U.S. patent application number 11/132933 was filed with the patent office on 2005-10-06 for method for producing a gas discharge lamp.
Invention is credited to Eberhardt, Angela, Ilmer, Michael, Seibold, Michael.
Application Number | 20050217320 11/132933 |
Document ID | / |
Family ID | 7917255 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050217320 |
Kind Code |
A1 |
Eberhardt, Angela ; et
al. |
October 6, 2005 |
Method for producing a gas discharge lamp
Abstract
A method for producing containers for gas discharge lamps, which
consists in melting glass by incident light radiation.
Inventors: |
Eberhardt, Angela;
(Augsburg, DE) ; Ilmer, Michael; (Rott am Inn,
DE) ; Seibold, Michael; (Muenchen, DE) |
Correspondence
Address: |
OSRAM SYLVANIA INC
100 ENDICOTT STREET
DANVERS
MA
01923
US
|
Family ID: |
7917255 |
Appl. No.: |
11/132933 |
Filed: |
May 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11132933 |
May 19, 2005 |
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10048324 |
Jun 3, 2002 |
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6901772 |
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10048324 |
Jun 3, 2002 |
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PCT/DE00/02498 |
Jul 28, 2000 |
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Current U.S.
Class: |
65/43 ; 65/34;
65/59.23 |
Current CPC
Class: |
C03B 23/20 20130101;
H01J 9/266 20130101; H01J 9/40 20130101; H01J 2209/264
20130101 |
Class at
Publication: |
065/043 ;
065/034; 065/059.23 |
International
Class: |
C03C 027/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 1999 |
DE |
19936863.5 |
Claims
1-13. (canceled)
14. A method for producing a discharge lamp that has a flat
radiator discharge vessel with a base plate, a frame having a
sealing surface, a cover plate, and spacing elements, the method
comprising: positioning the spacing elements to hold the base and
cover plates apart from one another so that an interspace is formed
between the sealing surface of the frame and one of the plates, the
spacing elements comprising a glass element and an intermediate
element arranged between the glass element and one of the plates;
softening the intermediate element of the spacing elements in order
to close the interspace; and sealing the sealing surface in a
region of the closed interspace by irradiation with light.
15. The method of claim 14 wherein the intermediate element of the
spacing elements is softened by irradiation with light.
16. The method of claim 15 wherein the intermediate element of the
spacing elements contains at least one ion from the group of Co,
Cu, Cr, Ni, Ce, Nd, Pr, Cd, Ti, Mn, V, Pb, Zn, Bi and Fe.
17. The method of claims 15 wherein the intermediate element of the
spacing elements contains an additive selected from sulfides,
tellurides or selenides of Zn, Sb, Pb, Mo, W, Ag, Co, Cu, Cr, Ni,
Ce, Nd, Pr, Cd, Ti, Mn, V or Fe.
18. The method of claim 14 wherein the discharge vessel is joined
with a solder glass in a first continuous furnace before the
intermediate element is softened, and the glass element and
intermediate element are not softened during the joining with the
solder glass.
19. A method for producing a discharge lamp that has a flat
radiator discharge vessel with a base plate, a frame having a
support with a sealing surface, a cover plate, and spacing
elements, the method comprising: positioning the spacing elements
to hold the base and cover plates apart from one another so that an
interspace is formed between the sealing surface of the support and
the cover plate, the spacing elements comprising a glass element in
contact with the cover plate and an intermediate element arranged
between the glass element and the base plate; filling the discharge
vessel with a filling gas; softening the intermediate element of
the spacing elements by irradiation with infrared light in order to
close the interspace; and sealing the sealing surface in a region
of the closed interspace by irradiation of the support with
infrared light.
20. The method of claim 19 wherein the intermediate element of the
spacing elements or the support contain at least one ion from the
group of Co, Cu, Cr, Ni, Ce, Nd, Pr, Cd, Ti, Mn, V, Pb, Zn, Bi and
Fe.
21. The method of claims 19 wherein the intermediate element of the
spacing elements or the support contain an additive selected from
sulfides, tellurides or selenides of Zn, Sb, Pb, Mo, W, Ag, Co, Cu,
Cr, Ni, Ce, Nd, Pr, Cd, Ti, Mn, V or Fe.
22. The method of claim 19 wherein the discharge vessel is joined
with a solder glass in a first continuous furnace before the
discharge vessel is filled with the filling gas, and the glass
element and intermediate element are not softened during the
joining with the solder glass.
23. The method of claim 19 wherein the discharge vessel is heated
in a vacuum furnace during the filling, softening and sealing
steps, and the discharge vessel is evacuated prior to filling.
Description
[0001] The invention relates to a method for producing a discharge
vessel of a gas discharge lamp.
[0002] In particular, the invention is aimed at producing gas
discharge lamps that are designed for dielectrically impeded
discharges, and thus in the case of which at least one polarity of
electrodes is separated by a dielectric layer from the discharge
volume in the discharge vessel.
[0003] With the aid of preferred refinements, the invention is
aimed at, moreover, the production of flat radiator lamps--in
particular for dielectrically impeded discharges. The technology of
gas discharge lamps, in particular of gas discharge lamps for
dielectrically impeded discharges and, in turn, in particular, of
flat radiator gas discharge lamps, is assumed here as prior art. As
an example, reference is made in addition to the prior German
patent application 197 11 890.9 by the same applicant, the
disclosure content of which with regard to the lamp technology of
flat radiator gas discharge lamps for dielectrically impeded
discharges is hereby incorporated by reference.
[0004] The invention is based on the above-named technical problem
of specifying an improved method for producing discharge vessels of
gas discharge lamps.
[0005] The preamble of claim 1 forms the basis of DE-A 197 11 892
A1, which shows a flat radiator designed for dielectrically impeded
discharges, in the case of which radiator two plates of the
discharge vessel are interconnected in a gastight fashion at the
edge.
[0006] The prior art also includes WO98/26440 which discloses a
method for producing plasma displays. There, cover plates of a
display housing are laid on spacing elements and fastened. A very
narrow interspace remains open in this case, and is sealed after
evacuation. Illustrated in this case is a technique in which
irradiation with light softens glass material to such an extent
that the surface tension leads to rounding with the aid of which
the said narrow interspace is bridged and sealed.
[0007] U.S. Pat. No. 5,693,111 further discloses a method for
producing plasma displays in the case of which gastight connections
between plates and display housing frames are produced by laser
irradiation.
[0008] Finally, DE-A 27 18 273 shows a method for producing a
vacuum object in the case of which housing parts are bonded
together in order then to be fastened to one another in a gastight
fashion by irradiation with light and fusing of glass parts.
[0009] The above-named technical problem is solved according to the
invention by a method for producing a discharge lamp that has a
flat radiator discharge vessel with a base plate, a frame and a
cover plate, characterized in that glass is fused by irradiation
with light in order to form a tight connection between two glass
parts of the discharge vessel and/or a tight sealing of an opening
of the discharge vessel, spacing elements holding the plates so far
apart from one another before the sealing of the discharge vessel
that an interspace exists as filling opening between the frame and
one of the plates, the spacing elements being softened in order to
bring the plates closer and to close the interspace, and a sealing
surface arranged in the region of the closed interspace being
sealed by irradiation with light.
[0010] Preferred refinements of the invention are the subject
matter of the dependent claims.
[0011] Part of the invention consists in fusing glass by
irradiation with light when producing the discharge vessel. The
fused glass can serve in this case to connect the parts of the
discharge vessel which for this purpose are to consist at least
essentially of glass at least in the relevant region. At the same
time, the fused glass can also serve to seal a filling opening
remaining in the discharge vessel for the purpose of (pumping out
and) filling with the discharge gas atmosphere, or an opening
serving other purposes. The sealing of an opening is also possible
without connecting parts of the discharge vessel by having the
fused glass seal a filling opening in a part of the discharge
vessel.
[0012] In any case, the irradiation with light must result in
fusing to such an extent that the softening of the glass leads to a
permanent connection and, if appropriate, to a matching of the
shape to the neighboring parts of the discharge vessel. The term
fusing does not necessarily signify a transition into a phase that
is liquid in the actual meaning of the word. Rather, it also
includes a sufficient softening which leads, on the one hand, to a
sufficient adhesion of the softened material to the neighboring
parts of the discharge vessel and, if required, to a matching of
shape.
[0013] Conventionally, in the production of discharge vessels glass
fusing steps have typically been carried out by heating in a
furnace or else by direct contact with a flame.
[0014] The advantage resides in that irradiation with light offers
a possibility of coupling energy in more quickly and directly and,
if required, also in a directed fashion. Since no contact with a
hot medium is required for heating by means of irradiation with
light, it is also possible in this case to work in a very clean gas
atmosphere or in a vacuum, without correspondingly having to accept
disadvantages for coupling heat to the discharge vessel.
[0015] A further measure according to the invention is aimed at
spacing elements, provided in addition to the frame, between the
two plates, which hold the plates so far apart from one another
before the sealing of the discharge vessel that a filling opening
results between the frame and one of the plates. When the spacing
elements are softened, optionally by irradiation with light, the
upper one of the two plates sinks down, thereby closing the filling
opening. The sealing section arising from the disappearance of the
filling opening can then, in turn, be sealed by irradiation with
light.
[0016] In accordance with a preferred refinement of the invention,
the irradiation with light is performed in a locally concentrated
fashion. This means that the irradiation with light is
substantially limited to the local region of the glass to be fused,
at least within the framework of the optical possibilities, such
that a relatively large portion of the remainder, that is not to be
fused, of the discharge vessel is not directly affected by heat
being coupled in.
[0017] The possibility thereby exists of achieving substantially
higher temperatures at the sites covered by the locally
concentrated irradiation with light than in the remainder of the
discharge vessel. Firstly, it is possible thereby to suppress or
limit to a substantially smaller part the outgassings, occurring at
higher temperatures, from the materials of the discharge vessel, at
least for the part that is not affected by the irradiation with
light.
[0018] Furthermore, the thermal loading of the unaffected parts of
the discharge vessel is reduced, it thereby being possible to avoid
mechanical damage owing to stresses or thermal changes in the
material.
[0019] In particular, it is possible at sites of the discharge
vessel that are remote from the region covered by the irradiation
with light to use materials which have a low thermal resistance, in
particular a lower melting point than the glass to be fused. For
example, this goes for what are termed solder glasses, which are
used, for example, in joining different parts of discharge vessels
of flat radiators and, in addition to intense outgassing, also
exhibit relatively low melting points. Other examples for
temperature-sensitive components are metal electrodes or line
bushings and, finally, all regions in which materials with
different coefficients of thermal expansion meet one another.
[0020] On the other hand, the localizability of the irradiation
with light permits the use of glasses even with high softening
temperatures for the purpose of joining glass parts or sealing
filling openings and the like, for example even with softening
temperatures of 700.degree. C. and above. A typical temperature
range for the fusing according to the invention is between 350 and
1000.degree. C. In this case, the invention can, of course, also be
advantageous in lower temperature ranges, in particular even in
conjunction with glasses that soften at low temperatures, for
example if the aim is to limit in vacuum an outgassing of solder
glass materials that is already substantial starting from
400.degree.-500.degree. C.
[0021] Precisely with regard to the possibility even of fusing
types of glass that do not soften until relatively high
temperatures, the invention is preferably aimed at those glasses
which outgas as little as possible even in the event of
heating.
[0022] These are preferably nonporous and binder-free glasses by
contrast with pulverulent solder glasses. To this extent, the
method according to the invention further improves the purity of
the discharge gas in that not even the region fused by the
irradiation with light shows excessive outgassing.
[0023] A further preferred measure of the invention consists in
selecting the glass to be fused such that it absorbs more strongly
in the irradiated spectral region than do the neighboring parts of
the discharge vessel. It is thereby possible to achieve a
localization of the heating by amplified power absorption in the
desired glass material independently of optical measures. For one
thing, the irradiated total light power can be reduced in
conjunction with strong absorption of the glass to be fused.
Furthermore, there is a consequent increase, if appropriate in
addition to the previously described measures for local
concentration, in the achievable temperature difference between the
glass to be fused and the remainder of the discharge vessel--with
the advantages previously represented.
[0024] In addition to a suitable choice of the actual types of
glass, such a selective absorption of the irradiated light can also
be produced by special additives. Preference is given in this case
to metal ions such as ions of Co, Cu, Cr, Ni, Ce, Nd, Pr, Cd, Ti,
Mn, V, Pb, Zn, Bi or Fe, in particular Fe ions. Also preferred are
sulfides, tellurides or selenides of Zn, Sb, Pb, Mo, W, Ag, Co, Cu,
Cr, Ni, Ce, Nd, Pr, Cd, Ti, Mn, V or Fe, in particular FeS.
[0025] The glass provided with these additives absorbs particularly
strongly in the infrared region. Consequently, an infrared
radiation is preferred for the invention. The infrared light or
other light can be produced by a conventional light source that can
be focused by conventional optical means and directed onto the
region to be illuminated, for example by mirrors, diaphragms and
the like. However, use is preferably made of a laser. A YAG laser
comes into consideration, in particular. In order to irradiate
regions that are extended (possibly linearly as an alternative to
conventional optical measures the irradiation spot of the laser can
also be moved along the region to be illuminated, for example by
mirror movements or movements of an optical conductor system. In
this case, the region to be irradiated need not be continuous. It
is also possible in a similar way to irradiate a plurality of sites
distributed along the discharge vessel.
[0026] So far, stress has been laid on the importance of the most
pronounced selectivity possible for the power absorption in the
region of the glass to be fused. Low temperatures of the discharge
vessel were fundamentally regarded in this case as favorable.
However, it is to be added to this that for the purpose of
desorbing adsorbates, in particular water, located on the inner
walls of the discharge vessel, it is to be recommended to carry out
thermal desorption before introducing the filling gas and
subsequently sealing the discharge vessel by temperatures of at
least above 1500 or 200.degree. C.
[0027] Furthermore, it can also be worth recommending increasing
the temperature of the discharge vessel if excessive thermal
stresses are to be expected because of the strong local heating by
the irradiation with light. For this reason, before the local
irradiation with light, during the same and immediately thereafter
the discharge vessel is kept at a slightly raised temperature.
According to the invention, temperatures of above 150, preferably
above 200 and, in the most favorable case, above 250.degree. C.
come into consideration here. Favorable upper limits are
500.degree. C., preferably 450, 400 and, in the best case,
350.degree. C. This step can be combined with the previously
mentioned thermal desorption, or can be provided in the cooling
phase after such a desorption. The upper temperature limits are
conditioned by the fact that the outgassing processes to be avoided
increase at higher temperatures.
[0028] With regard to the device suitable for such method steps,
the invention is further aimed at carrying out the method in a
vacuum furnace for the purpose of pumping out and filling in
conjunction with a temperature that is raised in a controlled
fashion. An infrared-transparent window or a bushing for an optical
conductor can be used in this case for the laser as heating light
source for fusing the glass.
[0029] As already mentioned at the beginning, the fusing of glass
according to the invention when producing a discharge vessel is
suitable, on the one hand, for assembling parts of the discharge
vessel ("joining") or, on the other hand, also for sealing
openings, in particular filling openings, in the discharge vessel.
Such an opening can be a filling opening for pumping out and
filling, which has to be sealed after the filling. However, it can
also be an opening through which, for example, an electrical
bushing is laid and which is to be tightly sealed, the aim being to
seal the bushing in. In each case, it is favorable to provide the
glass to be fused as sealing element as a thickened rim of the
opening. As it softens, the glass can then seal the opening
uniformly from all sides of the opening. If the opening is a
filling opening, the diameter of the opening can be 1-5 mm, for
example.
[0030] As already mentioned at the beginning, the invention is
preferably aimed at flat radiator discharge vessels. These can be
constructed from a base plate and a cover plate as well as a frame
connecting the two plates. A favorable arrangement of a filling
opening can be situated in the frame in this case, because the
light emission is particularly little impaired thereby. This also
holds, moreover, for electrical bushings.
[0031] Also possible, however, are arrangements in the base plate
or in the cover plate, in which case preference is to be given to a
skilful accommodation in an edge region; in order not to disturb
the light emission and the course of the discharge electrodes. In
particular, in the case of very flat lamps the frame can also
consist simply of a solder glass strand.
[0032] A combined case, in which, on the one hand, a filling
opening is sealed and, on the other hand, glass parts of the
discharge vessel are tightly connected, forms a further aspect of
the invention, in accordance with which in the case of a flat
radiator discharge vessel a filling opening that is removed by
being fused is present between the frame and one of the plates. For
this purpose, a sealing surface between one of the plates and the
frame has unevenesses which are either removed by the irradiation
with light and the softening of the glass, or to which the softened
glass is matched.
[0033] A variant of this consists in that the sealing surface has a
multiplicity of small unevenesses, being corrugated, for example.
If the corrugated part, for example the frame or a part of the
frame, consists of the preferably infrared-absorbing, glass to be
fused, the corrugation can be smoothed by irradiation with light,
and the plate can be connected to the corrugated surface of the
frame by the simultaneous softening. Of course, the glass softening
can also have the effect of matching the glass to a corrugated
surface of a part that does not soften and thereby connecting it
thereto.
[0034] Alternatively, the unevenesses can comprise a few elevations
at salient points, one raised point sufficing in principle.
[0035] Furthermore, it is also possible to use an absorbing support
on the frame, and to produce the frame from a material that is
optimized using other criteria.
[0036] Since the possibilities described for connecting the frame
to one plate is associated with a macroscopic movement between
these two parts, a stop can be advantageous in this case. Since it
is generally easier to irradiate light onto the sealing surface
between the uppermost of the two plates and the frame, it is
particularly preferred to provide a stop for a moving plate
situated on top. It is to be borne in mind in this case that this
plate can by no means be situated on top in the operating state of
the lamp.
[0037] Furthermore, the plate can be inclined toward the stop such
that in the event of any slippage gravity will cause it to slip in
the direction of the stop.
[0038] The spacing elements according to the invention that are
mentioned further above can be of multipartite design only a part
of each spacing element, an intermediate element, being softened
during production. In particular, the intermediate element can be a
cushion below or above a spacing element which softens at lower
temperatures than does the remainder of the spacing element.
[0039] In order to take up the last mechanical displacements during
sealing of the discharge vessel, that is to say when the frame is
being tightly connected to one plate, it can be advantageous during
the irradiation with light onto the sealing surface to leave the
discharge vessel still at a somewhat higher temperature at which
the spacing elements are somewhat soft. Again, during sealing of
the discharge vessel the spacing elements can be somewhat softened
(again) by a further irradiation with light, in order to equalize
the last stresses.
[0040] Conventionally, glass discharge vessels, in any case those
for flat radiator lamps, are joined with solder glass from a
plurality of parts before filling and heated in the furnace. If the
invention is used only in a last step of using glass parts of the
discharge vessel, for example in conjunction with the possibilities
that had been treated of simultaneously sealing a filling opening,
or else only for sealing a filling opening in one of the parts, a
method step can be carried out in a first continuous furnace before
the step of irradiation with light. In this case, the outgassings
from the solder glass that are associated with the raised
temperatures cannot yet lead to contamination of the discharge
vessel. At the same time, adsorbates can already be desorbed. The
discharge vessel, that has preferably cooled down somewhat, can
thereupon be pumped out further and then filled with the filling
gas. The discharge vessel is sealed thereafter in one of the ways
described. In a further second continuous furnace, the already
sealed discharge vessel can then be cooled down in a controlled way
by lowering the temperature under control.
[0041] The invention is explained below in more concrete terms with
the aid of a plurality of exemplary embodiments, it being possible
for the features disclosed thereby also to be essential for the
invention individually or in other combinations than those
represented. In the drawing:
[0042] FIG. 1 shows a schematic cross sectional view through a flat
radiator discharge vessel before sealing according to the invention
in accordance with a first exemplary embodiment according to the
invention;
[0043] FIG. 2 shows an illustration of a detail from FIG. 1, with a
sealed filling opening;
[0044] FIG. 3 shows an illustration of a detail with an alternative
filling opening in relation to FIG. 1 before sealing in accordance
with a second exemplary embodiment according to the invention;
[0045] FIG. 4 shows the exemplary embodiment from FIG. 3 after the
sealing;
[0046] FIG. 5 shows a schematic representation of a production line
for the method according to the invention;
[0047] FIG. 6 shows a schematic side view of a flat radiator
discharge vessel before the sealing according to the invention in
accordance with a third exemplary embodiment according to the
invention;
[0048] FIG. 7 shows a variant of FIG. 6 according to a fourth
exemplary embodiment of the invention;
[0049] FIG. 8 shows a further variant of FIGS. 6 and 7 according to
a fifth exemplary embodiment, and
[0050] FIG. 9 shows a schematic cross sectional view through a flat
radiator discharge vessel according to a sixth exemplary embodiment
of the invention.
[0051] In the first two exemplary embodiments of the invention
illustrated in FIGS. 1-5, a filling opening in a discharge vessel
is sealed by fusing with the aid of a glass sealing element.
According to the first exemplary embodiment, the sealing element
can be arranged in one of the plates, while according to the second
it can be arranged in the frame of a flat radiator discharge
vessel.
[0052] FIG. 1 shows a schematic cross section through a flat
radiator discharge vessel. In this case, the numeral 1 denotes a
base plate and the numeral 2 a cover plate, while the numeral 3
denotes a frame that connects the two plates. These components
consist of glass and have been interconnected in a preceding
joining method step via a solder glass layer denoted by 4. The
resulting discharge vessel has a substantially rectangular cross
section and (not illustrated) a rectangular plan view. It serves to
produce a flat radiator with dielectrically impeded discharges for
background illumination of a flat display screen, or else for
normal lighting. In accordance therewith, electrode strips are
printed on inside the frame 3 on the side of the base plate 1
situated on top in the figure, a portion of the electrodes being
covered with a dielectric layer. These details are of no further
interest here and are therefore not illustrated. Reference is made
to the disclosure content of the already cited application 197 11
890.0.
[0053] In any case, the presence of electrode strips on the base
plate 1 is the reason for the arrangement of a filling opening 5 in
the cover plate 2. In this case, for the sake of simplicity the
filling opening 5 in FIG. 1 is situated essentially in the middle;
however, for reasons already explained an edge position is
preferred in a concrete embodiment.
[0054] A glass sleeve 6 is inserted as sealing element into the
filling opening 5 in the form of a thickened collar. The sealing
element 6 consists of a glass colored brown by FeS that is strongly
absorbing in the infrared. According to the invention, this sealing
element 6 is irradiated with the aid of a YAG laser emitting in the
infrared region, in the process of which it is heated to
temperatures above 700.degree., softens and is drawn into the
filling opening 5 as drops by the surface tension. After cooling,
the filling opening 5 is sealed in the manner illustrated
schematically in FIG. 2, the heating of the sealing element 5 not
impairing the remainder of the discharge vessel. It is indicated in
the drawing that the sealing element 6 that seals the filling
opening 5 produces a slight corrugation with respect to the
remainder of the cover plate 2, and is, however, colored brown in
an optically detectable fashion. The already mentioned arrangement
near the wall is to be preferred for this reason.
[0055] An alternative to this is shown in FIGS. 3 and 4, the as yet
unsealed state of a filling opening 5 being illustrated in FIG. 3,
and the sealed state in FIG. 4. In accordance with FIG. 3, a
filling opening 5' is provided in a frame 3', the frame 3'
therefore having a gap. In a way similar to that illustrated in
FIG. 1, a collar sleeve 6', which corresponds otherwise to the
above explanations relating to FIG. 1, is inserted into the filling
opening 5'.
[0056] After irradiation by the YAG laser, the filling opening 5'
is sealed by the fused sealing element 6', as illustrated in FIG.
4. This variant offers an impairment of the light emitting
properties of the gas discharge lamp which is as small as
possible.
[0057] In accordance with FIG. 5, the part of the production method
according to the invention is performed in a schematically
illustrated production line composed of three stations 7, 8 and 9.
As is illustrated by the arrow drawn in on the left in FIG. 5, a
structure assembled from the base plate 1, the cover plate 2, the
frame 3 and the sealing element 6 and provided with solder glass 4
at the suitable sites is introduced into the first station 7, a
continuous furnace for the purpose of joining these semi-finished
products. The discharge vessel is joined in the furnace by heating
to a temperature of between 400.degree. and 520.degree. C. A
protective gas atmosphere is present in the continuous furnace in
this case. The contaminants, in particular binders from the solder
glass 4, that emerge at the raised temperatures are expelled by
thorough rinsing.
[0058] The temperature in the continuous furnace 7 is raised so far
that the solder glass 4 softens at a viscosity of the joining
solder of substantially less than 10.sup.6 dPas, and connects the
parts to be joined. This typically requires temperatures of
520.degree. C. The protective gas atmosphere serves essentially to
prevent oxidation of the luminescent material (not illustrated in
the figures) in the discharge vessel at the raised temperatures. A
vacuum furnace (substantially more complicated, and therefore more
expensive) is not required in station 7.
[0059] After the joining and cooling to a temperature with a
viscosity of the solder glass 4 of above 10.sup.10 dPas, the
discharge vessel is introduced into the second station 8, the
sealing element 6 still corresponding to the state illustrated in
FIGS. 1 and 3. Consequently, the interior of the discharge vessel
is still open above the filling opening 5. Pumping off is therefore
performed in the vacuum furnace 8 through the filling opening 5,
the discharge vessel being kept at a raised temperature of
250.degree.-300.degree. C. suitable for supporting further
desorption processes and with regard to the in the case of the
following sealing of the sealing element 6.
[0060] Alternatively, the sealing element 6 can also not be applied
until in the vacuum furnace 8.
[0061] An atmosphere corresponding to the desired gas filling of
the gas discharge lamp is set up in the vacuum furnace 8 after it
has been sufficiently pumped out, and penetrates into the discharge
vessel through the filling opening 5.
[0062] A coupling device, illustrated schematically and denoted by
10, with an optical conductor bushing for a YAG laser arranged
outside the furnace 8 can now be used to launch power into the
sealing element 6 in a pinpointed fashion until said element fuses
at a temperature of over 500.degree. C., more typically 700.degree.
C., and is drawn into the filling opening 5 as drops by the surface
tension. After the laser 10 has been shut down, the sealing element
6 cools in the shape illustrated in FIGS. 2 and 4 and encloses the
gas filling enclosed in the discharge vessel.
[0063] The closed discharge vessel is then introduced into the
third station 9, a further continuous furnace, and cooled to
approximately 50.degree. C. there by a defined control of the
furnace temperature or by moving the lamp along a section,
corresponding to a defined temperature profile, inside the
continuous furnace 9. The finished discharge vessel can be removed
thereafter in accordance with the arrow drawn in on the right in
FIG. 5. Since, as already mentioned, it is a discharge vessel
provided with electrode strips and bushings of the same (compare
the already cited application 197 11 890.9) that is involved, the
gas discharge lamp is thereby essentially finished.
[0064] A further aspect of the production method relates to the
glass sphere 11, drawn schematically in FIG. 1, as spacing element
which rests on an "intermediate element" 12 made from solder glass.
Of course, a plurality of these spacing elements 11 are provided.
These are support bodies for providing mutual support to the plates
1 and 2 against the external pressure when the discharge vessel has
underpressurized gas fills. Reference may be made for this purpose
to application 198 17 478.0 from the same applicant. The aim of the
arrangement of these spacing elements 11 on the solder glass
cushions 12 is that in the as yet unjoined state, that is to say
before insertion into the `first ` continuous furnace 7, the
spacing elements hold the cover plate 2 high beyond the frame 3.
Consequently, it is firstly possible during joining to achieve a
better pump cross section for rinsing the interior of the discharge
vessel and expelling the binder and other contaminants. In
particular, however, it is ensured thereby that after the cover
plate 2 is caused to sink down onto the frame 3 or the upper solder
glass layer 4 thereof by the softening of the solder glass 12 and
by the weight of the cover plate 2, all the support elements 11
bear uniformly against the cover plate 2. What is involved is
therefore a selfadjusting action with regard to the dimensional
accuracy of the support elements between the plates 1 and 2. In the
following description of a further exemplary embodiment, it becomes
clear in what way such spacing elements can be associated with the
invention.
[0065] The third example in FIG. 6, which would be an exemplary
embodiment only in conjunction with spacing elements in accordance
with FIG. 1, has, in turn, a base plate 1 and cover plate 2 and a
frame 3. The frame 3 can be connected in various ways to the
baseplate 1, or be designed in one piece with it. In particular, it
could also be joined to the base plate 1 by fusing glass as a
consequence of irradiation with light. However, the exemplary
embodiment serves the purpose of illustrating the connection of the
cover plate 2 to the frame 3. For this purpose, an
infrared-absorbing glass support with a top side 13 is laid onto
the frame 3 and is locally raised with the aid of small columns 14
at the corners of the discharge vessel. The cover plate 2 is
situated in the remaining region at a spacing, corresponding to the
height difference between the columns 14 and the remainder of the
support 13, above the top side 13 of the support, that is to say
the sealing surface.
[0066] The columns 14 are softened by localized heating of the
columns 14 by irradiation from an infrared laser through the cover
plate 2 (which absorbs substantially less than does the glass
material of the support with the columns 14), such that the cover
plate 2 sinks onto the sealing surface 13 on the support. It is
then possible by heating the entire sealing surface 13
appropriately with the aid of infrared irradiation to achieve an
intimate sealing of the discharge vessel over the entire upper
circumference of the frame 3, that is to say over the entire
sealing surface 13.
[0067] In this example, columns 14 are provided at all four corners
of a flat radiator discharge vessel of rectangular plan view. Four
interspaces therefore result between the sealing surface 13 and the
cover plate 2, leading in each case to one side of the rectangular
plan view. The columns 14 can be adapted in height depending on the
requirements made of the power cross section for pumping out and
filling the discharge vessel.
[0068] In the case of excess height, however, there can be the
danger of lateral migration of the cover plate 2 when sinking onto
the sealing surface 13. The fourth example of FIG. 7 provides a
remedy in this regard, which would likewise be an exemplary
embodiment only in conjunction with spacing elements. Columns 14
are likewise provided there, but only at two adjacent corners of
the rectangular plan view. A stop body 15 is arranged in the case
of the production method at the side edge opposite the two corners
with the columns 14. Even if, as indicated with exaggeration in the
drawing, the height of the columns 14 is considerable, in the case
of migration of the cover plate 2 no substantial lateral
displacement can occur as the cover plate 2 sinks onto the sealing
surface 13. In the case of migration or slipping, gravity will
cause the cover plate 2 to strike the stop 15, which will retain
said cover plate in the correct position while the column 14 is
dismantled. Thus, it is possible thereby to achieve large column
heights 14, although the total surface area, achieved in the case
of a fixed column height, of the filling openings between the cover
plate 2 and sealing surface 13 is halved by comparison with the
variant from FIG. 6.
[0069] A further fifth example is shown in FIG. 8, which would
likewise be an exemplary embodiment only in conjunction with
spacing elements. Here, there is a frame 16 between the base plate
1 and the cover plate 2 made from infrared-absorbing glass material
(at least in the upper region, in any case). The upper region of
the frame 16 and the sealing surface 13' situated thereupon are
corrugated such that the cover plate 2 bears against the frame 16
at a relatively large number of sites between which individual
openings 18 occur in a fashion corresponding to the troughs of the
corrugation--in each case. Here, as well, softening or fusing of
the upper region of the frame 16, particularly in the region of the
peaks of the corrugation, causes the cover plate 2 to sink down in
a planar fashion onto the sealing surface 13', and thereby seal the
discharge vessel.
[0070] Of course, it is also possible to provide a support in the
sense of the third and fourth example with a corrugated sealing
surface 13' and, conversely, it is possible in the case of an
example corresponding to FIG. 8 to provide a sealing surface with
columns provided at a few salient points, in accordance with the
third and fourth example. Moreover, as in the first and second
example, spacing elements can also occur in the third, the fourth
and the fifth example, although they are not illustrated in FIGS.
6, 7 and 8.
[0071] The last and sixth exemplary embodiment in FIG. 9 uses the
spacing elements 11 with special intermediate elements 17 in a way
typical of the invention: in this case, the cover plate 2 is
situated on the spacing elements 11 before the sealing according to
the invention, but not on a sealing surface 13" of the frame. The
sealing surface 13" is the top side of an infrared-absorbing
support 7 on the actual frame 3. The intermediate elements 17 made
from nonporous glass are then softened by laser irradiation with
the aid of infrared-absorbing inserts, such that the spacing
elements 11, glass spheres in this case as well, sink down with the
cover plate 2.
[0072] As a result, the cover plate 2 comes to bear against the
sealing surface 13" on the support 7, and can thereafter be fused
with the latter, in turn, by laser irradiation. Thus, in this
exemplary embodiment the element (the intermediate element 17) that
is softened by irradiation with light and therefore removes an
opening is not identical to the element, specifically the support
7, having the sealing surface 13".
[0073] Here, as well, the laser irradiation can be performed
through the cover plate 2, for example, because the elements 17 and
7 to be softened absorb selectively.
[0074] The sinking down of the cover plate 2 onto the glass spheres
11 that sink into the intermediate elements 17 results in a
self-adjusting action such that the cover plate 2 finally rests
with a uniform contact pressure on all the glass spheres 11
provided and on the sealing surface 13". Such a self-adjusting
function by softening of intermediate elements can, of course, also
be provided in the case of the other exemplary embodiments. In
particular, the intermediate elements can also be "reheated" after
the sealing of the discharge vessel, in order to eliminate stresses
that have remained.
[0075] The third, fourth, fifth example and sixth exemplary
embodiment have in common that the laser irradiation spot is moved
on the sealing surface in order to achieve heating over two
dimensions. This can be performed most simply by appropriate
manipulation of an optical conductor that transports the laser
beam. In this way, the laser can be arranged outside the vacuum
furnace 8 illustrated in FIG. 5, and use may be made of an
manipulating mechanism with appropriate vacuum bushings in
conjunction with an optical conductor bushing for the purpose of
locally targeted irradiation. It is also possible, by means of a
somewhat raised temperature of the overall discharge vessel, to
achieve a certain softening of an intermediate element for the
purpose of equalizing stresses, consideration being given, however,
only to glasses or solder glasses of low melting point. By
contrast, the targeted laser irradiation has the advantage of
greater freedom in selection of material for the intermediate
element 17. It can be advantageous to seal the actual sealing
section once again thereupon.
[0076] Apart from the details explained of the irradiation with
light onto the appropriate elements in the case of the various
exemplary embodiments, the production corresponds to the examples
and exemplary embodiments illustrated in FIGS. 6-9, or to the
explanations relating to FIG. 5.
* * * * *