JP2006185859A - Sealing line for discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sealing line for a discharge lamp such as a cold-cathode fluorescent lamp used as the back light of a liquid crystal display (LCD) of a personal computer capable of solving problems like damage to a sealing line caused by gas leakage and brittleness. <P>SOLUTION: In this sealing line, one end is welded to an electrode disposed in a glass bulb of the discharge lamp, and an external lead is welded to the other end. The material of the sealing line is a molybdenum containing a CaO of 0.05 to 0.3% by weight ratio. A material formed by adding a nickel of 0.005 to 0.01% by weight ratio to that material can provide more excellent properties. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a discharge lamp such as a cold cathode fluorescent lamp used as a backlight of a liquid crystal display device (LCD) such as a personal computer, and more particularly to a sealing line of the discharge lamp.

  A liquid crystal display (LCD) used for OA equipment such as a personal computer or a word processor has a backlight for illuminating the LCD. A cold cathode fluorescent lamp is used as the light source of the backlight.

  An electrode portion such as a cold cathode fluorescent lamp is composed of an electrode portion, a sealing wire, and an external lead wire. The electrode portion has a cup shape, and the material is niobium, molybdenum, nickel, tungsten, or the like. Further, since the sealing wire is glass-sealed, it is tungsten, molybdenum, kovar, or zimet wire having a thermal expansion coefficient similar to that of quartz glass. Furthermore, the material of the external lead wire is nickel, dimethyl or the like. These parts are usually joined by resistance welding to constitute an electrode.

  FIG. 1 shows a discharge lamp of this type, in which an electrode portion 2 and a sealing wire 3 are manufactured separately and joined by welding. Conventionally, the electrode part 2 and the sealing wire 3 are made of nickel as the cup-shaped electrode part and the Kovar with high ductility as the sealing wire (pin) 3. Thereafter, molybdenum having excellent sputtering resistance was adopted as the material of the electrode part. The thermal conductivity of Kovar is 17 W / m · K, while that of molybdenum is about 160 W / m · K. Similarly, molybdenum has a higher electrical conductivity. Further, since molybdenum and Kovar have similar thermal expansion coefficients, the same glass as that of Kovar (so-called Kovar glass) can be used as sealing glass.

  In the above discharge lamp, the cup-shaped electrode part and the sealing wire (pin) are integrated by electric resistance welding, but when the electrode part material is nickel, the sealing wire material is molybdenum having a high melting point. Even if it exists, since it can weld at comparatively low temperature, problems, such as embrittlement of a sealing wire, do not arise. Even when the electrode portion is molybdenum, even when the sealing wire is Kovar, the melting point of Kovar is low and the ductility is high, so that the problem of embrittlement does not occur.

  However, when the cup-shaped electrode part is molybdenum and the sealing wire is also molybdenum, since the melting point of both is high, the welding temperature becomes high, and further, even when sealed with glass, it is heated to 1000 ° C. or higher. There was a problem that the sealing wire made of molybdenum was recrystallized and embrittled by heating twice. When this type of discharge lamp is assembled to a liquid crystal display, the sealing wire is bent, so that if this sealing wire is brittle, it may be broken during bending.

  As a molybdenum material having heat resistance that hardly causes embrittlement even when heated to a high temperature, there is a molybdenum material added with calcium as shown in Patent Document 1 by the present applicant. This material is molybdenum containing 0.02 to 0.2% by weight of calcium, and has been used well for applications such as a tube material that requires heat resistance. In addition, a heat-resistant molybdenum material as shown in Patent Document 2 by the applicant of the present application is known as a material excellent in workability and superior in heat resistance to conventional molybdenum materials. The heat-resistant molybdenum material contains 0.05 to 0.3% by weight of calcium in terms of CaO, 0.02 to 0.1% by weight of nickel, and the balance is molybdenum.

Japanese Patent Publication No. 3-19293 Japanese Patent Laid-Open No. 3-90532

  However, the materials described in Patent Documents 1 and 2 have been used exclusively as materials incorporated into the interior of the electron tube itself, such as an anchor, support, grid, etc. of the electron tube, and are used for the glass sealing part of the discharge lamp. It never happened. Moreover, since the material described in Patent Document 2 contains 0.02 to 0.1% by weight of nickel, there is a problem in workability, and fine streaks in the drawing direction are formed on the wire surface during the drawing process. There was a problem of sticking. If such a streak is present on the surface, there has been a fatal problem that gas leaks after glass sealing.

  Therefore, the present invention has an object to provide a sealing wire that has high welding strength with respect to an electrode portion made of molybdenum, is not easily embrittled even by heating during welding or glass sealing, and does not cause problems such as gas leakage. .

  In order to solve the above problems, the present invention employs the following configuration. That is, the discharge lamp sealing wire according to the present invention is characterized in that the material is molybdenum containing 0.05 to 0.3% of CaO by weight. As this sealing wire, the one containing 0.005 to 0.01% by weight of nickel as described in claim 2 is preferable.

  This discharge lamp sealing wire is molybdenum containing 0.05 to 0.3 wt% of CaO as described above. Thus, molybdenum containing a trace amount of CaO has a high recrystallization temperature and does not recrystallize to about 1400 ° C. For this reason, recrystallization does not progress so much even by heating at the time of resistance welding (about 1400 to 1500 ° C.) and does not become brittle.

  In addition, when a small amount of nickel is contained in molybdenum, ductility is improved and bending strength (number of repeated bendings) is improved. However, if the amount of nickel is increased, workability is deteriorated. Fine cracks in the longitudinal direction occur. For example, when the nickel content is 0.02 to 0.1 wt% as in the material described in Patent Document 2, such a problem occurs, so that it is not suitable as a sealing wire.

  Therefore, as a result of various tests, in the present invention, the nickel amount is set to 0.005 to 0.01 wt%. It has been found that when this amount is used, there is no problem in ductility and workability, and a molybdenum wire having a high bending strength with no scratches on the surface can be obtained.

  As described above, the discharge lamp sealing wire according to the present invention is made of a material obtained by adding a trace amount of calcium oxide to molybdenum, and therefore can be manufactured relatively easily. And since the recrystallization temperature is high, when used as a sealing wire that is repeatedly heated and often bent after heating, it exhibits excellent performance that has not been obtained in the past. In addition to the above calcium oxide, the addition of a very small amount of nickel can further improve the strength.

  Embodiments of the present invention will be specifically described below. The sealing wire of the present invention is used in a discharge lamp (discharge cold cathode fluorescent lamp) as illustrated in FIG. The fluorescent lamp 1 has, for example, a straight tube shape with an outer diameter of about 2.6 mm, an inner diameter of 1.6 mm, and a length of about 200 mm. In terms of material, sealing portions 5 and 5 are provided at both ends of a tubular glass bulb 2 made of borosilicate glass or aluminosilicate glass having a linear expansion coefficient of 5 to 5.5 ppm, and electrode portions are provided on the sealing portions. An electrode in which 4 and the sealing wire 3 are integrated by welding 10 is sealed. A fluorescent film 11 is provided on the inner surface of the glass bulb 2.

  This type of electrode is often made of tungsten, molybdenum or alloys thereof, but recently there is a tendency to use molybdenum because of the high price of glass that is compatible with tungsten. For this reason, in the following description, an example using molybdenum as a material will be described. The sealing wire 3 in the electrode in which the electrode portion 4 and the sealing wire 3 are joined and integrated has, for example, an outer diameter of about 0.8 mm, and as shown in FIG. 2, a bead glass coating layer 7 made of Kovar glass. Sealed.

  Moreover, the electrode part 4 is a cup shape in which the hollow part 4a was formed, and the dimensions are, for example, an outer diameter of 1.2 mm, an inner diameter of 0.9 mm, and a length of about 5 mm. The external lead wire 8 is a nickel wire and is welded to the rear end portion of the sealing wire 3.

  The sealing wire 3 is manufactured by a known powder metallurgy method. That is, calcium and nickel are added to and mixed with molybdenum powder as a raw material, and heated in a non-oxidizing atmosphere such as a hydrogen atmosphere to perform preliminary sintering and main sintering to obtain an ingot having a predetermined size. The ingot is subjected to swaging processing and drawing processing to obtain a wire having a predetermined size. In the present invention, trace amounts of calcium oxide and nickel are added to molybdenum which is the main raw material, and this addition may be added in the form of a water-soluble compound as in the case of known doping.

  The obtained wire is subjected to necessary processing such as cutting and polishing to obtain a sealed wire having a predetermined size. This sealing wire is joined to the outer end portion of the cup-shaped electrode portion by electric resistance welding. At the time of this welding, it is common to perform welding with a Kovar foil or the like sandwiched between the cup-shaped electrode portion and the front end surface of the sealing wire.

  The outer peripheral part of the sealing wire integrated with the electrode part by welding is sealed with glass. As this glass, a glass having a thermal expansion coefficient substantially equal to that of molybdenum is used. At the time of sealing, the sealing wire is heated to 1000 ° C. or higher in order to melt the glass. A nickel wire as a lead wire is welded to the rear end portion of the sealing wire. The welding temperature at this time is relatively low, and molybdenum recrystallization does not occur.

  This sealing wire is welded to a molybdenum electrode portion having excellent heat resistance and resistance to sputtering, but since the recrystallization temperature is high, embrittlement due to welding or sealing does not occur. Further, even if nickel is added, the amount added is very small, so that the workability is not significantly reduced, and cracks due to swaging or drawing are hardly generated on the surface. For this reason, the problem of gas leak does not arise. In addition, discharge lamps used as backlights for liquid crystal displays often bend the lead wire at a right angle or more when assembled, but even if this bending force acts on the sealing wire or welded part, it is ductile by nickel. Has improved, so there will be no accidents such as scratches or breakage.

  Doping was performed by dissolving nickel nitrate in water or ethanol so that a nickel amount equivalent to 0.01 wt% was added to molybdenum powder having an average particle size of 2.5 microns. As described above, the amount of nickel was preferably 0.005 to 0.01 wt%. When the amount of Ni is larger than this, workability is deteriorated and the surface of the wire is easily damaged. On the other hand, if the amount of nickel is less than this, the sintering property, ductility and the like are not improved.

  Calcium oxide (CaO) was further added to the molybdenum powder doped with nickel as described above. The amount added was 0.1 wt%. The amount of CaO is preferably 0.05 to 0.3%, and if it is less than this range, the effect of preventing embrittlement can not be expected, and if it is too much, workability deteriorates and cracks are likely to occur. Neither is preferred. This addition may be mixed as a powder or may be sprinkled and mixed as a liquid.

  The obtained powder was dried and press-molded in a predetermined mold, followed by preliminary sintering and main sintering in a hydrogen stream. The obtained ingot was swaging processed and then drawn to obtain a line having a predetermined dimension. The surface of this wire was chemically cleaned (electropolishing may be performed) to remove the processing lubricant, and then cut into a predetermined length to obtain a sealed wire.

  The obtained sealing wire was welded to the electrode part (denoted by 10), and the nickel wire 8 as the external lead wire was joined by resistance welding. Thereafter, the sealing wire portion 3 was heated with a heater in a non-oxidizing atmosphere to weld (seal) Kovar glass (manufactured by Nippon Electric Glass Co., Ltd., product number BFK). As a result, the electrode part and the glass winding part (sealing part) were physically and hermetically bonded. The length of the glass winding part was 2-3 mm, and the outer diameter was about 2 mm.

  The end portion of the arc tube (glass bulb) was welded and sealed to the above-mentioned glass winding portion, followed by annealing treatment. Subsequently, a cold cathode fluorescent lamp was completed through an exhaust process in the arc tube, a mercury introduction process, and a lead wire solder finishing process. This discharge lamp was practically excellent because no gas leak occurred and the strength of the sealing portion was high.

  As is clear from the above description, the sealing wire for a discharge lamp according to the present invention can be manufactured relatively easily by powder metallurgy, and has aspects such as electrical conductivity, thermal conductivity, and thermal expansion coefficient. And excellent in bending strength and the like. It goes without saying that this sealing wire can be used for other applications requiring brittleness resistance and heat resistance.

It is a partial cross section figure of a discharge lamp. It is an enlarged view of the principal part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge lamp 2 Glass bulb 3 Sealing wire 4 Electrode part 5 Sealing part 7 Sealing glass 8 External lead wire

Claims (2)

A sealing wire in which one end is joined to an electrode portion arranged in a glass bulb of a discharge lamp and an external lead wire is joined to the other end, and the material thereof is 0.05 by weight of CaO. A sealing wire for a discharge lamp, which is molybdenum containing ˜0.3%. The sealing wire for a discharge lamp according to claim 1, containing nickel in a weight ratio of 0.005 to 0.01%.

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