FIELD OF THE INVENTION
-
The present invention relates to electron emission
electrode structures designed for long life, discharge lamps and
discharge lamp devices.
BACKGROUND OF THE INVENTION
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Electron emission electrodes for discharge lamps may be
broadly divided into hot cathodes and cold cathodes. Of these,
electrodes in which oxides of transition metals and alkaline
earth metals, including barium, are coated on filament coils of
tungsten, for example, are often used as hot cathodes.
-
Also, electrodes in which electron emitters, including
barium tungstate, are impregnated into porous tungsten, for
example, are known as other hot cathodes.
-
At the same time, resource-saving and energy-saving have
been promoted in recent years. Therefore, higher efficiency and
capillarisation (miniaturisation) of tubes have been devised for
the discharge lamps for back-lighting installed in OA equipment,
such as facsimile machines, and image equipment, such as liquid
crystal television, not to speak of discharge lamps for
general-purpose lighting, such as fluorescent lamps. In
addition, the demand for these has increased.
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However, of the above-mentioned hot cathodes, with the
former, the filament coil electrodes, the filament length became
shorter as the tube was miniaturised. Therefore, large
quantities of electron emitters could not be maintained, and,
as well as being unable to obtain a satisfactorily long life,
there was little strength against vibration because of the fine
wire.
-
Also, although the latter, the porous tungsten electrodes,
are used in large current type high-pressure discharge lamps,
such electrodes are difficult to produce. Moreover, in the small
current domain of low-pressure discharge lamps, such as
fluorescent lamps, there were problems such as their not
operating stably as hot cathodes.
-
In this way, it was not possible to design capillarisation
of discharge lamp tubes with the hot cathodes mentioned above.
Therefore, cold cathodes made of metals such as nickel or
aluminium-zirconium alloy were used. However, there were large
cathode drop losses with these cold cathodes, and large lamp
currents could not be achieved.
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Therefore, as a means of designing discharge lamp
miniaturisation and at the same time obtaining large lamp
currents, the electrode structure stated in Laid-Open Patent
Heisei 1-65764 Gazette, for example, was developed. In this
Laid-Open Patent Heisei 1-65764 Gazette, a hot cathode was
described in which the thermal electron emission portion was
formed by semiconductor ceramic particles in a container that
was shaped as a cylinder having a bottom and of which the front
side was open.
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Also, according to the description in this Gazette, by
making the thermal electron emission part a particulate, the heat
capacity of the thermal electron emission part became lower than
that of the container. Thus, during glow discharge, the
temperature rise of the thermal electron emission part was rapid,
and transition to arc discharge was accelerated by making thermal
electron emission easier. In this case, because a greater
current density can be obtained, the discharge lamp tube can be
capillarised by making the external diameter of the electrode
smaller.
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However, with the semiconductor ceramic of the thermal
electron emission part described in this Laid-Open Patent Heisei
1-65764 Gazette, the thermal electron emission part does not
reach the specified temperature during glow discharge for
reasons such as insufficient activation of the surface.
Therefore, sometimes an arc spot is not formed on the thermal
electron emission part, and the discharge surrounds the
periphery of the container. Then, if the discharge surrounds
the container, the inner wall of the discharge lamp becomes
blackened due to the high cathode fall voltage, and the electrode
life is shortened. In particular, if the thermal electron
emission capability of the thermal electron emission part is
reduced, surrounding by the discharge will occur more readily
before the life of the electrode has run out, and the shortening
of life will be accelerated.
-
Also, for example, according to Laid-Open Patent Heisei
6-302297 Gazette and National Publication Patent Heisei 9-507956
Gazette, the hot cathode may be held in a holder. This holder
is connected to lead wires for supplying current that are led
to the outside of the discharge lamp.
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During glow discharge, the holder plays the role of a cold
cathode and the electron are supplied by the secondary emmision.
When the temperature rises during glow discharge, thermal
electron emission from the semiconductor ceramic dominates over
the second emmision, and transition to arc discharge takes place.
-
However, with these structures stated in these Laid-Open
Patent Heisei 6-302297 Gazette and Published Patent Heisei
9-507956 Gazette, the temperature of the thermal electron
emission part is difficult to rise during glow discharge, and
it takes some time before transition to arc discharge. Also,
if the glow discharge time is long, trouble will occur with the
hot cathode because the cold cathode will undergo a large
sputtering effect. That is to say, the active substance on the
surface of the semiconductor ceramic will be sputtered.
Sputtered substances from the container and the inner leads will
accumulate on the surface of the semiconductor ceramic, and,
because the work function will become higher, the disadvantage
of reduction of the thermal electron emission capability will
occur. This will cause reduction of the electrode life and
blackening of the inner wall of the discharge lamp tube.
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As stated above, with the semiconductor ceramic of the
thermal electron emission part described in Laid-open Patent
Heisei 1-65764 Gazette, for reasons such as insufficient
activation of the surface, the thermal electron emission part
does not reach the specified temperature during glow discharge.
Therefore, sometimes an arc spot is not formed on the thermal
electron emission part, and the discharge readily surrounds the
periphery of the container. Then, if the discharge surrounds
the container, the inner wall of the discharge lamp tube becomes
blackened due to the high cathode fall voltage, and the electrode
life is shortened.
-
Also, with the structures described in these Laid-Open
Patent Heisei 6-302297 Gazette and Published Patent Heisei
9-507956 Gazette, the temperature of the thermal electron
emission part is difficult to rise during glow discharge, and
it takes some time before transition to arc discharge. Also,
if the glow discharge time is long, trouble will occur with the
hot cathode because the cold cathode will undergo a large
sputtering effect.
-
That is to say, there is the problem that the active
substance on the surface of the semiconductor ceramic will be
sputtered. Sputter substances from the container and the inner
leads will accumulate on the surface of the semiconductor ceramic,
and the disadvantage will occur of the work function becoming
higher and causing reduction of the thermal electron emission
capability. This will cause reduction of the electrode life and
blackening of the inner wall of the discharge lamp tube.
-
The present invention has been devised in the light of the
above problems. Its purpose is to provide electron emission
electrode structures that shorten the time for transition from
glow discharge to arc discharge and, at the same time, can
stabilise the arc discharge and can prevent electrode life
reduction and lamp inner wall blackening, discharge lamps that
use these electrode structures and lamp devices in which these
discharge lamps are installed.
DISCLOSURE OF THE INVENTION
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The present invention provides the inventions in the
following numbered sections.
- (1) An electron emission electrode structure comprising:
an electron emitter heated by a discharge, composed of an
aggregate of electron emission granules, and emitting
thermal electrons from an exposed surface
and - a discharge focussing means which is in the close vicinity
of, or in contact with, at least a part of the exposed surface
of this electron emitter and focuses the discharge on the
exposed surface.
This thermal electron emission electrode comprises an aggregate
of granules. On starting, the exposed surface of this aggregate
surface produces a glow discharge as a cold cathode, and the
temperature is raised by ions, accelerated by the high cathode
fall voltage, heating the whole of the electrode. The
temperature rises readily since, in addition to the heat
capacities of the particles of the electron emitter being small,
the thermal resistance between adjacent particles is also high.
After this, when the temperature at which sufficient thermal
electrons can be emitted is reached by the concentrated heating
of the particles, transition from glow discharge to arc discharge
takes place.
That is to say, by providing a discharge focuser, the
electrical field can be focused on at least a part of the exposed
surface of the electron emitter, composed of an aggregate of
granules, at the time of glow discharge. Thus, the temperature
of the electron emitter can be raised in a short time. - (2) An electron emission electrode structure comprising:
- an electron emitter heated by a discharge, composed of an
aggregate of particles or granules, which emits thermal
electrons from an exposed surface;
- a discharge focussing means which is in the close vicinity
of, or in contact with, at least a part of the exposed surface
of this electron emitter and focuses the discharge on that
exposed surface
and - a container housing the electron emitter.
Then, by making the container itself a conductor when the
container is of a conductive material, or by providing a
conductor, separate from the container, in the close vicinity
of the electron emitter inside the container when the container
is of insulating or semi-insulating material, the electrical
field can be focused on the conductor during glow discharge. Thus, the arc discharge will occur on the exposed surface
of the electron emitter surface facing the open part of the
container.Also, the arc spot can be formed quickly and stably by
raising the temperature of the electron emitter in a short time.
Thus, when this electrode is used in a discharge lamp, by
accelerating the transition from glow discharge to arc discharge,
there will be no blackening of the inner wall of the tube and
the life will be elongated. - (3) An electron emission electrode structure that has the
characteristic of being composed of:
- an electron-emitter, composed of an aggregate of granules,
that is heated by a discharge and emits thermal electrons
from an exposed surface
and - a container that houses this electron emitter, and focuses
the discharge on the exposed surface of the electron emitter
by making a part that is in the close vicinity of, or in
contact with, at least one part of that exposed surface a
conductor.
- (4) An electron emission electrode structure, as in (3),
that has the characteristic of the container being made of metal.
The material of the container is composed of at least one
metal that has a comparatively low vapour pressure, even at the
temperature reached by the electrode during discharge, such as,
for example, W, Mo, Re, Ta, Ti, Zr, Ni or Fe, or of alloys of
these metals, or of the carbides, C, the nitrides, N, the
silicides, Si, or the borides, B, of these metals. Also, when
switched ON, these substances act as good conductors and
satisfactorily perform the passage of current to the electron
emitters housed inside. Thus, arc spots are readily formed, and
good electron emission is obtained.Also, semiconductor substances composed of the oxides of
Ba, Sr, Ca, Th, etc., may be added to the above metals. These
containers have smaller thermal capacities than those formed
entirely of metals, while at the same time, it is difficult for
the heat to escape. Thus, arc spots will readily form on the
electron emitter granules.
- (5) An electron emission electrode structure, as in (4),
that has the characteristic of the outer surface of the metal
container having an insulating coating.
Discharge from the part with the insulating coating is
difficult. The electrical field focuses on the part where the
metal is exposed, and a glow discharge can be generated focused
on the exposed surface part of the electron emitter. The
insulating coating can be formed using at least one metal oxide,
such as aluminium oxide, silicon oxide, zirconium oxide or
tantalum oxide, or of mixtures of these.
- (6) An electron emission electrode structure, as in (2),
that has the characteristic of the container being insulating
or semi-insulating.
- (7) An electron emission electrode structure, according
to (6), that has the characteristic of the container being
composed of metal oxide.
With (6) and (7), the container is a semi-insulating, for
example, semiconductor ceramic obtained by adding an additive
(such as Ta2O3) to a mother crystal (such as BaTiO3 or BaZrO3).
This container does not have good conductivity at normal
temperature but, as the temperature rises, its resistivity
decreases and it becomes a good conductor. Then, once it has
become a conductor, the temperature of the container becomes high
and continues to maintain the discharge by stimulating
activation of the electron emitter housed in the container.Also, in the case of a highly insulating container, a
conductive metal plate or coating made of a film of metal carbide,
metal nitride, etc. may be provided on the surface of the
container so that electrical connection with the electron
emitter housed in the container is established.
- (8) Any electron emission electrode structure, as in (2)
to (7), that has the characteristic of the container being
supported in a holder.
- (9) An electron emission electrode structure, as in (1),
in which the discharge focusing means is a metal lug that is in
the close vicinity of, or in contact with, at least a part of
the exposed surface of the electron emitter.
By making the tip of a rod-shaped or plate-shaped metal lug
sharp, the electrical field near this portion becomes even more
enhanced during glow discharge. It is desirable to make the
sharp part of this tip a shape that will produce electrical field
focusing, including making the tip such shapes as a sharp needle
shape, angular, conical or pyramidal, or such shapes as a
truncated cone, a truncated pyramid or an arc.In the case when the container is conductive and a conductor
is provided separately from the container, it is desirable that
the two should be electrically connected so that they are of the
same potential.
- (10) An electron emission electrode structure, as in (9),
that has the characteristic of the metal lug being tongue-shaped.
- (11) An electron emission electrode structure, as in (1),
that has the characteristic of the discharge focusing means being
a conductive rod-shaped lug that passes through the electron
emitter and protrudes from the exposed surface.
- (12) An electron emission electrode structure, according
to (10), that has the characteristic of the rod-shaped lug
protruding from the centre of the exposed surface.
- (13) An electron emission electrode structure, according
to (11), that has the characteristic of the rod-shaped lug
protruding off-set from the centre of the exposed surface.
By the protruding rod-shaped lug protruding from a position
displaced from the central axis of the exposed surface of the
electron emitter, the temperatures of the electron emitter in
contact with, or in the close vicinity of, the container inner
wall and the periphery of the protruding part, where arc spots
readily form, rise more rapidly. Thus, transition from glow
discharge to arc discharge can be improved.
- (14) An electron emission electrode structure, as in (2),
that has the characteristic of the discharge focusing means being
a metal mesh that covers the open part of the container.
By providing a conductor composed of metal mesh facing the
exposed surface of the electron emitter on the open part of the
container front surface, the temperature of the electron emitter
can be raised and the arc spot can be caused to form, since the
electrical field is focused by the mesh during glow discharge.
Thus, the transition to arc discharge during glow discharge is
accelerated, and when this electrode is used in a discharge lamp,
there is no blackening of the tube inner wall, nor shortening
of life.For this mesh, either a mesh woven from metal wire, such
as Ni, W or stainless steel, or a mesh formed by punching multiple
holes in a metal plate, can be used.
- (15) An electron emission electrode structure, according
to any of (9) to (13), that has the characteristic of the discharge
focusing means being formed in the container or in the holder.
- (16) An electron emission electrode structure, as in (1)
or (2), that has the characteristic of the granules of the
electron emitter being formed mainly of the oxide of at least
one alkaline earth metal, transition metal or rare earth metal.
It is desirable that the granular particles of the electron
emitter should be formed mainly of the oxide of at least one
alkaline earth metal, transition metal or rare earth metal.As formation materials, for example, materials composed
mainly of alkaline earth metals with metal oxides, such as BaO,
SrO, CaO and Ba4Ti2O9, BaTaO3, SrTiO3, SrZrO3, and materials
composed mainly of alkaline earth metals with oxides of rare
earth (such as Sc, Y, La and lanthanide) metals, such as BaCeO3,
can be used.Also, these having low work functions, their cathode drop
losses are small. Moreover, since they do not react readily with
components of the atmosphere, they exhibit actions such as ease
of manufacture.
- (17) An electron emission electrode structure, as in (1)
or (2), that has the characteristic of a film of a carbide and/or
a nitride of at least one alkaline earth metal, transition metal
or rare earth metal being formed on the surface of the granules
of the electron emitter.
As the films, composed of a carbide and/or a nitride of at
least one alkaline earth metal, transition metal or rare earth
metal, that are the films formed on at least a part of the surface
of the granules of the electron emitter, the carbides and
nitrides of such as Ti, Ta, Zr, Nb, Hf and W, for example, carbides
such as TaC and TiC, or nitrides such as TiN and ZrN, form thin
films of high melting point substances. By this means, the
electrode substances, and particularly the alkaline earth metals
that contribute to emission (electron emission), can reduce the
sputtering and vaporisation due to ion bombardment.
- (18) A discharge lamp that has the characteristic of being
provided with;
- a glass tube filled with a gas that provides a discharge
and - electron emission electrode structures that are composed
of
- electron emitters, provided inside the tube, that are
heated by the discharge of the gas and are composed
of aggregates of granules that emit thermal electrons
from exposed surfaces
and - discharge focusing means that are in the close
vicinity of, or in contact with, at least parts of the
exposed surfaces of these electron emitters and focus
the discharge on those exposed surfaces.
- (19) A discharge lamp device that has the characteristic
of being provided with:
- a glass tube filled with gas that provides a discharge and
that forms a discharge path;
- electron emission electrode structures that are composed
of
- electron emitters, provided at the ends of the glass
tube, that are heated by the discharge of the gas and
are composed of aggregates of granules that emit
thermal electrons from exposed surfaces;
- discharge focusing means arranged in the close
vicinity of, or in contact with, at least parts of the
exposed surfaces of these electron emitters and
focussing the discharge on those exposed surfaces;
and - a power source circuit device connected to the electron
emission electrode structures to apply to a voltage between
these electrode structures.
- (20) A discharge lamp device that has the characteristic
of being provided with:
- a discharge lamp composed of electron emission electrode
structures made up of
- electron emitters, provided inside a glass tube filled
with gas to provide a discharge, composed of
aggregates of granules heated by the discharge of the
gas and emitting thermal electrons from exposed
surfaces;
- discharge focusing means arranged in the close
vicinity of, or in contact with, at least parts of the
exposed surfaces of these electron emitters and
focussing the discharge on those exposed surfaces;
and - a casing housing the discharge lamp.
-
-
Lighting equipment that uses this discharge lamp device can
be widely used for back lighting in liquid crystal display
equipment, liquid crystal television, decorative equipment,
etc., for reading originals in facsimile machines, etc., for
exposure and for charge removal in such OA equipment as copiers,
and as appliances and lighting fixtures for normal illumination.
BRIEF DESCRIPTION OF THE DRAWINGS
-
- Figure 1 is a partially cut-away plan view showing the
discharge lamp (fluorescent lap) device of a embodiment of the
present invention.
- Figure 2 is a vertical cross-section showing a hot cathode
that is an embodiment of the present invention that is sealed
into the discharge lamp (fluorescent lamp) in Figure 1,
- Figure 3 is a graph showing the relationship between the
discharge current (A) and the cathode fall voltage (V) of the
hot cathode in Figure 2 above having an insulating body,
- Figure 4 is a graph showing the relationship between the
discharge current (A) and the cathode fall voltage (V) of the
hot cathode in Figure 2 above not having an insulating body,
- Figure 5 is an oblique view showing a hot cathode that is
the electrode of another embodiment of the present invention,
- Figure 6 is a graph showing the relationship between the
input power during glow discharge (W) and the reciprocal of the
glow-to-arc transition time τ g (sec-1) of a fluorescent lamp
using the hot cathode shown in Figure 5 above.
- Figure 7 is a plan view showing a hot cathode of another
embodiment of the present invention.
- Figure 8 is an elevational view of the hot cathode shown
in Figure 7,
- Figure 9 is a plan view showing a hot cathode of another
embodiment of the present invention,
- Figure 10 is an elevational view of the hot cathode shown
in Figure 9,
- Figure 11 is a plan view showing a hot cathode of another
embodiment of the present invention.
- Figure 12 is an elevational view of the hot cathode shown
in Figure 11,
- Figure 13 is an oblique view showing a hot cathode of another
embodiment of the present invention,
- Figure 14 is an oblique view showing a hot cathode of another
embodiment of the present invention,
- Figure 15 is a partially-sectional plan view of a
fluorescent lamp using the hot cathode shown in Figure 14,
- Figure 16 is an oblique view showing a hot cathode of another
embodiment of the present invention,
- Figure 17 is a plan view showing a hot cathode of another
embodiment of the present invention,
- Figure 18 is (a) a plan view and (b) a vertical cross-section
showing a hot cathode of another embodiment of the present
invention,
- Figure 19 is a partially cut-away cross-section showing a
hot cathode of another embodiment of the present invention, and
- Figure 20 is an oblique view showing a discharge lamp device
of a embodiment of the present invention.
-
PREFERRED EMBODIMENTS OF THE INVENTION
-
The following is a description, with reference to the
drawings, of a embodiment of an electron emission electrode
structure and a discharge lamp of the present invention.
-
Fig.1 is a partially cut-away plan showing the discharge
lamp, and Fig.2 is a vertical cross-section showing the electron
emission electrode structure.
-
In Fig.1, 1 is a discharge lamp, for example, a fluorescent
lamp. In lamp 1, hot cathodes 3A and 3A, as the electrode
structures, are positioned facing each other inside the two ends
of glass tube 2, which is composed of a translucent container
that is a straight tube of external diameter, for example, from
3mm to 15mm, but here 4mm, and overall length about 300mm. At
the same time, lead wires 4 and 4, which are connected to hot
cathodes 3A and 3A, are hermetically sealed into the respective
ends.
-
Also, the inside of glass tube 2 is filled with a rare gas,
for example argon, (Ar), at 20Torr and mercury, as the discharge
medium. The distance between hot cathodes 3A and 3A is set at
about 260mm. Moreover, the inner wall surface of glass tube 2
is coated with a fluorescent layer (not illustrated).
-
Also, hot cathode 3A is composed of container 6, which is
filled with electron emitter 5, holder 7A, which holds container
6, and lead wire 4, which supports holder 7A and at the same time
forms an electrical connection. (There are cases when the lead
wire is not included as part of the hot cathode.)
-
Container 6 is composed with conductive materials such as
tantalum, Ta, and zirconium, Zr, as its main constituents. It
is formed in the shape of a cylindrical tube with a bottom (cup)
having circular base 61 and open part 62 at its ends and, at the
same time, circumferential depression 63 is formed on the surface
of its outer periphery.
-
Also, holder 7A is made of nickel, and is formed in the shape
of a cylindrical tube with a bottom (cup), having circular base
71 and open part 72, that accepts container 6. Container 6 and
holder 7A are incorporated by the rim of open part 72 of holder
7A being inserted and locked into depression 63 of container 6.
Thus, the two are mechanically and electrically connected, and
the construction is such that container 6 and holder 7A are
installed coaxially.
-
Then, electron emitter 5 is loaded into, and housed in,
container 6. Electron emitter 5 is composed of an aggregate of
multiple granules 51 ... of semiconductor ceramic, in which the
main constituents are particulate oxides of barium, Ba, and
tantalum, Ta, of particle diameter 10µm to 500µm, and
preferably 20µm to 100µm, with the addition of a small quantity
of zirconium oxide, ZrO2. Also, 8 is insulation composed of
aluminium oxide coated on the outer surface of container 6 below
depression 63 and on the inner surface of holder 7A.
-
Moreover, lead wire 4 is welded to approximately the centre
of bottom surface 71 of holder 7A. Thus, as described above,
hot cathode 3A is composed of container 6, holder 7A, electron
emitter 5 and lead wire 4.
-
Apart from those mentioned above, the conductive materials
that form container 6 can be at least one of tungsten, W,
molybdenum, Mo, rhenium, Re, titanium, Ti, tantalum, Ta,
zirconium, Zr, niobium, Nb, hafnium, Hf, nickel, Ni, or iron,
Fe, or alloys of these, or the carbides, C, nitrides, N, silicides,
Si, or borides, B, of these metals. Also, semiconductor
substances composed of the oxides of barium, Ba, strontium, Sr,
calcium, Ca or thorium, Th, may be added to the above metals.
-
Also, as other formation materials for container 6, for
example, semiconductor ceramic obtained by adding an additive
(such as Ta2O3) to a mother crystal (such as BaTiO3 or BaZrO3)
can be used. Alternatively, for example, materials composed
mainly of a mixture of alkaline earth metals and metal oxides,
i.e., BaO, SrO, CaO and Ba4Ti2O9, BaTaO3, SrTiO3, SrZrO3, and
materials composed mainly of a mixture of alkaline earth metals
and oxides of rare earth metals, i.e., Sc, Y, La and lanthanide,
such as BaCeO3, can be used.
-
Furthermore, in the case of container 6 being formed from
the above alkaline earth metal, transition metal and rare earth
metal materials, films of high-melting point substances,
composed of a carbide or a nitride of at least one alkaline earth
metal, transition metal or rare earth metal, for example,
carbides such as TaC and TiC, or nitrides such as TiN and ZrN,
can be formed on its surface. By this means, the dispersion and
vaporisation of electrode container 6 due to ion bombardment can
be reduced.
-
Also, in the case of container 6 being of insulating
material, a conductive metal plate or rod may be positioned in
close vicinity, and a film composed of a metal carbide or a metal
nitride may be formed.
-
Also, for electron emitter 5, apart from the above-mentioned
materials, oxides such as those of barium, Ba,
strontium, Sr, calcium, Ca, or materials of which the main
constituents are alkaline earth metals + metal oxides, such as
Ba4Ti2O9, BaTaO3, SrTiO3 and SrZrO3, or materials of which the main
constituents are alkaline earth metals + rare earth (such as
scandium, Sc, yttrium, Y, lanthanum, La and lanthanide) metal
oxides can be used.
-
Moreover, in the case of electron emitter 5 being formed
from the above alkaline earth metal, transition metal and rare
earth metal materials, films of high-melting point substances,
composed of a carbide or a nitride of at least one alkaline earth
metal, transition metal or rare earth metal, for example,
carbides such as TaC and TiC, or nitrides such as TiN and ZrN,
can be formed on its surface, in the same way as for container
6. By this means, the dispersion and vaporisation of electron
emitter 5 due to ion bombardment can be reduced.
-
Furthermore, when manufacturing container 6 and electron
emitter 5, the two may be sintered at the same time.
-
Also, holder 7A, can be formed from materials which contain
at least one conductive metal, such as nickel, Ni, tantalum, Ta,
titanium, Ti, zirconium, Zr, aluminium, Al, and tungsten, W.
-
Moreover, holder 7A is not limited to a cover structure that
holds container 6 and covers almost the entire surface of its
side and bottom 61. It may also be a support, such as a frame.
Furthermore, in the case of lead wire 4 being directly connected
to container 6 and performing support and electrical connection
of container 6, there is no particular requirement for holder
7A.
-
Also, the formation of insulation 8 may be by draining off
and applying a liquid in which fine particles of aluminium oxide
of 0.1µm or less have been dispersed in an alcohol group solvent,
and removing the solvent and moisture after application by
heating for about 5 minutes in atmosphere at about100°C to 200°C.
Alternatively, application may be by immersing the required
parts in this liquid, pouring the liquid into the parts, etc.
Moreover, insulation 8 may be formed using at least one metal
oxide, such as aluminium oxide, Al2O3, silicon oxide, SiO2,
zirconium oxide, ZrO2 and tantalum oxide, Ta2O5, or mixtures of
these.
-
Then, fluorescent lamp 1 is completed by sealing hot
cathodes 3A and 3A with the above composition inside glass tube
2 as the electrode structures. After this, lead wires 4 and 4
(or their connectors in the case of their having connectors) are
connected to power source circuit system C, which possesses a
high-frequency lighting circuit or the like. When such
connection is made, current will flow to each container 6, which
is composed of a conductor and is supported by, and electrically
connected to, a holder 7A, via each holder 7A, which is similarly
composed of a conductor.
-
Then, a discharge starts and fills between hot cathodes 3A
and 3A that take as conductors containers 6 that are positioned
facing each other at the two ends of glass tube 2, which becomes
the discharge path. Ultraviolet light is generated by the rare
gas and mercury in tube 2 being ionised and excited. This
ultraviolet light is converted to visible light by the
fluorescent layer, and this visible light is radiated externally
by passing through the wall of tube 2.
-
The discharges from hot cathodes 3A and 3A, which are
positioned facing each other on the discharge path, are glow
discharges as cold cathodes when starting. Ions that are
accelerated by the high cathode fall voltage heat the entire
electrode and raise its temperature, and granules 51, ... of
electron emitter 5 readily rise in temperature since, in addition
to their small heat capacity, the thermal resistance between
adjacent granules 51 is high. After this, when, through
concentrated heating of granules 51, the temperature is reached
at which sufficient thermal electrons can be emitted, transition
from glow discharge to arc discharge takes place, an arc spot
is formed on granules 51, and the electrodes act as hot cathodes.
-
The transition to arc discharge takes place after glow
discharge has covered on almost the whole of conductive container
6, with the exception of its outer surface. This arc discharge
originates from exposed surface 55 of the surface layer of
electron emitter 5 that is loaded into and housed in container
6, or from the surfaces of particles 51 that are in contact with
the inner wall of open part 62. The reason for this is that it
is difficult for current to flow because electron emitter 5 is
a semiconductor ceramic and its electrical resistance is high.
Therefore, the arc spot is formed on particles 51, ... of electron
emitter 5 that are in contact with, or in the close vicinity of,
the inner wall of container 6, which is a conductor. When the
electron emitting substances in the particles 51 that form
electron emitter 5 scatter and are dissipated, this arc spot
shifts to adjacent particles 51, and the discharge is maintained.
-
Also, a gap is formed between the outer surface of container
6 and the inner surface of holder 7A, which are superposed
coaxially, and the discharge would attempt to surround this part
through this gap acting as a hollow cathode. However, in the
present invention, the discharge is stable because the discharge
does not surround the bottom of container 6 due to insulation
8 being formed on the outer surface of container 6 and the inner
surface of holder 7A.
-
As a result, by making this hot cathode 3A the discharge
focusing means, conductive container 6 does not have that action.
Thus, the temperature of electron emitter 5 rises appropriately,
there is no great shifting of the arc spot during lighting, and
there is no flicker in the discharge; the arc spot is
appropriately formed, and a stable discharge can be maintained.
-
Also, the above fluorescent lamp 1 can shorten the
transition time from glow discharge to arc discharge, and reduce
the cathode fall voltage. Improvement of the luminous efficacy
can be devised and, at the same time, as the result of being able
to reduce sputter due to ion bombardment, long life can be devised
by preventing blackening of the inner wall of tube 2.
-
Fig.3 and Fig.4 show the results of measuring the cathode
fall voltages (V) in the cases of forming and not forming films
of insulation 8 on the outer surface of container 6 and the inner
surface of holder 7A.
-
Compared with the case shown in Fig.4 of not forming a film
of insulation 8, in the case shown in Fig.3 of forming a film
of insulation 8, the cathode fall voltage (V) for the discharge
current (A) is almost stable and hardly fluctuates. Also, the
cathode fall voltage (V) for the same current value of discharge
current (A) is smaller, and shortening of cathode life can be
prevented.
-
Next, another embodiment of a hot cathode that is an
electrode structure of the present invention will be described
with reference to Fig.5. Fig.5 is an oblique view showing hot
cathode 3B. Since, apart from the holder, this is the same as
in Fig.1, like reference numerals have been assigned to like
parts and their descriptions have been omitted.
-
Holder 7B shown in Fig.5 is formed in a cylindrical shape
with a bottom in the same way as in the above embodiment. A pair
of projecting parts 73 and 73 that protrude from the edge of
opening 72 are located and formed on holder 7B. These projecting
parts, 73 and 73, have claw-shaped tongue pieces 74 that are bent
inward approximately at right angles, facing electron emitter
5, above opening 62 of container 6. The tips of these tongue
pieces, 74 and 74, are formed in acute-angled triangular shapes,
and their two acute tips, 75 and 75, are arranged to face exposed
surface 55 of the surface layer of electron emitter 5 and to face
each other with a separation between.
-
Consequently, by bending tip 75 of tongue piece 74 at the
edge of container 6, container 6 can readily be installed in,
and supported by holder 7B without causing damage to container
6, and container 6 can be prevented from shifting in the axial
direction. Also, even though thermal expansion may occur in
holder 7B during discharge, etc., it will support container 6
and can prevent container 6 falling off.
-
Projecting parts 73 and 73 are formed from holder 7B as
incorporated parts. However, provided projecting parts 73 and
73 are electrically connected to holder 7B, they may also be
formed separately from holder 7B and incorporated later. Also,
projecting parts 73 are not limited to a pair of two; one, or
three or more may also be formed.
-
With this hot cathode, 3B, by installing tongue pieces 74
of projecting parts 73, which become discharge focussing
conductors, facing electron emitter 5 on opening 62 of container
6, glow discharges will occur at tips 75. Then, focussing of
the electrical field on tips 75 takes place. The temperature
rise of granules 51, ... of electron emitter 5 located in the close
vicinity is accelerated, and these glow discharges can readily
form arc spots on the surface of granules 51 of electron emitter
5. In this way, transition from glow discharge to arc discharge
takes place in a short time, and it becomes difficult for ion
sputtering to occur. Thus, blackening of the inner wall of glass
tube 2 and reduction of electrode life can be prevented.
Incidentally, the sharper the tips 75 of tongue pieces 74, the
more readily electrical field focussing takes place. Therefore,
it is desirable to make them acute angles.
-
Also, Fig.6 is a graph comparing input power (W) and the
reciprocal of the glow-to-arc transition time [τg(sec-1)] for
a discharge lamp of the present invention using electrode 3B in
which the conductor formed is composed of tongue piece 74 of this
embodiment (characteristic shown by dot mark ) and for a prior
art construction discharge lamp not provided with a conductor
(characteristic shown by x mark X).
-
As shown in Fig.6, the lamp formed with projecting part 73
(the conductor) can achieve a large reciprocal of the glow-to-arc
transition time τ g at a small input power W. Consequently, by
forming projecting part 73 (the conductor), the glow-to-arc
transition time can be shortened, and the time in which ion
sputtering, etc., occurs can also be shortened.
-
Next, some other embodiments of hot cathodes that are
electrode structures of the present invention will be described
with reference to Fig.7 to Fig.10. Fig.7 and Fig.8 show the same
hot cathode 3C, Fig.7 being a plan and Fig.8 being an elevation
of Fig.7. Similarly, Fig.9 and Fig.10 show the same hot cathode
3D, Fig.9 being a plan and Fig.10 being an elevation of Fig.9.
Both hot cathodes 3C and 3D have the same composition, except
for the holders, as that shown in Fig.1 or Fig.5; like reference
numerals have been assigned to like parts and their descriptions
have been omitted.
-
With hot cathode 3C shown in Fig. 7 and Fig. 8 also, container
6 is housed in holder 7C. Holder 7C is formed in a cylindrical
shape with a bottom, resembling the holder of hot cathode 3C shown
in Fig.5, and a pair of projecting parts 73 and 73 located
protruding upward from the edge of opening 72 are formed as
incorporated parts. Projecting parts 73 and 73 have tongue
pieces 74 constituting conductors that are bent inward at
approximately right angles facing exposed surface 55 of electron
emitter 5 above, but at a little distance from, opening 62 of
container 6 as discharge focussing conductors. Also, tips 76
and 76, which are formed in arc shapes, of the two tongue pieces,
74 and 74, are positioned facing each other and facing, but
separated from, exposed surface 55 of the surface of electron
emitter 5.
-
Even though tips 76 and 76 of projecting parts 73 and 73
are formed in arc shapes, as shown in Fig.7 and Fig.8, electrical
field focussing can occur between tips 76 and 76.
-
Here, with the embodiment shown in Fig.7 and Fig.8, a
starting voltage test and a rapid flashing cycle test were
performed for comparison using hot cathode 3C, which displays
a embodiment having projecting parts 73 that constitute
conductors provided with tips 76 formed in arc shapes, and a hot
cathode not possessing projecting parts 73.
-
For the tests, fluorescent lamp 1 was used, in which the
tube diameter of glass tube 2 was approximately 6mm, the distance
between hot cathodes 3C and 3C was approximately 150mm, and into
which mercury drop and argon gas of at approximately 100Torr were
filled. Projecting parts 73 were formed using nickel plate of
width approximately 1mm.
-
Also, in the starting test, the lamps were left for 3 hours
in a location with an ambient temperature of 25°C. The voltage
at transition from glow discharge to arc discharge was taken as
the starting voltage. As shown in Table 1, it was found that
with the lamp in which projecting
parts 73 were formed, the
starting-up voltage was greatly reduced.
Starting Voltage (kVrms) |
Without projecting parts (conductors) | 1.75 | 1.81 | 1.83 | 1.68 |
With projecting parts (conductors) | 1.43 | 1.56 | 1.23 | 1.37 |
-
Also, for the rapid flashing cycle test, a lighting circuit
with characteristics of secondary release voltage approximately
2.3kVrms, lamp current approximately 20mA and lamp voltage
approximately 200Vrms was used. Flash lighting was repeated,
taking 30 seconds of lighting and 30 seconds OFF as one cycle,
and the number of times to failure of arc spot formation on the
granule was measured. It was found, as shown in Table 2, that
with a lamp in which projecting parts
73 (conductors) were formed
the number of times to failure to light was greatly increased,
and the flash life was improved.
Number of Times Flashed (Tens of Thousands) |
Without projecting parts (conductors) | 5.2 | 7.5 | 9.7 | 10.4 |
With projecting parts (conductors) | 32.3 | 40.0 | 37.8 | 45.0 |
-
Next, another embodiment of hot cathode 3D that is an
electrode structure of the present invention, shown in Fig. 9 and
Fig.10, will be described.
-
With hot cathode 3C shown in Fig.7 and Fig.8, projecting
parts 73 having tongue pieces 74 were formed from, and
incorporated with, holder 7C. However, this hot cathode, 3D,
is one to which lug 77, formed in a rod shape to constitute a
conductor, is formed bent at right angles, separately from holder
7D, is connected. The tip of rod-shaped lug 77 is caused to face
exposed surface 55 of the surface of electron emitter 5 inside
container 6.
-
Even with making the discharge focussing means rod-shaped
lug 77 in this way, the same action and effects can be obtained
as with the above-mentioned projecting parts 73 shown in Fig.7
and Fig.8. Incidentally, if the tip of rod-shaped lug 77 is
sharpened, the effect of focussing the electrical field can be
further improved.
-
Also, another embodiment of a hot cathode that is an
electrode structure of the present invention will be described
with reference to Fig.11 and Fig.12. Fig.11 and Fig.12 show the
same hot cathode 3E, Fig.11 being a plan and Fig.12 being an
elevation. Parts that are the same as in Fig.1 to Fig.10 have
been assigned like reference numerals, and their descriptions
have been omitted.
-
Hot cathode 3E shown in Fig.11 and Fig.12 is provided with
conductive net-like metal mesh 78, which is either vertically
and horizontally woven from metal wire or formed by punching
multiple holes in a metal plate, on front opening 62 of container
6 so that it covers exposed surface 55 of the surface of electron
emitter 5, in place of the above-mentioned plate-shaped tongue
pieces 73 and rod-shaped lug 77.
-
Even with making the discharge focussing means conductive
mesh 78 in this way, the same action and effects can be obtained
as with the hot cathodes of the above-mentioned embodiments.
-
For this mesh, 78, either one woven from metal wire or one
produced by punching multiple holes in a metal plate can be used,
employing such metals as nickel, Ni, tungsten, W, or stainless
steel.
-
Moreover, other embodiments of hot cathodes that are
electrode structures of the present invention will be described
with reference to Fig.13 to Fig.16. Fig.13, Fig.14 and Fig.16
are oblique views showing hot cathodes 3F, 3G and 3H. Fig.15
is a partially-sectioned plan of part of a fluorescent lamp, 1,
into which hot cathodes 3G of Fig. 14 are sealed. Parts that are
the same as in Fig.1 to Fig.12 have been assigned like reference
numerals, and their descriptions have been omitted. Hot
cathodes 3F, 3G and 3H shown Fig.13, Fig.14 and Fig.16 all use
conductive rod-shaped lugs of metal, etc., composed of electrode
rods, as discharge focussing means.
-
For hot cathode 3F shown in Fig.13 as an electrode rod, a
through-hole (not illustrated) is formed in the centre of bottom
61 of container 6F. Electrode rod 4A, that constitutes a
conductor composed of tungsten, W, molybdenum, Mo, titanium, Ti,
tantalum, Ta, nickel, Ni, etc., is installed to pass through this
hole, between granules 51, ... of particulate electron emitter 5
that is filled into, and housed in, container 6, and to project
from approximately the centre of opening 62. Electrode rod 4A
that constitutes this rod-shaped lug may either be the tip of
lead wire 4 serving a dual purpose, or be formed as a separate
entity from lead wire 4, to which it is connected by welding,
etc.
-
Incidentally, when, for example, lead wire 4 serves the
dual purpose of electrode rod 4A, it is secured in the
through-hole of container 6 by welding. Also, discharge will
occur more readily if the tip of electrode rod 4A that constitutes
the conductor and projects from opening 62 is formed as an acute
angle.
-
By projecting the tip, that constitutes a conductor, of
conductive lead wire 4, that passes through container 6 and the
centre of electron emitter 5 and serves the dual purpose of
electrode rod 4A, above opening 62 in this way, the electrical
field can be focussed on this tip. Thus, granules 51, ... of
electron emitter 5 that are in contact with, or in the close
vicinity of, electrode rod 4A can be activated by raising the
temperature of electrode rod 4A. Then, an arc spot occurs on
the surfaces of granules 51 that are in contact with the outer
surface of electrode rod 4A and, when electron emission from
these granules 51 is complete, the arc spot shifts to the
neighbouring granules 51. Thus, an action that can stably
maintain the discharge is exhibited by the arc spot gradually
shifting to neighbouring granules 51, ... .
-
Also, in hot cathode 3G shown in Fig.14, lead wire 4 that
serves the dual purpose of electrode rod 4A, which is composed
of a rod-shaped lug in hot cathode 3F shown in Fig.13, is in the
same axial direction as the axis of container 6G, but passes
through in a position displaced from central axis 69.
-
That is to say, lead wire 4 that serves the dual purpose
of electrode rod 4A is on the central axis of container 6G outside
container 6G on the base end side. However, bent section 41 is
formed in the vicinity of, and outside, bottom 61 of container
6G. Thus, the composition is such that the part that constitutes
the conductor and projects from inside container 6G and from
opening 62 is positioned offset from central axis 69 of container
6G.
-
Also, fluorescent lamp 1A is completed by sealing hot
cathodes 3G and 3G into the ends of glass tube 2, as shown in
Fig.15. With these hot cathodes 3G, a current flows in
conductive electrode rod 4A and container 6G when switched ON,
and a discharge takes place between hot cathodes 3G that face
each other. At this time, electrode rod 4A in container 6G is
closer to the inner wall of container 6G than if it were on central
axis 69 of container 6G. Therefore, the temperatures of
electrode rod 4A that constitutes a conductor and of container
6G, which together form hot cathode 3G, can be raised, and the
activation of particles 51, ... can be increased by the temperature
rise of electron emitter 5 that accompanies this. Thus,
transition from glow discharge to arc discharge is good.
-
Also, even with electrode rod 4A being in an off-set
position and not in a position on the central axis of container
6G, since generation of the arc spot shifts to particles 51, ...
of electron emitter 5 that border on opening 62, an appropriate
arc discharge can be produced with hardly any effect on the
emission properties from the slight displacement. In this lamp
1A, lead wires 4 that are sealed into the ends of tube 2 are sealed
in approximately on the central axis of tube 2. Therefore, the
sealed parts do not cause any lumps of glass, unevenness, etc.,
due to displacement of lead wires 4 and there is no occurrence
of cracks.
-
Incidentally, it has been confirmed that, when granules 51
of particulate electron emitter 5 in the vicinity of the inner
wall of container 6G become unable to emit thermal electrons
through having used up their electron-emitting substance, other
granules 51, that are adjacent in the circumference direction
of the inner wall of container 6G, will emit thermal electrons.
Thereafter, the electron-emission function gradually shifts to
granules 51 that are adjacent in this inner wall circumferential
direction.
-
Also, when the relationship between mean input power W and
the reciprocal of glow-to-arc transition time τ g of fluorescent
lamp 1A that uses hot cathodes 3G and 3G is compared, it is almost
the same result as that shown in Fig. 6. However, the lamp in which
electrode rods 4A are formed projecting from containers 6G can
achieve a greater reciprocal of glow-to-arc transition time
τ g at a smaller input power. Consequently, by forming
projecting electrode rods 4A, the glow-to-arc transition time
can be shortened, and thus the time during which ion sputtering,
etc., occurs is reduced.
-
Furthermore, hot cathode 3H of another embodiment will be
described with reference to Fig.16. Fig.16 is an oblique view
of a hot cathode. With hot cathode 3H, shown in Fig.16 as an
electrode, electrode rod 4A that serves the dual purpose of lead
wire 4 is positioned along the central axis of container 6H and,
at the same time, branch connection 42 is formed in lead wire
4. Multiple, for example four, rod electrodes 4B are provided
from branch connection 42 in branch-like form approximately
parallel to electrode rod 4A. All their tips project from
opening 62 as rod-shaped lugs.
-
Incidentally, the positioning of electrode rods 4A and 4B,
..., which are formed as rod-shaped lugs constituting conductors,
may be with electrode rods 4B, ... equally spaced, or unequally
spaced, taking electrode rod 4A as the centre. Moreover, the
number of these branches may be one or more.
-
Also, by providing multiple electrode rods 4A and 4B, ... that
constitute conductors in this way, the temperature rise is made
more vigorous, not only in the environs of electrode rods 4A and
4B, ..., but also in the environs of their tips, and an emission
domain is formed over the whole area of electron emitter 5. Thus,
the glow-to-arc transition time can be shortened, and the time
during which ion sputtering, etc., occurs can be reduced. Also,
after using up granules 51, ... of electron emitter 5 in the environs
of one electrode rod 4A or 4B, the arc spot is formed in the
environs of another electrode rod 4A or 4B. Thus, life becomes
longer.
-
Also, Fig.17 to Fig.19 show other embodiments of hot
cathodes 3J to 3L as electrode structures. In the drawings, like
reference numerals have been assigned to parts that are the same
as in Fig.2, and their descriptions have been omitted. The
configurations of the respective containers of hot cathodes 3J
to 3L shown in Fig.17 to Fig.19 differ from those shown in Fig.2
to Fig.16.
-
Fig. 17 is a plan view of conductive hot cathode 3J. Viewed
from above, while the outer circumference of container 6J shown
in hot cathode 3J forms a circle, the peripheral configuration
of the inner wall of opening 62, that houses granules 51, ... of
electron emitter 5, is formed as wave-shaped uneven periphery
63.
-
Also, in a discharge lamp into which these hot cathodes are
sealed, because the inner wall of container 6J is indented, the
length of the inner wall periphery can be made longer than if
it were merely a circle concentric with the outer wall. That
is to say, the area with which granules 51, ... of electron emitter
5 are in contact can be made larger. Thus, when the lamp is ON,
the absolute number of granules 51, ... of electron emitter 5 that
are in contact with, or are in the close vicinity of, uneven
periphery 63 of uneven inner wall 62 of conductive container 6J
becomes larger.
-
Also, when this discharge lap is ON, an arc spot is
generated in granules 51 of electron emitter 5 that are in contact
with, or are in the close vicinity of, uneven inner wall 62 of
container 6, which is the conductor, and moreover from granules
51 on the surface. Thus, when the electron-emitting material
in granules 51 is dispersed and exhausted, the arc spot shifts
to adjacent particles 51 and the discharge is maintained.
-
As a result, as well as discharge initiation being simple,
the arc spot will not shift much during lighting, and a stable
discharge, in which there is no discharge flicker, can be
maintained. Also, the above lamp can shorten the transition time
from glow discharge to arc discharge, and can reduce the cathode
fall voltage. Thus, improvement of luminous efficacy can be
devised and, at the same time, as the result of being able to
reduce sputtering clue to ion bombardment, blackening of the inner
wall of lamp 2 can be prevented and long life can be designed.
-
Also, Fig.18 shows another hot cathode 3K; (a) is a plan
and (b) is a vertical cross-section.
-
Hot cathode 3K has an incorporated circular projection from
the circular bottom of container 6K toward the centre of the
opening. Inside container 6K there is ring-shaped depression
65, and granules 51, ... of electron emitter 5 are loaded in a ring
shape into depression 65. In this case, central projection 64
is also a conductor, and the arc spot that is the origin of
discharge can be caused to be generated on the entire lengths
of the peripheries of inner wall 62 and projection 64. Thus,
the same operational effect as in the above-mentioned
embodiments can be displayed.
-
With hot cathodes 3J and 3K shown in Fig.17 and Fig.18 the
overall lengths of the inner wall peripheries of containers 6J
and 6K are longer than simple circles. Thus, these hot cathodes
have the advantage that arc discharge can be maintained because
arc spots generate readily in those parts and thermal electron
emission is performed over long periods.
-
Also, the shapes of containers are not limited to right
circles. They may also be elliptical, or polygonal, such as
regular square-shaped or oblong-shaped. Moreover, the shapes
of the inner wall peripheries are not limited to the wave-shaped
indentations formed in the right circular inner wall shown in
the drawing. They may also be wave-shaped, saw-toothed, etc.,
indentations formed in elliptical or polygonal, such as regular
square-shaped or oblong-shaped, inner walls. Furthermore, the
shape of the above-mentioned central projection 64 also is not
limited to right circular. It may be elliptical or polygonal,
and it may be formed as one or multiple projections, either
separate or linked together, and in addition, its periphery may
be indented.
-
Incidentally, when this is expressed numerically, for
example in the case of a circular container, the relationship
should be
where
L is the inner wall peripheral
length of the depression of the container, and
S is the projected
area of the opening. In short, the longer the peripheral length
of the container inner wall can be made, the better.
-
Also, with hot cathode 3L shown in Fig.19, the shape of
container 6L differs from those described previously. That is
to say, all those previously described were formed as equal-diameter
cylinders, but this container 6L is formed with opening
62 of greater diameter than bottom surface 61.
-
With container 6L, formed in a trumpet shape with opening
62 of large diameter in this way, the outer periphery of container
6L and opening 72 of holder 7L are in a state of contact, and
the gap apparently disappears. Thus, passage of the discharge
through the gap to surround the air space between the two can
be prevented.
-
Also, particulate electron emitter 5 composed of a large
quantity of granules 52, ... and 53, ... can be placed on the exposed
surface at the front where arc spots that are the origins of
discharges readily form. By this means, with discharge lamps
into which these hot cathodes 3L are sealed the arc discharge
is stable, no flickering occurs during lighting, and life can
be lengthened.
-
Furthermore, the inventors of the present invention studied
the discharge lamps disclosed in the above embodiments. They
found that, through the relationship between the pressure (Torr)
of the sealed-in rare gas, the mean particle diameter D (µm)
of granules 51 of particulate electron emitter 5 and the
discharge current IL (mA) the transition from glow discharge to
arc discharge could be accelerated and, at the same time, the
arc discharge could be stabilised over long periods.
-
Namely, fluorescent lamps were produced in the following
way. Hot cathodes 3B and 3B, shown in Fig.5, were placed in
opposition at an inter-electrode distance of approximately 260mm
at the two ends of straight tubular glass tubes 1 of external
diameter approximately 4mm and overall length approximately
300mm, such as shown in Fig.1 for example. A fluorescent layer
was formed on the inner surfaces of tube 1, and argon, Ar, as
the rare gas, together with mercury, Hg, droplet were sealed
inside. The sealing-in pressure and the mean particle diameters
of granules 51 of granular electron emitter 5 were varied.
-
Electron emitters 5 made up of aggregates of granules 51, ...
of particle diameter 10µm to 100µm were housed in bottomed
cylindrical containers 6 that composed these hot cathodes 3B.
Also, containers 6 and granules 51, ... of electron emitters 5 were
formed from a material of which the main constituents were the
oxides of barium, Ba, and tantalum, Ta, with a small quantity
of zirconium oxide, ZrO2. To improve anti-sputter capability,
thin films of tantalum carbide, TaC, were coated on their
surfaces.
-
Moreover, the variations made in the pressure of the gas
sealed inside
tube 1, the mean particle diameter of
granules 51
of
electron emitter 5, and the discharge current are the results
shown in Tables 3 ∼ 5. Incidentally, the mean particle diameter
was found from the arithmetical mean of the particle distribution.
Also, for the gas pressure, in the case of including mercury
vapour at about room temperature in the total pressure of the
sealed in gas, for example in the total pressure of approximately
70Torr for argon, Ar,/neon, Ne, the sealed-in gas pressure became
70Torr.
-
Here, for transition from glow discharge to arc discharge,
the case of exceeding 1 second was taken as mark X (bad) and the
case of 1 second or less was taken as mark o (good). For the
flashing test, 10 seconds ON and 10 seconds OFF was repeated,
and the case of a life of less than 100,000 times was taken as
mark X, while a life of 100,000 times or more was taken as mark
o. For arc discharge during life, the case of discharge from
other than granules 51 although barium, Ba, remained on the
surfaces of particles 51 was taken as mark X, and the case of
discharge from granules 51 while barium, Ba, remained in granules
51 was taken as mark o.
-
Also, in the case of the relationship
where the rare gas sealed-in pressure is taken as
P torr, the
mean particle diameter of
granules 51 of
particulate electron
emitter 5 as
D µm, and the discharge current as
IL mA, transition
from glow discharge to arc discharge can be accelerated. At the
same time, the arc discharge can be stabilised, and blackening
of the inner wall of
glass tube 1 and shortening of life can be
prevented.
-
Moreover, according to the above expression, the higher the
sealed-in gas pressure, the better. However, the starting
voltage will become higher and the luminous efficacy will reduce
if the specified sealed-in gas pressure becomes higher.
Therefore, here are also limits to the sealed-in gas pressure
in line with the specifications. Incidentally, even when tests
were carried out with other sealed-in gases, for example, a
mixture gas of sodium, Na, neon, Ne, and argon, Ar, a mixture
gas of barium, Ba, and argon, Ar, and a mixture gas of barium,
Ba, and xenon, Xe, it was possible to obtain the same results.
-
Furthermore, in cases of using mixtures of differing
particle diameter distributions for particulate electron
emitter 5 as the electron emission electrode structure,
discharge lamps were obtained in which light adjustment could
readily be carried out.
-
That is to say, multiple thermal electron emitters 5 having
two, large and small, peak values of mean particle diameter
distribution made up of semiconductor ceramic, such as barium
and tantalum oxide, BaTaO3, were loaded into, and housed in, for
example, containers 6L of hot cathodes 3L shown in Fig.19. This
particle diameter distribution was made up of a mixture of
comparatively large diameter granules 52, ... having a mean
particle diameter peaking at approximately 100µm and
comparatively small diameter granules 53, ... having a mean
particle diameter peaking at approximately 30µm. The particle
size distribution was in the range of 10µm to 150µm.
-
Then, the fluorescent lamps into which these hot cathodes
3L and 3L were sealed were lit via a dimming circuit device (not
illustrated). When the lamp current for the case of not
performing dining was about 30mA, out of the electron emitter
5 housed in container 6L, arc spots originated on 1 or 2
comparatively large diameter granules 52, ... of particle diameter
approximately 100µm, and maintained a stable discharge.
However, with the comparatively small diameter granules 53, ...
of particle diameter approximately 30µm, arc spots originated
straddling several particles. Therefore, the thermal
accumulator structure was destroyed and the arc spots readily
shifted to other granules. Consequently, effectively, the
stable arc spots originated on comparatively large diameter
granules 52 of particle diameter approximately 100µm.
-
Also, when, for dimming, the current was altered and these
lamps were lit by about 5mA, arc spots originated on 1 ∼ 2
comparatively small diameter granules 53, ... of particle diameter
approximately 30µm, and maintained a stable discharge. However,
with the comparatively large diameter granules 52, ... of particle
diameter approximately 100µm, because their thermal capacities
were comparatively large compared with the comparatively small
diameter granules 53, ... of particle diameter approximately 30
µm, sufficient heat for thermal electron emission could not be
obtained with a current as low as approximately 5mA.
Consequently, effectively, it came about that stable arc spots
originated on comparatively small diameter granules 53 of
approximately 30µm for which electron emission was good.
-
Therefore, with discharge lamps that use mixed electron
emitters of differing particle diameter distributions in this
way, it is possible to cause origination of arc spots by raising
the temperature of the electron emitter that has a peak particle
diameter corresponding to the lamp current. Consequently, by
applying this to discharge lamps that perform light adjustment
by controlling the current in answer to the current value, it
is possible to carry out stable arc discharge and dimming.
-
Incidentally, this particle diameter distribution peak
value is not limited to mixtures of two types; there may be three
or more types. However, the effect is greater when the
difference between adjacent mean particle diameter values is 1.5
or more.
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Furthermore, Fig.20 is an oblique view showing an
embodiment of discharge lamp device 9 concerned in the present
invention. In Fig.20, a casing 91 is shown. Reflector mirror
92, supporting members 93 and 93 (one of which is not shown),
such as sockets, that support fluorescent lamp 1, and power
source circuit device C are provided inside casing 91.
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This discharge lamp device, 9, can be used for the backlight
of a liquid crystal display device or for a facsimile original
reader. Since, as stated above, the light emission
characteristic of fluorescent lamp 1 is improved and it has long
life, the light emission characteristics of the above devices
also will be increased, and their maintenance will be simpler
because lamp 1 will not require replacing for long periods.
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Incidentally, the present invention is not limited to the
embodiments stated above. For example, the electrode
structures of the above embodiments are composed by housing
particulate electron sitters in containers. However,
electrode structures may also be produced by placing particulate
emitters in sintering containers, and connecting lead wires,
etc., to the bodies that are removed from these containers after
sintering. Containers support electrode structures inside
tubes and act as means for electrical connection with lead wires,
but they are not indispensable.
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Also, the containers that compose the hot cathodes that are
the electrode structures are described above as being made of
metals having conductivity. Nevertheless, they may also be made
from semi-insulating so-called conductive ceramics, in which
semiconductor ceramic substances are mixed with conductive
metals, or they may be made of semiconductor ceramic substances
or insulating materials, with conductivity given to their
surfaces. In short, provided it is something that acts as a good
conductor when switched ON and satisfactorily performs passage
of current to the electron emitter housed inside it, it may be
applied.
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Moreover, discharge lamps are not confined to fluorescent
lamps. They may be applied in other discharge lamps, such as
ultraviolet emission lamps. Also, the discharge lamps may be
rare gas light-emitting lamps, and there is no need to load in
mercury as a discharge medium. Moreover, the configuration of
the glass tubes is not limited to straight tube-shaped tubes.
Lamps may use curved tubes, such as U-shaped, W-shaped and
ring-shaped, or they may use board-shaped tubes.
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Also, the number of electrodes provided in one discharge
lamp is not limited to a pair (two). A lamp may have three or
more electrodes, and it goes without saying that they can be
applied to lamps in which part of the electrode is provided on
the outside surface of the tube.
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Furthermore, the discharge lamp device is not limited to
the composition of the embodiment. It is possible to vary the
shape, construction, etc., in many ways.
Also, the casing that houses the lamp, etc., is not limited to
the box-shaped casing shown here. The casings include
board-shaped housings on which the lamp, its supporting members,
etc., are mounted in exposed fashion. Moreover, the power source
circuit device for lighting and the reflector mirror may be
provided separately from the discharge lamp device, and are not
indispensable items.
POSSIBILITIES FOR INDUSTRIAL USE
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When using the electron emission electrode structures
concerned in the present invention in the above way, a rapid
release of thermal electrons is possible when starting the
discharge lamp, and the glow-to-arc transition time is
accelerated. Furthermore, it is possible to provide long-life
electrodes that can prevent blackening of the inner wall and
shortening of the life of the lamp tube. For this reason, with
lighting devices which use this lamp, the light emission property
and life property can be improved and, at the same time,
maintenance work can be simplified. These lamps can be widely
used for back-lighting for liquid crystal display devices and
liquid crystal televisions; in OA equipment such as for original
reading in facsimile machines and for exposure and discharge in
copiers, and in appliances, lighting fixtures, etc., for normal
illumination.