Discharge lamp and method of producing the same

Details Discharge lamp and method of producing the same Discharge lamp and method of producing the same

1999-03-16

2002-04-09

Ramsey, Kenneth J. (Department: 2879)

Electric lamp or space discharge component or device manufacturi

Process

With assembly or disassembly

C445S040000, C313S636000

Reexamination Certificate

active

06368175

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a long-life discharge lamp and a method of producing the same.
PRIOR ART
At present, discharge lamps, such as high-pressure mercury lamps and metal halide lamps, are used for various applications, and become widespread and indispensable in the modern society. These days, such discharge lamps are expected to have higher performance to be more beneficial in society. In particular, in order to meet the needs for global environmental conservation, producing discharge lamps having longer service lives is a matter expected most anxiously. Under these circumstances, numerous technologies for extending the lives of discharge lamps have been invented so far.
Generally speaking, in a discharge lamp, a pair of electrodes is sealed in a quartz glass tube, and a discharge space, in which the two electrodes are opposed to each other, is charged with an appropriate noble gas so as to be used as a light-emitting portion. In this light-emitting portion, mercury or a metal halide is charged so that the lamp is used as a mercury lamp or a metal halide lamp. The glass of the lamp is usually formed of quartz glass, and the electrodes are formed of tungsten.
A double-ended high-pressure discharge lamp is disclosed in Japanese Patent Publication JP-A 2-223131, wherein a quartz glass tube is heated at two portions thereof to form two neck portions, a first tungsten electrode having been preformed is disposed at a first neck portion, the quartz glass tube is heated to seal the first electrode, a discharge gas and a light-emitting substance are introduced and one end of the tube is sealed, a second electrode is then disposed at a second neck portion, and the quartz glass tube is heated to seal the second electrode in the same way, whereby the space between the first and second sealing portions is used as a light-emitting portion. In this conventional technology, sealing the electrodes is carried out by heating using a conventional burner, and charging the gas and sealing the ends of the quartz glass tube are carried out in a glove box having a highly clean atmosphere of a charged gas while the quartz glass tube is held therein, and then sealing the second electrode is carried out in the atmospheric air.
Existence of impurities, such as H
2
O, included in the materials of the components of the discharge lamp is one of the most influential factor in the service life thereof. For example, the quartz glass of the discharge lamp usually includes OH groups, and the OH groups in the quartz glass are released to the discharge space during lamp lighting, and accelerates the evaporation of the tungsten electrodes heated at high temperature (about 3000 K), thereby quickly causing the blacking and devitrification of the light-emitting tube quite frequently, and lowering the service life of the discharge lamp.
Production methods for preventing the OH groups included in the quartz glass from affecting the service life of the lamp in order to extend the service life of the lamp are disclosed, for example, in Japanese Patent Publications JP-A 9-102277 and JP-A 9-102278. These prior art lamp production methods are characterized in that (1) instead of an oxygen-hydrogen burner, a propane-oxygen burner or a plasma burner is used as a heat source for heating the quartz glass in order to reduce the content of OH groups to be mixed during processing and that (2) the quartz glass or the lamp is heated in vacuum after the processing to eliminate the OH groups mixed during the processing by releasing the OH groups as H
2
O, thereby returning the content of OH groups in the quartz glass to the level obtained before the processing.
As an effect obtained by these production methods, the luminous flux maintenance ratio after 2400 hours of lighting is improved from 85% (in the case when a lamp is processed by using an oxygen-hydrogen burner) to 91% in accordance with the descriptions of the production methods.
Furthermore, Japanese Patent Publication JP-A 2-220328 discloses a discharge lamp production method wherein high-temperature vacuum heat treatment is carried out at 1200° C. for six hours. In this production method, as shown in
FIGS. 16A and 16B
, an electrode assembly is inserted from one end of a quartz glass tube
201
having a light-emitting tube portion
206
and opened at both ends. The electrode assembly comprises a tungsten electrode
208
, a molybdenum seal foil
209
and a molybdenum lead
210
. The portion of the quartz glass tube
201
, in which the seal foil
209
is disposed, is heated up to a temperature suited for forming, i.e., about 2200° C. or more, and at the same time, argon Ar is passed through the tube
210
from the open end thereof. When a temperature for crushing is reached, crushing jaws
213
press the quartz glass tube to seal the seal foil
209
, thereby forming a first sealing portion
214
(the first electrode sealing step). In this production method, the quartz glass tube
201
, in which the first electrode is sealed, is then subjected to high-temperature vacuum heat treatment at 1200° C. for about 6 hours.
In the discharge lamp production methods disclosed in Japanese Patent Publications JP-A 9-102277 and JP-A 9-102278, no consideration is given to impurities included in the lamp component materials other than those included in the quartz glass.
In particular, impurities, such as H
2
O included in the sealed-in gas and the light-emitting substance, and adsorbed water on the surface of the quartz glass, are present inside the light-emitting tube immediately after the completion of the lamp, and thus cause adverse effects on the characteristics of the lamp earlier than the impurities released from the quartz glass. For this reason, a problem of being unable to sufficiently prevent deterioration in service life during an early lighting period is caused in the production methods disclosed in Japanese Patent Publications JP-A 9-102277 and JP-A 9-102278.
The above Japanese Patent Publications JP-A 9-102277, JP-A 9-102278 and JP-A 2-220328 disclose methods of reducing the content of OH groups included in the quartz glass by high-temperature vacuum heat treatment in accordance with the conventional lamp production method. When glass is heated at high temperature and affected thermally, the OH groups combined with Si and O (the components of the glass) are generally decomposed and apt to become gas molecules (H
2
gas and H
2
O gas).
Accordingly, when the high-temperature heat treatment is conducted, the content of OH groups is reduced apparently. In actual practice, however, the reduction is just caused by the change of the OH groups into the forms of H
2
gas and H
2
O gas, and impurities affecting the service life of the lamp may sometimes not be eliminated actually. In addition, the H
2
gas and H
2
O gas are apt to diffuse in the glass than the impurities (OH groups) combined with Si and O.
For these reasons, if these gas component atoms are not eliminated sufficiently, impurities released from the glass are increased by the heat treatment, instead of being decreased, thereby causing a problem of accelerating the reduction of the service life of the lamp.
Furthermore, when the electrode assembly (
208
,
209
and
210
) is sealed in the quartz glass tube
201
opened at both ends thereof by heating while argon Ar is flown therethrough as disclosed in Japanese Patent Publication JP-A 2-220328, small argon bubbles are liable to remain at the seal foil
209
, thereby causing a problem of being unable to sufficiently maintain hermetical sealing at the sealing portion
14
. Moreover, since both ends of the quartz glass tube
201
are open, an atmospheric gas easily flows into the tube together with argon. For example, when the first electrode sealing step shown in
FIGS. 16A and 16B
is carried out in an atmosphere of air, the air flows into the quartz glass tube
201
together with argon, thereby causing a problem of oxidizing and deteriorating the electrode
208
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to

Affiliated with

Also associated with

Rating

Discharge lamp and method of producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Discharge lamp and method of producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Discharge lamp and method of producing the same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2898885