Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2003-03-26
2003-12-30
Ramsey, Kenneth J. (Department: 2875)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S040000, C313S639000, C313S570000
Reexamination Certificate
active
06669522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high pressure discharge lamp and a method for producing the high pressure discharge lamp. More specifically, the present invention relates to a long-life high pressure discharge lamp which, even after being used for a long time, has a low degree of blackening or decrease in luminance and is capable of preventing leakage of a contained gas or a blowout of a bulb, and a method for manufacturing such a high pressure discharge lamp.
2. Description of Related Art
In general, a high pressure discharge lamp has a structure, for instance, as shown in FIG.
4
. In the high pressure discharge lamp
110
shown in
FIG. 4
, each electrode of a pair of electrodes
102
and
102
made of tungsten is disposed so as to be opposite the other in a quartz glass bulb
101
, which includes a round-shaped central portion. Each of these electrodes
102
and
102
is inserted from a respective insertion opening
104
located at an end of the bulb
101
and each of the insertion openings
104
is airtightly sealed with the respective electrode
102
via a sleeve-shaped molybdenum foil
105
which is a thermal cushioning material. A halogen gas, such as mercury gas or methylene bromide gas, and an inert gas, such as argon, are contained and sealed in the bulb
101
.
In general, a relatively large amount of mercury, for instance, in an amount of more than 0.15 mg/mm
3
, is contained in the high pressure discharge lamp
110
. When the lamp
110
is lit and a trigger voltage is applied to the electrodes
102
and
102
, a glow discharge is induced between the electrodes under the atmosphere of the above-mentioned inert gas and the contained mercury is vaporized to emit light of high luminance and excellent color rendering property due to a plasma discharge by the high-pressure mercury vapor. Since light of high luminance and excellent color rendering property is obtained by using the high pressure discharge lamp as explained above, the lamp has recently attracted attention as a light source for devices such as a projection type liquid crystal display and used for a variety of purposes.
During the initial phase of using the high pressure discharge lamp, problems associated with the use thereof were pointed out that blackening of the inner surface of a bulb is caused and the luminance of the lamp is lowered after being lit for a considerably long time. These problems are attributed to the fact that, as shown in
FIG. 4
, tungsten atoms or molecules W are vaporized by the discharge which occurs at high temperatures and deposited onto the inner surfaces of the bulb
101
. Accordingly, in order to prevent the generation of blackening, a halogen gas is used and sealed in the bulb
101
. The halogen gas produces halogen ions at high temperatures which bond to and vaporize the tungsten deposited onto the inner surface of the bulb
101
and re-deposit the tungsten onto a base portion of the electrode at which temperature is relatively low. This is a so-called “halogen cycle” and this cycle is repeated so that the generation of blackening of the bulb may be prevented.
A halogen compound, such as methylene bromide, is generally used as the above-mentioned halogen gas. The halogen compound, when the lamp is lit, is decomposed in the bulb
101
and generates halogen ions. In general, the halogen gas is contained so that the partial pressure of the halogen gas in the bulb
101
becomes 1×10
−6
&mgr;mol/mm
3
or greater which is considered to be an amount effective for preventing the generation of blackening.
Also, an inert gas, such as argon, is contained in the bulb
101
in an amount in the range between about 6×10
3
Pa and 6×10
4
Pa in order to induce a glow discharge at the start of lighting the lamp
110
.
However, although a halogen gas is contained in the bulb
101
in order to prevent a decrease in the luminance of the lamp
110
due to the generation of blackening as mentioned above, the halogen gas, when present excessively, tends to erode and deteriorate the electrodes
102
and molybdenum, foils
105
at the sealing portions of the bulb
101
. If the erosion proceeds, a contained gas may leak from the sealing portions or a blowout of the bulb
101
may be caused since the pressure inside the bulb
101
exceeds 100 atmosphere due to the vapor pressure of the contained mercury. For this reason, studies have been conducted to achieve a total improvement of the high pressure discharge lamp, the improvement including the structure thereof and an amount of various components contained in the bulb
101
in order to prevent problems such as the generation of blackening, leaking of contained gases and a blowout of the bulb
101
.
For example, the Japanese Unexamined Patent Application, First Publication No. 11-149899 discloses an amount of mercury contained between 0.12 and 0.35 mg/mm
3
, an amount of a halogen gas between 7
−7
and 10
−2
&mgr;mol/mm
3
, and an amount of potassium oxide contained in an electrode of 12 ppm or less.
The Japanese Patent No. 2829339 discloses an amount of mercury contained between 0.2 and 0.35 mg/mm
3
, and an amount of a halogen gas between 10
−6
and 10
−4
&mgr;mol/mm
3
.
The Japanese Patent No. 2980882 discloses an amount of mercury of 0.16 mg/mm
3
or more, an amount of a halogen gas between 2×10
−4
and 7×10
−3
&mgr;mol/mm
3
, and preferably a bulb wall loading of 0.8 W/mm
2
or more and an amount of an inert gas of 5×10
3
or more.
The Japanese Unexamined Patent Application, First Publication No. 11-297274 discloses an amount of mercury which becomes between 100 and 200 atmospheres when a lamp is lit, and an amount of a halogen gas between 1.1×10
−5
and 1.2×10
−7
mol/cc.
However, no matter how the amount of components contained in the bulb of the high pressure discharge lamp is adjusted as described in the above-mentioned documents, problems of the decrease in the luminance of a lamp due to the generation of blackening, leakage of contained gas, and blowout of the bulb cannot be solved by any single means at the same time.
Accordingly, an object of the present invention is to provide a high pressure discharge lamp in which the above-mentioned problems have been solved and a method for producing such a high pressure discharge lamp.
Another object of the present invention is to provide a long-life high pressure discharge lamp which, even after being used for a long time, has a low degree of blackening or decrease in luminance and is capable of preventing leakage of the contained gas or a blowout of the bulb, and a method for manufacturing such a high pressure discharge lamp.
The inventors of the present invention, after pursuing diligent studies to achieve the above-mentioned objectives, discovered that although an air in a bulb is vacuumed by using such means as a vacuum pump in advance of the introduction of various components to be contained in a conventional high pressure discharge lamp, oxygen components such as oxygen gas or carbon dioxide still remain in the bulb to some extent and these oxygen components inhibit the above-mentioned halogen cycle when the lamp is lit. It was observed that an excessive amount of a halogen gas must be contained in the bulbs of the conventional high pressure discharge lamps for the reason mentioned above and this shortens the life of the high pressure discharge lamps.
The inventors of the present invention also discovered that the above-mentioned problems may be solved by a high pressure discharge lamp including a quartz glass bulb in which each electrode of a pair of electrodes is disposed so as to be opposite the other in an airtightly sealed quartz glass bulb containing at least mercury and a halogen gas, wherein the partial pressure of oxygen (O) in the quartz glass bulb is about 2.5×10
−3
Pa or less and the partial pressure of the halogen gas in the quartz glass bulb is in the range between about 1×10
−8
&mgr;mol/mm
3
Macchiarolo Peter
McGinn & Gibb PLLC
NEC Microwave Tube, Ltd.
Ramsey Kenneth J.
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