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(11) | EP 0 964 429 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | ELECTRODE STRUCTURE FOR ELECTRON EMISSION, DISCHARGE LAMP, AND DISCHARGE LAMP APPARATUS |
| (57) This is an electron emission electrode structure that can shorten the transition
time from glow discharge to arc discharge and, at the same time, stabilise the arc
discharge and prevent reduction of electrode life and blackening of the tube inner
wall, together with a discharge lamp that uses this electrode structure and a discharge
lamp device in which this discharge lamp is installed. It is electron emission electrode structure 3A that is composed of electron emitter 5, made of an aggregate of granules 51, ..., that emits thermal electrons from an exposed surface when heated by a discharge, and a discharge focussing means that is in the close vicinity of, or in contact with, the above exposed surface of electron emitter 5 and focuses the discharge on the above exposed surface, together with discharge lamp 1 that uses electrode structure 3A and discharge lamp device 9 in which discharge lamp 1 is installed. |
FIELD OF THE INVENTION
[0001] The present invention relates to electron emission electrode structures designed for long life, discharge lamps and discharge lamp devices.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] Also, electrodes in which electron emitters, including barium tungstate, are impregnated into porous tungsten, for example, are known as other hot cathodes.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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
[0018] 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;
anda 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;
anda casing housing the discharge lamp.
[0019] 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
[0020]
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
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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).
[0025] 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.)
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] Furthermore, when manufacturing container 6 and electron emitter 5, the two may be sintered at the same time.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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).
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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 |
[0062] 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 |
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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, ... .
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] Also, Fig.18 shows another hot cathode 3K; (a) is a plan and (b) is a vertical cross-section.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] 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.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] 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.
[0111] 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.
[0112] 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.
[0113] 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.
[0114] 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.
[0115] 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
[0116] 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.
an electron emitter heated by a discharge, composed of an aggregate of electron emission
particles or granules emitting thermal electrons from an exposed surface thereof;
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.
an electron emitter heated by a discharge, composed of an aggregate of electron emission particles, emitting thermal electrons from the exposed surface thereof;
a discharge focussing means which is in the close vicinity of, or in contact with,
at least a part of the exposed surface of the electron emitter and focuses the discharge
on the exposed surface;
and
a container housing the electron emitter.
an electron emitter heated by a discharge, composed of an aggregate of electron emission
particles or granules, emitting thermal electrons from the exposed surface;
and
a container which houses this electron emitter, and focuses the discharge on the exposed surface by making a part that is in the close vicinity of, or in contact with, at least one part of the exposed surface of the electron emitter a conductor.
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 the exposed surfaces.
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
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 the exposed surfaces;
anda power source circuit device that is connected to the electron emission electrode structures and applies a voltage between these electrode structures.
a discharge lamp composed of electron emission electrode structures comprising
electron emitters, provided inside a glass tube filled with gas that provides a discharge,
composed of aggregates of granules that are heated by the discharge of the gas and
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 the exposed surfaces
anda casing that houses the discharge lamp.