U.S. patent application number 12/076901 was filed with the patent office on 2008-07-31 for protective film for plasma display panel and method for manufacturing this protective film, and plasma display panel and method for manufacturing thereof.
This patent application is currently assigned to ULVAC, INC.. Invention is credited to Muneto Hakomori, Toshiharu Kurauchi, Shunji Misawa, Kazuya Uchida.
Application Number | 20080182034 12/076901 |
Document ID | / |
Family ID | 36319128 |
Filed Date | 2008-07-31 |
United States Patent
Application |
20080182034 |
Kind Code |
A1 |
Kurauchi; Toshiharu ; et
al. |
July 31, 2008 |
Protective film for plasma display panel and method for
manufacturing this protective film, and plasma display panel and
method for manufacturing thereof
Abstract
A plasma display panel 1 of the present invention has a
protective film 14 over a sustaining electrode 15 and a scanning
electrode 16, with the main components of the protective film being
CaO and SrO, and the concentration of the CaO in the protective
film 14 is 20 mol % or more and 90 mol % or less. This protective
film 14 has a smaller work function than a conventional MgO film so
light can be emitted at a lower discharge voltage than in the past.
If the discharge voltage is lower, the protective film 14 will be
sputtered more slowly so that the service life of the plasma
display panel 1 will be longer. Also, since the plasma gas contains
xenon gas, the plasma display panel of the present invention has
higher brightness.
Inventors: |
Kurauchi; Toshiharu;
(Ibaraki, JP) ; Hakomori; Muneto; (Kanagawa,
JP) ; Uchida; Kazuya; (Ibaraki, JP) ; Misawa;
Shunji; (Ibaraki, JP) |
Correspondence
Address: |
Kratz, Quintos, & Hanson, LLP
Suite 400, 1420 K Street, N.W.
Washington
DC
20005
US
|
Assignee: |
ULVAC, INC.
Chigasaki-shi
JP
|
Family ID: |
36319128 |
Appl. No.: |
12/076901 |
Filed: |
March 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11594987 |
Nov 9, 2006 |
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12076901 |
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PCT/JP05/19993 |
Oct 31, 2005 |
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11594987 |
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Current U.S.
Class: |
427/535 ;
427/551; 427/58 |
Current CPC
Class: |
H01J 11/40 20130101;
H01J 11/12 20130101; H01J 9/02 20130101; C23C 14/08 20130101 |
Class at
Publication: |
427/535 ; 427/58;
427/551 |
International
Class: |
B05D 3/06 20060101
B05D003/06; H05H 1/00 20060101 H05H001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2004 |
JP |
2004-321820 |
Claims
1. A method for manufacturing a protective film, comprising the
step of forming a protective film containing SrO and CaO, wherein a
first vapor deposition material having a main component which is
SrO and a second vapor deposition material having a main component
which is Cao are separately disposed inside a same vacuum chamber,
and wherein the amounts of vapor generated from the first and
second vapor deposition materials are controlled and the first and
second vapor deposition materials are vaporized such that the CaO
content in the protective film will be at least 20 mol % and at
most 90 mol %.
2. The method for manufacturing a protective film according to
claim 1, in which the protective film is formed over a first panel
with a first electrode disposed on a surface thereof, and a second
panel with a second electrode disposed on a surface thereof,
wherein a dielectric film is disposed over at least one of the
first and second electrodes, and wherein the protective film is
formed on a surface of the dielectric film by allowing each of the
vapors of the first and second vapor deposition materials to reach
the dielectric film.
3. The method for manufacturing a protective film according to
claim 1, wherein the first and second vapor deposition materials
are vaporized while disposing the first vapor deposition material
on a first hearth and disposing the second vapor deposition
material on a second hearth different from the first hearth.
4. The method for manufacturing a protective film according to
claim 1, wherein the first and second vapor deposition materials
are vaporized such that the CaO content in the protective film is
at least 20 mol % and at most 90 mol %, by allowing an electron
beam to emit from a first electron beam gun into the first vapor
deposition material and by allowing an electron beam to emit from a
second electron beam gun into the second vapor deposition
material.
5. A method for manufacturing a plasma display panel, comprising
the steps of: separately disposing a first vapor deposition
material containing SrO, and a second vapor deposition material
containing CaO inside the same vacuum chamber; forming a protective
film containing SrO and CaO, with the CaO content being at least 20
mol % and at most 90 mol %, on the surfaces of first and second
panels by heating the first and second vapor deposition materials
while controlling the amounts of vapor generated; and adhering the
first and second panels together and sealing them, wherein the
steps at least from the step of forming the protective film to the
sealing step are carried out in a vacuum atmosphere.
6. The method for manufacturing a plasma display panel according to
claim 5, wherein the first and second vapor deposition materials
are heated while the first vapor deposition material is disposed on
a first hearth and the second vapor deposition material is disposed
on a second hearth different from the first hearth.
7. The method for manufacturing a plasma display panel according to
claim 5, wherein the first and second vapor deposition materials
are vaporized and the amount of the vapor generated from the first
and second vapor deposition materials are controlled such that the
CaO content will be at least 20 mol % and at most 90 mol % by
allowing an electron beam to emit from a first electron beam gun
into the first vapor deposition material and by allowing an
electron beam to emit from a second electron beam gun into the
second vapor deposition material.
8. A method for manufacturing a plasma display panel, the plasma
display panel having a first panel and a second panel, a scanning
electrode and a sustaining electrode being disposed on a surface of
the first panel while being insulated from each other, an address
electrode being disposed on a surface of the second panel and a
fluorescent film being disposed on the address electrode, wherein
an insert gas is charged in between the first and second panels,
and by applying voltage between the address electrode and the
scanning electrode, a write discharge occurs, and by applying AC
voltage between the scanning electrode and the sustaining
electrode, a sustaining discharge is brought about, and ultraviolet
rays discharged from the plasma which is generated by the
sustaining discharge are irradiated to the fluorescent film,
thereby being emitted, the method for manufacturing a plasma
display panel comprising the steps of: separately disposing a first
vapor deposition material having a main component which is SrO and
a second vapor deposition material having a main component which is
CaO inside a same vacuum chamber; forming a protective film having
the CaO content with at least 20 mol % and at most 90 mol % on the
scanning electrode and the sustaining electrode by controlling the
amount of vapor generated from the first and second vapor
deposition materials; and adhering the first and second panels
together and sealing them.
9. The method for manufacturing a plasma display panel according to
claim 8, wherein the steps at least from the step of forming the
protective film to the sealing step are carried out in a vacuum
atmosphere.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority benefit of Japanese
Application No. 2004-321820, filed on Nov. 5, 2004, the entire
disclosure of which is incorporated herein by reference.
[0002] This application is a continuation of International
Application No. PCT/JP2005/019993, filed on Oct. 31, 2005, the
entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to a plasma display panel, and
more particularly to a protective film for this panel, and to a
method for manufacturing a protective film.
BACKGROUND OF THE INVENTION
[0004] PDPs (plasma display panels) have been widely used in the
field of display devices in the past, and a larger screen, higher
quality, and lower cost have been required of PDPs in recent
years.
[0005] A three-electrode surface discharge type, which is made up
of a front panel comprising a sustaining electrode and a scanning
electrode formed on a glass substrate, and a rear panel comprising
an address electrode formed on a glass substrate, with these panels
put together, is generally coming to the main current of PDP.
[0006] An insert gas is enclosed between the front and rear panels,
and voltage is applied between the scanning electrode and the
address electrode to create a discharge, whereupon the insert gas
is plasmatized so that ultraviolet rays are emitted. If a
fluorescent film is disposed at the location where the emitted
ultraviolet rays are irradiated, the ultraviolet rays will cause
the fluorescent film to luminance and emit colored light.
[0007] A dielectric film is usually formed over the sustaining
electrode and the scanning electrode; and an MgO protective film is
formed over this dielectric film to protect it.
[0008] When AC voltage is applied to the scanning electrode and the
sustaining electrode to sustain discharge, cations generated by
plasmatizing the insert gas are incident on the scanning electrode
side and the sustaining electrode side, respectively. However, the
scanning electrode and the sustaining electrode, and the dielectric
film over these electrodes, are protected against the cations by
the protective film.
[0009] Therefore, the dielectric film is not damaged by the plasma,
and the sustaining electrode and scanning electrode are maintained
in a state of being insulated by the dielectric film; and
furthermore, since there is no change in the electrostatic
capacitance of the dielectric film, the electrical characteristics
of the plasma display panel are maintained.
[0010] In order to increase the brightness of a PDP in response to
the growing requirements for higher performance in recent years, a
method has been proposed in which luminescent intensity is
increased by raising the concentration of xenon in a mixed gas of
neon and xenon, which is usually used as the insert gas, from the
conventional level of about 5% to 10% or higher.
[0011] However, when the protective film is made of MgO, if the
xenon concentration in the insert gas is raised, the discharge
voltage goes up, anti-sputtering property of the protective film
decrease, and the function as a protective film subsequently
declines. Therefore, there has been a problem of shortening a panel
service life. There also has been a problem of increasing in cost
of manufacturing a PDP drive control system because the driver
circuit for driving the PDP must be able to handle higher
voltage.
[0012] The discharge voltage of a PDP depends on the secondary
electron emission coefficient of the protective film. It has been
proposed that the discharge voltage is possible to be reduced if an
oxide of an alkaline earth metal, which has a smaller work function
than MgO, is used as the protective film.
[0013] For instance, Japanese Laid-Open Patent Application
2002-231129 (patent document 1) introduces SrO, CaO, BaO, SrO+BaO,
BaO+CaO, and SrO+CaO+BaO as protective films.
[0014] These protective films are less resistant against sputtering
by cations during discharge than MgO is, and are disadvantageous in
terms of PDP service life such that technology attempts to solve
the problem of shorter service life by forming a protective film
not only on the front panel of a PDP, but also on the rear panel
where at least a fluorescent film is formed.
[0015] However, a problem encountered on carrying out the above
prior art is that increasing the protective film formation steps
drives up the cost of manufacturing a PDP. Another problem that
remains to be solved is that aging treatment of the protective
film, which is considered necessary at the outset of discharge,
takes as long or longer than with MgO. The present invention
provides a protective film that has superior anti-sputtering
property and lower discharge voltage than an MgO film, and a method
for forming this protective film, as well as a PDP manufacturing
method for shortening the time for the initial discharge aging
treatment of the PDP in which this protective film is used.
SUMMARY OF THE INVENTION
[0016] In order to solve the above problems, embodiments of the
present invention include a protective film disposed on the surface
of one or both of first and second electrodes, which is exposed to
a plasma formed between the first and second electrodes when
voltage is applied between the first and second electrodes, wherein
said protective film contains SrO and CaO, and the CaO content is
20 mol % or more and 90-mol % or less.
[0017] Embodiments of the present invention include a protective
film, wherein the first electrode is disposed on the surface of a
first panel, and the second electrode is disposed on the surface of
a second panel.
[0018] Embodiments of the present invention include a plasma
display panel, having a first panel with a first electrode disposed
on its surface, and a second panel with a second electrode disposed
on its surface, an insert gas being charged in between the first
and second panels, a protective film being disposed on the surface
of one or both of the first and second electrodes, the protective
film being exposed to a plasma formed between the first and second
panels, wherein said protective film contains SrO and CaO, and the
CaO content is 20 mol % or more and 90 mol % or less.
[0019] Embodiments of the present invention include a plasma
display panel wherein a third electrode is disposed on the surface
of the first panel.
[0020] Embodiments of the present invention include a plasma
display panel wherein the insert gas contains neon and xenon, and
the xenon content is at least 10 vol %.
[0021] Embodiments of the present invention include a method for
manufacturing a protective film, in which a protective film
containing SrO and CaO is formed, wherein a first vapor deposition
material whose main component is SrO and a second vapor deposition
material whose main component is CaO are separately disposed inside
the same vacuum chamber, and the amounts of vapor generated from
the first and second vapor deposition materials are controlled and
the first and second vapor deposition materials are vaporized such
that the CaO content in the protective film will be 20 mol % or
more and 90 mol % or less.
[0022] Embodiments of the present invention include a method for
manufacturing a protective film, in which the protective film is
formed over a first panel with a first electrode disposed on its
surface, and a second panel with a second electrode disposed on its
surface, wherein a dielectric film is disposed over one or both of
the first and second electrodes; and the protective film is formed
on a surface of the dielectric film by allowing each of the vapors
of the first and second vapor deposition materials to reach the
dielectric film.
[0023] Embodiments of the present invention include a method for
manufacturing a plasma display panel, comprising the steps of
disposing separately a first vapor deposition material containing
SrO, and a second vapor deposition material containing CaO inside
the same vacuum chamber; forming a protective film containing SrO
and CaO, with the CaO content being 20 mol % or more and 90 mol %
or less, on the surfaces of first and second panels by heating the
first and second vapor deposition materials while controlling the
amounts of vapor generated; and adhering the first and second
panels together and sealing them, wherein everything at least from
the step of forming the protective film to the sealing step is
carried out in a vacuum atmosphere.
[0024] The present invention is constituted as above, and a display
device in which the protective film of the present invention is
used has first and second electrodes. An insert gas that forms a
plasma is charged into this device, and voltage is applied between
the first and second electrodes, whereupon a plasma of the insert
gas is formed inside the device, and the cations in the plasma are
attracted to whichever of the first and second electrodes located
on the negative potential side.
[0025] When DC voltage is applied between the first and second
electrodes, if the protective film of the present invention is
disposed over at least the electrode to which the negative
potential is applied. Alternatively, when AC voltage is applied
between the first and second electrodes, if the protective film of
the present invention is disposed over one or both electrodes, the
electrode or electrodes and the surrounding members will be
protected from cations by the protective film.
[0026] With the above-mentioned plasma display panel in which a
sustaining electrode and a scanning electrode are disposed on a
first panel, and an address electrode on a second panel, the first
and second electrodes are either a combination of the sustaining
electrode and the address electrode, or a combination of the
scanning electrode and the address electrode.
[0027] More particularly, the protective film of the present
invention may be disposed over both the sustaining electrode and
the scanning electrode with the above-mentioned plasma display
panel since a plasma is formed by applying a high AC voltage
between the sustaining electrode and the scanning electrode.
[0028] In general, with a plasma display panel, a dielectric film
is disposed over a sustaining electrode and a scanning electrode so
that the protective film of the present invention may be disposed
over the dielectric film surface on the sustaining electrode, and
over the dielectric film surface on the scanning electrode so that
the dielectric film can be protected.
[0029] The protective film used in the present invention contains
both SrO and CaO, and the CaO concentration in the protective film
of the present invention is 20 mol % or more and 90 mol % or less;
and therefore, resistance against sputtering by cations during
discharge is better than with a conventional protective film (Mgo
film), and the discharge voltage of the PDP is lower. Consequently,
the service life of the panel is extended, and the cost of the
driver circuit used to drive the PDP is reduced.
[0030] If, in order to increase the brightness of a plasma display
panel, the insert gas is a mixed gas of neon and xenon, and the
xenon is contained in an amount of at least 10 vol %, discharge
voltage will increase and the protective film will be more easy to
be etched. However, it does not lead to shorter panel service life
since the protective film of the present invention has high
anti-sputtering property.
[0031] According to the present invention, it is possible to stably
form a PDP protective film with excellent electron emission
characteristics which is composed of the protective film of the
present invention containing both SrO and CaO. Also, the xenon
concentration is raised in the mixed gas of neon and xenon that is
charged into the PDP, which increases the brightness and allows a
PDP with a long service life to be manufactured at low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a perspective view illustrating an example of the
plasma display panel of the present invention;
[0033] FIG. 2 is a perspective view illustrating the method for
manufacturing a plasma display panel of the present invention;
[0034] FIG. 3 is a graph of the protective film composition when a
mixed vapor deposition material of SrO and CaO is used; and
[0035] FIG. 4 is a graph of the relation between discharge voltage
and aging time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] In FIG. 1, reference numeral 1 indicates an example of the
plasma display panel of the present invention. This plasma display
panel 1 has first and second panels 10, 20.
[0037] The first panel 10 has a first glass substrate 11, and a
plurality of sustaining electrodes 15 and scanning electrodes 16
are respectively disposed on the surface of the first glass
substrate 11. In FIG. 1, just one sustaining electrode 15 and one
scanning electrode 16 are depicted.
[0038] Here, each sustaining electrode 15 and each scanning
electrode 16 has a long, narrow shape, and the sustaining
electrodes 15 and scanning electrodes 16 are alternately lined up
next to each other, with a predetermined gap in between, on the
surface of the first glass substrate 11.
[0039] A dielectric film 12 made of an insulating material is
disposed on the surface of the first glass substrate 11 on which
the sustaining electrodes 15 and scanning electrodes 16 are
disposed. Adjacent sustaining electrodes 15 and scanning electrodes
16 are spaced from each other, the dielectric film 12 is formed so
as to cover the top and sides of the sustaining electrodes 15 and
scanning electrodes 16; and the spaces between adjacent sustaining
electrodes 15 and scanning electrodes 16 are filled with the
dielectric film 12 so that the sustaining electrodes 15 and the
scanning electrodes 16 are insulated from one another.
[0040] A protective film 14, having main components that are both
SrO and Cao, is disposed over the entire surface of the dielectric
film 12; and therefore, the protective film 14 is disposed over
each of the sustaining electrodes 15 and each of the scanning
electrodes 16.
[0041] The second panel 20 has the second glass substrate 21. A
plurality of linear address electrodes 25 are disposed in parallel,
with a specific gap therebetween, on the surface of the second
glass substrate 21.
[0042] Slender barrier ribs 23 are disposed in the lengthwise
direction of the address electrodes 25 in between the address
electrodes 25 on the surface of the second glass substrate 21.
[0043] One of three fluorescent films containing fluorescent
colorants of different colors (a red fluorescent film 22R, a green
fluorescent film 22G, and a blue fluorescent film 22B) is disposed
between each pair of adjacent barrier ribs 23 so that each of the
address electrodes 25 is covered by a fluorescent film of one color
(22R, 22G, or 22B).
[0044] The first and second panels 10 and 20 are adhered together
in a state in which the surface where the protective film 14 is
exposed faces the surface on which the barrier ribs 23 are formed;
and the sustaining electrodes 15 and the scanning electrodes 16 are
perpendicular to the address electrodes 25. The height from the
surface of the second glass substrate 21 to the ends of the barrier
ribs 23 is greater than the height from the surface of the second
glass substrate 21 to the surface of the address electrodes 25 so
the distal ends of the barrier ribs 23 come into contact with the
protective film 14 of the first panel 10, and the space between the
protective film 14 and the fluorescent films 22R, 22G, and 22B is
partitioned by the barrier ribs 23.
[0045] Reference numeral 29 in FIG. 1 indicates a luminescence
space, consisting of the spaces over the fluorescent films 22R,
22G, and 22B partitioned by the barrier ribs 23, and the
luminescence spaces 29 are filled with an insert gas that is a
mixture of neon gas and xenon gas, and contains equal to or more
than 10 vol % xenon gas.
[0046] The process by which this plasma display panel 1 is lighted
will now be described.
[0047] When voltage is applied between a selected scanning
electrode 16 and address electrode 25, write discharge occurs in
the luminescent cell where these electrodes intersect.
[0048] AC voltage is then applied between the scanning electrode 16
to which the above voltage was applied and the sustaining electrode
15 corresponding to this scanning electrode 16, which brings about
sustaining discharge.
[0049] As discussed above, the protective film 14 of the present
invention is positioned over the sustaining electrodes 15 and the
scanning electrodes 16, with the dielectric film 12 sandwiched in
between, this protective film 14 containing both SrO and Cao as
main components, and the CaO concentration thereof being 20 mol %
or more and 90 mol % or less.
[0050] Because the protective film of the present invention has
higher electron discharge characteristics than a conventional
protective film (MgO film), even when the xenon concentration of
the insert gas is raised, sustaining discharge is brought about at
a relatively low discharge voltage, the sustaining discharge
converts the insert gas into a plasma, and ultraviolet rays are
generated.
[0051] Accordingly, the surfaces of the first and second panels 10
and 20 are exposed to the plasma by plasmatizing the insert gas,
but the dielectric film 12 is protected against etching by the
plasma since the protective film 14 is disposed over the surface of
the dielectric film 12.
[0052] As discussed above, the plasma display panel 1 of the
present invention can be driven at a low discharge voltage, which
means that even though the protective film 14 is exposed to the
insert gas plasma, it is etched only very slowly. Therefore, the
plasma display panel 1 of the present invention has a longer
service life than conventional plasma display panels.
[0053] As discussed above, the sustaining electrodes 15 and the
scanning electrodes 16 are disposed perpendicular to the address
electrodes 25, and luminescence occurs at the luminescent cells
where the selected scanning electrodes 16 intersect with the
address electrodes 25.
[0054] When ultraviolet light is emitted at the luminescent cells,
and UV rays are incident on the fluorescent films 22R, 22G, and 22B
located in these luminescent cells, visible light of either red,
green, or blue is emitted from the fluorescent films 22R, 22G, and
22B.
[0055] In order to extinguish the luminescent cells, a voltage
weaker than that during the sustaining discharge is applied between
the selected scanning electrodes 16 and the sustaining electrodes
15 adjacent to those scanning electrodes 16, which brings about a
discharge (erasing discharge) that is weaker than the sustaining
discharge; and this neutralizes the wall charge within the
luminescence spaces 29 and extinguishes the luminescent cells.
[0056] Next, an example of the process of forming the protective
film 14 of the present invention will be described.
[0057] Reference numeral 2 in FIG. 2 indicates an example of a film
formation apparatus. This film formation apparatus 2 comprises two
electron beam guns (EB guns) 5a and 5b, and first and second
hearths 3 and 4 (four each). A first vapor deposition material
composed of SrO is disposed on each of the first hearths 3, and a
second vapor deposition material composed of CaO is disposed on
each of the second hearths.
[0058] The first hearths 3 are arranged in a row inside a vacuum
chamber, and the second hearths 4 are arranged parallel and next to
the first hearths 3 inside the same vacuum chamber as the first
hearths 3.
[0059] The inside of this vacuum chamber is evacuated ahead of
time, each of the first hearths 3 and each of the second hearths 4
are placed in the same vacuum atmosphere. While this vacuum
atmosphere is maintained, electron beams 6a, 6b are emitted from
the electron beam guns 5a, 5b into the hearths 3, 4, whereupon SrO
is vaporized from within the first hearths 3 and Cao from within
the second hearths 4 so that SrO vapor and CaO vapor are released
within the vacuum atmosphere.
[0060] The first glass substrate 11, on the surface of which the
sustaining electrodes 15, the scanning electrodes 16, and the
dielectric film 12 have been formed, is conveyed through this
vacuum atmosphere and is transferred above and parallel to the
first and second hearths 3, 4 with the surface on which the
sustaining electrodes 15 and scanning electrodes 16 were formed
facing down.
[0061] Since the row of first hearths 3 and the row of second
hearths 4 are disposed close together, when the first glass
substrate 11 passes above first and second hearths 3, 4, the SrO
vapor and CaO vapor both reach the first glass substrate 11.
[0062] The first panel 10 will be obtained with a protective film
14 that contains the predetermined proportions of SrO and CaO
formed over the first glass substrate 11 if the amount of SrO vapor
generated and the amount of CaO vapor generated are controlled to
predetermined proportions by varying the first and second hearths
3, 4 to be irradiated with the beams by adjusting the beam path, or
by adjusting the beam irradiation time and the beam irradiation
intensity to each of the first and second hearths 3, 4.
[0063] The number of first and second hearths 3, 4 is not limited
to four each in the method for forming the protective film of the
present invention, and there may be from one to three of each of
the first and second hearths 3, 4, or there may be five or more of
each. Also, the first and second hearths 3, 4 may be disposed in
the same number within the vacuum chamber, or different numbers of
first and second hearths 3, 4 may be disposed. In other words, as
long as the SrO and CaO can be disposed independently in the same
vacuum chamber, neither the shape nor the number of the first and
second hearths 3, 4 is limited in any particular way.
[0064] The number of electron beam guns 5a, 5b is also not limited
to two, and as long as the first and second hearths 3, 4 can both
be irradiated with electron beams, just one gun, or three or more,
may be used.
[0065] The first panel 10 on which the protective film 14 has been
formed is conveyed through the vacuum atmosphere without being
exposed to the outside atmosphere, the first panel 10 and the
above-mentioned second panel 20 are conveyed into the same heating
vacuum chamber. Then, with the inside of the heating vacuum chamber
maintained under a vacuum atmosphere, the surface of the first
panel 10 on which the sustaining electrodes 15 and the scanning
electrodes 16 have been formed is opposed to the surface of the
second panel 20 on which the address electrodes have been formed,
and positioned such that the sustaining electrodes and scanning
electrodes will intersect with the address electrodes at the proper
locations.
[0066] After the first and second panels 10, 20 have been adhered
together under heating inside the heating vacuum chamber, they are
conveyed through the vacuum atmosphere, without being exposed to
the outside atmosphere, into a cooling chamber in which a vacuum
atmosphere has been formed, and the combined first and second
panels 10 and 20 are cooled while the vacuum atmosphere inside the
cooling chamber is maintained. The above-mentioned insert gas is
then charged in between the first and second panels 10, 20 in a
vacuum atmosphere; and this insert gas is sealed to obtain the
plasma display panel 1.
[0067] Thus, with the manufacturing method of the present
invention, the steps at least from forming the protective film 14
on the first panel 10 up to adhering the first and second panels 10
and 20 together and the conveyance between the steps are performed
in a vacuum atmosphere, and the first and second panels 10 and 20
are not exposed to the outside atmosphere.
[0068] Specifically, from the time the protective film 14 is formed
until the first and second panels 10 and 20 are adhered together
and the protective film 14 is sealed off, the protective film 14 is
not exposed to the outside atmosphere so even though the main
components of the protective film 14 are made of highly
water-absorbent materials, such as SrO and CaO, the absorption of
moisture is prevented.
[0069] If SrO or CaO absorbs water, it changes into a hydroxide or
the like, and when such SrO or CaO is used in the protective film
of a plasma display panel, this alteration will cause a
deterioration in discharge time lag, an increase in discharge
voltage, and other such problems, and will also result in the
initial aging performed to stabilize the discharge characteristics
taking longer time. Moisture that gets into the protective film 14
moves to the fluorescent films 22R, 22G, and 22B, and modifies the
fluorescent films 22R, 22G, and 22B and diminishes the display
performance of the plasma display panel, but with the manufacturing
method of the present invention as discussed above, since the
protective film 14 is prevented from absorbing moisture in the
manufacturing process, discharge drive is possible at a lower
discharge voltage, and a plasma display panel 1 with excellent
display performance is obtained.
EXAMPLES
SrO-CaO Concentration
[0070] Plasma display panels 1 having 300 luminescent cells in the
surface thereof were obtained by producing protective films 14 of
the first and second panels using various concentrations of SrO and
CaO. With each plasma display panel 1, the height of the barrier
ribs 23 was 150 .mu.m, the height of the space in which discharge
occurred (that is, the height from the tops of the fluorescent
films 22R, 22G, 22B on the address electrodes 25 to the top of the
protective film 14 on the sustaining electrodes 15 and the scanning
electrodes 16) was 80 .mu.m; the insert gas was a mixture of neon
and xenon (a mixed gas composed of neon and xenon); the xenon
concentration of 12 vol %; and the charging pressure of the inert
gas was 400 Torr.
[0071] Table 1 shows the CaO concentration (mol %) in the
protective film 14.
[0072] The CaO concentrations (mol %) in the protective film 14 are
shown in the following Table 1.
TABLE-US-00001 TABLE 1 Results of measuring discharge voltage and
sputtering resistance of SrO--CaO compound oxide film CaO First
cell Last cell concentration lighting extinguishing Etching depth
after in film (mol %) voltage (V) voltage (V) 2000 hours of aging
(.ANG.) 0 155 103 7960 10 160 98 3440 20 165 103 2010 40 162 103
1790 60 165 105 1750 80 182 122 1870 90 196 134 1970 MgO 225 145
2700
[0073] Next, the first cell lighting voltage required to start the
discharge of the first of the 300 luminescent cells, and the last
cell extinguishing voltage at which the last cell was extinguished
when the fully-lit PDP drive voltage was gradually lowered were
measured using each of the plasma display panels 1, and these
measurement results are given in Table 1. Table 1 also gives
measurement results in a case where the protective film 14 was
composed of MgO, instead of the protective film of the present
invention as described above that contains both SrO and CaO.
[0074] In addition, a protective film 14 that was the same as those
used in the various plasma display panels 1 was exposed for 2000
hours to a plasma of the above-mentioned charging gas (a neon and
xenon mixed gas, containing 12 vol % xenon), the depth to which the
protective film 14 was etched (the reduction in film thickness) was
measured, and these results are also given in Table 1.
[0075] As is clear from Table 1, a protective film containing both
SrO and CaO and a protective film composed of just SrO both have a
lower discharge voltage than an MgO film.
[0076] Also, if we define anti-sputtering property as the inverse
of the etching rate at the predetermined voltage given in Table 1,
and if we let the anti-sputtering property of an MgO film be 1,
when the CaO concentration is 10 mol % or less, the anti-sputtering
property of the protective film of the present invention containing
both SrO and CaO is less than 1, which is not excellent. However,
when the CaO concentration is within the range of 20 mol % or more
and 90 mol % or less, the anti-sputtering property is over 1, which
is excellent.
[0077] The anti-sputtering property of the protective film of the
present invention containing SrO and CaO and having a CaO
concentration of 20 mol % is approximately 1.34, the
anti-sputtering property when the CaO concentration is 60 mol % is
approximately 1.54, and the anti-sputtering property when the CaO
concentration is 90 mol % is approximately 1.37 so the
anti-sputtering property of the protective film of the present
invention is best when the CaO concentration is 60 mol %.
[0078] When the CaO concentration is 20 mol % or more and 60 mol %
or less, the first cell lighting voltage stabilizes at about 160 V
and the last cell extinguishing voltage also stabilizes at about
100 V. With such CaO concentration range, there is little variance
in discharge characteristics due to differences in CaO
concentration so even if there is variance in concentrations
between cells, this will not affect drive control.
[0079] With the protective film in this embodiment, when the CaO
concentration is within the range of 20 mol % or more and 90 mol %
or less, if a gas being a mixture gas of neon and xenon that
contains 12 vol % xenon is used as the insert gas in order to
increase brightness, the discharge voltage will be lower and
anti-sputtering property better than when an MgO film is used,
which affords a PDP with a longer service life. Therefore, you know
that an adequate effect can be anticipated even no less than the 10
vol % xenon concentration specified for a conventional MgO
film.
[0080] Also, an effect can be anticipated if the height of the
discharge space and the insert gas pressure are at the specified
settings depending on the PDP design specifications, and an effect
can also be anticipated if the PDP has a diagonal size of 42 inches
or more.
Vapor Deposition Material Concentration
[0081] Using a mixed material of SrO and CaO as the vapor
deposition material, this mixed material was irradiated with an
electron beam to form the protective film of the present invention
containing both SrO and CaO, and the composition of the protective
film formed by the aforesaid method was analyzed.
[0082] FIG. 3 is a graph of the results of the above compositional
analysis. When a mixed material of SrO and Cao is vaporized, a
discrepancy comes out between the composition of the mixed material
and the composition of the resulting protective film because SrO
and CaO have different vaporization pressures. As shown in FIG. 3,
the CaO concentration in the vapor deposition material and the CaO
concentration in the protective film are in a specific relationship
having a displacement point.
[0083] Although not shown in the drawings, it was confirmed that
this relationship varies dramatically with reduction in the amount
of vapor deposition material. Therefore, it is surmised that the
composition of the protective film that is formed varies over time
from the start of film formation although not shown in the
drawings.
[0084] In contrast, with the method for forming a protective film
of the present invention, as shown in FIG. 2, SrO and CaO are
vaporized separately, and the vaporization rate from each
vaporization source can be optimized by changing the hearths that
are irradiated with the beams, adjusting how long the hearths are
irradiated with the beams, the beam irradiation intensity, and
other such factors as discussed above. Therefore, with the present
invention, in which SrO and CaO are vaporized separately, it is
easy to control the ratio of SrO to CaO, and a protective film
having a stable compositional ratio can be formed.
[0085] When the protective film of the present invention containing
both SrO and CaO is to be formed by electron beam vapor deposition,
SrCO.sub.3 and CaCO.sub.3, which are stable in the atmosphere, are
generally used for the vapor deposition materials. However, when a
protective film was formed from these vapor deposition materials,
there was no decrease in the discharge voltage of the PDP.
[0086] The composition of the resulting protective film was
analyzed. As a result, the protective film contained a large amount
of carbon, and it is believed that the secondary electron emission
characteristics decreased. It was found that a protective film with
a low discharge voltage can be stably obtained by using SrO and
CaO, which are vapor deposition materials that are unstable in the
atmosphere, and vaporizing them separately.
Continuous Treatment in Vacuum Atmosphere
[0087] Treatment was performed according to the procedure shown in
Table 2 to comparatively evaluate the effect of performing
everything from the formation of the protective film 14 up to the
adhering under heating (adhering the first and second panels 10 and
20 together) and subsequent cooling, continuously in a vacuum.
TABLE-US-00002 TABLE 2 Comparison procedures of Continuous
treatment in vacuum versus continuous treatment in dry atmosphere
Example Comparative Example Means continuous treatment in vacuum
continuous treatment in dry atmosphere 1 vapor deposition vapor
deposition of SrO--20 mol % CaO film of SrO--20 mol % CaO film 2
adhering under heating for adhering under heating for 30 minutes at
30 minutes at 450.degree. C. in vacuum 450.degree. C. in dry
nitrogen with a dew point of -40.degree. C., with no exposure to
the atmosphere 3 cooling to room temperature cooling to room
temperature in dry nitrogen in vacuum with a dew point of
-40.degree. C., with no exposure to the atmosphere, followed by
vacuum exhaust 4 introduction of Ne--12% Xe discharge introduction
of Ne--12% Xe discharge gas up to gas up to 53.2 kPa, 53.2 kPa,
followed by gas sealed followed by gas sealed 5 measurement of
discharge voltage measurement of discharge voltage
[0088] Using the plasma display panels 1 of the examples and
comparative examples, discharge was performed continuously, the
change in discharge voltage over time was measured while discharge
was performed continuously, and these results are given in the
graph of FIG. 4.
[0089] Table 2 and FIG. 4 clearly indicate that the discharge
voltage of the PDP manufactured by the method of the present
invention stabilized at aging of 1 hour of initial discharge.
[0090] In contrast, as discussed in Japanese Laid-Open Patent
Application 2002-231129, in a comparative example in which
everything from the formation of the protective film up to adhering
the first and second panels 10 and 20 together was performed in a
dry atmosphere of dry gas (N.sub.2 gas), discharge voltage did not
stabilize even after 10 hours, and it took a very long time for the
discharge voltage to stabilize.
[0091] When a mixture of SrO and CaO was used for a protective
film, it was found that a continuous process performed under a
vacuum was far more effective at shortening the initial aging time
than a manufacturing process involving a dry atmosphere.
[0092] A surface discharge type of PDP was used as an example
above. The protective film of the present invention can also be
applied to a PDP in which a dielectric film is also disposed on the
second panel 20 side, as discussed in Patent Document 1, or to an
opposed discharge type of PDP or other such PDP that requires a
protective film, and to PDP manufacturing methods.
[0093] When the protective film of the present invention is formed
on the second panel 20 as well, it is preferable for everything
from the formation of the protective film up to adhering the first
and second panels 10, 20 together to be performed in a vacuum
atmosphere, with no exposure to the outside atmosphere.
[0094] The first and second substrates can be made of not only
glass substrates but also various materials, such as plastic or
ceramic substrates. It is preferable for at least the substrate on
the side where light is emitted to be transparent.
[0095] The method for forming the protective film is not limited to
EB vapor deposition provided CaO vapor and SrO vapor can be
generated separately. It is also possible, for example, to heat
hearths 3 holding SrO and hearths 4 holding CaO with an electric
coil or other such heating means, and generate CaO vapor and SrO
vapor separately.
[0096] The above description is concerned with the disposition of
the protective film 14 of the present invention over the sustaining
electrodes 15 and the scanning electrodes 16 via the dielectric
film 12, but the present invention is, however, not limited to the
above-description, and the protective film 14 may be disposed so as
to come into contact with the surface of the sustaining electrodes
15 and the surface of the scanning electrodes 16.
[0097] Also, the address electrodes 25 and the fluorescent films
22R, 22G, and 22B will also be protected from the plasma if the
protective film 14 is formed over the surface of the fluorescent
films 22R, 22G, and 22B.
[0098] The above description pertains to the formation of a plasma
by applying voltage between scanning electrodes and sustaining
electrodes disposed on the same panel, but the present invention is
not limited to this. For instance, a plasma may be formed by
applying DC or AC voltage between electrodes disposed on different
panels. When DC voltage is applied between electrodes on different
panels, the protective film of the present invention may be
disposed on at least the electrode located on the negative
potential side, and when AC voltage is applied between electrodes
on different panels, the protective film of the present invention
may be disposed on one or both of the electrodes.
* * * * *