JPH01161653A - Short arc discharge lamp - Google Patents

Abstract

PURPOSE:To prevent large deformation from being generated in the end shape of a cathode by forming an electrode, especially a cathode, out of tungsten sintered substance which contains lanthanum oxide by 1-5 weight percent. CONSTITUTION:A large anode 2 and a cathode 3 far smaller than this are provided oppositely at both end sealed parts 1a, 1a of an air-tight container 1 made of quartz glass and xenon gas at specified pressure is charged inside of it. And the cathode 3 consists of mixed sintered substance which contains tungsten and lanthanum oxide at the rate of 1-5 weight percent of the whole for the lanthanum oxide, and its end shape is formed in a tapered shape at an opening degree of about 8-45 deg. to obtain stable arc. Since the cathode of this lamp is small in temperature change by the current change, the deformation also becomes small. Hereby, even if it is used by a lighting method with large current fluctuation, it does not generate large shape change at the early stage at the cathode end part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to short arc discharge lamps such as xenon lamps and ultra-high pressure mercury lamps.

(Prior technology) Conventionally, short arc discharge lamps such as xenon lamps and ultra-high pressure mercury lamps are similar to point light sources because the distance between the tips of the anode and cathode, which are placed opposite each other in the sealing portions at both ends of a quartz glass airtight container, is short. By taking advantage of its advantages and using it in combination with an optical system, light collection efficiency can be made extremely high, and it is widely used in fields such as movie projectors and semiconductor exposure equipment.

For example, in the case of a projector that uses a xenon lamp as a light source, the lamp must be turned on continuously, and the light from this lamp must be chopped by a shutter in synchronization with the advance of the film frame. In order to eliminate the flickering that occurs during the process, there are known products that reduce flickering by increasing the number of times of chopping within a unit time.

However, this method of chopping light using a shutter has a problem in that efficiency is low because the xenon lamp is lit with a constant current even while the shutter is closed.

In contrast, a method that does not use a shutter has been developed. In this method, the minimum amount of current necessary to maintain the xenon lamp's discharge is constantly passed through the lamp, effectively stopping the lamp from emitting light. ).

It emits light by periodically superimposing large pulse currents.

A pulse current superimposition method that uses a flashing lamp, or a pulse current superimposition method that uses a shutter but periodically superimposes a large pulse current in synchronization with the shutter to emit light, reduces flicker and produces a large amount of light only when the light is emitted. Since a pulsed current is passed, efficiency can be improved.

However, in both methods, the current increases rapidly when the pulse current is superimposed, and the current fluctuations are large, resulting in severe electrode deterioration and wear and tear.In particular, the tip shape of the small, tapered cathode made of thoriated tungsten quickly undergoes a large change in shape. There are drawbacks such as the lamp becoming unstable during lighting, causing flickering of the screen, or the lamp not lighting up in a short period of time due to poor starting performance.

Also, short arc ultra-high pressure mercury lamps.

It is used as a powerful ultraviolet light source, for example, in semiconductor exposure equipment, but in order to increase exposure speed and improve productivity, a flash lighting method has been adopted in which a large current is applied to the standby lamp to turn it on. It has become. Therefore, in this case as well, as in the case of the xenon lamp mentioned above, the current fluctuations are large and the flash frequency is high, causing severe deterioration and wear of the electrodes. In particular, the shape of the cathode tip changes early, causing The strength becomes unstable.

This may cause defects such as variations in the product after exposure.

(Problems to be Solved by the Invention) As mentioned above, when a short arc discharge lamp is used in a lighting method with large current fluctuations, such as a pulse current superimposed lighting method or a flash lighting method, the shape of the tip of the electrode, especially the cathode, may deteriorate prematurely. This has the drawback of causing large deformation and various inconveniences.

Therefore, the present invention solves the above-mentioned drawbacks of conventional lamps, and provides a long-life short arc discharge lamp that does not cause early large deformation of the cathode tip shape even when used in a lighting method with large current fluctuations. The purpose is to

[Structure of the invention]

(Means for Solving the Problems) The short arc discharge lamp of the present invention has an electrode, particularly a cathode.
It is configured to be formed of a tungsten sintered body containing ~5% by weight of lanthanum oxide.

(effect) Although the effect of the configuration of the present invention is not clear.

When the current fluctuations are very large and the electrode, especially the cathode, is used in a way that alternates between thermally unstable and stable states and repeats them at short intervals, the conventional cathode material thoriated tungsten is used. It is presumed that the cathode of the lamp of the present invention, which is made of a sintered body of lanthanum oxide and tungsten, which has a smaller work stroke, undergoes less temperature change due to current changes, and therefore less deformation.

(Example) The present invention will be described in detail below based on an example shown in one drawing. FIG. 1 shows a partially cutaway front view of a xenon lamp having a lamp voltage of 20 V, a lamp current of 25 A, and a lamp rated power of 500 W according to the present invention. In the diagram (1) is the maximum outer diameter of 3
011iI is an airtight container made of quartz glass, and a large anode (2) and a much smaller cathode (3) are placed opposite each other in the sealing parts (la) and (la) at both ends, and a predetermined It is filled with high pressure xenon gas. In addition, the above cathode (3)
is a mixed sintered body containing tungsten and lanthanum oxide in a proportion of 2% by weight of the lanthanum oxide.

Its tip is tapered with an opening angle of about 8'' to 45 degrees in order to obtain a stable arc.

The xenon lamp having such a configuration was lit for 80 hours at a large current of 25 A (ampere) with a flashing cycle of 10 minutes on and 10 minutes off, but no major deformation was observed at the cathode tip.

Next, the above-mentioned xenon lamp having a cathode in which the content of lanthanum oxide was varied within the range of 0.5 to 5% by weight, and the conventional cathode made of thoriated tungsten (thoria content: 2.0%) were used. FIG. 2 shows the results of a flashing test conducted on the same xenon lamp with the same cycle as above.

The horizontal axis of the figure is the actual lighting time in the above cycle, and the vertical axis is the degree of deformation of the cathode tip, and the rate of change in the distance from the opposite anode tip (
The above-mentioned separation distance when the lighting is on for 0 hours is assumed to be a rate of change of 0%. ).

As is clear from the figure, each cathode containing lanthanum oxide has a smaller degree of deformation than the conventional cathode and is therefore more effective.

However, if only 0.5% of lanthanum oxide is contained, the effect may be reduced when considering variations in the cathode manufacturing process, that is, the mixing, molding, and sintering processes of each raw material powder. The lower limit of content is 1%
It is preferable that

On the other hand, as shown in Figure 9, the upper limit of the content is almost the same whether it is 3% or 5%, so it is meaningless to include more than 5%. Therefore, the content of lanthanum oxide is 1~
It is preferably within the range of 5%.

In addition, a xenon lamp with a lamp rated power of 3.6
A flashing test was conducted with a cycle of 10 minutes on and 10 minutes off by applying a large current to 20, and for a short arc ultra-high pressure mercury lamp with a rated power of 1y, the current ratio during flashing to the base current was 167%. The tests were conducted using a flash lighting method with a flash time of about 0.2 to 0.4 milliseconds, but lanthanum oxide was
The cathode made of a mixed sintered body containing tungsten at a ratio of 5% by weight did not undergo any major shape change at the tip end.

〔Effect of the invention〕

As described above, according to the configuration of the present invention, even when used in a pulse current superimposed lighting method or a flash lighting method in which a large pulse current is superimposed in two periods to light the lamp, a large shape change is caused at the tip of the cathode at an early stage. Therefore, the distance between the electrode tips becomes stable, and a short arc discharge lamp having stable characteristics over a long period of time can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of a xenon lamp according to an embodiment of the present invention, and FIG. 2 is a graph showing the results of a comparative test of the degree of deformation of the cathode tip due to blinking lighting. (11...airtight container, (la)...
...Sealing part. (2)...anode, (3)...cathode.

Claims (1)

[Claims] An anode and a cathode are disposed opposite to each other at both end sealed portions of an airtight container made of quartz glass, and the cathode contains tungsten and lanthanum oxide in a proportion of 1 to 5% by weight of the whole. A short arc discharge lamp characterized in that it is formed from a mixed sintered body made of.