JP5321427B2 - Short arc type discharge lamp - Google Patents

Description

  The present invention relates to a short arc type discharge lamp. In particular, the present invention relates to a short arc type mercury lamp and a short arc type xenon lamp.

  The short arc type discharge lamp has a structure in which an anode and a cathode are arranged to face each other with a gap of about several millimeters in a light emitting portion, and an arc is generated between the anode and the cathode to obtain light emission. Among these, short arc type mercury lamps are used in various exposure processes such as semiconductors, liquid crystals, and printed circuit boards. The short arc type xenon lamp is used as a light source of a projector device for digital cinema, for example.

The cathode of this type of discharge lamp is usually composed of tungsten as a substrate, and this tungsten contains an electron-emitting material commonly called an emitter. The emitter contributes to arc formation at the cathode tip by being transported (diffused) to the cathode tip during lamp operation.
However, if the emitter is depleted or the supply to the tip becomes insufficient as the lamp is turned on, a good arc is not formed, and there is a problem that the arc oscillates and the lamp voltage fluctuates significantly.

In order to solve this problem, a technology such as a storage tank for the emitter is provided inside the cathode, a sufficient amount is kept so as not to be depleted, and a stable supply is made to the tip surface using an elongated hole. Have also been proposed (JP-A-11-96965, JP-A-11-154488).
However, if an opening is provided in the tip end face of the cathode, an arc is not formed in the opening, and this causes a problem of reduced brightness.
FIG. 4 shows such a state. When an opening is formed on the tip surface of the cathode, no arc is generated above the opening. In particular, the central portion of the cathode front end surface has the highest arc luminance, that is, a bright portion, and the fact that no arc is formed in that portion has a great influence.

JP-A-11-96965 Japanese Patent Laid-Open No. 11-154488

  The problem to be solved by the present invention is to provide a cathode structure capable of stably supplying an emitter to the tip region over a long period of time and having high arc brightness.

In order to achieve the above object, a short arc type discharge lamp according to the present invention comprises a light emitting portion containing an electron-emitting substance and having a tip having a substantially truncated cone shape and an anode. Is a slope region of the truncated cone, and an elongated hole having an opening is formed within a length 2D in the axial direction of the cathode from the cathode tip, where D is the diameter of the tip surface of the cathode. It is characterized by.
Further, the opening of the elongated hole is formed so as to straddle the boundary between the tip surface of the cathode and the inclined region of the truncated cone.

The short arc type discharge lamp according to the present invention has the following effects.
(1) By forming an elongated hole extending backward from the tip of the cathode, the emitter can be supplied stably.
(2) The effect of reducing the arc brightness can be reduced by forming the elongated hole opening on the slope of the cathode.

1 shows a schematic configuration of a short arc type discharge lamp according to the present invention. An enlarged view of the tip structure of the cathode is shown. 3 shows another embodiment of a cathode according to the present invention. The tip structure of the cathode of the conventional discharge lamp is shown. Experimental results are shown.

  FIG. 1 shows a schematic configuration of a short arc type mercury lamp which is an example of a short arc type discharge lamp according to the present invention. The discharge lamp is composed of an arc tube 10 made of quartz glass, and the arc tube is composed of a light emitting part 11 and a rod-shaped sealing part 12 extending from the light emitting part 11 to both ends. The cathode 20 and the anode 30 are disposed opposite to each other with a gap of, for example, 5.0 mm inside the light emitting unit 11, and an arc bright spot is formed at the tip of the cathode 20. The light emitting portion 11 has a spherical shape or a spindle shape elongated in the tube axis direction.

  The cathode 20 is a cylindrical rod made of thorium-doped tungsten (tungsten containing thorium), for example, and the tip is formed in a substantially truncated cone shape and is supported by the cathode rod 23. The anode 30 is made of, for example, tungsten, and is a cylindrical rod as a whole. The anode 30 is formed in a substantially bullet shape having a flat surface at the tip, and is supported by the anode rod 33.

  The cathode bar 23 and the anode bar 33 each extend toward the sealing portion 12. A molybdenum foil (not shown) is embedded in each sealing portion 12. The cathode bar 23 and the anode bar 33 are bonded to a molybdenum foil to form an airtight sealing structure. An external lead 13 protrudes from the outer end of the sealing portion 12. A power supply device (not shown) is connected to the external lead 13 to supply current. Note that the cathode 20 and the anode 30 do not have to be physically separate from the cathode rod 23 and the anode rod 33, respectively, and they may be physically integrated.

  The light emitting unit 11 is filled with mercury and a rare gas containing argon or krypton. The amount of mercury enclosed is in the range of 1.0 to 20 mg / cc per inner volume of the light emitting space, and is included, for example, 2 mg / cc. The amount of rare gas sealed is 0.2 to 0.5 MPa, for example, 0.3 MPa. The total internal pressure during steady lighting of mercury and rare gas is about 2.5 MPa.

  FIG. 2 shows an enlarged structure of the cathode 20. (A) shows sectional drawing of a longitudinal direction, (b) shows the state which looked at the structure shown to (a) from the front end surface side. The cathode 20 has a substantially truncated cone shape as a whole, and is composed of an inclined portion 21 (tapered portion) at the tip and a cylindrical main body portion 22. A tip surface 24 is formed at the tip of the inclined portion 21, and four elongated holes 25 having openings formed so as to straddle the boundary between the tip surface 24 and the inclined portion 21 are formed so as to extend in the longitudinal direction of the electrode. The

  Here, the emitter contained in the cathode 20 is generally diffused toward the tip of the cathode by three types classified as intragranular diffusion, grain boundary diffusion, and surface diffusion. The diffusion rate is the fastest surface diffusion, followed by grain boundary diffusion and intragranular diffusion. The present invention can utilize surface diffusion by the inner surface of the elongated hole 25 by forming the elongated hole 25 in the inclined portion 21 of the cathode 20. A method of forming the elongated hole 25 is, for example, machining using a drill or the like.

  As for numerical examples of the cathode 20, the tip end face of the cathode is about φ0.5 mm to φ2.0 mm, and in one example, φ2.0 mm, and the diameter of the elongated hole is about φ0.2 mm to φ1.0 mm, and in one example, φ0.4 mm. The length (depth) of the elongated hole is 2.0 mm to 10.0 mm, and in one example is 3.0 mm. Further, the cathode is not limited to tungsten containing thorium, and tungsten containing rare earth elements such as tungsten containing lanthanum, tungsten containing cerium, tungsten containing yttria, and the like is also used.

FIG. 3 shows another embodiment of the cathode according to the present invention. In the structure shown in FIG. 2, the opening of the elongated hole 25 is formed so as to straddle the distal end surface 24 and the inclined portion 21, whereas in the structure shown in FIG. 3, the opening of the elongated hole 25 is completely formed in the inclined portion 21. Has been.
The advantage of this structure is that the arc formed at the cathode tip is hardly affected by the elongated hole. Even in the case of the structure shown in FIG. 2, since the opening of the elongated hole is formed on the relatively outer periphery of the tip surface, it is not easily affected by the decrease in arc luminance. However, the structure shown in FIG. 3 can further exert the effect.

  Next, an experiment showing the effect of the present invention will be described. Using eight types of discharge lamps (Lamp A, Lamp B, Lamp C, Lamp D, Lamp E, Lamp F, Lamp G, Lamp H) with different slot positions, the arc brightness and the lamp voltage fluctuation The relationship of the time when the width starts to increase beyond the normal level (hereinafter also referred to as “voltage fluctuation occurrence time”) was observed. The reason for using the voltage fluctuation occurrence time as an index is that when the supply of the emitter is insufficient, the arc becomes unstable and the lamp voltage fluctuates. Each of the 8 types of lamps is a tungsten rod cathode cut with a tip diameter (D) of φ1.2 mm and a taper angle of 60 °. Except for lamp A, it is a slender strip with a tip of φ0.35 mm and a depth of 5 mm. The hole is processed. The opening position of the elongated hole is slightly different depending on the lamp. Each of the lamps using these cathodes was lit at a mercury filling amount of 4 mg / cc and a rated power of 5.5 kW.

  Specifically, the lamp A has a cathode structure that does not have an elongated hole, and the lamp B has a cathode structure that has one elongated hole in which an opening is formed at the center of the front end surface of the cathode. Has a cathode structure having four elongated holes in which openings are formed at a position straddling the tip surface of the cathode and the inclined portion, and the lamp D is an inclined portion of the cathode, and 1D (D is the tip of the cathode) from the tip surface. The lamp E has an elongated structure having four elongated holes with openings formed at the same position as the diameter), and the lamp E is a slanted portion of the cathode and is formed with an opening formed at a position 2D from the tip surface. The lamp F has a cathode structure having four holes, and the lamp F has a cathode structure having four elongated holes which are inclined portions of the cathode and have openings formed at positions 3D from the front end surface. 4 slender holes with an opening formed at the 4D position from the tip of the inclined surface of the cathode That has a cathode structure, the lamp H is a cathode structure with four elongated holes having an opening at a 5D position from the front end surface a slope portion of the cathode. In the lamps D to H, the distance from the tip surface means the distance L in FIG.

  Here, the brightness of the arc is measured by arranging a lens in the horizontal direction of the lamp and projecting it on the CCD, and adopts the highest numerical value at the beginning of lighting for each lamp, and the lamp A in which no elongated hole is formed. This is expressed as a relative value when the arc brightness of 100% is taken as 100%. The voltage fluctuation occurrence time was measured by measuring the lamp voltage. Ramp voltage is sampled every second to obtain the standard deviation every hour, the time when this standard deviation exceeds the threshold is the voltage fluctuation occurrence time, and the relative time when the voltage fluctuation occurrence time of lamp A is 100% Expressed as a value.

  As a result of the experiment, the maximum brightness of lamp B is 97.5%, the voltage fluctuation occurrence time is 155%, the maximum brightness of lamp C is 100.6%, the voltage fluctuation occurrence time is 210%, and the maximum brightness of lamp D is 99.9% The voltage fluctuation occurrence time is 206%, the maximum brightness of lamp E is 99.9%, the voltage fluctuation occurrence time is 195%, the maximum brightness of lamp F is 100%, the voltage fluctuation occurrence time is 107%, The maximum brightness of G was 100.1%, the voltage fluctuation occurrence time was 103%, the maximum brightness of lamp H was 99.8, and the voltage fluctuation occurrence time was 101%.

  FIG. 5 is a graph showing the experimental results. In the lamp B in which the opening of the elongated hole is provided at the center position of the cathode front end surface, the arc brightness is lowered by 2.5 points with respect to the lamp A. On the other hand, in the lamp C in which the opening was formed so as to straddle both the front end face and the inclined portion, and the lamps D to H in which the opening was formed in the inclined portion, no reduction in arc brightness was observed. Rather, the lamp C has an increase in arc brightness of 0.6 points, and it can be assumed that electrons are strongly emitted from the periphery of the opening. As a result, in terms of arc luminance, it was confirmed that even if the elongated hole opening was provided in the inclined part of the cathode, at least no adverse effect occurred, and the opening was provided so as to straddle the tip surface and the inclined part. It has been found that the arc brightness can be increased.

  Next, in the voltage fluctuation occurrence time, 4 long slots with openings formed at positions straddling the front end face of the cathode and the inclined portion from the lamp B having one elongated hole with an opening formed at the center of the front end face of the cathode. The lamp C having one has a longer voltage fluctuation occurrence time. This is considered to be due to an increase in the supply amount of the emitter due to an increase in the number of holes. Further, it can be seen that the voltage fluctuation occurrence time is shortened as the opening position of the elongated hole is farther from the cathode tip, that is, as the distance L is increased in the structure shown in FIG. This is considered to be due to the fact that when the opening of the elongated hole faces the arc, even if the emitter that has moved by diffusion on the hole surface evaporates, it is ionized inside the arc and returns to the cathode again. On the other hand, if the opening of the elongated hole does not face the arc, the emitter is evaporated and scattered without returning to the cathode. For this reason, it is desirable that the slot opening face the arc at least until the end of the lamp life. From the figure, when D exceeds 2, the voltage fluctuation occurrence time is drastically reduced. Therefore, it is preferable that the opening of the elongated hole is less than the distance 2D (D is the diameter of the tip surface) from the tip surface of the cathode. Recognize. The size of the cathode tip surface (tip diameter D) is designed according to the load on the cathode, and the tip diameter is designed wider as the load is higher. For this reason, it can be said that it is optimal for the index of the part where the arc faces.

  Further, in the lamps C to H, no phenomenon was observed in which the internal space of the elongated hole was blocked with particles. This is presumably because the growth and deformation of the tungsten particles constituting the electrode did not occur because the hole was formed at a low temperature position.

  Here, in the discharge lamp of the present invention, the number of the elongated holes formed in the cathode is not limited, and may be one or plural. However, when a plurality of electrodes are provided, it is desirable to form them symmetrically about the electrode axis when viewed from the front end surface (in the structure as shown in FIG. 2b). This is because the emitters are supplied in a well-balanced manner.

  Furthermore, in the discharge lamp of the present invention, the shape of the elongated hole formed in the cathode is not limited to a circle, but may be an oval, a triangle, or a square.

  Furthermore, the discharge lamp of the present invention is not limited to the short arc type mercury lamp in which mercury is enclosed, and may be a short arc type xenon lamp in which xenon is enclosed as a luminescent gas.

  Furthermore, the discharge lamp of the present invention is not limited to a discharge lamp containing thorium oxide as an emitter, and may be one containing lanthanum oxide or yttrium oxide.

  Furthermore, in the discharge lamp of the present invention, the tip surface of the cathode is not limited to a flat surface, and may be a curved surface. In this case, the diameter D of the front end surface of the cathode is the diameter of a circle formed by the joint between the curved surface and the tapered portion, and the distance L from the front end surface of the cathode is the distance from the front end of the cathode to the opening end of the elongated hole. To do.

DESCRIPTION OF SYMBOLS 1 Discharge lamp 10 Light emission tube 11 Light emission part 12 Sealing part 20 Cathode 24 End face of cathode 25 Elongated hole 30 Anode

Claims (2)

In a short arc type discharge lamp containing an electron-emitting material and having a light emitting part including a cathode having a substantially truncated cone shape at the tip and an anode,
The cathode is a slope region of the truncated cone, and when the diameter of the tip surface of the cathode is D, an elongated hole having at least a part of an opening within 2D in the axial direction of the cathode from the cathode tip A short arc type discharge lamp characterized in that is formed.   2. The discharge lamp according to claim 1, wherein the opening of the elongated hole is formed so as to straddle a boundary between a tip surface of the cathode and a slope region of the truncated cone.

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