Note: Descriptions are shown in the official language in which they were submitted.
3~
PHN 8639
The invention relates to a low-pressure mercury
vapour discharge lamp having a respective electrode
disposed at each end of a tubular discharge vessel, an
electrically conducting metal strip being disposed on the
outer surface of the wall of the discharge vessel, which
strip extends to near the electrodes and which is fast-
ened to that wall by means of a glue. Such a lamp is
known from United Kingdom Patent Specification 651,492
which issued to The General Electric Company Ltd., London
on April 4, 1951.
The electrically conducting strip is fastened
in accordance with the above-mentioned United ~ingdom
Patent Specification to the outer surface of the wall of -
the discharge vessel by means of a thermoplastic glue.
~n example of such a glue is polyethylene, which furnishes
the desired adhesion under the influence of pressure and
heat.
The drawback of the use o such a glue, however,
is the thermoplastic character thereof, so that the layer
~0 of glue softens at a relatively small increase in tempera-
ture. This occurs, for example, if the lamp is burning
in a closed luminaire. Where the temperature of the wall
can become so high that the strip becomes loose. In addit-
ion, polyethylene remains fluid for a long time, also
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PHN 8639
13-10-1977
3~
during the application of the conducting str:ip owing to
the re:Latively high temperature during manufacture, so
that -the special rollers by means of which the strip is
disposed on the wall can easily get contamina-ted by glue
which is forced out frorn under the strip.
It is an object of the invention to provide a
lamp which obviates these drawbacks.
~ccording to the invention a low-pressure rner-
cury vapour discharge lamp having a respective electrode
disposed at each end of a tubular discharge vessel and an
electrically conducting metal strip fastened to the outer
surface of the wall of the discharge vessel by rneans of a
glue, which strip extends near to both the electrodes is
characteri~ed in that the glue is a thermosetting glue.
A low-pressure mercury vapour dis~charge~lamp
according to the inventlon has the advantage that a proper
adhesion o~ the strip to the wall of the discharge vessel
is obtained in a very short period of time so that the
machine which is used for fastening the~strip (which strip
may consist of, for example~ an aluminium wlre of foilj
is occupied by each lamp for a very short time only, this
in contradistinction with lamps in which the strip is fas-
tened to the wall of the discharge vessel by means of
polyethylene. After the layer of glue has set, softening
of the glue cannot occur anymore; even at the high tempe-
ratures prevailing in a closed luminaire.
An epoxy resin glue is preferably used as ther-
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PHN 863g
13-10-1977
38~
mosetting glues. An example of a sui-table glue is bis-
phenol-A epoxy rcsin nitrile rubber in a ra-tio in parts
per weight of 4:1 7 to which a hardener, for example di-
cyane diam:ide and, possibly, an accelerator such as
N-benzyl dimethylarnine is added. When applying such a glue
at a temperature of + 175 C sufficient hardening is
achieved within a few seconds.
The invention will be explained with reference
to a drawing.
In the drawing Fi&. 1 shows an embodiment of
a low-pressure mercury vapour discharge lamp according
to the inventlon, and ~
Fig. 2 shows a cross-section along the line
II-II of the lamp of Fig. 1.
In Flg. 1 rFference~1 indicates a tubular low-
pressure mercury vapour discharge lamp having a power
of 49 W. Disposed at each of the ends of the discharge
vessel there is a cylindrical aluminium sleeve 2 provided
with a plate 2a of an electrically insulated material in
which two current supply poles 3 and 4 for the electrode
are located. The outer surface of the wall of' the discharge
vessel is provided with an electrically conducting alumi-
nium igniting strip 5 which extends to near both electrodes
and which is fastened to the glass wall of the discharge
vessel by means of an epoxy resin glue. By means of an
ultra-sonically welded joint one end of this strip is
electrically connected to the edge of -the aluminium sleeve
l~Z3~ 13-10-1977
2, the latter being electrically connected to the elec-
trode through a silver layer 6a applied on the insulating
pla-te 2a and a resistive layer 6b o~ graphite having a
value of approximately 1M~ . At this resistance value
the lamp is safe to touch. When operating the alumium
strip is 2 mm wide and 0.1 mrn thick. As shown in fig. 2,
the inner wall of the discharge vessel is provided with a
luminescent layer 8, consisting of calcium halophosphate
activated by manganese and antimony. The alumium strip
5 is fastened to the other surface of the glass walL 1
of the lamp by a thermosetting epoxy resin glue layer 9
which is disposed between the strip and the lamp wall
and is 50 /um thick.
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