Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2000-03-02
2001-05-01
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
Reexamination Certificate
active
06224449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high pressure discharge lamps using ceramic discharge tubes and processes for the production thereof.
2. Related Art Technique
In the above high pressure discharge lamp, a plugging members (ordinarily called ceramic plugs) are inserted into both end portions of the ceramic discharge tube to close these end portions, a through-hole is provided in each of the plugging members, and a metallic current conductor having a given electrode system fixed thereto is inserted into the through-hole. An ionizable light-emitting material is sealed in an inner space of the ceramic discharge tube. As such a high pressure discharge lamp, a high pressure sodium light-emitting lamp, a metal halide lamp, etc. are known. In particular, the metal halide lamp has a good color rendering property. Use of ceramics as materials for discharge tubes has made it possible to use such high pressure discharge lamps at high temperatures.
In such a discharge lamp, it is necessary to effect gas-tight sealing between the end portions of the ceramic discharge tube and respective electrode unit-holding members. A main portion of the ceramic discharge tube takes a tubular shape or a barrel shape of which both end portions are reduced in size or a straight cylindrical shape. The ceramic discharge tube is made of, for example, a sintered alumina body. In order to seal the end portions of the ceramic discharge tube, for example, JP-A-6 318435 discloses the following structure. That is, plugging members are inserted into interiors of end portions of the ceramic discharge tube, and held there. A through-hole is formed in each of the plugging members in an axial direction thereof, and a slender electrode unit-holding member is fixedly inserted into the through-hole. The plugging member is made of a cermet containing both alumina and a metal constituting the electrode unit-holding member at such a given ratio that the coefficient of thermal expansion of the plugging member may fall between the coefficient of thermal expansion of the electrode unit-holding member and that of the ceramic discharge tube.
In the formation of the above sealed structure, it is designed that the inner diameter of each end portion of the ceramic discharge tube becomes slightly smaller than the outer diameter of the plugging member if the ceramic discharge tube is fired in such a state that a preform of the plugging member is not inserted into a preform of the ceramic discharge tube. Consequently, the plugging member is firmly radially inwardly tightened and held inside the end portion of the ceramic discharge tube. This is the same as to the plugging member and the electrode unit-holding member.
However, the present inventors have further advanced investigations upon such sealed structures, and discovered that they had the following problems. That is, the plugging member and the electrode unit-holding member are sealed based on a pressure between them. However, since the discharge lamp repeatedly undergoes a number of cycles between turning on and turning off, it is necessary that reliability of the sealed portion is further enhanced judging from the difference in thermal expansion. In particular, in case of the metal halide having high corrosive property, a sealed structure having high corrosion resistance and high reliability needs to be developed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel sealed structure for a high pressure discharge lamp, which sealed structure-has high corrosion resistance and high reliability against the metal halide without substantially imparting thermal stress between a plugging member and a ceramic discharge tube.
The high pressure discharge lamp according to the present invention has a ceramic discharge tube having an inner space filled with an ionizable light-emitting material and a starting gas, plugging members each at least partially fixed to an inner side of a respective one of the end portions of the ceramic discharge tube and each having a through-hole provided therein, conductive members inserted into or through the through-holes of the plugging members, respectively, and electrode units provided in said inner space, wherein a material of the plugging members is the same as that of the ceramic discharge tube, and each of the plugging members is gas-tightly joined to the corresponding conductive member with a metallizing layer.
Further, the present invention is directed to the process for production of the above high pressure discharge lamp, which process includes the steps of: inserting the conductive members into or through through-holes of non-fired preforms of the respective plugging members; providing metallizing layers between the through-holes of the non-fired preforms and the respective conductive members; and then integrally firing the non-fired preforms, the metallizing layers, and the conductive members.
The high pressure discharge lamp according to another aspect of the present invention includes a ceramic discharge tube having an inner space filled with an ionizable light-emitting material and a staring gas, conductive members inserted into or through through-holes of the ceramic discharge tube at end portions, respectively, and electrode units provided in said inner space, wherein the end portions of the ceramic discharge tube and each of the conductive members is gas-tightly joined together with a metallizing layer.
The present invention is also directed to a process for the production of the above high pressure discharge lamp, which process is characterized by comprising the steps of: inserting the conductive members into or through through-holes of a non-fired preform of the ceramic discharge tube; providing layers of a metallizing material between the through-holes of the non-fired preform and surfaces of the respective conductive members; and then integrally firing the non-fired preform, the metallizing material, and the conductive members.
The present inventors thought of a technical idea that the material of the plugging members fixed to the end portions of the ceramic discharge tube is the same as that of the ceramic discharge tube and that the plugging members are gas-tightly joined to the respective conductive members with the metallizing layers. They discovered through their experiments that extremely high gas-tightness was held between the plugging members and the respective conductive members, and that the high pressure discharge lamp still kept high reliability even when it repeatedly underwent a number of cycles between turning on and turning out. The inventors reached the present invention based on the above discovery.
The present inventors further discovered that when the conductive member was directly and gas-tightly sealed to the inner side of the end portion of the ceramic discharge tube via the metallizing layer, extremely high gas-tightness was maintained between the plugging member and the conductive member, and that the high pressure discharge lamp still kept high reliability even when it repeatedly underwent a number of cycles between turning on and turning out. Owing to this, an extremely large merit is industrially obtained, since the plugging members can be omitted, and the number of the constituent parts decreases, and the production steps can be largely simplified.
In addition, this technique is extremely effective in making the high pressure discharge lamp compact. That is, the width dimension of the high pressure discharge lamp is limited by the dimension of the end portion thereof. However, since the plugging member was inserted into or through the inner side of the end portion of the ceramic discharge tube, it was difficult to make the dimension of the ceramic discharge tube smaller in the width direction than a certain limit, and consequently it was difficult to make the volume of the inner space of the ceramic discharge tube smaller than a given level. As a result, when the output was concretely suppressed to a level of not more than 2
Asai Michio
Niimi Norikazu
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
Ramsey Kenneth J.
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