JP2008147085A - Metal halide lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal halide lamp of high color temperature, with crack leakage hardly occurring, and substantially containing no mercury. <P>SOLUTION: The metal halide lamp is equipped with an airtight container 1 which has a discharge part 11 with discharge space 14 formed inside, a discharge medium in which a metal halide 2 containing at least scandium halide and sodium halide and rare gas are filled in the discharge space 14 and mercury is not contained in substance, a pair of electrodes 3a2, 3b2 of which tip is arranged oppositely in the discharge space 14. The mol ratio of sodium halide to scandium halide is 1.5 or less, and the metal halide 2 contains zinc halide of 1.0 wt.% or more and 5.0 wt.% or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an essentially mercury-free metal halide lamp used for automobile headlamps and the like.

  A metal halide lamp that does not contain mercury (hereinafter referred to as a mercury-free lamp) is known, for example, from Japanese Patent Application Laid-Open No. 2004-288629 (Patent Document 1). At present, the discharge medium of mercury-free lamps is mainly composed of sodium-scandium metal halide and xenon. In addition, as inventions of sodium-scandium-based mercury-free lamps, JP-A-11-238488 (Patent Document 2), JP-A-2002-93368 (Patent Document 3), JP-T-2004-528686 (Patent Document) 4) is known.

  The mercury-free lamps described in Patent Documents 1 to 4 are inventions for the purpose of obtaining characteristics equivalent to or higher than those of a metal halide lamp containing mercury at a color temperature of about 4000K. On the other hand, recently, there is a need for a lamp having a high color temperature exceeding 5000K, and research and development of a mercury-free lamp having a high color temperature and good characteristics is being promoted.

JP 2004-288629 A JP 11-238488 A JP 2002-93368 A Special table 2004-528686 gazette

  In a sodium-scandium-based mercury-free lamp, the balance between scandium halide and sodium halide is the most important for achieving a high color temperature. However, it has been confirmed that when the enclosure balance of sodium and scandium is adjusted so that the color temperature is 5000 K or higher, cracks are generated in the sealing portion and lamps that cause leaks (hereinafter referred to as crack leaks) occur frequently.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a metal halide lamp which is essentially mercury-free and has a high color temperature and is unlikely to cause crack leakage.

  In order to achieve the above object, a metal halide lamp according to the present invention includes an airtight container having a discharge portion in which a discharge space is formed, a metal halide containing at least scandium halide, sodium halide, and rare earth in the discharge space. An essentially mercury-free discharge medium encapsulated with a gas, and a pair of electrodes whose ends are opposed to each other in the discharge space, wherein the molar ratio of sodium halide to scandium halide is 1.5 or less The metal halide further contains 1.0 wt% or more and 5.0 wt% or less of zinc halide.

  According to the present invention, occurrence of crack leak can be suppressed in a metal halide lamp having a high color temperature and essentially free of mercury.

(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 for explaining a first embodiment of a metal halide lamp of the present invention.

  The hermetic vessel 1 constituting the discharge vessel of the metal halide lamp has an elongated shape made of quartz glass, and a substantially elliptical discharge portion 11 is formed at a substantially central portion thereof. Plate-shaped sealing portions 12a and 12b are formed at both ends of the discharge portion 11, and cylindrical non-sealing portions 13a and 13b are formed at both ends thereof. The airtight container 1 may be made of not only quartz glass but also a material having excellent heat resistance and translucency such as ceramic.

  A discharge space 14 having a substantially cylindrical shape at the center and a tapered shape at both ends is formed in the discharge portion 11 in the axial direction. The volume of the discharge space 14 is preferably 10 to 40 μl when an application is designated for a headlight of an automobile.

  The discharge space 14 is filled with a discharge medium containing the metal halide 2 and a rare gas.

  The metal halide 2 is composed of scandium halide, sodium halide, indium halide, and zinc halide. The molar ratio of sodium halide to scandium halide must be 1.5 or less in order to make the color temperature 5000 K or more. In addition, zinc halide is encapsulated for the purpose of suppressing electrode dissolution, and it is desirable that the encapsulated amount is very small. A suitable amount of zinc halide in the present invention is 1.0% by weight or more and 5.0% by weight or less.

  Here, as the halogen bonded to the metal halide 2, it is most preferable to select iodine having low reactivity among the halogens. However, when all of the metal halide is combined with iodine and sealed in the discharge space 14, electrode melting is likely to occur during lighting, so it is desirable to combine halogen other than iodine such as bromine with iodine.

  As the rare gas, xenon which has high luminous efficiency immediately after starting and mainly acts as a starting gas is enclosed. Note that the pressure of the rare gas desirably affects the rise of the luminous flux, and is preferably 8 to 18 atm at room temperature (25 ° C.). In addition to xenon, neon, argon, krypton, or the like may be used, or a combination thereof may be used.

  Here, the discharge space 14 essentially does not contain mercury. This “essentially mercury-free” means that it contains no mercury at all, or an amount equivalent to that which is hardly enclosed even when compared with a conventional mercury-containing discharge lamp, for example, less than 2 mg per ml, preferably Shall be allowed even in the presence of mercury of 1 mg or less.

Mounts 3a and 3b are sealed inside the sealing portions 12a and 12b.
The mounts 3a and 3b include metal foils 3a1 and 3b1, electrodes 3a2 and 3b2, coils 3a3 and 3b3, and external lead wires 3a4 and 3b4.

  Metal foil 3a1, 3b1, for example, a thin metal plate made of molybdenum.

  The electrodes 3a2, 3b2 are straight rods and are made of a material mainly composed of tungsten, for example, a material obtained by doping tungsten with thorium oxide. The front ends thereof are opposed to each other while maintaining a predetermined inter-electrode distance in the discharge space 14. Here, the “predetermined inter-electrode distance” is preferably an apparent inter-electrode distance of 5 mm or less for a short arc lamp and about 4.5 mm when used for an automotive headlamp. Further, the diameter R of the tip portion of the electrodes 3a2, 3b2 is preferably not less than 0.25 mm and not more than 0.38 mm.

  On the other hand, the base end side is connected to the end of the metal foils 3a1, 3b1 on the discharge part 11 side by welding. That is, the electrode portions from the joint portions with the metal foils 3a1 and 3b1 to the discharge space 14 are sealed with the quartz glass of the sealing portions 12a and 12b.

  The coils 3a3 and 3b3 are made of, for example, doped tungsten, and are spirally wound around the electrodes 3a2 and 3b2 from the end portions of the metal foils 3a1 and 3b1 toward the discharge space 14.

  The external lead wires 3a4 and 3b4 are made of, for example, molybdenum, and are connected to end portions of the metal foils 3a1 and 3b1 on the opposite side to the discharge portion 11 by welding or the like. The other end sides of the external lead wires 3a4 and 3b4 extend to the outside of the sealing portions 12a and 12b along the tube axis. Note that one end of an L-shaped support wire 3c made of nickel is connected to the lead wire 3b4 on the front end side extending to the outside, and the other end extends in the direction of a socket 6 described later. A portion of the support wire 3c parallel to the tube axis is covered with an insulating sleeve 4 made of ceramic.

  A cylindrical outer tube 5 having an action of blocking ultraviolet rays by adding an oxide such as titanium, cerium, or aluminum to quartz glass is provided outside the hermetic container 1 configured as described above along the tube axis. The airtight container 1 is provided substantially concentrically. These connections are made by melting the cylindrical non-sealing portions 13a, 13b at both ends of the hermetic container 1 and both ends of the outer tube 5. Note that the space formed by the hermetic container 1 and the outer tube 5 can be filled with a rare gas such as nitrogen, neon, argon, xenon, or a mixture of two or more.

  A socket 6 is connected to the non-sealed portion 13a side of the outer tube 5 in a state where the hermetic container 1 is covered inside. The metal band 71 attached to the outer peripheral surface of the outer tube 5 in the vicinity of the non-sealing portion 13a is connected to the four metal tongue pieces formed on the opening end of the socket 6 on the airtight container 1 holding side. 72 (two are shown in FIG. 1). And in order to strengthen a connection further, the contact point of the metal band 71 and the tongue piece 72 is welded. A bottom terminal 8a is formed at the bottom of the socket 6 and is connected to the lead wire 3a4. A bottom terminal 8b is formed on the side of the socket 6 and is connected to the support wire 3c.

  These metal halide lamps are arranged with the tube axis in a substantially horizontal state, and a lighting circuit (not shown) is electrically connected to the bottom terminal 8a and the side terminal 8b. More than twice as much power, for example, about 75 W at the start and about 35 W at the stable time are supplied and turned on.

  An embodiment of the metal halide lamp of the present invention will be described with reference to FIG. Note that the various tests shown below are performed based on this specification unless otherwise specified.

Discharge vessel 1: quartz glass, discharge space 14 volume = 25 μl, inner diameter A = 2.5 mm, outer diameter B = 6.2 mm, longitudinal sphere length C = 7.8 mm,
Metal halide 2: ScI ₃ = 0.20 mg, NaI = 0.08 mg, InBr = 0.14 mg, ZnI ₂ = 0.01 mg, (molar ratio of sodium halide to scandium halide = 1.14)
Noble gas: xenon = 10.0 atm,
Mercury: 0 mg,
Metal foils 3a1, 3b1: made of molybdenum,
Electrodes 3a2, 3b2: made of triated tungsten, diameter R = 0.33 mm, distance between electrodes D = 4.2 mm,
Coils 3a3, 3b3: made of doped tungsten, coil diameter = 0.06mm, coil pitch = 250%,
External lead wires 3a4, 3b4: made of molybdenum, diameter = 0.6 mm,
Lighting conditions: 75W (2.8A) immediately after lighting, 35W (0.7A) when stable,
In the above embodiment, the lamp characteristics are realized such that the color temperature is 5400 K, the lamp voltage is 51 V, and the total luminous flux is 2250 lm.

FIG. 3 is a diagram for explaining changes in color temperature and lamp voltage when the molar ratio of NaI to ScI ₃ is changed.

As can be seen from the results, the color temperature increases as the molar ratio of NaI to ScI ₃ decreases, and it can be seen that a color temperature of 5000 K can be achieved at 1.5. That is, in order to obtain a color temperature of 5000 K or higher, the molar ratio of NaI to ScI ₃ should be 1.5 or lower. The lamp voltage also tends to increase as the molar ratio of NaI to ScI ₃ decreases, and the lamp voltage is 50 V or more at 1.5 or less.

  Next, the test which changes the enclosure amount of zinc iodide was done. The results are shown in FIG. In addition, the presence or absence of crack leak in the figure indicates the flashing cycle of the rated life test mode (EU mode) defined in JEL, which is the standard for automotive headlamp HID light source, and the crack is not sealed in the sealed part within 1000 hours. It is the result of confirming whether it has occurred and leaked.

  FIG. 4 shows that crack leakage occurs when the amount of zinc iodide enclosed is less than 1.0% by weight, but crack leakage does not occur when the amount is 1.0% by weight or more. On the other hand, as apparent from FIG. 5 showing the result of FIG. 4, the total luminous flux is lower and the lamp voltage is higher as the amount of zinc iodide enclosed is increased. When the amount of zinc iodide enclosed is greater than 5.0% by weight, the lamp voltage has increased too much, causing flickering. Therefore, it is desirable that the amount of zinc iodide enclosed be 1.0% by weight or more and 5.0% by weight or less. The results shown in FIGS. 3 and 4 are almost the same even if the type of halogen bonded to the metal halide is different.

  The cause of the above-described crack leak and the effect of encapsulating zinc halide are considered as follows.

FIG. 6 is a view showing an X-ray photograph of the vicinity of the electrode after lighting for 43 hours in the EU mode, in which (a) is lamp 1 (ZnI ₂ = 0 wt%), and (b) is lamp 4 (ZnI ₂ = 1). 0.0% by weight). As can be seen from the figure, in the lamp 1, the tip of the electrode is melted violently, whereas in the lamp 4, the tip of the electrode is not melted, and the initial lighting state is maintained. From this, it is considered that the crack leakage is related to the dissolution of the tip of the electrode. As a result of the inventor's investigation, when the tip of the electrode is melted as in the lamp 1, first, an arc spot is hardly formed, and the electron radiation is lowered to increase the temperature of the electrode shaft. It is presumed that the cause of the crack leak is that the temperature of the sealing portion rises as the position where the spot is formed approaches the sealing portion side. On the other hand, the reason why the electrode was difficult to dissolve in the lamp 4 in which a small amount of zinc iodide was sealed is considered to be that the arc spot was stably formed at the tip of the electrode.

  Here, as is well known from Patent Document 2 and the like, zinc halide has conventionally been enclosed in a mercury-free lamp as a lamp voltage forming medium instead of mercury. On the other hand, a mercury-free lamp having a molar ratio of sodium halide to scandium halide of 1.5 or less as in the present invention has a lamp voltage of about 45 to 50 V suitable as a mercury-free lamp. Zinc halide is not required. Further, since zinc halide has a side effect of lowering the total luminous flux and darkening the lamp as shown in FIG. 5, it was considered that it is not necessary to enclose zinc halide in a mercury-free lamp having a high color temperature. However, as described above, it was discovered that zinc halide has the action of suppressing the dissolution of the tip of the electrode, so that even if the lamp voltage and total luminous flux characteristics deteriorate, a small amount of zinc halide is intentionally sealed. A need has arisen, leading to the present invention.

  Here, in order to suppress dissolution of the electrode tip and crack leakage caused thereby, it is preferable to suitably combine the diameter R of the electrode tip and the halogen bonded to the metal halide.

  FIG. 7 is a diagram for explaining the presence or absence of electrode dissolution and crack leak when the diameter R of the electrode tip is changed.

  From the results, it can be seen that it is not preferable whether the diameter R of the electrode tip is small or large. Conventionally, it has been known that when the diameter R of the electrode tip is small, the tip becomes too hot, which is undesirable. For this reason, it has been thought that the larger the diameter R of the electrode tip, the lower the temperature of the tip, and the less difficult it is to dissolve. It was. This is considered to be caused by a delay in the time during which the arc spot is stably formed at the tip of the electrode. Therefore, the diameter R of the electrode tip is preferably 0.25 mm or more and 0.38 mm or less.

  The halogen bonded to the metal halide is preferably composed of iodine having low reactivity, but it is desirable not to be composed only of iodine but also to combine other halogens such as bromine. This is because, when the metal halide is composed of only iodine, the reason is not clear, but lamps with dissolved electrodes frequently occur. On the other hand, it was confirmed that dissolution of the electrode was suppressed by binding bromine to 10% or more and 50% or less of a halogen other than iodine, for example iodine, to metal halide.

  Therefore, in the present embodiment, the molar ratio of sodium halide to scandium halide is 1.5 or less, and further, by containing 1.0% by weight or more and 5.0% by weight or less of zinc halide, color A mercury-free lamp having a temperature of 5000 K or higher can be realized, and crack leakage due to electrode dissolution that is likely to occur when the lamp is configured can be suppressed. In addition, the diameter R of the tip portion of the electrodes 3a2, 3b2 is 0.25 mm or more and 0.38 mm or less, and the halogen bonded to the metal halide 2 is composed of iodine and other halogens, thereby further effecting electrode dissolution. Thus, crack leakage can be suppressed.

The whole figure for demonstrating 1st Embodiment of the metal halide lamp of this invention. The figure for demonstrating one Example of the metal halide lamp of this invention. Diagram for explaining the change of color temperature and lamp voltage when changing the molar ratio of NaI for ScI _3. Diagram for explaining the change of various lamp characteristics when changing the enclosed amount of ZnI _2. Graphed FIG Changes in total luminous flux and lamp voltage for charging amount of ZnI ₂ in FIG. The figure which shows the X-ray photograph of the electrode vicinity after lighting for 43 hours by EU mode. The figure for demonstrating the presence or absence of an electrode melt | dissolution and a crack leak when changing the diameter of an electrode front-end | tip part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Airtight container 11 Discharge part 12a, 12b Sealing part 13a, 13b Non-sealing part 14 Discharge space 2 Metal halide 3a, 3b Mount 3a1, 3b1 Metal foil 3a2, 3b2 Electrode 3a3, 3b3 Coil 3a4, 3b4 External lead wire 3c Support wire 4 Insulating tube 5 Outer tube 6 Socket 71 Metal band 72 Tongue piece 8a Bottom terminal 8b Side terminal

Claims (3)

An hermetic vessel having a discharge part in which a discharge space is formed, and an essentially mercury-free discharge medium in which at least a scandium halide, a metal halide containing sodium halide and a rare gas are enclosed in the discharge space. A pair of electrodes whose front ends are opposed to each other in the discharge space,
A metal halide lamp, wherein a molar ratio of sodium halide to scandium halide is 1.5 or less, and the metal halide further contains 1.0 wt% or more and 5.0 wt% or less of zinc halide. .   The metal halide lamp according to claim 1, wherein a diameter R of a tip portion of the electrode is 0.25 mm or more and 0.38 mm or less.   The metal halide lamp according to claim 1 or 2, wherein the halogen bonded to the metal halide is composed of iodine and another halogen.

Images