JPH1196965A - Short-arc type mercury lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short-arc type mercury lamp having increased radiant quantities of ultraviolet rays with an increased volume of mercury and capable of supplying an electron emitting substance well at all times. SOLUTION: A negative electrode 2 and a positive electrode 3 are disposed facing with each other in a luminous tube, the luminous tube made of quartz is filled with mercury and rare gas, a hole 20 extending longitudinally within the negative electrode 2 is provided in an end part of the negative electrode for causing an electron-emitting substance to surface-diffuse, a ratio d/D of the bore d of the hole 20 to the maximum outer diameter D within 0.5 mm from the end of the negative electrode is 0.08<d/D<0.5, and the depth L of the hole 20 is equal to or greater than the maximum outer diameter D of the end part of the negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a short arc type mercury lamp. In particular, the present invention relates to a short arc type mercury lamp having high light-collecting efficiency and excellent light stability used in an exposure apparatus for printed circuit boards, liquid crystals, and semiconductors.

[0002]

2. Description of the Related Art In recent years, a short arc type mercury lamp which emits ultraviolet light having a wavelength of 300 nm to 450 nm has been used in a liquid crystal exposure process or a printed circuit board exposure process. The size of the substrate is increasing year by year, and the exposure area is naturally increasing. Therefore, an increase in the amount of ultraviolet light emitted from the light source is required.

In order to increase the amount of ultraviolet light radiation,
It is contemplated to increase the amount of mercury encapsulated. Specifically, it has been attempted to increase the mercury vapor pressure during lighting up from about 10 atmospheres to a higher pressure, for example, about 25 atmospheres. By the way, such an increase in the amount of mercury is caused by an increase in the amount of ultraviolet light radiation, that is,
It is significant in making it bright. However, this has the adverse effect of shortening the life of the discharge lamp. The reason for this is that an increase in the amount of mercury leads to more severe wear of the cathode, and this wear of the cathode undesirably deforms the supply path of the electron-emitting substance (commonly called an emitter), and as a result, This is because good supply of the electron-emitting substance to the cathode tip is hindered.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a short arc type mercury lamp capable of increasing the amount of mercury to increase the amount of ultraviolet light emitted and constantly supplying an electron emitting material in a satisfactory manner. Is to do.

[0005]

To solve the above problems, a short arc type mercury lamp according to claim 1 is provided.
A cathode and an anode are arranged opposite to each other in an arc tube, mercury and a rare gas are sealed in the arc tube made of quartz, and a hole for diffusing the surface of the electron emitting material is formed at the tip of the cathode.
It is provided so as to extend in the longitudinal direction inside the cathode, and a ratio d between the outer diameter d of the hole and the maximum outer diameter D of the cathode tip portion is provided.
/ D is 0.08 <d / D <0.5, and the depth L of the hole is not less than the maximum outer diameter D of the tip of the cathode.

Further, in the short arc type mercury lamp according to the second aspect, the hole is filled with an electron-emitting substance having a higher concentration than the electron-emitting substance contained in a portion in contact with the hole. It is characterized by the following. further,
The short arc type mercury lamp according to claim 3 is characterized in that the high-concentration electron emitting material is a sintered body containing tantalum, tungsten and thorium oxide. Further, the short arc type mercury lamp according to claim 4 is:
A tungsten carbide layer is formed on an outer surface of the cathode except for a tip portion.

[0007]

In order for the discharge lamp to always maintain stable operation, it is necessary that the electron emitting material be well supplied to the arc boundary at the tip of the cathode. For this reason, it is extremely important how well the electron-emitting substance contained in the region other than the tip of the cathode is guided to the tip. Generally, there are surface diffusion, grain boundary diffusion, and intragranular diffusion as a method for guiding the electron emitting substance to the arc boundary at the tip of the cathode.
Surface diffusion is the movement of a substance along the surface of a layer, and in the case of a cathode, means the movement of an electron-emitting substance on the surface of the cathode. Next, grain boundary diffusion refers to the movement of atoms at the interface between metal crystal grains, and in the case of a cathode, the movement of the electron-emitting substance at the interface between tungsten atom crystal grains that constitute the cathode. Means In addition, intragranular diffusion means that atoms move through each metal crystal grain, and in the case of a cathode,
This means that the electron-emitting substance moves through the tungsten particles. Of these, surface diffusion is the most dominant, and it can be safely assumed that increasing the surface diffusion can maintain a good supply of the electron-emitting substance. The invention according to claim 1 has been made based on such knowledge, and the surface diffusion is increased by providing a predetermined hole at the cathode tip. Here, the present inventor has found that U.S. Pat. ing. However, the prior art disclosed in the prior art has a problem that a hole is not provided at the tip of the cathode, and the supply of the electron-emitting substance by surface diffusion cannot be sufficiently performed.

Further, in the invention according to the second aspect, since a high-concentration electron-emitting substance is embedded in the hole, surface diffusion using the inner surface of the hole can be effectively used. To further explain this point, it is possible to diffuse the surface using the inner surface of the hole if the cathode material itself contains the electron-emitting material without putting the electron-emitting material in the hole. is there. However, in this case, until the electron-emitting substance contained in the cathode material reaches the hole, the electron-emitting substance depends on grain boundary diffusion or intragranular diffusion. This is because the diffusion efficiency is inferior. That is, by putting a high-concentration electron-emitting substance into the hole, it becomes possible to supply the electron-emitting substance to the cathode tip only by surface diffusion without using almost any grain boundary diffusion or intragranular diffusion.

Further, the invention according to claim 3 is characterized in that the high-concentration electron-emitting substance is a sintered body containing Ta (tantalum), W (tungsten) and ThO2 (thorium oxide). Has the advantage that grain boundary diffusion always occurs.

Furthermore, in the invention according to claim 4, since the tungsten carbide layer is formed on the surface of the cathode except for the tip end portion, thorium, which is an electron emitting substance, is reduced by the reduction action of the tungsten carbide layer. It can be generated well.

[0011]

FIG. 1 is an overall view of a short arc type mercury lamp according to the present invention. A cathode 2 and an anode 3 are arranged opposite to each other in a quartz arc tube 1, and the respective electrodes are connected to metal foils 8 and 9 inside sealing portions 6 and 7 via internal leads 12 and 13. External leads 10 and 11 are connected to the metal foils 8 and 9. Mercury and a rare gas are sealed in the arc tube 1. And the mercury vapor pressure during lighting is
It becomes 10 atm. Here, the present invention is applied to, for example, a high-pressure mercury lamp of 25 atm or more to increase the amount of ultraviolet light radiation as described above. With a mercury lamp less than this, the wear of the cathode is not so problematic, that is, the supply of the electron-emitting substance can be sufficiently provided.

FIG. 2 is an enlarged view of a cathode of a short arc type mercury lamp according to the present invention. The cathode 2 is tungsten,
Alternatively, it is made of a material containing thorium oxide and has a substantially truncated cone shape having a flat tip portion 2a. A hole 20 is provided from the tip 2a so as to extend in the longitudinal direction of the cathode, and a storage section 30 for an electron-emitting substance is provided inside the cathode. In this storage unit 30, a sintered body 21 containing tantalum (Ta), tungsten (W), and ThO2 (thorium oxide) is arranged. In the figure, a hole is also provided below the storage unit 30 (at the base of the cathode), but this hole is provided for convenience in manufacturing the structure of the cathode according to the present invention.

[0013] A tungsten carbide layer 22 is coated on the outer surface of the cathode 2 and on the inclined portion except for the tip end portion. As a result, the carbon of the tungsten carbide layer and the oxygen of thorium oxide contained in the cathode are combined, so that thorium, which is an electron-emitting substance, can be generated quickly. The reason why the tungsten carbide layer is not formed at the tip is that the tungsten carbide is melted by the arc.

Here, the inner diameter d of the hole 20 is determined to a predetermined value in relation to the outer diameter D of the tip 2a. Specifically, d /
It is necessary that the value of D be greater than 0.08 and less than 0.5. The reason for this is that if the value of d / D is less than 0.08, it becomes impossible to supply the electron-emitting substance sufficiently by surface diffusion, and if the value of d / D is more than 0.5, the electron emission position becomes unstable. Because it becomes. Note that the tip 2a is not necessarily flat, but may be a curved surface. Therefore, the outer diameter D is defined as the maximum outer diameter within 0.5 m from the cathode tip. As an example of such a hole, the inner diameter d of the hole is Φ0.2 mm, and the outer diameter D of the tip 2a is Φ1.3 mm. The storage unit 30 has an inner diameter Φ
2.5 mm and length 10.0 mm.

The depth L of the hole 20 is also determined to a predetermined value in relation to the outer diameter D of the tip 2a. Specifically, L> D
It is necessary to be. This is because, when the depth L of the hole 20 is equal to or smaller than the outer diameter D of the tip 2a, the arc touches the deepest part in the hole, and the growth of grains near the deepest part occurs, and the diffusion of the electron emitting material is prevented. This is because it inhibits. The depth L is, for example, 1.2 mm.

As described above, the sintered body 21 of the electron emitting material is made of tantalum (Ta), tungsten (W), ThO 2
It is a sintered body of (thorium oxide). This has an advantageous effect in that the growth of tungsten grains is suppressed by raising the temperature. However, surprisingly, rare-earth cesium, lanthanum, yttrium, or the like can also be used as the electron-emitting material. Further, it is preferable that the sintered body of the electron emitting substance arranged in the storage unit 30 has a higher concentration than the electron emitting substance contained in the surrounding cathode itself. This is because the supply amount of thorium to the cathode front end surface is increased, and thorium diffuses into the surrounding cathode at the grain boundaries to suppress the growth of tungsten grains, thereby promoting smoother grain boundary diffusion. For example, the thorium concentration of the surrounding cathode is 1 wt%, and the sintered body is 2 wt%.

FIG. 3 also shows an enlarged view of the cathode of the short arc type mercury lamp of the present invention, but shows another embodiment different from FIG. That is, the difference is that the sintered body of the electron emitting material is not arranged in the hole 20. In this case, the electron emitting material contained in the cathode material will be used,
This electron emitting material utilizes surface diffusion on the inner surface of the hole 20. The advantage of this structure is that the surface diffusion at the rear end of the cathode can be effectively used.

FIG. 4 also shows an enlarged view of the cathode of the short arc type mercury lamp of the present invention, but shows another embodiment different from FIGS. That is, similarly to the structure shown in FIG. 2, the sintered body 21 of the electron-emitting substance is disposed in the storage unit 30, but this sintered body 21 is not only disposed in the storage unit 30 but also in the hole 20. It differs in that it is further buried in the middle and toward the tip of the cathode. An advantage of this structure is that the diffusion of thorium in the pores proceeds more smoothly as the temperature rises toward the cathode tip.

As such a short arc type mercury lamp, for example, a lamp having a rating of 40 V and a rating of 2000 W is used. Further, the storage section shown in this embodiment is not always necessary, and may be constituted only by holes. Further, the present invention is not limited to the lamps for DC lighting, but can be applied to lamps for AC lighting.

[0020]

According to the short arc type mercury lamp of the present invention, the amount of mercury can be increased to increase the amount of ultraviolet light emitted, and the hole provided in the cathode makes use of the surface diffusion to always provide a favorable light. An electron emitting material can be supplied.

[Brief description of the drawings]

FIG. 1 shows a short arc type mercury lamp of the present invention.

FIG. 2 is an enlarged view of a cathode of a short arc type mercury lamp according to the present invention.

FIG. 3 is an enlarged view of a cathode of a short arc type mercury lamp according to the present invention.

FIG. 4 is an enlarged view of a cathode of a short arc type mercury lamp according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc tube 2 Cathode 3 Anode 4 Sealing part 5 Sealing part 6 Foil part 7 Foil part 8 External lead member 9 External lead member 20 Hole 21 Sintered body 22 Tungsten carbide layer 30 Storage part

Claims (4)

[Claims] 1. A short arc type mercury lamp in which a cathode and an anode are arranged opposite to each other in an arc tube, and mercury and a rare gas are sealed in the arc tube made of quartz. A hole for surface diffusion of the electron emitting material is provided so as to extend in the longitudinal direction inside the cathode, and the outer diameter d of the hole and 0.5 mm from the tip of the cathode are provided.
The ratio d / D to the maximum outer diameter D within 0.08 <d / D <
0.5, wherein the depth L of the hole is equal to or greater than the maximum outer diameter D of the tip of the cathode. 2. The electron emission material according to claim 1, wherein the hole has an electron emission material having a concentration higher than that of the electron emission material contained in a portion in contact with the hole. Short arc type mercury lamp. 3. The short arc type mercury lamp according to claim 2, wherein said high-concentration electron emitting material is a sintered body containing tantalum, tungsten and thorium oxide. 4. The short arc type mercury lamp according to claim 1, wherein a tungsten carbide layer is formed on an outer surface of the cathode except for a tip portion.