JP4339363B2 - Cold cathode fluorescent lamp and electrode manufacturing method - Google Patents

Description

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

  Cold cathode fluorescent lamps are widely used as light sources for backlights of liquid crystal displays. In general cold cathode fluorescent lamps, a fluorescent material layer is formed on an inner wall surface, a rare earth gas is enclosed in a glass tube, a pair of electrodes disposed opposite to both ends of the glass tube, and one end of each electrode. A lead wire connected to the other end and drawn out of the glass tube.

  The electrode used in the cold cathode fluorescent lamp has a cylindrical shape with one end opened and the other end closed. Also, nickel (Ni), which is inexpensive and excellent in workability, is usually used as the electrode material. In the following description, the closed end of the electrode is referred to as the bottom.

  FIGS. 4A to 4E show examples of different cross-sectional shapes of electrodes currently used. The electrodes 30 and 31 shown in FIGS. 4 (a) and 4 (b) are electrodes manufactured by pressing, and the electrodes 40 and 4 shown in FIGS. 4 (c), (d) and (e), 41 and 42 are electrodes manufactured by cold heading (header processing). That is, most of the currently used electrodes are manufactured by either pressing or header processing.

  When an electrode is manufactured by press working, a metal plate having a thickness of 0.1 to 0.2 mm is pressurized and formed into a cup shape as shown in FIG. 4 (a) or (b) (deep drawing). On the other hand, when manufacturing an electrode by header processing, the end surface of a metal wire is struck to form a cup shape as shown in FIG. 4 (c), (d) or (e).

  As shown in FIGS. 4A to 4E, the electrodes 31 and 32 manufactured by pressing and the electrodes 40, 41 and 42 manufactured by header processing are not greatly different in cross-sectional shape. In particular, the bottom inner surface 50 of each electrode is common in that it has a flat and linear shape.

  The above is the outline of the conventional cold cathode fluorescent lamp, in particular, the electrode. However, the conventional electrode and the cold cathode fluorescent lamp equipped with the electrode have the following problems in terms of sputtering resistance and dark startability. was there.

(About spatter resistance)
As described above, cold cathode fluorescent lamps equipped with the above electrodes are frequently used as light sources for backlights of liquid crystal displays, but as the size of liquid crystal displays is increased, the resolution is increased, and the brightness is increased. The applied voltage tends to increase. When the voltage applied to the electrode is increased, the ionized noble gas is accelerated more than before. As a result, the ionized rare gas collides with the electrode surface, particularly the inner surface of the bottom of the electrode at a high speed, and the electrode constituent material (mainly nickel) is easily released to the outside. That is, the sputtering phenomenon becomes remarkable. In particular, in a conventional electrode in which the bottom inner surface has a flat and linear shape, the ionized rare gas intensively collides with the center of the bottom inner surface, and the bottom center is locally worn. When wear further progresses and reaches the lead wire joined to the bottom outer surface, the electrode and the lead wire are broken. For this reason, the lifetime of an electrode becomes short and the lifetime requested | required of the light source for liquid crystal backlights cannot be obtained.

  Further, the released electrode constituent material reacts with mercury in the glass tube to form amalgam, and the formed amalgam is deposited on the inner surface (in particular, the inner surface) of the electrode. Then, electron emission from the inner surface of the bottom of the electrode to the outside of the electrode is inhibited.

  In this regard, Patent Document 1 describes an electrode having a semispherical bottom inner surface (Patent Document 1 [0022], FIG. 1 and the like). However, Patent Document 1 does not disclose the technical significance of making the bottom inner surface of the electrode hemispherical. The technique described in this document is based on the premise that an electrode is manufactured from a high melting point material such as tungsten (W) or molybdenum (Mo) in order to solve the technical problem of an electrode based on nickel. Technology (Patent Document 1 [0005]). Therefore, Patent Document 1 does not disclose or suggest an effective means for solving the above-described problem regarding the sputtering resistance in the electrode based on nickel.

(About dark startability)
In general, a backlight unit of a liquid crystal display has a sealed structure. That is, a cold cathode fluorescent lamp as a light source for backlight is often arranged in a dark space where extraneous light does not reach. On the other hand, cold cathode fluorescent lamps require initial electrons that trigger discharge when they are started. Usually, the initial electrons include thermal electrons, photoelectrons, electrons emitted by a high electric field, and natural cosmic rays. However, in the cold cathode fluorescent lamp installed in the dark space cut off from the outside, any of the above initial electrons is remarkably insufficient, and the startability is deteriorated.

  Therefore, it is known to improve the dark startability by dispersing an electron emitting substance (for example, yttrium (Y)) in the electrode (Patent Document 1 [0013]).

  However, when an electrode in which yttrium is dispersed is manufactured by the above-described press working widely used as an electrode manufacturing method, there is a problem that the dark startability is not sufficiently improved. The inventors of the present invention conducted intensive research on the cause and found the following causes. That is, when manufacturing an electrode in which yttrium is dispersed by press working, the following steps are generally performed.

  First, a nickel-based metal material (ingot) in which an appropriate amount of yttrium is dispersed is manufactured by a melting method. Subsequently, a strip-like metal plate having a thickness of 0.1 to 0.2 mm is manufactured by performing rolling treatment and surface polishing treatment a plurality of times on the ingot. Next, the metal plate is pressed to form a cup shape as shown in FIGS. 4A and 4B, and then a final polishing process is performed.

However, when yttrium is added to nickel, the ductility of the material is remarkably lowered and the material surface becomes brittle. For this reason, not only ingot rolling becomes difficult, but also sagging of nickel and yttrium fall off at the electrode surface during pressing and final polishing. When nickel sagging occurs, yttrium segregated at the grain boundaries is covered with nickel, and yttrium is hardly exposed on the electrode surface. Moreover, even if yttrium is removed, yttrium exposed on the electrode surface portion is reduced. As a result, even if the electrode is made of a material in which yttrium is added to nickel, the dark startability is not sufficiently improved.
JP 2005-71972 A

  Depending on the prior art, it has been generally used as an electrode material for cold cathode fluorescent lamps, and it is sufficient to solve the above-mentioned problems related to sputtering resistance and dark startability while using nickel as a base material that is inexpensive and excellent in workability. Could not be resolved.

  An object of the present invention is to improve the sputtering resistance and initial electron emission of an electrode in which an electron emitting material is dispersed in a base material of nickel, thereby extending the life of a cold cathode fluorescent lamp and dark startability. Is to improve.

  The cold cathode fluorescent lamp of the present invention includes a glass tube in which at least a rare gas is sealed in an internal space hermetically sealed with a sealing glass, and a phosphor layer is formed on an inner wall surface, and is disposed in the internal space. And a lead wire having one end joined to the outer surface of the bottom of the electrode and the other end penetrating the sealing glass and drawn out of the glass tube. Further, the electrode is formed of a nickel-based metal material in which yttrium and / or yttrium oxide is dispersed, and the bottom outer surface is a flat surface, and the bottom inner surface opposite to 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 yttrium and / or yttrium oxide to the exposed area of nickel on the inner surface of the electrode is preferably 0.21% or more.

  The electrode manufacturing method of the present invention is a method for manufacturing an electrode used in a cold cathode fluorescent lamp, and the end surface of a nickel-based metal wire in which yttrium and / or yttrium oxide is dispersed is hit and recessed, and the inner surface is curved. It forms in the cylinder shape which has the bottom part of this, and the opening part which opposes this bottom part, It is characterized by the above-mentioned.

  In the electrode manufacturing method of the present invention, it is desirable that a dispersion amount of yttrium and / or yttrium oxide in the metal wire is 0.18 wt% or more and 0.68 wt% or less.

  According to the present invention, the sputtering resistance and the initial electron emission property of an electrode in which an electron emitting material is dispersed in nickel as a base material are improved. As a result, it is possible to extend the life of the cold cathode fluorescent lamp and improve the dark startability.

  Hereinafter, an example of an embodiment of a cold cathode fluorescent lamp of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the structure of the cold cathode fluorescent lamp of this example.

  In the cold cathode fluorescent lamp 1 shown in FIG. 1, both ends of a glass tube 2 made of borosilicate glass are hermetically sealed with 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. However, the material of the glass tube 2 may be lead glass, soda glass, low lead glass, or the like.

  The inner wall surface 4 of the glass tube 2 is provided with a phosphor layer (not shown) over almost the entire length thereof. The phosphor constituting the phosphor layer can be appropriately selected from existing or new phosphors such as halophosphate phosphors and rare earth phosphors according to the purpose and application of the cold cathode fluorescent lamp 1. Furthermore, the phosphor layer can be composed of a phosphor in which two or more kinds of phosphors are mixed.

  A predetermined amount of rare gas such as argon, xenon, neon and mercury is enclosed in the internal space 5 of the glass tube 2 surrounded by the inner wall surface 4, and the internal pressure is reduced to about several tenths of the atmospheric pressure. ing.

  A pair of electrode units 6 is provided at both ends of the glass tube 2 in the longitudinal direction. Each electrode unit 6 includes a cylindrical electrode 7 and a lead wire 9 joined to the bottom outer surface 8 of the electrode 7. The electrode 7 included in one electrode unit 6 is disposed at a position slightly inside the longitudinal direction end of the internal space 5 of the glass tube 2 in a direction facing the electrode 7 included in the other electrode unit 6. One end of the lead wire 9 is welded to the bottom outer surface 8 of the corresponding electrode 7, and the other end penetrates the bead glass 3 and is drawn out of the glass tube 2. The above is the basic structure of the cold cathode fluorescent lamp 1 of this example.

  Next, each electrode unit 6 shown in FIG. 1 will be described in more detail with reference to FIGS. FIG. 2 is an enlarged perspective view showing the electrode unit 6 provided in the cold cathode fluorescent lamp 1, and FIGS. 3A and 3B are longitudinal sectional views showing examples in which the sectional shape of the electrode 7 is different.

  As shown in FIG. 2, the electrode 7 constituting the electrode unit 6 has a cylindrical (cup-shaped) appearance in which an opening 10 is provided at one end in the longitudinal direction and the other end is closed by a bottom 11. 3A and 3B, the bottom inner surface 12 of the electrode 7 is a curved surface having a predetermined curvature, and the bottom outer surface 8 is a flat surface. One end surface 13 of the lead wire 9 is welded to the flat bottom outer surface 8 of the electrode 7 (FIG. 2).

The electrode 7 is obtained by processing a metal wire (wire) having substantially the same diameter as the electrode 7 into a cup shape as shown in FIGS. Specifically, nickel (Ni) in which yttrium (Y) or yttrium oxide (Y ₂ O ₃ ) is melt-dispersed is cured to produce a nickel-based metal material (base material ingot). Note that yttrium or yttrium oxide is selectively deposited in the grain boundary region in the base material ingot due to its properties.

  Next, the base material ingot is processed into a metal wire having a predetermined wire diameter. Specifically, a metal wire is manufactured by sequentially executing hot rolling, wire drawing, annealing, grinding, wire drawing, and annealing. Next, the metal wire is cut into a predetermined length, and one end face of the cut metal wire is struck with a punch to be recessed, and the bottom inner surface 12 of the electrode 7 is curved as shown in FIGS. 3 (a) and 3 (b). In addition, the opening 10 facing the bottom inner surface 12 is formed at the same time.

  Thus, since the electrode 7 is manufactured by header processing, unlike the electrode formed by press processing, there is no sagging of nickel or yttrium falling on the surface. Therefore, yttrium or yttrium oxide dispersed in the base material ingot (metal wire) is sufficiently exposed on the electrode surface. As a result, electrons constantly emitted from yttrium or yttrium oxide become initial electrons, and excellent startability can be obtained even in a dark space. Furthermore, since yttrium or yttrium oxide exists uniformly not only on the surface of the electrode 7 but also inside the electrode, even if yttrium or yttrium oxide on the surface is consumed by sputtering or the like, the yttrium or yttrium oxide on the surface is successively deposited on the surface. Appears and good startability continues for a long time.

  Here, when the amount of yttrium or yttrium oxide added to nickel in manufacturing the base material ingot exceeds 1.1% by weight, the base material ingot is hardened, and drawing and header processing become difficult. From the viewpoint of ease of processing, it is desirable that the amount of yttrium or yttrium oxide added to nickel is 0.68% by weight or less.

  On the other hand, if the amount of yttrium or yttrium oxide is too small, the dark startability cannot be sufficiently improved. Specifically, it is desirable that the exposed area of yttrium or yttrium oxide on the inner surface of the electrode is 0.21% or more with respect to the exposed area of nickel. If yttrium or yttrium oxide is sufficiently exposed on the inner surface of the electrode, the effect of improving the dark startability can be obtained. Therefore, the exposed area ratio of yttrium or yttrium oxide on the outer surface of the electrode may be 0.21% or less.

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

  From the above, it is desirable that 0.18 wt% or more and 0.68 wt% or less of yttrium or yttrium oxide is dispersed in the base material ingot (metal wire).

  Furthermore, since the bottom inner surface 12 of the electrode 7 is a curved surface (spherical surface), the ionized high-speed noble gas collides with the entire surface of the bottom inner surface 12 substantially uniformly. Therefore, a part of the bottom inner surface 12 is intensively sputtered and local wear does not occur. Moreover, since the amount of sputtering of the electrode constituent material (nickel) is also reduced, the amount of amalgam generated is also reduced. As a result, electron emission to the outside by the amalgam deposited on the inner surface of the electrode is not inhibited.

In the above description, yttria (Y ₂ O ₃ ) is given as an example of yttrium oxide. However, yttrium oxide dispersed in an electrode or yttrium oxide mixed with nickel in the production of a base material ingot is not limited to yttria. Yttrium has a high activity and is easily oxidized. Therefore, it is convenient to mix with nickel in the form of yttrium oxide. However, the electrode may be formed of a metallic material mixed with nickel in the form of metallic yttrium (Y). Moreover, you may manufacture an electrode from the base material ingot formed by mixing yttrium oxide and yttrium, and nickel. Note that yttrium is easily oxidized as described above, and yttrium may be changed to yttrium oxide in the process of manufacturing the base material ingot by mixing yttrium and nickel and in other processes. Also in this case, both yttrium and yttrium oxide are dispersed in the electrode manufactured from the base material ingot. In short, when yttrium oxide is dispersed in the electrode, the yttrium oxide is yttrium oxide formed in the manufacturing process of the base material ingot or the like, even if it is mixed with nickel in the form of yttrium oxide. Also good.

  In addition, a better dark startability can be obtained by dispersing a metal having a deoxidizing action on the electrode. The reason is that a part of the oxidized yttrium is reduced by the intervention of a metal having a deoxygenating action. It has also been confirmed that the sputtering resistance is improved by the presence of a metal having a deoxidizing action.

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

  When the metal having a deoxidizing action is titanium (Ti), the mixing ratio is preferably 0.009 wt% to 0.800 wt%. Moreover, when it is manganese (Mn), it is desirable that the mixing ratio is 1.1 weight%-4.0 weight%. In the case of zirconium (Zr) or hafnium (Hf), the mixing ratio is preferably 0.05% by weight to 1.10% by weight.

It is typical sectional drawing which shows an example of embodiment of the cold cathode fluorescent lamp of this invention. It is an expansion perspective view of the electrode unit shown in FIG. (A) and (b) are the expanded sectional views which show the example from which the cross-sectional shape of the electrode shown in FIG. 1 differs. (a)-(e) is an expanded sectional view which shows the example from which the cross-sectional shape of the conventional electrode differs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cold cathode fluorescent lamp 2 Glass tube 3 Bead glass 4 Inner wall surface 5 Inner space 6 Electrode unit 7 Electrode 8 Bottom outer surface 9 Lead wire 10 Opening part 11 Bottom 12 Bottom inner surface 13 End surface

Claims (2)

A method for producing an electrode used in a cold cathode fluorescent lamp,
An electrode characterized in that an end surface of a nickel-based metal wire in which yttrium or yttrium oxide is dispersed is hit to be recessed, and the inner surface is formed into a cylindrical shape having a curved bottom and an opening facing the bottom. Production method. The method of manufacturing an electrode according to claim 1, wherein the dispersion amount of yttrium and / or yttrium oxide in said metal wire is not more than 0.18 wt% or more 0.68% by weight.

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