JP2007179849A - High pressure discharge lamp and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide discharge lamps which are prevented from fault such as devitrification and blacking etc. of an airtight container, to provide a method of manufacturing the same, and to provide electrodes used for these high pressure discharge lamps. <P>SOLUTION: The high pressure discharge lamp 10 includes a heat-resistant and transparent airtight container 1, a pair of electrodes 1b and 1b which contain tungsten (W) as a main component, as well as thorium (Th) and thorium oxide (ThO<SB>2</SB>) and are sealed and opposed apart in the airtight container 1 and the rate of content of thorium (Th) at least from the opposed surface up to a depth of 5 nm is 0.25 to 4.98AC%, and a discharge medium sealed in a discharge space 1c of the airtight container 1. With this configuration, work function of the electrodes 1b decreases and temperature of the electrodes drops, and then evaporation of thorium (Th) and thorium oxide (ThO<SB>2</SB>) is reduced. These effects prevent the inside surface of the airtight container 1 from blacking and improve lumen maintenance factor of the high pressure discharge lamp 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-pressure discharge lamp such as a metal halide lamp and a method for manufacturing the same.

A high-pressure discharge lamp encloses a pair of electrodes in a discharge space formed inside a heat-resistant and translucent airtight container, and encloses a discharge medium mainly composed of rare gas, metal vapor, or metal halide. ing. The pair of electrodes is connected to a sealed metal foil hermetically embedded in a pair of long and narrow sealing portions integrally formed at both ends of the hermetic container by welding the base ends thereof, and the intermediate portion is loosened to the sealing portion. In general, the structure is such that the main electrode portion at the front end is exposed to the discharge space by, for example, protruding into the discharge space. These high-pressure discharge lamps use an electrode containing thorium oxide (ThO ₂ ) in tungsten (W) as an emitter material in order to stably form a discharge arc. However, thorium oxide (ThO ₂ ) evaporates more when the electrode temperature rises excessively and causes blackening of the hermetic container. Therefore, it is necessary to eliminate this blackening. In order to solve this problem, a discharge lamp electrode is known in which evaporation of thorium oxide (ThO ₂ ) due to an increase in electrode temperature is minimized (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-306421

However, the discharge lamp electrode described in Patent Document 1 has a reduced concentration of thorium oxide (ThO ₂ ) on the surface side, but only by changing the concentration distribution of thorium oxide (ThO ₂ ), Blackening during the lamp life could not be sufficiently suppressed, and there was room for further improvement.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-pressure discharge lamp that suppresses the occurrence of problems such as blackening of an airtight container that occurs during lamp lighting, and a method for manufacturing the same.

The high-pressure discharge lamp of the invention according to claim 1 is a heat-resistant and light-transmitting hermetic container; and contains thorium (Th) and thorium oxide (ThO ₂ ) mainly composed of tungsten (W). A pair of electrodes which are respectively sealed and opposed to each other and have a thorium (Th) content of 0.25 to 4.98 AC% at a depth of 5 nm from at least the surfaces facing each other; And a discharge medium sealed in a discharge space of the hermetic vessel.

  In the present invention and each of the following inventions, the definitions and technical meanings of terms are as follows unless otherwise specified.

  The hermetic container is configured to have heat resistance and translucency, and includes an enclosure portion and a pair of sealing portions that form a discharge space therein. “Heat resistance” means to sufficiently withstand the normal operating temperature of the discharge lamp. Therefore, the airtight container may be made of any material as long as it is a material having heat resistance and can emit light in a desired wavelength region generated by discharge to the outside. It is formed using quartz glass or the like. If necessary, it is allowed to form a halogen-resistant or halogenated-resistant transparent coating on the inner surface of the hermetic container or to modify the inner surface of the hermetic container.

  The pair of sealing portions seals the surrounding portion, and is a means that supports the shaft portion of the electrode and contributes to airtight introduction of current from the lighting circuit to the electrode. It extends from one to the other. And in order to seal an electrode and to introduce | transduce an electric current from a lighting circuit to an electrode airtightly, the appropriate airtight sealing conduction means, Preferably the sealing metal foil is embed | buried airtightly inside.

The pair of electrodes contains tungsten (W) as a main component, contains thorium (Th) and thorium oxide (ThO ₂ ), and the composition ratio of thorium (Th) on the surfaces facing each other is 0. It is 25 to 4.98 AC%, preferably 0.35 to 4.98 AC%, more preferably 0.5 to 4.98 AC%. Here, the composition ratio of thorium (Th) on the surface means AC% of thorium (Th) at a depth of 5 nm from the surface of the electrode. “AC%” is an abbreviation of atomic concentrate%, measured by XPS (X-ray Photoelectron Spectroscopy), and as a result, in the range from the surface to a depth of 5 nm in an area of 400 × 400 μm. The percentage of the number of atoms of thorium (Th) relative to the total number of all atoms and molecules including tungsten (W), thorium (Th) atoms and the number of thorium (Th) oxide molecules present in is there. In XPS, photoelectrons emitted from atoms and molecules in the irradiated part are measured when the sample is irradiated with X-rays. The photoelectrons emitted at this time have a unique binding energy value (eV) for each atom or molecule, and by measuring this value, it is possible to quantify the elements and measure the qualitative characteristics. .

Further, the pair of electrodes includes, for example, a shaft portion, and a base end portion of the shaft portion is fixed to the sealing portion by welding or the like to the sealing metal foil, and the intermediate portion is preferably airtight. It is loosely supported by the sealing part of the container, and is disposed so as to be opposed to both ends of the discharge space so that a part of the intermediate part and the tip part face the discharge space of the hermetic container. Further, an electrode made of a refractory metal mainly composed of tungsten (W) is formed by doping tungsten (W) with thorium oxide (ThO ₂ ) as an emitter material in order to stabilize the arc. Further the electrode surface tungsten oxide (WO ₂₎ or reducing work electrode shaft during manufacture or the lamp during manufacture for the purpose of removing other impurities is carried out, is used as an electrode. Thorium oxide (ThO ₂ ) is also reduced by conventional reduction work, and some thorium (Th) is present on the surface. However, since the reduction rate of thorium oxide (ThO ₂ ) varies greatly depending on temperature control or the like, thorium (Th) does not exist so much on the electrode surface in normal reduction work. The present inventors have found that thorium (Th) present on the electrode surface is greatly related to the electrode temperature of the lamp, and when the lamp is manufactured using an electrode having a high composition ratio of thorium (Th), the emission is reduced. The present invention has been found by focusing on the fact that the increase in the electrode temperature of the lamp is alleviated and the blackening is reduced. For example, Japanese Patent Laid-Open No. 2005-142071 discloses that an electrode formed by doping tungsten (W) as a main component and thorium oxide (ThO ₂ ) is reduced by using tungsten carbide (W ₂ C). A method for increasing the amount of thorium (Th) is shown. However, since this method improves the emission effect, it exhibits a certain effect against flicker and the like, but has not been improved with respect to prevention of blackening. That is, because tungsten carbide (W ₂ C) is used for reduction, carbon (C) remains as an impurity on the electrode surface, which causes blackening. The electrode material of the present invention is formed by doping thorium oxide (ThO ₂ ) with about 0.36 to 7.00 mass% tungsten (W) at the time of manufacturing the electrode shaft, and at the time of manufacturing the electrode shaft or lamp. Thorium (Th) present on the surface when used as an electrode by the reduction treatment step is a predetermined composition ratio. However, if the AC% of thorium (Th) on the electrode surface is in this range, even if a method other than the reduction treatment is used, it is included in the scope of the present invention.

  Furthermore, the electrode may be configured to operate with either alternating current or direct current. Alternating current

However, the pair of electrodes preferably have the same structure, but is not limited thereto.

  In general, in the discharge medium, the luminescent substance may be either a metal vapor or a rare gas (for example, in the case of a xenon lamp). A single luminescent metal such as mercury (in the case of a high-pressure mercury lamp) or a luminescent metal halide (in the case of a metal halide lamp) can be enclosed as a metal vapor source of the luminescent metal. In addition to the luminescent metal, mercury or a metal halide having a relatively high vapor pressure (in the case of a mercury-free lamp) can be enclosed as a lamp voltage forming substance. Further, a rare gas can be used as a starting gas and a buffer gas in common with each of the lamps.

By the way, the blackening of the hermetic container is mainly caused by the surface material of the electrode being scattered and adhering to the vicinity of the electrode of the hermetic container. As a result of experiments, it was clarified that (Th) must be contained near the surface. This is because thorium (Th) has a lower work function and better emission effect than tungsten (W) and thorium oxide (ThO ₂ ). It is thought that evaporation of thorium (Th) and thorium oxide (ThO ₂ ) is reduced by suppressing the temperature rise due to tungsten sputtering due to collision of the ionized discharge medium. When thorium (Th) is formed by reducing thorium oxide (ThO ₂ ), it is necessary to increase the reduction rate in order to increase the composition ratio of thorium (Th) on the electrode surface. However, since only raise the constituent ratio of thorium (Th) is limited by increasing the reduction ratio, in order to further increase the composition ratio of thorium (Th) of the electrode surface, the doping amount of thorium oxide (ThO ₂₎ Need to be increased. However, when the doping amount of thorium oxide (ThO ₂ ) is increased, the amount of thorium (Th) and thorium oxide (ThO ₂ ) scattered by sputtering increases, which causes devitrification and blackening. Further, even if thorium (Th) is present on the electrode surface above a certain level, the effect of lowering the electrode temperature does not change so much. Furthermore, there is a tendency to limit the amount of Th used from the viewpoint of environmental load. From such a viewpoint, thorium oxide (ThO ₂ ) is preferably doped with about 0.36 to 7.00 mass% with respect to tungsten (W) at the time of manufacturing the electrode shaft portion.

  In the present invention, the composition ratio of thorium (Th) within at least 5 nm from the electrode surface is specified, but the layer having a composition ratio of thorium (Th) of 0.25 to 4.98 AC% is thicker. Is effective in suppressing the electrode temperature rise.

In the present invention, the composition ratio of thorium (Th) on the electrode surface is regulated to an optimum value, so that the work function of the electrode is reduced, the electron is radiated well as an emitter material to stabilize the arc and the electrode temperature is lowered. Therefore, evaporation of thorium (Th) and thorium oxide (ThO ₂ ) can be reduced. These effects prevent blackening from occurring on the inner surface of the hermetic container and improve the luminous flux maintenance factor of the high-pressure discharge lamp.

  Whether or not the high-pressure discharge lamp has the configuration of the present invention is determined with respect to an unlit high-pressure discharge lamp that has been completed to be ready for shipment, with the tip exposed in the discharge space of the hermetic vessel. Assume that a part of the removed intermediate portion is measured by XPS for determination.

The present invention also defines a method for manufacturing a high-pressure discharge lamp having an electrode rich in thorium (Th) on its surface. That is, in the second step, the electrode material is subjected to a reduction treatment so that the composition ratio of thorium (Th) at least 5 nm from the surface is 0.25 to 4.98 AC%. The reduction treatment of the electrode material is performed by heating the electrode material at a high temperature for a desired time and further heating in a vacuum in an H ₂ atmosphere. The electrode material becomes an electrode by sealing it in an airtight container.

  In the present invention, known steps can be adopted as the first, third and fourth steps.

In the present invention, thorium oxide (ThO ₂ ) formed on the surface of the electrode can be effectively reduced to thorium (Th) by performing the reduction treatment in the second step. And, since a high pressure discharge lamp is manufactured by sealing an electrode having a composition ratio of thorium (Th) of 0.25 to 4.98 AC%, the lamp voltage is lowered and the electrode temperature at the time of lamp lighting is lowered as compared with the conventional case. It is possible to obtain a high-pressure discharge lamp in which the occurrence of defects such as blackening and devitrification of the hermetic container is suppressed and the luminous flux maintenance factor is improved.

  According to the first aspect of the present invention, since the composition ratio of thorium (Th) within at least 5 nm from the surface of the electrode is 0.25 to 4.98 AC%, the temperature rise of the electrode can be suppressed, and the scattering of the electrode material can be achieved. In addition, it is possible to provide a high-pressure discharge lamp that suppresses a decrease in luminous flux maintenance factor due to blackening of the airtight container due to evaporation or the like.

  According to claim 2, a high pressure discharge lamp is manufactured by sealing an electrode having a composition ratio of thorium (Th) within a range of at least 5 nm from the surface to 0.25 to 4.98 AC% by reduction treatment. It is possible to provide a high-pressure discharge lamp in which a decrease in the luminous flux maintenance factor due to the scattering of the substance and the evaporation of the electrode substance accompanying the increase in electrode temperature is suppressed.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  1 and 2 show a metal halide lamp for an automobile headlamp as an embodiment for implementing the high-pressure discharge lamp of the present invention. FIG. 1 is a front view of the entire lamp, and FIG. 2 is an enlarged view of an arc tube. FIG. In this embodiment, the high-pressure discharge lamp 10 includes a luminous tube IT, an insulating tube T, an outer tube OT, and a base B.

  The arc tube IT includes an airtight container 1, a pair of electrodes 1b and 1b, a sealing metal foil 2, a pair of external lead wires 3A and 3B, and a discharge medium.

  The airtight container 1 includes an enclosing portion 1a and a pair of sealing portions 1a1. The surrounding portion 1a is hollow and has an outer shape formed into a spindle shape. The surrounding portion 1a is integrally provided with a pair of elongated sealing portions 1a1 at both ends thereof, and an elongated substantially cylindrical discharge space 1c is formed therein. . The internal volume of the discharge space 1c is 0.1 cc or less. The surrounding portion 1a can have a relatively large thickness. That is, the thickness at the substantially central portion of the distance between the electrodes can be made larger than the thickness at both sides. As a result, the heat transfer of the hermetic vessel 1 is improved and the temperature rise of the discharge medium attached to the lower part of the discharge space and the inner side surface of the hermetic vessel 1 is accelerated, so that the rise of the luminous flux is accelerated.

  The electrode 1b is mainly composed of tungsten (W), and its base end portion Eb is welded to a sealing metal foil 2 described later embedded in the sealing portion 1a1, and the intermediate portion is loosely supported by the sealing portion 1a1. As a result, it is disposed at a predetermined position, and as shown in FIG. 2, a part Em of the intermediate part and a tip part Et face the discharge space 1c. Further, the base end portion Eb of the electrode 1b is welded to one end of the sealing metal foil 2 in the sealing portion 1a1.

  The electrode 1b has a thorium (Th) composition ratio of 0.25 to 4.98 AC% at least within 5 nm from the surface where the electrodes 1b1 and 1b of the tip portion Et facing the discharge space 1c face each other. It has become.

  In addition, in the case of a metal halide lamp used for an automobile headlamp, if necessary, the vicinity of the tip of the electrode can be made larger in diameter than the shaft, the tip of the electrode can be hemispherical, or a truncated cone can be formed. . That is, the number of times the lamp blinks is very large, and a larger current flows at the time of starting than at the normal time. Accordingly, if the entire electrode is made large in diameter, the constituent material of the hermetic container that is in contact with the electrode shaft Each time is blinking, it tends to crack due to thermal stress. Thus, by forming a large diameter portion in the vicinity of the tip of the electrode, the electrode can be made to flash, but since the shaft portion is not large in diameter, cracks are less likely to occur. In the case of such a tip shape, the surface in which the composition ratio of thorium (Th) is 0.25 to 4.98 AC% is defined by the surface in the region from the tip to the length of 1/2 of the shaft diameter. . By making the tip of the electrode hemispherical or frustoconical, the starting point of the discharge arc is easily stabilized and the flickering of the discharge is reduced. Furthermore, in the case of an electrode operated by direct current, since the temperature of the anode is generally large, if the large diameter portion is formed in the vicinity of the tip portion, the heat radiation area can be increased and frequent flashing can be dealt with. . On the other hand, the cathode does not necessarily have to have a large diameter portion.

  In FIG. 1, after forming the lower sealing portion 1 a 1, the sealing tube 1 a 2 is integrally cut from the lower portion of the sealing portion 1 a 1 without being cut and extends into the base B.

  The sealing metal foil 2 is made of molybdenum foil, and is hermetically embedded in the sealing portion 1 a 1 of the hermetic container 1. Also, the sealing metal foil 2 is a means for functioning as a current conducting conductor while cooperating with the sealing portion being embedded inside the sealing portion and maintaining the sealing portion airtight inside the enclosure portion of the hermetic container. If the airtight container is made of quartz glass, molybdenum is the most suitable material. Since molybdenum oxidizes at about 350 ° C., it is buried so that the temperature of the outer end is lower. Although the method for embedding the sealing metal foil in the sealing portion is not particularly limited, for example, a reduced pressure sealing method or a pinch sealing method can be employed. For automobile headlamps or the like that have a small internal volume of 0.1 cc or less, preferably 0.05 cc or less, and in which a rare gas such as xenon is sealed at room temperature at a pressure of 5 atmospheres or more, more preferably 8 atmospheres or more. In the case of a high-pressure discharge lamp to be used, it is preferable to combine both.

  The distal ends of the pair of external lead wires 3A and 3B are welded to the other end of the sealing metal foil 2 in the sealing portions 1a1 at both ends of the airtight container 1, and the proximal end sides are led out to the outside. In FIG. 1, an external lead wire 3A led upward from the discharge vessel IT is folded back along an outer tube OT (to be described later) and introduced into a base B (to be described later) to be connected to one of the base terminals (not shown). ing. In FIG. 1, the external lead wire 3B led downward from the discharge vessel IT extends along the tube axis, is introduced into the base B, and is connected to the other base terminal.

  In the enclosure 1a of the hermetic vessel 1, a light emitting metal halide, a lamp voltage forming metal halide and a rare gas are sealed as a discharge medium. The light emitting metal is sodium (Na) and scandium (Sc), and the lamp voltage forming metal is zinc (Zn).

  The outer tube OT has an ultraviolet ray cutting performance, houses the discharge vessel IT therein, and the reduced diameter portions 4 at both ends are glass-welded to the sealing portion 1a1 of the discharge vessel IT. However, the inside is not airtight but communicates with the outside air.

The insulating tube T is made of ceramics and covers the external lead wire 3A.

The base B is standardized for automobile headlamps, supports the discharge vessel IT and the outer tube OT along the central axis, and is detachable from the back of the automobile headlamp. It is configured to be mounted.

  The configuration of the lamp, the discharge medium to be sealed, and the electrical characteristics will be described.

The airtight container 1a is made of quartz glass having a sphere length of 7 mm, a maximum outer diameter of 6 mm, a maximum inner diameter of 2.4 mm, and an internal volume of 0.025 cc. The electrode 1b is made of a tungsten (W) wire having a diameter of 0.40 mm and a composition ratio of thorium (Th) at a depth of 5 nm from the surface being 0.50 AC%, and the distance between the opposing electrodes is 4.2 mm. . The discharge medium is filled with 0.3 mg of ScI ₃ —NaI—ZnI ₂ as a metal halide and 10 atm of xenon (Xe) as a rare gas. The outer tube OT has an outer diameter of 9 mm and an inner diameter of 7 mm, and the internal atmosphere is atmospheric pressure (atmosphere). The electrical characteristics are 85W applied power immediately after lighting, 2.8A applied current immediately after lighting, 42V stable lamp voltage, and 35W stable lamp power.

Next, Examples 1 and 2 of electrode materials as the first form of the high-pressure discharge lamp of the present invention will be described with reference to Table 1.

As can be understood from Table 1, as shown in Samples 3 and 4 in the first embodiment, according to the present invention, blackening occurs if the electrode has thorium (Th) (AC%) of 0.25 or more. It is suppressed. In each case, an experiment was performed using an electrode shaft formed by doping tungsten (W) with 2% by mass of thorium oxide (ThO ₂ ). Conventional product 1 and conventional product 2 are electrodes manufactured by a conventional reduction method, and Examples 1 and 2 are electrodes in which the composition ratio of thorium (Th) is increased. The degree of occurrence of blackening is determined by the total luminous flux at 300 hours after the lamp is turned on.

In the high-pressure discharge lamp 10 of this embodiment, since the composition ratio of thorium (Th) on the electrode surface is set to a predetermined value or more, the work function of the electrode is reduced, and the arc is stabilized by emitting electrons as an emitter material. At the same time, since the electrode temperature is lowered, evaporation of thorium (Th) and thorium oxide (ThO ₂ ) can be reduced. These effects prevent blackening from occurring on the inner surface of the hermetic container and improve the luminous flux maintenance factor of the high-pressure discharge lamp.

The front view of the whole lamp | ramp which shows the metal halide lamp for vehicle headlamps as one form for implementing the high pressure discharge lamp of this invention Similarly, front view of the enlarged main part of the arc tube

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Airtight container 1b ... Electrode Et ... Tip part 10 ... High pressure discharge lamp

Claims (2)

A heat-resistant and translucent airtight container;
Tungsten (W) as the main component, containing thorium (Th) and thorium oxide (ThO ₂ ), sealed in a hermetic container, facing each other, and at least the depth from the surface facing each other A pair of electrodes having a thorium (Th) content of 0.25 to 4.98 AC% in the range of 5 nm;
A discharge medium enclosed in a discharge space of an airtight container;
A high-pressure discharge lamp comprising: Reduction is performed so that the content of thorium (Th) in the range of 5 nm depth from the surface of the electrode material containing tungsten (W) as a main component and containing thorium oxide (ThO ₂ ) is 0.25 to 4.98 AC%. After the treatment, the electrode materials are sealed and sealed inside the hermetic container so that the surfaces of the reduced electrode materials face each other, and the discharge space of the hermetic container is exhausted to enclose the discharge medium. A method of manufacturing a high-pressure discharge lamp.

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