Title: Gas discharge tube and method for forming electron emission layer in gas discharge tube
Abstract: A gas discharge tube includes a plurality of light-emitting portions that are provided outside of the tube, at least two discharge electrodes, and an electron emission film formed on the entire inner wall of the tube for improving discharge characteristics.
Patent Number: 6,932,664 Issued on 08/23/2005 to Yamada, et al.
| Inventors:
|
Yamada; Hitoshi (Kawasaki, JP);
Tokai; Akira (Kawasaki, JP);
Ishimoto; Manabu (Kawasaki, JP);
Shinoda; Tsutae (Kawasaki, JP)
|
| Assignee:
|
Fujitsu Limited (Kawasaki, JP)
|
| Appl. No.:
|
076333 |
| Filed:
|
February 19, 2002 |
Foreign Application Priority Data
| Jul 31, 2001[JP] | 2001-232449 |
| Current U.S. Class: |
445/24; 445/25; 445/26; 313/607; 427/226 |
| Intern'l Class: |
H01J 009/24; H01J 061//00 |
| Field of Search: |
313/607,634,483-485,306,581,201,621,243,488
445/24-26,14
427/226,67
|
References Cited [Referenced By]
U.S. Patent Documents
| 3809944 | May., 1974 | Jongerius et al.
| |
| 4983881 | Jan., 1991 | Eliasson et al.
| |
| 5013966 | May., 1991 | Saikatsu et al.
| |
| 5049777 | Sep., 1991 | Mechtersheimer.
| |
| 6376691 | Apr., 2002 | Celinska et al.
| |
| 6686489 | Feb., 2004 | Celinska et al.
| |
| Foreign Patent Documents |
| SHO 61-103187 | May., 1986 | JP.
| |
| HEI 11-162358 | Jun., 1999 | JP.
| |
Primary Examiner: Williams; Joseph
Assistant Examiner: Dong; Dalei
Attorney, Agent or Firm: Staas & Halsey
Claims
1. A method comprising:
injecting a coating solution at a predetermined amount from one opening of a
tube having an opening in each of both ends thereof, said coating solution containing
an organic metal compound that turns into an inorganic metal compound having an
electron emission ability by a burning process;
forming a coating film on the entire inner wall of the tube by causing the coating
solution to go along the inner wall of the tube while entirely sealing the opening
of the tube;
burning the coating film to form an electron emission film on the entire inner
wall of the tube;
providing a plurality of light-emitting portions in the tube;
providing at least two discharge electrodes on an outside of the tube for applying
voltages to the light emitting portions, and
locally solidifying the coating film formed in the vicinity of a tailing end
of the coating solution going along the inner wall of the tube, wherein the local
solidification of the coating film comprises
drying the coating film by moving a heat source utilizing visible light or an
infrared ray and/or a microwave with the movement of the coating solution and irradiating
the coating film with the visible light or infrared ray and/or microwave, or
fixing the metal compound in the coating film to the inner wall of the tube by
moving a ultraviolet ray irradiating device with the movement of the coating solution
and irradiating the coating film with the ultraviolet ray,
the tube thereby being a gas discharge tube having an electron emission film
formed on the entire inner wall of the tube for improving discharge characteristics.
2. The method as claimed in claim 1, wherein the organic metal compound comprises
magnesium hexanoate and the electron emission film comprises magnesium oxide film.
3. The method as claimed in claim 1, further comprising:
using one or more forces of centrifugal force, gas pressure and liquid pressure
for causing the coating solution to go along the tube.
4. The method as claimed in claim 1, further comprising:
drying the coating film by sending blast into the tube alternately from both
ends of the tube.
5. A method comprising:
injecting a coating solution at a predetermined amount from one opening of a
tube having an opening in each of both ends thereof, said coating solution containing
an organic metal compound that turns into an inorganic metal compound having an
electron emission ability by a burning process;
forming a coating film on the entire inner wall of the tube by causing the coating
solution to go along the inner wall of the tube while entirely sealing the opening
of the tube;
burning the coating film to form an electron emission film on the entire inner
wall of the tube;
providing a plurality of light-emitting portions in the tube;
providing at least two discharge electrodes on an outside of the tube for applying
voltages to the plurality of light-emitting portions, the electron emission film
being made of magnesium oxide; and
locally solidifying the coating film formed in the vicinity of a tailing end
of the coating solution going along the inner wall of the tube, wherein the local
solidification of the coating film comprises
drying the coating film by moving a heat source utilizing visible light or an
infrared ray and/or a microwave with the movement of the coating solution and irradiating
the coating film with the visible light or infrared ray and/or microwave, or
fixing the metal compound in the coating film to the inner wall of the tube by
moving a ultraviolet ray irradiating device with the movement of the coating solution
and irradiating the coating film with the ultraviolet ray,
the tube thereby being a gas discharge tube having an electron emission film
formed on the entire wall of the tube for improving discharge characteristics.
6. A method comprising:
injecting a coating solution at a predetermined amount from one opening of a
tube having an opening in each of both ends thereof, said coating solution containing
an organic metal compound that turns into an inorganic metal compound having an
electron emission ability by a burning process;
forming a coating film on the entire inner wall of the tube by causing the coating
solution to go along the inner wall of the tube while entirely sealing the opening
of the tube;
burning the coating film to form an electron emission film on the entire inner
wall of the tube;
providing a plurality of light-emitting portions in the tube;
providing at least two discharge electrodes on an outside of the tube;
providing a common electrode extending in a longitudinal direction of the tube;
providing a plurality of separate electrodes that oppose to the common electrode
with respect to the tube and which are arranged at spaced intervals in the longitudinal
direction of the tube, the light-emitting portions being formed in the tube at
positions where the separate electrodes and the common electrode oppose to each
other; and
locally solidifying the coating film formed in the vicinity of a tailing end
of the coating solution going along the inner wall of the tube, wherein the local
solidification of the coating film comprises
drying the coating film by moving a heat source utilizing visible light or an
infrared ray and/or a microwave with the movement of the coating solution and irradiating
the coating film with the visible light or infrared ray and/or microwave, or
fixing the metal compound in the coating film to the inner wall of the tube by
moving a ultraviolet ray irradiating device with the movement of the coating solution
and irradiating the coating film with the ultraviolet ray,
the tube thereby being a gas discharge tube having an electron emission film
formed on the entire wall of the tube for improving discharge characteristics.
7. A method comprising:
injecting a coating solution at a predetermined amount from one opening of a
tube having an opening in each of both ends thereof, said coating solution containing
an organic metal compound that turns into an inorganic metal compound having an
electron emission ability by a burning process;
forming a coating film on the entire inner wall of the tube by causing the coating
solution to go along the inner wall of the tube while entirely sealing the opening
of the tube;
burning the coating film to form an electron emission film on the entire inner
wall of the tube; and
locally solidifying the coating film formed in the vicinity of a tailing end
of the coating solution going along the inner wall of the tube, wherein the local
solidification of the coating film comprises
drying the coating film by moving a heat source utilizing visible light or an
infrared ray and/or a microwave with the movement of the coating solution and irradiating
the coating film with the visible light or infrared ray and/or microwave, or
fixing the metal compound in the coating film to the inner wall of the tube by
moving a ultraviolet ray irradiating device with the movement of the coating solution
and irradiating the coating film with the ultraviolet ray,
the tube thereby being a gas discharge tube having the electron emission film
formed on the inner wall of the tube to improve discharge characteristics.
8. The method as claimed in claim 7, wherein the organic metal compound comprises
magnesium hexanoate and the electron emission film comprises magnesium oxide film.
9. The method as claimed in claim 7, further comprising:
using one or more forces of centrifugal force, gas pressure and liquid pressure
for causing the coating solution to go along the tube.
10. The method as claimed in claim 7, further comprising:
drying the coating film by sending blast into the tube alternately from both
ends of the tube.
11. The method as claimed in claim 7, further comprising:
forming at least two discharge electrodes on an outside of the tube.
12. A method comprising:
injecting a coating solution at a predetermined amount from one opening of a
tube having an opening in each of both ends thereof, said coating solution containing
an organic metal compound that turns into an inorganic metal compound having an
electron emission ability by a burning process;
forming a coating film on the entire inner wall of the tube by causing the coating
solution to go along the inner wall of the tube while entirely sealing the opening
of the tube;
burning the coating film to form an electron emission film on the entire inner
wall of the tube;
providing a plurality of light-emitting portions in the tube;
providing at least two discharge electrodes on an outside of the tube for applying
voltages to the light emitting portions; and
locally solidifying the coating film formed in the vicinity of a tailing end
of the coating solution going along the inner wall of the tube,
wherein the local solidification of the coating film comprises drying the coating
film by moving a heat source utilizing visible light or an infrared ray and/or
a microwave with the movement of the coating solution and irradiating the coating
film with the visible light or infrared ray and/or microwave, the tube thereby
being a gas discharge tube having an electron emission film formed on the entire
inner wall of the tube for improving discharge characteristics.
13. A method comprising:
injecting a coating solution at a predetermined amount from one opening of a
tube having an opening in each of both ends thereof, said coating solution containing
an organic metal compound that turns into an inorganic metal compound having an
electron emission ability by a burning process;
forming a coating film on the entire inner wall of the tube by causing the coating
solution to go along the inner wall of the tube while entirely sealing the opening
of the tube;
burning the coating film to form an electron emission film on the entire inner
wall of the tube;
providing a plurality of light-emitting portions in the tube;
providing at least two discharge electrodes on an outside of the tube for applying
voltages to the light emitting portions; and
locally solidifying the coating film formed in the vicinity of a tailing end
of the coating solution going along the inner wall of the tube,
wherein the local solidification of the coating film comprises fixing the metal
compound in the coating film to the inner wall of the tube by moving a ultraviolet
ray irradiating device with the movement of the coating solution and irradiating
the coating film with the ultraviolet ray, the tube thereby being a gas discharge
tube having an electron emission film formed on the entire inner wall of the tube
for improving discharge characteristics.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to Japanese applications No. 2001-232449 filed on
Jul. 31, 2001, whose priority is claimed under 35 USC §119, the disclosures
of which are incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas discharge tube and a method for forming
an electron emission film into the gas discharge tube, and more particularly to
a thin gas discharge tube having a diameter of approximately 0.5 to 5 mm and a
method for forming an electron emission film into the gas discharge tube suitably
adapted for such a gas discharge tube.
2. Description of the Related Arts
A conventional gas discharge tube is provided with electrodes at end edges with
respect to the longitudinal direction of the discharge tube for extending a discharge
in the longitudinal direction. Films of an electron emission material (electron
emission film) that improves discharge characteristics are directly formed on filaments
serving as the electrodes. Therefore, the filaments to which the electron emission
film is vapor-deposited are adhered to be fixed onto the end edges of the discharge
tube in manufacturing the gas discharge tube.
There are other gas discharge tubes than the above-mentioned discharge tube,
one of which is provided with a lot of electrodes on the side of the tube. A display
device in which a plurality of such slender, long gas discharge tubes are arranged
has been known.
A screen of this display device is composed of a great number of light emitting
elements (tubular-light-emitting elements: gas discharge tubes) arranged in a line
direction (a column direction) of the screen. The light emitting elements are formed
of hollow, slender, long glass tubes having a diameter of approximately 0.5 to
5 mm whose outer walls are provided with electrodes and in which a discharge gas
is enveloped. Known display devices of the above-mentioned type are a large gas
discharge display panel disclosed in Japanese Unexamined Patent Publication No.
Sho 61(1986)-103187 and an image display device disclosed in Japanese Unexamined
Patent Publication No. Hei 11(1999)-162358. The display device of this type has
advantages of reduced assembling man-hour, light-weight and low cost, easy to change
the screen size or the like.
A gas discharge tube used for this display device has a structure of having a
plurality
of electrodes that can generate facing discharge or surface discharge inside the
discharge tube. A discharge is generated in a direction between the side faces
of the discharge tube so as to obtain a great number of light-emitting points in
one tube.
Considering withstand voltage of a driving circuit and a cost of circuit
components, voltage for generating a discharge between electrodes (voltage for
initiating a discharge) in the gas discharge tube is desired to be low. Accordingly,
an electron emission film is formed onto a discharge face for improving discharge characteristics.
This gas discharge tube is provided with electrodes at the outer wall of the
tube as described above, so that the formation of the electrodes is easy, but the
electron emission film is not attributed to the improvement of the discharge characteristics
since the electron emission film is not in direct contact with the discharge gas
even though the electron emission film is directly formed onto the electrodes.
In order to solve this problem, the electron emission film may be formed onto
the inner wall of the tube, not on the electrodes positioned outside of the discharge
tube. This can improve the discharge characteristics.
However, it is extremely difficult to form the electron emission film on
the inner wall of the slender, long glass tube having a diameter of 2 mm or less
and a length of 200 mm or more.
For example, a film-formation by a vapor deposition method brings a non-uniform
distribution of the film thickness in the tube since evaporating molecules of a
material for forming an electron emission film introduced from the tube edge is
significantly accumulated in the vicinity of the tube edge. The uneven thickness
of the electron emission film causes variations in the voltage for initiating the
discharge at a great many of light-emitting points in the tube, thereby arising
a problem of narrowing the margin of the light-emitting operation.
SUMMARY OF THE INVENTION
The present invention is accomplished in view of these circumstances, and aims
to improve discharge characteristics and reduce the unevenness of the light-emitting
operation among many light-emitting points by forming an electron emission film
on the inner wall of a gas discharge tube with a uniform thickness.
The present invention provides a gas discharge tube comprising a plurality of
light-emitting portions that are provided outside of the tube and comprise at least
two discharge electrodes, and an electron emission film formed on the entire inner
wall of the tube for improving discharge characteristics.
The gas discharge tube according to the present invention has the electron emission
film formed on the entire inner wall of the tube, whereby discharge characteristics
is improved upon generating a discharge between discharge electrodes via the gas
discharge tube.
The present invention also provides a method for forming an electron emission
film into a gas discharge tube comprising a step of injecting coating solution
from one opening of a tube at a predetermined amount, said coating solution including
an organic metal compound that becomes an inorganic metal compound having an electron
emission ability by a burning process; a step of forming a coating film on the
entire inner wall of the tube by causing the coating solution to trickle down the
inner wall of the tube while entirely sealing the opening of the tube; and a step
of burning the coating film for forming an electron emission film on the entire
inner wall of the tube.
The method for forming an electron emission film according to the present invention
comprises a step of injecting coating solution from one opening of a tube at a
predetermined amount; a step of forming a coating film on the entire inner wall
of the tube by causing the coating solution to trickle down the inner wall of the
tube while entirely sealing the opening of the tube and a step of burning the resultant
film, whereby an electron emission film having a uniform thickness can be formed
on the entire inner wall of the tube. The formation of the electron emission film
having a uniform thickness can reduce the voltage for initiating the discharge
of the gas discharge tube as well as can widely assure a margin of a light-emitting
operation at many light-emitting points.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description
given hereinbelow and the accompanying drawings which are given by way of illustration
only, and thus are not to be considered as limiting the present invention.
FIGS. 1(
a) and 1(
b) are explanatory views showing
a display device using a gas discharge tube according to the present invention;
FIG. 2 is an explanatory view showing an entire construction of one embodiment
of the gas discharge tube according to the present invention;
FIGS. 3(
a) and 3(
b) are explanatory views showing
an inner construction of the gas discharge tube in the embodiment;
FIGS. 4(
a) to 4(
c) are explanatory views showing
that a coating solution for forming an electron emission film is introduced into
the gas discharge tube;
FIGS. 5(
a) to 5(
d) are explanatory views showing
a method for introducing a coating solution into the gas discharge tube;
FIGS. 6(
a) to 6(
c) are explanatory views showing
another method for introducing a coating solution into the gas discharge tube;
FIG. 7 is an explanatory view showing a device for introducing a coating solution
into the gas discharge tube;
FIGS. 8(
a) to 8(
d) are explanatory views showing
another method for introducing a coating solution into the gas discharge tube;
FIGS. 9(
a) and 9(
b) are explanatory views showing
a method for drying a coating film;
FIG. 10 is an explanatory view showing another method for introducing a coating
solution into the gas discharge tube;
FIGS. 11(
a) to 11(
c) are explanatory views showing
a method for burning a dried coating film;
FIGS. 12(
a) to 12(
e) are explanatory views showing
Embodiment 1 for a method for forming an electron emission film in the gas discharge
tube; and
FIG. 13 is an explanatory view showing Embodiment 2 for a method for forming
an electron emission film in the gas discharge tube.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The method for forming an electron emission film according to the present invention
can suitably be adapted to a gas discharge tube made of a slender tube having a
diameter of about 0.5 to 5 mm.
In the present invention, the coating solution may contain an organic metal compound
that becomes an inorganic compound having an electron emission ability by burning.
A mixture solution of an organic metal compound that becomes an inorganic compound
having the electron emission ability by burning and an inorganic compound can be
used as the coating solution. Specifically, the organic metal compound is coated
onto the entire inner wall of the tube with a solvent, and then, this coated film
is burned to obtain the inorganic metal compound having the electron emission ability,
to thereby form the electron emission film on the entire inner wall of the tube.
The coated film obtained by applying the coating solution is desirably burned
at a temperature of about 350 to 480° C. The burning process changes the organic
metal compound contained in the coating solution into the inorganic metal compound
having an electron emission ability. Examples of the inorganic metal compound having
the electron emission ability are metal oxides such as magnesium oxide, alumina
and the like.
In order to form the electron emission film made of a metal oxide such as magnesium
oxide, alumina and the like, the organic metal compound contained in the coating
solution may be an organic metal compound including a metal such as magnesium,
aluminum and the like. Examples of the organic metal compound are magnesium stearate,
magnesium valerate and the like. When a magnesium oxide film is formed as the electron
emission film, magnesium hexanoate (also referred to magnesium caproate) is desirably
used as the organic metal compound containing magnesium.
Examples of a solvent for the above-mentioned organic metal compound include
ethanol, 1-propanol, 1,3-propanediol, 1-butanol and the like. In case where magnesium
hexanoate is used as the organic metal compound, a mixture solution of ethanol
and propylene glycol monomethyl ether acetate is desirably used since magnesium
hexanoate is freely soluble in this mixture solvent and the use of the mixture
solvent improves the coating property of the coating solution.
The present invention will be explained hereinbelow with reference to the embodiments
shown in the drawings. It is to be noted that the present invention is not limited
to the embodiments described below and can be modified in various ways.
A gas discharge tube and a method for forming an electron emission film in the
gas discharge tube is preferably adapted to a gas discharge tube for display. An
entire construction of this gas discharge tube for display is firstly explained.
FIG.
1(
a) is a perspective view showing in partial a display device
using gas discharge tubes according to the present invention, while FIG.
1(
b)
is an explanatory view showing a gas discharge tube having an electrode formed therein.
A display device
60 of this embodiment has a plurality of gas discharge
tubes
1 that are arranged in a line direction of a screen and formed on
a substrate
61 at the back side of the display device. An electrode supporting
member
62 is arranged between each gas discharge tube
1. The electrode
supporting member
62 has an electrode X formed at one side and an electrode
Y formed at the other side for selectively generating emission with an optional
combination of a plurality of portions (cells) in the lengthwise direction of the
gas discharge tube
1. Wiring conductive patterns
61x and
61y
are provided on the substrate
61 for applying voltage to these electrodes
X and Y.
Provided also on the outer wall surface of the gas discharge tube
1
are electrodes X and Y at each position corresponding to the electrodes X and Y
on the electrode supporting member
62, thereby forming an electrode matrix
capable of displaying an optional image. Inert gas (discharge gas) including Ne
(neon), Xe (xenon) and the like is enclosed in the gas discharge tube
1.
FIG. 2 is an explanatory view showing an entire construction of a gas discharge
tube according to one embodiment of the present invention. The gas discharge tube
(hereinafter simply referred to as discharge tube) of this embodiment has on its
outer wall a great number of electrode pairs comprising at least two electrodes.
These electrodes generate a discharge in a sideward direction of the tube for obtaining
a great number of emitting points in one tube.
In the same figure, numeral
1 designates a gas discharge tube, numeral
2 a front electrode and numeral
3 a back electrode. The gas discharge
tube
1 is made of an insulating material such as glass or the like. The
front electrode
2 corresponds to the electrode X in FIG.
1(
b)
and the back electrode corresponds to the electrode Y in the same figure. The front
electrode
2 and the back electrode
3 are mounted to the outer wall
of the gas discharge tube
1. An application of alternate voltage between
the front electrode
2 and the back electrode
3 generates a discharge
between the front electrode
2 and the back electrode
3 in the gas
discharge tube
1.
The front electrode
2 and the back electrode
3 are, when each having
a structure capable of applying voltage to the discharge gas in the tube, not necessarily
formed in direct contact with the outer wall of the gas discharge tube
1.
Such a structure may be possible that a member to which an electrode is formed
gets in contact with the gas discharge tube
1.
Although this embodiment shows the electrode structure in which one emitting
point is formed by a first electrode (front electrode
2) and a second electrode
(back electrode
3) which are opposed to each other, the invention is not
limited thereto. A structure having a third electrode may be possible. Further,
an electrode structure for generating a surface discharge may be adapted, although
the figure of this embodiment shows the electrode structure for generating an opposition discharge.
FIGS.
3(
a) and
3(
b) are explanatory views showing
the inner structure of the gas discharge tube, wherein FIG.
3(
a)
shows a longitudinal sectional view and FIG.
3(
b) shows a cross-sectional
view. In these figures, numeral
4 designates a fluorescent layer, numeral
5 an electron emission film and numeral
6 a supporting plate.
With respect to the gas discharge tube
1 of the present invention, an
application of high voltage between the front electrode
2 and the back electrode
3 excites the discharge gas enveloped in the tube, with the result that
vacuum ultraviolet light is generated in the de-excitation process of the excited
inert gas. The fluorescent layer
4 receives the vacuum ultraviolet ray and
generates visible light.
The electron emission film
5 generates charged particles by a collision
with discharge gas having energy of more than a predetermined amount.
The supporting plate
6 serves for introducing the fluorescent layer
4
into the discharge tube. This supporting plate
6 may not be provided.
The gas discharge tube
1 of this embodiment has the electron emission
film
5 formed at a discharge generating portion, whereby a production of
minimum amount of charged particles required for generating the discharge can be
realized with low voltage.
FIGS.
4(
a) to
4(
c) are explanatory views showing
a state for introducing coating solution for forming an electron emission film
into the gas discharge tube, before the electrodes are formed on the gas discharge
tube, wherein FIG.
4(
a) shows a thin tube having an inner diameter
of 0.5 mm to 2 mm, FIG.
4(
b) shows a thick tube having an inner diameter
of 2 mm or more and FIG.
4(
c) shows a modified tube.
In the figures, numeral
7 designates a discharge tube, numeral
8
coating solution for forming an electron emission film and numeral
9 a coating
film formed with the coating solution.
The coating solution
8 for forming the electron emission film contains
the organic metal compound which turns into the electron emission film through
thermal treatment. The use of such coating solution enables the coating film to
be formed regardless of the thickness, length and shape of the gas discharge tube
7. Further, the coating film having an optional film thickness can be obtained
with the selection of density and solvent of the organic metal compound. Moreover,
the coating solution
8 trickles down the gas discharge tube with the section
of the gas discharge tube
7 sealed to form the coating film, resulting in
establishing a uniform balance of physical force regarding the coating process,
such as gravity, liquid viscosity, liquid surface tension, friction between the
coating solution and the wall face of the tube or the like, in the circumferential
direction of the tube in the vicinity of the phase boundary. Consequently, the
thickness of the coating film of the tube, particularly of the straight tube can
be made uniform.
FIGS.
5(
a) to
5(
d) are explanatory views showing
an introducing method of a coating solution.
As shown in this figure, the method for introducing a coating solution
11
into the gas discharge tube
10 includes the steps of preparing the gas discharge
tube
10 (see FIG.
5(
a)), injecting the coating solution
11
to the edge portion of the gas discharge tube
10 (see FIG.
5(
b))
and fixing the gas discharge tube
10 onto a rotating stage of a rotating
device
12. The rotating device
12 imparts centrifugal force to the
coating solution
11 for sending the same into the gas discharge tube
10.
A spinner is used for the rotating device
12 in this embodiment.
The rotating stage of the rotating device
12 rotates for imparting centrifugal
force to the coating solution
11 (see FIG.
5(
c)), whereby
the coating solution
11 is introduced into the gas discharge tube
10
to form a uniform coating film to the inner wall face of the gas discharge tube
10 (see FIG.
5(
d)).
Imparting strong centrifugal force to the coating solution
11 even
after the coating solution
11 is uniformly applied into the gas discharge
tube
10 causes a separation and evaporation of the solvent as well as a
solation of the organic metal compound in the coating solution
11. Therefore,
the coating film formed uniformly on the inner wall of the tube has a high viscosity,
which enables to maintain the shape of the coating film even without the drying process.
FIGS.
6(
a) to
6(
c) are explanatory views showing
another method for introducing the coating solution into the gas discharge tube.
In this method, the coating solution
11 is injected into a gas discharge
tube
13, and then, compressed air
14 including dry air, dry nitrogen
or the like is applied thereto for introducing the coating solution
11 into
the gas discharge tube
13. The use of the compressed air
14 can realize
a simplified, small-sized coating apparatus as well as a reduction of coating-process
time. A blast is continued even after the coating process is finished, thereby
enabling to promote the drying of the coating film, enhance the viscosity of the
coating film and maintain the shape of the coating film.
FIG. 7 is an explanatory view showing an introducing apparatus of the coating
solution into a gas discharge tube.
In this figure, numeral
14a designates dry gas, numeral
15
a heater, numerals
16,
17,
18 and
19 valves.
Upon drying the coating film, air is hard to be circulated when a long thin
gas discharge tube is used, since such a tube has a large piping resistance. Therefore,
great pressure is required for sending the dry air, with the result that the coating
film receives force toward the direction of the blast. Consequently, there arises
a problem that the coating film is carried away.
In order to prevent such a problem, a blast is sent alternately from both ends
of the gas discharge tube by using the apparatus shown in FIG.
7. The alternate
blasting causes well-balanced force applied to the coating film for preventing
the coating film from being carried away in one direction. Further, blasting air
is warmed for promoting the drying of the coating film in order to prevent the
coating film being carried away.
In this apparatus, the dry air
14a is heated by the heater
15,
and then, the heated dry air
14a is introduced via the valve
19
into the gas discharge tube
13 to which the coating film is formed. The
valves
17 and
18 are closed at this time, so that the gas passing
through the gas discharge tube
13 to thereby include solvent evaporation
in the coating film goes into the atmosphere via the valve
16.
Thereafter, the dry air
14a heated by the heater
15
is introduced via the valve
17 into the gas discharge tube
13 on
which the coating film is formed. The valves
16 and
19 are closed
at this time, so that the gas passing through the gas discharge tube
13
to thereby include solvent evaporation in the coating film goes into the atmosphere
via the valve
18.
In this way, the dry air or the heated dry air is alternately introduced from
both ends of the tube for drying the coating film, resulting in enabling the shape
of the coating film to be maintained to thereby form a dried application film.
FIGS.
8(
a) to
8(
d) are explanatory views showing
another method for introducing the coating solution into the gas discharge tube.
In this figure, numeral
20 designates a gas discharge tube, numeral
21a
coating solution, numeral
22 a liquid pump and numeral
23 a coating
film. A roller pump is used as the liquid pump
22.
In this introducing method, the gas discharge tube
20 is firstly prepared
(see FIG.
8(
a)), the coating solution
21 is sucked by the
liquid pump
22 (see FIG.
8(
b)), the suction is continued to
perform the coating process (see FIG.
8(
c)) for forming the coating
film (see FIG.
8(
d)). This introducing method can prevent the evaporation
of the solvent in the coating solution
21, can keep the component in the
coating solution constant and can form a uniform coating film. Further, an air
pass is formed in the direction reverse to the coating direction, thereby being
capable of simultaneously drying the coating film.
FIGS.
9(
a) and
9(
b) are explanatory views showing
a drying method of the coating film, wherein FIG.
9(
a) shows an entire
construction of the gas discharge tube and FIG.
9(
b) shows a portion
of the gas discharge tube on which the coating film is formed.
As shown in these figures, a heat source
28 is arranged at the last end
of the coating solution
25 upon introducing the coating solution
25
into the gas discharge tube
24. The heat source
28 is moved in accordance
with the movement of the coating solution
25 for drying the coating film
26.
The heat source
28 promotes to dry the coating film
26, or changes
the coating film
26 to have a high viscosity. Although infrared ray is used
for the heat source in this embodiment, microwave or ultraviolet ray can be used
as the heat source.
A collimator
29 is locally irradiating the coating film
26 with
the
heat source
28. This collimator
29 covers the non-irradiated portions
for reducing a temperature rise of the coating solution remaining in the tube,
resulting in controlling the composition change of the coating solution such as
the evaporation of the solvent in the coating solution or the like.
The coating solution
25 trickles down the gas discharge tube
24
to form the coating film
26. Thereafter, the coating film
26 is dried
by the heat source
28 to obtain a dried coating film
27. This method
can promote the local drying of the coating film. The use of the collimator
29
reduces heat propagation to the non-dried portion, so that the evaporation of the
solvent at the boundary of the coating solution and air can be reduced.
At this time, an area where a stabilized film thickness is obtained can be formed
by utilizing a tension generating between a meniscus of the coating solution
25,
which trickles down the wall of the tube with maintaining a state of filling the
cross section of the tube, and the dried coating film
27. Moreover, the
liquid face at the last end of the coating solution
25 is moved while locally
irradiating this area with the heat source
28 via the collimator
29
to accelerate the drying of the coating film
26. Thereby the film thickness
distribution exhibits a constant state from the meniscus of the coating solution
25 to the dried coating film
27, and the dried coating film
27
has an extremely uniform thickness.
FIG. 10 is an explanatory view showing another method for introducing the coating
solution into the gas discharge tube.
In this figure, numeral
30 designates a gas discharge tube, numeral
31
a coating solution, numeral
32 a liquid pump, numeral
33 a heat source,
numeral
34 a shield plate, numeral
35 a heater, numeral
36
a pump and numeral
37 a condenser. A roller pump is used as the liquid pump
32, since the absorption amount of the roller pump is not so changed due
to external force. The shield plate
34 is movably provided for preventing
the evaporation of the solvent in the coating solution which remains in the gas
discharge tube
30.
In this method, the coating solution
31 is sucked by the liquid pump
32
for performing the coating process to the tube while drying the coating film by
the heat source
33. Since the roller pump having the sucking amount not
so changed by the external force is used as the liquid pump
32, the roller
pump serves as a stopper toward the external force, thereby being able to control
the fluctuation at the coating solution surface that is attributed to the pressure
of the evaporation from the solvent because of the drying process of the coating
film. This brings a stabilized coating speed. Further, dew drops of the solvent
evaporation is prevented by using the heater
35 at the area where the dried
coating film has already been formed, so that the solvent evaporation generated
at the drying process of the coating film does not adhere again to the dried coating film.
Additionally, the pump
36 has mechanisms of rapidly removing
the solvent evaporation and of maintaining the pressure in the tube to approximately
atmospheric pressure, whereby the evaporation of the solvent from the coating solution
surface is prevented as well as the composition of the coating solution can be
kept constant. Consequently, the dried coating film having a uniform thickness
can be formed. Further, the solvent is rapidly removed by the condenser
37.
FIGS.
11(
a) to
11(
c) are explanatory views showing
a method for burning the dried coating film.
In this figure, numeral
30 designates a gas discharge tube, numeral
38
a dried coating film, numeral
39 air which is introduced into the gas discharge
tube
30 and numeral
40 an electron emission film formed by burning.
The dried coating film
38 is formed on the inner wall of the gas discharge
tube
30 with a uniform thickness.
Upon burning the dried coating film
38, the air
39 containing
oxygen is sent to the gas discharge tube
30, whereby the electron emission
film
40 can be formed to have good quality. As the gas discharge tube
30
becomes longer or the diameter of the tube
30 becomes thinner, the oxygen
supply required for burning the organic metal compound is tend to be insufficient.
Therefore, the air
39 containing oxygen is sent into the tube for eliminating
the shortage in oxygen supply, to thereby obtain the excellent electron emission
film
40.
A compound serving as the electron emission film
40 is a metal oxide that
has an electron emission ability as well as a resistance to heat and a resistance
to plasma.
If magnesium is contained in the organic metal compound in the coating solution,
an inorganic magnesium compound can be produced by the thermal treatment, while,
if aluminum is contained, an inorganic aluminum compound can be produced.
In case where the electron emission film is formed of magnesium oxide, film characteristics
having a high electron emission ability can be obtained, while film characteristics
having a high electron emission ability and humidity resistance can be obtained
in the case of an electron emission film formed of alumina.
Embodiment
Embodiment 1
FIGS.
12(
a) to
12(
e) are explanatory views showing
Embodiment 1 of a method for forming an electron emission film to the inside of
the gas discharge tube.
A gas discharge tube
41 used in this embodiment is made of glass, and
has
an outer diameter of 1.0 mm, inner diameter of 0.8 mm and length of 200 mm. Magnesium
hexanoate is used for an organic metal compound that becomes an electron emission
film by burning. Used for the coating solution
42 is the one containing
ethanol of 1 part and propylene glycol monomethyl ethyl acetate of 1 part per 1
part of magnesium hexanoate.
The gas discharge tube
41 is prepared (see FIG.
12(
a)),
and then, the coating solution
42 is introduced to the edge portion of the
gas discharge tube
41 (see FIG.
12(
b)). Thereafter, the coating
solution
42 is uniformly applied to the inner wall of the gas discharge
tube by using a rotating device
43 that is a spinner (see FIG.
12(
c)).
At this time, the coating solution
42 is applied with covering the section
of the gas discharge tube
41 (see FIG.
12(
d)).
Subsequently, the gas discharge tube
44 on which the coating
film having a uniform thickness is formed is put into a burning furnace to be burned
at the maximum temperature of 410° C. for 30 minutes (see FIG.
12(
e)),
resulting in obtaining a gas discharge tube
45 on which a uniform and transparent
electron emission film of magnesium oxide was formed.
The thickness of the electron emission film was 6000 Å. Gas of Ne-Xe mixture
was enclosed into this gas discharge tube with a pressure of 350 Torr to measuring
voltage initiating the discharge.
When the electron emission film is not formed, the discharge is not started
until a voltage of AC700V is applied. It was confirmed that the discharge was started
with a voltage of AC380V when the gas discharge tube with the electron emission
film formed by the method according to the invention was used.
Embodiment 2
FIG. 13 is an explanatory view showing Embodiment 2 of a method for forming
an electron emission film on the gas discharge tube.
The gas discharge tube
41 used in this embodiment is also made of glass.
This gas discharge tube has an outer diameter of 1.0 mm, inner diameter of 0.8
mm and length of 1000 mm. Magnesium hexanoate is used for an organic metal compound
that becomes an electron emission film by burning. Used for the coating solution
is the one containing ethanol of 0.5 parts and propylene glycol monomethyl ethyl
acetate of 0.8 part per 1 part of magnesium hexanoate.
The coating solution
47 is introduced into a gas discharge tube
46
for filling the tube, and then, the coating solution
47 is moved by a roller
pump
48 at a speed of 50 mm per minute, to thereby apply the coating solution
47 onto the inner wall of the gas discharge tube
46. The coated portion
is subject to an infrared ray lamp
49 for obtaining a dried coating film.
A shielding plate
50 is moved with the coating solution in order not to
rise the temperature of the coating solution
47 during the coating process.
Evaporation of the solvent is ejected from the side reverse to the coating direction
of the gas discharge tube
46. To prevent this evaporation from being condensed
on the dried coating film, a heater
51 is used for keeping the gas discharge
tube
46 warm. The temperature of the heater
51 is 80° C. The
solvent evaporation is liquefied by a condenser
52 disposed at the edge
of the gas discharge tube
46 for rapidly removing the solvent evaporation
in the gas discharge tube
46.
In this way, a dried coating film having a uniform thickness can be formed in
the gas discharge tube having the outer diameter of 1.0 mm, inner diameter of 0.8
mm and the length of 1000 mm. This gas discharge tube was burned at 410° C.
with air introduced into the tube, to thereby form an electron emission film of
magnesium oxide with good quality.
Explained hereinbefore is the method for forming the electron emission
film on the inner wall of the gas discharge tube comprising the step of preparing
coating solution containing an organic metal compound, the step of applying this
coating solution onto the inner wall of the gas discharge tube and the step of
burning the applied coating solution for forming the electron emission film. It
is to be noted that there is another method for directly forming the electron emission
film on the inner wall of the gas discharge tube by using CVD method.
In the case of forming the electron emission film of magnesium oxide by the CVD
method, usable materials include cyclopentadienyl (cp)-containing materials and
β-diketone-containing materials. Examples of the cp-containing materials
include bis(cyclopentadienyl) magnesium, bis(ethylcyclopentadienyl) magnesium and
the like. Examples of β-diketone-containing materials include acetylacetonatomagnesium,
dipivaloylmethane magneisum and the like.
bis(cyclopentadienyl)magnesium
Mg(C5H5)2
[cp2Mg]
White crystal
Sublimation: 150° C./0.1 Torr
Melting Point: 176 to 178° C.
Become white smoke, Hydrolyzed in water
bis(ethylcyclopentadienyl)magnesium
Mg(C2H5C5H4)2
[Etcp2Mg]
Achromic liquid
Boiling Point: 72° C./0.7 Torr
Melting Point: -;17 to -;18° C.
Become white smoke, Hydrolyzed in water
Acetylacetonatomagnesium
Mg(acac)2
White Powder
Sublimation: 120 to 140° C./1 Torr
Melting Point: 256° C.
Having hygroscopicity but no extreme reactivity
Dipivaloylmethanemagnesium
Mg(DPM)2
White Powder
Sublimation: 150° C./0.05 Torr
Melting Point: 135 to 150° C.
Having hygroscopicity but no extreme reactivity
The electron emission film may be directly formed on the inner wall of the gas
discharge tube with a known CVD method by using the above-mentioned materials.
By this, the voltage initiating the discharge of the gas discharge tube can be
reduced, to thereby assure a wide margin of the light-emitting operation at many
points. Further, an electron emission film can uniformly be formed at the inner
wall of a long, slender tube having a diameter of 2 mm or less and a length of
300 mm or more.
According to the present invention, the voltage initiating the discharge
of a gas discharge tube can be reduced, to thereby assure a wide margin of a light-emitting
operation at many points.
*
