JP2005085472A - Cold cathode lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold cathode lamp which has a small size and high luminance by forming electrodes with a material having a small work function, and has an electrode structure ensuring the long life of the lamp and high degree of freedom using a material which is hard to make mercury amalgam as the surface material of the electrodes, in the cold cathode lamp in which the electrodes are installed at both ends inside a glass tube, and a gas is sealed in the tube as a discharge medium. <P>SOLUTION: At least surfaces of the electrodes are made of carbide of zirconium (Zr), carbide of tungsten (W), carbide of tantalum (Ta), carbide of titanium (Ti), carbide of niobium (Nb), carbide of hafnium (Hf) or carbide of molybdenum (Mo), or a mixture of two or more thereof. High-melting metal carbide has a work function lower than that of an original metal, and formability of mercury amalgam is low. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cold cathode discharge lamp, and more particularly to an electrode material.

  A fluorescent lamp is often used as a light source for a backlight of a liquid crystal display device such as a liquid crystal television or a liquid crystal display of a personal computer, or an image reading unit of an OA device such as a facsimile, a copying machine, or an image scanner. . Of these, cold cathode discharge lamps are often used. Cold cathode fluorescent lamps can use plate-like, cylindrical or rod-like electrodes, and have a simpler electrode structure than hot-cathode fluorescent lamps that use coiled filaments for the electrodes. This is because it is possible to reduce the size of the light source, and further downsizing the equipment using such a light source.

  By the way, regarding the electrode material of the cold cathode discharge lamp, conventionally, nickel (Ni) has been overwhelmingly used. This is because it is cheaper and has better workability than other refractory metal-based electrode materials such as molybdenum (Mo) and niobium (Nb), which are cited as electrode materials, and Ni is also used in terms of lamp characteristics. This is because there has been no particular inconvenience until now. However, in recent years, with the improvement in performance of the liquid crystal display device or OA device as described above, the cold cathode discharge lamp of the light source is also strongly required to have higher luminance, lower power consumption, and smaller size. It has become like this.

  However, each of these requirements requires different things against the cold cathode discharge lamp, and it is difficult to satisfy all the requirements simultaneously. In order to reduce the size of the lamp, it is effective to shorten the length of the electrode, which is the non-light-emitting part of the total length of the lamp. To increase the brightness, it is effective to increase the lamp current, If the electrode length is shortened, the surface area of the electrode decreases, so even if the same lamp current is applied as before, the current density at the electrode increases, the cathode fall voltage increases, and sputtering on the electrode surface becomes intense. As a result, side effects such as an increase in power consumption and heat generation at the electrode part, a shortened lamp life due to electrode wear and glass tube wall blackening occur. On the other hand, when the lamp current is increased in order to increase the brightness of the lamp, the current density at the electrode increases, so that the same problem as when the electrode is shortened is caused.

  In order to avoid such a problem, it is conventionally known that it is effective to make electrons easily emitted from the electrode. For example, as described in Patent Document 1, barium ( Application of electron-emitting materials containing Br), strontium (Sr) or calcium (Ca) has been performed. However, in this case, the lamp discharges as expected while the electrode has an electron-emitting substance, but as the electron-emitting substance is consumed, the lamp becomes difficult to discharge and has a lifetime.

  In view of this, it has been considered that a metal having a work function smaller than Ni is used for the electrode in order to facilitate the emission of electrons without using the above-described easily depleted electron-emitting material (for example, Patent Document 1). And Patent Document 2). For example, in the cold cathode fluorescent lamp according to Patent Document 2, aluminum (Al) or zirconium (Zr) having a work function smaller than that of Ni is formed on the inner bottom of a cylindrical electrode (hollow electrode) made of Ni or the like. Alternatively, a disk-shaped or bottomed cylindrical internal electrode formed of these alloys is provided. In this way, compared to the case where the entire electrode is made of only Ni, electrons are easily emitted and taken in due to a lower work function, and the cathode fall voltage is reduced, so that the lamp can be used without increasing power consumption or heat generation. The current can be increased. Alternatively, the lamp can be miniaturized by shortening the electrode length. Similarly, in the cold cathode discharge lamp according to Patent Document 1, an inner electrode made of Al or Zr is provided inside the hollow electrode so that the work function of the inner electrode is smaller than that of the outer hollow electrode. Yes.

JP-A-9-204899 (paragraphs [0009] and [0026]) JP 2002-117804 A (paragraph [0009])

  In a cold cathode discharge lamp, a metal having a lower work function than Ni, such as Al or Zr, is used for a part of the electrode, thereby increasing the lamp current while suppressing an increase in power consumption or heat generation, or shortening the electrode length. As is well known, Al and Zr are strong metals that easily produce mercury amalgam, and the electrodes of fluorescent lamps that contain mercury vapor as the discharge medium gas. As a material, it is a shy metal.

  For this reason, in the cold cathode discharge lamps according to Patent Document 1 and Patent Document 2, the entire electrode is not composed of only Al or Zr. While increasing the surface area so that the entire electrode has a hollow electrode structure such as a cylindrical shape, and simultaneously confining the sputtering at the electrode in the cylinder of the electrode, while achieving high brightness with the so-called hollow electrode effect, Al or Zr, which is easy to make amalgam, is used only at the bottom of the cylindrical electrode, the contact area between Al and Zr and the discharge gas is minimized, and the Al or Zr released by sputtering on the electrode surface is reduced. By reducing the chance of atoms being associated with mercury atoms in the discharge medium, the lifetime of the lamp due to the formation of mercury amalgam is avoided.

  However, as long as the discharge phenomenon is used, a spatter phenomenon inevitably occurs on the electrode surface, and therefore, formation of mercury amalgam by Al or Zr cannot be completely prevented. Eventually, in the techniques according to Patent Document 1 and Patent Document 2, the electrodes are limited to those having a hollow electrode structure, and the life of the lamp is inevitably shortened.

  In particular, since Al has a high sputtering rate and wear due to sputtering, it is not suitable for the electrode material of the discharge lamp for this reason.

  In view of the above, an electrode material having a work function lower than that of zirconium, effective in reducing the size of the electrode or increasing the lamp current, hardly forming mercury amalgam, and effective in preventing the shortening of the lamp life is desired.

  Therefore, the present invention is a cold cathode discharge lamp in which electrodes are attached to both ends of a glass tube and a discharge medium gas is sealed in the tube. The electrode is formed of a material having a small work function, and is small and has high luminance. An object is to provide a cold cathode discharge lamp.

  The present invention also provides a cold cathode discharge lamp having a long lamp life and a high degree of freedom in electrode structure by using a material that is difficult to make mercury amalgam and forming the surface of the electrode with the electrode material. Objective.

  The cold cathode discharge lamp of the present invention is a cold cathode discharge lamp in which electrodes are attached to both ends inside a glass tube, and a gas of a discharge medium is enclosed in the tube. At least the surface of the electrode is a carbide of zirconium (Zr), Tungsten (W) carbide, tantalum (Ta) carbide, titanium (Ti) carbide, niobium (Nb) carbide, hafnium (Hf) carbide, molybdenum (Mo) carbide or a mixture of two or more thereof It is characterized by being.

  According to the present invention, there is provided a cold cathode discharge lamp in which electrodes are attached to both ends inside a glass tube and a gas of a discharge medium is sealed in the tube, the electrode length is short, the lamp current is large, the small and high voltage. A cold cathode discharge lamp with brightness can be provided. Further, it is possible to provide a cold cathode discharge lamp with little formation of mercury amalgam and having a long life and a high degree of freedom in electrode shape.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side view including a partially cutaway cross section of a cold cathode discharge lamp 100 according to an embodiment of the present invention. Referring to FIG. 1, Ni—Cr—Fe alloy leads at both ends of a glass tube 1 having an outer diameter of 1.6 to 6 mm, a wall thickness of 0.2 to 0.6 mm, and a length of about 50 to 1000 mm. 4 is sealed. Inside the glass tube 1, a mixed gas of a rare gas such as xenon or argon and mercury vapor is sealed as a discharge medium gas. The pressure of the gas is 1,300 to 20,000 Pa. A phosphor layer 2 is formed on the inner surface of the glass tube 1. The portion of each lead 4 entering the glass tube has a large diameter, and the electrode 3 according to the present invention is fixed to the tip of the large diameter portion 4A.

The two electrodes 3 have at least Zr carbide (ZrC), W carbide (WC), Ta carbide (TaC), Ti carbide (TiC), Nb carbide (NbC), and Hf carbide (HfC). Or it is Mo carbide () or a mixture of two or more thereof. Table 1 shows the work functions of various refractory metals and the work functions of carbides of these refractory metals.
Table 1

  As shown in Table 1, the seven refractory metal carbides ZrC, WC, TaC, TiC, NbC, HfC, and MoC described above all have a work function lower than Ni and lower than Zr. Therefore, as compared with the cold cathode discharge lamp using Zr according to Patent Document 1 or Patent Document 2 described above as an electrode, more lamp current can be passed if the shape and dimensions of the electrode 3 are the same. That is, the luminance can be increased. Alternatively, if the lamp current is the same, the length L of the electrode 3 can be shortened. In other words, the total length of the lamp (the total length of the glass tube 1) can be shortened while keeping the distance between the electrodes the same.

  Below, the structure of the electrode 3 is demonstrated using some Examples.

  FIG. 2A is a perspective view showing a state in which the large diameter portion 4 </ b> A of the lead 4 is connected to one end portion of the rod-like electrode 3. The electrode 3 has a solid rod shape, and Zr, W, Ta, Ti, Nb, Hf or Mo, which is a refractory metal, is cut into a rod shape and heated in a stream of hydrocarbon, acetylene or the like to be carbonized. In this way, a carbide layer of the metal is formed on the surface of the metal of the metal.

  Alternatively, it can be obtained by cutting a refractory metal carbide ZrC, WC, TaC, TiC, NbC, HfC or MoC itself into a rod shape.

  FIG. 2B is a perspective view showing a state in which the large diameter portion 4 </ b> A of the lead 4 is connected to one of the cylindrical electrodes 3. The electrode 3 has a cylindrical shape with no bottoms on both sides, and is connected by inserting a large diameter portion 4A of a lead from one opening. This cylindrical electrode 3 is formed by pressing a refractory metal Zr, W, Ta, Ti, Nb, Hf or Mo plate into a cylindrical shape and heating it in an air stream such as hydrocarbon or acetylene for carbonization. It is obtained by forming a carbide layer of the metal on the surface of the metal of the bare metal by processing.

Alternatively, another electrode metal other than the above seven types of metals, for example, a Ni thin plate is pressed into a cylindrical shape, and the refractory metal carbides ZrC, WC, TaC, TiC, NbC, The HfC or MoC layer can be obtained by forming by sputtering, ion plating, or vapor deposition.
Can be obtained.

  FIG. 2C is a perspective view showing a state in which the large diameter portion 4 </ b> A of the lead 4 is connected to the bottom surface of the cup-shaped electrode 3. The electrode 3 has a cup shape with one end face of the cylinder having no lid and one bottom face with a bottom, and a plate of Zr, W, Ta, Ti, Nb, Hf or Mo of a refractory metal is pressed into a cylindrical shape. In this case, it is obtained by forming a carbide layer of the metal on the surface of the metal of the bullion by heating it in a stream of hydrocarbon, acetylene or the like and carbonizing it.

  Alternatively, an electrode metal other than the above seven types of metals, for example, a thin Ni plate, is pressed into a cylindrical shape, and the refractory metal carbides ZrC, WC, TaC, TiC, NbC, The HfC or MoC layer can be obtained by forming by sputtering, ion plating, or vapor deposition.

  Next, the present inventor compared the lifetime of the lamp when the electrode 3 is made of metal Zr or metal Ti and when it is made of the metal carbide ZrC or TiC. For cold cathode discharge lamps with the same shape, dimensions, discharge medium gas type, gas pressure, phosphor layer 2, electrode structure, etc., but with only the electrode material changed, the formation of mercury amalgam was caused by an accelerated test. When the lamp life was determined, the life of the metal Zr electrode and the Ti electrode was 500 h, whereas the carbide ZrC electrode and the TiC electrode were 10,000 h. As a result, the superiority of carbide was confirmed.

  According to the present invention, it is possible to further reduce the size and increase the brightness of a cold cathode discharge lamp, which is advantageous in reducing the tube size as compared with a hot cathode discharge lamp. This shows that the present invention contributes to miniaturization of liquid crystal display devices such as liquid crystal televisions and liquid crystal displays, or OA devices such as facsimiles, copiers, and image scanners as an example.

1 is a perspective view including a partially cutaway cross section of a cold cathode discharge lamp according to an embodiment of the present invention. It is a perspective view which shows the Example of the electrode in the cold-cathode discharge lamp of this invention, A fraction (a) is a rod-shaped electrode, A fragment (b) is a cylindrical electrode, A fragment (c) is The case of a cup-shaped electrode is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass tube 2 Phosphor layer 3 Electrode 4 Lead 4A Large diameter part of lead 100 Cold cathode discharge lamp

Claims (10)

In the cold cathode discharge lamp in which electrodes are attached to both ends inside the glass tube and the gas of the discharge medium is sealed in the tube,
At least the surface of the electrode is zirconium (Zr) carbide, tungsten (W) carbide, tantalum (Ta) carbide, titanium (Ti) carbide, niobium (Nb) carbide, hafnium (Hf) carbide or molybdenum ( A cold cathode discharge lamp characterized by being a carbide of Mo) or a mixture of two or more thereof. 2. The cold cathode discharge according to claim 1, wherein the electrode is formed by using Zr, W, Ta, Ti, Nb, Hf, or Mo as a base material and carbonizing a metal surface of the base material. 3. lamp. In the electrode, the surface of the base material of the electrode is coated with Zr carbide, W carbide, Ta carbide, Ti carbide, Nb carbide, Hf carbide, Mo carbide or a mixture of two or more thereof. The cold cathode discharge lamp according to claim 1, wherein: The electrode itself is a carbide of Zr, a carbide of W, a carbide of Ta, a carbide of Ti, a carbide of Nb, a carbide of Hf or a carbide of Mo, or a mixture of two or more thereof. 2. The cold cathode discharge lamp according to 1. The cold cathode discharge lamp according to claim 1, wherein the electrode has a rod shape. The cold cathode discharge lamp according to claim 1, wherein the electrode has a cylindrical shape. The cold cathode discharge lamp according to claim 1, wherein the electrode has a cup shape. The cold cathode discharge lamp according to claim 1, wherein a phosphor layer is provided on an inner wall of the glass tube. The cold cathode discharge lamp according to claim 8, wherein the discharge medium contains mercury gas and rare gas. A sealed glass tube;
A discharge medium gas containing rare gas and mercury gas enclosed in the glass tube;
A phosphor layer formed on the inner wall of the glass tube;
Electrodes provided at both ends inside the glass tube, and at least the surface is Zr carbide, W carbide, Ta carbide, Ti carbide, Nb carbide, Hf carbide or Mo carbide, or two or more thereof And a cathode having a structure covered with a mixture of the above.

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