JP2000133201A - Electrode of cold cathode fluorescent lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce mercury consumption during lighting and the blackening of a tube end, to lengthen life, and to increase brightness by forming a metal cylinder part with at least one of Mo, a compound containing Mo, Ta, and a compound containing Ta. SOLUTION: A pair of electrodes 3 is sealed so as to face each other within both ends of a glass bulb. The electrode 3 has a sleeve 4 made of at least one of high melting point metals such as Ta, Mo, and compounds containing them, and opened both ends, and the sleeve 4 is formed in a cylinder whose inner diameter is 0.4-1.5 mm and total length is 2.0-5.0 mm for example. By forming the electrode 3 so as to have the cylinder part whose facing inside surfaces are opened, electrons are easily emitted from the inner surface of the electrode by a shape effect such as a hollow cathode effect, and cathode drop voltage is reduced. Since metal of Mo and the like used as the material has high melting point and high electric conductivity and sputtering during discharge is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical cold-cathode fluorescent lamp used in particular as a back light source for liquid crystal display screens of OA equipment, liquid crystal televisions, etc., and more particularly to reduction of mercury consumption. The present invention relates to a cold cathode fluorescent lamp electrode having at least a long life, low power consumption and high efficiency.

[0002]

2. Description of the Related Art An electrode of a cold cathode fluorescent lamp used as a back light source of a liquid crystal display device or the like is made of nickel (Ni), aluminum (Al), iron (Fe), tungsten (W), or the like, and has a cylindrical shape. It was formed in the shape of a parallel plate or a column (rod). In order to cover the low electron emission characteristics of these electrode constituent metals, a material having good electron emission characteristics such as lanthanum boride (LaB ₆ ) and barium oxide (BaO) is applied to the electrode surface, and sputtering is performed. Luminous efficiency is increased by coating by a method such as CVD. A specific example will be described below.

The electrode of the cold cathode fluorescent lamp disclosed in Japanese Patent Application Laid-Open No. Hei 3-184252 is formed in a cylindrical shape made of tungsten having both ends opened, or a perforated plate having an infinite number of holes formed in the side surface of the cylindrical electrode. By forming it on a cylindrical electrode, a hollow electrode at the time of discharge is formed in the cylindrical inner diameter portion so as to prolong the life with a large current.

Further, the invention described in Japanese Patent Application Laid-Open No. 9-82275 discloses a nickel sleeve having an opening on the inner side facing the inside and a closed outer end, filled with a mercury alloy inside the tube diameter and the overall length (axial length). An electrode structure is provided in which a suitable nickel sleeve is inserted, and an emitter is attached between the two nickel sleeves having different sizes and on the inner surface of the outer nickel sleeve.

In the invention described in Japanese Patent Application Laid-Open No. 10-21876, the tip of a conductive metal rod is inserted from the outer opening of a nickel sleeve having both ends opened, and the lower portion of the nickel sleeve is inserted from the outside by means such as caulking. Sink in
The conductive metal rod is physically fixed to the nickel sleeve, the surface area of the electrodes is increased, and the surface of the electrodes facing each other has a structure in which the hollow cathode effect is maximized. In addition, the emission luminance characteristics are improved, the occurrence of blackening is reduced, and the consumption of mercury due to sputtering is reduced.

[0006]

However, among the above-mentioned conventional examples, in the case of the electrode disclosed in Japanese Patent Laid-Open No. 3-184252, the cylindrical electrode is made of tungsten. It is difficult to process this tungsten into a cylindrical electrode in terms of manufacturing technology, the degree of freedom in size and shape is small, and the manufacturing cost is high. As a result, the cost of the cold cathode fluorescent lamp using the cylindrical cylindrical electrode made of tungsten also becomes high, and has a problem that it is impractical.

JP-A-9-82275, JP-A-10-82275
In the electrode disclosed in JP-A-21876, since the material of the cylindrical electrode is nickel or the like having a relatively low melting point, the metal constituting the electrode is easily sputtered by ions in the tube generated by discharge during lighting, and this sputtering is performed. The electrode material thus deposited adheres to the inner surface of the phosphor coating or the inner surface of the glass bulb, and there is a problem that the degree of reduction of the luminous flux during long-time operation is increased.

Further, the sputtered electrode material reacts with mercury in the tube to form amalgam, and the amalgamated mercury cannot be converted into mercury vapor, and thus does not contribute to discharge. That is, if the electrode is made of a substance that is easily sputtered such as nickel, mercury that can contribute to electric discharge is quickly consumed, thereby causing a problem that the life of the cold cathode fluorescent lamp is shortened. .

The present invention has been made in view of the above circumstances, and provides a cold-cathode fluorescent lamp which reduces the amount of mercury consumed during lighting and blackening of a tube end to achieve a long life and high brightness. The purpose is to:

[0010]

In order to achieve the above object, according to the first aspect of the present invention, a discharge medium is sealed in a glass bulb having a phosphor film formed on an inner surface thereof, and opposing inner surfaces of both ends. In an electrode of a cold cathode fluorescent lamp obtained by sealing an electrode having a pair of metal cylindrical portions having an open surface side, the metal cylindrical portion is molybdenum, a compound having molybdenum, tantalum, tantalum. And at least one selected from metals or metal compounds.

According to a second aspect of the present invention, a metal compound having at least one selected from the group consisting of an alkaline earth metal element and a rare earth metal element in the metal cylindrical portion is provided. Characterized in that the emitter is provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway explanatory view of a cold cathode fluorescent lamp, and FIG. 2 is an enlarged sectional view of a main part showing a configuration of an electrode according to an embodiment of the present invention. In these figures,
A phosphor film 2 for converting ultraviolet light into visible light is formed on the inner surface of a glass bulb 1 having an outer diameter of about 2.2 mm and an inner diameter of about 1.8 mm, and a few mmg of mercury and a rare gas as a sealing gas are formed inside. It is sealed at a pressure of 60 Torr. A pair of electrodes 3, 3 are sealed at opposite positions inside the glass bulb 1 at both ends. The electrode 3 includes a sleeve 4 having both ends opened by using any one material selected from refractory metals such as tantalum, a tantalum compound, molybdenum, and a molybdenum compound, and a tube of the glass bulb 1 of the sleeve 4. A conductive metal rod 5 made of Kovar having a distal end inserted from an end side opening, and a lead-in wire 6 electrically connected to the conductive metal rod 5 being sealed at both ends of the glass bulb 1. Is airtightly penetrated and led to the outside so that power can be supplied from an external power supply, and it is configured to function as a discharge electrode. The sleeve 4 has, for example, a cylindrical shape with an inner diameter of 0.4 to 1.5 mm and a total length of about 2.0 to 5.0 mm, and the conductive metal rod 5 has a diameter of 0.3 to 1.4 mm.
The conductive metal rod 5 is physically fixed to the sleeve 4 by providing a concave portion 7 which is depressed inward at the lower portion of the sleeve 4. As described above, when the electrode 3 has a structure having a cylindrical portion having an opening at the opposed inner side surface, electrons are easily emitted from the inner surface of the electrode due to the effect of the shape such as the hollow cathode effect. Good electron emission reduces blackening at the tube end. Also, tantalum, molybdenum, or one selected from these compounds is used as the electrode material. These metals are easy to mold and inexpensive, have a high melting point and high conductivity, suppress spatter during discharge, and therefore hardly combine with mercury in the glass bulb, reducing consumption of mercury. In addition, the blackening of the tube end is suppressed due to the low temporal change during discharge, and the life of the cold cathode fluorescent lamp is prolonged.

[0014]

Test Example 1 The relationship between the lighting time and the luminance retention rate of the cold cathode fluorescent lamps shown in FIGS. 1 and 2 was tested. Molybdenum was used as an electrode constituent material, and the test was performed under the conditions of an ambient temperature of 25 ° C. and a lamp current of 5 mA. For comparison, a cold cathode fluorescent lamp in which the electrode constituting material was nickel and the other conditions were the same, such as the inner diameter of the glass bulb, the electrode shape, and the amount of enclosed mercury, was also tested under the same conditions. The result is as shown in FIG. The test proved that the cold cathode fluorescent lamp of the present embodiment in which the electrode constituting material indicated by the solid line is molybdenum maintains a high luminance of 60% even after 20,000 hours has passed. In contrast, the conventional cold cathode fluorescent lamp in which the electrode material indicated by the dotted line in the figure is nickel and whose nickel material was nickel was found to have a short life when the luminance maintenance ratio dropped sharply from 60% to 10% after 17000 hours had elapsed. This indicates that mercury in the glass bulb 1 has been consumed and a rare gas discharge has occurred.

An embodiment of the present invention will be described with reference to FIG. The electrode 3 is made of tantalum, a tantalum compound,
Any one selected from refractory metals such as molybdenum and molybdenum compounds is used as the electrode material. The electrode 3 has an inner diameter of 0.8 mm, an outer diameter of 1.0 mm, and a total length (axial length) of 3.0 mm. And is electrically connected to the introduction line 6. Other configurations are the same as those of the embodiment shown in FIGS. 1 and 2 described above.

An embodiment of the present invention will be described with reference to FIG. The description of the same configuration as in FIGS. 1 and 2 is omitted. The sleeve 4 uses, as a material, any one selected from high melting point metals such as tantalum, a compound having tantalum, molybdenum, and a compound having molybdenum. An emitter 8 is attached to the inner surface of the sleeve 4 from the upper end edge of the sleeve 4 to the tip end surface of the conductive metal bar 5, and to the outer surface of the sleeve 4, the emitter 8 is attached to a part of the upper end edge of the sleeve 4. Have been. The emitter 8 may be applied to the entire outer surface of the sleeve 4. The emitter 8 is a substance having a function of emitting a large amount of electrons at a lower temperature and a lower electric field than the material (Ta, Mo, or a compound thereof) constituting the electrode 3. It is preferable to use a metal compound having a small work function, which is an amount of energy required for liberating the methane, and having a low vapor pressure to extend the life of the cold cathode fluorescent lamp. That is, a substance having a lower work function has a higher electron emissivity, and a substance having a lower vapor pressure is preferable because it evaporates and disappears during use and hardly changes with time.

The substance satisfying such conditions is specifically selected from the group consisting of alkaline earth metal oxides, alkaline earth metal double oxides, rare earth metal oxides, rare earth metal borides and the like. At least one or more metal compounds can be listed. Examples of the alkaline earth metal oxide include CaO, BaO, and SrO, and examples of the alkaline earth metal double oxide include BaAl ₂ O ₄ and BaW.
Examples of O ₄ , CaWO ₄ and rare earth metal oxides include Y
_{2 O 3, La 2 O 3} , but the rare earth metal borides can be listed, for example, _{LaB 6, CeB} 6, YB 6, etc., BaO Among _{these, BaAl 2 O 4, Y 2} O 3,
LaB ₆ is most preferred.

The relationship between the lighting time and the luminance maintenance ratio of the cold cathode fluorescent lamp shown in FIG. 5 was tested. Molybdenum was used as an electrode constituent material, and a cold cathode fluorescent lamp composed of an electrode having an emitter was used under the conditions of an ambient temperature of 25 ° C. and a lamp current of 5 mA. For comparison, a conventional cold cathode fluorescent lamp in which other conditions such as a glass bulb inner diameter, an electrode shape, and an amount of enclosed mercury were the same and the electrode constituent material was nickel and provided with an emitter was also tested under the same conditions. . The result is as shown in FIG. The test confirmed that the cold cathode fluorescent lamp described with reference to FIG. 5 indicated by the dotted line in FIG. 5 maintains the luminance maintaining ratio of 85% even after 4000 hours. In contrast,
The conventional product whose electrode material indicated by the dotted line in the figure is nickel is 30
After approximately 00 hours, the brightness maintenance rate is 85% to 18%
And it was found to have a short life. This rapid drop is due to rare gas discharge due to mercury consumption in the glass bulb.

[0019]

According to the present invention, since an electrode having a good shape of electron emission efficiency from the cathode such as the hollow cathode effect is made of a high melting point material, the change with time during discharge is extremely small, and stable light emission is obtained. There is an effect that a long-life cold-cathode fluorescent lamp which can be obtained for a long time, suppresses evaporation and spatter, has a low degree of blackening around the electrode of the glass bulb, and consumes less mercury can be provided.

Further, since a high melting point material having a low work function and a low vapor pressure is used as the emitter material, the evaporation and sputtering of the electron-emitting substance can be further suppressed in combination with the effects of the electrode structure and the constituent materials. This has the effect of reducing the consumption of mercury sealed in the glass bulb and providing a cold cathode fluorescent lamp with high luminance and long life.

[Brief description of the drawings]

FIG. 1 is a partially cutaway explanatory view of a cold cathode fluorescent lamp.

FIG. 2 is an enlarged sectional view of a main part showing a configuration of an electrode.

FIG. 3 is a graph showing a relationship between a lighting time and a luminance maintenance ratio.

FIG. 4 is an enlarged sectional view of a main part showing a configuration of an electrode.

FIG. 5 is an enlarged sectional view of a main part showing a configuration of an electrode.

FIG. 6 is a graph showing a relationship between a lighting time and a luminance maintenance ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass bulb 2 Phosphor coating 3 Electrode 8 Emitter

Claims (2)

[Claims] 1. A discharge lamp is sealed in a glass bulb having a phosphor film formed on an inner surface thereof, and an electrode comprising a pair of metal cylindrical portions each having an opening on the opposite surface is sealed inside both ends. In the electrode of the cold cathode fluorescent lamp, the metal cylindrical portion is made of at least one metal or metal compound selected from molybdenum (Mo), a compound having molybdenum, tantalum (Ta), and a compound having tantalum. An electrode for a cold cathode fluorescent lamp. 2. The method according to claim 1, wherein the metal cylindrical portion is provided with an emitter made of a metal compound having at least one element selected from the group consisting of an alkaline earth metal element and a rare earth metal element. The electrode of the cold cathode fluorescent lamp according to claim 1.