JP2015026554A - Discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure in which an emitter is prevented from being excessively evaporated from a cathode and exhausted on early state and smooth lighting can be performed even in initial lighting, in a discharge lamp which is formed by adding any other emitter than thorium to the cathode within a luminous tube.SOLUTION: A main body part 31 in a cathode 3 is formed from a high melting point metal material not containing thorium, a distal end portion 32 is formed from a high melting point metal material containing an emitter (excluding thorium) and within a sealed space formed within the main body part 31 and/or the distal end portion 32, a sintered body 34 is embedded which contains an emitter (excluding thorium) of a higher concentration than that of the emitter contained in the distal end portion 32. A protrusion (male screw 34a) on an outer surface of the sintered body 34 and a recess (female screw 33a) on an inner surface of the sealed space 33 are engaged with each other.

Description

  The present invention relates to a discharge lamp including an emitter for improving electron emission at a cathode, and particularly to a discharge lamp including an emitter other than thorium.

Generally, in a discharge lamp with high input and high brightness, an emitter is added to the cathode to facilitate electron emission. For example, Japanese Unexamined Patent Application Publication No. 2012-15008 (Patent Document 1) discloses a cathode for a discharge lamp containing thorium oxide as an emitter.
However, thorium is subject to legal regulations as a radioactive substance, and careful management is required for its management and handling. Therefore, an alternative substance to replace thorium is desired.

As an alternative to the thorium, materials using rare earth elements and their compounds have been proposed. Rare earth elements are materials that have a low work function (generally indicating the amount of energy required when electrons are emitted from the material surface to the outside) and are excellent in electron emission, and are expected as substitutes for thorium.
Japanese Patent Laid-Open No. 2005-519435 (Patent Document 2) additionally describes tungsten as a cathode material as an emitter as lanthanum oxide (La ₂ O ₃ ), hafnium oxide (HfO ₂ ), zirconium oxide (ZrO ₂ ). A discharge lamp containing the above is disclosed.

However, since rare earth oxides such as lanthanum oxide (La ₂ O ₃ ) have a higher vapor pressure than thorium oxide (ThO ₂ ), they are relatively easy to evaporate. Therefore, when a rare earth oxide is used instead of thorium oxide as an emitter to be contained in the cathode, the rare earth oxide is excessively evaporated and depleted at an early stage. Due to the exhaustion of the emitter, there is a problem that the electron emission function at the cathode is lost, flicker occurs, and the lamp life is shortened.
In addition, only the emitter that contributes to the electron emission characteristics is present at the tip of the cathode, and it can be said that this is because the transport from the cathode rear end toward the tip is not performed quickly. For this reason, in discharge lamps using emitter materials other than thorium, there are still problems such as unstable lighting at an early stage. In particular, in a discharge lamp with a high input of 1 kW or more, it is remarkable that the vapor of rare earth elements or barium-based substances leads the discharge lamp to unstable lighting.

JP 2012-15008 A JP-A-2005-519435

  In view of the above-mentioned problems of the prior art, the present invention provides a discharge lamp in which a cathode and an anode are arranged opposite to each other inside an arc tube, and even if an emitter other than thorium is added to the cathode, An object of the present invention is to prevent the exhaustion, maintain the electron emission function for a long time, extend the life of the flicker of the lamp, and provide a structure excellent in lighting startability at the initial lighting.

  In order to solve the above problems, in the present invention, the cathode is composed of a main body portion and a front end portion joined to the front end side thereof, and the main body portion is made of a refractory metal material not containing thorium, The tip portion is made of a refractory metal material containing an emitter (excluding thorium) and contained in the tip portion in a sealed space formed inside the body portion and / or the tip portion. A sintered body containing an emitter (except for thorium) having a higher concentration than the emitter concentration is embedded, and a convex portion is formed on the outer surface of the sintered body, and a concave portion is formed on the inner surface of the sealed space. And are engaged with each other.

According to the present invention, in the cathode, a tip portion containing an emitter other than thorium is joined to the tip of the main body portion, and the tip is placed in a sealed space formed inside the main body portion and / or the tip portion. Since a sintered body containing an emitter (except for thorium) with a higher concentration than that of the part is embedded, when the discharge lamp is initially turned on, the emitter (excluding thorium) included in the tip part By covering the tip portion, good lighting performance is provided.
And depending on the lighting time, the emitter initially contained in the tip is consumed, but from the sintered body containing the high concentration emitter inside the cathode, the emitter is diffused and supplied to the tip, so Good lighting performance is stably maintained for a long time without the emitter being depleted at the tip.
Furthermore, since the sintered body is screwed and embedded in the inner surface of the sealed space inside the cathode, the sintering of the sintered body having a lower degree of sintering proceeds due to a temperature rise due to lamp lighting. Even if the volume is reduced, the thread of the male screw of the sintered body and the thread groove of the female screw in the sealed space are kept in contact in either of the axial directions. This has the effect of ensuring good transmission and thermal diffusion of the emitter from the sintered body to the electrode body or tip.

1 is an overall view of a discharge lamp having a cathode structure according to the present invention. The cathode structure figure showing the example of the present invention. The manufacturing process figure of the cathode of this invention. Sectional drawing explaining the effect of the cathode structure of this invention. The expanded sectional view of FIG.

FIG. 1 shows the overall structure of a discharge lamp having a cathode structure according to the present invention. In a discharge lamp 1, a cathode 3 and an anode 4 are disposed inside an arc tube 2 so as to face each other.
As shown in FIG. 2, the cathode 3 includes a main body portion 31 and a distal end portion 32 joined to the distal end thereof.
The main body 31 is made of a refractory metal material such as tungsten or molybdenum that does not contain thorium.
The distal end portion 32 is joined to the distal end side of the main body portion 31, that is, the surface facing the anode 4 by an appropriate joining means such as solid phase joining or welding. The tip portion 32 contains an appropriate amount of emitter other than thorium (hereinafter, the emitter contained in the tip portion is also referred to as a first emitter).
As the first emitter other than thorium, for example, lanthanum oxide (La ₂ O ₃ ), cerium oxide (CeO ₂ ), gadolinium oxide (Gd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), praseodymium oxide (Pr) ₆ O ₁₁ ), neodymium oxide (Nd ₂ O ₃ ), hafnium oxide (HfO ₂ ), or the like is used alone or in combination.

Here, the content of the first emitter is set low, for example, 0.5 wt% to 5.0 wt%. This first emitter is for ensuring startability when the lamp is initially turned on, and the concentration is set low to prevent the emitter from being excessively evaporated by being exposed to the discharge arc. Because.
That is, when the content of the first emitter is less than 0.5% by weight, the emitter concentration necessary for electron emission cannot be ensured in the initial stage of lighting, and the lamp voltage increases and the fluctuation increases. In addition, if the content exceeds 5.0% by weight, the sintered body becomes brittle during the production of tungsten materials and the like, and breakage due to cracks in the sintering process and the swaging process occurs. Not only is it easy to make it, but even if it can be manufactured, when used at the tip, the evaporation of the emitter becomes noticeable and promotes blackening (white turbidity) of the valve, which is not preferable.

As shown in FIG. 2, a sealed space 33 is formed inside the cathode 3, and a sintered body 34 containing an emitter other than thorium is embedded in the sealed space 33.
A female screw 33a is screwed on the inner surface of the sealed space 33, while a male screw 34a is screwed on the outer surface of the sintered body 34. Yes.
In FIG. 2A, the sealed space 33 is formed on the main body 31 side, and the sintered body 34 is substantially embedded in the main body 31.
In FIG. 2B, the sealed space 33 is formed so as to straddle the main body portion 31 and the tip portion 32, and the sintered body 34 is embedded so as to straddle the main body portion 31 and the tip portion 32. .
In FIG. 2C, the sealed space 33 is formed on the distal end portion 32 side, and the sintered body 34 is substantially embedded in the distal end portion 32.
Of course, the dimensions of the tip 32, particularly the thickness, will differ depending on which of these forms, and which one to select depends on the ease of manufacture and the tip 32. It is appropriately selected in consideration of the cost depending on the thickness or the total manufacturing cost.

The sintered body 34 includes an emitter other than thorium (hereinafter, the emitter contained in the sintered body 34 is also referred to as a second emitter). Similarly, lanthanum oxide, cerium oxide, gadolinium oxide, samarium oxide, praseodymium oxide, neodymium oxide, or a combination of hafnium oxide mixed with a constituent material such as tungsten, and sintered are used.
And the density | concentration of the 2nd emitter contained in this sintered compact 34 is set to the density | concentration higher than the density | concentration of the 1st emitter contained in the said front-end | tip part 32, The density | concentration is 10 weight%, for example ~ 80% by weight.
If the concentration of the second emitter is less than 10% by weight, it becomes difficult to secure the amount of emitter supplied to the cathode tip 32 due to the size of the sintered body 34 that can be stored inside the cathode 3. . Further, if it exceeds 80% by weight, the proportion of the constituent material such as tungsten in the sintered body 34 is reduced, and the product due to reduction of the oxide is reduced. It will shorten the life.

  Since the second emitter contained in the sintered body 34 is embedded in the cathode 3, it is not directly exposed to the discharge arc and is not heated more than necessary, so that it excessively evaporates. There is nothing. In addition, the sintered body 34 is appropriately heated as the lamp is turned on, and the second emitter in the sintered body 34 has a distal end through thermal contact and concentration diffusion via a contact surface with the main body 31 or the distal end 32. It is moved and supplied to the part 32 side. Thereby, the emitter is not depleted at the tip portion 32, and stable lighting performance is maintained.

The manufacturing process of the cathode according to the present invention will be described with reference to FIG.
The sintered body 34 embedded in the sealed space 33 inside the cathode 3 is mixed at a mixing ratio of emitter (CeO ₂ ) and tungsten (W) of 1: 2, and a binder (stearic acid) is added. Then, molding is performed by a pressure press. Then, after degreasing and preliminary sintering in hydrogen at a temperature of 1000 ° C., main sintering in vacuum is performed in a tungsten furnace at 1700 to 2000 ° C., preferably 1800 to 1900 ° C. for 1 hour. That ’s it. If sintering is performed at a much higher temperature than this, the emitter mixed in at a high concentration evaporates and disappears, and the meaning of mixing at a high concentration is lost.
Thereafter, a male screw 34 a is cut on the surface of the sintered body 34.

On the other hand, the main body 31 of the cathode 3 is ZrO ₂ doped tungsten, and the tip 32 is La ₂ O ₃ and ZrO ₂ doped tungsten. Both are sintered in a vacuum at a temperature of 2300 ° C to 2500 ° C. Thus, when tungsten containing the emitter is sintered at a higher temperature (for example, 3000 ° C.), the emitter is evaporated and disappears, which is not preferable.
In the case where the main body portion 31 does not contain an emitter, sintering can be performed at a higher temperature, for example, 2700 ° C. to 3000 ° C.
A female screw 33 a is cut on the inner surface of the sealed space 33 formed in the main body 31 and / or the tip 32 of the cathode 3.

First, as shown in FIG. 3A, the sintered body 34 is screwed with a male screw 34 a of a sintered body 34 into a female screw 33 a on the inner surface of the sealed space 33 that opens to the distal end side of the main body 31. Are screwed in and embedded in the sealed space 33.
Next, as shown in FIG. 3B, the tip 32 is brought into contact with the main body 31, and both are joined by diffusion bonding, spot welding, or the like in a pressed state.
After joining the tip portion 32 and the main body portion 31, as shown in FIG. 3C, the tip of the cathode 3 is cut into a predetermined shape.
As a result, as shown in FIG. 3D, the tip 32 is joined to the tip of the main body 31, and the sintered body 34 is screwed into the sealed space 33 inside the cathode 3 to be hermetically embedded. The final shape is obtained.

Also, as a manufacturing method other than the above, by using a method in which a sintered body is filled and powdered in a sealed space in the cathode without being molded and sintered in advance, and then sintered in the sealed space after pressure molding. Is also possible.
That is, a groove-like recess extending in the circumferential direction is formed in advance in the inner surface of a void serving as a sealed space in the main body or the tip, and an emitter (CeO ₂ ) not including a binder is formed in the void. Tungsten (W) powder is mixed and filled. When this is subjected to pressure molding with a pressure press, the powder enters the recesses of the voids to form the projections.
This is degreased and pre-sintered at a temperature of 1000 ° C. in hydrogen and then subjected to main sintering. The main sintering is performed in a vacuum in a tungsten furnace at 1700 to 2000 ° C., preferably 1800 to 1900 ° C. for 1 hour. The mixing ratio of the emitter (CeO ₂ ) and tungsten (W) is, for example, 1: 2 (weight ratio).
When the sintered body is sintered by this method, the circumferential recess formed in the inner surface of the space (sealed space) may be screw-shaped (spiral) or formed in the circumferential direction. It may be an independent groove shape.

The functions and actions of the main body 31 and the tip 32 and the sintered body 34 constituting the cathode 3 of the present invention formed as described above will be described with reference to FIGS.
As described above, the sintered body 33 in which the emitter is mixed at a high concentration is sintered at a temperature lower than that of the main body portion 31 and the front end portion 32 in order to avoid evaporation loss of the emitter. The swaging process is not performed unlike the tip portion 32. For this reason, when the lamp is heated to a high temperature, the sintering proceeds, the volume thereof is reduced, and the contact state with the inner wall surface of the sealed space 33 tends not to be sufficient.
However, in the present invention, since they are screwed to each other by screws, even if the sintered body 34 is reduced in the axial direction and the radial direction, as shown in FIG. The contact with the screw groove 33a of the sealed space 33 is maintained in any of the axial directions.

Therefore, as shown in FIG. 5, heat transfer from the cathode main body 31 (or the tip 32) is sufficiently ensured through the contact surface between the screw thread 34a and the screw groove 33a. The diffusion of the emitter from 34 to the main body (tip 32) is ensured without delay. Thereby, the diffusion of the emitter from the sintered body 34 of the high-concentration emitter to the cathode main body 31 and the tip 32 is smoothly performed, and the grain boundary is diffused to the tip 32. There will be no situation such as exhaustion of Emita.
This phenomenon is completely the same when the convex portion formed on the surface of the sintered body is engaged with the concave portion formed on the inner surface of the sealed space.

A specific example of the cathode structure of the present invention is as follows.
Discharge lamp: xenon lamp for digital cinema Electrical characteristics: current 160-170A, voltage 39-45V, rated power: about 7000W
Cathode outer diameter: φ12 mm, total length: 20 mm
Tip dimensions: Taper angle 40 °, tip diameter 0.6-1.0 mm
Gas pressure: about 1.0 MPa in static pressure (estimated pressure of 5.0 MPa during lighting)
Sintered body: Emitter is barium oxide
Barium oxide powder and tungsten powder are mixed, put into a mold and pressed to form a cylinder
Shaped powder compact. After pre-sintering this at about 1000 ° C.,
Firing at 1500-1800 ° C. near the recrystallization temperature to produce a sintered body.
The external thread surface of this sintered body is cut with a lathe.

As described above, in the present invention, in the discharge lamp in which an emitter other than thorium is added to the cathode, the emitter is contained in the tip portion joined to the main body portion. Secure start-up ensures reliable lighting.
Then, since the sintered body hermetically embedded in the cathode contains the second emitter having a higher concentration than the first emitter at the tip, the second emitter diffuses as the lamp is turned on. Since it is supplied by moving to the tip side, there is no concern that the emitter will be depleted at the tip, and stable lighting is ensured by continuous emitter supply.
Since this sintered body is hermetically embedded in the cathode and is not directly exposed to the discharge arc, emitters with low vapor pressures other than thorium may be excessively evaporated and depleted in a short time. Absent.
Furthermore, since the concave and convex portions are engaged with the sealed space of the sintered body and the cathode, even if the degree of sintering of the sintered body progresses and decreases as the lamp is turned on, the sintered portion is sintered at any of the concave and convex portions. The contact state between the body and the main body portion or the tip portion is maintained, and heat transfer from the main body portion or the tip portion to the sintered body is smoothly performed through the contact portion. The emitter is reliably diffused to the tip, and the supply of the emitter to the tip is not delayed.

DESCRIPTION OF SYMBOLS 1 Discharge lamp 2 Arc tube 3 Cathode 31 Main-body part 32 Tip part 33 Sealed space 33a Female screw 34 Sintered body 34a Male screw 4 Anode

Claims (2)

In the discharge lamp in which the cathode and the anode are arranged opposite to each other inside the arc tube,
The cathode comprises a main body part and a tip part joined to the tip side thereof,
The main body is composed of a refractory metal material not containing thorium,
The tip is composed of a refractory metal material containing an emitter (excluding thorium),
A sintered body containing an emitter (excluding thorium) having a higher concentration than the emitter concentration contained in the tip is embedded in a sealed space formed inside the main body and / or the tip. And
A discharge lamp characterized in that a circumferential convex portion is formed on the outer surface of the sintered body, and a circumferential concave portion is formed on the inner surface of the sealed space, which are engaged with each other. 2. The discharge lamp according to claim 1, wherein the convex portion on the outer surface of the sintered body is a male screw, and the concave portion on the inner surface of the sealed space is a female screw, which are screwed together.

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