JP2003187741A - Electrode for discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a discharge lamp which controls the evaporation of electronic radioactive material from a mold section during lamp- lighting, which prevents lamp devitrification, white turbidity and the like due to the evaporation of the electronic radioactive material and which prevents thermal distortion and the evaporation at a cathode edge, even if supplied electric power increases accompanying turning to high luminance. <P>SOLUTION: In the electrode for the discharge lamp with the mold section 4 composed of a refractory metal 42 which has a pair of facing electrodes located in a bulb-forming discharge space of a short arc type discharge lamp and which includes the electronic radioactive material on one side of the electrodes, the lamp comprises an opercular body 43 composed of the refractory metal which does not contain the electronic radioactive material is formed at an edge of the mold section 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of a discharge lamp, and more particularly to an electrode structure of a short arc type discharge lamp molded with an electron emissive material.

[0002]

2. Description of the Related Art Generally, in a short arc type discharge lamp, a rare gas, mercury or the like as a substance involved in light emission is enclosed in a bulb made of a light transmissive material such as quartz glass, and a pair of opposed lamps are arranged inside the bulb. Arc discharge is generated between the arranged electrodes to emit light of a desired wavelength. And, in the electrodes of these short arc type discharge lamps,
An electron emissive material (emitter member) for easily emitting electrons from the electrode is contained.

However, in such a lamp, the electron emissive material evaporates from the tip of the electrode while the lamp is operating.
There is a problem that the electron emissive material contained in the electrodes is exhausted and the lamp goes out when the lamp is started.

Conventionally, in order to solve these problems, an electrode structure using a mold part has been proposed.
According to Japanese Unexamined Patent Publication No. 9-306421, a mixture containing thorium oxide as an electron emissive material is embedded in the tip of the cathode,
The concentration of thorium oxide on the tip side of this mixture should be 2 to 15
%, And the concentration of thorium oxide on the rear end side is 10 to 40%
It is described that In the present invention, the depletion of the electron emitting substance at the tip of the cathode is to be compensated by the high concentration of electron emitting substance at the rear end of the mixture.

According to Japanese Patent Laid-Open No. 11-297196, a primary compact made of a mixed powder of particulate barium-based electron emissive material and Tungste powder is crushed at the tip of the cathode, and then this primary compact is formed. It describes a manufacturing method of sintering in the inserted state, in the present invention, since the density of the mixture formed at the cathode tip can be increased,
It is possible to reduce the evaporation of the electron emissive material.

[0006]

However, in the inventions disclosed in the above-mentioned respective publications, the cathode tip portion containing the electron-emitting substance is directly exposed to the arc when the lamp is lit, so that the cathode tip portion is inevitably inevitable. The electron emissive material existing in the portion evaporates and is emitted outside the cathode. This tendency is particularly remarkable when a barium-based material having a low melting point is used as the electron emitting substance. In other words, simply by supplying the electron emissive material so that the electron emissive material is not exhausted from the cathode tip, the evaporated electron emissive material adheres to the inside of the bulb, causing devitrification and white turbidity of the bulb, and the illuminance of the lamp. There is a problem that it causes a decrease. Further, under the situation that the life of the lamp is required to be extended in recent years, the reduction of the illuminance maintenance rate of the lamp due to the evaporation of the electron emissive material is a fatal problem.

Further, in the inventions disclosed in the above-mentioned publications, when the electron emissive substance is evaporated from the cathode tip portion, a minute void is generated at the cathode tip portion after the evaporation. The cathode tip portion in which the minute voids are generated is abnormally heated due to a decrease in thermal conductivity, and there is a problem that the cathode tip portion is locally melted and deformed.

Further, as the market demands for higher brightness of the lamp, the input current to the electrode becomes higher, and as a result, the temperature of the tip of the electrode rises, so that the electron emissive substance evaporates from the tip of the cathode. A minute void is generated. When the voids are generated, the cathode tip portion cannot be thermally endured and is deformed. In addition, such a tendency becomes more and more remarkable as the input power increases with the increase in the brightness of the lamp.

In view of the above-mentioned various problems of the prior art, an object of the present invention is to provide a mold part in which an electron emissive material is arranged at the cathode tip part of a short arc discharge lamp, from the mold part when the lamp is lit. In addition to suppressing the evaporation of the electron-emissive substance, it prevents devitrification and white turbidity of the lamp due to the evaporation of the electron-emissive substance. An object is to provide an electrode for a discharge lamp having an electrode structure that is neither deformed nor evaporated.

[0010]

The present invention employs the following means in order to solve the above problems.

A first means is to arrange a pair of electrodes facing each other in a bulb forming a discharge space of a short arc type discharge lamp, and to form a mold part made of a refractory metal containing an electron emitting substance on one of the electrodes. In the discharge lamp electrode having the above, a lid-like body made of a refractory metal containing no electron emissive substance is formed at the tip of the mold part.

According to a second means, in the first means, the average particle diameter of the member forming the lid-like body is larger than the average particle diameter of the refractory metal portion containing the electron-emitting substance in the mold portion. Is characterized by.

A third means is the means according to any one of the first means and the second means, wherein the thickness of the lid-like body is in the range of 0.1 mm to 1.0 mm. To do.

A fourth means is characterized in that, in any one of the first means to the third means, the member forming the lid-like body is made of tungsten or tantalum.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a view showing a short arc type discharge lamp using a discharge lamp electrode according to the present invention. In the figure, 1 is a short arc type discharge lamp, 2 is an arc tube part of the short arc type discharge lamp, 3 is a sealed part of the short arc type discharge lamp, 4 is a cathode of the short arc type discharge lamp, and 5 is a short arc. It is an anode of a mold discharge lamp.

As shown in the figure, a short arc type discharge lamp 1 is provided with an arc tube portion 2 made of substantially spherical quartz glass in the center and sealing parts 3 at both ends thereof.
A substance that participates in light emission, such as mercury, xenon, or a rare earth metal, is sealed inside the cathode, and the cathode 4 and the anode 5 are arranged to face each other.

FIG. 2 is a sectional view showing the structure of a part of the discharge lamp electrode 4 according to the present invention, and FIG. 3 is an enlarged view of the discharge lamp electrode 4 shown in FIG.

In these figures, 41 is a cathode body, 4
2 is a mold part made of a mixture of an electron emissive substance and a refractory metal material such as tungsten, and 43 is a mold part 42.
Is a lid-like body formed of a refractory metal material such as tungsten or tantalum that does not contain an electron emissive substance formed at the tip of the.

Here, the lid-like body 43 is formed on the tip of the mold portion 42 in a substantially conical shape and has an average thickness in the range of 0.1 to 1 mm, and as shown in FIG. The average particle size of the refractory metal material forming the lid-like body 43 is larger than the average particle size of the refractory metal part containing the electron emissive material forming the mold part 42.

Here, the reason why the average particle size of the refractory metal material forming the lid-like body 43 is made larger than the average particle size of the refractory metal portion containing the electron-emitting substance forming the mold part 42 is the lid-like body. When the crystal grain size of the refractory metal material constituting 43 is small, the electron emissive substance evaporates excessively because many electron emissive substances evaporate due to thermal diffusion on the grain interfaces that are the wall surfaces between the crystals. I will end up. Further, the surface area of the cathode tip directly exposed to the arc increases, and as a result, the evaporation amount of tungsten in the lid 43 increases, which causes blackening of the lamp bulb and further shortening of the life of the lamp.

On the other hand, if the average particle size is too large, the number of crystal grain boundaries that serve as a supply path for the electron emissive material is reduced, so that the electron emissive material is insufficiently supplied to the cathode tip, and the cathode tip is liable to arc discharge. In order to stabilize, the temperature is raised to try to emit thermions. Therefore, the temperature of the tip of the cathode rises abnormally, which causes deformation of the lid 43 or blackening of the bulb due to evaporation of tungsten, as described above.

Therefore, although the average particle size of the high melting point metal material forming the lid-like body 43 is made larger than the average particle size of the high melting point metal part containing the electron emissive substance forming the mold part 42, its size is excessively large. Alternatively, it is necessary to set the crystal grain size to have an appropriate size so as not to be too small.

As described above, in the discharge lamp electrode 4 according to the present invention, the lid-like body 43 made of a refractory metal material such as tungsten is formed at the tip of the mold portion 42 without containing an electron emissive substance. Therefore, the mold part 42 is not directly exposed to the arc discharge, and the evaporation of the electron emissive material from the mold part 42 can be suppressed. As a result, the devitrification of the valve due to the evaporation of the electron emissive material and the devitrification of the valve can be prevented. White turbidity can be reduced.

According to the discharge lamp electrode 4 of the present invention, the particle size of the refractory metal material of the lid 43 is larger than the particle size of the refractory metal part of the mold portion 42 containing the electron emitting substance. Since the electron-emitting substance is appropriately supplied to the lid-like body 43 by grain boundary diffusion, the arc discharge is stabilized, and the devitrification or turbidity of the bulb due to excessive evaporation of the electron-emitting substance is caused. It is possible to suppress the occurrence of minute voids due to the evaporation of the electron emissive substance, and to suppress the deformation of the cathode tip.

According to the present invention, the lid-like body 43 is attached to the mold portion 42.
Although it is formed with a thickness in the range of 0.1 to 1 mm (average thickness) above, by setting this thickness to 0.1 mm or more, excessive evaporation of the electron emissive material can be suppressed, and By setting the thickness to 1 mm or less, it becomes possible to suppress instability of arc discharge and extinguishing phenomenon at the time of lighting due to defective supply of the electron emissive material.

Further, since a relatively easily available material such as tungsten or tantalum is used as the refractory metal material used for the lid 43, the cost is higher than that when other refractory metal materials are used. Can be reduced.

Next, a method for manufacturing the discharge lamp electrode according to the present invention will be described.

First, a tungsten powder mainly having a particle diameter of 10 μm and having a different particle diameter is mixed with an electron emitting substance, stearic acid is added thereto, and then the mixture is compressed by a pressing machine to form a molded body which becomes the mold portion 42. Next, this molded body is pre-sintered in a hydrogen stream and packed in a concave portion formed at the tip of the cathode body 41 as a mold chip. Next, a tungsten powder having a larger average particle size than the particle size of the tungsten powder containing the electron-emitting substance that constitutes the temporarily sintered mold chip is pressed onto the tip of the mold chip,
After that, sintering is performed to form a cathode tip portion that becomes the lid-like body 43. Next, the tip of the cathode is cut into a predetermined cathode shape to obtain a cathode 4 as shown in FIGS.

FIG. 4 is a diagram showing a temporal change in the illuminance maintenance rate of the discharge lamp electrode according to the present invention and the discharge lamp electrode according to the prior art.

In the figure, the horizontal axis is the lighting time (H) and the horizontal axis is the illuminance maintenance rate (%). In the figure, the discharge lamp electrode according to the present invention and the prior art are shown together with the history of the lighting time. The change in the illuminance maintenance ratio with the discharge lamp electrode in which the mold part is directly exposed to the discharge space is shown.

As is apparent from the figure, in the conventional discharge lamp electrode in which the mold portion was directly exposed, the illuminance maintenance ratio (%) rapidly decreased to 80% by the time when 200 hours passed after the start of use, Even after that, the illuminance maintenance rate (%) gradually decreased, and after 2000 hours, the illuminance maintenance rate (%) decreased to about 60%. On the other hand, according to the discharge lamp electrode of the present invention, no sharp decrease in the illuminance maintenance rate was observed with the start of use, and thereafter, the illuminance maintenance rate gradually decreased, but after 2000 hours, Also, the illuminance maintenance rate (%) is maintained at about 80%.

As can be seen from these test results, according to the discharge lamp electrode of the present invention, the evaporation of the electron emissive material from the mold part is suppressed, and the devitrification and turbidity of the bulb due to the evaporation of the electron emissive material are reduced. It is understood that it is done.

[0033]

According to the first aspect of the present invention, since the lid-like body made of a refractory metal containing no electron emissive material is formed at the tip of the mold part, the valve due to evaporation or evaporation of the electron emissive material. Devitrification and cloudiness can be reduced,
Further, since the cathode tip portion does not contain an electron emissive substance, even if the cathode tip portion is exposed to arc discharge, there is no generation of minute voids at the tip portion, and the tip portion due to the formation of minute voids It is possible to prevent deformation and evaporation of the cathode tip portion due to abnormal heating.

According to the second aspect of the present invention, the average grain size of the member forming the lid-shaped body is made larger than the average grain size of the high melting point metal portion containing the electron emissive material of the mold portion. A passage through which the electron emissive substance evaporates due to thermal diffusion is suppressed at the grain interface, which is the wall surface of, and therefore, the electron emissive substance can be prevented from excessively evaporating. Further, since the surface area of the lid-like body that is directly exposed to the arc is suppressed, as a result, it is possible to prevent the blackening of the lamp bulb and the shortening of the life of the lamp due to the increase of the evaporation amount of the member constituting the lid-like body. be able to.

According to the third aspect of the invention, since the thickness of the lid-like body is formed in the range of 0.1 mm to 1.0 mm, it is possible to suppress the excessive evaporation of the electron emissive material, and It is possible to prevent instability of arc discharge and extinguishing phenomenon at the time of lighting due to poor supply of electron emissive material, and it is possible to arbitrarily set the thickness within this range according to various lamp ratings.

According to the invention described in claim 4, since tungsten or tantalum is used as the member constituting the lid-like member, these members are relatively easily available, and other refractory metal materials are used. The cost can be reduced as compared with the case of using it.

[Brief description of drawings]

FIG. 1 is a view showing a short arc type discharge lamp using a discharge lamp electrode according to the present invention.

FIG. 2 is a cross-sectional view showing a partial configuration of a discharge lamp electrode according to the present invention.

FIG. 3 is an enlarged view of the electrode for a discharge lamp shown in FIG.

FIG. 4 is a diagram showing changes in the illuminance maintenance rate of the discharge lamp electrode according to the present invention and the discharge lamp electrode according to the related art.

[Explanation of symbols]

1 Short arc type discharge lamp 2 arc tube 3 Sealing part 4 cathode 41 cathode body 42 Mold part 43 Lid 5 anode

Claims (4)

[Claims] 1. A discharge lamp having a pair of electrodes facing each other in a bulb forming a discharge space of a short arc type discharge lamp, and having a mold part made of a refractory metal containing an electron emitting substance on one of the electrodes. An electrode for a discharge lamp, characterized in that a lid-like body made of a refractory metal containing no electron emissive material is formed at the tip of the mold part. 2. The average particle size of a member forming the lid-like body is larger than the average particle size of a portion of the refractory metal containing an electron emitting substance in the mold portion.
The electrode for a discharge lamp according to. 3. The electrode for a discharge lamp according to claim 1, wherein the lid-shaped body has a thickness in the range of 0.1 mm to 1.0 mm. 4. The discharge lamp electrode according to claim 1, wherein the member forming the lid-like body is made of tungsten or tantalum.