JP2002260580A - Electrode for discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance heat-radiation characteristics of an electrode used for a discharge lamp such as a xenon lamp and an ultra-high pressure mercury lamp, for stable discharge. SOLUTION: The outer circumference of a rod-like electrode whose main component is tungsten is engaged with a bush whose main component is tungsten. The bush is preferred to be formed as a porous body, with a ruggedness on the outer circumference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode used for a discharge lamp such as a xenon lamp and an ultra-high pressure mercury lamp.

[0002]

2. Description of the Related Art A discharge lamp has been widely used as a light source for general illumination, a light source for a projector, a light source for a photoresist exposure device, a light source for an ultraviolet curing device, and the like. FIG.
FIG. 1 illustrates the structure of a xenon lamp as an example of a conventional discharge or the like. In a quartz bulb 1, tungsten or tritan (triated tungsten) electrodes are provided to face each other. 3 'is a cathode electrode and 4 is an anode electrode. Xenon gas is sealed in the quartz bulb 1.

[0003] In this type of discharge lamp, when the cathode (cathode) becomes extremely high in use, the arc becomes unstable and the discharge characteristics deteriorate, so that a heat radiation layer is provided on the outer periphery of the rod-shaped electrode body. It has been proposed (Japanese Unexamined Patent Application Publication
306546). The heat dissipation layer of the cathode described in this publication is obtained by sintering tungsten powder on the outer peripheral surface of the electrode body, but is not a heat dissipation layer obtained by sintering such a powder, but a tubular coil for heat dissipation on the electrode body. Is also being developed. FIG. 5 shows an example of this discharge electrode, in which a coil C made of tungsten is fitted around the outer periphery of a round rod-shaped electrode body B having a sharp tip.

[0004] If the arc is in a poor state, electric discharge may occur from the vicinity of the base of the cathode to the surrounding metal fittings, and the metal fittings around the cathode may be damaged by the arc. For this reason, a low work function material, for example, barium oxide (BaO) is formed in the gap of the heat radiation coil.
Or strontium oxide (SrO) to facilitate the start of discharge and maintain stable discharge.

[0005]

When the temperature of the discharge electrode rises extremely, the stability of the arc deteriorates. However, as in the above-mentioned conventional discharge electrode, a coil is wound around a rod-shaped electrode body. In the structure, the contact between the electrode main body and the outer peripheral surface of the coil becomes a line contact, and the contact area is small. Therefore, there is a problem that the amount of heat transfer from the electrode main body to the coil is small, and effective heat radiation is difficult to be performed. . Therefore, the present invention
A heat radiation layer made of sintered tungsten powder is provided on the outer peripheral surface of the electrode body, or a conventional discharge electrode in which a cylindrical coil is wound around the electrode body is improved so that more effective heat radiation is performed. It is an issue.

[0006]

In order to solve the above problems, the present invention has the following arrangement. That is, the discharge lamp electrode according to the present invention includes a rod-shaped electrode main body containing tungsten as a main component and a cylindrical body provided on an outer peripheral portion of the electrode main body, and the cylindrical main body contains tungsten as a main component. It is a feature that it is a bush.

In the discharge lamp electrode of the present invention, a bush containing tungsten as a main component is used instead of a conventional coil as a cylindrical body provided on an outer peripheral portion of an electrode main body containing tungsten as a main component. It contacts the outer periphery of the rod-shaped electrode body. Therefore, the amount of heat transferred from the electrode body to the bush is large, and abnormal temperature rise of the electrode body can be effectively prevented. In addition, if the bush is formed as a porous body, it is effective because it can be impregnated with a substance for improving discharge performance. In addition, if unevenness is formed on the outer peripheral surface of the bush, the surface area of the outer surface of the bush is increased, so that heat dissipation is improved. In particular, it is effective to form a large number of radiator-shaped fins on the outer peripheral surface of the bush.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. FIG. 1 is an explanatory view showing the configuration of a xenon lamp, which is one type of discharge lamp. This xenon lamp 1 has a cathode (cathode) 3 and an anode (anode) 4 inside a quartz bulb 2.
, And xenon gas is sealed inside the quartz bulb 2.

As shown in FIG. 2, the cathode 3 is formed by fitting a cylindrical bush 5 to the outer periphery of a cathode body 3a having a sharp tip. It is sealed with a stop 7. As shown in FIG. 1, the anode 4 is formed by connecting a lead rod 8 to an end of a round bar-shaped main body 4a having a diameter larger than that of the cathode 3.
It is sealed with. Although the tip of the anode body 4a is formed in a conical shape having a flat top surface 4b, it may be formed in a hemispherical shape.

The bush 5 is made of a sintered body of tungsten, and has a through hole in the center thereof for fitting the electrode (cathode) body 3a. A large number of fin-shaped protrusions 10 are provided on the outer peripheral portion of the bush 5.

The bush 5 for the cathode in this embodiment
Is formed as a porous body, and the porous portion is impregnated with a low work function material, for example, barium oxide (BaO) or strontium oxide (SrO). In the illustrated example,
The anode 4 is not provided with a bush, but may be provided with a tungsten sintered bush similar to the cathode. In this case, there is no need to impregnate the anode bush with the low work function substance as described above. For this reason, it is preferable to manufacture the bush for the anode more densely than the bush 5 for the cathode. Further, the cathode bush may be made of a dense material in some cases.

The cathode 3 and the anode 4 both contain tungsten as a main component, and the cathode 3 is made of thoriated tungsten to which trier is added. On the other hand, although the anode 4 is made of pure tungsten, lanthanum oxide (La ₂ O) is added to tungsten in order to raise the recrystallization temperature.
₃ ) It is preferable that one or more of high melting point oxides such as yttrium oxide (Y ₂ O ₃ ) and cerium oxide (CeO ₂ ) are added in a trace amount. The added amount of these high melting point oxides is usually 0.01 to 0.3% by weight in total.

The electrodes for electric discharge or the like, that is, the cathode 3 and the anode 4 can be manufactured by a known powder metallurgy method. In the case of the anode 4, the high melting point oxide powder is added to and mixed with the tungsten powder, press-formed and sintered to form an ingot, and then subjected to necessary processing such as forging and machining to obtain a predetermined shape. The addition of the high melting point oxide to the tungsten powder can be achieved by adding and mixing the powder,
A method in which a compound solution such as a chloride or a nitrate is added to the tungsten powder and the reduction is performed again can be adopted.

The tungsten powder as a raw material may be a pure tungsten powder, but it is preferable to use a so-called doped tungsten powder to which a small amount of a compound (doping agent) such as aluminum, potassium, silicon or the like is added because the high-temperature characteristics are excellent. . The particle size of the powder is a particle size generally used in powder metallurgy, and is usually several microns to several tens of microns. The molding pressure is a pressure at which a molded body having a desired strength is obtained, and is usually about 1500 kgf / cm ² . Further, the sintering temperature is usually about 3000 ° C. or higher. If the sintering temperature is low, sufficient density cannot be obtained, and it is not suitable for use as an anode. The remaining amount of the above dopant after sintering is mainly potassium (K), and is 60
It is about ppm.

On the other hand, in the case of the cathode 3, a predetermined amount of tria (thorium oxide) powder may be mixed with tungsten powder to produce the same method as described above. In this case, it is not necessary to add a dopant or a high melting point oxide.

The bush 5 is formed by molding a tungsten powder by an appropriate molding method such as extrusion molding, injection molding, mold (press) molding, etc., degreases and temporarily sinters at a relatively low temperature.
It can be relatively easily manufactured by press-molding tungsten powder, pre-sintering, and machining into a predetermined shape. The electrode body is inserted into the hollow portion of the obtained bush, and heat treatment (sintering of the bush and tight fitting to the electrode body due to shrinkage of the bush) is performed, followed by main sintering. This main sintering is performed, for example, by heating to a high temperature of about 2200 ° C. in a vacuum. By this sintering, a discharge electrode in which the bush and the electrode body are integrated is obtained. The heat treatment and the main sintering may be performed at the same time.

FIG. 3 shows an embodiment different from the above. In the embodiment shown in FIGS. 3A and 3B, the cathode bush 20 has a cylindrical portion 21 fitted to the cathode main body 3a and a cylindrical portion 21 having the same shape. , And plate-like projections 22 projecting in the radial direction. These projections are convex portions, and the interval portions are concave portions. 3 (c) and 3 (d) show still another embodiment. In this embodiment, a bush 30 is formed on a cylindrical portion 31 fitted to the cathode main body 3a and an outer peripheral portion of the cylindrical portion. Are formed in the form of streaks 32 in the axial direction. The space between these projections is a groove-shaped recess. The shape of the irregularities provided on the outer peripheral portion of the bush is not limited to these, and irregularities of various shapes having excellent heat dissipation can be provided.

The discharge lamp electrode thus obtained is
Since a bush having irregularities is fitted to the outer peripheral portion of the rod-shaped electrode body, an arc is generated from the convex portion of the bush on the cathode side toward the anode side at the start of discharge, and then the generation position of the arc gradually increases. Move to the cathode tip. Therefore, a stable discharge can be secured. Further, since the inner surface of the bush is in close contact with the electrode main body, heat can be favorably transferred from the electrode main body to the bush. further,
Since irregularities are formed on the outer peripheral surface of the bush, the surface area is increased by that amount, so that heat is satisfactorily released.

Further, if the bush is manufactured as a porous body as in the above embodiment, a large amount of a low work function substance for improving discharge performance can be impregnated and held in the porous portion, which is advantageous. is there. In this case, the porosity can be easily adjusted, so that the porosity may be optimal depending on the application. In addition, since it is manufactured by powder molding, it can be easily manufactured to a desired shape and size, and can be excellent in heat radiation effect.

[0020]

As is apparent from the above description, the discharge lamp electrode according to the present invention can obtain a good discharge starting state, and can satisfactorily release the heat of the electrode body, thereby providing a stable discharge. It became possible to obtain performance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a xenon lamp.

FIG. 2 is a side view of a cathode.

FIG. 3 is a side view (a) and a sectional view (b) of a cathode different from the above, and a side view (c) and a sectional view (d) of a further different cathode.

FIG. 4 is an explanatory view of a conventional discharge lamp having a cathode.

FIG. 5 is an explanatory diagram of a conventional cathode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Xenon lamp 2 Quartz bulb 3 Cathode 4 Anode 5 Bush 10,11 Projection

Claims (3)

[Claims] 1. A rod-shaped electrode main body mainly composed of tungsten, and a cylindrical body provided on an outer peripheral portion of the electrode main body, wherein the cylindrical body is a bush mainly composed of tungsten. Characteristic electrode for discharge lamp. 2. The discharge lamp electrode according to claim 1, wherein the bush is formed as a porous body. 3. The discharge lamp electrode according to claim 1, wherein an outer peripheral portion of the bush is formed in an uneven shape having a plurality of convex portions.