Note: Descriptions are shown in the official language in which they were submitted.
i. 20S31gO
1 BACKGROUND OF THE INVENTION
This invention relates generally to a discharge
tube, and more particularly to the type of discharge
tube which includes a pair of electrode devices provided
in a discharge space in opposed relation to each other,
each of the electrode devices being constituted by an
arc discharge electrode and a glow discharge electrode.
The Applicant of the present invention has
proposed, in Japanese Patent Publication Nos. 02-186551
and 04-22057, discharge tubes of the type in which a
pair of electrode devices, each composed of an arc
discharge electrode and a glow discharge electrode, are
disposed in a discharge space in opposed relation to
each other. These discharge tubes are used as a back
light lamp for a liquid crystal display device, an
illumination fluoresc~nt lamp, or the like. As described
above, each of the pair of opposed electrode devices of
the discharge tube comprises the arc discharge electrode
and the glow discharge electrode, and the two electrodes
are disposed adjacent to each other. Thanks to the
synergistic effect of the arc discharge and the glow
discharge, a discharge of an ultra-high brightness can
be obtained in a stable manner, so that the discharge
tube of an ultra-high brightness can be obtained. And
besides, electron-radiating substances, vaporized and
-- 1 -- *
~'-'A'
20S31~0
1 emitted in a scattered manner from the arc discharge
electrode, are captured by the glow discharge electrode,
and since the electron-radiating substances thus captured
can be again used for the electron radiation, there can
be obtained the discharge tube of an extremely long
service life.
Recently, there has been provided an arc dis-
charge electrode which is formed by mixing an electron-
radiating substance, such as barium, lanthanum boride
and cesium, with powder of tungsten, and then by press-
molding or compacting this mixture together with a lead
wire, using a mold, and subsequently by sintering this
compact.
SUMMARY OF THE INVENTION
It is an object of this invention to provide
a discharge tube which has the above-mentioned sintered
arc discharge electrode and has a long service life.
According to the present invention, there is
provided a discharge tube comprising a tube body whose
interior defines a discharge space; and a pair of
electrode devices mounted within the discharge space
in opposed relation to each other, each of the pair of
electrode devices comprising an arc discharge electrode
and a glow discharge electrode, and an electron-radiating
substance vaporized and emitted in a scattered manner
from the arc discharge electrode being captured by the
glow discharge electrode;
. 2053140
1 the improvement wherein the arc discharge
electrode is composed of a sintered body containing the
electron-radiating substance therein.
In the present invention, the vaporization
and emission of the electron-radiating substance from
the arc discharge electrode can be reduced, as compared
with the conventional discharge tube in which the surface
of the arc discharge electrode is coated with such an
electron-radiating substance. Therefore, the lifetime
of the arc discharge electrode is prolonged, and this
further prolongs the service life of the discharge
tube.
Further, since the lead wire can be integrally
molded in the arc discharge electrode, the electrode
device can be directly mounted on the discharge tube,
and this facilitates the manufacture of the discharge
tube.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a longitudinal cross-sectional view
of a first embodiment of a discharge tube of the present
invention;
Fig. 2 is a schematic perspective view of an
electrode device shown in Fig. l;
Fig. 3 is a perspective view of a sintered
arc discharge electrode shown in Fig. 2;
Fig. 4 is a partly-broken, perspective view of
a glow discharge electrode shown in Fig. 2;
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1 Fig. 5 is a perspective view of a modified
glow discharge electrode;
Fig. 6 is a partly-broken, perspective view
of a modified electrode device used in the discharge
tube of Fig. l;
Fig. 7 is a partly-broken, perspective view
of one end portion of a second embodiment of a discharge
tube of the present invention;
Fig. 8 is a partly-broken, perspective view
of an electrode device used in a test;
Figs. 9 and 10 are partly-broken, perspective
views of further embodiments of the invention, respec-
tively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention
will now be described with reference to the drawings.
Fig. 1 is a longitudinal cross-sectional
view of a discharge tube. This discahrge tube comprises
a glass tube body 1 whose inner surface is coated with
a fluorescent material 2. Two electrode devices 4
are mounted within the tube body 1, and are positioned
respectively at the opposite end portions of the tube
body 1 by lead wires 3 extending respectively through
the opposite end walls of the tube body 1. The elec-
trode devices 4 in a pair are disposed in an opposedrelation to each other. A mixture gas of argon and
mercury is sealed in the discharge tube for the purpose
2~53140
.,
1 of discharging.
As shown in Fig. 2, each of the electrode
devices 4 comprises a generally cup-shaped flow discharge
electrode 5 composed of a sintered metal body, and an
arc discharge electrode 6 which is composed of a sintered
metal body and is received within the glow discharge elec-
trode 5 coaxially therewith. The arc discharge electrode
6 is supported by the lead wire 3 which extends through a
through hole, which is extended through the closed end
portion of the cup-shaped glow discharge electrode 5,
and fixedly secured thereto by pressing or compressing.
Fig. 3 is a perspective view of the arc
discharge electrode 6. For forming the arc discharge
electrode 6, barium is mixed with powder of tungsten,
and by the use of a mold, this powder mixture is press-
molded or compacted into a cylindrical shape, with
one end portion of the lead wire 3 being embedded in
one end portion of this cylindrical compact. Then,
this cylindrical compact is sintered to provide the arc
discharge electrode 6. Cesium, lanthanum boride and
other suitable materials may be added to the above
mixture.
Fig. 4 shows the glow discharge electrode 5.
For forming the glow discharge electrode 5, a mixture
of tungsten and nickel is press-molded or compacted
into a cup-shape by the use of a mold, and then this
compact is sintered to provide this glow discharge
electrode 5. The through hole is formed axially through
2053140
1 the closed end portion of the cup-shaped glow discharge
electrode 5. As will be appreciated from Fig. 2, after
the lead wire 3 is passed through this through hole,
the closed end portion of the glow discharge electrode
5 is compressed or pressed radially inwardly, so that
the arc discharge electrode 6 is held within the cup-
shaped glow discahrge electrode 5 coaxially therewith.
Although the mixture of tungsten and nickel is used
here, the nickel may be replaced by aluminum. Also,
instead of using the above sintered metal, the glow
discharge electrode 5 may be formed from a pipe of
aluminum, nickel, iron or any other suitable material;
however, in this case, the discharge characteristics
are somewhat lowered.
In order to obtain a getter effect (for
absorbing gases), zirconium may be added to the above
mixture of tungsten and nickel, or the sintered body may
be coated with zirconium. Alternatively, as shown in
Fig. 5, a getter member 11 may be provided adjacent to
the outer periphery of the glow discharge electrode 5.
In this case, the rear end portion of the getter member
11 is bent and welded to the lead wire 3 extending
through the through hole. Preferably, a zirconium-
mercury getter should be used as the getter member 11.
If such a getter is used, there is no need to seal mercury
in the discharge tube, since mercury is already contained
in the getter.
Fig. 6 shows a modified form of the above
20531~0
1 embodiment.
In this embodiment, a filament coil electrode
6a is further connected to a distal end of an arc
discharge electrode 6 of an electrode device 4. With
the sintered arc discharge electrode 6 having no such
filament coil electrode 6a, it takes 1 to 2 minutes
before the normal discharge is obtained after turning
on the discharge tube; however, with the construction
of Fig. 6, the normal discharge can be obtained in
about 10 to 20 seconds after turning on the discharge
tube. More specifically, the filament coil electrode
6a first begins an arc discharge, and the sintered arc
discharge electrode 6 is heated by the heat generated
by this arc discharge, so that the normal discharge
condition can be soon obtained. And besides, since the
discharge of the filament coil electrode 6a is added,
the brightness is enhanced.
The filament coil electrode 6a is formed by
coating an active oxide onto the surface of a coil and
then by hardening this coil.
The above embodiments are examples of cold-
cathode fluorescent discharge tubes. Exmaples of hot-
cathode fluorescent discharge tubes will be described
below.
A further embodiment of the invention will
now be described with reference to Fig. 7. Fig. 7 shows
only one end portion of a discharge tube. A semi-
cylindrical glow discharge electrode 25, composed of a
2~!~3i 40
1 sintered body, is disposed within a discharge tube
body, and extends perpendicular to the axis of the tube
body, with its open side (that is, the concave surface)
being directed toward the other end of the discharge
tube. The glow discharge electrode 25 is supported by
a lead wire 23, extending through the end of the dis-
charge tube, and an anchor 27 extending from the end of
the discharge tube. An arc discharge electrode 26,
composed of a sintered body containing an electron-
radiating substance, is received in the semi-cylindrical
glow discharge electrode 25 and extends along the axis
thereof. The arc discharge electrode 26 is supported
at one end thereof by the above lead wire 23, and
is supported at the other end thereof by another lead
wire 28 extending through the end of the discharge
tube.
Example 1
Results of a test of a discharge tube according
to the present invention will be described with reference
to Fig. 8. The specifications of this discharge tube
are as follows:
Oscillation frequency: 50 KHz
Oscillation voltage: 700 v (effective value)
Sealed gas:
Argon: 50 torr
Mercury: 5 mg
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Outer diameter of glass tube: 6.5 mm
(thickness: 0.5 mm)
Length of glass tube: 250 mm
Fluorescent material: triple-wavelength fluorescent
material (white color)
Atmosphere temperature: 20 deg. C
Opposed electrodes (see Fig. 8):
Outer diameter (Dl) of glow
discharge electrode: 4.5 mm
Inner diameter (dl) of glow
discharge electrode: 3.5 mm
Overall length (Ll) of glow
discharge electrode: 4.5 mm
(Effective length: 3.5 mm)
Outer diameter (D2) of arc
discharge electrode: 2.5 mm
Length (L2) of arc discharge
electrode: 2.0 mm
Distance (DIS) between the
distal end of arc discharge
electrode and the end of the
tube: 7.0 mm
Outer diameter (Ds) of
lead wire: 1.5 mm
1 The results of the test are as follows:
Discharge current: 16 mA (effective value)
Brightness of discharge tube: 30,000 nt
Lifetime: 20,000 hr
The reason for the achievement of the above
ultra-high brightness and ultra-long lifetime will be
described. A blackening phenomenon caused by the electron
radiating substance which is evapolated by electron and
2Qs3t4n
1 ion impacts develops in the cup-shaped electrode, and
this substaine still exhibits the function of electron
radiation. Therefore, the blackening of the glass tube
was prevented so that the lifetime of the discharge
tube can be prolonged. Also, the glow discharge and
the arc discharge occur at the same time, and therefore
the ultra-high brightness can be obtained by the
synergistic effect of these two discharges.
Figs. 9 and 10 show further embodiments of
the invention, respectively.
In each of the above-mentioned embodiments,
the arc discharge electrode 6 is received in the cup-
shaped glow discharge electrode 5. During the manu-
facture of the discharge tube, in the evacuation step
(final stage) of creating vacuum (10 6 to 10 8) in the
discharge tube, in order to prevent a flickering of the
emitted light (that is, to stabilize the discharge),
the electrode device is heated by a bombarder to 900
to l,000C so as to remove dirt and harmful gases on
the surface of the electrode. At this time, the arc
discharge electrode 6 is likely to be hindered by the
cup-shaped glow discharge electrode 5 from being suf-
ficiently heated. As a result, in some cases, dirt and
harmful gases may not be satisfactorily removed from
the electrode 6.
The electrode device shown in Fig. 9 is analogous
in structure to the electrode device of Fig. 2, but
differs therefrom in that an arc discharge electrode 6a
-- 10 --
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1 is projected by a distance of about 2 mm from a rear
end of a glow discharge electrode 5. With this arrange-
ment, during the above heating, the heat is propagated
from the projected rear end portion of the arc discharge
electrode 6a toward its distal end received within the
cup-shaped glow discharge electrode 5, so that the whole
of the arc discharge electrode 6a can be sufficiently
heated rapidly, thus overcoming the above problem with
the manufacture. However, in this case, it is necessary
that the amount of radiation of electrons from the
arc discharge electrode 6a should be determined to be
greater than the amount of radiation of electrons from
the glow discharge electrode 5. In this case, it is
preferred that a Dumet wire should be used as a lead
wire 3.
Fig. 10 shows a modified form of the construc-
tion of Fig. 9. In this embodiment, a cup-shaped glow
discharge electrode 5 is formed by tightly winding a
tungsten wire with a diameter of 0.3 to 0.5 mm into a
funnel-like coil-shape. With this arrangement, the
thickness of the cup-shaped glow discharge electrode 5
can be reduced.
Example 2
A test of a discharge tube as shown in Fig. 1
and incorporating the electrode devices of Fig. 9 was
carried out. The specification of this discharge tube
are as follows:
20~3~40
.
Oscillation frequency: 50 KHz
Oscillation voltage: 2,500 v (peak value)
Sealed gas:
Argon: 70 torr
Mercury: 5 mg
Outer diameter of glass tube: 5.8 mm
(thickness: 0.5 mm)
Length of glass tube: 260 mm
Fluorescent material: triple-wavelength fluorescent
material (white color)
6000 K (Kelvin)
Atmosphere temperature: 20 deg. C
Opposed electrodes (see Fig. 8):
Outer diameter of arc
discharge electrode: 1.5 mm
Length of that portion
of arc discharge electrode
received in glow discharge
electrode: 2.0 mm
Length of the projected
portion of arc discharge
electrode: 2.0 mm
1 The results of the test are as follows:
Discharge current: 14 mA (effective value)
Brightness of discharge tube: 28,000 nt
Life time (reduction of
brightness by half): 20,000 hr
Also, another test was carried out, using a
discharge tube of the same specifications employing the
electrode devices of Fig. 10, and similar results were
obtained. In this case, the diameter of the coil-
shaped tungsten wire was 0.2 mm.
- 12 -
21)53140
1 With the above constructions, there can be
manufactured the discharge tubes which are high in
mass-productivity, and inexpensive, and have good dis-
charge characteristics, and stable in operation.
A further improved effect can be obtained by
coating an electron-radiating substance, such as barium,
to either the surface of the arc discharge electrode
6a or this surface and the inner surface of the glow
discharge electrode 5. By doing so, the brightness of
the discharge tube is further improved.
This embodiment is suitable for a hot-cathode
fluorescent discharge tube.
As described above, in the discharge tube
comprising the pair of opposed electrode devices each
including the arc discharge electrode and the glow
discharge electrode, since the arc discharge electrode
composed of the sintered body containing the active oxide
is used, the service life of the discharge tube is
further prolonged, and the discharge tube is highly
resistant to vibration and impact. And besides, since
the arc discharge electrode can be molded and sintered
integrally with the lead wire, the assembling and manu-
facture of the discharge tube can be carried out easily.
