Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
2000-07-10
2002-06-25
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S626000
Reexamination Certificate
active
06411037
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arc tube for a discharge lamp device in which a region including at least a molybdenum foil of an electrode assembly having an electrode, the molybdenum foil and a molybdenum lead wire connected integrally in series is sealed and fixed to a primary pinch seal portion and a secondary pinch seal portion on both ends respectively and the electrodes are opposed to each other in a central sealed chamber portion filled with a luminescent substance, and to a method of manufacturing the arc tube for a discharge lamp device.
2. Description of the Related Art
FIG. 7
shows a conventional discharge lamp device having such a structure that a front end portion of an arc tube is supported by one lead support
3
protruded forward from an insulating base
2
, a rear end of the arc tube
5
is supported in a concave portion
2
a
of the base
2
, and a portion of the arc tube
5
provided close to the rear end thereof is held by a metal support member S fixed to a front surface of the insulating base
2
. A front end side lead wire
8
b
led from the arc tube
5
is fixed to the lead support
3
through welding, while a rear end side lead wire
8
a
penetrates through a bottom wall
2
b
formed in the concave portion
2
a
of the base
2
and is fixed through welding to a terminal
9
provided on the bottom wall
2
b
. The symbol G denotes a cylindrical ultraviolet radiation shielding glove which serves to cut a ultraviolet component having such a wavelength area as to be harmful to a human body in light emitted from the arc tube
5
and is integrally welded to the arc tube
5
.
The arc tube
5
has such a structure that electrodes
6
are provided opposite to each other between a longitudinal pair of pinch seal portions
5
b
and a sealed chamber portion
5
a
filled with a luminescent substance is formed. A molybdenum foil
7
for connecting the tungsten electrodes
6
protruded into the sealed chamber portion
5
a
and molybdenum lead wires
8
a
and
8
b
led from the pinch seal portions
5
b
is sealed and fixed into the pinch seal portions
5
b
. Thus, airtightness can be maintained in the pinch seal portions
5
b
and
5
b.
More specifically, it is desirable that the electrode
6
should be formed of tungsten having a high durability. However, the tungsten has a very different coefficient of linear expansion from that of glass, is less stuck to the glass and has a poor airtightness. Accordingly, when the molybdenum foil
7
having a coefficient of thermal expansion approximating to that of the glass and stuck comparatively well to the glass is connected to the tungsten electrode
6
and is then sealed at the pinch seal portion
5
b
, the airtightness of the pinch seal portion
5
b
can be maintained.
As a method of manufacturing the arc tube
5
, first of all, an electrode assembly A having the electrode
6
, the molybdenum foil
7
and the lead wire
8
connected integrally is inserted from one of open end sides of a cylindrical glass pipe W having a spherical swollen portion w
2
formed in the middle of a linear extended portion w
1
and a position q
1
in the vicinity of the spherical swollen portion w
2
is subjected to primary pinch seal as shown in FIG.
8
A. As shown in
FIG. 8B
, then, a luminescent substance P is put into the spherical swollen portion w
2
from the other open end side. As shown in
FIG. 8C
, subsequently, another electrode assembly A is inserted and a position q
2
in the vicinity of the spherical swollen portion w
2
is heated and is subjected to secondary pinch seal while the spherical swollen portion w
2
is cooled with liquid nitrogen such that the luminescent substance is not vaporized. Thus, the spherical swollen portion w
2
is sealed. Consequently, the arc tube
5
having a chipless sealed chamber portion
5
a
is completed. At the primary pinch-sealing step shown in
FIG. 8A
, an antioxidant gas (generally, an inert gas or a reducing gas) is supplied into the glass pipe W to carry out the pinch seal such that the electrode assembly A is not oxidized. At the secondary pinch-sealing step shown in FIG.
8
(
c
), the open end is sealed as indicated by the reference numeral q
3
. Consequently, a discharge starting gas introduced into the glass pipe W is filled in the glass pipe W and the spherical swollen portion w
2
is cooled with the liquid nitrogen such that the discharge starting gas and the luminescent substance are not vaporized. Thus, the glass pipe W is almost evacuated to carry out the pinch seal.
In the conventional method of manufacturing an arc tube, however, the vicinity of a boundary between the molybdenum lead wire
8
a
led from the primary pinch seal portion (the pinch seal portion on the rear end side) and the pinch seal portion particularly becomes fragile so that a mechanical strength thereof is reduced. Consequently, a disconnection is easily caused.
The present inventor has investigated the cause of the drawback. Although the antioxidant gas is introduced into the glass pipe W in order to prevent the electrode assemblies A from being oxidized during the primary pinch seal, it is not led to the open end side of the linear extended portion w
1
in a lower portion immediately after the next pinch seal. Consequently, it has been confirmed that the molybdenum lead wire
8
set in a high temperature state is oxidized in contact with oxygen in the air or a part of a molybdenum structure is evaporated or recrystallized due to a high temperature and is therefore made fragile.
JP-A-10-27574 has disclosed a structure in which pinch seal is carried out by supplying an antioxidant gas from a gas supply nozzle having a smaller diameter toward an open end on an electrode assembly A insertion side of a glass pipe at a primary pinch-sealing step. With such a structure, however, the antioxidant gas supplied from the gas supply nozzle partially hits against the lead wire
8
but the whole lead wire
8
cannot be covered. Therefore, it is impossible to effectively prevent the lead wire from becoming fragile.
SUMMARY OF THE INVENTION
In consideration of the drawbacks of the related art, it is an object of the present invention to provide an arc tube for a discharge lamp device in which a mechanical strength of a molybdenum lead wire in a primary pinch seal portion is not reduced, and a method of manufacturing the arc tube for a discharge lamp device.
In order to achieve the above-mentioned object, a first aspect of the present invention is directed to an arc tube for a discharge lamp device in which a region including at least a molybdenum foil of a pair of electrode assemblies having an electrode, the molybdenum foil and a molybdenum lead wire connected integrally in series is sealed and fixed to a primary pinch seal portion and a secondary pinch seal portion on both ends, and the electrodes are provided opposite to each other in a central sealed chamber portion filled with a luminescent substance and the lead wire is led from the pinch seal portions on the both ends, wherein, in the primary pinch seal portion, an electrode assembly insertion region of a glass pipe for the arc tube is pinch-sealed with the whole electrode assembly inserted into the glass pipe held in an antioxidant gas atmosphere so that the lead wire has a tensile strength of 10000 kgf/cm
2
or more.
If the tensile strength of the lead wire is less than 10000 kgf/cm
2
, an environment-proof property against vibrations, impacts and an external change in a temperature and a lifetime characteristic against a change in a temperature caused by turning on and off are affected. Therefore, it is desirable that a tensile strength of 10000 kgf/cm
2
or more should be maintained.
The lead wire on the primary pinch seal portion side is held in the antioxidant gas atmosphere having no oxygen during the primary pinch seal. Therefore, the oxidation can be prevented and cooling is also carried out with the antioxidant gas at the primary pinch-sealing step. Consequently, it is possible to prevent a molybdenum st
Fukuyo Takeshi
Irisawa Shinichi
Ohkawai Nobuo
Ohshima Yoshitaka
Koito Manufacturing Co. Ltd.
Patel Vip
Sughrue & Mion, PLLC
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