Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
1999-12-21
2003-11-11
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S624000, C313S625000, C313S634000, C313S042000, C313S043000
Reexamination Certificate
active
06646379
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a metal vapor discharge lamp using a translucent ceramic arc tube.
BACKGROUND OF THE INVENTION
This kind of conventional metal vapor discharge lamp is disclosed, for example, in Publication of Japanese Patent Application No. Hei 6-196131 A (conventional lamp
1
), No. Hei 7-240184 A (conventional lamp
2
), or No. Sho 61-245457 A (conventional lamp
3
), etc.
The conventional lamp
1
includes, as shown in
FIG. 6
, a translucent ceramic arc tube
11
and small tubular portions
12
a
,
12
b
provided at both sides of the central main tube portion
13
of the arc tube
11
. Inside the small tubular portions
12
a
,
12
b
, feeder bodies
14
a
,
14
b
are inserted. The feeder bodies
14
a
,
14
b
are connected to electrodes
15
a
,
15
b
, respectively. The feeder bodies
14
a
,
14
b
are made of a hydrogen permeable material
16
a
,
16
b
and a halide-resistant material
17
a
,
17
b
. The gap between the small tubular portions
12
a
,
12
b
and the feeder bodies
14
a
,
14
b
is sealed with a glass frit
18
a
,
18
b.
As the hydrogen permeable material
16
a
,
16
b
, niobium, tantalum, or the like, are used, which makes it possible to bring the coefficient of thermal expansion closer to that of alumina that is the material for the small tubular portions
12
a
,
12
b
, so as to prevent the occurrence of cracks at the time of sealing. However, niobium etc. is vigorously reacted with a halide that is filled in the main tube portion. Therefore, the halide-resistant material
17
a
,
17
b
such as tungsten, molybdenum or a conductive cermet, etc. is used for the member at the portion where the filled material exists during the lamp operation, while the hydrogen permeable portion
16
a
,
16
b
made of niobium is completely sealed with the glass frit
18
a
,
18
b
. Thus, this configuration inhibits the reaction between the feeder body
14
a
,
14
b
and the filled material.
The conventional lamp
2
includes, as shown in
FIG. 7
, a translucent ceramic arc tube
19
, plug bodies
20
and a pair of electrodes
21
. The arc tube
19
includes a central bulging portion
22
having a spherical or an elliptic spherical shape, and small tubular portions
23
having a diameter smaller than that of the central bulging portion
22
. The small tubular portions
23
extend from both ends of the bulging portion
22
, and the small tubular portions
23
and the central bulging portion
22
are formed in one piece. Each plug body
20
is inserted into the small tubular portion
23
and has a conducting means conducting from the inside to outside of the arc tube. The electrodes
21
are provided in the bulging portion
22
and supported by one end of the plug bodies
20
, respectively.
In this configuration, an external lead wire
24
that passes through the inside of the plug body
20
conducts from the inside to outside of the arc tube
19
. The plug body
20
is bonded to the small tubular portion
23
with glass adhesive
25
made of, for example, a frit glass, which are poured into the gap between the inner surface of the end of the small tubular portions
23
at the opposite side to the electrode
21
and the outer surface of the plug body
20
. Furthermore, mercury as a buffer metal, a metal halide as a discharge metal, noble gas such as argon gas, etc. are filled in the arc tube. The filled amount of the metal halide is larger than the amount that evaporates during the lamp operation.
In general, when the temperature of the glass adhesive
25
increases during the lamp operation, the glass adhesive
25
deteriorates due to a chemical reaction with a metal halide. This deterioration causes the occurrence of leaks of the sealed materials from the arc tube. During the lamp operation, in the conventional lamp
2
, excess metal halides are condensed in the gap between the inner surface of the small tubular portion
23
and the outer surface of the plug body
20
except for the bonding portion with the glass adhesive
25
. This condensed metal halide thermally isolates the glass adhesive
25
from a high temperature gas inside the discharge space. Thus, the deterioration of the glass adhesives
25
due to the chemical reaction with metal halides can be prevented and the occurrence of leaks in the arc tube
19
is prevented.
Furthermore, the conventional lamp
3
has. as shown in
FIG. 8
, an arc tube including a translucent alumina tube
26
, the ends of which are plugged with conductive cermet
27
via a sealing material
28
, and dysprosium halide is filled in the arc tube. As a main component of the sealing material
28
, an oxide of rare earth metal is used. The conductive cermet
27
is obtained by sintering a mixture of tungsten powder, etc. and aluminum powder, etc., used for the discharge material. Therefore the conductive cermet
27
has the coefficient of thermal expansion that is very close to that of aluminum, so that cracks in the sealed portion can be reduced. Furthermore, since the metal oxide of rare earth metal is used as a main component of the sealing material
28
, the reaction between the filled material and the sealing material
28
can be inhibited during the lamp operation.
In the configuration of the conventional lamp as described above, when a metal such as tungsten, molybdenum, or the like, whose coefficient of thermal expansion is different from that of aluminum is used, cracks easily occur in the sealed portion, and leaks easily occur in the arc tube at the step of sealing and during the lamp operation. In order to avoid such disadvantages, it is preferable that the conductive cermet whose coefficient of thermal expansion is close to that of aluminum is used for the halide-resistant portion. However, it is difficult to bond the conductive cermet to niobium as the hydrogen permeable material. Therefore, the reliability in this portion is not obtained and the utilization factor of the feeder body is lowered.
Furthermore, when a metal such as niobium, etc. is used for the feeder body, since the bonding at the interface between niobium and the glass frit is weaker than the bonding at the interface between the glass frit and alumina, i.e. between two oxides, the filled materials gradually leak from the interface between niobium and the glass frit. As a result, the lamp voltage is lowered.
Furthermore, since the coefficient of thermal expansion of niobium is 7.2×10
−6
, and the coefficient of thermal expansion of alumina is 8.0×10
−6
, not a little thermal stress occurs at the time of sealing and during the lamp operation. Therefore, in a high power lamp having an electrode rod of a large diameter, the thermal stress is too large to be neglected and cracks occur in the sealed portion. Furthermore, niobium is embrittled due to the reaction with nitrogen at high temperatures. Therefore, in the case of the high power lamp in which the temperature of the ends of the feeder body is easily increased, it is unsuitable to operate the arc tube in a nitrogen atmosphere.
Furthermore, in the configuration in which the ends of the arc tube are sealed with the plug body having an external lead wire that passes through the inside thereof, the bonding between the external lead wire and the plug body is not sufficient and the filled materials leak to the outside from the arc tube along the lead wire, so that the lamp voltage during the lamp operation is significantly lowered.
Furthermore, in the configuration in which the end of the arc tube is sealed with the conductive cermet, since the front surface of the sealing material is close to the discharge space and so has a high temperature, the sealing material is softened, or a sealing material reacts with the filled material. Consequently, the lamp characteristics are significantly deteriorated for a short time.
Furthermore, when the luminous efficiency of the conventional lamps were respectively examined, they were low. For example, the luminous efficiency was about 80 (lm/M) for a high-color-rendering lamp. Although a lamp having a higher luminous
Akiyoshi Kenji
Kakisaka Shunsuke
Nakayama Shiki
Nishiura Yoshiharu
Nohara Hiroshi
Merchant & Gould P.C.
Patel Nimeshkumar D.
Roy Sikha
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