JPH03260618A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To suppress the generation of uneven display due to the rise of local temperature by arranging the electrode part of a cooling cathode discharge tube (CDT) for a backlight source on the outside of a liquid crystal display element (LCDE). CONSTITUTION:The electrode part 4 of the cooling CDT 2 for the backlight source in a translucent LCDE 1 is arranged on the outside of the LCDE 1. A portion having an extremely large potential inclination is formed in a discharge path arranged immediately before an electrode in the CDT 2 and air in the tube of the portion and the surface of the electrode are heated. Thereby, partial temperature size can be removed by arranging the electrode part 4 on the outside of the LCDE 1 and the whole system including the part sealing liquid crystal in its inside and the sealing part of a liquid crystal cell is prevented from generating heat, so that uneven display can be suppressed and effective display quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a transmission type liquid crystal display device using a cold cathode discharge tube as a back light source so that good display quality can be obtained over the entire display surface.

[Prior Art] If a transmissive type liquid crystal display element is illuminated from the back with an artificial light source, it will not become extremely difficult to see depending on the usage environment like a reflective type liquid crystal display device, and moreover, it can be used with cathode ray tubes, etc. Since they take up far less space and weigh less than display devices, they have come to be widely used as display devices for portable office automation equipment.

Although several types of backlight sources are used for the above-mentioned applications, cold cathode discharge tubes are widely used because of their low price and relatively small tube diameter.

However, in cold cathode discharge tubes that utilize glow discharge, the voltage drop that occurs just before the electrodes is relatively large, and although the power consumption of the tube as a whole is not very large, the amount of heat generated in this portion cannot be ignored.

On the other hand, from the viewpoint of usage, the display device must be made as thin and compact as possible, but in this case, the problem becomes how to dissipate the heat generated in the electrode portion.

As a countermeasure to the above problem, for example, Japanese Patent Application Laid-Open No. 636526
The publication discloses forming radiation fins on a support member of a cold cathode discharge tube.

[Problems to be Solved by the Invention] However, the above-mentioned conventional countermeasure techniques do not take into account that the part where heat is actually generated is the front part of the electrode, which is closer to the light emitting column part of the discharge tube than the discharge tube support part. The temperature of the discharge tube support increases due to heat conduction from the heat generating part in front of the electrode, so cooling the support part is of course effective, but the real heat generating part in front of the electrode is the liquid crystal display element. As a result, the display function of the liquid crystal display element becomes uneven due to a local temperature rise of the liquid crystal display element, and the display quality may deteriorate.

As described above, this type of liquid crystal display device is constructed to be as thin as possible, so it is difficult to expect uniformity of the temperature around the discharge tube due to convection of the atmosphere around the discharge tube.

The present invention solves the above-mentioned conventional problems and provides a transmissive liquid crystal display device with a light source that prevents deterioration in display quality due to local temperature rise of the liquid crystal display element, which is compatible with cold cathode discharge tubes for back light sources. The purpose is to

[Means for Solving the Problems] In order to achieve the above object, in the present invention, in a transmission type liquid crystal display device using a cold cathode discharge tube as a back light source, the electrode part of the cold cathode discharge tube is replaced with the liquid crystal display element. It was placed outside of the cell to prevent heating both as a whole and locally, including the part in which the liquid crystal is sealed, as well as the sealed part of the liquid crystal cell.

[Operation] As described above, in a cold cathode discharge tube, a portion with an extremely large potential gradient is formed in the discharge path immediately in front of the electrode.

Therefore, heat is generated in the gas inside this tube and on the electrode surface. In the present invention, since this portion is placed outside the liquid crystal display element, there is no local temperature rise in the liquid crystal display element. Furthermore, since the portion immediately before the electrode with an extremely large potential gradient does not emit enough light to serve as a light source, the loss of luminous flux is virtually non-existent.

Embodiment FIG. 1 is a plan view of an embodiment of the present invention, and FIG. 2 is a side view thereof. In the figure, 1 is a transmission type liquid crystal display element, 2 is a cold cathode discharge tube, 3 is a frame, and 4 is an electrode portion of the cold cathode discharge tube. In this embodiment, as can be seen from these figures, a total of four cold cathode discharge tubes are arranged, two on each side of the back surface of the element, sandwiching the liquid crystal display element, avoiding the area directly behind the liquid crystal display element. has been done. The back of the liquid crystal display element is made of transparent or translucent plastic, etc., and the light that enters from the side is directed internally toward the center while repeating total reflection for the light that enters the surface at a large angle of incidence. The other part of the rays that entered the surface at a small angle of incidence are emitted from the point of incidence toward the back surface of the liquid crystal display element, and as a result,
A known light guide is arranged to provide substantially uniform illuminance to the entire back surface of the liquid crystal display element. With the structure of the example described above, local heating of the liquid crystal enclosing part (cell) including the surrounding sealing part was suppressed, and a good display was obtained without any difference in display state depending on the location, that is, with no display unevenness.

On the other hand, in the case of the conventional structure in which the electrode part of the cold cathode discharge tube is not placed on the outside, a temperature difference occurs between the center part and the four corners of the liquid crystal display element, and the temperature difference is 6 degrees Celsius or more. As a result, display unevenness occurred between the four corners and the center. It is thought that this is because the threshold voltage fluctuated due to the difference in thermal expansion of the liquid crystal display element members.

Generally, liquid crystal becomes an isotropic liquid when the temperature exceeds a certain level, and one display element loses its display function, but even with conventional designs, the temperature rarely rises to that extent.

[Effects of the Invention] As explained above, according to the present invention, it is possible to suppress the occurrence of display unevenness in a transmission type liquid crystal display element using a cold cathode discharge tube as a back light source, and to obtain good display quality. .

[Brief explanation of drawings]

FIG. 1 is a plan view of an embodiment of the present invention, and FIG. 2 is a side view thereof.

Claims (1)

[Claims] 1. A transmissive liquid crystal display device using a cold cathode discharge tube as a back light source, characterized in that the electrode portion of the cold cathode discharge tube is disposed outside the liquid crystal display element.