JP4413713B2 - Metal halide lamp - Google Patents

Description

  The present invention relates to a metal halide lamp that essentially does not contain mercury in a discharge space used for an automotive headlamp or the like.

In a conventional metal halide lamp, a pair of electrodes having a shaft diameter of 0.3 mm or more are opposed to each other at a distance between electrodes of 5 mm or less inside a fireproof and translucent airtight container. The discharge medium such as halide and xenon is enclosed, and the lamp is lit at a lamp power of 60 W or less when stable. Moreover, the electrode of this metal halide lamp forms a curved surface with the tip that is the starting point of the arc having a radius of 1/2 or less of the diameter of the shaft portion. Here, this metal halide lamp does not contain mercury in its hermetic container. (For example, Patent Document 1)
JP 2003-242933 A (3rd, 4th page, FIG. 1)

  In metal halide lamps that do not enclose mercury, since the effect of mercury that evaporates quickly at the start of the lamp and increases the voltage cannot be obtained, it is difficult for the voltage to decrease even after the lamp has started, so a large current continues to be applied. The temperature of becomes high. As a result, the tip of the electrode at the highest temperature is melted and easily deformed, and when the electrode is deformed, the place where the arc is generated, that is, the starting point of the arc is moved, so that stable discharge is difficult to be performed and brightness flicker ( Thereafter, simply flickering.) Occurs. In addition, since the metal halide lamp that does not enclose mercury does not use mercury that has the effect of thickening the arc, the arc during discharge tends to be thin and unstable, and flickering is likely to occur.

  Patent Document 1 describes that flickering is less likely to occur by making the tip of the electrode a curved surface and preventing modification of the electrode structure. However, if the tip of the electrode is curved, the temperature may rise excessively, which not only facilitates electrode deformation but also makes the arc unstable and may cause flickering. There is.

  Recently, as described in Japanese Patent Application Laid-Open No. 2002-110083 and Japanese Patent Application Laid-Open No. 11-111215, with respect to such a flickering problem, tungsten containing thorium oxide doped with thorium oxide (hereinafter referred to as triated). Tungsten.) Electrodes are used. When triated tungsten is used as an electrode, it is known to stably promote arc discharge, and flickering can be suppressed. However, even if this tritated tungsten is used, there is a drawback that the electrode is deformed in a short time, the arc becomes unstable, and flickering occurs.

  An object of the present invention is to provide a metal halide lamp that suppresses the occurrence of flicker and the deformation of an electrode in a short time under the condition that the discharge space does not essentially contain mercury.

  A translucent airtight container having an arc tube portion forming a discharge space, sealing portions formed at both ends of the arc tube portion, a metal halide and a rare gas sealed in the discharge space, and essentially A discharge medium that does not contain mercury, a metal foil sealed inside the sealing portion, one end connected to the metal foil, and the other end opposed to each other in the discharge space, the tip portion Comprises a pair of electrodes having a straight rod shape and a diameter of 0.4 mm or less, the electrodes being triated tungsten electrodes doped with thorium oxide on an electrode composed mainly of tungsten, and the tip of the electrodes The average particle size Savg of the initial thorium oxide existing in the vicinity of the portion is 2 μm ≦ Savg ≦ 5 μm.

  According to the present invention, flickering and electrode deformation in a short time can be suppressed in a metal halide lamp that essentially does not contain mercury in the discharge space.

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

  The hermetic container 1 is made of, for example, translucent quartz glass and has a substantially elliptical arc tube portion 11 and sealing portions 121 formed of the same material as the arc tube portion 11 at both longitudinal ends thereof. 122. A discharge space 111 having a substantially cylindrical shape and an internal volume of 0.1 cc or less is formed in the arc tube portion 11 in the longitudinal direction. In the discharge space 111, an iodide which is a metal halide as a discharge medium is formed. Sodium, scandium iodide, zinc iodide, and xenon which is a rare gas are enclosed. Metallic sodium contained in sodium iodide and metallic scandium contained in scandium iodide mainly act as a luminescent metal, and metallic zinc contained in zinc iodide is a lamp voltage mainly replacing mercury. Acting as a forming medium, xenon acts primarily as a starting gas. As the halide, iodine having the lower reactivity than other halides is most preferable.

  Here, the discharge medium sealed in the arc tube portion 11 essentially does not contain mercury. 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. In other words, when the voltage of a metal halide lamp is increased to a required level by mercury vapor as in a conventional short arc lamp containing mercury, 20 to 40 mg per cc, or 50 mg or more in some cases is sealed. Then, it can be said that the amount of mercury of less than 2 mg is overwhelmingly small and essentially contains no mercury.

  Metal foils 21 and 22 made of, for example, molybdenum are sealed inside the crushed plate-like sealing portions 121 and 122, for example. Large end portions 311 and 321 having different diameters and small diameter shaft portions 312 and 322 are integrally formed at one end portions of the metal foils 21 and 22 on the discharge space 111 side, and, for example, tungsten is doped with thorium. Generally, one end of electrodes 31 and 32 made of a material called triated tungsten is connected by resistance welding so as to be almost integrated with the metal foils 21 and 22, and the other end of the electrodes 31 and 32 is an arc tube portion. 11 is extended to the discharge space 111 through the sealing portions 121 and 122 in the vicinity of the electrode 11, and is arranged so that the tips thereof are opposed to each other with a distance between electrodes of 5 mm or less. Here, the tip portions 311 and 321 of the electrodes 31 and 32 are located in the discharge space 111, and the small diameter portions 312 and 322 are located in the sealing portions 121 and 122, respectively.

  Coils 41 and 42 formed by winding a metal conductive wire several times are connected to the small diameter portions 312 and 322 of the electrodes 31 and 32 so as to be in contact with the outer peripheral surface thereof. The coils 41 and 42 are wound by a predetermined distance from the end portions on the metal foil 21 and 22 side toward the discharge space 111, and the other ends of the coils 41 and 42 are inherent in the sealing portions 121 and 122.

  In the metal foils 21 and 22, introduction conductors 51 and 52 are connected by welding or the like to the end opposite to the portion where the electrodes 31 and 32 are connected, and the other end of the introduction conductor 52 is It extends outside the sealing portion 122 and is connected so as to be substantially perpendicular to one end of the power supply terminal 53 formed in an L shape. The other end of the power supply terminal 53 extends in the direction of the introduction conductor 51 and substantially parallel to the sealing portions 121 and 122. The insulating tube 6 is attached to the power supply terminal 53 parallel to the sealing portions 121 and 122.

  A cylindrical outer tube 7 made of, for example, a material that blocks ultraviolet rays is provided outside the hermetic container 1 including these so as to cover the longitudinal direction thereof. A diameter-reduced portion 71 is formed at both ends of the outer tube 7 in the longitudinal direction, and the diameter-reduced portion 71 is glass-welded near the end of the sealing portion 122 opposite to the direction of the arc tube portion 11. In addition, the other reduced diameter portion (not shown) is glass-welded in the vicinity of the end portion of the sealing portion 121 opposite to the arc tube portion 11 direction.

  The outer tube 7 with the airtight container 1 covered inside is connected to the socket 9 via a fixed metal tool 8 formed so as to sandwich the outer peripheral surface thereof. A metal terminal 91 is formed along the outer peripheral surface of the small diameter portion of the socket 9, and the metal terminal 91 is electrically connected to the power feeding terminal 53 inside the socket 9. Although not shown, the introduction conductor 51 extending in the opposite direction to the arc tube portion 11 passes through the socket 9 and is located at the bottom portion of the socket 9.

  Next, the electrodes 31 and 32 will be described in detail. The electrodes 31 and 32 of the present embodiment are tritated tungsten electrodes doped with thorium oxide at a ratio of 1% by weight to tungsten, and the average particle size Savg of the initial thorium oxide existing at least near the tip of the electrode is It is formed so that 2 μm ≦ Savg ≦ 5 μm. Here, “initial” means a state in which the lamp is completed as a product through aging, a life test, etc., and is shipped to the market. An example of a method for manufacturing the electrodes 31 and 32 will be described. Tungsten powder and thorium oxide powder with a particle size of 1-6 μm are mixed in advance to produce a tritated tungsten powder, which is then placed in a mold and sintered to produce a sintered body. A fibrous (fiber) structure is formed by wire drawing. The triated tungsten electrode is secondarily recrystallized by high-temperature heat treatment and lighting such as aging after lamp incorporation. Thereby, it can manufacture by keeping the particle size of thorium oxide in triated tungsten in a suitable range.

  Here, before explaining the function and effect of the present invention, the function, electrode deformation, and flicker of the triated tungsten electrode will be described. FIG. 2 is a cross-sectional view of the vicinity of the tip surface of the electrode. Here, black dots in the figure are thorium oxide particles, and a thin layer on the surface of the electrode is a monoatomic layer 33 of thorium.

  When the metal halide lamp is turned on, arc discharge starts, and thorium oxide 33 contained in the triated tungsten starts to diffuse on the surfaces of the electrodes 31 and 32. The diffusion at this time is generally called grain boundary diffusion and intragranular diffusion, and it is known that grain boundary diffusion is fast diffusion through the boundary of tungsten crystal, and intragranular diffusion is slow diffusion through the crystal of tungsten. ing. Through these diffusions, thorium oxide that has reached the surfaces of the electrodes 31 and 32 forms a monoatomic layer 33 of thorium there. In the thorium monoatomic layer 33 formed on the surface, the work function is lower than that of the tungsten portion of the electrodes 31 and 32, and electrons are easily emitted from the portion, so that the starting point of the arc is stabilized. Therefore, in the case of the triated tungsten electrode, the starting point of the arc is generated in the portion of the monoatomic layer 33 of thorium formed at the tip of the electrode where the temperature becomes highest. The thorium monoatomic layer 33 suppresses deformation of the electrodes 31 and 32 due to arc discharge.

  However, thorium oxide disappears and the tips of the electrodes 31 and 32 are deformed as lighting and extinguishing are repeated or lighting is performed for a long time. In this deformed portion, thorium oxide disappears, and the monoatomic layer 33 of thorium is not formed on the surface, so that the work function becomes high and arc discharge is difficult to be performed. After the deformation of the electrode tip portion, thorium oxide particles are aggregated together in the portions closer to the sealing portions 121 and 122 than the tip portions of the deformed electrodes 31 and 32 because thorium oxide does not easily disappear. As the particle size increases, arc discharge starts from the thorium monoatomic layer 33 formed on the electrode surface in the vicinity. However, after a while, since the tips of the deformed electrodes 31 and 32 have risen in temperature, thorium oxide diffuses into the tips and temporarily forms a monoatomic layer 33 of thorium on the electrode surface. Arc discharge is generated from that portion. In this way, the starting point of the arc moves on the electrode surface due to the diffusion of thorium oxide, and flickering occurs.

  FIG. 3 is an enlarged view of the vicinity of the arc tube portion for explaining an example of the specification of the metal halide lamp of FIG. The tip portions 311 and 321 of the electrodes 31 and 32 have a diameter of 0.35 mm, the small diameter portions 312 and 322 have a diameter of 0.3 mm, the arc tube portion 11 has an inner diameter A of 2.7 mm, an outer diameter B of 6.0 mm, and a longitudinal length. The maximum length C in the direction is 6.5 mm, and the interelectrode distance D is 4.2 mm. The arc tube section 11 is filled with 0.2 mg of scandium iodide-sodium iodide-zinc iodide as a discharge medium and 10 atm of xenon as a rare gas as a discharge medium, and contains no mercury. Absent.

  FIG. 4 is a diagram in which the life test of 0 hours, 500 hours, and 1500 hours was performed to measure the presence or absence of flicker in the lamp specifications of FIG. 2 having different thorium oxide particle sizes. Here, in order to determine the presence or absence of flicker, after the lamps lit for each test time were stably lit for 4 minutes, the light quantity change rate was continuously measured for 5 minutes, and data as shown in FIG. There was no flicker when there was no change in the light amount continuously as in (a), and there was a change in the light amount of 5% or more compared to the 100% light amount at the start of measurement as in FIG. 5 (b). The case was flickering.

  In the lamp of test sample A in which the particle size S of an arbitrary 50 μm square thorium oxide at the initial electrode tip is 0.4 μm ≦ S ≦ 0.95 μm and the average particle size Savg is 0.7 μm, flickering occurs at 0 hours. However, flickering occurred at 500 hours and 1500 hours. Further, at 500 hours, thorium oxide disappears from the electrode tip to a distance of about 0.175 mm, that is, a distance corresponding to ½ of the electrode diameter, and although not shown, the tip of the electrode is rounded. It was deformed. Further, at 1500 hours, thorium oxide having a diameter of 0.35 mm equivalent to the electrode diameter disappeared from the tip of the electrode, and the deformation of the electrode was larger than that at 500 hours. Further, with respect to the particle size of thorium oxide, aggregation progressed with time, and the size gradually increased.

  In the lamp of the test sample B in which the initial thorium oxide particle size S is 1.2 μm ≦ S ≦ 3.1 μm and the average particle size is 2.3 μm, flickering occurs even after the test time of 500 hours and 1500 hours. I did not. Thorium oxide disappeared from the tip of the electrode to 0.07 mm corresponding to 1/5 of the electrode diameter at 500 hours, and disappeared to 0.088 mm corresponding to 1/4 at 1500 hours. Here, due to the disappearance of thorium oxide, a slight deformation was seen at the tip of the electrode, but the measurement results as shown in FIG. 4 did not greatly disturb the amount of light, and flickering also occurred visually. There wasn't. The particle size size of thorium oxide was not much different from the initial stage.

  The lamp of the test sample C in which the initial thorium oxide particle size S was 3.4 μm ≦ S ≦ 5.8 μm and the average particle size was 4.5 μm was almost in the same electrode state as the test sample B. Therefore, no flickering phenomenon was observed in this case.

  In the lamp of the test sample D in which the particle size S of the initial thorium oxide is 6.3 μm ≦ S ≦ 8.4 μm and the average particle size is 7.2 μm, the state of the electrode is not significantly different from that of the test samples B and C. Flicker has already occurred from 0 hours, and flicker has occurred since then.

  From the results, when the average particle size of the initial thorium oxide is small like the test sample A, the monoatomic layer of thorium on the surface of the electrode tip portion disappears by arc discharge as time passes, and the thorium oxide at the tip portion also It disappears and thorium impregnated in tungsten is exhausted. The tip of the electrode is in a tungsten state, and the electrode is deformed by heat. As a result, a single atomic layer of thorium formed on the surface away from the tip of the electrode, and a single atom of thorium that is temporarily generated on the surface of the tip of the electrode as the temperature of the tip of the electrode increases and thorium oxide moves. It is thought that the starting point of the arc moved by the layer and flickering occurred. Further, in this test sample A, thorium disappears excessively, and the lost thorium remains in the discharge space, so that it reacts with quartz glass and white turbidity is generated.

  On the other hand, when the average particle size of the initial thorium oxide is large as in the test sample D, since the monoatomic layer of thorium was not stably formed on the surface of the electrode from the initial stage, the starting point of the arc was It is thought that flickering occurred without stabilization.

  From the above, it is considered that the diffusion of thorium oxide is greatly related to the stable formation of a thorium monoatomic layer that is effective in suppressing flickering. If the particle size of thorium oxide is too small Since the diffusion rate of thorium oxide to the electrode surface is too high, thorium oxide disappears in a short time, and when the particle size of thorium oxide is too large, a monoatomic layer of thorium is not successfully formed on the electrode surface. From this, it is considered that the stable formation of the thorium monoatomic layer on the tip surface of the tungsten electrode is useful for preventing the movement of the starting point of the arc and suppressing the occurrence of flickering.

  For these reasons, the inventors have found that the size and location of thorium oxide particles are important for the generation of flickering and electrode deformation in the tritated tungsten electrode. That is, when the average particle size Savg of thorium oxide is about 2 μm ≦ Sav ≦ 5 μm as in test samples B and C, the diffusion rate of thorium oxide is not so fast that the disappearance time is not fast. The diffusion rate was not too slow and no monoatomic layer of thorium was formed on the electrode surface, and thorium oxide diffused at an appropriate rate, so that flickering did not occur and deformation of the electrode tip could be suppressed. Therefore, the average particle size Savg of thorium oxide in the vicinity of the initial electrode tip is preferably 2 μm ≦ Sav ≦ 5 μm. In addition, as a specific location “near the tip of the electrode”, it can be seen from the result of FIG. 4 that flickering occurs when thorium oxide at a distance up to half the electrode diameter disappears in the direction of the sealing portion. Therefore, a distance of at least 1/2 with respect to the diameter of the electrode is preferable in the direction from the electrode tip to the sealing portion.

  Therefore, in the present embodiment, in the triated tungsten electrode in which tungsten is doped with thorium oxide, the average particle size Savg of the initial thorium oxide existing near the tip portions 311 and 321 of the electrodes 31 and 32 is 2 μm ≦ Savg ≦ 5 μm. By doing so, the diffusion rate of thorium oxide can be controlled to an appropriate speed. Therefore, a thorium monoatomic layer can be stably formed on the surfaces of the electrodes 31 and 32, so that arc discharge can be stabilized for a long time, and flickering and deformation of the electrode in a short time are suppressed. be able to.

(Second Embodiment)
FIG. 6 shows a thorium oxide content in a triated tungsten electrode having a tip diameter of 0.4 mm, an initial thorium oxide particle size of 1.8 μm ≦ S ≦ 3.4 μm, and an average particle size of Savg 2.5 μm. FIG. 7 is a graph in which the average value of the luminous flux maintenance factor after performing a life test of 0 hours, 500 hours, 1000 hours, and 1500 hours in the lamp specifications of FIG. FIG. Here, the number of tests of each lamp is three. About each part of this 2nd Embodiment, the same part as each part of the discharge lamp apparatus of 1st Embodiment is shown with the same code | symbol, and the description is abbreviate | omitted.

  From the results, it can be said that the higher the content of thorium oxide is, the lower the luminous flux maintenance factor can be suppressed even when the test time elapses, and it can be said that the effect is particularly high when thorium oxide is 0.3% or more. Here, the upper limit of thorium oxide is not set. This is because, as described above, there is a tendency that as the weight percent of thorium oxide increases, the decrease in luminous flux maintenance factor tends to be suppressed. However, with the current technology, triated tungsten containing up to about 2 weight percent thorium oxide is manufactured. It is said that it can be done.

  Therefore, in this embodiment, in the triated tungsten electrode in which thorium oxide is doped into tungsten, the initial thorium oxide content of the electrodes 31 and 32 is 0.3% by weight or more, so that the luminous flux maintenance factor is lowered. Can be suppressed.

  The present invention is not limited to the above-described embodiment, and may be modified as follows, for example.

  As the electrode, a doped tungsten electrode formed by doping tungsten with aluminum, potassium, silicon, or the like, or a tritium tungsten electrode doped with thorium oxide on rhenium tungsten composed of tungsten and rhenium may be used.

The whole figure for demonstrating 1st Embodiment of the metal halide lamp of this invention. Sectional drawing of the tip part surface vicinity of an electrode. FIG. 2 is an enlarged view of the vicinity of an arc tube portion for explaining specifications of the metal halide lamp of FIG. 1. The figure which measured the presence or absence of the flicker of the lamp | ramp which performed the life test in the lamp | ramp specification of FIG. 3 from which the particle | grain size of thorium oxide differs. The figure which shows the example of the data which measured the light quantity change of the lamp | ramp. The figure which measured the average value of the luminous flux maintenance factor after performing a lifetime test in the lamp specification of FIG. 3 from which thorium oxide content differs. Figure showing graph of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Airtight container 11 Arc tube part 111 Discharge space 121,122 Sealing part 21,22 Metal foil 31,32 Electrodes 311,312 Tip part 41,42 Coil 51,52 Lead conductor 53 Feed terminal 6 Insulation tube 7 Outer pipe 8 Fixation 9 metal fittings

Claims (2)

A translucent airtight container having an arc tube portion forming a discharge space, sealing portions formed at both ends of the arc tube portion;
A discharge medium in which a metal halide and a rare gas are enclosed in the discharge space, and essentially free of mercury;
A metal foil sealed inside the sealing portion;
One end is connected to the metal foil, the other end is opposed to the discharge space, the tip is a straight bar, and a pair of electrodes having a diameter of 0.4 mm or less,
The electrode is a tritated tungsten electrode in which thorium oxide is doped on an electrode whose main component is tungsten, and the average particle size Savg of the initial thorium oxide existing near the tip of the electrode is 2 μm ≦ Savg ≦ 5 μm A metal halide lamp characterized by The metal halide lamp according to claim 1, wherein the triated tungsten electrode has an initial thorium oxide content of 0.3 wt% or more.

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