlight configuration of the liquid crystal display device.

FIG. 3 is a cross-sectional view showing another embodiment of the backlight configuration of the liquid crystal display device.

FIG. 4 is a graph showing a relationship between the angle of an opening (aperture angle) of a fluorescent tube and the luminance of a tube surface.

FIG. 5 is a graph showing a relationship between a tube diameter of a fluorescent tube and a tube surface luminance.

FIG. 6 is a graph showing the relationship between the power consumption of a fluorescent tube and the luminance of the tube surface.

FIG. 7 is a graph showing a relationship between a current supplied to a fluorescent tube and luminous efficiency.

FIG. 8 is a graph showing the relationship between the temperature of the fluorescent tube and the luminous efficiency.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Display part, 2 light-diffusion plate, 3 light-guide plate, 4 reflector, 5 fluorescent tube, 6 cooling pipe, 7 fluorescent substance, 8 reflective surface part, 9 thermal contact member, 10 edge type backlight

Claims (3)

[Claims] 1. A display unit having a light guide plate disposed on a back side thereof, and a plurality of fluorescent tubes disposed in a cylindrical shape with their axes parallel to each other, wherein at least a side end of the light guide plate is provided. An edge-type backlight disposed therein, wherein each of the fluorescent tubes constituting the edge-type backlight has a reflecting surface portion formed on a part of a tube surface facing a center side of a cylinder formed by each of the fluorescent tubes. A liquid crystal display device characterized by the above-mentioned. 2. The edge type backlight has a cooling pipe in a cylinder formed by each fluorescent tube, and each of the fluorescent tubes is thermally contacted with the cooling pipe. Item 2. The liquid crystal display device according to item 1. 3. The liquid crystal display device according to claim 2, wherein the cooling pipe is connected to a heat sink.