JP2007115615A - Discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress flickering, deterioration in luminous flux maintenance factor and the rise of a lamp voltage. <P>SOLUTION: The discharge lamp is provided with a light emitting tube 11 in which a discharging space 13 is formed with a discharging medium sealed inside; a transparent air tight container 1 with a pair of sealing parts 121 and 122 formed on both ends of the light emitting tube 11; and a pair of electrodes 31 and 32 with one end sealed by the sealing parts 121 and 122, and with the other end installed facing each other inside the discharging space 13. The electrodes 31 and 32 are composed of materials with tungsten as main components doped with a thorium oxide and tantalum and/or a tantalum oxide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a discharge lamp used for an automobile headlamp, a projector, or the like.

As a prior art, in a short arc discharge lamp having a substantially spherical arc tube and a cathode and an anode arranged opposite to each other in the arc tube, the crystal structure of the cathode tip portion is from the rear end side of the cathode. There is an invention of a short arc discharge lamp comprising a plurality of coarse crystals and containing 0.1% by mass or less of an electron-emitting material contained in the tip portion of the cathode. Here, thorium oxide is used as the electron-emitting material. (For example, Patent Document 1)
Japanese Patent Laid-Open No. 2002-110083

  As described in Patent Document 1, it is possible to obtain an effect of suppressing flickering by doping an electron-emitting material such as thorium oxide into a tungsten electrode, as disclosed in Japanese Patent Application Laid-Open Nos. 2002-110091 and 2001-243912. Already known.

  The effect of suppressing flickering is that thorium oxide in the electrode diffuses during lighting and reaches the electrode surface, and then reduces on the electrode surface to separate into metal thorium and oxygen. This metal thorium is the work function of the electrode. It is believed that this occurs because electrons are more likely to be emitted from the electrodes.

  However, oxygen generated during reduction is combined with tungsten of the electrode to become tungsten oxide. And since the melting point of the tungsten oxide is lower than that of tungsten, it was found that when the temperature of the electrode becomes high, it sublimates at a temperature lower than that of tungsten and adheres to the inner surface of the arc tube. As a result, the luminous flux maintenance factor decreases, or the lamp voltage increases as the distance between the electrodes increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a discharge lamp capable of suppressing a decrease in luminous flux maintenance factor and an increase in lamp voltage while suppressing flicker.

  In order to achieve the above object, a discharge lamp of the present invention has an arc tube portion in which a discharge space for enclosing a discharge medium is formed, and a pair of sealing portions formed at both ends of the arc tube portion. A translucent hermetic container, and one end sealed in the sealing portion and the other end is provided with a pair of electrodes opposed to each other in the discharge space, and the electrodes include thorium, yttrium, zirconium, hafnium, One or more kinds of electron-emitting substances selected from lanthanum and cerium oxides, and a main component doped with at least tantalum and / or tantalum oxide are made of a material comprising tungsten. To do.

  According to the present invention, it is possible to suppress a decrease in luminous flux maintenance factor and an increase in lamp voltage while suppressing flicker.

(First embodiment)
Hereinafter, a discharge lamp according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall view for explaining a first embodiment of a discharge lamp of the present invention.

  The hermetic vessel 1 is made of a material having a fire resistance that can sufficiently withstand a high temperature while the discharge lamp is lit, and a translucent material that can transmit the generated light with as little loss as possible, for example, quartz glass. The arc tube portion 11 having a substantially elliptical shape in the axial direction is formed at a substantially central portion in the tube axis direction. Plate-shaped sealing portions 121 and 122 made of the same material and having a pair of flat pinch surfaces and a pair of side surfaces corresponding to a thickness portion are formed at both ends of the arc tube portion 11.

  Inside the arc tube portion 11, in the axial shape, a central portion is substantially cylindrical, and tapered discharge spaces 13 are formed at both ends thereof. Here, the volume of the discharge space 13 is 0.1 cc or less in the case of a short arc type discharge lamp, and in particular, when the application is specified for an automobile, the internal volume of the discharge space is 0.01 cc to 0.04 cc. Is desirable.

  The discharge space 13 is filled with a discharge medium made of a metal halide and a rare gas. Metal halides include sodium, scandium halide, which mainly acts as a luminescent medium that generates visible light, zinc halide, which acts as a lamp voltage forming medium, and indium luminescence for the purpose of improving emission chromaticity during lighting. Of halide is enclosed. Most preferably, halides bound to these metals are bound to iodine, which is less reactive among halides. However, the halide to be bonded is not limited to iodine, but may be bromine or chlorine, and a plurality of halides may be used in combination.

  As the rare gas, xenon which has high luminous efficiency immediately after starting and mainly acts as a starting gas is enclosed. The pressure of xenon is preferably 5 atm or more, more preferably 10 to 15 atm at normal temperature (25 ° C.). In addition to xenon, neon, argon, krypton, or the like may be used as the rare gas, or a combination thereof may be used.

  Note that mercury is essentially not contained in the discharge space 13. This “essentially free of mercury” means that it does not contain any mercury, or accepts an amount of mercury of less than 2 mg per cc, preferably 1 mg or less. Considering that this amount was 20 to 40 mg per cc enclosed in the conventional short arc type mercury-containing discharge lamp, and in some cases 50 mg or more, it was less than 2 mg allowed in the discharge lamp of the present embodiment. The amount of mercury is overwhelmingly small and essentially free of mercury.

  The metal foils 21 and 22 made of, for example, molybdenum are sealed inside the sealing portions 121 and 122 so that the flat surfaces thereof are parallel to the pinch surfaces of the sealing portions 121 and 122. Electrodes 31 and 32 made of a material mainly composed of tungsten and doped with thorium oxide and tantalum or / and tantalum oxide are connected to ends of the metal foils 21 and 22 on the arc tube portion 11 side by welding. The electrodes 31 and 32 may be further doped with potassium. In this embodiment, thorium oxide is used as the electron-emitting material. However, among other oxides of yttrium, zirconium, hafnium, lanthanum, and cerium that have the same mechanism for improving the electron-emitting property of the electrode. It is possible to use one or a plurality of electron-emitting materials selected from

  The electrodes 31 and 32 have a stepped shape in which the distal end side has a larger diameter than the proximal end side, and the diameter of the large diameter distal end side is 0.40 mm or less. And the front end side of the electrodes 31 and 32 is arrange | positioned so that the front-end | tips may mutually oppose, maintaining the predetermined distance between electrodes within the discharge space 13. FIG. Here, the “predetermined interelectrode distance” is preferably 5 mm or less for a short arc lamp, and further about 4.2 mm when used for an automobile headlamp.

  A method for manufacturing the electrodes 31 and 32 will be described. First, powders of tungsten, thorium oxide, tantalum, tantalum oxide, etc. are mixed and stirred and sintered. Then, after the sintered body is manufactured, an electrode having a desired shape is formed by rolling and drawing. Here, when potassium is also doped during stirring, the recrystallization temperature can be increased. In other words, the degassing step is advantageous because the treatment can be performed at a relatively high temperature. In addition, the doping amount of potassium which can acquire an advantageous effect in that case is 25-75 ppm.

  In addition, one end of external lead wires 41 and 42 made of molybdenum is connected to the end portions of the metal foils 21 and 22 on the opposite side to the arc tube portion 11 by welding or the like. The other end sides of the external lead wires 41 and 42 extend to the outside of the sealing portions 121 and 122.

  On the outside of the airtight container 1 configured as described above, a cylindrical outer tube 5 is provided so as to cover most of the airtight container 1 along the tube axis, and both end portions thereof are both end portions of the airtight container 1. Connected by welding to the outer end of the. The outer tube 5 has translucency and ultraviolet blocking properties by adding at least one or a plurality of oxides such as titanium, cerium, aluminum, potassium, and barium to quartz glass.

  In the space sealed by the hermetic container 1 and the outer tube 5, for example, nitrogen can be sealed, or a rare gas such as neon, krypton, argon, xenon or the like can be sealed or mixed. With this configuration, it is possible to improve the startability of the lamp and to make it difficult to contain moisture in the space during manufacture. In addition, since the rare gas sealed in the outer tube 5 has a specific thermal conductivity, when a plurality of rare gases are mixed and sealed, light emission is achieved by adjusting their mixing ratio. The temperature at the time of lighting of the tube part 11 can be kept at a predetermined temperature. That is, when neon and xenon are mixed and sealed, the temperature of the arc tube section 11 can be lowered by increasing the proportion of neon having a high thermal conductivity, and conversely the proportion of xenon having a low thermal conductivity can be increased. Thus, the temperature of the arc tube portion 11 can be increased.

  A socket 6 is connected to the sealing portion 121 side of the outer tube 5 that holds the airtight container 1 inside. In this connection, a metal band 71 attached to the outside of the outer tube 5 is formed on the socket 6 by four metal tongues 72 (two of which are shown in FIG. 1) extended. It is done by pinching. A metal terminal 61 for supplying power from the lighting circuit is formed along the outer peripheral surface at the end of the socket 6, and the external lead wire 42 extending toward the outside of the sealing portion 122 and one end thereof are formed. Are connected, and the other end is connected inside the socket 6 to a power supply terminal 81 extending in the direction of the socket 6. And most of the power supply terminal 81 substantially parallel to the tube axis is covered with an insulating tube 82 made of ceramic or the like so that the potential of the power supply terminal 81 during lighting is not affected.

  The discharge lamp constituted by these is lit at about 35 W when stable, and at about 75 W, which is about twice as much power as when stable, in order to accelerate the rise of the luminous flux at the start.

  FIG. 2 is an enlarged view for explaining the specification of the discharge lamp of FIG. 1, and the dimensions, materials, and the like are as follows.

Discharge vessel 1: made of quartz glass, volume of discharge space 13 = 0.026 cc, inner diameter A = 2.5 mm, outer diameter B = 6.2 mm, maximum length C in the longitudinal direction C = 7.8 mm,
Discharge medium: sodium iodide = 0.27 mg, scandium iodide = 0.14 mg, zinc iodide = 0.08 mg, indium bromide = 0.005 mg, a total of 0.5 mg of metal halides, xenon = 11.0 atm, Mercury = 0mg
Electrodes 31 and 32: Tungsten oxide doped with thorium oxide + tantalum, tip diameter = 0.38 mm, tip length = 1.0 mm, base end diameter = 0.30 mm, distance between electrodes D = 4.4 mm
FIG. 3 is a diagram for explaining the luminous flux maintenance factor when the test is performed by changing the weight ratio of tantalum to 0 to 30% by weight in the lamp specification of FIG. 2, and FIG. 4 is a graph showing FIG. FIG. The weight ratio of thorium oxide in this test is 1.0% by weight, and the number of tests is 6 for each. In addition, the test conducted this time is a flashing lighting test in the EU 120 minute mode, which is the life test condition of the same after 15 ECE aging cycles which are the aging conditions specified in JEL-215 of the Japan Light Bulb Industry Association. is there.

  As shown in the figure, it is understood that the luminous flux maintenance factor changes by changing the weight ratio of tantalum. For example, in the case of the lamp 4 having a tantalum weight ratio of 10% by weight, a higher luminous flux maintenance factor can be achieved than a conventional lamp not doped with tantalum. In addition, when the amount of tantalum doped is small, such as the lamp 1 doped with 0.01% by weight of tantalum, the effect is even higher. However, it can also be seen that the lamp 5 and the lamp 6 doped with more than 10% by weight of tantalum have a lower luminous flux maintenance factor than the conventional lamps not doped with tantalum. The result is also clear in the relationship between the tantalum content and the luminous flux maintenance factor after 1000 hours shown in FIG.

  The reason why the luminous flux maintenance factor is improved by doping an appropriate amount of tantalum as described above is considered as follows.

  In conventional lamps not doped with tantalum, thorium oxide that has existed inside the electrode moves to the electrode surface due to the phenomenon of so-called grain boundary diffusion that moves through the boundaries of the tungsten crystals (hereinafter referred to as grain boundaries) during lighting. Then, it is reduced and separated into metallic thorium and oxygen. The metal thorium diffuses and reaches the electrode tip that is hotter than the other electrode parts because the arc spot is formed, and lowers the work function at the tip part. Stabilizes spots and suppresses flicker. However, the oxygen separated by reduction combines with tungsten to form tungsten oxide. Since this tungsten oxide has a lower melting point than tungsten, it sublimates and adheres to the inside of the arc tube when the electrode temperature rises, so that the luminous flux maintenance factor decreases.

  On the other hand, as shown in FIG. 6, tantalum has a work function of around 4.20 eV when tungsten is doped in a small amount, and is lower than about 4.61 eV, which is the work function of pure tungsten. I understand. (Note that the work function when tungsten is doped with a small amount of thorium is about 3.50 eV) Therefore, when tantalum is doped, the work function becomes lower than that of a tungsten electrode, and the work function is the same as when thorium is used. Decreases, and the arc spot is stabilized. In addition, tantalum has an effect of delaying the grain boundary diffusion of thorium oxide in order to strengthen the bond strength of the tungsten crystal grain boundary. Accordingly, it is possible to suppress the excessive generation of oxygen that forms the tungsten oxide, so that it is possible to suppress the sublimation of the tungsten oxide and adhere to the inside of the arc tube, thereby suppressing the decrease in the luminous flux maintenance factor. .

  However, when the weight ratio of tantalum is increased, the melting point of the electrode itself is lowered as shown in FIG. That is, if the temperature of the electrode rises, the electrode is likely to scatter and adhere to the inner surface of the arc tube to cause blackening, thereby reducing the luminous flux maintenance factor.

  The weight ratio of tantalum is also related to the lamp voltage during the lifetime. FIG. 8 is a diagram for explaining the lamp voltage change in the test of FIG. 3, and FIG. 9 is a graph of FIG.

  As can be seen from the results, when the weight ratio of tantalum is 10% by weight or less, an increase in lamp voltage can be suppressed as compared with a conventional lamp not doped with tantalum. Moreover, if tantalum is 1.0 weight% or less, a raise of a lamp voltage can be suppressed further. However, on the contrary, if tantalum exceeds 10% by weight, it can be seen that the amount of change in lamp voltage is large.

  The increase in the lamp voltage is mainly related to the deformation of the electrode tip during the lifetime. That is, in the conventional lamp which is not doped with tantalum, the electrodes are likely to disappear as described above, and as a result, the distance between the electrodes is shortened, so that the lamp voltage is increased. In addition, thorium oxide gradually disappears during the lifetime, so that the work function increases. If the work function is increased, electrons are not easily emitted, so that the lamp voltage is increased.

  On the other hand, when the weight ratio of tantalum is 10% by weight or less, the crystal grain boundary of tungsten is strengthened, so that thorium emission is suppressed and tungsten oxide is hardly formed. In addition, since the melting point can be kept relatively high, electrode disappearance hardly occurs. On the other hand, when the weight ratio of tantalum exceeds 10% by weight, the electrodes disappear and the distance between the electrodes is shortened, so that the lamp voltage increases.

  For these reasons, the weight ratio of tantalum is preferably 10% by weight, more preferably 1.0% by weight or less. In the present invention, the effect is obtained only by doping a small amount of tantalum, and therefore the lower limit is not particularly set. That is, if even a small amount of tantalum is doped, it means that it is included in this range.

  FIG. 10 is a diagram for explaining the flickering non-defective rate when the same test as in FIG. 3 is performed by changing the weight ratio of thorium oxide to 0 to 1.0% by weight in the lamp specification of FIG. It is. In this test, the case where the light amount hardly changes with time as shown in FIG. 11A is regarded as a non-flickering non-defective product, and the light amount is 5% or more as compared with the light amount of 100% with respect to time as shown in FIG. The case where it flickers was regarded as a defective product. In addition, the content of tantalum in the test is 1.0% by weight, and the number of tests is 10 for each.

  FIG. 10 shows that flicker can be suppressed by doping at least 0.3 wt% or more of thorium oxide. Therefore, it is preferable that the thorium oxide is doped by 0.3% by weight or more. However, if the amount of thorium oxide increases, it may cause white turbidity and the like, so it is desirable that the weight ratio is 2.5% by weight or less.

  Therefore, in this embodiment, by using a tungsten material doped with thorium oxide and tantalum for the electrodes 31 and 32, tantalum strengthens the grain boundary of tungsten while suppressing flickering, thereby maintaining the luminous flux maintenance factor. And a rise in lamp voltage can be suppressed.

  In addition, by setting the weight ratio of doped tantalum to 10.0% or less, a decrease in luminous flux maintenance factor and an increase in lamp voltage can be suppressed. By setting the weight ratio to 1.0% or less, a higher effect can be obtained. Can do.

  In addition, by selecting thorium oxide as the electron emitting material, the electrodes 31 and 32 can be used at a higher temperature than when other radioactive materials are used. Moreover, flicker can be suppressed by making the weight ratio of doped thorium oxide 0.3% or more.

  Moreover, it can process at high temperature at the time of the degassing process of an electrode by setting it as the structure by which potassium is further doped to the electrodes 31 and 32. FIG.

  Furthermore, even when the electrode of the material of the present invention is used in a discharge lamp that is essentially free of mercury and is likely to flicker, it is possible to suppress a decrease in luminous flux maintenance factor and an increase in lamp voltage while suppressing flicker. it can.

The whole figure for demonstrating 1st Embodiment of the discharge lamp of this invention. The enlarged view for demonstrating the specification of the discharge lamp of FIG. The figure for demonstrating the luminous flux maintenance factor when changing the weight ratio of a tantalum and testing. FIG. 4 is a graph of FIG. 3. The figure for demonstrating the relationship between tantalum content and the luminous flux maintenance factor at the time of 1000 hours progress. The figure for demonstrating the work function of a tantalum. The figure for demonstrating the relationship between the weight ratio of a tantalum, and melting | fusing point. The figure for demonstrating the lamp voltage change in the test of FIG. FIG. 9 is a graph of FIG. FIG. 3 is a diagram for explaining a flickering non-defective rate when a test is performed by changing the weight ratio of thorium oxide in the lamp specification of FIG. 2. The figure for demonstrating determination of a flicker presence or absence.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Airtight container 11 Arc tube part 121,122 Sealing part 13 Discharge space 131 Horizontal part 14 Metal halide 21,22 Metal foil 31,32 Electrode 41,42 External lead wire 5 Outer tube 6 Socket 71 Metal band 72 Tongue piece 81 Feeding terminal 82 Insulating tube

Claims (6)

A translucent airtight container having an arc tube portion in which a discharge space for enclosing a discharge medium is formed, and a pair of sealing portions formed at both ends of the arc tube portion;
One end is sealed by the sealing portion, and the other end includes a pair of electrodes disposed opposite to each other in the discharge space,
The electrode comprises one or more electron-emitting materials selected from thorium, yttrium, zirconium, hafnium, lanthanum, and cerium oxides, and a main component doped with at least tantalum and / or tantalum oxide from tungsten. A discharge lamp characterized in that it is made of a material.   The discharge lamp according to claim 1, wherein a weight ratio of tantalum and / or tantalum oxide doped in the electrode is 10.0% or less, more preferably 1.0% or less.   The discharge lamp according to claim 1 or 2, wherein the electron-emitting material doped in the electrode is thorium oxide.   The discharge lamp according to any one of claims 1 to 3, wherein a weight ratio of the electron-emitting substance doped in the electrode is 0.3% or more.   The discharge lamp according to any one of claims 1 to 4, wherein the electrode is further doped with potassium. 6. The discharge lamp according to claim 1, wherein the discharge medium is essentially free of mercury.

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