KR20080067978A - Cold cathode fluorescent lamp and method of manufacturing electrode - Google Patents

Abstract

A cold cathode fluorescent lamp and an electrode manufacturing method are provided to extend a lifetime of the CCFL(Cold Cathode Fluorescent Lamp) by improving an initial electron emission performance of an electrode. A cold cathode fluorescent lamp(1) includes a glass tube(2), a tube-type electrode(7), and a lead wire(9). The glass tube includes a fluorescent layer formed on an inner wall thereof. Rare gas is filled in an inner space of the glass tube. The tube-type electrode is arranged inside the inner space of the glass tube. The lead wire includes first and second end portions. The first end portion is adjoined with a bottom outer surface of the electrode. The second end portion penetrates a sealing glass and is elongated outside the glass tube. The electrode is made of a nickel group metal material, to which at least one of yttrium and yttrium oxide is dispersed. The bottom outer surface has a flat surface. A bottom inner surface, which is opposite to the bottom external surface, has a curved shape.

Description

COLD CATHODE FLUORESCENT LAMP AND METHOD OF MANUFACTURING ELECTRODE

This application is based on Japanese Patent Application No. 2007-7958, filed Jan. 17, 2007 and also claims the benefit of priority over the application, the disclosure of which is incorporated herein by reference in its entirety. have.

The present invention relates to a cold cathode fluorescent lamp, and more particularly, to an improvement in an electrode used for a cold cathode fluorescent lamp.

Cold cathode fluorescent lamps are widely used, for example, as backlights for liquid crystal displays. A typical cold cathode fluorescent lamp has a glass tube in which a phosphor layer is formed on an inner wall surface and a rare gas is contained therein, a pair of electrodes disposed at both ends of the glass tube so as to face each other, and one electrode bonded to the electrode. And a lead wire having an end portion and the other end portion extending out of the glass tube.

The above-mentioned electrode used for a cold cathode fluorescent lamp has a cylindrical shape which is open at one end and closed at the other end. Nickel (Ni) is usually used as the material of the electrode because nickel is inexpensive and has high processability. In the following description, the sealed end of the electrode is called the bottom.

1A-1E show examples of different electrodes in cross-sectional shape. The electrodes 30 and 31 shown in Figs. 1A and 1B are electrodes manufactured by press working. The electrodes 40, 41, and 42 shown in Figs. 1C, 1D, and 1E are electrodes manufactured by cold heading. Almost all electrodes currently used are manufactured by press working or cold rolling.

When the electrode is manufactured by press working, a metal plate having a thickness of 0.1 to 0.2 mm is formed into a cup shape (by performing deep drawing) as shown in Fig. 1A or 1B. When the electrode is manufactured by cold pressing, the end face of the metal wire is hit and pressed to form a cup shape as shown in Fig. 1C, 1D or 1E.

As shown in Figs. 1A to 1E, the electrodes 31 and 32 produced by press working and the electrodes 40, 41 and 42 produced by cold rolling are not significantly different in cross-sectional shape. In particular, flatness and straightness are common to the bottom inner surface 50 of the electrode.

However, as described below, a cold cathode fluorescent lamp having an electrode and an electrode has a known problem in two aspects: sputtering resistance and dark startability.

(About sputtering resistance)

Cold cathode fluorescent lamps having the above-mentioned electrodes, as mentioned above, are often used as backlights for liquid crystal displays. However, as the size, resolution, and illuminance of the liquid crystal display increase, the voltage applied to the electrode tends to increase. As the voltage applied to the electrode becomes high, the ionized rare gas is accelerated to impinge at high speed on the electrode surface, especially the bottom inner surface. In other words, the sputtering phenomenon becomes remarkable. In particular, in the case of an electrode having a flat and straight bottom surface, collisions of ionized rare gases are concentrated on the bottom inner surface, so that the bottom is locally worn at the center. If wear progresses and reaches the lead wire bonded to the outer surface of the bottom, the electrode and lead wire are separated from each other. This mechanism shortens the life of the electrode and also cannot obtain the life required for the liquid crystal display backlight.

In addition, the released electrode material reacts with mercury in the glass tube to form amalgams, and the formed amalgams are deposited on the inner surface (especially the inner surface) of the electrode to prevent electron radiation from the bottom inner surface of the electrode to the outside.

Japanese Patent Laid-Open No. 2005-71972 discloses an electrode having a hemispherical bottom inner surface (see paragraph and Fig. 1). However, Japanese Patent Laid-Open No. 2005-71972 does not include a description of the technical meaning of making the bottom surface of the electrode bottom half hemispherical. The technique disclosed in Japanese Patent Laid-Open No. 2005-71972 assumes the use of a high melting point material such as tungsten (W) or molybdenum (Mo) to solve the technical problem of an electrode formed of nickel as a base material. Therefore, Japanese Patent Laid-Open No. 2005-71972 does not disclose or propose an effective means for solving the above-mentioned problems related to sputtering resistance in an electrode formed of nickel as a base material.

(About dark bootability)

BACKGROUND A backlight unit such as a liquid crystal display usually has a sealing structure. That is, a cold cathode fluorescent lamp provided as a backlight is usually placed in a dark space where no external light can enter. On the other hand, cold-cathode fluorescent lamps require initial electrons to cause discharge at the time of startup. Hot electrons, optoelectronics, electrons emitted by high electric fields, cosmic rays of nature, and the like are commonly used as early electrons. However, in the dark space isolated from the outside, the amount of each of these electrons is quite insufficient, so the startability of the cold cathode fluorescent lamp is low.

Techniques for improving dark startability by dispersing an electron emitting material (eg yttrium (Y)) are known (see paragraph [0013] of Japanese Patent Laid-Open No. 2005-71972).

However, in the case where an electrode in which yttrium is dispersed is produced by press working generally used as a method for producing an electrode, dark startability is not sufficiently improved. The inventors of the present invention have studied this phenomenon seriously and found the cause of this phenomenon as described below. When the electrode in which yttrium is disperse | distributed is manufactured by press work, the process outlined below is performed.

A nickel-based metal material (ingot) in which an appropriate amount of yttrium is dispersed is first produced. Ingots are rolled and surface polished a predetermined number of times to produce a strip-shaped metal plate having a thickness of 0.1 to 0.2 mm. The metal plate is pressed into a cup shape as shown in Fig. 1A or 1B, and final polishing is finally performed on the molded product.

However, the addition of yttrium leads to a significant decrease in the brittleness of the material, making the material surface brittle. Therefore, rolling of an ingot becomes difficult to implement. Molten nickel flows on the electrode surface and separation of yttrium from the electrode surface also occurs during press working and final polishing. The result of the flow of molten nickel is that yttrium separated at grain boundaries is covered with nickel and substantially no yttrium is exposed to the electrode surface. The amount of yttrium exposed on the electrode surface is also reduced by the yttrium falling off. This means that fabricating an electrode using a material prepared by adding yttrium to nickel is not effective in improving dark startability.

It is an object of the present invention to improve the dark startability and lifetime of cold cathode fluorescent lamps by improving the initial electrospinning ability and sputtering resistance of electrodes made of materials composed of nickel and electroluminescent materials dispersed in nickel.

According to the present invention, a glass tube comprising at least a rare gas filling an inner space hermetically sealed by a sealing glass and having a phosphor layer formed on the inner wall surface, a tubular electrode disposed in the inner space, A cold cathode fluorescent lamp is provided that includes a lead wire having one end joined to a bottom outer surface and the other end extending through the sealing glass and extending out of the glass tube. The electrode is formed of a nickel-based metal material in which one or both of yttrium oxide and yttrium oxide are dispersed, the bottom outer surface is a flat surface, and the bottom inner surface opposite from the bottom outer surface is a curved surface.

In the cold cathode fluorescent lamp of the present invention, the ratio of the exposed area of either or both of yttrium and yttrium oxide on the electrode inner surface to the exposed area of nickel is preferably at least 0.21%.

According to the present invention, there is provided a method for manufacturing an electrode used in a cold cathode fluorescent lamp, comprising the steps of providing a nickel-based metal wire in which one or both of yttrium and yttrium oxide are dispersed, and a bottom portion having a curved inner surface. And stamping and denting one end surface of the metal wire to form a metal wire in a tubular shape having an opening facing the bottom portion. This is provided.

In the method of manufacturing the electrode of the present invention, the amount of dispersion of either or both of yttrium and yttrium oxide of the metal wire is preferably 0.18 wt% or more and 0.68 wt% or less.

From the following description with reference to the accompanying drawings which illustrate embodiments of the present invention, the advantages, features, and other and other objects of the present invention will become apparent.

According to the present invention, the dark startability and sputtering resistance of the cold cathode fluorescent lamp are improved, and the life of the electrode is extended.

DETAILED DESCRIPTION Examples of cold cathode fluorescent lamps according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 2 is a schematic cross-sectional view showing the structure of a cold cathode fluorescent lamp according to the present exemplary embodiment.

The glass tube 2 shown in Fig. 2 is formed of borosilicate glass. The glass tube 2 is hermetically sealed by the opposing end part by the sealing glass (bead glass 3). The outer diameter of the glass tube 2 is in the range of 1.5 to 6.0 mm, preferably in the range of 1.5 to 3.0 mm. The material of the glass tube 2 may alternatively be lead glass, soda glass, low-lead glass, or the like.

A phosphor layer (not shown) is provided on the inner wall surface 4 of the glass tube 2 over the entire length of the glass tube 2. The phosphors forming the phosphor layer may be selected from existing or new phosphors such as halophosphate phosphors and rare earth phosphors depending on the purpose and use of the cold cathode fluorescent lamp 1. In addition, the phosphor layer may be formed of a phosphor prepared by mixing two or more phosphors.

A predetermined amount of rare gas such as argon, xenon or neon and a predetermined amount of mercury are enclosed in the inner space 5 of the glass tube 2 surrounded by the inner wall surface 4, and the inner pressure of the inner space 5 is The pressure is reduced to below atmospheric pressure.

A pair of electrode units 6 are provided at both ends of the glass tube 2, respectively. Each electrode unit 6 has a tubular electrode 7 and a lead wire 9 bonded to the bottom outer surface 8 of the electrode 7. The electrode 7 provided in the electrode unit 6 faces the electrode 7 provided in the other electrode unit 6, and is inside the glass tube 2 at a predetermined short distance from the end of the internal space 5. It is arranged in a position set inside the end of the space 5. One end of each lead wire 9 is welded to the bottom outer surface 8 of the corresponding electrode 7, and the other end extends out of the glass tube 2 by penetrating the bead glass 3. . The cold cathode fluorescent lamp 1 in the present exemplary embodiment has the above-described basic structure.

The electrode unit 6 shown in FIG. 2 will be described in more detail with reference to FIGS. 3 and 4. 3 is an enlarged perspective view of the electrode unit 6 provided in the cold cathode fluorescent lamp 1. 4A and 4B are longitudinal cross-sectional views showing embodiments of different electrodes 7 in cross-sectional shape.

As shown in Fig. 3, the electrode 7 constituting the electrode unit 6 has an opening 10 at one end thereof and a cylinder (like a cup) closed by the bottom 11 at the other end thereof. ) Has the shape of the shape. As shown in Figs. 4A and 4B, the bottom inner surface 12 of the electrode 7 is a curved surface with a predetermined curvature, and the bottom outer surface 8 is a flat surface. One end face 13 of the lead wire 9 is welded to the flat bottom outer surface 8 of the electrode 7 (see FIG. 3).

The electrode 7 is formed by performing cold rolling so that a metal wire having a diameter substantially the same as the diameter of the electrode 7 is formed into a cup shape as shown in FIGS. 3 and 4. More specifically, a nickel-based metal material (base material ingot) is produced from nickel (Ni) in which yttrium (Y) or yttrium oxide (Y ₂ O ₃ ) is melted and dispersed. Yttrium or yttrium oxide is selectively precipitated in the crystal boundary region of the base material ingot for reasons related to its properties.

The above-described base material ingot is processed into metal wire of a predetermined wire diameter. More specifically, the processing step is as follows. Hot rolling, wire drawing, annealing, grinding, wire drawing and annealing are carried out continuously to form a metal wire. Subsequently, the metal wire is cut to a predetermined length, and one end face of the cut metal wire is hit with a punch and pressed in. In this process, the bottom inner surface (curved surface) 12 and the opening 10 facing the bottom inner surface 12 are formed simultaneously, as shown in Figs. 4A and 4B.

As described above, since the electrode 7 is made by cold rolling, the electrode 7 has no molten nickel flowing on the surface, unlike the electrode formed by press working, and the degree of yttrium falling off from the surface. none. Therefore, yttrium or yttrium oxide dispersed in the base material ingot (metal wire) is sufficiently exposed on the electrode surface. As a result, electrons emitted from yttrium or yttrium oxide always serve as initial electrons, ensuring improved startability even in dark spaces. In addition, since yttrium or yttrium oxide is uniformly present not only on the surface of the electrode 7 but also on the inner portion of the electrode, even if yttrium or yttrium oxide on the surface is worn down by sputtering or the like, yttrium or yttrium oxide on the inner portion thereof. This continues to appear. Therefore, improved startability is maintained for a long time.

If the amount of yttrium or yttrium oxide added to nickel when the base material ingot is made exceeds 1.1 wt%, the base material ingot hardens to such an extent that it is difficult to process the ingot by wire drawing or cold rolling. From the viewpoint of workability, it is preferable to set the amount of yttrium or yttrium oxide to 0.68% by weight or less.

If the amount of yttrium or yttrium oxide is too small, the dark startability cannot be sufficiently improved. It is preferable that the exposed area of yttrium or yttrium oxide on the inner surface of the electrode is 0.21% or more of the exposed area of nickel. If yttrium or yttrium oxide is sufficiently exposed to the inner surface of the electrode, the effect of improving dark startability is obtained. Therefore, the exposed area of yttrium or yttrium oxide on the electrode outer surface may be 0.21% or less.

In order to set the ratio of the exposure area of yttrium or yttrium oxide to the exposed area of nickel to 0.21% or more, it is necessary to make the base material ingot by uniformly dispersing yttrium oxide or yttrium in nickel at least 0.18% by weight.

From the foregoing, it is preferable to disperse the amount of yttrium or yttrium oxide of 0.18% by weight or more and 0.68% by weight or less in nickel.

Since the bottom inner surface 12 of the electrode 7 is a curved surface (spherical surface), ionized high speed rare gas collides uniformly with respect to the entire bottom inner surface 12. Therefore, there is virtually no possibility that any part of the bottom inner surface 12 will be worn locally by sputtering. The sputtering rate of the electrode material (nickel) is also reduced, and thus the amount of amalgam produced is also reduced. As a result, there is substantially no possibility that radiation of electrons from the electrode is disturbed by amalgam deposited on the electrode inner surface.

In the above description, yttria (Y ₂ O ₃ ) is mentioned as an example of yttrium oxide. However, yttrium oxide mixed with nickel or yttrium oxide dispersed in the electrode in the process of making the base material ingot is not limited to yttria. Yttria has high activity and easily oxidizable properties. Therefore, it is convenient to mix yttrium in the form of yttrium oxide when mixing with nickel. However, the electrode may be formed of a metal material prepared by mixing metal yttrium (Y) and nickel. The electrode can also be made from a base material ingot made by mixing yttrium oxide, yttrium and nickel. Since yttrium can be easily oxidized, there is a possibility of converting yttrium to yttrium oxide in the manufacturing stage, which makes the base material ingot by mixing yttrium and nickel in another stage. Also in this case, both yttrium and yttrium oxide are dispersed in the electrode made from the base material ingot. In summary, yttrium oxide dispersed in the electrode is present by mixing nickel in the form of yttrium oxide, or by oxidizing at the stage of making the base material ingot or at another step.

In order to obtain better dark startability, metal with deoxidation effect can be dispersed in the electrode. This is because some of the oxidized yttrium is reduced by the metal having a deoxidation effect. It was confirmed that the sputtering resistance was improved by the metal having the deoxidation effect.

Examples of the metal having a deoxidation effect include titanium (Ti), manganese (Mn), zirconium (Zr), and hafnium (Hf).

If the metal having a deoxidation effect is titanium, the proportion of titanium in the mixture is preferably 0.009 to 0.800 wt%. If the metal having a deoxidation effect is manganese, the ratio of manganese in the mixture is preferably 1.1 to 4.0% by weight. If the metal having a deoxidation effect is zirconium or hafnium, the proportion of zirconium or hafnium in the mixture is preferably 0.05 to 1.10% by weight.

While specific embodiments have been used to describe preferred embodiments of the invention, it is to be understood that these descriptions are for illustrative purposes only, and that changes and modifications may be made without departing from the spirit or scope of the following claims.

1A-1E are enlarged cross-sectional views showing embodiments of prior art electrodes that differ in cross-sectional shape.

2 is a schematic cross-sectional view showing an example of a cold cathode fluorescent lamp in an exemplary embodiment of the present invention.

3 is an enlarged perspective view showing the electrode unit shown in FIG. 2;

4A and 4B are enlarged cross-sectional views showing different embodiments in the cross-sectional shape of the electrode shown in FIGS. 1A-1E.

<Explanation of symbols for the main parts of the drawings>

1: cold cathode fluorescent lamp

2: glass tube

3: bead glass

4: inner wall surface

5: interior space

6: electrode unit

7: electrode

8: bottom outer surface

9: lead wire

12: bottom inner surface

Claims (4)

A glass tube comprising at least a rare gas filling an inner space hermetically sealed by a sealing glass, the glass tube having a phosphor layer formed on an inner wall surface; A tubular electrode disposed in the inner space, A cold cathode fluorescent lamp comprising a lead wire having one end joined to a bottom outer surface of the electrode and the other end penetrating the sealing glass and extending out of the glass tube, The electrode is formed of a nickel-based metal material in which one or both of yttrium oxide and yttrium oxide are dispersed, the bottom outer surface is a flat surface, and the bottom inner surface opposite from the bottom outer surface is a curved surface. lamp. The cold cathode fluorescent lamp according to claim 1, wherein the ratio of the exposed area of either or both of yttrium and yttrium oxide on the inner surface of the electrode to the exposed area of nickel is at least 0.21%. It is a method of manufacturing the electrode used in the cold cathode fluorescent lamp, Providing a nickel-based metal wire in which one or both of yttrium oxide and yttrium oxide are dispersed, Stamping and denting one end surface of the metal wire to form the metal wire in a tubular shape having a bottom portion with a curved inner surface and an opening opposite the bottom portion. The method of manufacturing the electrode. The method of manufacturing an electrode for use in a cold cathode fluorescent lamp according to claim 3, wherein the dispersing amount of either or both of yttrium and yttrium oxide of the metal wire is 0.18 wt% or more and 0.68 wt% or less.

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