JP5527222B2 - Short arc type discharge lamp - Google Patents

Description

  The present invention relates to a short arc type discharge lamp, and more particularly to a short arc type discharge lamp applied to an exposure light source for a semiconductor or liquid crystal manufacturing field or a backlight light source for a projector.

  The short arc type discharge lamp is used as a light source for an exposure apparatus or a backlight of a projector by combining with an optical system because the tip distance between a pair of electrodes opposed to each other in the arc tube is short and close to a point light source. Yes.

Japanese Patent Laid-Open No. 10-188890 discloses a conventional short arc type discharge lamp.
FIG. 8 shows the conventional short arc type discharge lamp. An arc tube 10 of the short arc type discharge lamp 1 includes a light emitting portion 11 formed in a substantially spherical shape at the center and sealing portions at both ends thereof. 12 is provided. In the light emitting section 11, a cathode 21 and an anode 31 made of tungsten or the like are disposed so as to face each other, and a light emitting material such as mercury or xenon is enclosed in the light emitting space S.
The electrode shafts 22 and 32 connected to the cathode 21 and the anode 31 are sealed by the sealing portion 12 via a metal foil (not shown).

In recent years, however, in the short arc type discharge lamp used in the manufacturing process of semiconductors and liquid crystal panels, as shown in Japanese Patent Laid-Open No. 2000-181075, constant power is always used for power saving. Instead of lighting, the lighting method (normal lighting) is turned on only during exposure (normal lighting), and it is turned on (standby lighting) with a minimum power smaller than the rated power when waiting for substrate movement, etc. Standby lighting) is adopted.
For example, it is repeated that the light is lit for 0.1 to 10 seconds at the rated power during exposure, and is lighted for 0.1 to 100 seconds at a standby power smaller than the rated power during standby.

By the way, when the lamp is turned on / off or when the input power is changed during full standby lighting, the heat flux flowing from the arc to the anode changes, so the anode temperature changes and internal stress is applied to the anode. Will occur.
At this time, as shown in FIG. 9, the central portion 50 of the anode tip surface facing the arc is the portion where the temperature change is the largest, and therefore the thermal expansion also increases. On the other hand, the annular part 51 around the central part 50 has less temperature change than the central part 50 and its thermal expansion is also small.
Therefore, the central portion 50 receives compressive stress from the peripheral annular portion 51 due to the thermal expansion, and as a result, deforms so as to protrude from the tip surface.

Such a protrusion remains without returning to its original shape even after the temperature at the anode tip is stabilized during rated lighting. In addition, especially during full standby lighting, such deformation repeatedly occurs, and the protrusions are enlarged and accumulated.
Then, the discharge concentrates on the enlarged protrusion, the protrusion is abnormally overheated, the electrode material evaporates and adheres to the inner wall of the arc tube, the inner wall of the arc tube becomes black, and the rapid There was a problem of causing a decrease in illuminance.

In order to solve the above-mentioned problems of the prior art, the present inventors previously disclosed in Japanese Patent Application No. 2009-165272 an insert that is separate from the anode in the opening formed at the center of the tip of the anode. A structure is proposed in which a cushioning material made of a metal having a lower yield stress is interposed.
An outline thereof is shown in FIGS. 10A and 10B, and an opening 35 that opens to the distal end surface 33 is formed in the central portion of the distal end surface 33 of the anode 31 made of tungsten. An insert 36 made of the same material as that of the anode 31 is formed separately from the anode 31 and has a shape aligned with the opening 35. The insert 36 sandwiches the cushioning material 37 therebetween, It is press-fitted and inserted into the opening 35 by means such as driving.
The buffer material 37 is made of a metal material having a lower yield stress at the same temperature than that of the anode 31 and the insert 36, and specifically, a metal foil made of tantalum, molybdenum, niobium, rhenium, or the like.

With such a structure, when the insert 36 constituting the center of the tip of the anode 31 is thermally expanded, the buffer material 37 between the insert 36 and the opening 35 undergoes high-temperature creep deformation, and the insert 36 The thermal expansion is absorbed and relaxed, and is not subjected to compressive stress due to the annular portion 33a around the opening 35.
As a result, it is possible to expect an effect that the insert 36 constituting the center of the tip is not deformed and a local protrusion is not formed.

However, it has been found that there may be a new problem depending on conditions in the above structure due to further increase in lighting power and severe full standby lighting conditions.
As shown in FIG. 11, the buffer material 37 is thermally expanded and plastically deformed as the temperature rises. At this time, the shock absorbing material 37 receives a compressive force between the insert 36 and the peripheral annular portion 33a at the tip of the anode 31 and escapes in the axial direction, causing a phenomenon that the buffer material 37 protrudes from the tip surface 33 of the anode 31. Sometimes.
Thus, if the buffer material 37 protrudes from the tip of the anode, the protruding end 37a is excessively heated and evaporates, which causes blackening of the arc tube and a decrease in illuminance.

In addition, as shown in FIG. 12, it has been found that there may be a new problem that a protrusion 38 is formed around the insert 36 inserted into the anode 31.
The anode 31 receives an arc discharge when the lamp is lit, and the arc discharge has the highest temperature at the center, and the temperature decreases from the center toward the periphery. For this reason, the insert 36 located at the center of the anode becomes high temperature, and the amount of thermal expansion of the insert 36 is larger than that of the anode 31. On the other hand, on the anode 31 side, the side in contact with the buffer material 37 has the highest temperature, so the amount of expansion is the largest, and the amount of expansion decreases toward the periphery. Then, although the expansion of the insertion body 36 is absorbed by the buffer material 37, the expansion on the buffer material side of the anode 31 cannot be released to the peripheral side where the expansion amount is small. 37 has already absorbed the expansion from the insertion body 36 and cannot fully absorb this expansion amount of the anode 31. Therefore, it is presumed that the amount of expansion is directed toward the tip and the protrusion 38 is formed.
Thus, when the protrusion 38 is formed around the insert 36 on the tip end surface of the anode, the distance between the electrode of the protrusion 38 and the cathode is shortened, and the arc is concentrated on the protrusion 38. As a result, the protrusion 38 is excessively heated and evaporates, which causes blackening of the arc tube and a decrease in illuminance.

Japanese Patent Laid-Open No. 10-188890 JP 2000-181075 A

The problem to be solved by the present invention is to reduce the thermal stress generated at the anode tip, particularly in the short arc type discharge lamp adopting the full standby lighting method, in view of the problems of the above-mentioned prior art. It is intended to provide a short arc type discharge lamp having an anode structure capable of preventing the central portion of the lamp from being deformed and preventing blackening.
At the same time, a new problem related to the proposal by the previous application, that is, the full standby lighting condition becomes severe in the short arc type discharge lamp having the anode structure in which the insert is press-fitted with a buffer material interposed at the tip of the anode. For example, the buffer material may protrude from the tip of the anode, and a structure that solves the new problem of forming protrusions around the insert is also provided.

  In order to solve the above-mentioned problems, an opening is formed in the center of the tip of the tip surface of the anode in the short arc type discharge lamp according to the present invention, and an insert separate from the anode is formed in the opening. It is inserted through a buffer material made of a metal having a lower yield stress than the material, and the tip of the buffer material is set back from the tip surface of the anode.

  In addition, a concave groove is formed in the tip surface of the anode over a part of the anode adjacent to the tip of the buffer material and a part of the insert.

According to the short arc type discharge lamp of the present invention, the tip of the cushioning material interposed between the anode and the insert press-fitted into the center of the tip is retracted from the tip surface of the anode. -Even when the temperature of the anode tip changes and the insert thermally expands during standby lighting, the insert is not absorbed by the cushioning material and the tip of the insert is not deformed and projected. The tip of the buffer material does not protrude beyond the tip surface of the anode, and the discharge arc does not concentrate and evaporate there.
In addition, since a concave groove is formed across a part of the anode adjacent to the tip of the buffer material and a part of the insert, thermal expansion of the adjacent insert across the buffer material and the anode side Thermal expansion can be escaped into the concave groove, and there is no such thing as local deformation and protrusion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a main part of a tip end portion of an anode of a first embodiment of a short arc type discharge lamp according to the present invention. FIG. 2 is an operation explanatory view of the first embodiment of FIG. Sectional drawing of the principal part of 2nd Example. Operation | movement explanatory drawing of 2nd Example of FIG. Sectional drawing of 3rd Example. Sectional drawing of 4th Example. The graph showing the effect of this invention. FIG. Explanatory drawing of the principal part of FIG. The anode sectional view concerning a prior application. Explanatory drawing of the defect of the anode of FIG. FIG. 11 is another explanatory diagram of defects of the anode in FIG. 10.

1A and 1B are cross-sectional views of the first embodiment, in which FIG. 1A is an assembled cross-sectional view, and FIG.
In FIG. 1, the front end surface 33 of the anode 31 is composed of a flat surface 33a and a tapered surface 33b, and more specifically, an opening that opens to the flat end surface 33a at the central portion thereof, more specifically, at the central portion of the flat surface 33a. 35 is formed. An insert 36 made of the same material as that of the anode 31 is formed separately from the anode 31 and has a shape aligned with the opening 35. The insert 36 sandwiches the cushioning material 37 therebetween, It is press-fitted and inserted into the opening 35 by means such as driving.

Specifically, an insert 36 made of the same tungsten is inserted into the opening 35 on the tip surface of the anode 31 made of tungsten, and the opening 35 and the insert 36 make it easy to press-fit the insert 36. For this reason, it is preferable to have a slightly tapered shape.
The buffer material 37 is made of a metal material whose yield stress at the same temperature is smaller than that of the anode 31 and the insert 36, specifically, tantalum, molybdenum, niobium, rhenium or the like. In this embodiment, the metal foil Then, it is wound around the outer periphery of the insert 36 and is inserted into the opening 35 together with the insert 36.

  At this time, as shown in FIG. 1B, the cushioning material 37 is configured such that its tip 37 a is sufficiently retracted from the tip surface 33 of the anode 31. By doing so, as shown in FIG. 2, even if the buffer material 37 is thermally expanded at the time of lighting, the expansion amount X is accommodated in the space between the anode 31 and the insert 36, and the tip 37a is the anode 37a. It does not protrude from the tip surface 33 of 31.

With the above configuration, when the insert 36 constituting the center of the tip of the anode 31 is thermally expanded, the cushioning material 37 sandwiched between the insert 36 and the surrounding annular portion causes high temperature creep deformation. In this way, the thermal expansion of the insert 36 is absorbed and relaxed, and is not subjected to compressive stress due to the peripheral annular portion. As a result, the insert 36 constituting the center of the distal end is not deformed, and no local protrusion is formed.
In addition, since the tip 37a of the cushioning material 37 is retracted from the tip surface 33 of the anode 31, the tip does not protrude beyond the tip of the anode even when thermally expanded.

3A and 3B are sectional views of the second embodiment, in which FIG. 3A is an assembled sectional view, and FIG. 3B is an enlarged sectional view of a main part thereof.
In this embodiment, as shown in FIG. 3, the tip surface 33 of the anode 31 has a concave groove 39 extending over a part of the anode adjacent to the tip of the buffer material 37 and a part of the insert 36. Is formed. The concave groove 39 is formed by cutting after inserting the insert 36 into the anode 31. Therefore, the tip 37a of the buffer material 37 is also cut at the same time, and the tip 37a is located so as to face the concave groove 39 and is in a position retracted from the tip surface 33 of the anode 31.
Of course, also in this case, the tip 37a of the cushioning material 37 may be in a position further retracted from the bottom surface of the concave groove 39, and the position is determined to such an extent that the original cushioning function of the cushioning material 37 is not impaired. do it.

By doing so, as shown in FIG. 4, even if the cushioning material 37 is thermally expanded, the tip 37 a is accommodated in the concave groove 39 and does not protrude from the tip surface 33. Therefore, the arc does not concentrate on the tip 37 a of the buffer material 37, and a decrease in illuminance due to evaporation of the buffer material 37 can be prevented.
Further, even if a part of the anode 31 and the insert 36 adjacent to each other with the cushioning material 37 interposed therebetween are thermally expanded, the thermal expansion part escapes into the concave groove 39, and the part is more than the tip surface 33. It does not deform so as to protrude, and does not form a protrusion.
In addition, although the shape of the ditch | groove 39 showed the thing of a cross-sectional semicircle, other shapes may be sufficient and the processing method may be based on laser processing other than cutting.

In the above embodiment, the insert 36 is located within the flat surface 33a of the tip surface 33 of the anode 31, but as shown in FIG. 5, the insert 36 is the tip flat surface 33a. And the boundary between the insert 36 and the anode 31 may be the boundary between the flat surface 33a and the taper surface 33b. Also, as shown in FIG. 6, the insert 36 has a flat surface 33a. In some cases, the boundary with the anode 31 is located on the tapered surface 33b.
In these cases, the tip flat surface 33 a of the anode 31 is constituted by the tip flat surface of the insert 36.
Even in these cases, as shown in FIG. 5 and FIG. 6, by providing the concave groove 39 at the boundary between the insert 36 and the anode 31, the same effect as in the second embodiment shown in FIG. Can be obtained.

Experiments were conducted to confirm the effect of the present invention.
<Anode structure>
The anode shown in FIG. 3 was prepared as the anode of the present invention, and the anode shown in FIG. 10 was prepared as a comparative example. Then, as an example of the prior art, the one shown in FIG. 9 without an insert or cushioning material was prepared.
<Anode material>
The anode body was made of tungsten, the insert was made of tungsten, and the buffer material was made of tantalum.
<Specifications>
Each lamp was prepared with an enclosed mercury amount of 25 mg / cc and electrical characteristics of 25 kW (160 V, 156 A).
Each anode was formed with a tip diameter of 9 mm, a barrel diameter of 35 mm, and a length in the electrode axis direction of 60 mm.
The insert of the comparative example was formed with a tip diameter of 9 mm and a length of 15 mm. In the present invention, the same insert as that of the comparative example was provided, and an R1 groove having a depth of 0.5 mm was provided at a position of a tip diameter of 9 mm by cutting with a lathe.
The buffer material of the comparative example and the present invention had a thickness of 50 μm, and the comparative example was provided so that the end of the buffer material was positioned at the position of the anode tip surface when the lamp was not lit.
<Lighting method and measurement method>
The lighting cycle of 2 seconds at an input power of 25 kW and 7 seconds at 12.5 kW was repeated, and the illuminance meter arranged outside the arc tube of the lamp was used to measure the I-line (wavelength 365 nm) illuminance as the lighting time passed. In the experiment, the measurement was terminated when the relative illuminance (illuminance maintenance ratio) was below 80% in the prior art, and the comparative example and the present invention were measured when the relative illuminance (illuminance maintenance ratio) was below 90%. finished.

FIG. 7 shows the experimental results. The experimental results show that the illuminance at the start of lighting is 100%, and the illuminance after the lighting time has elapsed is expressed as relative illuminance with respect to the illuminance at the start of lighting.
In the conventional example (■), when the lighting time was 500 hours, the illuminance maintenance rate was below 90%, and even if the lighting time was continued, the illuminance maintenance rate was not improved and continued to decrease.
In the comparative example (）), the illuminance maintenance rate was less than 90% when the lighting time was 750 hours.
In the present invention (◯), the illuminance maintenance rate exceeded 90% until 1250 to 1300 hours, and was less than 90% when 1350 hours had elapsed.

<Discussion>
In the conventional example, a protruding portion is formed at the tip of the anode, and the protruding portion evaporates and scatters, thereby blackening the inner surface of the arc tube, and the illuminance maintenance rate of 90% is 500 hours, which is higher than that of the comparative example and the present invention. It is estimated that the illuminance maintenance rate was low.
On the other hand, in the comparative example, by providing the insert and the cushioning material, the expansion of the insert is absorbed by the cushioning material, so that the formation of the protruding portion from the distal end surface of the insert is suppressed, and the illuminance is higher than in the past. It is estimated that the maintenance rate has increased and the illuminance maintenance rate of 90% has reached 750 hours.
However, the buffer material protrudes from the tip of the anode, or a protrusion is formed on the anode portion around the insert, and the protruding portion of the buffer material and the protrusion of the anode evaporate, thereby blackening the inner surface of the arc tube. It is estimated that the illuminance maintenance rate was lower than that of the present invention. When the anode tip surface of the comparative example was observed after 750 hours of lighting, an annular protrusion was formed so as to surround the tip surface of the insert.
In the present invention, the illuminance maintenance rate of 90% was 1350 hours, which was significantly longer than the conventional example of 500 hours and the comparative example of 750 hours. This is because by providing a concave groove and removing the buffer material, part of the insert and part of the anode tip surface, it is possible to prevent the buffer material from protruding from the tip surface of the insert, and It is presumed that the formation of a protrusion on the insertion surface side of the distal end surface is also suppressed. As a result, it is presumed that the present invention was able to significantly increase the illuminance maintenance rate because evaporation by the protrusion of the buffer material and evaporation of the protrusion at the tip end face of the anode could be suppressed.

21 Cathode 31 Anode 33 Anode tip surface 33a Flat surface 33b Tapered surface 34 Peripheral annular portion 35 Opening 36 Insert 37 Buffer material 37a Buffer material tip 39 Concave groove

Claims (2)

In a short arc type discharge lamp in which an anode and a cathode are arranged opposite to each other in an arc tube,
An opening is formed in the center of the tip of the tip surface of the anode, and an insert separate from the anode is inserted into the opening via a buffer material made of a metal having a lower yield stress than the anode material. Become
A short arc type discharge lamp characterized in that the front end of the buffer material recedes from the front end surface of the anode. 2. The short according to claim 1, wherein a concave groove is formed on a tip surface of the anode so as to extend over a part of the anode adjacent to the tip of the buffer material and a part of the insert. Arc type discharge lamp.

Images