Electric lamp and discharge devices – With gas or vapor – Having particular electrode structure
Reexamination Certificate
1998-08-07
2001-04-10
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having particular electrode structure
C313S632000
Reexamination Certificate
active
06215247
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrode for a high pressure discharge lamp which is used with maintaining a high input of electricity and a process for the producing the same. More particularly, the invention is concerned with a construction of an electrode which can easily be designed and which can be used over a prolong period of time in a stable manner, and the process for producing the same.
2. Description of the Prior Art
In general, in the case of forming a pattern for wiring a semiconductor, a high input discharge lamp, which irradiates a ultraviolet ray, is used as a light source. For applying such a discharge lamp to an exposing area, e.g., of a semiconductor wafer, or of a liquid crystal panel, whose size has been enlarged, and to an exposing pattern, which has been miniaturized, it has been known that a flash light manner is utilized, in which low input and high input are alternatively repeated and exposure is carried out at the time of high input.
Also, a short arc type mercury discharge lamp has been suggested to be applied to a miniaturized exposing pattern, which utilizes a large electric current and a decreased amount of mercury incorporated in the discharge lamp so that an i-ray, which is a mercury luminescent line having a narrow half band width, is effectively emitted
The construction of the prior art discharge lamp, however, has the following disadvantages: In the case of the discharge lamp in a flash light manner or the discharge lamp utilizing large electric current, the cathode undergoes severe damage during the course of discharge, the cathode is significantly consumed, and due to the consumption of the cathode, the tube wall of the discharge lamp is blacken. What is worse, due to the deformation, the distance between the anode and the cathode is changed to thereby change the position of arc discharge, making it impossible to be used as the discharge lamp.
Further, in the flash light manner, due to a vast change in the arc strength discharged between the cathode and the anode, defective exposure occurs, and the unstable state of the arc can be controlled only with difficulty. Furthermore, the power supply for use in controlling the arc to be stable, has a complicated structure, and expensive.
A method has been known from German Patent Application No. P 3723271.1, in which a porous membrane made of, e.g., a carbide, is covered with a portion of the cathode except for the edge portion in such a manner that the thickness of the membrane is gradually decreased as being closer to the edge portion to suppress the consumption of the cathode. However, this method which involves the operation of treating the cathode at a prescribed site and a step of releasing the absorbed gas of the cover, requires a lot of effort and the operation thereof is complicated.
Moreover, a method has also been known from Japanese Laid-Open Patent Application No. 4-137349, in which a dispersion of carbon powder is applied to the cathode to form a carbonized portion on the cathode. However, since the carbonization is carried out in the state where the dispersion of carbon powder is applied on the surface of the cathode to be used as the cathode in this method, the carbon which is formed on the surface of the cathode is scattered during the course of lighting the discharge lamp, and has an adverse affect. Impurities (e.g., potassium and oxides on the surface of the carbon) contained in the carbon adhered onto the cathode shortens the service life of the discharge lamp.
SUMMARY OF THE INVENTION
The present invention is devised in order to solve the problems described above, and an object of the present invention is to provide a construction of electrode for a high discharge lamp, which can suppress the consumption and the damage of the cathode as little as possible even if the discharge lamp is used at a large amount of current, whereby the lighting of the discharge lamp can be continued over a prolong period of time in a stable state. Another object of the present invention is to provide a process for producing an electrode for a discharge lamp, which can produce the cathode with ease, in which the controlling portion of the power source can be simplified and in which a treatment with carbon can be carried out without adversely affecting with a service life of the discharge lamp. Still another object of the present invention is to provide a construction of electrode for a high discharge lamp which can be used for a longer period of time by subjecting the anode to carburization.
The present invention which solves the above problems is a construction of electrode for a high pressure discharge lamp used with maintaining a high input of electricity, which discharge lamp comprises a portion composed of a luminescence tube having a swelled portion at the middle thereof, and an anode and a cathode placed opposite to each other, said cathode being composed of a metal with a high melting temperature doped with a electron-emitting substance and having a tapered portion toward the discharge side, the slope portion of said tapered portion being subjected to carburization at said tapered portion, and a non-treated portion being formed at the edge of the tapered portion continuous to the carburized portion.
The cathode may be composed of the tapered portion and a cylindrical portion continuous thereto, and the carburized portion is formed from the tapered portion to a prescribed portion of the cylindrical portion.
It is also advantageous that the anode comprises a non-treated portion at the edge thereof and a carburized portion formed by carburization continuous to said non-treated portion.
The carburized portion may have a uniform thickness and/or may be fromed within the metal.
The present invention also relates to a process for producing an electrode for a high pressure discharge lamp comprising the following steps:
a first step for applying an applying liquid comprising a sintered medium having graphite incorporated therein to a cathode or both of the cathode and anode for a discharge lamp at the position except for the edge portion and drying the medium,
a second step for carrying out a previous heat treatment of the applying liquid in vacuo at a temperature appropriate to removing the impurities contained in the applying liquid to remove the impurities,
a third step for heating the applying liquid at a temperature appropriate to sintering the applying liquid in an inert gas to sinter the sintering medium onto the electrode,
a fourth step for removing the sintered applying medium, and
a fifth step for heating the electrode, from which the applying medium has been removed, in vacuo at a carbonization temperature appropriate to obtaining a desired depth of the carbonized layer.
REFERENCES:
patent: 3248591 (1966-04-01), Arndt
patent: 4906895 (1990-03-01), Pabst et al.
patent: 5629585 (1997-05-01), Altmann et al.
patent: 5929565 (1999-07-01), Mayama et al.
patent: 64-24355 (1989-01-01), None
patent: 4-137349 (1990-09-01), None
patent: 2-256150A (1990-10-01), None
patent: 2-304857 (1990-12-01), None
patent: 4-137349 (1992-05-01), None
patent: 4-179045 (1992-06-01), None
Fujimori Akiyoshi
Kurano Masahiro
Guharay Karabi
Liniak Berenato Longacre & White
ORC Manufacturing Co. Ltd.
Patel Nimeshkumar D.
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