Electric lamp and discharge devices – With getter – Electrode includes getter – supports getter – or is connected...
Reexamination Certificate
2000-07-13
2002-10-29
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With getter
Electrode includes getter, supports getter, or is connected...
C313S557000, C313S559000, C313S560000
Reexamination Certificate
active
06472818
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to light bulbs generally used in stores, exhibition halls and the like.
BACKGROUND OF THE INVENTION
The conventional light bulbs, such as halogen bulbs, generally contain therein a getter for suppressing a water cycle effect which is responsible for shortened service life of the bulbs (see Japanese Examined Patent Publication No.57-1862 (1982) and Japanese Unexamined Patent Publication nods.8-129994 and 8-1299905(1996)).
As shown in
FIG. 6
, a light bulb disclosed in Japanese Unexamined Patent Publication No.8-129994, for example, includes a quartz glass envelope
18
which is formed with a sealing portion
17
at one end thereof and contains therein a pair of lead-in wires
19
,
20
extended externally of the sealing portion
17
, a tungsten filament
21
suspended between the lead-in wires
19
,
20
along an envelope axis, and a quartz glass stem
22
interposed between the filament
21
and the sealing portion
17
and supporting the pair of lead-in wires
19
,
20
.
The quartz glass envelope
18
is filled with predetermined amounts of a gas mixture of argon and nitrogen and of hydrogen bromide.
A tantalum getter
23
is supported at a place closer to the filament
21
than to the quartz glass stem
22
, or at an upper part of the lead-in wire
20
.
Since a conventional halogen bulb like this has the tantalum getter
23
disposed closer to the filament
21
than to the quartz glass stem
22
, tantalum oxides liberated from the tantalum getter
23
reduced in mechanical strength due to its reaction with oxygen are carried to the vicinity of the filament
21
by convection currents occurring within the quartz glass envelope
18
. Subsequently, the liberated tantalum oxides floating near the filament
21
are thermally decomposed so that tantalum is deposited on the filament surface
21
to form thereon an alloy of tantalum and tungsten (hereinafter, simply referred to as alloy). Since this alloy has a melting point (2,850° C.) lower than that (3,400° C.) of tungsten, a lower melting point portion is formed on a part of the filament
21
. The lower melting point portion evaporates excessively to cause the filament
21
to break. Thus, the bulb life is shortened.
The invention contemplates a solution to this problem and has an object to provide a light bulb which can prevent a filament coil from breaking, thereby securing extended bulb life.
DISCLOSURE OF THE INVENTION
A halogen bulb according to the invention comprises a glass bulb having a sealing portion at one end thereof and containing a pair of lead-in wires extended externally of the sealing portion, a filament coil suspended between the lead-in wires, and a stem interposed between the filament coil and the sealing portion and supporting the lead-in wires, wherein a getter is located in an exposed manner between the sealing portion and the stem.
In this arrangement, the stem hinders convection currents occurring around the filament coil from carrying tantalum oxides liberated from the getter to and around the filament coil. Accordingly, an alloy of tantalum forming the getter and tungsten forming the filament coil can be prevented from forming on the surface of the filament coil and hence, the filament coil can be prevented from breaking. As a result, a light bulb having an extended service life can be provided.
REFERENCES:
patent: 4380714 (1983-04-01), Bouman et al.
patent: 4415833 (1983-11-01), Oetken et al.
patent: 57-1862 (1982-01-01), None
patent: 8-129994 (1996-05-01), None
patent: 8-329905 (1996-12-01), None
Ikeda Taku
Maeda Kazuo
Matsushita Electronics Corporation
Parkhurst & Wendel LLP
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