JP2010153339A - High-pressure discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the scatter in an early period of an emitter supported in an electrode coil surface, and maintain high ultraviolet luminance over a long period in a high-pressure discharge lamp in which a metal additive and an inert gas are sealed inside a silica glass light-emitting tube, an electrode having tungsten as the body at both ends of the light-emitting tube is sealed and adhered, and an electrode part becomes high temperature when lighted. <P>SOLUTION: The electrode is constituted of an electrode core rod and an electrode coil by having tungsten as the body. An electron emission material (emitter) is coated on the electrode coil by a binary compound oxide which is constituted of yttrium oxide and aluminum oxide, and in which molar percentage of yttrium oxide to the whole is 60% or more and 90% or less. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a high-pressure discharge lamp, particularly a high-pressure discharge lamp mainly composed of ultraviolet radiation, in which an electrode and an electron emitting material applied to the electrode are improved.

In general, a high-melting point metal such as tungsten is used for the electrode of the high-pressure discharge lamp, and a good startability can be obtained by applying an electron-emitting material (hereinafter referred to as an emitter) mainly made of a metal oxide to the electrode. In addition, it is already well known that blackening of the inner wall of the arc tube due to sputtering of the electrode material during lighting is suppressed and a high irradiance maintenance rate is achieved.

The electrode structure is generally composed of an electrode core rod and an electrode coil. The electrode coil portion has a two-layer winding structure around the electrode core rod, and the inner coil has a gap. The outer coil is formed by “tight winding”, and the emitter is held in the gap of the inner coil. As the emitter, a tungstic acid compound containing low barium and calcium (Ba ₂ CaWO ₆ , hereinafter referred to as tungstate), or a refractory metal oxide such as yttrium oxide or scandium oxide is often used as the emitter. It has been.

By the way, high-pressure discharge lamps mainly composed of ultraviolet radiation are used for industrial applications such as semiconductors and printing fields. However, in recent years, as the size of workpieces and processing speed increase, There has been a demand for lamps with high load and high power, and as the lamp power increases, the current flowing through the electrodes also increases. Therefore, in the case of a lamp using a tongue state as the emitter, the tip temperature of the electrode at the time of lighting, that is, the operating temperature, becomes a high temperature that exceeds the melting point of the tongue state. As a result, not only does the lamp fail to start, but the tongue state itself adheres to the inner wall of the arc tube, causing a decrease in UV illuminance and short life. there were.

On the other hand, in a so-called metal halide lamp in which a metal halide is enclosed in the arc tube as a luminescent substance, an alkaline earth metal such as barium or calcium contained in the tungstate reacts with the halide, so as an emitter, Instead of the tungstate, a lamp using a metal oxide having a high melting point and a relatively low work function, such as yttrium oxide or scandium oxide, is widely used (see Patent Document 1).

However, yttrium oxide and scandium oxide have a melting point of 2500 to 2700 ° C., and the problem of scattering from the gap due to high temperature as described above hardly occurs. Therefore, the impure gas is adsorbed in the manufacturing process, and as a result, there is a problem that stable lamp characteristics cannot be obtained. In order to solve such problems, it is necessary to heat the electrode coated with the emitter to a temperature higher than the melting point of the emitter to form a dense sintered body with few voids. In order to realize this, there is a problem that an expensive firing furnace is required, and further, recrystallization of tungsten constituting the electrode is promoted during heating, so that the electrode becomes brittle, that is, the strength is reduced. There is a risk.
JP-A-7-153421

The present invention was created in order to solve the above-described problems. A high-pressure discharge lamp that suppresses the early scattering of the emitter and thus maintains a high ultraviolet illuminance over a long period of time can be obtained by a simple method. The issue is to provide.

In order to solve the above problems, the present invention has the following configuration. That is, the high-pressure discharge lamp according to claim 1 is formed by enclosing a metal additive and an inert gas inside a quartz glass arc tube, and sealing electrodes mainly composed of tungsten at both ends of the arc tube. In the high-pressure discharge lamp, the electrode is composed of an electrode core rod and an electrode coil, and an electron emitting substance (emitter) made of a binary complex oxide composed of yttrium oxide and aluminum oxide is formed on the surface of the electrode coil. The mole percentage of yttrium oxide in the entire binary composite oxide is 60% or more and 90% or less.

The high-pressure discharge lamp according to claim 2 is the high-pressure discharge lamp according to claim 1, wherein a current per unit cross-sectional area flowing through the electrode core is 1.0 A / mm ² or more and 10 A / mm ² or less. It is characterized by that.

Since the high-pressure discharge lamp according to claim 1 uses a binary complex oxide composed of yttrium oxide and aluminum oxide, in which the molar percentage of yttrium oxide is within the above range, as the emitter fixed to the electrode coil. It can be melted at a temperature that can be realized by a commonly used electric furnace, and the porous state that causes impure gas adsorption can be fixed on the electrode coil in a uniform solid state that is not formed inside. In addition, the electrode is not embrittled, and thus exhibits an effect that stable characteristics are maintained for a long time.

In the high-pressure discharge lamp according to claim 2, since the current per unit cross-sectional area flowing through the electrode core rod is limited within the above range, the temperature of the electrode coil portion can be suppressed below the melting point of the emitter, and the lifetime There is little consumption of the emitter inside, and the effect of maintaining a high UV illuminance maintenance rate for a long time is exhibited.

Hereinafter, the operation and the best embodiment of the present invention will be described by way of examples with reference to diagrams.
Table 1 shows the work functions and melting points of main metal oxides. Yttrium oxide is an oxide having the second lowest work function after alkaline earth metal oxides such as barium oxide and calcium oxide, that is, high electron emission property, but has a very high melting point of about 2700 ° C.

This binary complex oxide obtained by adding aluminum oxide to yttrium oxide has three crystal structures, that is, 3Al ₂ O ₃ .5Y ₂ O ₃ (garnet structure), Y ₂ depending on the mole percentage of each metal oxide. It is known to take O ₃ · Al ₂ O ₃ (perovskite structure) and 2Y ₂ O ₃ · Al ₂ O ₃ (monoclinic structure). As shown in the phase diagram of FIG. 4, the melting point of the Al ₂ O ₃ —Y ₂ O ₃ binary composite oxide can be arbitrarily set within a range of approximately 1800 ° C. to 2400 ° C. depending on the amount of aluminum oxide added. It is possible to adjust to. Furthermore, when the mole percentage of yttrium oxide in the binary complex oxide is 60% or more and 90% or less, the melting point is about 1800 ° C. to 2000 ° C. It becomes a temperature range in which the temperature can be raised in the heating device.

Therefore, in the present invention, in order to take advantage of the high electron emission characteristics of yttrium oxide and to reduce the melting point of the emitter to a temperature at which the fixing work on the electrode coil can be easily performed, aluminum oxide is added to yttrium oxide and Al ₂ O ₃ —Y ₂ O ₃ binary composite oxide having a mole percentage of yttrium oxide in the range of 60% or more and 90% or less (a region indicated by hatching in FIG. 4) is used as the emitter.

When the mole percentage is less than 60%, the amount of yttrium oxide that functions as an emitter decreases, so that the effect of improving electron emission is reduced, and a relatively high amount of aluminum oxide having a low melting point is contained. Therefore, the aluminum oxide is sputtered during the lifetime, which causes a harmful effect of causing a decrease in illuminance, which is not preferable. On the other hand, when the mole percentage is larger than 90%, as shown in FIG. 4, the melting point of the binary composite oxide is remarkably increased, so that heating at a higher temperature is required. The variation of the composition ratio is a region where the melting point is greatly changed, and considering the variation of various elements in the manufacturing process, it is inferior in terms of ensuring the stability of characteristics, and is not suitable for mass production.

Next, in the present invention, the current per unit cross-sectional area (current density) flowing through the electrode core is preferably 1.0 A / mm ² or more and 10 A / mm ² or less. When a large current with a current density exceeding 10 A / mm ² flows through the electrode rod, not only the electrode tip temperature but also the temperature of the electrode coil portion carrying the emitter becomes very high, and the melting point of the emitter Therefore, it becomes difficult to obtain a high UV illuminance maintenance rate over a long period of time. Note that when the current density is less than 1.0 A / mm ² , the electrode temperature does not rise, contrary to the case where a large current flows, and the diffusion of the emitter, that is, the supply of the emitter to the electrode tip is hindered. Sputtering of tungsten, which is a material constituting the electrode, is caused, and similarly, it is difficult to obtain a high ultraviolet illuminance maintenance rate for a long time.

Examples of the present invention will be described. FIG. 3 is a diagram showing the external shape of a high-pressure discharge lamp of an embodiment of the present invention in which an electrode 1 manufactured through the process described below is incorporated. Note that the present invention is not limited to the form of the lamp shown in FIG. 3, and can be applied to various forms, for example, a short arc type lamp having a generally spherical arc tube. .

1 and 2 are views for explaining a process of fixing an emitter to an electrode coil of a high-pressure discharge lamp according to the present invention, which is a schematic cross-sectional view of an electrode portion. The electrode 1 is in contact with the outer periphery of the tungsten electrode core 2 and is provided with a single tungsten coil 3 composed of a roughly wound inner coil 3a and a densely wound outer coil 3b. . In order to fix the binary complex oxide emitter on the electrode coil, first, powdery yttrium oxide and aluminum oxide are mixed so that the molar percentage of yttrium oxide to aluminum oxide is 60% or more and 90% or less. After mixing and adding a binder such as water or an organic solvent, the mixture is sufficiently stirred to form a suspension, and the suspension is impregnated into the electrode coil by a vacuum impregnation machine. Thus, as shown in FIG. 1, the emitter suspension 4 is introduced into the gap surrounded by the inner winding coil 3a and the outer winding coil 3b. Then, this electrode is dried, and the emitter is melted by heating to about 1800 ° C. to 2000 ° C. in a nitrogen atmosphere using a high-frequency heating device, and the emitter is uniformly fixed to the tungsten surface constituting the electrode core rod and coil. Let FIG. 2 shows a state in which the emitter 5 is fixed to the surfaces of the electrode core bar 2, the inner winding coil 3a, and the outer winding coil 3b.

Next, experimental results relating to various characteristics of the high-pressure discharge lamp thus produced will be described. Table 2 shows a flashing test (cycle of 4.75 hours on, 0.25 hours off) for a high-pressure mercury lamp incorporating the electrode produced by the above method and having a light emission length of 60 mm and a rated power of 400 W. , The ultraviolet illuminance maintenance rate measured after lighting for 500 hours, and the molar percentage of yttrium oxide in the binary complex oxide constituting the emitter is 60%, 80%, 90% (with yttrium oxide) Experiments were performed in which the relative molar ratio of aluminum oxide was changed in three ways: 6: 4, 8: 2, 9: 1 (Example A to Example C). The current per unit cross-sectional area flowing through the electrode core was ² to 3 A / mm ² in all cases.

As a result, when the molar percentage of yttrium oxide was 60%, 80%, and 90%, they were 86%, 87%, and 94%, respectively. On the other hand, in the case of a high-pressure mercury lamp having the same structure in which an electrode using a conventional tongue state as an emitter is incorporated, the test result is the same, and as a result, the ultraviolet illuminance maintenance rate is 71%. It was shown that a significant improvement in the travel was realized.

In addition, when the appearance of the lamp at the time of lighting for 500 hours is observed in the above test, in the case of a lamp having a conventional tongue state as an electrode, black that appears to be due to the adhesion of barium, calcium, and tungsten to the inner surfaces of both ends of the arc tube. Furthermore, devitrification accompanied by crystallization of glass promoted by the oxide of these alkali metals as nuclei caused by scattering of barium and calcium on the inner surface of the light emitting region of the arc tube. It was confirmed that On the other hand, in the lamp of the present invention in which an electrode using an yttrium oxide-aluminum oxide composite oxide as an emitter was incorporated, only a small amount of aluminum adhered to the inner surface of the arc tube around the electrode.

INDUSTRIAL APPLICABILITY The present invention can be suitably used for a high-pressure discharge lamp mainly composed of high-load, high-power ultraviolet radiation used for industrial applications such as semiconductor and printing fields.

It is a figure for demonstrating the preparation process (impregnation of emitter material) of the electrode of the high pressure discharge lamp which concerns on this invention. It is a figure for demonstrating the preparation process (attachment of an emitter) of the electrode of the high voltage | pressure discharge lamp which concerns on this invention. 1 is a schematic view showing the appearance of an embodiment of a high-pressure discharge lamp according to the present invention. It is a state diagram of Al ₂ O ₃ -Y ₂ O ₃ binary complex oxide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Electrode core rod 3 ... Single coil, 3a ... Inner winding coil, 3b ... Outer winding coil 4 ... Emitter suspension 5 ... Electron radioactive substance (emitter)
6 ... arc tube 7 ... sealing part 8 ... base

Claims (2)

In a high pressure discharge lamp in which a metal additive and an inert gas are sealed inside a quartz glass arc tube, and an electrode mainly composed of tungsten is sealed at both ends of the arc tube, the electrode includes an electrode core rod and an electrode. An electron-emitting material made of a binary complex oxide composed of yttrium oxide and aluminum oxide is applied to the surface of the electrode coil, and oxidation is occupied in the entire binary complex oxide. A high-pressure discharge lamp characterized in that the molar percentage of yttrium is 60% or more and 90% or less. 2. The high-pressure discharge lamp according to claim 1, wherein a current per unit cross-sectional area flowing through the electrode core bar is 1.0 A / mm ² or more and 10 A / mm ² or less.

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